7.2.1.4 Copper Ferrocyanide and Copper Ferricyanide

PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet

Surname or Family name: Fernando

First name: Kapila Other name/s:

Abbreviation for degree as given in the University calendar: Ph.D.

School: School of Chemical Sciences and Engineering Faculty: Engineering

Title: The Treatment of Cyanidation Tailings Using Ion Exchange Resin

Abstract 350 words maximum: (PLEASE TYPE)

This thesis explores the behaviour of metal cyanide complexes under oxidative acid conditions in ion exchange systems, with the objective of developing an ion exchange based process for the treatment of gold cyanidation tailings. The novel cyanide detoxification process developed from this study employs strong base ion exchange resins to extract cyanide from tailings. Variations in the stability of cyanide complexes are exploited to concentrate, recover, or destroy cyanide species loaded on the resin, through the use of an oxidative acid eluent containing H2O2 and H2SO4. This eluent removes all base metal cyanide complexes from strong base resins, while regenerating the resin. The spent eluent, containing the base metals recovered from the tailings, can be used as a source of such base metals. Copper can be recovered separately from other base metals if necessary. Low levels of precious metals present in the tailings are accumulated on the resin as the ion exchange bed is cycled between loading and elution stages. They can be recovered economically, so as to offset the cost of the tailings detoxification. Cyanide is initially concentrated as an alkaline solution, which can be detoxified within the process or recovered for recycling.

This process was successfully tested at pilot scale by treating approximately 14,000 m^ of cyanide contaminated tailings solution, over 14 loading/elution cycles on a standard strong base ion exchange resin bed. This treatment reduced the total cyanide concentration of the contaminated solution from approximately 50 mg/L to an average of 1.5 mg/L. The reagent cost was approximately AUD 0.50 per m^ of treated liquor. When the resin was repeatedly loaded with mixed metal cyanide species and eluted with the oxidative acid eluent, a gradual deterioration of the ion exchange resin performance was noted. The reduction of net operating capacity of the columns due to resin deterioration was in the order of 1-3% per loading/elution cycle. The oxidation of resin catalysed by copper, the precipitation of metal hexacyanoferrates on the resin and the oxidation of Au(CN)2' to Au(CN)4" were identified as possible factors giving rise to the reduction of resin loading capacity.

Declaration relating to disposition of project thesis/dissertation

I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all fomns of media, now or here after known, subject to the provisions of the Copyright Act 1968.1 retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.

I also authorise Univ^ity Microfiln}$^^^se the 350 abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral

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THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS (19180'^ THE UNIVERSITY OF NEW SOUTH WALES SCHOOL OF CHEMICAL SCIENCES AND ENGINEERING

THE TREATMENT OF CYANIDATION TAILINGS USING ION EXCHANGE RESIN

by Kapila Fernando, B.E Chemical Engineering (Hons.)

A Thesis Submitted to the School of Chemical Sciences and Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

The University of New South Wales NOVEMBER 2007 ORIGINALITY, COPYRIGHT AND AUTHENTICITY STATEMENT

I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.

I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.

I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.

I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. DEDICATION

To my Mum and Dad, Gertrude and Raymond Fernando, for this achievement was only made possible because of their unwavering support and sacrifice. ACKNOWLEDGEMENTS

Over IV2 years, there were many who contributed to this work. Some were involved directly, guiding and directing my research. Others supported in subtle ways, through encouragement and friendship, but were just as necessary for me to reach this milestone.

To my academic supervisors It was a privilege to embark on this research project under Prof Tam Iran's direction and supervision. Tam, you taught me how to undertake independent research, balance creativity, and lateral thinking with the imperative to generate coherent arguments backed by tangible resuhs. You were a true mentor.

I also want to thank Dr. Frank Lucien for his guidance and support, especially in the write-up of this thesis. Your insightful comments and decisive instructions were instrumental for me to present my thoughts in a coherent and lucid manner.

To those at ANSTO, Imperial and May Day mines I am truly grateful to ANSTO and its management for supporting my research work. I especially acknowledge the support and encouragement from my supervisor, Lubi. Thank you for giving me the time to complete this project. I also would like to thank Clement, Bruce, and Kevin from Imperial Mining for supporting the pilot plant testing program. I am very grateful for Graham for his support while we were working at May Day mines.

To my co-workers and researches I gratefully acknowledge the support of my co-workers and researchers who worked with me to explore various aspects of cyanide chemistry and ion exchange systems. Steve, Sarah, Ken, Grzegorz, Rueben, and Myong Jun, I enjoyed working with you at various stages of this research project. Thank you for your contribution to this work.

To my colleagues at ANSTO Martin, Roland, Gordon, Melody, Enrique, Liz, Patricia, Robert, and Henri, I could not have completed this without your support. You all contributed to this project in various ways. You helped me to refme my thoughts, conduct experimental work, and carry out analyses. Most importantly, those of you who work directly with me were generally accommodating me when I was stressed out trying to juggle full time work and a Ph.D. program. Special thanks to Bob and Lorraine for making me see that this effort is worthwhile.

To all my friends who encouraged and supported me over a IV2 year journey From my church and bible study groups: Tom, Caroline, Brian, Julie, Mike, Peter, Louise, Brett, Kristie, Dana, Sally, Tsola, Damian, Laura, and Craig. Thanks for your prayers and encouragement. I also want to thank Enoka, Niru, Mini, Mike, Aruna, Brendan, Natasha, Tom, San-San, Wendy, Michael, Matt, Tim, and James for their support. My high school buddies, Priantha, Hiran, and Manisha, thanks for putting up with an absentee friend. Finally, I am grateful to Hilary and Leah for proofreading and editing this thesis.

I was fortunate to have the support and friendship of many during this journey. They helped me to achieve this goal while keeping me grounded in reality. My sincere gratitude is extended to all of you. ABSTRACT

This process was successfully tested at pilot scale by treating approximately 14,000 m^ of cyanide contaminated tailings solution, over 14 loading/elution cycles on a standard strong base ion exchange resin bed. This treatment reduced the total cyanide concentration of the contaminated solution from approximately 50 mg/L to an average of 1.5 mg/L. The reagent cost was approximately AUD 0.50 per m^ of treated liquor. When the resin was repeatedly loaded with mixed metal cyanide species and eluted with the oxidative acid eluent, a gradual deterioration of the ion exchange resin performance was noted. The reduction of net operating capacity of the columns due to resin deterioration was in the order of 1-3% per loading/elution cycle. The oxidation of resin catalysed by copper, the precipitation of metal hexacyanoferrates on the resin and the oxidation of Au(CN)2" to Au(CN)4' were identified as possible factors giving rise to the reduction of resin loading capacity.

m RELEVANT PUBLICATIONS

1. Fernando, K., Lucien, F., Tran, T. and Carter, M.L., Ion Exchange Resins for the Treatment of Cyanidation Tailings, Part 3 - Resin Deterioration under Oxidative-Acid Conditions. (Draft submitted to Minerals Engineering for publication, November 2007)

2. Fernando, K., Tran, T. and Zwolak, G., The Use of Ion Exchange Resins for the Treatment of Cyanidation Tailings Part 2 - Pilot Plant Testing, Minerals Engineering, 18(1), 2005, pp. 109-117.

3. Fernando, K., Tran, T., Laing, S. and Kim, M. J., The Use of Ion Exchange Resins for the Treatment of Cyanidation Tailings Part 1 - Process Development of the Selective Base Metal Elution, Minerals Engineering, 15(12), 2002, pp. 1163-1171.

4. Tran, T., Fernando K., Lee K. and Lucien F., Use of Ion Exchange Resin For the Treatment of Cyanide and Thiocyanate During the Processing of Gold Ores, Cyanide: Social, Industrial and Economic Aspects, Proceedings of a Symposium, Annual Meeting of The Metallurgical Society (TMS), 2001, pp. 289-302.

5. Tran, T., Lee, K., Fernando, K., Rayner, S., Use of Ion Exchange Resin for Cyanide Management During the Processing of Copper-Gold Ores, Proceedings of the AusIMM Annual Conference 2000 (MINPREX 2000 Congress), AusIMM, 2000, pp. 207-216.

fV TABLE OF CONTENTS

Introduction

2 Cyanide Chemistry and Gold Cyanidation 5 2.1 Cyanide Chemistry 5 2.1.1 Free Cyanide and Cyanide Compounds 5 2.1.2 Metal Cyanide Complexes 7 2.1.2.1 Copper Cyanide Complexes 10 2.1.2.2 Iron Cyanide Complexes 13 2.1.2.3 Other Non-WAD Cyanide Species 16 2.1.3 Reactions Between Metal Cyanide Complexes and Metal Cations 18 2.1.4 Cyanate and Thiocyanate 21 2.1.5 Toxicity of Cyanide 22 2.2 Gold Cyanidation and Cyanidation Tailings 23 2.3 Chemistry of Cyanidation Tailings 26 2.4 Cyanide Detoxification Techniques 27 2.4.1 Biological Treatment 28 2.4.2 Precipitation with Iron Cyanide 29 2.4.3 Direct Oxidation 30 2.4.3.1 Alkaline Chlorination 30 2.4.3.2 Sulphur Dioxide/Air Process 31 2.4.3.3 Copper Catalysed Hydrogen Peroxide Oxidation 32 2.4.3.4 Cyanide Oxidation by Ozone 33 2.4.3.5 Review of Direct Oxidation Processes 34 2.4.4 Cyanide Recovery by Acidification 34 2.4.5 Ion Exchange Resin Processes 37 2.4.5.1 The Cyanosave™ Process 38 2.4.5.2 The Cy-Tech Ion Exchange System 39 2.4.5.3 The Augment Process 40 2.4.5.4 The Vitrokele Technology™ Process 41 2.4.5.5 The Ion Exchange Process Patented by Frey and Colleagues 42 2.4.5.6 Review of Ion Exchange Resin Cyanide Detoxification Processes 43 2.5 Ion Exchange Process for Gold Extraction 45 2.5.1 Development of Ion Exchange Processes for Gold Extraction 45 2.5.2 Process Characteristics 45 2.5.3 Recent Developments 47 3 The Fundamentals of Ion Exchange 48 3.1 A Brief History of Ion Exchange Technology 49 3.2 Ion Exchange Fundamentals 50 3.2.1 Physical Properties of Resins 51 3.2.2 Classification of Ion Exchange Resins 53 3.2.2.1 Strong Cationic Exchange Resins 54 3.2.2.2 Strong Anionic Exchange Resins 55 3.2.2.3 Weak Cationic Exchange Resins 56 3.2.2.4 Weak Anionic Exchange Resins 57 3.2.2.5 Speciahy Ion Exchange Resins 58 3.2.3 Ion Exchange Capacity 59 3.2.4 Ion Exchange EquiUbria 61 3.2.4.1 Swelling and Adsorption of Water 61 3.2.4.2 Sorption of Electrolyte and Donnan Potential 63 3.2.4.3 Ion Exchange Selectivity 64 3.2.5 Ion Exchange Kinetics 66 4 Development of the Oxidative Acid Elution Concept 69 4.1 Background 69 4.2 Process Overview 70 4.3 Characteristics of Ion Exchange Resin Used 73 4.4 Oxidative Acid Elution 74 4.4.1 Originality of Oxidative Acid Elution 74 4.4.2 Process Chemistry of Oxidative Acid Elution 74 4.5 Selection of Oxidant and Elution Conditions 77 4.6 Study of the Effect of Oxidant Concentration on the Elution of Copper 79 4.6.1 Experimental 79 4.6.2 Results and Discussion 80 4.7 Elution of Resin Loaded with Mixed Metal Cyanide Species 83 4.7.1 Experimental 83 4.7.2 Results and Discussion 87 4.8 Conclusion 94 5 Resin Durability and Elution of Mixed Cyanide Complexes 96 5.1 The Effect of Oxidative Acid Elution Conditions on Resin Performance 96 5.1.1 Experimental 97 5.1.1.1 Loading and Oxidative Acid Elutions 97 5.1.1.2 HCN Management 98 5.1.1.3 Total Base Capacity Measurements 98 5.1.1.4 Strong Base Capacity Measurements 100 5.1.2 Results and Discussion 101 5.2 The Effect of Copper and Iron Cyanide Species on Resin Performance 103 5.2.1 The Effect of Copper Cyanide in the Loading Solution 104 5.2.1.1 Experimental 106 5.2.1.2 Results and Discussion 107 5.2.2 The Effect of Iron Cyanide Species in Solution 111 5.2.2.1 Experimental 111 5.2.2.2 Results and Discussion 113 5.2.3 The Effect of Iron Cyanide Concentration in Solution 120 5.2.3.1 Experimental 120 5.2.3.2 Results and Discussion 121 5.2.4 The Effect of Loading Solution pH 123 5.2.4.1 Experimental 123 5.2.4.2 Results and Discussion 124 5.3 Behaviour of Non-WAD Cyanide Species 125 5.4 Conclusion 127 6 Pilot Scale Testing of the Overall Cyanide Detoxification Process 129 6.1 Background 130 6.2 Overview of Operations 131 6.3 Loading of Cyanide Species to the Resin Bed 133 6.3.1 Experimental Process Conditions 133 6.3.2 Results and Discussion 134 6.4 Oxidative Acid Elution 138 6.4.1 Experimental Process Conditions 138 6.4.2 Results and Discussion 139 6.5 Cyanide Detoxification 144 6.6 Resin Deterioration and Precious Metal Elution 145 6.7 Conclusion 147 7 Evaluation of Resin Degradation During Oxidative Acid Elution 148 7.1 Evidence of Resin Degradation 148 7.2 Characterisation of Resin 149 7.2.1 Sample Preparation 149 7.2.1.1 Fresh Resin 150 7.2.1.2 Resin Samples from Studies on Resin Durability 150 7.2.1.3 Resin Samples from Pilot Scale Tests 151 7.2.1.4 Copper Ferrocyanide and Copper Ferricyanide Specimens 151 7.2.1.5 Resin Samples from Pilot Scale Tests 152 7.2.2 Total Base Capacity Tests 153 7.2.2.1 Experimental 153 7.2.2.2 Results and Discussion 154 7.2.3 Ion Exchange Kinetics 155 7.2.3.1 Experimental 155 7.2.3.2 Results and Discussion 156 7.2.4 Elemental Loading on Resin 158 7.2.4.1 Experimental 158 7.2.4.2 Results and Discussion 158 7.2.5 XRD and Diffuse Reflectance Spectroscopy 161 7.2.5.1 Experimental 161 7.2.5.2 Results and Discussion 161 7.2.6 Optical and Electron Microscopy Imaging of Resin 168 7.2.6.1 Experimental 168 7.2.6.2 Results and Discussion 168 7.3 Review of Resin Deterioration 174 7.3.1 Factors Contributing to Resin Deterioration 174 7.3.2 Resin Deterioration Mechanisms 175 7.3.2.1 The Effect of Copper on Resin Deterioration 175 7.3.2.2 Resin Deterioration Due to the Precipitation of Hexacyanoferrates 176

Vll 7.3.2.3 Resin Deterioration Due to Loading of Gold on Resin 176 7.4 Conclusion 179 8 Environmental Impact and Operating Costs 181 8.1 Environmental Impact 181 8.2 Operating Cost and Reagent Consumption 183 8.3 Conclusions 185 9 Conclusions 187

10 Recommendations for Further Research 191 10.1 The Impact of the Oxidant on Resin in the Presence of Copper 191 10.2 The Effect of Other Non-WAD Cyanide Species 192 10.3 The Nature of Gold Loading on Resin 192 10.4 Regeneration of Deteriorated Resin 193 11 References 194

12 Appendices 201

vm LIST OF TABLES

Table 2.1 Some metal cyanide complexes and their stability in water 9 Table 2.2 Stability of copper cyanide species 10 Table 2.3 Solubility of some iron cyanide compounds 20 Table 4.1 Summary of elution conditions used to recover copper from resin 81 Table 4.2 Loading conditions used to load mixed cyanide species to the ion exchange resin bed 86 Table 4.3 Elution conditions used to elute mixed cyanide species to the ion exchange resin bed 88 Table 4.4 Loading of mixed cyanide species to the resin bed 89 Table 4.5 Cumulative loading of metals to resin bed on successive loading/elution cycles 92 Table 4.6 Mass balance for overall loading and elution of metals during 7 loading/elution cycles 93 Table 5.1 Total and strong base capacities of Purolite A500 resin over 30 loading and oxidative acid elution cycles 101 Table 5.2 Loading conditions used to load resin with mixed iron and copper cyanide species 105 Table 5.3 Elution conditions used to elute resin loaded with mixed copper and iron cyanide species 105 Table 5.4 Total base capacity of Column A over 15 cycles 107 Table 5.5 Net operating capacity of Column A in the absence of iron in loading solution 109 Table 5.6 Total base capacity of Columns A, B, and C over 15 loading/elution cycles 113 Table 5.7 The effect of iron cyanide on the loading capacity of resin bed 117 Table 5.8 The effect of ferrocyanide concentration on the loading capacity of resin bed 122 Table 5.9 The effect of loading solution pH on the loading capacity of resin bed 124 Table 6.1 Key operating parameters of the pilot plant 131

Table 6.2 Average CNTOT in liquor before and after treatment in the pilot plant 135 Table 6.3 Average metal concentrations in liquor before and after treatment in the pilot plant 136 Table 6.4 Loading of metals to the resin bed in pilot scale tests 137 Table 6.5 Oxidative acid elution conditions of the pilot plant 138 Table 6.6 Average metal concentrations in spent eluent of the pilot plant 141 Table 6.7 Mass balance for copper for the first 6 loading/elution cycles of the pilot plant 142 Table 6.8 Reagent consumption and copper recovery resuhs of the pilot plant 143 Table 7.1 Resin Sample Specifications 152 Table 7.2 Total base capacity of resin samples 154 Table 7.3 Non-removable elemental loading in resin 159 Table 7.4 List of XRD peaks produced by resin sample R-950Cu/25Fe 164 Table 7.5 List of XRD peaks produced by resin sample R-950Cu/50Fe 165 Table 8.1 Pilot plant costs for the treatment of cyanide contaminated solution 184 LIST OF FIGURES

Fig. 2.1 Distribution of HCN and cyanide with the pH of the solution 6 Fig. 2.2 Eh-pH diagram for Cu-CN"-H20 system at 25 ^C 11 Fig. 2.3 Equilibrium distribution of copper cyanide species in a system of 1.57 mM Cu^ and 5.19 mM CN" system at 25 ^C 12 Fig. 2.4 Eh-pH diagram for Fe-CN"-H20 system at 25 ^C 14 Fig. 2.5 Eh-pH diagram for Au-CN"-H20 system at 25 ^C 17 Fig. 2.6 Eh-pH diagram for CN"-H20 system at 25 ^C 21 Fig. 2.7 Publications and patents on ion exchange resin based cyanide management processes 38 Fig. 3.1 Cation exchange resin schematic showing negatively charged co- ions attached to the resin matrix and H^ counter-ions 50 Fig. 3.2 Gregor's model of an ion exchange resin 62 Fig. 4.1 Flow chart of the ion exchange cyanide detoxification process 72 Fig. 4.2 Eh-pH diagram of commercially used oxidants 76 Fig. 4.3 Theoretical reduction potential of hydrogen peroxide in acidic solutions 78 Fig. 4.4 Copper concentration profile of the eluent for various H2O2 concentrations 81 Fig. 4.5 Recovery of cyanide against hydrogen peroxide concentration in eluent 82 Fig. 4.6 The accumulation of cyanide in the scrubber with time for Cycle 3 83 Fig. 4.7 Schematic diagram of the ion exchange resin test rig used for bench scale testing of selective base metal elution 84 Fig. 4.8 The breakthrough of elements during a typical loading cycle 90 Fig. 4.9 The concentration profile of copper and zinc in the spent eluent of the third elution cycle 91 Fig. 5.1 Ion exchange resin rig used for process validation tests 99 Fig. 5.2 Total base and strong base capacities of Purolite A500 resin over 30 loading and oxidative acid elution cycles 102 Fig. 5.3 Appearance of resin column over 30 loading/elution cycles 102 Fig. 5.4 Total base capacity of Column A over 15 loading/elution cycles 108 Fig. 5.5 Copper breakthrough curves of Column A 108 Fig. 5.6 The net operating capacity of Column A over 15 cycles 109 Fig. 5.7 Discolouration of resin in Column A 110 Fig. 5.8 Total base capacities of Columns A, B, and C over 15 loading/elution cycles 114 Fig. 5.9 Copper breakthrough curves of Column B 115 Fig. 5.10 Copper breakthrough curves of Column C 115 Fig. 5.11 Iron breakthrough curves of Column B 116 Fig. 5.12 Iron breakthrough curves of Column C 116 Fig. 5.13 The reduction of net operating capacity of Columns A, B, and C 118 Fig. 5.14 Discolouration of resin in Column B 119 Fig. 5.15 Discolouration of resin in Column C 120 Fig. 5.16 The reduction of net operating capacity of Columns A, B, and D 122 Fig. 5.17 The reduction of net operating capacity of Columns A, D, and E 125 Fig. 6.1 Simplified flowchart of the pilot plant 132

Fig. 6.2 CNTOT breakthrough curve of Cycle 7 134 Fig. 6.3 Gold breakthrough curves of Cycles 1 to 7 137 Fig. 6.4 Effect of H2O2 concentration on elution of copper from the resin bed 140

Fig. 6.5 H2SO4 concentration profile in feed and discharge eluent streams 141 Fig. 6.6 Gold concentration in the precious metal elution circuit of the pilot plant 146 Fig. 7.1 Cr elution profiles of degraded resin after 15 loading/elution cycles 157 Fig. 7.2 cr elution profile of resin samples from the pilot scale tests 157 Fig. 7.3 Powder X-Ray diffraction patterns of fresh resin 162 Fig. 7.4 Powder X-Ray diffraction patterns of resin sample R-PP07 162 Fig. 7.5 Powder X-Ray diffraction patterns of resin sample R-PP14 163 Fig. 7.6 Powder X-Ray diffraction patterns of resin sample R-950Cu/25Fe 164 Fig. 7.7 Powder X-Ray diffraction patterns of resin sample R-950Cu/50Fe 165

Xll Fig. 7.8 Reflectance spectra in the 200-1000 nm range 167 Fig. 7.9 Appearance of resin from resin durability tests 169 Fig. 7.10 Appearance of resin from pilot plant tests 169 Fig. 7.11 Fracture surface of fresh Purolite A500 strong base ion exchange resin 170 Fig. 7.12 Fracture surface of resin sample R-950Cu/50Fe 171 Fig. 7.13 Fracture surface of resin sample R-PP07 172 Fig. 7.14 Fracture surface of resin sample R-PP14 172 Fig. 8.1 Natural degradation of cyanide in the treated liquor 182

xm LIST OF APPENDICES

Appendix 1 202 Appendix 2 203 Appendix 3 205 Appendix 4 206 Appendix 5 210 Appendix 6 213 Appendix 7 217 Appendix 8 221 Appendix 9 225 Appendix 10 228 Appendix 11 231 Appendix 12 245 Appendix 13 247 Appendix 14 248 Appendix 15 249 Appendix 16 252 Appendix 17 254 Introduction

Cyanidation of gold ore has been practiced in most parts of the world for over a century. The cyanidation process, patented by the McArthur and Forrest brothers, was first used at Crown Mine in New Zealand in 1889. From this period onwards, cyanidation has held its ground as the primary gold extraction process used in the resource sector.

Cyanide is a well-known toxin. Due to the toxicity of cyanide, and several high profile accidents which led to the release of cyanide into aquatic environments, environmental protection authorities around the world have imposed stringent limits on cyanide discharges from gold cyanidation operations. These restrictions have led to a gradual reduction of the application of cyanidation in the mining sector. Over the past two decades, the concern over cyanide contamination has intensified to the extent that cyanidation is no longer considered a preferred option in areas with significant ground water reserves or open aquatic environments. As a result of these developments, tailings detoxification and cyanide management have emerged as key processes in gold cyanidation. Today, the development and optimisation of cyanide management techniques are key areas of study in hydrometallurgy.

In recent years, several new cyanide management processes have been developed and the efficiency of existing processes has been increased. However, a cost effective and environmentally acceptable process, capable of operating under the full range of conditions encountered in cyanidation operations, has not been reported to date. This thesis explores the behaviour of metal cyanide complexes under oxidative acid conditions in ion exchange systems, with the objective of developing an ion exchange based cyanide detoxification process suitable for gold cyanidation operations. The cyanide detoxification process resulting from this study employs ion exchange adsorption of cyanide species on resin and the decomposition of metal cyanide complexes under oxidative acid conditions, to concentrate, recover, or destroy cyanide from tailings solutions.

Commercial strong base ion exchange resins are used in this process to remove cyanide complexes from tailings. After loading, the resin is regenerated using a novel oxidative acid elution. The oxidative acid elution allows the recovery of base metals while allowing the cycling of the resin bed between loading and elution stages. The cyanide collected on resin is oxidised to cyanate by the oxidant in the eluent. The option of recovering a fraction of cyanide for recycling is also available. This process also allows for the scavenging of precious metals from tailings. The research presented herein gives special attention to the study of the behaviour of metal cyanide complexes during these unit operations. The durability of resin is investigated and key mechanisms of resin deterioration are identified.

The approach taken in compiling this thesis is one that generally follows the chronological order of the development of this process. After reviewing the process chemistry and the state-of-the-art of prior research in this field, a process concept is presented based on the hypothesised behaviour of metal cyanide complexes in ion exchange systems and the potential selective decomposition of such species under oxidative acid conditions.

Following this, the discussion focuses on the chemistry and behaviour of metal cyanide complexes studied earlier under laboratory conditions to validate the hypotheses made. The thesis then examines results of a testwork program conducted on a pilot scale to benchmark its performance characteristics against those of existing cyanide detoxification processes. The process chemistry of resin deterioration is given special attention and the commercial viability of the process is discussed. Finally, key conclusions are summarised and recommendations for further research are presented.

Chapter 2 introduces the key concepts in cyanide chemistry and gold cyanidation. A general overview of cyanide chemistry is given from the perspective of its application in the cyanidation of gold ores. The state-of-the-art of cyanide detoxification techniques in gold cyanidation and the past developments in the use of ion exchange processes in this sector are reviewed. A discussion of the fundamentals of ion exchange is given in Chapter 3. The classification of ion exchange resins, their synthesis, and their properties are reviewed. Chapters 2 and 3 form the theoretical backdrop for the research work reported in the remainder of this thesis.

Chapter 4 compiles the process concept for the novel cyanide detoxification process based on the hypothesised behaviour of metal cyanide complexes in ion exchange systems. This chapter also discusses the theoretical basis and the conceptual development of an oxidative acid elution technique. Further, the fundamental process chemistry of the oxidative acid elution is explored to gain an understanding of the behaviour of cyanide complexes on the resin phase in the presence of the oxidative acid eluent.

Chapter 5 reports studies on the durability of the resin when the oxidative acid eluent was repeatedly used to elute base metal cyanide complexes from resin. Attention is given to studying the effect of elution conditions on the loading capacity of resins. The effect of the co-loading and elution of iron and copper cyanide species is also investigated.

Chapter 6 reports the pilot scale testing of this novel cyanide detoxification process. The resuhs of a 12 month pilot plant testing program where the process was successfully employed to treat some 14,000 m^ of cyanide contaminated liquor at May Day mines (Cobar, New South Wales, Australia) are presented. An investigation of resin deterioration is given in Chapter 7. To gain a further insight into the behaviour of metal cyanide complexes in the resin phase under oxidative acid elution conditions, deteriorated resin samples were examined using several characterisation techniques. Results of resin characterisation were used to identify key factors contributing to the deterioration of resin.

Chapter 8 discusses the environmental impact of this novel cyanide detoxification process in relation to its application in the treatment of gold cyanidation tailings. Also presented in Chapter 8 are the operating costs of the process, estimated from the pilot scale testing program reported in Chapter 6.

Chapter 9 compiles some key conclusions drawn from this research project, identifying the technical feasibility, commercial viability and the positive environmental impact of this process. Areas for further research identified as a result of this research work are listed in Chapter 10.

The conceptual development of this novel process, reported in Chapter 4, and the resin durability studies, reported in Chapter 5, were conducted at the laboratories of the University of New South Wales (UNSW) and the Australian Nuclear Science and Technology Organisation (ANSTO). Pilot scale testing (Chapter 6) was conducted at May Day mine (Cobar, Central New South Wales). The characterisation of deteriorated resin, reported in Chapter 7, was conducted at the ANSTO laboratories. Cyanide Chemistry and Gold Cyanidation

This chapter introduces some key concepts in cyanide chemistry and gold cyanidation. The properties of cyanidation taiHngs are discussed and the state-of-the- art of cyanide detoxification techniques employed in the mining sector is reviewed. Further, this chapter also briefly reviews the application of ion exchange processes in gold cyanidation, where synthetic ion exchange resins are used as an alternative to activated carbon.

2.1 CYANIDE CHEMISTRY

The term 'cyanide' refers to a singularly charged anion consisting of one carbon atom and one nitrogen atom joined with a triple bond. The cyanide radical is very reactive - it forms simple salts with alkali and alkaline earth metal cations. It also forms ionic complexes of varying strengths with numerous transition and post- transition metals.

2.1.1 Free Cyanide and Cyanide Compounds

The complex chemistry and reactivity of cyanide can be explained by the bonding in the cyanide radical. The cyanide ion contains one sigma bond, two pi bonds and empty bonding orbitals. The first of the two orbitals in its structure are filled with the maximum number of electrons and the other orbitals are empty. Because the 's' and 'p' (1+2) orbitals are filled with electrons, it behaves like a halogen and produces salts with alkali and alkaline earth metals with remarkably similar properties to those of halides. Hence, it is considered a pseudo-halogen. It can be oxidised to cyanogen (CN)2, which is analogous to halogen molecules such as CI2 and Bri. Hydrogen cyanide is a weak acid in aqueous solutions. It decomposes to H^ and CN" ions as shown in Equation 2.1:

HCN < > CN- + H^ (2.1)

At 20 C, the dissociation constant for this reaction is shown in Equation 2.2:

HMrCN K = 2.03x10 -10 pK. = 9.31 (2.2) [HCN

HCN solubility decreases with increased temperature and increased salinity. At a pH of 11, over 99% of the cyanide remains in solution as CN", while at pH 7, over 99% of the cyanide will exist as HCN.

100%

8 9 10 11 pH of solution

Fig. 2.1 Distribution of HCN and cyanide with the pH of the solution Figure 2.1 shows the distribution of HCN and cyanide with the pH of the solution. HCN is a colourless gas. It has the odour of bitter almonds, but not all individuals can detect this odour. Cyanide compounds of alkali and alkaline earth metals can be considered as corresponding sahs of hydrocyanic acid. They are colourless and dissolve freely in water, dissociating into free cations and cyanide anions, as shown in Equations 2.3 and 2.4:

NaCN > Na^ + CN* (2.3) CW + H^O > HCN + OH" (2.4)

Simple cyanide compounds are stable under atmospheric conditions. Most cyanide salts are hygroscopic, and some are deliquescent, particularly its sodium sah. Simple cyanides decompose on heating, producing cyanogen. Due to their complete dissociation in aqueous solutions, they are highly reactive. Simple cyanide salts are the primary source of cyanide used in industry. The most common source of cyanide is sodium cyanide, available as a solid or a concentrated solution.

2.1.2 Metal Cyanide Complexes

In addition to its pseudo-halogen behaviour, cyanide forms complexes with most metals, particularly those of the transition series. The empty anti-bonding orbitals on the cyanide ion can form bonds with 'd' orbitals of transition series metals. In forming these bonds, an electron pair is exchanged between the cyanide ion and the metal, resulting in a bond called 'back bonding'. Most of these complexes form in a step-wise manner, leading to increasing complexation of cyanide with the metal anion with increasing cyanide concentration in solution. This produces negatively charged complex anions in which the metal cation is surrounded by cyanide anions. The overall charge of these complex anions is determined by the valency and the coordination number of the central metal cation. The stability of these complexes depends on the metal ion involved and, as such, their dissociation constants vary significantly. The cyanide complexes of some transition and heavy metals (copper. zinc, silver, cadmium, and mercury) are significant to the gold mining sector as they are found in most cyanidation liquors.

Metal cyanide complexes are classified under two different schemes in the literature. One system uses the stability of cyanide complexes as the basis for classifying cyanide species, while the other uses the extent of dissociation of cyanide species under acidic conditions.

Kyle (1997) uses the former system, classifying cyanide complexes into three categories: 'weak', 'moderately strong', and 'strong' (Table 2.1). According to this classification, cyanide complexes of zinc and cadmium are considered 'weak' cyanide complexes as they readily dissociate in aqueous solutions with low free cyanide levels. Cyanide complexes of copper, nickel, silver, and mercury are considered 'moderately strong' cyanide complexes. They dissociate slightly, releasing a small amount of cyanide ions when the free cyanide concentration in the solution is low. Cyanide complexes of gold, iron, and cobalt, on the other hand, do not dissociate under such conditions and are therefore considered strong cyanide complexes.

The most widely used classification of cyanide compounds is the latter system, which is based on the extent of decomposition of metal cyanide complexes in mild acidic conditions. Metal cyanides differ widely in their reactivity with acids. Those which readily dissociate in acidic solutions liberating HCN and corresponding metal cations, such as the cyanides of zinc, cadmium, and nickel, are considered 'weak acid dissociable cyanide' complexes (CNWAD). Those that do not dissociate under such conditions, such as the cyanide complexes of cobalt, iron, and gold are called 'non- weak acid dissociable cyanide' complexes or CNnon-WAD- Those that slowly dissociate under acidic conditions are considered 'partially weak acid dissociable cyanide' complexes or CN partiaiiy-wAD (Flynn and Haslem, 1995). This classification system is used in this thesis. Table 2.1 Some metal cyanide complexes and their stability in water Compound Formula Classification ^ Dissociation constant (Kd) Hexacyanoferrate (III) Fe(CN)6'- Strong 1.0 X Hexacyanoferrate (II) Fe(CN)6'- Strong

Dicyanoaurate(II) Au(CN)2'" Strong 1.0 X

Hexacyanocobaltate(III) CO(CN)6^- Strong 1.0 X Tetracyanomercurate Hg(CN)4'- Moderately Strong Dicyanocuprate CU(CN)2" Moderately Strong 2.0 X

Tricyanocuprate CU(CN)3^" Moderately Strong 5.0 X Tetracyanonikelate Ni(CN)4^" Moderately Strong 1.0 X Dicyanosilverate Ag(CN)2'- Moderately Strong 1.0 X Tricyanocadminate Cd(CN)3" Weak 2.5 X Tetracyanocadminate Cd(CN)4^' Weak 1.4 X Tetracyanozincate Zn(CN)4^" Weak

1 Kyle (1997) 2 Smith and Mudder (1992) 3 Flynn and Haslem (1995)

Although non-WAD cyanide species are stable under mildly acidic conditions, they decompose to release free cyanide when exposed to direct ultra-violet light in aqueous solutions. Metal cyanide complexes form salt type compounds with alkali, alkaline earth, transition, and heavy metal cations. Potassium ferrocyanide (K4Fe(CN)6) and copper ferrocyanide Cu2Fe(CN)6, are typical examples of these compounds. The solubility of these compounds depends on the metal cyanide and the cation.

Of particular relevance to the subject matter of this thesis is the chemistry of copper and iron cyanides. The ability of non-WAD cyanide species to form stable double salts with transition metal cations is also of crucial significance. These are discussed in detail in the following sections. 2.1.2.1 Copper Cyanide Complexes

Copper forms four cyanide complexes in copper (I) form. These are CuCN, Cu(CN)2' 2 4 Cu(CN)3 and Cu(CN)3 The monocyanide species is insoluble, but dissolves in alkaline cyanide solutions forming higher cyanide complexes. All other species are colourless in aqueous solutions. In solution, Cu(CN)2" has a linear geometry, while 2 1 Cu(CN)3 " has trigonal-planer geometry. Cu(CN)4 complex takes a tetrahedral shape in aqueous solutions (Fagen, 1998).

In alkaline solutions where Cu^ and CN" ions are present, all soluble copper cyanide species are found in equilibrium. The speciation of copper cyanide in alkaline solutions has been studied to a significant depth due to their ubiquitous nature in cyanidation liquors. Table 2.2 gives the stability constants of copper cyanide complexes in aqueous solutions. As expected, the distribution of these species depends on the pH of the solution, Cu^ to CN' ion ratio and the total cyanide concentration. The salinity of the solution also influences the speciation of copper cyanide complexes. A number of authors have reported that in alkaline solutions of relatively low cyanide concentrations (i.e. 0.01 M CN"), the predominant species is Cu(CN)3^" (Tran et al., 1997; Flynn and Haslem, 1995). Marsden and House (1992) have shown that copper cyanide species are stable in solutions with a pH of 4 or above, with the univalent Cu(CN)2^" being the predominant species in mildly acidic solutions. In alkaline solutions, the divalent Cu(CN)3^' becomes the predominant species.

Table 2.2 Stability of copper cyanide species Species Formation constant (Log Kf) Cu(CN) 10.5 CU(CN)2^" 21.7 CU(CN)3^' 27.0 Cu(CN)4^" 28.5

Source: Flynn and Haslem, 1995. An Eh-pH diagram for Cu^-CN'-HiO system at 25 ^C is given in Figure 2.2. Hsu and Tran (1996) have modelled the equilibrium distribution of copper cyanide species in a system of 1.57 mM Cu^ and 5.19 mM CN" at 25 ^C. They have confirmed that under such conditions, the distribution of copper cyanide species is highly dependent on the pH of the system.

2.0

Cu 2+ 1.0 - CuO - ^

^h 0

-1.0 Cu (Cu)=10'^M (CN)=10"^M ' -2.0 4.0 8.0 12.0 16.0 pH Fig. 2.2 Eh-pH diagram for Cu-CN'-HiO system at 25 V (Source: Marsden and House, 1992)

Under conditions modelled by Hsu and Tran, the divalent species Cu(CN)3^' outnumbered all other copper cyanide species by about two orders of magnitude when the pH of the system was above 10. At pH 7, the system was comprised of almost entirely of Cu(CN)3^' and Cu(CN)2^", each present in approximately equal concentrations. As the pH was further decreased, the concentration of Cu(CN)2^" increased while that of Cu(CN)3 " decreased rapidly. At approximately pH 4.5, the concentration of CuCN increased sharply, resulting from the dissociation of all other copper cyanide species. This is illustrated in Figure 2.3. c o 10 -2 3 O CuCN CU(CN)3 = (0 r • • —• CN <1> o 10" ad> w Cu{CN)43 Cu(CN)2

10"

o o c oo lo- ci 4 6 10 12 14 pH of solution

Fig. 2.3 Equilibrium distribution of copper cyanide species in a system of 1.57 mM Cu^ and 5.19 mM CN" system at 25 ^C (Adapted from Hsu and Tran, 1996)

Lukey and colleagues (1999) have used Raman Spectroscopy to determine the effect of highly saline water on the equilibrium distribution of copper cyanide complexes in solution for various CN/Cu molar ratios. They have concluded that for CN/Cu molar ratios between 2.2 and 2.5, both Cu(CN)2^" and Cu(CN)3^' exist in solution. They have reported that as the CN/Cu molar ratio was increased beyond 3.0, Cu(CN)3 " and Cu(CN)4^" become predominant in solution. They have also shown that the equilibrium distribution of each of these copper cyanide complexes changes in highly saline solutions, preferentially forming Cu(CN)4^" when the free cyanide concentration is not limiting.

Leao and colleagues (2001) have reported that the adsorption of copper cyanide on ion exchange resins is influenced by its speciation in solution. They found that HP555s ion exchange resin (a macrospores strong base ion exchange resin with polystyrene matrix and triethylammonium functional groups) preferentially adsorbed Cu(CN)3^" from solution over Cu(CN)4^". On the other hand, Amberlite IRA958 resin, which has a polyacrylic matrix supporting trimethylammonium functional groups, was reported to show no preference to one species over the other (Leao et al., 2001).

Leao and colleagues proposed that the rejection of Cu(CN)4^' by HP555s resin is partially due to the steric hindrance caused by the bulky triethylammonium functional groups, which favours the trigonal planner Cu(CN)3^" ions over tetrahedral

CU(CN)4 " ions. They also suggested that Amberlite IRA958 resin, which contains relatively compact trimethylammonium functional groups, was not producing steric hindrance to bonding with Cu(CN)4^". This explained the non-preferential loading of both these copper cyanide species to IRA958 resin.

2.1.2.2 Iron Cyanide Complexes

Cyanide complexes of iron are unique in characteristics and behaviour. As shown in Table 2.1, iron cyanide complexes have some of the lowest dissociation constants. Iron forms two complexes with cyanide, depending on its oxidation state. Iron (II) forms ferrocyanide, Fe(CN)6'^' and iron (III) forms ferricyanide, Fe(CN)6^'. The chemistry of these complexes is markedly different from other cyanide species. While they undergo a much broader range of reactions than other cyanide complexes, they show a high degree of stability, dissociating only in the presence of ultra-violet light and other extreme conditions.

Ferrocyanide, or Fe(CN)6'^', is formed by the addition of ferrous ions to a solution of free cyanide. The reaction of Fe(II) salts with cyanide to form ferrocyanide is rapid (Flynn and Haslem, 1995). Under ambient redox potentials, it is the usual type of iron cyanide complex in solutions (Smith and Mudder, 1991). Figure 2.4 shows an Eh-pH diagram for Fe-CN'-H20 system at 25 ^C. According to Figure 2.4, ferrocyanide is likely to be stable in solution at pH values of approximately 6.5 and above. However, Smith and Mudder (1992), and Kyle (1997), have reported that ferrocyanide complexes tend to decompose rapidly above pH 9. 2.0 1 —r 1 ^^Fe(CN)^

. ^ FeOOH / FeOOH 1.0

^ ^ ^

Eh 0 ^ ^ Fe(CN)^-\Fe3p4

-1.0 — Fe (Fe)=10'^M Fe{OH)^- (CN)=10^M 1 -2.0 L 1 4.0 8.0 12.0 16.0 pH

Fig. 2.4 Eh-pH diagram for Fe-CN"-H20 system at 25 ^C (Source: Marsden and House, 1992)

Ferrocyanide is not oxidised to ferricyanide by air in natural or alkaline conditions without the aid of a catalyst or light. It is oxidised by hydrogen peroxide in acidic conditions, but not in alkaline conditions. Chlorine, hypochlorite, and ozone oxidise ferrocyanide to ferricyanide (Flynn and Haslem, 1995).

Due to the high stability of ferric hydroxide in alkaline solutions, ferricyanide cannot be directly synthesised by a reaction of ferric ions with free cyanide. It is most conveniently formed by the oxidation of ferrocyanide solutions (Smith and Mudder, 1991). However, the region of stability of ferricyanide is dependent on the free cyanide concentration and the pH of the solution (Marsden and House, 1992). As shown in Figure 2.4, outside the narrow region of stability of ferricyanide, goethite (FeOOH) is formed. Ferricyanide is slowly reduced to ferrocyanide by free cyanide in alkaline solutions. This reaction is strongly catalysed by copper (Flynn and Haslem, 1995; Duke et al., 1976). For these reasons, iron cyanide found in gold cyanidation tailings is usually ferrocyanide or its constituent ions. Ferricyanide could exist as a transient species depending on factors such as Eh and pH of the solution, level of aeration, dissolved oxygen content, total cyanide content, and the age of the solution.

Both these cyanide complexes form highly stable complexes with other cations. Most alkali and alkaline earth salts of hexacyanoferrates are soluble in water, with the exception of barium hexacyanoferrate. The transition metal and heavy metal hexacyanoferrates are generally insoluble in water, hence hexacyanoferrates are considered 'inert' compounds. Salts of ferrocyanide are considerably more stable than their corresponding ferricyanide analogues (Kyle, 1997). Hexacyanoferrate complexes of metals that are capable of forming strong complexes with cyanide or amine complexes (i.e. cadmium, copper, nickel, and silver), dissolve in solutions of excess free cyanide or ammonia (Smith and Mudder, 1991).

As shown in Equation 2.5, hexacyanoferrates form an oxidation-reduction couple. Since the two free ions are more abundant in alkaline or neutral conditions than in acidic conditions, the oxidation of ferrocyanide to ferricyanide occurs easily in neutral or mildly alkaline conditions. Therefore, despite the absence of H^ in the reaction, due to the difference of dissociation constants of corresponding acids, the reaction depends on the pH of the solution. However, as discussed previously, at pH values above 9, ferrocyanide is reported to be unstable in aqueous solutions.

Fe(CN)/- + e- < > Fe(CN);- (2.5)

Ferrocyanide binds strongly with both strong base and weak base ion exchange resins. Smith and Mudder (1991) have reported that the elution of ferrocyanide ions from strong base ion exchange resins is very difficult because of the strong negative charge of the ferrocyanide ion. Leao and colleagues (2001) have reported that the loading of ferrocyanide is more difficult than the loading of the ferricyanide species. As in the case of copper cyanide complexes (Section 2.1.2.1), they have stated that resins with sterically bulky triethylammonium functional groups are less likely to retain ferrocyanide because four triethylammonium groups have to act together to hold the ferrocyanide ion. The length of the ethyl chain makes it difficult for the four bulky exchange groups to come within close proximity. Ferricyanide requires only three exchange groups for its adsorption. Therefore, ferricyanide is preferred over ferrocyanide by resins with triethylammonium functional groups.

In the presence of ultra-violet light, ferrocyanide and ferricyanide undergo photolysis and hydrolysis, where water sequentially displaces cyanide ligands. Broderius and Smith (1980) have reported that these compounds can release significant levels of cyanide when exposed to high levels of ultra-violet light. (Ferrocyanide releases up to 85% of the cyanide bound to the complex and ferricyanide releases up to 49% of its cyanide.) Under extreme conditions such as boiling with phosphoric acid, hexacyanoferrates decompose into their constituents. Such decomposition is also brought about by strong complexing agents such as EDTA or tartaric acid, and by certain catalytic metal ions such as mercury or magnesium (Smith and Mudder, 1991).

2.1.2.3 Other Non-WAD Cyanide Species

Other cyanide complexes such as Dicyanoaurate(II) (Au(CN)2^")5 Tetra- cynoaurate(III) (Au(CN)4'), hexacyanocobaltate(III) (Co(CN)6^'). and, to a limited extent, hexacyanochromate(III) (Cr(CN)6^'). are considered non-WAD cyanide compounds. They behave, in many ways, in a similar manner to ferrocyanide and ferricyanide species. Like their iron counterparts, Au(CN)2', Au(CN)4' and Co(CN)6^" do not dissociate under acidic conditions. Cr(CN)6^' decomposes in acidic solutions giving HCN, but the decomposition requires several days to reach completion. CO(CN)6 " is a very stable species and is formed in cyanidation solutions by the oxidation of the pentacyanocobaltate(II) Co(CN)5^' by air. The corresponding free acid is stable and can be isolated as a stable solid (Flynn and Haslem, 1995). In the laboratory, it is most conveniently synthesised by the reaction of C0CI2 with KCN in the presence of air in aqueous solutions (Poskozim, 1969). It is not destroyed by oxidants such CIO", O3 or CIO2. The only known method of decomposition of is photocatalysis, taking place when irradiated with blue or near-ultra- violet light, 500 to 300 nm wavelength (Flynn and Haslem, 1995).

Uj li

o a. 0c S 1 GC

PH Fig. 2.5 Eh-pH diagram for Au-CN'-H20 system at 25 ^C Concentration of all soluble gold species = 0.1 mM (Source: Marsden and House, 1992) Cr(CN)6 ' is formed when Cr(III) salts react with excess cyanide in solution. It is unaffected by most oxidants but some unsubstantiated reporting of its oxidation to Cr04^' has been documented by Flynn and Haslem (1995). Like Co(CN)6^", it decomposes by photocatalysis when irradiated with blue or near-ultra-violet light.

Au(CN)2' is formed when metallic gold or gold compounds react with free cyanide. It is soluble in alkaline solutions and does not decompose under acidic or oxidative conditions. Au(CN)4" can be formed by oxidising Au(CN)2' in aqueous solutions (Smith et al., 1965). Figure 2.5 gives an Eh-pH diagram for Au-CN'-HiO system. Due to the high oxidation potentials required to oxidise gold to its trivalent stage, it is not found in cyanidation plant liquors (Adams et al., 1992), but as the syntheses reported by Smith and colleagues (1965) indicate, Au(CN)4' will form when a strong oxidant is introduced into a cyanide liquor containing Au(CN)2". Little is reported about the photochemical decomposition of Au(CN)4". Destructive oxidation of this species by commonly occurring oxidants under normal conditions is not addressed in the literature.

2.1.3 Reactions Between Metal Cyanide Complexes and Metal Cations

Most anionic metal cyanide complexes form stable double salts with metal cations. In some cases, the product of this reaction contains the same species present in the reactants. However, if the cation produces a stronger cyanide complex than the initial metal ion found in the reactant cyanide species, a rearrangement within the double salt could take place, as shown in Equations 2.6 and 2.7. With the exception of the reaction of ferrocyanide and ferricyanide with metal cations, little is known about the details of these reactions (Flynn and Haslem, 1995).

Zn(CN)4'' + Ni'^ + XH2O > Ni[Zn(CN)4].XH20 (2.6)

Ni[Zn(CN)4 ]. X H2O > Zn[Ni(CN)4 ]. X H^O (2.7) Due to their unique properties, hexacyano complexes, taking the form of M[M'(CN)6], are an important subset of metal cyanide double salts. They are generally known as Prussian Blue analogous compounds due to their similarity to Prussian Blue, Fe4[Fe(CN)6]3. They have a simple cubic framework in which octahedral [M'(CN)6]"' complexes are linked via octahedrally connected nitrogen bound M"^ ions. (Kaye et al., 2005). Hexacyano complexes of Co(III), Fe(II), Fe(III), Mn(III) and Cr(III) all give precipitates with heavy metal cations (Flynn and Haslem, 1995). Hence they are used for co-precipitating other heavy metals. Hexacyanocobaltates have been studied as inorganic exchangers to remove fission products from radioactive wastes (Mekhail et al., 1991).

Hexacyanoferrates have been noted especially for their ability to co-precipitate other heavy metals from cyanidation solutions (Adams et al., 2000). They also show remarkable electro-catalytic, electrochromic, ion exchange, ion sensing, and photo- magnetic properties (de Tacconi et al., 2003). Some hexacyanoferrate compounds form as colloids of gelatinous precipitates, which are not always stoichiometric. They could contain variable quantities of alkali ions from the hexacyanometallate salt used in their synthesis. Their extent of hydration also varies significantly, subject to precipitation conditions.

Solubility equlibria of metal hexacyanoferrates have not been exhaustively studied yet and the available data is sometimes unreliable (Flynn and Haslem, 1995). Solubility of some key ferrocyanide and ferricyanide sahs has been tabulated by Huiatt and colleagues (1982). The solubility of these compounds is not greatly affected by the pH of the solution between the range of pH 2 to pH 11 (Smith and Mudder, 1991). Solubility figures reported by Huiatt and colleagues are shown in Table 2.3.

Early powder X-Ray diffraction studies into the structures of metal ferricyanide and ferrocyanides found that most compounds have very similar diffraction patterns (Weiseret al, 1941). Table 2.3 Solubility Species Formula Solubility (g/L) Ammonium Ferricyanide (NH4)3 Fe(CN)6 Very soluble Ammonium Ferrocyanide (NH4)4Fe(CN)6®3 H2O Soluble Cadmium Ferrocyanide Cd2Fe(CN)6 »X H2O Insoluble Cobalt Ferrocyanide Co2Fe(CN)6 »X H2O Insoluble Copper (I) Ferricyanide Cu3 Fe(CN)6 Insoluble Copper (II) Ferricyanide Cu3 (Fe(CN)6)2 • I4H2O Insoluble Copper (II) Ferrocyanide Cu2Fe(CN)6 «X H2O Insoluble Iron(II) Ferricyanide Fes (Fe(CN)6)2 Insoluble Iron(II) Ferrocyanide Fe2Fe(CN)6 Insoluble Iron(III) Ferrocyanide Fe4 (Fe(CN)6)3 2.5 X lO-'^ Lead Ferricyanide Pb3 (Fe(CN)6)2 »5 H2O Slightly soluble Magnesium Ferrocyanide Mg2Fe(CN)6®12H20 330 Manganese (II) Ferrocyanide Mn2Fe(CN)6*7 H2O Insoluble Potassium Ferricyanide K3 Fe(CN)6 330 (4 V) Potassium Ferrocyanide K4Fe(CN)6®3 H2O 278 (12 ^C) Silver Ferricyanide Ag3 Fe(CN)6 0.00066 (20 ^C) Tin (II) ferrocyanide Sn2Fe(CN)6 Insoluble Zinc Ferrocyanide Zn2Fe(CN)6 2.5 X 10-^ Zinc Ferricyanide Zn3 (Fe(CN)6)2 2.2 X 10-^ Source: Huiattet al., 1982.

Subsequent studies have distinguished the differences between the diffraction patterns and highlighted that the conditions of precipitation and the extent of hydration of these species significantly affects the powder X-Ray diffraction patterns (Ayers et al., 1970; Cola et al, 1977). To overcome these difficulties, I. R. and UV- Visible Spectra have also been applied (Ghosh, 1974; Cola et al., 1977). Tacconi and colleagues (2003) have been successful in applying Diffuse Reflectance Spectrometry in the UV-Visible range to distinguish between various transition metal ferricyanides and ferrocyanides. 2.1.4 Cyanate and Thiocyanate

Many oxidants convert cyanide to cyanate. Smith and Mudder (1992) propose that the presence of cyanate in cyanidation taihngs could be attributed to the reaction between free cyanide and hydrogen peroxide, which is formed during the dissolution of gold in cyanide liquors. This is illustrated in the simplified reaction given in Equation 2.8:

HCN + 1/2 0. HCNO (2.8)

Figure 2.6 gives the Eh-pH diagram for CN-H2O system at 25 ^C. The thermodynamics of the cyanide-cyanate system suggest that cyanide is unstable under ambient conditions in relation to cyanate. However, the conversion of cyanide to cyanate is restricted by the kinetics of the reaction. A strong oxidant, a catalyst, or ultra-violet light, is required to drive this reaction forward.

2.0 1 1 \

1.0 -

CNO~ — ^ ^

^h 0 -

^ ^, -1.0 HCN CN- (CNJ • 10-^ M "ZO 1 1 1 0 4.0 8.0 12.0 16.0

pH Fig. 2.6 Eh-pH diagram for CN'-HiO system at 25 ^C (Source: Marsden and House, 1992) Cyanate dissociates under room temperature (accelerated under weak acidic conditions or elevated temperatures) to form ammonia, formate, and/or carbonate (Smith and Mudder, 1991).

The reaction of free cyanide with sulphur rich minerals during cyanidation results in the formation of thiocyanate (SCN"). Thiocyanate is also classified as a pseudohalogen. However, unlike halogens, it forms insoluble salts with most transition group metals. Thiocyanate is relatively more stable than cyanate, but also decomposes to form ammonia, carbonate, and sulphate under acidic conditions. Cyanate and thiocyanate are significantly less toxic than cyanide, and hence significantly higher levels of thiocyanate and cyanate are permitted in tailings.

2.1.5 Toxicity of Cyanide

Cyanide is well known to be toxic to humans, aquatic life and the environment. The lethal dose of free cyanide for humans ranges from 50 to 200 mg/kg of body weight. Fish and aquatic invertebrates are particularly sensitive to cyanide exposure. Concentrations from 0.05 to 0.1 mg/L show acute toxicity to fish. The sensitivity of aquatic organisms to cyanide is highly species specific. The water temperature, the pH, and the dissolved oxygen content also affect the sensitivity of aquatic organisms to cyanide (Smith and Mudder, 1991).

The toxicity of cyanide to humans is due to its ability to bind elements such as iron, copper, and sulphur, which are found in many enzymes and proteins important to life processes. The most significant impact of cyanide is its binding to the ferric iron of the mitochondrial cytochrome oxidase system. Cyanide binds to the cytochrome a3 complex, inhibiting oxidative phosphorylation and paralysing cellular respiration. This leads to anaerobic metabolism, increased lactic acid production, reduced ATP stores, and anoxic cell death. When the central nervous system tissue is affected by this process, the resuh is a catastrophic suspension of all vital functions. 2.2 GOLD CYANIDATION AND CYANIDATION TAILINGS

Cyanidation of gold ore has been practiced in most parts of the world for well over 100 years. The cyanidation process was patented in 1889 by the McArthur and Forrest brothers. It was quickly established as a commercial practice in the mining sector. Marsden and House (1992) report its first use at Crown Mine in New Zealand in 1889. Robinson Deep (South Africa) adopted the process in 1890, followed by Consolidated Mercur (Utah, USA) in 1891, El Oro (Mexico) in 1900, and La Belliere (France) in 1904. From this period onwards, cyanidation has held its ground as the primary process for gold extraction.

Cyanide has a number of highly desirable properties as a lixivant for extracting gold and silver. It is able to form highly stable and soluble complexes with gold and silver under conditions easily facilitated in mining and mineral processing environments. It has a low production cost, is available in liquid and solid forms, and is compatible with most mining environments. For these reasons, cyanide leaching remains the most studied and employed lixivant system for extraction of gold and silver.

Gold cyanidation has been reported to involve a number of chemical reactions. Eisner has been credited with one of the earliest reports on this subject. In 1846, Eisner suggested a simple mechanism (shown in Equation 2.9) for gold dissolution (Smith and Mudder, 1991).

4Au + 8CN- + O2 + 2H2O > 4Au(CN)2" + 4 OH" (2.9)

This was accepted for several decades as the chief mechanism for gold dissolution. Subsequent research has shown that the reaction proceeds in two stages, as shown in Equations 2.10-2.13 (Marsden and House, 1992; Sananayake, 2005). 2Au + 4CN- + O2 + 2H2O > 2Au(CN)2 + 20H-+ H^O^ (2.10)

2Au + 4CN- + H2O > 2Au(CN)2' + 2 OH" (2.11)

CN" + H2O2 > CNO" + H2O (2.12)

H2O2 > 1/2 O2 + H2O (2.13)

As gold reacts with cyanide, hydrogen peroxide is formed at the interface of metallic gold by the reduction of oxygen. This can react with gold or with cyanide, or alternatively decompose to oxygen and water. Cyanate produced by the oxidation of cyanide further degrades to other products. The rate of gold dissolution depends on the temperature, concentration of free cyanide and the alkalinity of solution. The efficiency of gold dissolution is also affected by other species in the system such as sulfide containing minerals and cyanide soluble base metals.

There are several types of gold cyanidation circuits. All cyanidation processes use cyanide to mobilise gold from the ore by dissolving metallic gold to form the soluble Au(CN)2" complex. The dissolved gold is then separated from the ore, either by physical separation of liquor from the ore, or by adsorption of gold cyanide on an adsorbent. Some variations of gold cyanidation circuits are:

• grinding, cyanidation, liquid solid separation, clarification, de-aeration, zinc precipitation, and smelting

• grinding, cyanidation, carbon-in-pulp adsorption, stripping of carbon, and electro-winning

• grinding, cyanidation, resin-in-pulp adsorption, stripping of resin, and electro-winning

• crushing, heap leaching, carbon adsorption from solutions, stripping of carbon, and electro-winning

crushing, heap leaching, resin adsorption from solutions, stripping of carbon, and electro-winning crushing, vat leaching, carbon adsorption from solutions, stripping of carbon, and electro-winning

crushing, vat leaching, ion exchange adsorption from solutions, stripping of ion exchange, and electro-winning

grinding, flotation, fine grinding or roasting of flotation concentrate, cyanidation of concentrate, liquid solid separation, clarification, de-aeration, zinc precipitation, and smelting.

In processes where the gold bearing liquor is physically separated from the ore (such as heap leaching, vat leaching or cyanidation of flotation concentrate), the gold bearing clear liquor is brought into contact with an adsorbent (activated carbon or ion exchange resin), which adsorbs Au(CN)2" from the solution. While most of the resulting gold-free or 'barren' solution is returned to the cyanidation circuit for further gold dissolution, some solution is purged from the leaching circuit to prevent the deleterious build up of base metals and products of cyanide degradation (SCN", CNO", NH4"^ etc), which interfere with further gold dissolution.

In circuits where the ground ore is directly brought into contact with the absorbent media (such as carbon-in-pulp or resin-in-pulp), the loaded adsorbent is physically separated from the pulp and processed to extract gold. The gold depleted pulp or the 'leached slurry' is thickened to recover some of the liquor, which is recycled to the grinding/leaching circuit. The resulting thickened leached slurry, which contains the ore and some cyanide containing solution, is discharged from the circuit.

Consequently, regardless of the type of cyanidation circuit, a waste barren solution, or a slurry, is produced from gold cyanidation operations. These streams contain free cyanide, metal cyanide complexes and cyanide degradation products. The volume of these waste streams could vary significantly, depending on the type of operation. The disposal of several thousand litres of tailings per day is not uncommon for a small cyanidation operation using zinc precipitation. On the other hand, a large CIP operation could produce thousands of cubic metres of tailings slurry per hour. The treatment and disposal of these waste streams weigh heavily in the consideration of the environmental impact of cyanidation operations.

2.3 CHEMISTRY OF CYANIDATION TAILINGS

The chemical properties of cyanidation tailings depend on the type of ore processed.

Ores rich in cyanide soluble minerals produce tailings with high levels of CNWAD- Sulphidic ores containing cyanide soluble sulphide minerals produce thiocyanate (SCN") in tailings from the reaction of sulphide with cyanide. Copper oxide minerals such as azurite and malachite (double salt of copper carbonate and hydroxide), cuprite (Cu(I) oxide), tenorite (Cu(II) oxide), chalcocite (Cu(I) sulphide), and covellite (Cu(II) sulphide), are all very soluble in dilute cyanide liquors. Other complex sulphides such as bomite (copper iron sulphide), chrysocolla (copper silicate), and particularly chalcopyrite (copper iron sulphide), are less soluble under gold cyanidation conditions. Most of these minerals give rise to copper cyanide complexes in the leach solution.

Sulphides of zinc (sphalerite), iron (marcasite and pyrrhotite), antimony (stibnite), and nickel (iron-nickel sulphide, pentlandite), also form metal cyanide species and thiocyanate (SCN") when contacted with cyanide solutions. Cyanide species of iron, cobalt, and precious metals are not accounted for by CNWAD analysis, as they do not dissociate readily under mild acidic conditions. Thiocyanate, formed in significant quantities when sulphidic ores are subjected to cyanidation, can be a significant economic drawback and an environmental concern for cyanidation operations. Higher operating costs are incurred in such circumstances because of the increased requirement of cyanide for leaching and the need for detoxification of tailings. Due to the toxicity of cyanide and several high profile accidents which led to the release of cyanide into aquatic environments, the mining industry all over the world has faced stringent limitations on cyanide levels allowed in tailings dams. Although cyanidation has had well over a century of process refinements and optimisations, which has enabled it to maintain a competitive edge over many other gold extraction processes, the inevitable production of cyanide contaminated waste streams has restricted the applicability of cyanidation in many new gold processing operations.

Over the last two decades, the concern of cyanide contamination has intensified to the extent that cyanidation is no longer considered a preferred option in areas with significant ground water reserves or open aquatic environments. Currently in New South Wales, Australia, waste classification guidelines restrict the disposal of all aqueous wastes with CNTQT concentration over 1 mg/L. The discharge limits applied to gold cyanidation operations vary, depending on the net environmental impact of the discharge stream.

For these reasons, tailing detoxification and cyanide management have emerged as key unit operations in cyanidation practices. As environmental protection authorities continue to lower the limit of cyanide allowed to be discharged into tailings dams, new and more effective techniques for cyanide management are sought by plant operators to maintain compliance with regulatory requirements.

2.4 CYANIDE DETOXIFICATION TECHNIQUES

The removal and/or destruction of CNWAD species from tailings is broadly referred to as cyanide detoxification. Non-WAD cyanide species, due to their lower levels of toxicity, are overlooked in many processes. Cyanide detoxification processes available to the mining industry are discussed in the following section. Processes reviewed include those currently used in cyanidation operations as well as those under development. 2.4.1 Biological Treatment

Cyanide detoxification using biological processes has been successfully carried out since 1984 at Homestake Mining (Adams et al., 2001; Whitlock et al., 1985). The rotational biological contactors (RBC) used at Homestake Mining were successful in removing all cyanide complexes from tailings through a combination of oxidation and adsorption into biofilm. The reactor converted ammonia to nitrate, and metals were precipitated from solution and immobilised in the biofilm (Smith and Mudder, 1991). The full-scale facility was in continuous operation, treating high volumes of tailings pond solution, until the closure of Homestake Mine in 2002. After the successfiil use of RBCs for biological treatment of cyanidation tailings, Homestake developed another combined aerobic and anaerobic multi-stage suspended growth process for treatment of thiocyanate, ammonia, and nitrate contained in tailings ponds. Homestake Mining also developed a passive 'in-situ' anaerobic biological process, termed the 'Biopass System', for the treatment of residual cyanide and other pollutants in the draindown from a large heap leach pad located at its Santa Fe Mine. The use of the in-situ passive biological process is becoming a preferred approach for treatment of draindown and seepage from heap leach operations (Akcil and Mudder, 2003).

Packed cage RBC systems, with more bio-film mass than conventional RBC systems, have been tested as an alternative to RBCs by Sirianuntapiboon and Chuamkaew (2006). Another variation of biological reactors, closed system sequencing batch biofilm reactors (SBBR) have also been successfully tested in pilot scale tests (White et al., 2000; White and Schnabel, 1998). SBBR systems are reported to be suitable for operation around the year as well as in colder environments, as they can be operated indoors.

Notwithstanding these developments, and the demonstrated successful operation over almost two decades at Homestake Mining's operations, the mining sector has been slow to adopt biological treatment as an overall cyanide detoxification process. Large scale operations relying exclusively on biological processes have not been reported since the closure of Homestake Mine in 2002. However, natural biological processes are indirectly employed in almost every cyanide detoxification process. After tailings detoxification by other cyanide treatment processes, biological degradation contributes to the decomposition of the remaining low levels of cyanide contamination before tailings are discharged into the environment.

2.4.2 Precipitation with Iron Cyanide

When ferrous ions are introduced to cyanidation tailings, they react with free cyanide in the solution, producing ferrocyanide. When excess ferrous ions are added, the free ferrous ions react with ferrocyanide to form insoluble ferrous ferrocyanide and analogous compounds. Precipitation of cyanide as these insoluble double sahs was developed as a cyanide detoxification process (Babcock and Kuit, 1981). The process works well for free cyanide, but is ineffectual for treatment of cyanide complexes unless the solution is acidified. In acidified solutions, ferrous salts of other metal cyanide complexes precipitate out from the solution. The process is said to work well as a pre-treatment step for the removal of free cyanide. The process was initially tested in large scale by Cominco Limited gold mining and milling site, located on the shores of the Great Slave Lake. After testing at Cominco Limited, the process has been used to remove free cyanide in several mining operations in the US, Canada, and France (Smith and Mudder, 1991). In spite of these developments, its implementation as an overall cyanide detoxification process has not been reported.

The precipitation of cyanide species as insoluble cyanide double salts plays a supporting role in many other cyanide detoxification processes. Adams and Kyle (2000) have reported that mixed ammonia-cyanide-copper-iron precipitates have an important role in reducing total cyanide levels in oxidative cyanide detoxification processes. If copper is present in cyanidation solution, the precipitation of copper cyanide as cyanide double salts contributes to the efficiency of biological cyanide degradation processes. 2.4.3 Direct Oxidation

Chlorine, hydrogen peroxide, and S02/air mixtures are used for direct oxidation of cyanides in tailings streams. Most of these processes are now well established in the mining sector. A large amount of literature is available on direct oxidation processes.

2.4.3.1 Alkaline Chlorination

Alkaline chlorination was the first cyanide detoxification process developed for the treatment of cyanidation and electroplating wastes. Destruction of free cyanides in alkaline solutions could be achieved by the addition of sodium hypochlorite, calcium hypochlorite, or direct injection of chlorine gas into the tailings. The overall oxidation of free cyanide can be represented as shown in Equation 2.14:

5CI2 + 10 OH- + 2CN- > 2HC03' + 10 Cf + 4H2O + N2 (2.14)

The above reaction involves several distinct steps. Firstly, free chlorine or hypochlorites react with cyanide to form cyanogen chloride (CNCl) as shown in Equations 2.15 to 2.17:

NaCN + CI2 > CNCl + NaCl (2.15)

2NaOH + CI2 > NaOCl + NaCl + H^O (2.16)

NaOCl + NaCN + H^O > CNCl + 2NaOH (2.17)

Mishra (2002) reports that the formation of CNCl takes place irrespective of the solution pH. However, its volatilisation can be minimised by keeping the solution pH above 10. In alkaline conditions, CNCl rapidly hydrolyses to cyanate as shown in Equation 2.18 (Smith and Mudder, 1991; Thomson et al., 1994). Cyanate is relatively stable under alkaline conditions. However, in the presence of free chlorine or hypochlorite, cyanate hydrolyses as shown in Equation 2.19: CNCl + 2NaOH > NaOCN + NaCl + H^O (2.18)

2NaCN0 + 4H2O > (NH4)2C03 + Na2C03 (2.19)

Generally, the oxidation is carried out at pH 10.5 or above in an agitated tank. The dosage of chlorine or hypochlorite can be controlled by measuring the redox potential of the solution (Mishra, 2002). Under ambient conditions, alkaline chlorination will remove all CNWAD species from solution. However, iron and cobalt cyanide species are not destroyed unless elevated temperatures or ultra-violet light is used. The overall chlorine consumption can vary significantly, subject to other compounds amenable to oxidation by chlorine. Thiocyanate is a typical compound responsible for increasing chlorine demand. Consumption of 5 to 12.5 mg of chlorine

(as chlorine gas or hypochlorite) can be expected per mg of CNWAD in solution (Smith and Mudder 1991).

The overall alkaline chlorination process is a preferred option for treating tailings with little non-WAD cyanide species and low thiocyanate levels. Residual chlorine and chloramine products in the tailings, after alkaline chlorination, are a significant concern when applying this technique. The toxicity of these compounds to aquatic life is comparable to that of free cyanide. Hence, they need to be removed by dechlorination before the treated solution is discharged. Generally, this is carried out by introducing sodium sulphite (NSLJSO^) to the treated liquor.

2.4.3.2 Sulphur Dioxide/Air Process

In early 1980s, Inco commercialised the S02/air process to detoxify cyanide tailings using a mixture of SO2 gas and air (Ferguson and Walker, 1985; Devuyst and Robbins, 1992). In this patented process, sulphur dioxide (in gas, liquid, solutions of sulfite salts or off gas from burning elemental sulphur) and air are introduced into a well agitated vessel of cyanidation tailings. When gaseous SO2 is used, a 2% SO2 in air has been reported to be highly effective. The destruction of CNWAD species takes place as SO2 is oxidised to H2SO4, as shown in Equation 2.20 (Devuyst et al., 1989). The cyanide oxidation reaction is catalysed by copper. Good cyanide oxidation efficiency and kinetics has been seen when copper concentration is at 50 mg/L in solution. While CNWAD species are oxidised to respective metal cations and CNO", iron cyanide is precipitated as metal cyanide double salts (Mishra, 2002).

CN" + SO2 + O2 + H2O > CNO" + H2SO4 (2.20)

The reaction generates acid, and as the reaction progresses, the pH of the solution decreases. Hence, lime is added to the reaction vessel to maintain the pH of the solution between 8.0 and 10.0. The theoretical sulphur dioxide and lime consumptions are approximately 2.5 mg SO2 and 2.2 mg CaO per mg of CNWAD in solution. In practice, reagent consumption is higher.

Owing to its favourable economic and environmental performance, the SOi/air oxidation has gained immense popularity in the mining sector. After the recent technology transfer between Inco and CyPlus, a wholly-owned company of Degussa AG (Düsseldorf, Germany), it is now marketed as the CyPlus^'^ SOi/air process. Its application and popularity is similar to that of alkaline chlorination and hydrogen peroxide processes.

2.4.3.3 Copper Catalysed Hydrogen Peroxide Oxidation

Hydrogen peroxide treatment of cyanide was first tested in full scale at the Ok Tedi Mine in Papua New Guinea by Degussa Cooperation (Smith and Mudder, 1991). The oxidation is conducted in alkaline solutions to prevent the release of HCN gas. The reaction produces corresponding base metal hydroxides and cyanate, which in turn decay to carbonate and ammonia, as shown in Equations 2.21 to 2.23:

CN- + H2O2 > CNO" + H2O (2.21) Cu(CN)3' + 3H2O2 + 2 OH" > Cu(0H)2 + 3CN0- + SH^O (2.22)

CNO- + 2H2O > CO3' + NH/ (2.23)

The oxidation of CNWAD species by hydrogen peroxide is catalysed by copper. Vanadium, tungsten or silver also catalyse the reaction (Castrantas and Manganaro, 1997). In most operations, a reaction period between 20 minutes and 4 hours is adequate to oxidise cyanide species. Copper sulphate is added to the tailings to achieve the required process efficiency when required. In general, CNWAD/CU molar ratios between 5 and 10 have been found suitable (Smith and Mudder, 1991).

The optimum pH range for removal of cyanide and precipitation of metals is reported to be between 9.0 and 9.5. Under these conditions, peroxide consumption of 200% to 450% in excess of stoichiometric requirements is seen in commercial applications (Smith and Mudder, 1991). Higher copper concentrations increase the rate of the reaction, but also increase the residual metal concentration in the tailings.

Hydrogen peroxide is relatively unstable in treated tailings. It decomposes to water shortly after the treatment. Other than potential contamination of tailings with copper used to catalyse the process, hydrogen peroxide oxidation of cyanide does not leave residual chemicals. Hydrogen peroxide process is hence gaining popularity as a 'clean cyanide detoxification process' over the other oxidation processes.

2.4.3.4 Cyanide Oxidation by Ozone

The oxidation of cyanide by ozone has been known for some time. Some recent work using cyanidation plant tailings has indicated that ozone reacts with cyanide and thiocyanate, but does not react with cyanate. Carrillo-Pedroza and colleagues (2000) have demonstrated that cyanide concentration could be reduced from several hundred mg/L to less than 10 mg/L in a bubble column, when sparged with ozone. Significant reduction of thiocyanate has also been noted. No pilot plant tests or industrial applications have been reported on the use of ozone for cyanide detoxification.

2.4.3.5 Review of Direct Oxidation Processes

Processes based on chlorine, hydrogen peroxide and sulphur dioxide/air are widely practiced in the mining industry today. These oxidation techniques are preferred over other processes due to their proven process performance, low capital cost requirements, and relatively simple plant designs. In general, oxidation processes rely on the direct reaction between the oxidant and cyanide. Hence, these processes become less cost efficient when treating tailings with low cyanide levels, owing to the increasing excess oxidant requirement. If other base metals such as copper, zinc and iron, or sulphidic minerals are present in the ore, the cyanidation products of these compounds also react with the oxidants, increasing the total oxidant requirement. Furthermore, the environmental impact of residual or unused chemicals in tailings needs to be given consideration in direct oxidation processes such as alkaline chlorination and S02/air process. This could be a significant drawback in some operations.

2.4.4 Cyanide Recovery by Acidification

The recovery of cyanide from waste cyanide solutions by acidification, stripping with air, followed by re-absorption in lime slurries, has been accepted as a standard practice since 1929. According to Smith and Mudder (1991), it was first known as the Mille Crows Process (not to be associated with Merrill-Crowe system), and was employed to recover cyanide from tailings at the Flin Flon Mine in Canada. This was carried out from about 1930 to 1975. Approximately 90% recovery of cyanide was achieved, reducing the cyanide concentration in the tailings from 44 g/L to approximately 0.5 g/L. Several parallel operations in other parts of the world have also been documented by Smith and Mudder (1991). In the 1970s the process was refined by McNamara (1978), improving the volatilisation efficiency by using glass Raschig rings as packing (Riveros et al., 1998). This work also documented the chemistry of the process for the first time. Since then, the process has been generally known as the AVR (an acronym for Acidification, Volatilisation and Reneutralisation) process (Smith and Mudder, 1991).

Since this initial work by McNamara, several other improvements have been made to this process (Riveros et al., 1998). These modifications allow the tailoring of the general AVR concept to match the operational requirements of various operations, allowing the optimisation of cyanide detoxification and recovery, while minimising reagent consumption and operational hazards.

In general, the current AVR process has three primary unit operations. The first is the acidification of the tailings stream (solution or slurry) to convert most of the cyanide to HCN. To recover free cyanide, acidification to pH 7.0 to 8.5 will suffice. To

recover CNWAD, acidification to pH less than 2.0 is needed (Smith and Mudder 1991). Under these conditions, the majority of cyanide species decompose, releasing HCN as shown in Equations 2.24 and 2.25:

2NaCN + H2SO4 > Na2S04 + 2 HCN (2.24)

Na2Zn(CN)4 + 2H2SO4 > ZnS04 + Na2S04 + 4 HCN (2.25)

As given in Equations 2.26, copper cyanide precipitates as insoluble CuCN, releasing all but one cyanide ligand. Non-WAD cyanide species do not decompose under these conditions, but react with the base metal cations to form insoluble metal cyanide double salts as shown in Equation 2.27:

NA2CU(CN)3 + H2SO4 > CUCN^ + Na2S04 + 2 HCN (2.26)

Fe(CN)/- + > Zn2[Fe(CN)J.XH20 (2.27) In the second stage, the acidified solution or slurry is aerated to recover HCN gas from the liquid phase (Equation 2.28). The volatilisation is generally performed in packed columns, although aerated tanks have been investigated for volatilisation of HCN from slurries (Williams and Goldstone, 1988). Recovery of HCN up to 99% from the liquid phase is feasible (Smith and Mudder, 1991; Riveros et al., 1998). The resuhing HCN/air mixture is then scrubbed with a lime or NaOH solution to convert HCN to NaCN or Ca(CN)2 (Equation 2.29). This is recycled back to the leaching circuit.

^^ HCN(^) (2.28)

HCN(^) + NaOH(3^) > NaCN^^^^ + H,0 (2.29)

Finally, the acidified solution, which is now stripped of cyanide, is re-neutralised. When the pH is increased to between 9.0 and 10.5, metal cations in the solution precipitate as their corresponding hydroxides (Equation 2.30). It is important not to increase the pH any further to prevent the re-dissolution of some metals like zinc.

Zn^^ + 2 OH- > Zn(0H)2 ^ (2.30)

The resulting solution or slurry is now free of soluble cyanide species, transition metals, and heavy metals. Clear solution can be recycled to the cyanidation circuit after removing the insoluble matter, which includes metal hydroxides and precipitated metal cyanide double saUs.

This process is attractive for solutions with relatively high CNWAD levels, as it allows the recovery of cyanide. Metals recovered as hydroxide or cyanide precipitates also have a potential use. This process has become accepted by industry as an option for treating relatively concentrated cyanide liquors (over 500 mg/L CNWAD) (Tran et al., 2000). However, high reagent costs, high power consumption, and low efficiencies are encountered when treating slurries and dilute cyanide liquors. 2.4.5 Ion Exchange Resin Processes

The use of ion exchange resins for the treatment of cyanide wastes has been explored for over 50 years. In the early 1950s Walker and Zabban (1953) developed a bench scale process to concentrate aqueous cyanide waste streams arising from electroplating operations. The use of ion exchange resins for the management of tailings from gold processing operations was tested shortly following these developments. Goldblatt (1956; 1959), working with the waste cyanide solutions arising from the gold reduction works of Stilfontein Mining Corporation developed a process to recover cyanide, water, and gold using strong base ion exchange resins. Some years later, Tallmadge (1967) reported a study comparing the performance of several ion exchange systems for the recovery of cyanide from electroplating wastewaters. Since then, a large number of publications have been produced on the use of ion exchange resins for recovering cyanide from electroplating and industrial wastewaters.

Figure 2.7 shows the annual release of publications and issue of patents related to the management (including concepts such as recovery, treatment, detoxification, and oxidation) of cyanide wastes using ion exchange resins. Whilst this survey may not have captured all publications on the subject during the past 50 years, it nevertheless shows a significant interest in ion exchange processes for cyanide waste management in the late 1960s and early 1970s. A revival of interest can be seen in the early part of this decade.

The vast majority of publications and patents on the use of ion exchange processes for management of cyanide wastes have come from the electroplating sector. Publications and patents related to the use of ion exchange resins for cyanide waste management in gold cyanidation have been relatively rare. However, most ion exchange resin based gold extraction processes, where resin is used as an alternative adsorbent to activated carbon, claim cyanide recovery capabilities. •D C OS (0 c 15

~~o JQ E 3~~

~~1950 1960 1970 1980 1990 2000 2010 Year~~

~~Fig. 2.7 Publications and patents on ion exchange resin based cyanide management processes~~

At present, there are several ion exchange resin based cyanide management processes discussed in the literature. Some of these processes are still in the development stages, while others have been tested in pilot scale. Large commercial scale applications have not been reported yet.

~~2.4.5.1 The Cyanosave™ Process~~

The Cyanosave^^ process, which was reported to be suitable for recovering free and complex cyanides from gold mining effluents, was reported by Elvish and colleagues (1988). This process uses Vitrokele 911 resin as the adsorbent. Process performance results given by these authors are limited to resin loading data. Although the authors claimed that the resin can be stripped of cyanide to recover cyanide and to regenerate the resin, the process chemistry of the elution was not discussed. 2.4.5.2 The Cy-Tech Ion Exchange System

The Cy-Tech process was developed with the intention of producing environmentally acceptable effluents and recovering cyanide in a useable form (Smith and Mudder, 1991). The process uses a strong base anion exchange resin bed to recover cyanide complexes from solution as shown in Equation 2.31:

~~2(-NR3'HSO4") + M(CN)/" > (-NR3')2 MCCN)^'" + 2HSO4" (2.31)~~

The cyanide concentration in the column discharge, during the initial part of the loading stage, is very low, as cyanide is completely adsorbed by the resin bed. When the discharge cyanide concentration reaches the maximum allowable limit due to breakthrough of cyanide complexes, the column is eluted with strong sulphuric acid solution to regenerate the resin, as shown in Equation 2.32:

~~(-NR3^)2 M(CN)4^" + 3H2SO4 > 2(-NR3^ HSO^ ) + MSO4 + 4HCN (2.32)~~

The spent eluent with soluble metal sulphates and hydrogen cyanide is volatilised in a packed bed column. HCN gas recovered is then scrubbed with a NaOH solution to produce sodium cyanide for recycling. The eluent stripped of HCN exiting the volatilisation column is recirculated to the elution column, after adding fresh sulphuric acid. A portion of the elution circuit is bled off, where it is neutralised to precipitate metals.

Owing to the stability of Non-WAD cyanide species, it can be seen that Non-WAD cyanide species will not be eluted by the strong acid elution. Further, copper cyanide loaded to the resin will precipitate as CuCN on the resin. Details of how these problems are addressed in the Cy-Tech process are not available. 2.4.5.3 The Augment Process

The Augment Process uses commercial strong base anion exchange resins to recover and concentrate cyanide. It is reported that the resin is pre-treated by impregnating CuCN precipitate to increase the adsorption of free cyanides (Fleming, 1998). During the loading stage, copper cyanide and free cyanide are loaded to the resin as shown in Equation 2.33:

~~2{(-NR3^)2 S04''®CuCN} + CU(CN)3'" + 2CN- 3{(-NR3^)Cu(CN)2} + (-NR3^)CN- + 2S04' (2.33)~~

After loading, the resin is eluted with a concentrated copper cyanide eluent containing a CN:Cu ratio of 4:1, which changes the copper cyanide species on the resin from Cu(CN)2" to the Cu(CN)3^". This elution is reported to reduce the copper and cyanide loading on the resin by 50% and 25% respectively. Then, the resin is eluted with a strong sulphuric acid eluent, containing 100-150 g/L H2SO4 (Equation 2.34). The acid elution regenerates the resin, converting the copper cyanide complexes back to CuCN, and releasing all but one cyanide ligand bound to copper (Fleming, 1998). The regenerated resin is returned to the loading cycle, where further loading of cyanide takes place.

~~(-NR3')2 Cu(CN)3'" + H2SO4 > (-NR3"')2 804'" + CuCN + 2HCN (2.34)~~

As the copper cyanide elution reduces the copper loading by 50% in each cycle, the process manages to regulate the loading of copper to resin. However, the requirement to have copper cyanide impregnated on the resin reduces the net operating capacity of the ion exchange column. Also, this process has no means of removing non-WAD cyanide species from the resin bed, which are not decomposed by acid. 2.4.5.4 The Vitrokele Technology^^ Process

Vitrokele Technology^M is a process developed to recover gold from cyanidation liquors. This process also boasted cyanide recovery capabilities when it was first introduced. It was successfully used at Connemara, Zimbabwe, for recovering gold from heap leach liquor (Satalic et al., 1996). When cyanide recovery is the primary concern, the process requires the conditioning of resin by loading copper cyanide, similar to the Augment Process. The copper cyanide loaded on the resin is used to adsorb free cyanide from the solution. The cyanide loaded resin is then subjected to a sulphuric acid elution, where the cyanide is released as HCN. The HCN gas is then recovered by scrubbing with a lime solution. The process chemistry of the cyanide recovery aspect of Vitrokele Technology'^^ process, as documented by Satalic and colleagues, is given in Equations 2.35 to 2.37:

~~(-NR3")2S043 n " + CuCN + 2CN (-NR3")2 Cu(CN)3'" + so/ (2.35)~~

~~(-NR3')2 Cu(CN)3'" + H2SO4 (-NR3")2S0/" + CuCN + 2 HCN (2.36)~~

~~HCN(^) + > NaCN^,^ + H,0 (2.37)~~

When the cyanide recovery functionality of this process was tested in pilot scale at May Day mines in Cobar, NSW, the co-loading of copper to the resin led to operational difficulties. In spite of the use of a strong alkaline cyanide elution to remove copper from the resin, the ongoing accumulation of copper on the resin hampered the process efficiency. The pilot scale tests were completed in mid-1998, with the conclusion that the Vitrokele Technology^^ process was unable to effectively manage the loading of copper cyanides to Vitrokele 912 resin (Tran et al., 2000). 2.4.5.5 The Ion Exchange Process Patented by Frey and Colleagues

Frey and colleagues (1988) have patented a technique for recovering cyanide from waste solutions which couples ion exchange resin adsorption with a controlled oxidative elution of resin. In this process, strong base ion exchange resin is loaded with mixed cyanide species from waste solutions. Like all other ion exchange resin processes, this produces a tailings stream relatively free of cyanide species. The work reported 95% or more recovery of copper, zinc, nickel, and iron cyanide species and more than 90% recovery of free cyanide. The cyanide loaded resin is initially eluted with a dilute acid solution. According to Frey and colleagues (1988), the metal cyanide complexes on the resin are stripped as shown in Equations 2.38 and 2.39 (quoted from the patent):

~~R, - (M(CN)J + H.SO, M(CN)2 + 2HCN + R2-SO4 (2.38)~~

~~M(CN)2 + H2SO4 > 2HCN + MSO4 (2.39)~~

~~(Where M is a divalent metal forming a soluble cyanide complex)~~

The gas-liquid mixture leaving the resin bed is then stripped of HCN and collected in a mixing tank. The HCN liberated from the eluent is captured in a caustic scrubber solution, similar to the cyanide absorption stage of a standard AVR process.

In the spent eluent mixing tank, more acid is introduced to the spent eluent to adjust the pH to between 1.0 and 4.0. At this point, an oxidant is added to the mixing tank to oxidise cyanide species. Hydrogen peroxide, other alkali peroxides such as Na202, chlorates and hypochlorites, are suggested in the patent as possible oxidants. The authors state that the addition of the oxidant is controlled such that a large percentage of copper is oxidised to Cu^^, while a small amount of copper is retained as Cu^. The

^ I j patent recommends a Cu /Cu ion ratio of 20 for the solution in the mixing tank. Redox potential of+350 to +550 mV measured against a saturated calomel electrode is said to be suitable for controlling the system, maintaining the required ratio of ions. This fortified eluent is then fed back into the resin column to elute more metal cyanide species. The circulation of the eluent through the resin bed continues until all metal cyanide complexes are stripped from the resin bed. Throughout the elution process, acid and oxidants are added to the spent eluent mixing tank to maintain the pH and the ratio of Cu^VCu^ ions at the required levels.

Over 99% recovery of copper loaded onto the resin has been claimed in the patent. Typical elution time is reported to be between 3 to 8 hours. At the end of the elution, the resin bed is rinsed with water, preparing the resin bed for the next loading stage.

~~Metals collected in the spent eluent are recovered by electro-winning or precipitation.~~

Although this process claims the ability to remove copper from resin, any report of its use in commercial scale could not be found. This may be due to several factors. Firstly, the chemistry of the process claimed by the patent (given in Equations 2.37 and 2.38) is highly questionable. It stipulates elution of metal cations from the resin as neutrally charged, soluble complexes, in the form of M(CN)2. The existence of such species is not supported by other literature. Secondly, it requires precise redox potential control in the eluent, which is costly to implement in large scale in mining and mineral processing environments. Finally, the long elution stage, reported to take up to 8 hours, reduces the overall efficiency of this process.

~~2.4.5.6 Review of Ion Exchange Resin Cyanide DetoxiHcation Processes~~

Ion exchange based cyanide detoxification processes remove cyanide from tailings by adsorbing cyanide on resin. Most anion exchange resins are capable of adsorbing free and complex cyanides to some extent. The loading capacity of cyanide species on ion exchange resins vary. Loading capacities up to 100 g/L of resin of copper cyanide species on strong base ion exchange resins are possible under favourable conditions (Fernando, unpublished data). Given that commercially available ion exchange resins cost approximately AUD 5.00 per litre, ion exchange adsorption alone is not a very cost effective technique for removing cyanide from tailings. Additionally, such a process has to address the environmental and financial costs associated with the disposal of cyanide loaded resin.

Almost all ion exchange resin based processes employ some type of resin regeneration. Regenerated resin is used for further removal of cyanide from contaminated liquors. This cycling of resin between loading and cyanide elution stages allows the treatment of significant volumes of liquor with a small batch of resin. The cyanide recovered is recycled into the leach circuit in most circumstances.

Operating costs and efficiencies of resin regeneration processes vary. Intricate resin regeneration processes, which are difficult to control or require exotic chemicals, are not commercially attractive. Regeneration processes that fail to restore the resin to its original condition also are not favoured, as the ability of the resin to adsorb cyanide is gradually lost over a number of loading/elution cycles. In such processes, the cost of ion exchange resin loss has to be taken into account.

Overall, ion exchange resin processes have several advantages over other cyanide detoxification processes. They are capable of operating efficiently over the entire range of cyanide concentrations seen in most cyanide leach liquors and slurries. The ability to uptake cyanide and other contaminants from liquors to produce a discharge of less than 1 mg/L CNWAD has enabled ion exchange processes to be used as a polishing stage in other tailings treatment processes. On the other hand, their ability to uptake 30-40 g/L cyanide enables ion exchange processes to be used economically for the treatment of cyanide liquors containing up to 5,000 mg/L CNWAD species (Tran et al., 2000). For these reasons, ion exchange resin cyanide detoxification processes are being explored by the mining sector with increasing interest. 2.5 ION EXCHANGE PROCESS FOR GOLD EXTRACTION

The primary application of ion exchange resin processes in gold cyanidation is for gold extraction. This section gives a brief summary of the state-of-the-art in using ion exchange resins as an adsorbent for gold.

~~2.5.1 Development of Ion Exchange Processes for Gold Extraction~~

The application of ion exchange resins for the recovery of gold from cyanidation circuits was first developed in the former Soviet Union (Demidov et al., 1967; Bolinski and Shirley, 1996). In spite of their superior performance to activated carbon based processes, ion exchange processes did not attract the attention of the western world until the late 1980s.

The first ion exchange gold extraction plant was the Golden Jubilee resin-in-pulp plant, commissioned in South Africa (Seymore and Fleming, 1989). Following the success at Golden Jubilee mine, several other ion exchange resin processes have been developed. Some processes, such as the Vitrokele Technology^^ gold extraction process used in Connemara, Zimbabwe, have been successfully implemented in commercial scale (Satalic et al., 1996). A number of others have been tested at the laboratory scale and are in the initial stages of development.

~~2.5.2 Process Characteristics~~

Most gold ores contain cyanide soluble base metal minerals. Like gold and silver, these minerals react with cyanide to form soluble base metal cyanide complexes. As activated carbon does not show affinity to such cyanide species, after the recovery of precious metals from liquor, base metal cyanide compounds end up in the tailings stream. Ion exchange resins on the other hand are capable of recovering precious metal and base metal cyanide species from liquor without selectivity. Hence, unlike activated carbon adsorption, the tailings from ion exchange resin adsorption processes are relatively free from base metal cyanide species.

One of the shortcomings of this non-selective adsorption is the reduction of the capacity of the resin to uptake precious metals. In solutions containing high levels of base metal cyanide species, ion exchange resins uptake precious metals only up to a fraction of their theoretical loading capacity because of the co-loading of base metal cyanide species.

To overcome this obstacle, ion exchange resin processes employ a cyclic loading and elution technique, where base metals are selectively eluted from the resin between loading cycles, whilst retaining the precious metals. As the removal of base metals liberate adsorption sites for loading of more cyanide complexes in the proceeding loading cycle, the overall loading of precious metal can be increased to as much as 50 kg/tonne, before the precious metals are eluted from the resin. The base metal cyanide species found in cyanide leached solutions mainly arise from copper and zinc. Elution of zinc and most other weak acid dissociable cyanide (CNWAD) complexes from strong base resins is generally performed using a dilute sulphuric acid solution. However, copper cyanide does not decompose in the presence of dilute acid. The elution of copper from strong base resins has been a challenge in many ion exchange processes (Tran et al., 2000).

The Vitrokele Technologyprocess employs a strong sodium cyanide solution (50- 100 g/L) to elute copper from ion exchange resins (Tran et al., 2000). Pilot plant tests conducted at May Day mines showed that this elution technique was inefficient for resins loaded with significantly higher copper levels than gold. Incomplete removal of copper was noted during the sodium cyanide elution. In the subsequent acid wash, copper remaining on resin precipitated as copper cyanide, affecting the loading capacity of the resin (Tran et al., 2000; Tran et al., 2001). 2.5.3 Recent Developments

The introduction of ion exchange resin processes to gold cyanidation has been supported by recent fundamental studies. Investigations of adsorption characteristics of various resins have been made (Leao et al., 2001) and assessment methods of ion exchange resins for suitability as an adsorbent for gold have been developed (Jones, 1996). Other new developments include modelling of adsorption characteristics (Lukey et al., 2000a), the studies on the effect of saline solutions on the adsorption and elution of iron species from resins (Lukey et al., 1999; Lukey et al., 2000b), and the work conducted by Gomes and colleagues (2001) on the use of spent ion exchange resins as an absorbent for gold from cyanide solutions.

Lukey and colleagues (2001) have developed an equilibrium model, based on the principles of statistical thermodynamics and the Metropolis Monte Carlo (MMC) numerical method, to describe the muhi-component equilibrium adsorption of gold and copper cyanide onto an ion exchange resin containing trimethylammonium functional groups.

Some recent applied research in the field includes the study of the use of ion exchangers for managing copper cyanide and acid mine drainage (Jay 2003), and the study of the potential to recover copper from acidic and cyanide containing alkaline wastewater of electroplating industries (Yelcin et al., 2001). Hammen (1998) has reported the development of an ion exchange media for high velocity processing of cyanide contaminated liquors arising from gold mining and electroplating industries. Several other investigations of the use of anion exchange resins for recovering cyanide from waste solutions can be found in recent literature (Kurama et al., 2000; Leao etal., 1998). The Fundamentals of Ion Exchange

Fundamentals of ion exchange processes are discussed in this chapter. The classification of ion exchange resins, their synthesis and their properties are presented, followed by a qualitative treatment of ion exchange equilibria and kinetics. A quantitative treatment of ion exchange equilibria and kinetics is beyond the scope of background knowledge required for the discussion of experimental work presented in the ensuing chapters. For that, the reader may wish to refer to an authoritative text on ion exchange, such as 'Ion Exchange' (Helfferch, 1962) or 'Ion Exchange: Theory and Practice' (Harland, 1994).

A large number of ion exchange resins are commercially available today. These resins are generally marketed for specific applications. In marketing resin, the manufacturers tend to provide application specific information on resins, emphasising the benefits. Some resins are marketed as specialised resins, supported by non-comparative performance results. The theoretical basis for their speciality or enhanced performance is seldom revealed.

Marketing of 'specialised' or 'proprietary' resins for gold extraction with claims of superior performance, at exorbitantly inflated prices, has been an all too frequent occurrence in the mining sector in recent years. Therefore, a clear understanding of properties of ion exchange resins is essential to make an objective assessment of the suitability of commercially available resins for a given application. 3.1 A BRIEF HISTORY OF ION EXCHANGE TECHNOLOGY

Renowned authors of old, including Moses and Aristotle, are sometimes credited for the discovery of ion exchange phenomenon (Helfferch, 1962; Luce, 2003). However, the first scientific studies on ion exchange were made by Thompson and Way in the 1850s, when they studied the ion exchange properties of soils (Thompson, 1850; Way, 1850). In attempting to understand why ammonia was lost from manure, they passed ammonium sulphate through columns packed with soil, to find that the resulting leachate contained no ammonium salts, but had significant levels of calcium sulphate instead. They concluded that this was an ion exchange process, produced by the clay fraction of the soil. Since then, many advances have been made in understanding this phenomenon. By the turn of the century it was recognised as a key separation process, along with filtration, distillation, and adsorption. However, most ion exchangers used in the early days were natural material such as clays, zeolite, and humic acid, or technically enhanced naturally occurring materials such as sulphonated coal (Pietrzyk, 1990). In 1935 Adams and Holmes (1935) discovered that crushed vinyl records displayed ion exchange properties. In doing so, they reported the first synthetic organic polymer ion exchange material. Since this time, fuelled by its popularity in industrial applications and chromatography, many developments have been made in the field of ion exchange. The introduction of macroporous substrate ion exchange media in 1960s was one such critical development (Millar, 1973).

Modem ion exchangers are predominantly organic polymer substrates with selected functional groups chemically grafted to the substrate. Porosity and particle size of ion exchangers are controlled by conditions of polymerisation. Physical and chemical stability of polymers used as substrates have been improved. As a result of these advances, with the exception of their use in some analytical and specialised applications, inorganic exchangers (minerals, greensand, and zeolites) have been almost completely replaced by the resinous type ion exchangers. 3.2 ION EXCHANGE FUNDAMENTALS

Ion exchange is the reversible interchange of ions between a soHd (ion exchange material) and a liquid, in which there is no permanent change in the structure of the solid. For example, when ion exchanger carrying cation A^ as the exchangeable ion is placed in an aqueous solution phase containing B^ cations, an ion exchange reaction takes place, as shown in Equation 3.1:

~~RA" + RB" + A" (3.1)~~

The exchangeable cations A^ and B^ are called counter-ions. The fixed ions in the ion exchanger and the ions in solution which have the same polarity are called co- ions. The solution does not take any part in the ion exchange reaction, except allowing the movement of counter-ions to and from ion exchanger surface through diffusion. A schematic of a cation exchange resin with a negatively charged matrix and exchangeable positive ions is shown in Figure 3.1.

Fig. 3.1 Cation exchange resin schematic showing negatively charged co-ions attached to the resin matrix and H^ counter-ions Equation 3.1 is an example of a cation exchange reaction. An anion exchange reaction can be represented as shown in Equation 3.2, where the charges of the co- ions and counter-ions are reversed.

~~+ D" < > R^D" + C~ (3.2)~~

Ion exchange is used as a separation process in water treatment, mining, chemical, and pharmaceutical industries. It is also used in some non-water based processes. One of the key attractions of ion exchange as a separation process rests with the convenience of regenerating ion exchange material. Ion exchange material can be used over a large number of adsorption cycles, separated by cycles of regeneration. For example, in water softening it is used to remove calcium from hard water, as shown in Equation 3.3:

~~2 RNa^ + Ca'^ > R^Ca'^ + 2Na^ (3.3)~~

The exchanger R exchanges sodium ions for calcium and in doing so removes calcium from hard water and replaces it with an equivalent quantity of sodium. Subsequently, the calcium loaded resin may be treated with a sodium chloride solution to regenerate it back to the sodium form, so that it can be used again for calcium removal. The regeneration reaction is reversible; the ion exchanger is not permanently changed. As such, millions of litres of water may be softened using several thousand litres of resin.

~~3.2.1 Physical Properties of Resins~~

Ion exchange materials are sold as spheres or granules with a specific size and uniformity to meet the needs of their intended applications. The majority are prepared in spherical bead form, either as conventional resins with a polydispersed particle size distribution from about 0.3 mm to 1.2 mm, or as uniform particle sized (UPS) resin with all beads in a narrow particle size range. In water, ion exchange resins typically show bulk densities of 1.1 to 1.5 kg/L. The bulk density as installed in a column includes 35-40% voids volume for wet spherical ion exchange resins. Bulk densities in the range of 500-1000 g/L are typical for wet resins.

Physical properties, such as the type of the substrate, the particle size, the porosity, and the extent of cross linking, have a significant role in determining the overall performance of a resin. Porosity of resins determines the size of species that may enter a specific structure and its rate of ion exchange. The type of substrate affects the selectivity of the resin. Further, the swelling of the resin is inversely proportional to the extent of cross linking of the resin substrate.

The physical properties and the structure of resin are determined predominantly by the conditions of polymerisation of the resin. A conventional gel type styrenic ion exchange resin is built on a substrate prepared by co-polymerising styrene and di- vinyl-benzene (DVB) to produce a polystyrene di-vinyl-benzene (PSDVB) co- polymer. The polymerisation of styrene produces long chain molecules, while the introduction of DVB leads to the cross linking of the long chain molecules, as shown below.

~~o (3.4)~~

The extent of cross linking can be varied by controlling the ratio of DVB to styrene in the polymerisation reaction mixture. The PSDVB co-polymer and its variations are the most popular substrate for most analytical and industrial ion exchangers (Pietrzyk, 1990).

Gel-type resin produced by co-polymerising styrene and DVB is not naturally porous, but exhibits porosity because of the micro-pores between long chain styrene polymers which are cross linked by DVB. Under ambient conditions, gel resins contain pores no more than 4 nm in diameter, which is the average distance of separation of polymer chains (Harland, 1994). These long chain polymeric molecules, when attached with inorganic functional groups, will swell in the presence of polar solvents, increasing the porosity of the resin. Hence the apparent porosity of gel-type resins is a function of the extent of cross linking and the swelling of the resin.

The addition of an inert diluent to the polymerisation system of styrene and DVB results in producing a highly porous substrate, called a macroporous matrix. By choosing different solvents, a continuous range of porosities can be obtained. Co- polymers other than PSDVB can also be made into macroporous substrates. These resins have an average pore diameter of approximately 150 nm, with pore sizes ranging from several tens to several hundred nanometres (Harland, 1994). Due to this highly porous structure, macroporous resins require more rigid substrates than gel resins to prevent collapsing of the substrate. Hence the polymerisation conditions are chosen to yield a higher level of cross linking, generally over 16% (Pietrzyk, 1990).

~~3.2.2 Classification of Ion Exchange Resins~~

Chemically, there are two fundamental types of ion exchangers. One has functional groups which are completely dissociated under normal conditions. In the other type, the extent of dissociation is markedly dependent on the pH of its environment.

~~Ion exchangers with sulphonic acid or quaternary ammonium functional groups are examples of the former category, which are referred to as 'strong' anion or cation~~

S3 exchange resins. Carboxylic acids, phosphoric acids, secondary or tertiary amine functional groups are examples of the latter category, which are also known as 'weak' anion or cation exchangers. It should be noted that the terms 'strong' and 'weak' derive from the Arrhenius Theory of electrolyte group, referring to the extent of dissociation of these functional groups. Cation exchanges, whether they are weak or strong, have positively charged counter-ions available for exchange. Likewise, anion exchangers of both types have negatively charged exchangeable counter-ions.

~~3.2.2.1 Strong Cationic Exchange Resins~~

Strong cationic ion exchange resins resemble strong acids in chemical behaviour and hence are also known as strong acid ion exchangers. These resins are highly ionised in acid (e.g. R-SO3H) and sah (e.g. R-SOsNa) forms. They can convert a metal sah to the corresponding acid as shown in Equation 3.5:

~~2(R-S03H) + CUSO4 > [2(R-S03)]'-CU'" + H2SO4 (3.5)~~

Because of their complete dissociation, strong acid resins have exchangeable counter-ions over the entire pH range. In other words, the exchange capacity of strong acid resins is independent of the solution pH. These resins are used in the hydrogen form in deionisation to remove all other cations from water. They are used in the sodium form in water softening, as they remove calcium and magnesium from water. After exhaustion, the resin is converted back to the hydrogen form (regenerated) by contacting with a strong acid solution. Alternatively, the resin can be converted to the sodium form with a sodium chloride solution. Most strong acid ion exchange resins are sulphonated copolymers of styrene and DVB. They can be synthesised as given in Equation 3.6: polymerization sulfonating acid CH=CH2 CH=CH2 CHCH2CHCH2 CHCH;CHCH: catalyst swelling agent (3.6) © SO,-H styrene CH=CH2 •CHCH, divinylbenzene

~~3.2.2.2 Strong Anionic Exchange Resins~~

Strong anionic ion exchange resins behave similarly to strong alkalis and hence are also known as strong base resins. The hydroxide and salt forms of strong base resins are highly dissociated and, as such, strong base resins also have exchangeable counter-ions available over the entire pH range. Therefore, the exchange capacity of strong base resins is independent of solution pH. These resins are used in the hydroxide form for water deionisation. They will react with anions in solution as shown in Equation 3.7. Regeneration with concentrated sodium hydroxide (NaOH) converts the exhausted resin to the hydroxide form.

~~R-CH2N(CH3)3^0H- + NaCu(CN). R-CH2N(CH3)3^Cu(CN)2' + NaOH (3.7)~~

Strong base anion resins are sub classified as Type 1 and Type 2. Strong base anion exchange resins of Type 1 variety are quaternary amines, made by the reaction of trimethylamine with the chloromethyl groups of the co-polymer, generally obtained after chloromethylation of the substrate by the 'Freidel-Crafts' reaction. A typical synthesis route for Type 1 PSDVB strong base resin is shown in Equation 3.8:

~~CHCH2CHCH2 •CHCH2CHCH: (1) + N(CH3)3 CHCH2CHCH2~~

~~catalyst + CICHiOCHî as (3.8) CH2CI + CHjOH CH2N*(CH3)3C|- •CHCH2 •CHCH2 CHCH;-~~

(1) Type 2 variety is also a quaternary amine, but has one alkyl group in the quaternary amine replaced by the corresponding alcohol. Due to the reduced polarity of the amine group, Type 2 resins have a slightly lower basicity than that of the Type 1 resins, yet they are alkaline enough to remove the weak acid anions in most applications. Type 2 anion exchange resins can be synthesised by the reaction of dimethyl-ethanolamine with the chloromethyl groups of the co-polymer, in a reaction similar to that in Equation 3.8.

~~3.2.2.3 Weak Cationic Exchange Resins~~

Weak cationic or weak acid resins have carboxylic acid (COOH) as the functional group as opposed to the sulphonic acid group (SO3H) in strong acid resins. In its acid form, weak acid ion exchangers are only weakly ionised (pKa approximately 4 to 6). The degree of dissociation of weak acid functional groups is highly dependent on the pH; high pH conditions favour dissociation. As such, weak acid ion exchangers are not effective in acidic or neutral pH conditions.

Weak acid resins exhibit a much higher affinity to hydrogen ions than strong acid resins. This allows the regeneration of weak acid resins with significantly less acid than that required for strong acid resins. Almost complete regeneration can be accomplished with stoichiometric amounts of acid. Pietrzyk (1990) lists a number of methods for synthesis of weak acid ion exchangers. One typical synthesis route for weak acid cation exchange resins is the polymerisation of acrylic or methacrylic acid, their esters or acrylonitrile with DVB to form the cross linked polymer that contains COOH groups as Equation 3.9 displays.

~~CH3 CHa CH3 polymerization hydrolysis CH==CH2 + CH=»CH2 CCH2CHCH: • CCH2CHCH2 catalyst oiF COOR COOR 000- (3.9) Na* methacrylate O~~

CHCH. CHCH: 3.2.2.4 Weak Anionic Exchange Resins Weak base ion exchange resins contain primary, secondary, or tertiary amines as functional groups. They do not contain exchangeable ionic sites but exist as free bases in anhydrous form. Upon coming into contact with water, weak base anion exchange resins react with water to give an ionised hydroxide form (Equation 3.10).

~~R-CH2N(CH3)3 + H2O < > R-CH2NH(CH3)3'^ + OH" (3.10)~~

The hydroxide form does not dissociate highly in water, since high hydroxide concentrations in solution converts the resin into free base form. Therefore, ion exchange in neutral or alkaline conditions is unfavourable. The salt form of the resin may ion exchange with other anions (Equation 3.11), provided that the solution pH is less than 9. Hence these resins are only effective as ion exchangers when the pH of the solution is sufficiently low to maintain the protonated functional groups of the resin.

~~R-CH2NH(CH3)^Cr + CN" < > R-CH2NH(CH3)3^CN- + cr (3.11)~~

These resins are readily regenerated with caustic. Regeneration of weak base resins does not need to provide hydroxyl ions, but needs only to neutralise the absorbed acid. Weak base ion exchanges can be produced by reacting chloromethylated PSDVB with ammonia, a primary amine, or a secondary amine (Equation 3.12). CHCH2

~~NH.~~

~~CHjN^HgCI"~~

~~CHCHj CHCHo (3.12) RNH2~~

~~CHjCI CM2N^H2RCr~~

~~CHCH,~~

~~RoNH~~

~~CHjN^HRjCr~~

~~3.2.2.5 Specialty Ion Exchange Resins~~

Chelating resins are a special case of weak cation or anion exchange resins, where the counter-ions are bonded to the resin by both ionic and co-ordinate bonds. These resins have functional groups analogous to strong ligands, which form coordination bonds with transition metal ions. Chelating resins generally exhibit a high degree of selectivity towards transition or heavy metal cations.

Some commercially available chelating ion exchange resins have functional groups highly specific to some elements. A commercially available chelating resin, Amberlite GT73, contains thiol functional groups and has been designed for the removal of mercury compounds from water. Purolite S-930 is a macroporous polystyrene based chelating resin with iminodiacetic functional groups, designed for the removal of heavy metal cations from industrial effluents. It binds heavy metals, as Equation 3.13 displays. CH2-C^=0 / R-CH2-N ON^ + M 2+ R--CH2-N M + y ^ONa \ CH2-C = 0 (3.13) CH2--C =0

This high selectivity allows the use of chelating resins to separate heavy and transition metal cations from solutions containing high background levels of calcium, magnesium, and sodium ions. Regeneration properties of these resins are similar to those of weak acid resins. Cation exchange chelating resin can be converted to the hydrogen form with slightly greater than stoichiometric doses of acid because of the tendency of the heavy metal-chelating complex to become less stable under low pH conditions. Chelating functional groups can be incorporated into the resin substrate during the polymerisation reaction, or attached after the polymerisation. Several methods of attaching chelating groups, such as iminodiacetic acid to resinous substrates, are given by Pietrzyk (1990). One of the common techniques is the reaction of iminodiacetic salt with chloromethylated PSDVB.

~~3.2.3 Ion Exchange Capacity~~

Ion exchange capacity is a quantitative measure of the total amount of counter-ions available in an ion exchanger. It is arguably the most important characteristic of an ion exchange material, as it is a measure of its capability to carry out its primary purpose. The ion exchange capacity can be expressed in a number of different ways, depending on the intended application.

The Dry Weight Capacity (DWC) of an ion exchange resin is expressed as the total number of equivalents of exchangeable ions per unit weight of dry resin in a standard form. It is usually expressed in units of eq/kg or mEq/g. The standard form for anion exchange resin is the chloride form, and for cation exchange resin, the hydrogen form. The DWC is measured by direct titration - the neutralisation of resins from acid or base forms can be determined by titrating with an acid, or an alkali, using the pH of the solution to determine the end point. Typical pH titration curves observed in DWC measurements of ion exchange resins are identical to standard acid-base titration curves, where the end point is defined by the point of inflection in the titration curve.

Most ion exchange resin applications are based on wet resin volumes, rather than the dry weight of the resin. Hence the total exchange capacity measurement of the bulk wet volume is more meaningful for industrial applications. The Wet Volume Capacity (WVC) is expressed as the total equivalents of exchangeable counter-ions in resin in standard form. It is important to measure the WVC in standard form because the counter-ions influence the extent of swelling of the resin, and hence affect the volume measurement. WVC is expressed in units of eq/L or mEq/mL.

The total exchange capacity of a resin (either DWC or WVC) can be viewed as the sum of the strong and weak functional capacities. Distinguishing between strong and weak functional capacities is important when assessing the suitability of a resin for a given application. For reasons such as side reactions in manufacture, deliberate inclusion of opposing basicity groups and resin degradation (especially for Type 2 strong base resins), ion exchange resins with apparently similar total exchange capacities may have different levels of strong and weak exchange capacities. A measurement of the total ion exchange capacity of resin, followed by a measurement of the strong ion exchange capacity (where the weak exchange capacity is masked by controlling the pH of the resin as described by Harland (1994)), can be used to determine the weak ion exchange capacity of a resin.

The Net Operating Capacity (NOC) is a measure of the useful performance of an ion exchange material when it is operating in a column under a prescribed set of conditions. It is influenced by a number of factors, such as: the effectiveness of regeneration; the composition of solution processed; the flow rate through the column; the extent of channelling; the operating temperature; and the extent of resin degradation. 3.2.4 Ion Exchange Equilibria

The equilibrium distribution of ions and solutions between the solution phase and the ion exchanger has been studied since the pioneering work in ion exchange by Thompson and Way (Harland, 1994). The analysis of ion exchange equilibria involves the study of three fundamental processes taking place when an ion exchanger reaches equilibrium with its surrounding solution. These are:

• the swelling of an ion exchanger due to the adsorption of polar solvents • the uptake of co-ions from the external electrolyte solution (in addition to the adsorption of counter-ions) • the adsorption of counter-ions, and selectivity in adsorption, where some ions are preferentially adsorbed over others.

Significant advances have been made in describing these phenomena from empirical, thermodynamic, and molecular standpoints. For the sake of brevity, the discussion in this section is limited to a qualitative treatment of the subject, focusing on the behaviour of organic ion exchangers in aqueous solutions.

~~3.2.4.1 Swelling and Adsorption of Water~~

Organic ion exchangers tend to adsorb the water around them when placed in aqueous solutions. The behaviour of ion exchangers when placed in solvents was illustrated by Gregor in 1948, using Gibbs-Donnan membrane equilibrium and a mechanical model for the resin structure (Harland, 1994). In this model, the resin is regarded as a salt which hydrates as the water is taken up to the resin matrix. As Figure 3.2 shows, the counter-ions dissociate with the initial introduction of water, forming a concentrated electrolyte solution within the resin. This is followed by further ingress of water into the resin phase due to the osmotic action, which causes the resin to swell. The swelling of the resin is allowed by the stretching of the cross linked hydrocarbon matrix, which is represented by elastic springs in Gregor's model. However, the stretching does not continue unabated, but reaches equilibrium when the elastic forces of the polymer counterbalance the outward expansion pressure on the polymer caused by the solvent. The swelling is also reversible; when the solvent is removed, the ion exchanger contracts to its original size.

~~Crosslin king @ Counter-ion •AAA/WWWVWW-~~

~~ion Solution volume (infinite) Fixed anion~~

~~VVWVVWVWWW^~~

~~Fig. 3.2 Gregor's model of an ion exchange resin (Source: Hariand, 1994)~~

The extent of swelling depends on a number of factors including the type of solvent and its ionic strength, the ion exchanger substrate and the level of cross linking in the matrix. Pietrzyk (1990) lists the following factors as those which favour swelling:

• polar solvents • high ion exchange capacity • low cross linking in the substrate • low counter-ion oxidation state • strong solvation of the fixed inorganic groups • large and strongly solvated counter-ions • high dissociation between inorganic group and the counter-ion • low concentration of electrolyte in the solution. Cycling resins between extremes of external ion concentrations leads to repeated swelling and contracting of resin. This can cause resin fracture and disintegration over a period of time. The swelling of organic polymers is of considerable significance to ion exchange applications. The swelling of resin can impose a significant pressure on a fix bed ion exchange column - in some instances causing columns to burst. On the other hand, the contracting of resin can create cavities in ion exchange columns leading to channelling of solution, reducing the net operating capacity of resin beds.

~~3.2.4.2 Sorption of Electrolyte and Donnan Potential~~

When an ion exchanger is placed in a solution, non-exchange ions in the electrolyte also enter into the ion exchanger. The adsorption of non-exchange ions is controlled by electrostatic forces, which establishes equilibrium of electrolyte distribution between the resin and solution phases. This ionic equilibrium is referred to as the 'Donnan Equilibrium'. Donnan Equilibrium is characterised by an unequal distribution of diffusible ions between two ionic solutions separated by a membrane which is impermeable to at least one or more of the ions in the system.

For example, when a cation exchanger R'A^ is placed in a dilute solution containing strong electrolyte A^Y" (Equation 3.14), the resin phase initially contains a high concentration of counter-ion A^ and virtually no Y" co-ions.

~~Resin - solution interface R-, A^ , H.O A^ , Y" , H.O (3.14) Impermeable for R"~~

As the system moves towards equilibrium, the concentration differential of counter- ion Y" between the resin-solution interface causes some Y" ions to diffuse to the resin phase (Equation 3.15). Resin - solution interface R-, A" , Y" , H,0 A^ , Y- (3.15) Impermeable for R"

The uneven distribution of Y" co-ions give rise to an electrostatic potential across the resin-solution interface, preventing further migration of co-ions into the resin phase. This electrostatic potential is called the 'Donnan Potential'. It discourages further electrolyte solutes from entering the ion exchanger. The exclusion of electrolyte from the resin due to Donnan Potential is strongest if the ion exchanger has a high capacity and high degree of cross linking. Dilute solution concentrations and high valency counter-ions also favour the exclusion of the electrolyte.

Donnan Potential creates an unequal distribution of co-ions, an osmotic pressure difference, and a potential difference between the resin and solution phases. Therefore, it influences the speciation and hydration of exchangeable ions between resin and solution phases, contributing to the factors that make an ion exchanger prefer one type of counter-ion over another.

~~3.2.4.3 Ion Exchange Selectivity~~

Selectivity of ion exchange resins is defined as the unequal distribution of ions of interest between the aqueous phase and the resin phase. When two or more counter- ions are available for ion exchange with the functional groups of the ion exchanger, the preference of the functional groups to these counter-ions is not necessarily the same.

A number of factors affect the uneven distribution of ions between the resin and aqueous phases. The water phase is usually dilute and has a low ionic strength. The resin phase contains a high concentration of ions. Therefore, counter-ions in the resin phase have fewer water molecules bonded to them by hydrogen bonds. Because of this, the solvated diameter of counter-ions in the resin phase is not necessarily the same as that in the solution phase. Further, the Donnan Potential across the resin- solution interface influences the speciation and hydration of counter-ions in the resin phase. Lastly, the structure and the steric effects of the resin could also restrict the migration of larger counter-ions to the resin phase. Due to these differences between the two phases, one type of ion will be preferred by the resin phase over the other.

Ion exchange equilibrium can be expressed in a variety of ways. Ion Exchange Isotherms, Selectivity Coefficients, and Distribution Coefficients are commonly used to describe the uneven distribution of counter-ions in ion exchange systems. As an example, for the ion exchange equilibrium between two counter-ions A" and B^ on resin R, expressed as given in Equation 3.16, an ion exchange isotherm is obtained by plotting the molar fraction of a given counter-ion in solution against that in the resin phase.

~~+ aB^ < > aR^B^ + fi A" (3.16)~~

~~An ion exchange isotherm describes the behaviour of the system across the entire range of concentrations of counter-ions.~~

In such a system, the selectivity of the resin for ion B^ over A" is defined as the selectivity factor K^a- This is expressed using the mass action relationship, using concentration terms as given in Equation 3.17:

~~Kl = ^ ' \ ^ ^^ (3.17) [BT~~

Alternatively, the distribution coefficient for any one component in the system shown in Equation 3.16 can be expressed simply as the distribution ratio of the component between the two phases. In this case, the distribution coefficient for component A (KD(A)) is expressed as given in Equation 3.18: [A] K resin phase ^^ -g q\ - solution phase D(A) =

~~The distribution coefficient depends on the conditions of the system - such as the concentration of ion A" in solution, the presence of competing counter-ions and the relative saturation of the resin.~~

The selectivity of an ion exchanger is based on a number of factors. Pietrzyk (1990) states that both strong base and strong acid ion exchange resins preferentially adsorb ions with highly polarised counter-ions and lower solvated volumes. Ions with a higher valency number (complexes) or oxidation state (single ions) are also preferentially adsorbed by resins.

It should be noted that the vast majority of ion exchange equilibrium data has been modelled or empirically obtained for binary systems. In contrast, the real life performance of ion exchange systems, where the ion exchange process takes place in columns with constantly varying pH conditions (as the reaction phase passes from one end of the column to the other), in the presence of several competing counter- ions and organic macromolecules, is extremely challenging to model.

~~3.2.5 Ion Exchange Kinetics~~

The rate at which ion exchange takes place is a function of a number of system properties. Generally, ion exchange is a diffusion process. For an ion to be adsorbed on an ion exchanger, the ion in question has to diffuse through the solution, cross the Nemst Layer into the resin, diffuse through the resin to a functional group and then react with the functional group. To retain electro-neutrality, counter-ions must complete this process in reverse and arrive at the solution phase simultaneously. y^R^A" + aB^ < > aRpB^ + p (3.19) For the ion exchange reaction shown in Equation 3.19, the overall exchange process consists of the following steps:

1. B^ diffuses through the Nemst Layer surrounding the ion exchanger to the resin surface 2. B^ diffuses through the ion exchanger to exchange sites 3. B^ reacts with functional group R, releasing counter-ion A" 4. A" diffuses through the ion exchanger to the resin surface 5. A"" diffuses through the Nemst Layer surrounding the ion exchanger to the solution phase.

Steps 1 and 5 have to occur simuhaneously to maintain electro-neutrality in the resin and solution phases. Similarly, Steps 2 and 4 also must occur in unison to maintain electro-neutrality within the resin. Hence, the kinetics of the ion exchange process can be described as the combined effect of a film diffusion process, an intra- particulate diffusion process, and a chemical reaction.

Generally, in ion exchange processes the chemical reaction is not a rate determining step. In dilute solutions, film diffusion is the rate controlling step. In concentrated or well agitated solutions, film diffusion rate increases, leaving intra-particulate diffusion as the rate controlling step in concentrated solutions.

Several factors influence ion exchange kinetics. Co-ions do not directly influence the kinetics of ion exchange, but they affect the swelling of resin, and in so doing, control the diffusivity of counter-ions. Smaller ion exchange particle sizes favour ion exchange rates as they improve film and intra-particulate diffusion rates. For the same reasons, increased swelling (caused by low cross linking and high solvent polarity) and elevated temperatures accelerate the ion exchange rate.

As the diffusion rate of ions through the film and the ion exchanger is critical to the rate of ion exchange process, obviously counter-ions with smaller hydrated diameters would give faster ion exchange rates. In the solution phase, increased agitation reduces the thickness of the Nemst Layer, giving higher ion exchange rates when film diffusion is controlling. Harland (1994) gives a quantitative analysis of ion exchange kinetics and the effect of these parameters.

Ion exchange in simple solutions is a combination of charge and mass transfer through a homogenous media (solution), a heterogonous media (macroporous resin), and the interface between these phases. As with ion exchange equilibria, the kinetics of an ion exchange process in process plant conditions where system parameters (such as the temperature, pH, the presence of competing counter-ions, flow rates and properties of the exchanger itself) change with time, is very difficult to model.

Fortunately, in many practical situations, a rigorous mathematical model can be easily and more effectively substituted by carefully scaled pilot plant tests. Such pilot plant tests have proven invaluable in chemical engineering design and testing of ion exchange processes for industrial or commercial applications (Harland, 1994). Development of the Oxidative Acid Elution Concept

This chapter presents the process concept of a novel cyanide detoxification process based on the hypothesised behaviour of metal cyanide complexes in ion exchange systems. It also discusses the theoretical basis and the conceptual development of an oxidative acid elution technique, which underpins the cyanide detoxification process. Further, the fundamental process chemistry of the oxidative acid elution is explored in this chapter to gain an understanding of the behaviour of cyanide complexes on resin phase in the presence of the oxidative acid eluent.

~~4.1 BACKGROUND~~

Most ion exchange resins are capable of removing cyanide species from cyanide contaminated solutions. As long as the ion exchange resin bed is not saturated, recovery efficiencies over 95% and environmentally acceptable discharge levels are feasible (Section 2.4.5.5).

The key challenge in using ion exchange resins for treatment of cyanidation tailings is the elution and regeneration of exhausted resin. Some existing processes use a dilute mineral acid eluent, which is sufficient to remove free cyanide and most CNwad species from the resin. However, copper cyanide complexes do not dissociate under dilute acid conditions. Hence, unlike the cyanide complexes of zinc, cadmium, and nickel, copper cyanide complexes are not removed from the resin. Further, cyanide complexes of iron, cobalt, gold, and to some extent chromium, do not dissociate in acidic conditions. These elements remain in anionic form under acidic conditions, and hence stay attached to the resin.

The elution of copper is addressed in the Augment Process using a strong alkahne copper cyanide solution. The Vitrokele Technology"^^ process employs a strong alkaline cyanide solution to elute copper from the resin. However, complete removal of copper has not been possible. The Augment Process only reduces the copper loading by 50% (Fleming, 1998). The accumulation of copper on the resin is the key impediment in the Vitrokele Technology^^ process (Tran et al., 2000).

The cyanide detoxification process introduced by Frey and colleagues (1988) 2+ claimed successful elution of copper cyanide from resin using a 20:1 mixture of Cu and Cu^ ions. Elutions under these conditions were reported to take 3 to 8 hours, during which the redox potential of the eluent is maintained between +350 and +550 mV, measured against the saturated calomel electrode. For the reasons discussed in Section 2.4.5, this elution technique has not been adopted by others.

The inability to efficiently remove copper cyanide complexes from strong base resins has been the major impediment to the application of ion exchange for cyanidation tailings treatment (Tran et al., 2000). This operational need led to the development of a novel oxidative acid elution technique that is capable of eluting copper completely from the resin, and hence can be used to effectively regenerate strong base ion exchange resin between loading cycles.

~~4.2 PROCESS OVERVIEW~~

The cyanide detoxification process presented in this thesis combines an oxidative acid elution, in conjunction with strong base ion exchange adsorption, cyanide recovery by AVR and alkaline oxidation of free cyanide. The processes of strong base ion exchange adsorption for cyanide removal, AVR for cyanide recovery/concentration, and alkaline oxidation of cyanide, are well known unit operations. They have been practiced successfully for many years in gold cyanidation (Chapter 2). These standard unit operations were adopted without any significant developments or modifications in this process. The uniqueness of this cyanide detoxification process is in the use of a novel oxidative acid elution technique, which underpins hs effectiveness in treating cyanidation tailings containing mixed cyanide species. This oxidative acid elution technique allows the complete elution of all CNWAD species, including copper.

Figure 4.1 gives a flow chart of the overall cyanide detoxification process. Similar to many other processes, a strong base ion exchange resin column is used to adsorb cyanide species from tailings solutions. The adsorption of cyanide species continues until cyanide breakthrough is detected at the column outlet. After loading, the resin bed is eluted with an oxidative acid eluent. The oxidant decomposes copper and other CNWAD complexes to corresponding metal cations, while releasing some cyanide as HCN. A portion of cyanide loaded on the resin is oxidised to CNO" during the elution.

The spent eluent emerging from the column contains metals (as cations), CNO" from the oxidation of cyanide and HCN. This stream is fed to an AVR circuit, where the HCN in the spent eluent is stripped with an air stream. The spent eluent stripped of HCN gas is then fed to a cyanide oxidation reactor. The HCN gas is re-absorbed with a NaOH scrubber solution to make a concentrated NaCN solution. This NaCN solution could be used to recycle cyanide to the gold leaching circuit. If no cyanide recovery is needed, it is fed to the cyanide oxidation reactor, where the cyanide is oxidised by the unused oxidant in the spent eluent in an alkaline environment. The discharge from the cyanide oxidation reactor contains base metals as cations. It can be fed to a base metal recovery circuit to recover base metals (by precipitation or with the use of a solvent extraction/electro-winning (SX/EW) circuit). Recovery of Cyanide from Elution of Resin Column and Cyanide Recovery and Alkaline Oxidation of Cyanide Contaminated Liquor Cyanide Oxidation Stage 1 Concentration (Cyanide Oxidation Stage 2)

~~Fig. 4.1 Flow chart of the ion exchange cyanide detoxification process 4.3 CHARACTERISTICS OF ION EXCHANGE RESIN USED~~

Due to their superior ion exchange kinetics, large particulate macroporous resins give better performance in ion exchange resin beds than gel resins of similar particle size. Macroporous resins are also more likely to withstand osmotic shock than gel resins, due to their porous structure.

The effectiveness of weak base anion exchange resins is reduced dramatically at high pH, while strong base anion exchange resins maintain their loading capacity throughout the pH range. The loading of cyanide is generally performed at the high pH range (pH 9 to 12.5), depending on the type of tailings and the conditions of pre- treatment. Given the variability of pH in loading solutions, strong base anion exchange resins would produce reproducible and consistent results in cyanide removal, while the performance of weak base anion exchange resins would vary significantly.

Resins with triethylammonium functional groups have been known to show selectivity to smaller anions, while resins with trimethylammonium functional groups have been reported to adsorb most cyanide complexes without selectivity (Leao et al., 2001). Since all cyanide species need to be removed from solution, it can be seen that resins with trimethylammonium functional groups would be best suited for the purpose.

Therefore, it can be concluded that any macroporous strong base resin with trimethylammonium functional groups would be suitable for cyanide recovery from tailings streams. The ability of resins to withstand moderate oxidising conditions, as required for this novel elution technique, has not been investigated previously. The study of this aspect of resin performance is given particular emphasis in this thesis. 4.4 OXIDATIVE ACID ELUTION

~~4.4.1 Originality of Oxidative Acid Elution~~

~~This novel oxidative acid elution technique relies on the decomposition of metal~~

cyanide species to remove CNWAD complexes from resin. Unlike other elution techniques reported in the literature, this process brings a strong oxidant into direct contact with resin loaded with cyanide complexes, subjecting the resin to high redox potentials. The oxidant in the eluent reacts with metal cyanide complexes on the resin interface, decomposing all CNWAD cyanide complexes (including copper) to their respective metal cations and HCN. A portion of cyanide loaded on resin is oxidised to cyanate.

~~4.4.2 Process Chemistry of Oxidative Acid Elution~~

With the exception of copper, all CNWAD complexes are unstable in acidic environments. Copper precipitates as CuCN when a solution containing copper cyanide complexes are acidified. Therefore, when resin loaded with mixed CNWAD species are eluted with a dilute acid, while other cyanide complexes are effectively removed from the resin, copper is precipitated within the resin pores as insoluble copper cyanide.

It is well known that in the presence of suitable oxidants, copper cyanide species break down to release cyanide and copper(II) ions. Under acidic conditions, and with anions that cannot produce covalent bonds or bridging groups, copper(II) ions are stable as cations in solution.

Therefore, when ion exchange resin loaded with CNWAD species is brought into contact with an acidic eluent containing a suitable oxidant, all CNWAD complexes, including those of copper, decompose into their constituents. This is represented in Equations 4.1 to 4.3, where the oxidant is denoted by oxygen. Cyanide complexes of gold, silver, and iron, on the other hand, require highly oxidative conditions to decompose and are generally unaffected by the oxidative conditions required to oxidise copper cyanide.

~~(-NR3' >2 Zn(CN)/- + 2 H2SO4~~

~~(-NR3")S0/ + ZnSO^ + 4HCN (4.1)~~

~~(-NR3")2Cu(CN)3'' + H2SO (-NR3")S04'" + CuCN 4- 2HCN (4.2)~~

~~2CuCN + 2H2SO4 + 1/2 O2 > 2CUSO4 + 2HCN + H2O (4.3)~~

Alternatively, the oxidation of copper cyanide as shown in Equations 4.2 and 4.3 could proceed in one step, as shown in Equation 4.4, where X could take the values between 2 to 4, depending on the copper cyanide species.

~~+2XH2SO4 +1/20. 2(X-1)(-NR3^)S04 + H2O + 2CUSO4 + 2XHCN (4.4)~~

If the oxidation potential were to be varied (from non-oxidative to moderately oxidative) during elution, base metals (with the exception of copper) will be eluted during the initial stage of the elution while copper will be eluted in the latter stage. Precious metals, on the other hand, will remain on the resin, unaffected by the elution.

The oxidation potential required to oxidise Cu^ in CuCN in alkaline solutions is relatively low. As can be seen from the Eh-pH diagram for the Cu-CN'-HiO system shown in Figure 2.2, at solution potentials above approximately +250 mV against the Standard Hydrogen Electrode (SHE), Cu^^ is preferred over Cu^. The oxidation potential of most commercially available oxidants is given in Figure 4.2. All these oxidants are capable of giving oxidation potentials well above +250 mV against the SHE in dilute solutions. Therefore, any of these oxidants could be used to oxidise copper cyanide loaded on resin.

~~: 1.2 - Ill~~

~~6 8 AaorTY pH~~

~~Fig. 4.2 Eh-pH diagram of commercially used oxidants (Source: Flynn and Haslem, 1994) 4.5 SELECTION OF OXIDANT AND ELUTION CONDITIONS~~

For commercial scale applications, several other requirements need to be addressed. Most obvious are the reagent costs, hazards, operability issues, and environmental impact of the chemicals used. The selectivity of the oxidant used for the oxidation of copper cyanide is also significant. Oxidants that are gaseous or react in gas phase can also react with the HCN liberated from the resin (Equation 4.5).

~~HCN + 1/2 0 2 > HCNO (4.5)~~

The consumption of oxidant for cyanide oxidation/destruction is twice that required for the oxidation of copper(I) to copper(II), on an equal molar basis. Hence, if this reaction were allowed to take place during elution, the oxidant consumption would increase significantly. Further, if the base metal elution is coupled with cyanide recovery systems, oxidation of cyanide adversely affects the cyanide recovery. Therefore, the selectivity of oxidant to copper over cyanide is essential when cyanide recovery is required.

Popular oxidants used in the mineral processing industry include chlorine, ozone, hydrogen peroxide, sulphur dioxide/air, and ferric ions. With the exception of hydrogen peroxide and ferric ions, all of these oxidants can react with HCN during the elution or give oxidative gases which will be adsorbed in the caustic scrubbing solutions with HCN (where cyanide recovery is available), leading to a loss of cyanide. Ferric ions form ferricyanide in the presence of copper cyanide, and uhimately copper ferricyanide double salt, which may affect the loading performance of the resin. Therefore, of all the commercially available oxidants, hydrogen peroxide is the only suitable oxidant for oxidative acidic elution of copper from strong base resins. Figure 4.3 gives the reduction potential of hydrogen peroxide solutions in acidic solutions calculated using the Nemst equation for hydrogen peroxide concentrations of 0.1, 1 and 10 g/L. As can be seen, the reduction potential of hydrogen peroxide is relatively stable with respect to hydrogen peroxide concentration in the solution, but decreases as the pH increases. Dilute hydrogen peroxide solutions at pH less than 1.0 have theoretical reduction potentials in the range of+1650 to +1750 mV against the SHE.

Figure 4.3 shows that an eluent with a pH of 1.0, and hydrogen peroxide concentration in the range of 0.1 to 10 g/L, is sufficient to oxidise copper loaded on resin. The exact concentration of hydrogen peroxide could be varied to match the stoichiometric requirements of the reaction, taking into account factors such as the copper loading of the resin and the resin to eluent volume ratio.

The elution of resins with sulphuric acid is widely practiced in industry. In commercial ion exchange applications, the elution and regeneration of strong base resins are usually performed with sulphuric acid solutions (20-150 g/L). Sulphuric acid eluents of similar concentrations were selected for studies of the oxidative acid elution.

~~c 2.0 o~~

~~® X «W 1-5 O 0)~~

~~s S 1.0 o "5 - - - .0.1 g/LH202~~

~~oB 0.5 1.0g/LH202 3 ^ 10 g/L H202 •oo oc. 0.0 0 1 2 3 4 5 6 pH of solution~~

~~Fig. 4.3 Theoretical reduction potential of hydrogen peroxide in acidic solutions 4.6 STUDY OF THE EFFECT OF OXIDANT CONCENTRATION ON THE ELUTION OF COPPER~~

To evaluate the effect of hydrogen peroxide concentration on elution of copper cyanide complexes from strong base resins, a series of experiments were performed where a given amount of copper loaded resin was eluted using eluents containing various hydrogen peroxide concentrations. These tests were performed using Amberlite IRA 900 RF, a macromolecular polystyrene type 1 strong base anion exchange resin manufactured by Rohm and Haas.

~~4.6.1 Experimental~~

Pre-loaded resin was prepared by contacting 100 g of Amberlite IRA 900 RF resin with 160 mL of solution, containing 80.6 g/L (0.9 M) CuCN (UNILAB, Laboratory Reagent) and 88.22 g/L (1.8 M) NaCN (MERC, Analytical Reagent) in deionised water. The pH of the loading solution was adjusted to 12.0 by adding the required amount of NaOH (UNIVAR, Analytical Reagent). After six hours of loading, the resin was recovered from the loading solution, washed, and allowed to dry in a desiccator to a constant weight. A sample of loading solution taken prior to loading, the wash solution, and the spent loading solution, were each analysed for copper and total cyanide concentrations. Copper concentration was analysed by atomic adsorption spectrometry using a Varían Spectra A-20 Atomic Absorption Spectroscope (AAS) unit, while the analysis of total cyanide was performed according to ASTM 2036-97 (Method A) procedure, with potentiometric titration of cyanide with AgNOs (MERC, Analytical Reagent) to determine the cyanide concentration in the distillate. The copper and cyanide concentration in solutions and the corresponding volumes were used to determine the final copper and cyanide loading to the resin. Mass balance for copper and CN over the loading processes showed that the resin batch had a total copper loading of 91 mg/g and a total CN loading of 99 mg/g. Mass balance calculations are given in Appendix 1. The elution of resin was conducted on 5.0 g samples of pre-loaded resin described above, using 1000 mL of eluent in an agitated vessel at room temperature. All eluents contained 50 g/L H2SO4 (UNIVAR, Analytical Reagent). Some eluents contained H2O2 (UNIVAR, Analytical Reagent) as an oxidant. The H2O2 concentration in the eluent was varied between 0.065 and 0.8 g/L. The copper concentration of the eluent was monitored for three hours and the results were used to determine the rate of copper release from resin. During the elution, the solution in the vessel was sparged with air at 2 L/hr flow rate to remove the HCN gas from the eluent. The resulting HCN/air mixture was scrubbed with strong caustic solution to recover HCN. The recovery of cyanide in the caustic scrubbing column was monitored by direct Potentiometrie titration with AgNOs to investigate the rate of cyanide removal from the eluent. A total of seven tests were performed to determine the effect of hydrogen peroxide on copper elution. The first of this series was a controlled test, without hydrogen peroxide. The second test in the series was performed using approximately 50% of stoichiometric requirements of hydrogen peroxide, to oxidise the copper loaded on the resin. With the exception of these tests, all other tests had hydrogen peroxide in excess of the stoichiometric requirements for the reaction.

~~4.6.2 Results and Discussion~~

Table 4.1 gives a summary of test conditions used and the total recovery of copper into the eluent observed after three hours. The concentration profile of copper in the eluent for each test is shown in Figure 4.4. Copper concentration in solution observed during elution of these samples, and the calculation of copper recovery results, are given in Appendix 2. These resuhs suggest the total removal of copper from resin under the conditions tested, as long as the stoichiometric quantities of hydrogen peroxide were available to react with copper. As expected, the rate of reaction depended on the hydrogen peroxide concentration. It is believed that the 17% copper recovery seen in Test 1 is due to the oxidation of copper in the resin by dissolved oxygen in the eluent. Table 4.1 Summary of elution conditions used to recover copper from resin Parameter Test Test Test Test Test Test Test 1 2 3 4 5 6 7 Weight of resin used (g) 101 100 5j00 100 100 4^99 5.00 Initial H2SO4 concentration (g/L) 50 50 50 50 50 50 50 Initial H2O2 concentration (g/L) 0 0.065 0.13 0.2 0.26 0.40 0.80 Initial H2O2 to Cu molar ratio 0 0.27 0.55 0.82 1.09 1.65 3.28 Recovery of Cu after 3 hrs 17% 40% 55% 78% 88% 89% 94%

The recovery of cyanide noted after 24 hours is shown in Figure 4.5. Corresponding data and calculations are given in Appendix 3. These results indicate that the cyanide recovery efficiency is subject to the hydrogen peroxide concentration, with reduced yields at high oxidant concentrations. This loss of cyanide due to oxidation of cyanide at the high end of peroxide concentrations is consistent with expectations. The overall cyanide recovery from resin to the scrubber (after 24 hours) was more than 85% in all tests.

~~100 O 0.8 g/L H202~~

~~• 0.4 g/L H202~~

~~O 0.26 g/L H202~~

~~A 0.2 g/L H202~~

~~• 0.13 g/L H202~~

~~• 0.066 g/L H202~~

~~• No H202~~

~~1 2 3 Time (hrs)~~

~~Fig. 4.4 Copper concentration profile of the eluent for various H2O2 concentrations E i o XJ~~

~~o c o i8 0>) o o 0) q:~~

~~0 0.2 0.4 0.6 0.8~~

~~Initial H2O2 concentration (g/L)~~

~~Fig. 4.5 Recovery of cyanide against hydrogen peroxide concentration in eluent~~

The rate of cyanide recovery in the scrubber, and the rate of copper elution from resin during a typical run, are shown in Figure 4.6. The copper elution rate and cyanide collection rate, shown in Figure 4.6, are indicative of the rate of cyanide release to eluent and the rate of cyanide recovery from eluent, respectively. Corresponding data and calculations are given in Appendix 3. As significant differences exist between these two processes, it can be concluded that the rate determining step in the overall cyanide recovery from ion exchange resin is the mass transfer rate of HCN from liquid to gas phase.

From these results, it is evident that the removal of HCN from acidified solutions through aeration is not as rapid as it is generally assumed. Although cyanide recovery is of significant scientific and commercial interest, it nevertheless falls outside the primary focus of this work. As such, a cyanide recovery aspect of the oxidative acid elution was not given further attention. • Cyanide collected in the scrubber solution o Cu eluted from resin

~~12 18 24 Time (hrs)~~

~~Fig. 4.6 The accumulation of cyanide in the scrubber with time for Cycle 3~~

~~4.7 ELUTION OF RESIN LOADED WITH MIXED METAL CYANIDE SPECIES~~

~~4.7.1 Experimental~~

A series of bench scale tests were conducted to investigate the possibility of eluting mixed base metals using the oxidative acid elution. The tests were conducted on a fixed bed ion exchange resin test rig. To simulate process plant operating conditions, the tests were performed using cyanide leach liquor obtained from May Day mines (Cobar, New South Wales, Australia). Copper, gold, silver, zinc, and iron were the key cyanide complexes in the liquor. A total of seven loading and oxidative acid elution cycles were performed on the resin bed. The ion exchange resin rig was comprised of an ion exchange resin column of 200 mL capacity, feed and eluent storage tanks, a hydrogen cyanide stripping column, liquid pumps, valves, and pipelines. Purolite A500, a type 1 strong base anion exchange resin manufactured by Purolite International, was used as the ion exchanger. Loading solution and eluents were fed to the column from appropriate feed tanks through a variable speed peristaltic pump, which was also used to control the flow rate. A schematic diagram of the elution circuit of the test rig appears in Figure 4.7.

Loading of metal cyanide complexes was performed by downward flow of feed liquor through the column. After passing 25 L of solution at 25 bed volumes (BV) per hour (5 L/hr) flow rate through the column, the resin bed was rinsed with 1 L of water to remove any excess feed liquor trapped in the resin bed. Feed and discharge solutions were sampled at regular intervals to determine the loading performance. Mass balance was performed at the end of each loading stage for all feed and discharge streams to determine the resin loading of major elements.

~~Air+HCN~~

~~HCN Scrubbing column r~~

~~Ion Exchange H2S04 H202 Resin Column Spent 50g/L 5g/L r eluent and tank H2S04 50g/L~~

~~— w Pump Y Y~~

~~Air~~

Fig. 4.7 Schematic diagram of the ion exchange resin test rig used for bench scale testing of selective base metal elution Gold loading in the seventh cycle was increased by adding gold cyanide, AuCN (Sigma Aldrich, 99.99%), to the loading solution to clarify the effect of oxidative acid elution on gold adsorbed on resin. In addition to gold, copper, silver, iron, and zinc, which were the major elements in the pregnant liquor, cyanide complexes of cobah, chromium, iron, molybdenum, nickel, and lead, were also seen in concentrations less than 1 mg/L. The total cyanide concentration of the liquor was in the range of 400-500 mg/L (measured according to the ASTM 2036-97 procedure as described previously) and the chloride concentration was approximately 500 mg/L (measured using ion selective electrodes). The loading solution had a pH in the range of 12.0 to 12.5. A summary of conditions employed for loading mixed cyanide species to the resin is given in Table 4.2.

After each loading, the resin column was eluted to recover base metals. The elution was conducted by upward flow of eluents through the resin bed. In order to determine the feasibility of separately recovering copper from other base metals, the resin was initially eluted with a non-oxidative acidic eluent prior to using the oxidative acidic eluent. The first stage of the elution was performed using a 50 g/L H2SO4 solution, prepared by mixing H2SO4 (UNIVAR, Analytical Reagent) in de- ionized water.

In the second stage, an oxidative acid eluent containing 50 g/L H2SO4 and 5 g/L H2O2 (UNIVAR, Analytical Reagent) was used to elute the resin bed. These eluents were fed to the resin column from two separate eluent tanks at a controlled flow rate of 10 BV/h (2 L/hr). After sampling the spent eluent, it was stripped of dissolved hydrogen cyanide in an HCN stripping column, and directed to the spent eluent storage tank. The extract from the hydrogen cyanide stripping column, and vent ports of the spent eluent storage tank, were scrubbed with strong caustic solution before release. Continual monitoring of hydrogen cyanide at the release point confirmed that no hydrogen cyanide was released to the atmosphere. After each elution, the resin bed was rinsed with another 2 L of water in preparation for the next loading cycle. Table 4.2 Loading conditions used to load mixed cyanide species to the ion exchange resin bed Cycle Loading (downward flow) Rinse (upward flow)

Au Ag Cu Fe Zn Total CN FeedpH Flow rate Duration Volume Flow rate Duration Volume (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (BV/hr) (hrs) (L) (BV/hr) (hrs) (L) 1 1.23 13.4 356 0.52 8.55 420 12.1 25 5 25 10 0.5 1

~~2 1.23 13.4 356 0.52 8.55 480 12.4 25 5 25 10 0.5 1~~

~~3 1.23 13.4 356 0.52 8.55 450 12.3 25 5 25 10 0.5 1~~

~~4 1.01 9.08 272 0.31 5.10 458 12.3 25 5 25 10 0.5 1~~

~~5 1.18 10.2 302 0.41 6.02 430 12.1 25 5 25 10 0.5 1~~

~~6 1.21 10.3 313 0.44 6.07 425 12.2 25 5 25 10 0.5 1~~

7 17.4 7.98 245 0.27 4.47 320 12.0 25 5 25 10 0.5 1 The performance of the elution was evaluated using metal, acid, and peroxide concentrations in the feed and spent eluents. These measurements were used to produce elution profiles to chart the progress of elution with time and to conduct an overall mass balance to assess the total removal of metals from the resin bed. Elemental analysis of feed and discharge loading solution, feed and discharge eluents, and wash solutions were performed using inductively coupled atomic emission spectroscopy, with a Perkin Elmer Optima-3000 Inductively Coupled Plasma Atomic Emission Spectroscope (ICP-AES) instrument. The total cyanide analysis in the feed and barren liquors was performed according to ASTM 2036-97 procedure. The cyanide accumulation in the scrubber was determined by direct Potentiometrie titration with AgNOs.

In the first three cycles, 4 L of each type of eluent was used to ensure the complete removal of base metals and to optimise the separation of copper from other base metals. After sufficient data was collected to confirm elution characteristics, the volume of eluent used was varied to determine the minimum eluent requirements for complete removal of base metals from resin. Elution conditions are summarised in Table 4.3.

~~4.7.2 Results and Discussion~~

Concentrations of major metals in the discharge liquor are given in Table 4.4. Also given in this table are the loading of metals to the resin during each loading step. As can be seen in Table 4.4, precious metals and base metals are loaded indiscriminately to the resin. As expected, the high concentration of copper in the loading solution resulted in a correspondingly high loading of copper on to the resin. Appendix 4 gives the loading profile data for the seven cycles reported in Table 4.4. Table 4,3 Elution conditions used to elute mixed cyanide species to the ion exchange resin bed Cycle Non oxidative acid elution (upward flow) Oxidative acid elution (upward flow) 2"'' Rinse (upward flow) H2SO4 Eluent Flow rate Duration Volume H2SO4 H2O2 Eluent Flow rate Duration Volume Flow rate Duration Volume (g/L) pH (BV/hr) (hrs) (L) (g/L) (g/L) pH (BV/hr) (hrs) (L) (BV/hr) (hrs) _(L)_ 1 50 <1 10 2 4 50 5.2 <1 10 2 4 10 0.5 2 50 <1 10 2 4 50 5.1 <1 10 2 4 10 0.5 3 50 <1 10 2 4 50 4.9 <1 10 2 4 10 0.5 4 50 <1 10 0.5 1 50 5.8 <1 10 2.5 5 10 0.5 5 50 <1 10 0.5 1 50 5.2 <1 10 1.5 3 10 0.5 6 50 <1 10 0.5 1 50 5.0 <1 10 1.5 3 10 0.5 7 50 <1 10 0.5 1 50 4.9 <1 10 1.5 3 10 0.5 Table 4.4 Loading of mixed cyanide species to the resin bed Cycle Feed Discharge metal concentrations ^otal loading from the cycle No. volume (mg/L) (mg)

~~(L) Au Ag Cu Fe Zn Au Ag Cu Fe Zn~~

~~1 25 0.0 2.1 21.1 0.1 0.2 30 282 8372 10.0 209~~

~~2 25 0.0 3.5 26.1 0.2 0.2 30 247 8247 8.3 209~~

~~3 25 0.1 5.6 33.0 0.3 0.2 29 194 8075 5.6 208~~

~~4 25 0.1 3.8 18.4 0.1 0.0 23 133 6340 5.0 127~~

~~5 25 0.1 4.6 15.0 0.1 0.0 27 139 7175 7.8 150~~

~~6 25 0.2 7.9 27.7 0.2 0.0 26 60 7132 6.5 152~~

~~7 25 0.1 1.4 0.0 0.0 0.0 433 164 6125 6.8 112~~

A typical breakthrough curve for one of the loading cycles is given in Figure 4.8. The selectivity of the resin to highly polarised gold and zinc over silver, copper, and iron is clearly seen in Figure 4.8. Breakthrough of copper, iron, and silver was seen well ahead of gold, and is a good indicator of the relative saturation of the ion exchange resin.

Although precious metals and base metals are loaded indiscriminately to the resin, it was seen that the loading of elements gradually decreased with the progression of cycles. This may have been due to the accumulation of precious metals on the resin. Gradual degradation of resin could also produce such an effect. Accurate estimation of total loading capacity of the resin at the end of each loading cycle requires a definitive knowledge of the speciation of metal cyanide complexes loaded on the resin, which is extremely complicated in a multi-component system. Resin deterioration is further investigated under simplified and controlled conditions in Chapter 5. 5 10 15 20 25 Flow through the resin bed (L)

~~Fig. 4.8 The breakthrough of elements during a typical loading cycle~~

The elution profile of the third cycle is given in Figure 4.9, where the concentration of copper and zinc in the spent eluent exiting the resin bed is shown against the volume of eluent used. The elemental concentration profiles give clear evidence that copper and other base metals are eluted at separate stages, with little cross contamination. Most of the zinc in the resin is eluted in the first stage by the non- oxidative acid eluent (Peak A). Copper on the resin is only released when the oxidative acid eluent (mixture of H2O2/H2SO4) is introduced.

The second zinc peak in the spent eluent (Peak B) was seen in all elutions. This suggests that when resin loaded with mixed CNWAD species is eluted with non- oxidative acid eluents, some of the zinc is retained on the resin. As Zn(CN)4 " readily decomposes under acidic conditions, the only possible explanation for retention of zinc is the blockage of resin pores, which would prevent the acid coming into contact with Zn(CN)4^' ions loaded on inner parts of the resin. The precipitation of copper cyanide in the pores of the resin could have encapsulated zinc and other metal cyanide species which otherwise would have decomposed to release metal cations. U)

~~0 2 4 6 8 Volume of eluent passed through the resin bed (L)~~

~~Fig. 4.9 The concentration profile of copper and zinc in the spent eluent of the third elution cycle~~

It can be seen that when the oxidative acid eluent is introduced, copper is released into the eluent, indicating that the insoluble CuCN complex is decomposed by the oxidative acid eluent. The decomposition of copper cyanide species appears to be rapid; most of the copper loaded on the resin is removed within the first 30 minutes of the oxidative acid elution. Further, the dissolution of copper cyanide precipitate appears to have opened the resin pores, allowing the elution of zinc trapped in the inner parts of resin.

In the seven successive cycles of loading and oxidative acid elutions conducted on the resin bed, the accumulation of metals on the resin was tracked. The loading of metals during the adsorption stage, and the combined elution of metals in the two elution stages, are reported in Tables 4.5 and 4.6. The resuhs of individual cycles shown in Table 4.5 indicate that all copper and zinc loaded during adsorption are removed from resin in the subsequent elution. It can also be seen that precious metals are unaffected by the elutions. Hardly any precious metals appeared in the eluent. Table 4.5 Cumulative loading of metals to resin bed on successive loading/elution cycles Cycle Metal loading at the start of Metal loading from the current Metal elution from the No. cycle (mg) cycle (mg) current cycle (mg)

Au Ag Cu Fe Zn Au Ag Cu Fe Zn Au Ag Cu Fe Zn 1 0 0 0 0 0 30.8 282 8372 10.0 209 0 0 8346 5 202 2 31 282 26 5 8 30.2 247 8247 8.3 209 0 1 8879 7 215 3 61 527 0 7 2 29.0 194 8075 5.6 208 0 2 9360 17 224 4 90 719 0 0 0 23.9 133 6340 5.0 128 0 0 7270 12 125 5 114 851 0 0 3 27.7 138 7175 7.8 151 0 0 7704 0 152 6 141 990 0 7 1 26.4 60 7133 6.5 152 0 0 7378 0 163 7 168 1049 0 14 0 433.1 164 6125 6.8 112 1 0 6358 0 123 Table 4.6 Mass balance for overall loading and elution of metals during 7 loading/elution cycles Element Total loading to metals to resin Metals removed from resin bed from Metals retained on resin after bed from 7 adsorption cycles 7 elution cycles from resin bed 7 adsorption /elution cycles (mg) Mass % of mass Mass % of mass (mg) loaded (mg) loaded Au 601 1 0% 600 100% Ag 1,217 4 0% 1,214 100% Cu 51,467 55,294 107% -3,827 -7% Fe 50 41 81% 9 19% Zn 1,168 1,202 103% -35 -3% This is further evident in Table 4.6, which gives the overall loading and removal of metals during the seven cycles of loading and elution. After seven cycles, virtually all gold and silver recovered from the feed liquor remained on the resin. All copper and zinc loaded to the resin were found in the spent eluent. Mass balance calculations show closure within 7% and 3% for copper and zinc respectively, suggesting the complete removal of copper and zinc from resin.

The overall loading of iron during the seven cycles was approximately 19%. This is believed to be due to the low affinity of iron cyanide species to the resin. It is well known that iron cyanide complexes do not decompose in mild oxidative acidic conditions used in this test series. Therefore, it is unlikely that iron cyanide was removed during elution. As the concentration of iron was less than 1 mg/L in the feed solutions, the accuracy of the mass balance figures for iron are questionable.

~~4.8 CONCLUSION~~

The work presented in this chapter has enhanced the understanding of the behaviour of metal cyanide complexes on ion exchange resin in the presence of oxidative acid conditions. The study of the effect of H2O2 concentration on elution of base metals from resin showed that all copper loaded on resin can be completely eluted by the oxidative acid eluent, as long as stoichiometric requirements of hydrogen peroxide were available to react with copper. Cyanide recovery was found to depend on hydrogen peroxide concentration. At higher oxidant concentrations, some cyanide was oxidised in the resin, while at low oxidant concentrations, almost all cyanide loaded to the resin was recovered.

Loading of mixed base metal cyanide complexes confirmed that precious metals and base metals are loaded indiscriminately to strong base ion exchange resins. It was seen that the loading of all elements gradually decreased with the progression of cycles, resulting from the accumulation of precious metals on the resin, or a gradual deterioration of the resin. This phenomenon is further investigated in Chapter 5.

Testing of the oxidative acid elution on ion exchange columns proved that it was able to completely remove major base metals from strong base resins. The elemental concentration profiles gave clear evidence that copper and other base metals could be eluted at separate stages with little cross contamination. Precious metals loaded on the resin were unaffected by the oxidative acid elution. The behaviour of non-WAD cyanide species (such as ferricyanides and ferrocyanides) during the loading and elution of resin was not studied adequately in the column tests reported in Section 4.7. Further investigation of the behaviour of these non-WAD cyanide species is given in Chapter 5.

These studies confirm that the cyclic operation of a strong base ion exchange resin bed between adsorption and oxidative acid elution cycles could be used to successfully remove metal cyanide species from tailings. As the precious metal and non-WAD cyanide species are not eluted by the oxidative acid elution, a gradual increase in the loading of precious metal and non-WAD cyanide complexes would be seen when a resin bed is cycled between loading and oxidative acid elutions. After a number of such loading and oxidative acid elution cycles, the resin bed could be eluted and regenerated with eluent such as Zn(CN)4^" or SCN" to remove non-WAD cyanide complexes. Resin Durability and Elution of Mixed Cyanide Complexes

This chapter explores the durability of resin, when the oxidative acid eluent is repeatedly used to elute base metal cyanide complexes from resin. Attention is given to studying the effect of oxidative acid conditions on the total and strong base capacities of resin and the resulting effect on net operating capacities of resin beds. The effect of the co-loading of mixed cyanide species is also investigated, as the process development work (Chapter 4) suggested that non-WAD cyanide species are not eluted by the oxidative acid eluent.

~~5.1 THE EFFECT OF OXIDATIVE ACID ELUTION CONDITIONS ON RESIN PERFORMANCE~~

Some doubts prevailed about the ability of strong base ion exchange resins to withstand long term, repeated exposure to oxidative conditions. As briefly discussed in Section 3.2.3, quaternary ammonium functional groups of resin could potentially be partially or completely oxidised under the conditions of the oxidative acid elution. Further, the repeated cycling between high pH/low Eh adsorption conditions and low pH/high Eh elution conditions has the potential to cause resin fracture and disintegration. To investigate these possibilities, a batch of resin was subjected to a series of adsorption and oxidative acid elution cycles while observing key performance characteristics. 5.1.1 Experimental

To investigate the effect of the oxidant on resin, the total base and strong base capacities of a strong base ion exchange resin were measured while the column was subjected to 30 loading and oxidative acid elution cycles. An ion exchange resin column charged with 10 mL (wet settled volume, chloride form) of Purolite A500 resin was used as the ion exchanger. The loading solution, the wash water, and the eluent were fed to the ion exchange column using a DIONEX Gradient Pump (Figure 5.1). The total base capacity and the strong base capacity of the resin were measured and recorded prior to the first loading/oxidative acid elution cycle. Following this, the total base and the strong base capacities of the resin were measured and recorded after every six loading/oxidative acid elution cycles. The changes in physical properties and loading capacities of the resin were used to quantify the effects of repeated exposure to oxidative acid conditions.

~~5.1.1.1 Loading and Oxidative Acid Eiutions~~

Loading was conducted with an alkaline cyanide solution. As this study focused solely on the effect of repeated cycling between high pH/low Eh loading conditions and low pH/high Eh elution conditions, metal cyanide complexes were not introduced to the loading solution. The effect of metal cyanide complexes are studied in Section 5.2. In each cycle, the resin was loaded with 300 mL of solution containing 1250 mg/L (48mM) free cyanide (as CN"). The loading solution was prepared by dissolving the required amount of NaCN (MERC, Analytical Reagent) in deionised water. The pH of the loading solution was adjusted to 12.0 by adding the required amount of NaOH (UNIVAR, Analytical Reagent). Loading cycles were 60 minutes in duration. The loading solution was fed to the column at 30 BV/hr (5 mL/min) flow rate. After each loading cycle, the column was rinsed with 25 mL of deionised water at 30 BV/hr (5 mL/min) flow rate. After each loading and the subsequent rinse, the column was eluted with the oxidative acid eluent. For each elution, 200 mL of oxidative acid eluent was used. The eluent was passed through the resin bed at 30 BV/hr (5 mL/min) flow rate. The eluent contained 50 g/L H2SO4 (UNIVAR, Analytical Reagent) and 5 g/L H2O2 (UNIVAR, Analytical Reagent), in deionised water. It had a pH of less than 1. The calculated reduction potential of the eluent was approximately +1700 mV against the SHE. After each elution, the resin bed was given a second rinse using 75 mL of deionised water at 30 BV/hr (5 mL/min) flow rate, prior to the next loading cycle. A ftill cycle consisting of loading, first rinse, elution, and the final rinse required two hours. In total, 30 cycles were conducted on the resin bed. Figure 5.1 shows the experimental rig used, consisting of feed solution containers, the pump, and the ion exchange column. Detailed resuhs are given in Appendix 5.

~~5.1.1.2 HCN Management~~

The total amount of cyanide used in each run was deemed not to be a significant hazard (less than 0.5 g of cyanide used in each cycle). Therefore, unlike the process development work described in Chapter 4, a scrubber was not used to scrub HCN from the discharge of the column when elutions were conducted. Instead, the rig was operated in a fiime cupboard, which effectively prevented any trace amounts of HCN entering the laboratory atmosphere.

~~5.1.1.3 Total Base Capacity Measurements~~

The total base capacity of the resin was measured using a technique prescribed by Harland (1994). First, the 10 mL resin bed was converted to CI" form by passing 100 mL of 1 M HCl (UNIVAR, Analytical Reagent) through the resin bed at 30 BV/hr (5 mL/min) flow rate. Then the resin was rinsed with deionised water to remove any excess chlorides. The rinsing continued until an aliquot of wash solution registered less than 0.2 mM CI", determined by titration with 10 mM AgNOs (UNIVAR, Analytical Reagent) using K2Cr04 (UNIVAR, Analytical Reagent) as the indicator. w J mcMMicua fromHwietoa

~~H2O2 / H2SO4 eluent~~

~~Fe( d solution If \ Rinse water I \\ \ i Ion exchange resin column ix Discharge solution samples~~

~~Pump~~

Fig. 5.1 Ion exchange resin rig used for process validation tests The resin sample was then transferred to a measuring cylinder and the volume in CI' form was measured and recorded. After volume measurements were taken, the resin sample was placed back in the column and eluted with 200 mL of 0.5 M NaNOs solution (UNIVAR, Analytical Reagent) at 30 BV/hr (5 mL/min) flow rate to remove all adsorbed chloride ions. Then the resin was rinsed with 250 mL of deionised water. The spent NaNOs solution and rinse solution were collected and diluted to 500 mL. An aliquot from this solution was titrated with 10 mM AgNOs using K2Cr04 as the indicator. The CI" concentration in solution determined by titration was used to estimate the amount of CI" released from the ion exchange resin, and hence the total base capacity of resin. Details of total base capacity tests are given in Appendix 5.

~~5.1.1.4 Strong Base Capacity Measurements~~

The strong base capacity of resin was also measured using a technique prescribed by Harland (1994). As described above, the 10 mL resin bed was first converted to CI" form. Then the resin was rinsed with deionised water to remove any excess chloride ions from the resin. The rinsing continued until an aliquot of wash solution registered less than 0.2 mM CI" concentration. Following this, 50 mL of 2.5 M ammonia solution (LABSERV, Analytical Grade) was passed through the resin bed at 30 BV/hr (5 mL/min) flow rate to convert any weak base functional groups to free base form, which releases all CI" ions attached to them. The mass action of OH' ions in the ammonia solution also removes a small fraction of CI" ions attached to strong base ftinctional groups. To replenish CI" ions stripped from strong base functional groups, the resin bed was then rinsed with 300 mL of 50 mM NaCl (LABSERV, Analytical Grade) solution at 30 BV/hr (5 mL/min) flow rate. After this, the resin was rinsed with deionised water to remove any excess chloride ions from the resin. The rinsing continued until an aliquot of wash solution registered less than 0.2 mM CI" concentration. The resin sample was then eluted with 200 mL of 0.5 M NaNOs solution at 30 BV/hr (5 mL/min) flow rate to remove all adsorbed chloride ions from the resin. The resin was then rinsed with 250 mL of deionised water. The spent NaNOs solution and the rinse solution were collected and diluted to 500 mL. An aliquot from this solution was titrated with 10 mM AgNOs using K2Cr04 as the indicator. The CI" concentration in solution determined by titration was used to estimate the amount of CI' attached to the quaternary ammonium functional groups of the resin, i.e. the strong base capacity. Details of total base capacity tests are also given in Appendix 5.

~~5.1.2 Results and Discussion~~

Table 5.1 gives the total and strong base capacities of the resin batch over the 30 loading/oxidative acid elution cycles. The total base capacity of fresh resin was approximately 1.11 ± 0.02 mEq/mL, which is consistent with the manufacturer's specification of 1.15 mEq/mL. The strong base capacity of the resin was found to be equal to its total base capacity, confirming that the base functionality of the resin could be entirely attributed to quaternary ammonium functional groups.

As the resin was repeatedly subjected to loading/elution cycles, no statistically significant changes in total base or strong base capacities could be seen. After 30 loading and elution cycles, the resin showed a total base capacity of 1.10 ± 0.02 mEq/mL. The strong base capacity after 30 cycles was 1.09 ± 0.02 mEq/mL.

~~Table 5.1 Total and strong base capacities of Purolite A500 resin over 30~~

~~Resin Total base capacity Strong base capacity (mEq/mL) (mEq/mL)~~

~~Fresh resin 1.11 ±0.02 1.12 ±0.02~~

~~6 cycles 1.11 ±0.02 1.10 ±0.02~~

~~12 cycles 1.10 ±0.02 1.11 ±0.02~~

~~18 cycles 1.10 ±0.02 1.11 ±0.02~~

~~24 cycles 1.11 ±0.02 1.12 ±0.02~~

~~30 cycles 1.10 ±0.02 1.09 ±0.02 1.50~~

~~1.25~~

~~O- LU 1.00 E .E 0.75 £ ^o 0.50~~

~~•—Total base capacity o 0.25 a •4— Strong base capacity f8 O 0.00 12 18 24 30 Cycle number~~

~~Fig. 5.2 Total base and strong base capacities of Purolite A500 resin over 30 loading and oxidative acid elution cycles~~

~~" , rL ""~~

~~•is:~~

~~6.- •~~

~~tW"'•j- j~~

~~'If~~

~~Fresh resin After 12 cycles After 24 cycles After 30 cycles~~

Fig. 5.3 Appearance of resin column over 30 loading/elution cycles These results indicate that the anion exchange flinctionaUty of the resin has not deteriorated over the 30 cycles. This is further illustrated in Figure 5.2. The appearance of the resin column over the duration of 30 loading/elution cycles can be seen in Figure 5.3. No discolouration or disintegration of the resin beads is evident over the 30 cycles. Approximately 10% shrinkage of the resin was noted when the resin was in alkaline cyanide solution. When the resin was eluted with the oxidative acid eluent, the volume of the resin batch returned to 10.0 mL. This pattern was seen over the 30 cycles.

These results indicate that strong base ion exchange resins can be repeatedly cycled between loading and oxidative acid elution conditions over a moderate number of cycles, without damaging or ahering the performance of resin.

~~5.2 THE EFFECT OF COPPER AND IRON CYANIDE SPECIES ON RESIN PERFORMANCE~~

The loading and elution of mixed metal cyanide species (Section 4.7) indicated that 9+ copper cyanide is effectively oxidised to Cu ions by the oxidant. Non-WAD cyanide species on the other hand, were not stripped from the resin by the oxidative acidic eluent.

The presence of copper and iron in the loading solution introduces several variables into the system, which may impact on the durability of resin. For instance, if a small amount of copper remains on the resin after each elution, over a number of cycles this may build up to a significant level, reducing the loading capacity of resin. Further, although an oxidative acid eluent containing 5 g/L H2O2 in 50 g/L H2SO4 has no affect on the loading capacity of the resin (Section 5.1), the presence of copper may catalyse the oxidation of resin matrix or functional groups by the oxidant. The presence of Cu^^ cations and non-WAD cyanide species, such as those of iron, could also lead to the formation of insoluble metal cyanide double salts on the resin surface, hindering the ion exchange process.

Therefore, the effect of loading of copper cyanide and non-WAD cyanide on the performance of resin was investigated. As low levels of iron cyanide complexes are found in most cyanidation tailings, iron cyanide was used as the representative non- WAD cyanide species in these studies. The specific aspects investigated were:

~~1. the effect of copper cyanide in the loading solution on the long term performance of resin~~

~~2. the effect of the type of iron cyanide species in loading solution~~

~~3. the effect of iron cyanide concentration in loading solution~~

~~4. the effect of loading solution pH, when iron cyanide species are present in loading solution.~~

In this series of tests, five ion exchange columns (Columns A to E) were loaded and eluted with loading solutions containing various levels of copper and iron cyanide species. A summary of the loading and elution conditions employed are shown in Tables 5.2 and 5.3.

~~5.2.1 The Effect of Copper Cyanide in the Loading Solution~~

The impact of copper in the loading solution was investigated by performing multiple loading/elution cycles on an ion exchange resin column with a loading solution containing copper cyanide. Table 5.2 Loading conditions used to load resin with mixed iron and copper cyanide species Column Cu Fe Total Feed Flow Duration Volume (mg/L) (mg/L) CN pH rate (min) (mL) (mg/L) (BV/hr) A 950 Nil 1250 12.2 60 60 300 B 950 50 (Ferrocyanide) 1250 12.1 60 60 300 C 950 50 (Ferricyanide) 1250 12.1 60 60 300 D 950 25 (Ferrocyanide) 1250 12.1 60 60 300 E 950 25 (Ferrocyanide) 1250 8.5 60 60 300

Table 5.3 Elution conditions used to elute resin loaded with mixed copper and iron cyanide species Column Rinse Elution 2"' Rinse Flow Duration Volume H2SO4 H2O2 Feed Flow Duration Volume Flow Duration Volume rate (min) (mL) (g/L) (g/L) pH rate (min) (mL) rate (min) (mL) (BV/hr) (BV/hr) (BV/hr)

A 60 65 25 50 5 <1 60 40 200 60 15 75 B 60 65 25 50 5 <1 60 40 200 60 15 75 C 60 65 25 50 5 <1 60 40 200 60 15 75 D 60 65 25 50 5 <1 60 40 200 60 15 75 E 60 65 25 50 5 <1 60 40 200 60 15 75 5.2.1.1 Experimental

The ion exchange resin test rig used to study the effect of oxidative acid elution conditions on resin performance (Section 5.1) was used for these studies. The ion exchange resin column (Column A), was charged with 10 mL of Purolite A500 strong base anion exchange resin (wet settled volume in chloride form). In each cycle, the column was loaded with 300 mL of loading solution at a flow rate of 30 BV/hr (5 mL/min) for a period of 1 hour.

~~The loading solution of Column A contained 950 mg/L copper(I) (as copper cyanide)~~

in a 1250 mg/L CNTQT matrix. The loading solution was prepared by dissolving the required amounts of CuCN (UNILAB Laboratory Reagent) with NaCN in deionised water. The pH of the loading solution was adjusted to 12.2 by adding the required amount of NaOH. In all loading/elution cycles, the total loading of copper to the resin was determined by mass balance, using the copper concentration in feed and composite discharge liquors. During loading Cycles 1, 5, 10 and 15, the spent loading solution was sampled every five minutes to determine loading performance and breakthrough curves. Copper concentration in samples was measured using a Varian VISTA AX CCD Simultaneous Inductively Coupled Plasma Atomic Emission Spectroscope (ICP AES) unit.

After each loading cycle, the resin bed was rinsed with 25 mL of deionised water. Then it was eluted using 200 mL of eluent containing 50 g/L H2SO4 (UNIVAR, Analytical Reagent) and 5 g/L H2O2 (UNIVAR, Analytical Reagent). Finally, the resin bed was given a second rinse using 75 mL of deionised water prior to the next loading cycle. The two rinse solutions were combined with the spent eluent and analysed for copper using the same ICP AES technique described above. Appendix 6 gives the details of loading and elution results together with breakthrough curve data and total loading capacities observed. As discussed in Section 5.1.1.2, the HCN gas hazard was deemed insignificant to warrant the use of an HCN scrubber. The entire test rig was located in a fume cupboard as an additional safety measure (Figure 5.1). Over the 15 loading/elution cycles, the total base capacity of the column was measured to examine if the total base capacity was affected by the presence of copper cyanide in the loading solution. Total base capacity measurements were taken before the first loading/elution cycles and after the and cycles. The total base capacity measurements were taken using the technique prescribed by Harland (1994), following the procedures described in Section 5.1.1.3. Strong base capacity measurements require the rinsing of resin bed with a concentrated ammonia solution. If the resin is brought into contact with a strong ammonia solution, any copper left on resin will be complexed by the ammonia solution, altering the condition of the resin. This would make the measurement ineffectual. Hence, strong base capacity of resin was not measured in this part of the study.

~~5.2.1.2 Results and Discussion~~

The total base capacity measurements of Column A over the 15 cycles are shown in Table 5.4. As can be seen, approximately 13% reduction in the total base capacity was noted over the 15 cycles. This is ftirther illustrated in Figure 5.4. Further evidence for this reduction of resin loading capacity is found in breakthrough curves. Copper breakthrough curves of Cycles 1, 5, 10, and 15 are shown in Figure 5.5. These breakthrough curves show a clear drift over the 15 loading cycles. This drift can be attributed to the reduction of total base capacity of the resin bed. It gives ftirther evidence that the loading capacity of the resin has been affected by the oxidative acid elution.

~~Table 5.4 Total base capacity of Column A over 15 cycles Resin description Loading capacity Relative (mEq/mL) deterioration~~

~~Fresh resin 1.15 ±0.02 - After 12 loading/elution cycles 1.02 ±0.02 11% After 15 loading/elution cycles 1.00 ±0.02 13% 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15~~

~~Number of loading/elution cycles on Column A~~

~~Fig. 5.4 Total base capacity of Column A over 15 loading/elution cycles~~

~~1000 -•—Cycle 1 ^ 900 Cycle 5 d 800 O) -•—Cycle 10 £ 700 -•—Cycle 15 600 2 500 w 400 ^ 300 3 200 ^ 100~~

~~50 100 150 200 250 300 Feed volume (mL)~~

~~Fig. 5.5 Copper breakthrough curves of Column A Table 5.5 Net operating capacity of Column A in the absence of iron in~~

~~Cycles Total loading and elution of Cu: Column A Cu loading Cu elution Discrepancy (mg) (mg) 1 259 258 0% 15 246 237 4%~~

Table 5.5 gives the initial and final total loading and elution figures of copper on Column A. The total loading capacity of copper seen in the 15 cycles are plotted in Figure 5.6 against the number of loading/elution cycles. Detailed resuhs and calculations are given in Appendix 6. These results show a clearly detectable reduction of the total loading of copper over the 15 loading/elution cycles. It should be noted that the total loading shown in these results does not represent the maximum loading capacity of the resin, but the net operating capacity of the resin bed under the conditions tested. However, the trend seen here is similar to the reduction of the total base capacity shown in Figure 5.4.

~~T \ 1 1 1 1 1 1 1 1 r 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Cycle Number~~

Fig. 5.6 The net operating capacity of Column A over 15 cycles Gradual discolouration of resin was noted in Column A over the 15 loading/elution cycles (Figure 5.7). This discolouration also confirms that a notable change in the resin has occurred over this series of loading/elution cycles.

~~Fresh Resin After 5 cycles After 10 cycles After 15 cycles~~

~~Fig. 5.7 Discolouration of resin in Column A~~

The gradual decrease of total base capacity, the drift of breakthrough curves, the reduction in the total loading of copper, and the discolouration of resin suggest a small accumulation of copper on the resin. However, the Eh-pH diagram for Cu- H2O-CN" system (Figure 2.2) indicates that Cu(I) is not stable in relation to Cu(II) under elevated redox potentials in acidic conditions. It is well known that Cu(II) ions do not form stable anionic complexes in such conditions. Therefore, an accumulation of copper in the resin appears to be an unlikely scenario. Another possible reason for this decrease of total base capacity is the oxidation of resin by H2O2. The Cu^^ catalysed H2O2 oxidation, i.e. Fenton reaction, is known to increase the rate of H2O2 oxidation of organic compounds (Gemeay, 2004; Akagawa and Suyama, 2002). Hence, it can be suggested that the copper in the resin could catalyse the oxidation of resin by hydrogen peroxide, leading to oxidation of functional groups and/or deterioration of the resin substrate. Detailed resin characterisation studies in Chapter 7 attempt to shed more light on this phenomenon.

~~5.2.2 The Effect of Iron Cyanide Species in Solution~~

The impact on resin performance brought about by iron cyanide species was investigated by conducting multiple loading and elution cycles on ion exchange resin columns. Two ion exchange resin columns were used in this study. Both columns were loaded with solutions containing copper cyanide as a representative CNWAD species. One column was loaded with a solution containing low levels of ferrocyanide, in addition to copper cyanide. Ferricyanide was introduced to the loading solution of the other column. Breakthrough curves, net operating capacities, and total base capacities of these columns were measured and studied to determine the effect of iron cyanide species on resin performance. Results of Column A were used as a control experiment to distinguish the effect of iron cyanide species on the resin from that of copper cyanide.

~~5.2.2.1 Experimental~~

The same ion exchange resin test rig used in the study of the effect of oxidative acid elution conditions on resin performance (Section 5.1.1) was used for this study. As in the previous studies, the two ion exchange resin columns (Columns B and C) were charged with 10 mL of Purolite A500 strong base anion exchange resin (wet settled volume in chloride form). Each column was subjected to 15 loading and oxidative acid elution cycles.

Column B was loaded with a solution containing 950 mg/L copper(I) cyanide and 50 mg/L iron cyanide (as ferrocyanide) in a 1250 mg/L CNTQT matrix. Column C was loaded with a solution containing similar levels of copper and total cyanide, but containing 50 mg/L of iron as ferricyanide. In each cycle, columns were loaded with 300 mL of loading solution at a flow rate of 30 BV/hr (5 mL/min) for a period of one hour. Since Cu(CN)3 " has a stronger affinity to strong base ion exchange resins than Fe(CN)6'^" or Fe(CN)6^", copper cyanide completely replaces ferrocyanide and ferricyanide by mass action effect, if the loading is continued until the resin bed is exhausted. To ensure the loading of iron cyanide as well as copper cyanide, the resin bed was kept below 80% saturation during these loading steps.

The loading solutions were prepared using CuCN with NaCN in deionised water. Required amounts of potassium ferricyanide, K3Fe(CN)6 (UNIVAR, Analytical Reagent) or potassium ferrocyanide, K4Fe(CN)6 (Chem Supply, Analytical Reagent) were used to introduce iron cyanide species into the loading solutions. The pH of each loading solution was adjusted to 12.1 by adding the required amount of NaOH. In all loading/elution cycles, the total loading of copper and iron to the resin was determined by mass balance, using the elemental concentrations in feed and composite discharge liquors. During loading Cycles 1, 5, 10, and 15, the spent loading solution was sampled every five minutes to determine loading performance and breakthrough curves. Copper and iron concentrations in samples were measured using a Varian VISTA AX CCD Simultaneous ICP AES unit.

As in Section 5.2.1, after each loading cycle, resin beds were rinsed with deionised water, eluted using the oxidative acid eluent, and rinsed again before the next loading cycle. Sampling and analytical techniques of the eluent were identical to those used in Section 5.2.1.1. Appendices 7 and 8 give the details of each test series, together with breakthrough curve data and total loading capacities observed.

The total base capacity of each column was measured to examine if the resin performance was affected by the presence of iron cyanide in the loading solution. These measurements were taken before the first loading/elution cycle, and after the 12^*^ and 15^ cycles, following an identical procedure to that described in Section 5.2.1.1. Since both iron and copper are strongly complexed by ammonia, the strong base capacity measurements were deemed ineffectual in these studies.

~~5.2.2.2 Results and Discussion~~

The total base capacity measurements of Columns B and C over the 15 cycles are shown in Table 5.6. Resuhs of Column A are also shown for comparison purposes. Over 15 cycles, the total base capacities of Columns B and C were reduced by approximately 12-15%. This is comparable with the reduction of total base capacity seen in Column A, where there was no iron cyanide species in the loading solution.

This indicates that iron cyanide species do not cause a net reduction in the total base capacity of strong base resin. Figure 5.8 illustrates the resuhs given in Table 5.6, showing that the reduction of the total base capacities of Columns B and C is indistinguishable from that of Column A. It can also be seen that the reduction of the total base capacities is generally proportional to the number of cycles on the resin.

Table 5.6 Total base capacity of Columns A, B, and C over 15 loading/elution cycles Column Total base capacity Relative (mEq/mL) deterioration Fresh resin After 12 After 15 cycles cycles Column A: 1.15 ±0.02 1.02 ±0.02 1.00 ±0.02 13% Loading/elution cycles with 950 mg/L Cu Column B: 1.13 ±0.02 1.00 ±0.02 0.96 ± 0.02 15% Loading/elution cycles with 950 mg/L Cu and 50 mg/L Fe (Ferrocyanide) Column C: 1.12 ±0.02 1.00 ±0.02 0.99 ± 0.02 12% Loading/elution cycles with 950 mg/L Cu and 50 mg/L Fe (Ferricyanide) (0 0)

~~o 0.8~~

~~f«0 i = 0.6 8 0.4 CO n —Column A S 0.2 o • - Column B ••—Column C 0.0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Number of loading/elution cycles on columns~~

~~Fig. 5.8 Total base capacities of Columns A, B, and C over 15 loading/elution cycles~~

Copper breakthrough curves of Columns B and C are shown in Figures 5.9 and 5.10, respectively. Although Columns A, B, and C exhibit similar reductions in total base capacities (Table 5.6), the breakthrough curves of Columns B and C show a significant drift between the and the 15^^ cycles, in comparison to those of Column A. This suggests that iron cyanide species are producing a reduction in the net operating capacity of ion exchange resin beds, although not affecting the total base capacity of the resin.

While copper breakthrough curves of Columns B and C appear to drift significantly between the and the 15^^ cycles, breakthrough curves of Column B appeared to be very similar to the corresponding curves of Column C. For instance, the copper breakthrough curve of Cycle 1 of Column B is similar to that of Cycle 1 of Column C, and the copper breakthrough curve of Cycle 15 of Column B is similar to the corresponding curve of Column C. This suggests that ferrocyanide and ferricyanide have similar effects on net operating capacities of the resin beds. ••—Cycle 1 -A—Cycle 5 -•—Cycle 10 -•—Cycle 15

~~50 100 150 200 250 300 Feed volume (mL)~~

~~Fig. 5.9 Copper breakthrough curves of Column B~~

~~••—Cycle 1 -A—Cycle 5 -•—Cycle 10 -•—Cycle 15 0) Sf (0 o .<2 •B c 3 o~~

~~50 100 150 200 250 300 Feed volume (mL)~~

~~Fig. 5.10 Copper breakthrough curves of Column C D) E o E> (0 JZ o "5 c o U-~~

~~50 100 150 200 250 300 Feed volume (mL)~~

~~Fig. 5.11 Iron breakthrough curves of Column B~~

~~£O ) o s> (0 o w ""5 c 0) U-~~

~~50 100 150 200 250 300 Feed volume (mL)~~

Fig. 5.12 Iron breakthrough curves of Column C Breakthrough curves of iron for Columns B and C are shown in Figures 5.11 and 5.12 respectively. Breakthrough curves of both elements in Columns B and C clearly show a non-linear drift over the 15 cycles; i.e. the disparity in copper and iron breakthrough curves of Cycles 1 and 5 is significantly greater than that of Cycles 10 and 15. The uneven distribution of the breakthrough curve indicates that the impact of iron cyanide is feh mostly within the first five cycles.

The total initial and final loading of copper and iron to the resin in Columns A, B, and C are given in Table 5.7. The total loading of copper and iron during the 15 cycles is plotted in Figure 5.13 against the number of loading/elution cycles. Detailed results and calculations are given in Appendix 7.

Figure 5.13 suggests that the net operating capacity of resin reduces significantly when ferrocyanide or ferricyanide species are introduced to the loading solution. The reduction of the net operating capacity is approximately 40% in Columns B and C. This is clearly more than the reduction of the strong base capacity of the columns, which is approximately 12-15% (Table 5.6). Further, the speciation of iron cyanide does not seem to have any effect on the extent of the reduction of the net operating capacity; columns loaded with ferrocyanide and ferricyanide appear to have suffered almost identical reductions in net operating capacities over 15 loading/elution cycles.

Table 5.7 The effect of iron cyanide on the loading capacity of resin bed Cycles on Total loading of elements to resin bed resin bed Column A Column B Column C (No Iron Cyanide) (50 mg/L Ferrocyanide) (50 mg/L Ferricyanide) Cu(mg) Cu(mg) Fe (mg) Cu(mg) Fe (mg) 1 259 243 8.1 243 8.3 15 246 139 1.6 138 1.6 ^ 0.5

O 0.4 i * « f . # • • f • i ^ . . E .E 0.3 (0 S> i * i i 0 0.2 I •> O) c • Column A: No Iron Cyanide 1 0.1 o • Column B: 50 mg/L Ferrocyanide 3 • Column C: 50 mg/L Ferricyanlde o 0.0 I I 6 7 8 9 10 11 12 13 14 15 Cycle Number

~~Fig. 5.13 The reduction of net operating capacity of Columns A, B, and C~~

The net operating capacity of a resin column is a function of the total base capacity, ion exchange kinetics, process conditions and the selectivity of the resin to the species of interest in solution. Modifications in the ion exchange substrate such as the extent of swelling or blockage of pores, which do not change the total base capacity, can alter the net operating capacity of an ion exchange resin bed significantly. The significant change in the net operating capacities of columns loaded with iron cyanide species suggest such a physical change has occurred.

As the loading/elution cycles progressed, severe discolouration of resin was noted in Columns B and C. This is displayed in Figures 5.14 and 5.15, which show the appearance of these columns over the 15 cycles. Visible particles of a colloidal precipitate, similar in colour to the discoloured resin, could be seen in both columns. It was also seen that the speciation of iron cyanide complex has no bearing on the colour of the resin after 15 cycles. Fresh Resin After 5 cycles After 10 cycles After 15 cycles

~~Fig. 5.14 Discolouration of resin in Column B~~

I It is well known that Cu ions react with ferricyanides and ferrocyanides to form copper hexacyanoferrates (Cola et al, 1977; Flynn and Haslem, 1995). As such, it is suggested that the change in the net operating capacity of Columns B and C was produced by changes in the ion exchange kinetics due to the precipitation of copper hexacyanoferrates in the resin pores. Some suggested reactions for this are given in Section 5.3.

These resuhs confirm that when oxidative acid elution is used to elute resins containing a mixture of CNWAD and non-WAD cyanide complexes, a significant reduction of net operating capacity could be expected, along with a small reduction of the total base capacity of resin. The reduction of the net operating capacity can be attributed to the effect of non-WAD cyanide species, while the reduction of the total base capacity can be attributed to the oxidation of resin in the presence of Cu ions. Fresh Resin After 5 cycles After 10 cycles After 15 cycles

~~Fig. 5.15 Discolouration of resin in Column C~~

~~5.2.3 The Effect of Iron Cyanide Concentration in Solution~~

To further explore the role of iron cyanide in reducing the net operating capacity of resins, the effect of varying iron cyanide concentration in the feed solution was investigated. Ferrocyanide was used as the non-WAD cyanide species of interest. The effect of low levels of ferricyanide was assumed to be similar to that of ferrocyanide (Section 5.2.2).

~~5.2.3.1 Experimental~~

To study the effect of ferrocyanide concentration, the changes in net operating capacities of three resin columns were compared. Since previous work (Section 5.2.2) had indicated that the presence of iron cyanide species do not give rise to a measurable change in the total base capacities of resin, no measurements of total base capacities of resin were made.

Loading solution ferrocyanide concentrations of 0, 25, and 50 mg/L were selected to study the effect on net operating capacities of resin beds. This allowed the use of resuhs of Columns A and B. Column A had no iron cyanide in its loading solution, while Column B had 50 mg/L of iron as ferrocyanide in the loading solution. To gather data for the mid point in ferrocyanide concentration, another ion exchange resin column (Column D), was subjected to 15 loading and oxidative acid elution cycles. In each of the 15 cycles. Column D was loaded with 300 mL of solution containing 25 mg/L iron as ferrocyanide, 950 mg/L copper(I) as copper cyanide in a

1250 mg/L CNTOT background. As described in Section 5.2.2.1, the loading solution was prepared using CuCN, NaCN, and K4Fe(CN)6. Elution and rinse conditions of Column D were identical to the test runs on Columns A, B, and C. Sampling and analytical techniques used in this study were similar to those described in Section 5.2.2.1. Appendix 9 gives the details of tests on Column D, together with breakthrough curve data and total loading capacities observed.

~~5.2.3.2 Results and Discussion~~

The effect of iron cyanide concentration on the net operating capacity of resin beds was determined by comparing the net operating capacities of Columns A, B, and D. Table 5.8 shows the initial and fmal loading of iron and copper to columns for ferrocyanide concentrations of 0, 25, and 50 mg/L. The total loading of copper to columns over the 15 cycles is shown in Figure 5.16.

Over 15 cycles, the resin bed lost approximately 20% of its net operating capacity when ferrocyanide was present at 25 mg/L. A decrease of approximately 40% in the net operating capacity was noted when ferrocyanide was present in loading solution at 50 mg/L. These results indicate that the reduction of the net operating capacity of the resin bed increases with the ferrocyanide concentration. Table 5.8 The effect of ferrocyanide concentration on the loading capacity of resin bed Cycles on Total loading of elements to resin bed resin bed Column A Column D Column B (No Iron Cyanide) (25 mg/L Ferrocyanide) (50 mg/L Ferrocyanide) Cu(mg) Cu(mg) Fe (mg) Cu(mg) Fe (mg) 1 259 238 3.6 243 8.1 15 246 182 1.1 139 1.6

~~As with Columns B and C, discolouration of the resin bed was noted in Column D. Despite having a low ferrocyanide loading, the discolouration of Column D was similar to that of Columns B and C.~~

~~0.5~~

~~c 0.4 i • f • • f • f "5 i •i ? * £ ^ * i * « f • • « § E • • - J • i t i . T3 I 0.2 (0 E 3 • Column A: No Iron Cyanide 0.1 o • Column D: 25 mg/L Ferrocyanide~~

~~• Column B: 50 mg/L Ferrocyanide 0.0 1 1 1 ^ 1 1 1 1 1 1 1 1 ^ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Cycle Number~~

~~Fig. 5.16 The reduction of net operating capacity of Columns A, B, and D 5.2.4 The Effect of Loading Solution pH~~

Ferrocyanide is reported to be unstable in solutions above pH 9 (Smith and Mudder, 1991; Kyle, 1997). On this basis, it can be suggested that the deleterious effects of ferrocyanide on resin would diminish at high pH conditions where ferrocyanide is unstable. To test this assumption, net operating capacities of columns loaded under different pH conditions were examined over 15 loading/elution cycles. Since the presence of iron cyanide species does not give rise to a measurable change in the total base capacities of resin (Section 5.2.2), no measurements of total base capacities were used.

~~5.2.4.1 Experimental~~

For the purpose of investigating the effect of loading solution pH, a new ion exchange resin column (Column E), containing 10 mL of Purolite A500 ion exchange resin was loaded with a solution containing ferrocyanide at pH 8.5. Other

~~parameters such as ferrocyanide, copper, and CNTQT concentrations were identical to those for Column D, which was loaded with a solution at pH 12.1.~~

~~In each of the 15 cycles, Column E was loaded with 300 mL of solution containing 25 mg/L iron as ferrocyanide, 950 mg/L copper(I) as copper cyanide in a 1250 mg/L~~

~~CNTOT matrix. The loading solution was prepared using CuCN, NaCN, and K4Fe(CN)6, as described in Section 5.2.1.1. The loading solution pH was adjusted to~~

8.5 by adding the required amount of H2SO4 (UNIVAR, Analytical Reagent) while monitoring the pH of the solution. To minimise the risk of exposure to HCN gas, the pH adjustment of loading solution was performed in a fume cupboard. Elution and rinse conditions of Column E were identical to those of other columns. Sampling and analytical techniques used were also similar to those described in Section 5.2.1.1. Appendix 10 gives the details of tests on Column E, together with breakthrough curve data and total loading capacities of the column, calculated using mass balance over each loading and elution stage. 5.2.4.2 Results and Discussion

Table 5.9 gives the initial and final loading of copper and iron to the columns observed at these two pH values. As a control test, the results of Column A, where no iron cyanide species were present in the loading solution, are also presented in Table 5.9. The net operating capacities of Columns D and E appear to be similar over the 15 cycles, although there is some difference between the columns in the first 5 cycles. The changes in the net operating capacities of Columns A, D, and E over the 15 loading/elution cycles are plotted in Figure 5.17.

If the loading of ferrocyanide to the resin bed depends on the pH of the solution, the loading capacity of Column E should be more affected than that of Column D. However, the results above do not show such a difference. Discolouration of resin noted in Column E was similar to that of Columns B, C, and D.

Although ferrocyanide is unstable above pH 9 in solution phase, it may be possible for the ferrocyanide complex to be stable in resin phase when solution pH is above 9, due to differences in hydration, pH and steric effects in the resin phase. Therefore, it can be concluded that when strong base ion exchange resins are used to recover cyanide complexes in the presence of excess free cyanide, Fe ions are loaded as ferrocyanide, regardless of the speciation of Fe^^ ions in the solution.

Table 5.9 The effect of loading solution pH on the loading capacity of resin bed Cycles on Total loading of elements to resin bed resin bed Column A Column E Column D No Ferrocyanide (Solution pH: 8.5) (Solution pH: 12.1) Cu (mg) Cu(mg) Fe(mg) Cu(mg) Fe (mg) 1 259 257 4.8 238 3.6 15 246 184 1.3 182 1.1 0.5

O gE i I I ^ • « • • « c 0.3 • • . • • i : i i (5 i ^ i • 2 c o 0.2 O) c • Column A: No Iron Cyanide •B(0 0.1 • Column D: Solution pH: 12.1 o 3 • Column E: Solution pH: 8.5 o 0.0 T 4 6 7 8 9 10 11 12 13 14 15 Cycle Number

~~Fig. 5.17 The reduction of net operating capacity of Columns A, D, and E~~

~~5.3 BEHAVIOUR OF NON-WAD CYANIDE SPECIES~~

When the oxidative acid eluent is brought into contact with strong base ion exchange resins containing mixed cyanide species, the base metal cyanide complexes on the resin decompose yielding HCN, some CNG", and the corresponding metal cations. Such metal cations are free to migrate reversibly from the resin interface to the solution phase, as shown in Equation 5.1:

~~2(-NR3^)2CU(CN)3'" 6H2SO4 + H2O2 4(-NR3')HS0; + 2H2O + 2Cu'" +2 so/' + 6 HCN (5.1)~~

Ferricyanide and ferrocyanide are non-WAD cyanides. If these species are present on the resin, they are not oxidised by the eluent to Fe^"^ cations. Ferrocyanide could be oxidized to ferricyanide, but that is the limit of oxidation. Consequently, when the oxidative acid eluent is brought into contact with resin loaded with iron cyanide species, the iron cyanide complexes remain attached to the resin maintaining its anionic form, as illustrated in Equation 5.2:

~~2(-NR3')4Fe(CNV- + 2U,S0, + HA 2(-NR3^)3Fe(CN)/" + 2(-NR3^)HSO; + 2H2O (5.2)~~

Therefore, on resin phase, ferrocyanide ions co-loaded on resin with copper cyanide species could possibly undergo one of two reactions under oxidative acidic conditions. They could react with the oxidant, forming ferricyanide as shown in Equation 5.2, or react with Cu cations to form a stable cyanide double salt as shown in Equation 5.3. The reaction of Cu^^ cations with ferricyanide and ferrocyanide is well known (Cola et al., 1977; Flynn and Haslem, 1995).

~~2(-NR3^)4Fe(CN)/' + 2Cu'^ > 8(-NR3^) + Cu2Fe(CN)6 (5.3)~~

Ferricyanide found on resin, be it from the oxidation of ferrocyanide, or adsorbed from loading solution, is likely to react with Cu^^ cations in a similar manner, forming the corresponding double sah. This is shown in Equation 5.4:

~~2(-NR3')3Fe(CN)/- + > 6(-NR3')+ Cu3[Fe(CN)j2 (5.4)~~

In either case, a highly stable and insoluble copper-iron double sah is formed. These double salts, commonly referred to as copper hexacyanoferrates, are electrochemically neutral and hence do not occupy ion exchange sites. Therefore, the formation of copper hexacyanoferrates does not affect the total base capacity of resin, as seen in Columns B and C (Section 5.2.2). However, the formation of these compounds on the resin surface and in its pores is likely to reduce the intra-particular mass transfer rate of counter-ions. As this directly affects the ion exchange kinetics, a reduction of the net operating capacity could be expected in such circumstances, as seen in Columns B and C.

~~Cyanide complexes such as dicyanoaurate(II), Au(CN)2" tetracynoaurate(III),~~

AU(CN)4', and hexacyanocobahate(III), Co(CN)6^', and, to a limited extent, hexacyanochromate(III), Cr(CN)6^", behave in many ways similar to ferrocyanide and ferricyanide species. They are highly stable under oxidative conditions (Flynn and Haslem, 1995). If these anions are loaded to the resin, it is highly likely that they would act in a similar manner to ferrocyanide and ferricyanide species under conditions created by the oxidative acid elution, producing stable double salts. The formation of stable double sahs such as copper tetracynoaurate(III), Cu[Au(CN)4]2, copper hexacyanocobaltate, Cu3[Co(CN)6]2, and copper hexacyanochromate, Cu3[Cr(CN)6]2, is well known when Cu^^ cations are brought into contact with corresponding anions (Huiatt et al., 1982; Smith and Mudder, 1991; Flynn and Haslem, 1995). These compounds would also give rise to a reduction of the net operating bed capacity as copper hexacyanoferrates.

~~5.4 CONCLUSION~~

The work reported in this chapter shows that anion exchange functionality of strong base anion exchange resins does not deteriorate when the resin is repeatedly cycled between loading and oxidative acid elution conditions over a moderate number of cycles. However, two modes of resin deterioration were identified:

~~1. reduction of strong base capacity when copper is repeatedly loaded and eluted~~

~~2. reduction of net operating capacity due to the formation of an insoluble precipitate on the resin.~~

The reduction of loading capacity when copper was introduced to the system is likely to be a result of Cu^^ catalysed oxidation of resin by hydrogen peroxide. It is suggested that the reduction of the net operating capacity seen when iron cyanide was introduced to the system is due to the formation of copper hexacyanoferrates on resin. This phenomenon is further investigated in Chapter 7.

If the oxidative acid elution coupled with strong base ion exchange is applied for the recovery of cyanide species from typical cyanidation tailings, none of these modes of resin deterioration is likely to give rise to a significant reduction of cyanide detoxification performance over a moderate number (e.g. 30-50) of loading/elution cycles. However, the gradual deterioration of the resin needs to be considered in such operations, by either developing suitable elution techniques to regenerate the resin or replenishing the resin inventory on a routine basis to account for the loss of loading capacity. Pilot Scale Testing of the Overall Cyanide Detoxification Process

Preceding work (Chapters 4 and 5) demonstrated that the oxidative acid elution is capable of selectively removing base metal cyanide complexes from strong base ion exchange resins. It was seen that non-WAD cyanide complexes such as those of gold and iron would accumulate on resin over repeated loading/oxidative acid elution cycles, requiring the occasional elution with a highly polarised anion such as Zn(CN)4 • to remove them. No damage to the resin was caused by the oxidative acid eluent, which contained 5 g/L of H2O2 and 50 g/L H2SO4 in the absence of metal cyanide complexes. Copper cyanide loaded on the resin produced a small reduction of the strong base capacity over a number of cycles. It was noted that non-WAD cyanide species give rise to a gradual deterioration of the net operating capacity of the resin bed. It was also seen that precious metals could be accumulated on the resin and recovered.

These findings confirmed the feasibility of integrating this oxidative acid elution technique with strong base ion exchange adsorption, AVR cyanide recovery, and alkaline oxidation of cyanide by hydrogen peroxide to form a novel cyanide detoxification process as described in the process overview (Section 4.2). It was assumed that such a process would be suitable for treating cyanide contaminated liquor with moderate levels of CNWAD, provided that the non-WAD cyanide concentration was relatively low. This chapter reports the pilot scale testing of the overall cyanide detoxification process, where it was employed in the treatment of over 14,000 m^ of cyanide contaminated liquor, in order to investigate its feasibility. 6.1 BACKGROUND

The pilot scale testing was conducted at May Day mines, located in central New South Wales, Australia. May Day mine and the corresponding ion exchange resin plant was first developed in the mid-1990s, as an R&D project, to investigate the viability of the Vitrokele Technology^M process. It was the first pilot scale ion exchange resin gold recovery plant commissioned in Australia. Following the completion of the Vitrokele Technology™ R&D project, the site was used to conduct some preliminary tests of the oxidative acid elution process, along with other pilot scale tests associated with an ion exchange resin based gold extraction process, under the umbrella of the patented Elutech process (Tran et al., 2000).

After completing these two pilot scale test programs, the site was due for decommissioning and rehabilitation. By this time, approximately 14,000 m of low- grade leach liquor was remaining in the leach liquor pond, left over from previous operations. The detoxification and disposal of this liquor was a key requirement for the rehabilitation of the mine site. The cyanide and base metal levels of this liquor were well over the specified contaminant limits for environmental release, and therefore could not be discharged to the environment. On the other hand, the low precious metal concentration in the liquor did not warrant the use of a conventional pregnant liquor processing technique to treat the liquor.

This presented a good opportunity to test the effectiveness of this novel cyanide detoxification process. The treatment and disposal of the contaminated liquor was also a critical rehabilitation requirement for the mine site. With these objectives in mind, the ion exchange resin pilot plant at May Day mine was re-commissioned in mid-1999. The campaign saw the treatment of all liquor left on site in 14 loading/oxidative acid elution cycles during the period from mid-1999 to mid-2000. 6.2 OVERVIEW OF OPERATIONS

The ion exchange resin bed of the pilot plant contained two cubic metres of resin. A standard, commercially available, strong base macroporous ion exchange resin (Purolite A500) was selected for this study as it was used in process development work. The recovery of cyanide from liquor was performed in batches of 1000 m^ After the loading cycle, the resin bed was regenerated by eluting base metal cyanide complexes from it. Loading, oxidative acid elution, and the rinsing of the resin constituted a treatment cycle, which was repeated until the accumulation of precious metals reduced the efficiency of loading of cyanide species on the resin. Key operating parameters of the plant are given in Table 6.1. Figure 6.1 gives a simplified flow diagram of the ion exchange resin plant.

Gold and silver loaded on the resin were not removed by the oxidative acid elution. As loading/elution cycles were repeated, the loading of these elements on the resin increased. After seven loading cycles, this accumulation of precious metals on the resin started affecting the recovery of copper from the feed liquor. Therefore, after the loading cycle, instead of the usual oxidative acid elution, the resin bed was eluted with a strong zinc tetra cyanide solution (Na2Zn(CN)4), to recover the precious metals. This was followed by a standard oxidative acid elution, to strip Zn(CN)4 " from the resin and to convert the resin to sulphate form.

~~Table 6.1 Key operating parameters of the pilot plant Description Feed Discharge Flow rate Duration location BV/hr (hrs)~~

~~Loading Low grade liquor Tailings dam 25 20 dam rinse Process water Neutralising tank 5 BV/hr !/2~~

~~Base metal Eluent mixing tank Neutralising tank 5 BV/hr - y/i elution rinse Process water Neutralising tank 5 BV/hr 1 - IYA I Feed liquor Air~~

~~NaOH (20%) Ion HCN HCN exchange stripping < recovery column CO umn column~~

~~Spent eluent neutralising tank~~

~~To the tailings dam~~

~~Treated liquor < < Air in < H202 (50%) Process water > < H2S04 (98%) Oxidative acid eluent mixing tank~~

Fig. 6.1 Simplified flowchart of the pilot plant After the first precious metal elution, seven more loading cycles on the resin bed saw the completion of treatment of all contaminated cyanide liquor. After the loading cycle, another precious metal elution was conducted to recover the precious metal loaded onto the resin before the pilot plant campaign was concluded. Appendix 11 gives the specifications of pilot plant operating conditions, results of the first seven cycles, and the results of the first precious metal elution. Loading/elution Cycles 8- 14, and the subsequent precious metal elution, were similar in performance to the former series. A summary of this data is given in Appendix 12.

~~6.3 LOADING OF CYANIDE SPECIES TO THE RESIN BED~~

~~6.3.1 Experimental Process Conditions~~

Loading was conducted by downward flow of liquor through the resin bed at 25 BV/hr (50 m^/hr) flow rate for 20 hours. Feed solution to the plant contained approximately 50 mg/L of copper, 10 mg/L of silver, 0.8 mg/L of gold, and a total cyanide concentration of 45-65 mg/L. The pH of the loading solution was in the range of 11-12. After adsorbing the feed liquor, the resin bed was washed with process water to remove any free feed liquor, in order to prepare it for the oxidative acid elution.

The total cyanide (CNTQT) and metal concentrations in the feed and discharge liquors were monitored continuously during loading. CNTQT concentration measurements were made according to ASTM 2036-97 (Method A) procedure, with potentiometric titration of cyanide with AgNOs to determine the cyanide concentration in the distillate. 6.3.2 Results and Discussion

As the solution was passed through the resin bed, the cyanide in the Hquor was recovered by the resin. At the initial stages of loading, the cyanide recovery efficiency was very high; the CNTQT concentration of treated liquor was below 0.1 mg/L. As expected, the cyanide recovery efficiency reduced gradually during the loading phase as the column approached saturation. Typical CNTQT concentrations at the end of loading steps, after passing 1000 m^ of solution through the ion exchange resin column, were approximately 2 to 5 mg/L. The CNTOT concentrations observed in feed and discharge liquors during Cycle 7 are shown in Figure. 6.2.

~~60 Feed liquor • • 50~~

~~J 40 O) E - 30 e o 20~~

~~10 Discharge liquor~~

~~200 400 600 800 1000 Volume of liquor treated (m )~~

~~Fig. 6.2 CNTQT breakthrough curve of Cycle 7~~

The average CNTQT concentration in feed and discharge liquors in the first seven adsorption cycles are shown in Table 6.2. As can be seen, well over 95% of the cyanide species in the feed were removed from the liquor as it was passed through the resin bed. While the CNTQT concentrations at the end of each loading step were in the range of 2-5 mg/L, the average CNTOT level in the discharge liquor over the entire loading step was well below 2.5 mg/L in all cycles.

~~Table 6.2 Average CNTOT IN liquor before and after treatment in the pilot~~

~~Cycle Feed liquor Discharge liquor~~

~~Average CNTOT (mg/L) Average CNTOT (mg/L) 1 48.0 1.0 2 45.9 1.8 3 44.8 1.5 4 63.3 1.5 5 50.7 1.9 6 58.0 1.2 7 51.0 2.2~~

Table 6.3 shows the average concentration of key elements in feed and discharge liquors for the 14 cycles. The total loading of metals to resin bed (calculated by mass balance) is given in Table 6.4. These resuhs confirm that all metal cyanide complexes were taken up by the resin bed without selectivity, as seen in Chapter 4. Copper concentration in discharge liquors were below 0.1 mg/L in most cycles.

It can be seen from Table 6.3 that the adsorption of gold and silver was not as efficient as that of copper in the latter cycles. This is thought to be due to the accumulation of gold and silver in the resin bed. Silver was always the first element to break through as the resin bed approached saturation. Gold then followed, breaking through the resin bed towards the end of the loading stage. Gold concentration in the discharge liquor for the first seven cycles is shown in Figure 6.3. Table 6.3 Average metal concentrations in liquor before and after treatment in the pilot plant Cycle Average feed liquor Average discharge liquor Au Ag Cu Fe Zn Au Ag Cu Fe Zn (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) 1 0.78 8.42 56.0 <0.01 0.14 <0.01 0.14 <0.01 <0.01 <0.01 2 0.85 9.41 55.7 <0.01 0.02 <0.01 1.09 <0.01 <0.01 <0.01 3 0.84 9.16 54.6 <0.01 0.01 <0.01 1.28 <0.01 <0.01 <0.01 4 0.85 8.27 50.7 <0.01 <0.01 0.09 2.91 <0.01 <0.01 <0.01 5 0.80 7.81 48.4 <0.01 <0.01 0.07 2.97 <0.01 <0.01 <0.01 6 0.81 7.94 53.4 <0.01 <0.01 0.14 4.60 <0.01 <0.01 <0.01 7 0.88 9.56 62.7 <0.01 <0.01 0.20 4.32 <0.01 <0.01 <0.01 8 0.82 8.95 68.0 <0.01 <0.01 0.04 1.85 <0.01 <0.01 <0.01 9 0.86 8.72 58.1 <0.01 <0.01 0.08 2.01 <0.01 <0.01 <0.01 10 0.81 9.31 66.3 <0.01 <0.01 0.09 3.54 <0.01 <0.01 <0.01 11 0.82 9.11 56.9 <0.01 <0.01 0.16 5.69 <0.01 <0.01 <0.01 12 0.79 8.37 63.4 <0.01 <0.01 0.21 5.84 <0.01 <0.01 <0.01 13 0.85 8.97 60.2 <0.01 <0.01 0.28 5.87 0.04 <0.01 <0.01 14 0.84 8.74 58.8 <0.01 <0.01 0.31 6.15 0.12 <0.01 <0.01 Table 6.4 Loading of metals to the resin bed in pilot scale tests Cycle Metal loading per cycle Au Ag Cu Fe Zn (g) (kg) (kg) (kg) (g) 1 780 8.3 56.0 0 140 2 850 8.3 55.7 0 20 3 840 7.9 54.6 0 10 4 760 5.4 50.7 0 0 5 730 4.8 48.4 0 0 6 670 3.3 53.4 0 0 7 680 5.2 62.7 0 0 8 780 7.1 68.0 0 0 9 780 6.7 58.1 0 0 10 720 5.8 66.3 0 0 11 660 3.4 56.9 0 0 12 580 2.5 63.4 0 0 13 570 3.1 60.2 0 0 14 530 2.6 58.7 0 0

~~0.6 o Cycle 1 -B—Cycle 2 E> 0.5 (0 -A-Cycle 3 o Cycle 4 ^ 0.4 .12 ¡J -©—Cycle 5 c O) -•—Cycle 6 c E 0.3 o -H-Cycle 7 s c o o c 0.1 o o <3 200 400 600 800 1000 Volume of liquor processed (m )~~

~~Fig. 6.3 Gold breakthrough curves of Cycles 1 to 7 6.4 OXIDATIVE ACID ELUTION~~

After each loading step in the first six cycles, the oxidative acid eluent was used to remove base metals from the resin bed and to regenerate the resin for the next th loading step. After the 7 loading on the resin bed, instead of the oxidative acid elution, the resin bed was subjected to a precious metal elution with a concentrated Na2Zn(CN)4 solution to remove all precious metals before an oxidative acid elution was conducted. Similarly, the resin bed was regenerated using the oxidative acid eluent in Cycles 8 to 13 between loading steps. After the loading step, the precious metals loaded on the resin were recovered with a precious metal elution.

~~6.4.1 Experimental Process Conditions~~

Oxidative acid elutions on the resin bed were 2VA to VA hours in duration. The duration of these elutions were set to allow 24 hour loading/elution cycles. An eluent containing nominally 2 g/L H2O2 and 20 g/L H2SO4 (commercial grade) was used for the elution. The eluent was passed through the resin bed at 5 BV/hr (10 m^/hr) flow rate.

Table 6.5 Oxidative acid elution conditions of the pilot plant Cycle Duration Eluent H2O2 H2SO4 Total H2O2 Total H2SO4 flow rate in feed in feed (hr) (m^/hr) (g/L) (g/L) (kg) (kg) 1 3:30 10 1.9 21.0 65 732 2 2:45 10 1.8 20.6 48 566 3 2:45 10 1.8 18.8 49 516 4 2:45 10 1.8 20.7 50 569 5 2:45 10 1.7 19.8 48 545 6 3:30 10 1.7 20.1 57 702 The end point of oxidative acid elutions was determined using the consumption of H2O2 and the concentration of copper in the spent eluent. The concentration of H2O2 was measured by colourimetric titration with KMn04, while the concentration of H2SO4 was measured by direct titration with NaOH solution using Phenolphthalein. Table 6.5 gives the key operating conditions of oxidative acid elutions of Cycles 1 to 6. Detailed specifications of these oxidative acid elutions are given in Appendix 11.

~~6.4.2 Results and Discussion~~

As expected, significant levels of copper (2-3 g/L) were observed in the spent eluent solutions soon after the oxidative acid eluent was introduced into the resin column. After a short period of time from its first appearance in the spent eluent, copper concentration peaked at 3-4 g/L, and then decreased gradually. This pattern was seen in all cycles. During the early part of the elution, no H2O2 was seen in the spent eluent, indicating that all H2O2 fed to the column was consumed by the reaction with copper cyanide. As copper was removed from the resin bed, the concentration of H2O2 in the spent eluent gradually increased. In most cycles, after eluting the resin bed for approximately 2 to IVi hours, the concentration of H2O2 in the discharge approached the feed concentration, indicating that copper(I) was no longer present in the resin. The concentration profile of copper in the spent eluent during a typical elution (including the first water wash, oxidative acid elution, and the second water wash) is shown in Figure 6.4. The concentration of H2O2 in feed and discharge streams are superimposed on copper elution profile to highlight the effect of H2O2 on copper elution.

Acid concentration in the fresh eluent was maintained far in excess of the stoichiometric requirements to maintain the pH of the eluent at below 1.0. Consequently, H2SO4 appeared in the spent eluent shortly after it was introduced to the ion exchange resin bed. A typical concentration profile of H2SO4 in feed and discharge is given in Figure 6.5. H202in Feed

~~H202 in discharge~~

~~-e—Cu in discharge c o~~

~~•2J c o o c oo~~

~~10 20 30 40 50 Eluent volume (m )~~

~~Fig. 6.4 Effect of H2O2 concentration on elution of copper from the resin bed~~

The oxidative acid elution and the two rinse steps produced approximately 50 m^ of oxidative acidic solution. This contained approximately 1 g/L of copper, although it could have been further increased to 1.5-2 g/L if the spent oxidative acid eluent was not diluted by the spent rinse solutions. Key elemental concentrations observed in the combined spent eluent stream are shown in Table 6.6.

Mass balances for copper for each loading/elution cycle are given in Table 6.7. Mass balances for other elements were not accurate as a result of the accumulation of elements on the resin (gold and silver), or the marginally detectable concentration in feed and discharge solutions (iron and zinc).

As can be seen in Table 6.6, insignificant amounts of precious metals were noticed in the combined spent eluent stream. In large scale operations, the spent eluent stream could be used as a source of copper and zinc sulphate, provided that these metals are found in appreciable concentrations in the feed liquor. These base metals could be recovered from the spent eluent by precipitation or with the use of a SX/EW circuit. •-H2S04in feed H2S04 in discharge -e—Cu in discharge

~~10 20 30 40 50 Eluent volume (m )~~

~~Fig. 6.5 H2SO4 concentration profile in feed and discharge eluent streams~~

~~The mass balance of copper over loading/elution cycles show agreement to ±10% accuracy, confirming that all the copper loaded to the resin was eluted by the oxidative acid base metal elution.~~

Table 6.6 Average metal concentrations in spent eluent of the pilot plant Cycle Au Ag Cu Fe Zn (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) 1 <0.1 4.7 1150 2.5 10.5 2 <0.1 4.5 1070 2.5 6.0 3 0.1 2.8 1190 0.7 0.9 4 0.3 9.7 1080 2.5 2.9 5 0.2 22.4 1060 3.9 1.2 6 0.2 12.5 890 3.4 1.6 Table 6.7 Mass balance for copper for the first 6 loading/elution cycles of

~~Cycle Cu loaded to resin Cu eluted from resin (kg) (kg) 1 56.0 57.5 2 55.7 53.4 3 54.6 59.7 4 50.7 53.9 5 48.4 52.9 6 53.4 48.8~~

~~As discussed in Chapter 4, the reaction of H2O2 with copper cyanide loaded on the resin (where X could be 2, 3 or 4, depending on the copper cyanide complex) can be represented as follows:~~

~~+2XH2SO4 + HA > 2(X-1)(-NR3^)HS0; +2H2O + 2CUSO4 + 2XHCN (6.1)~~

As seen in Equation 6.1, regardless of the copper cyanide species on the resin, the stoichiometric ratio for H2O2 to copper in this reaction is 1:2; i.e. the consumption of H2O2 (on a molar basis) should be half of the copper recovered. Table 6.8 gives the consumption of H2O2 in these cycles, (calculations given in Appendix 11) It can be seen that the observed H2O2 consumption is significantly higher than stoichiometric requirements.

The H2O2 efficiency for elution was derived as the stoichiometric H2O2 requirement (based on the amount of copper recovered) over the total consumption observed (from mass balance over the elution). This efficiency ranges from 40% to 60% for the 6 cycles reported above, and is shown in the right most column of Table 6.8. Table 6.8 Reagent consumption and copper recovery results of the pilot

Cycle H2O2 Cu recovered H2O2 stoichiometric H2O2 efficiency in consumption from resin requirement reacting with Cu kg kmol kg kmol kmol % 1 39.3 1.15 57.5 0.90 0.45 39% 2 30.4 0.89 53.4 0.84 0.42 47% 3 32.7 0.96 59.7 0.94 0.47 49% 4 24.5 0.72 53.9 0.85 0.43 59% 5 28.5 0.84 52.9 0.83 0.42 49% 6 24.7 0.73 48.8 0.77 0.39 53%

Factors contributing to this high H2O2 consumption are thought to be the oxidation of cyanide by hydrogen peroxide and the decomposition of hydrogen peroxide, both processes catalysed by Cu cations. Additionally, as seen in Chapter 5, the oxidation of resin could also contribute to the H2O2 consumption. The oxidation of cyanide in the ion exchange bed by the oxidant is the first of the two stage cyanide destruction mechanisms employed in the overall cyanide detoxification process.

The H2SO4 consumption figures were not useful for any attempts to quantify the effect of acid concentration on the elution. This is because the concentrations of H2SO4 in the feed and the discharge streams were largely similar during most of the elution, as the H2SO4 concentration in the feed eluent was maintained far in excess of stoichiometric requirements. This produced a large relative error in the H2SO4 consumption figures calculated by numerical integration of the differences between H2SO4 concentrations in feed and discharge streams. Therefore, the effect of acid concentration was not studied. 6.5 CYANIDE DETOXIFICATION

Cyanide detoxification was performed in two stages. As CNwad species decomposed in the presence of the oxidative acid eluent, most of the cyanide was released to the eluent as HCN gas (Chapter 4). However, an appreciable amount of cyanide was oxidised to CNG", as suggested by the higher than the stoichiometric oxidant consumption seen. This was the first of the two cyanide oxidation mechanisms.

The second and the final stage of cyanide oxidation involved the oxidation of HCN gas released to the eluent. An AVR circuit was used for this purpose. Firstly, the spent eluent was fed to a packed column where the HCN was stripped from the eluent using a counter current air stream. The eluent stripped of HCN, still containing un-reacted H2O2 and H2SO4, was discharged into the spent eluent neutralising tank (Figure 6.1).

The HCN/air mixture emerging from the stripping column was scrubbed with a caustic (20% NaOH, commercial grade) solution in a packed column to produce an alkaline NaCN solution. Each oxidative acid elution produced approximately 1.5 m^ of alkaline NaCN solution. The cyanide concentration of the scrubber solution was variable. This scrubber solution could have been used as a source of free cyanide, if partial cyanide recovery was required. Since no cyanide recovery was desired in this operation, the alkaline cyanide solution was mixed with the spent oxidative acid eluent in the neutralising tank, to oxidise the cyanide in it using the remaining hydrogen peroxide in the spent eluent. This was the second and the final stage of cyanide oxidation. The final product of this process was a mildly acidic solution containing 1-1.5 g/L CUSO4, with some CNO" resulting from the oxidation of cyanide and a small amount of H2O2. The CNO" and H2O2 in this solution were unstable and decomposed over a period of few days, uhimately producing a mildly acidic CUSO4 solution. 6.6 RESIN DETERIORATION AND PRECIOUS METAL ELUTION

After seven loading/oxidative acid elution cycles, a significant reduction in the loading of gold and silver was noted (Table 6.3). Although the adsorption of copper was still within acceptable levels, gold recovery efficiency dropped below 75%. It was believed that a reduction of net operating capacity for gold was due to the accumulation of cyanide complexes of gold and sliver on the resin. Therefore, after seven cycles, the resin bed was subjected to a precious metal elution to restore the net operating capacity of the resin bed by removing the gold and silver.

This was conducted using a 0.15 M sodium zinc tetra-cyanide (Na2Zn(CN)4) solution at 60 °C. An electro-winning cell was employed to recover the precious metals from the Na2Zn(CN)4 eluent. The precious metal recovery circuit consisted of an eluent supply tank, the resin column, and the electro-winning cell, arranged in a closed circuit. After 90 hours of circulating the eluent through the resin bed, gold and silver concentrations of the column outlet and inlet reached equilibrium at about 10 mg/L (Figure 6.6). This indicated that no further gold and silver cyanide complexes were being removed from the resin bed. After the precious metal elution, an oxidative acid elution was applied. The oxidative acid elution decomposed Zn(CN)4^' anions loaded on the resin and converted the resin into sulphate form, regenerating the resin bed. Following this, the loading/oxidative acid elution cycles were recommenced.

Similarly, after another seven loading/elution cycles, a second precious metal elution was conducted to recover the gold and silver collected on the resin bed. The elution of non-WAD cyanide species using a concentrated zinc tetracyanide Zn(CN)4^" was of some scientific interest. However, as it falls outside the scope of this thesis, the chemistry and process dynamics of the precious metal elution will not be given ftirther consideration herein.

As expected, the net operating capacity increased markedly after the precious metal elution conducted after Cycle 7 (Table 6.3). However, the resuhs of Cycles 8 to 14 show that the performance of the regenerated resin was not as good as that of fresh resin. Unlike in the cycles on fresh resin, gold was seen in the discharge liquor of all cycles after the first precious metal elution. In Cycles 13 and 14, some copper was also found in the discharge liquor. This indicated that the loading capacity of the resin bed had not been ftilly restored by the precious metal elution.

~~70 IX column outlet (EW cell inlet) 60 -it— EW Cell outlet (mixing tank inlet) G—Mixing tank outlet (IXcolumn inlet) c 50 o 2CO _ 40 c d O G) 30 ë E o o 20 <3 10~~

~~15 30 45 60 75 90 Time (hrs)~~

~~Fig. 6.6 Gold concentration in the precious metal elution circuit of the pilot plant~~

Strong discolouration of resin became evident over a number of successive cycles. This fiirther alluded to the loading of a species not amenable to any of the elutions employed, such as a strongly polarised anion, or the precipitation of an inert species such as a metal hexacyanoferrate. However, the absence of iron in detectable levels in the feed solution raised doubts about the latter scenario. Further discussion of this phenomenon is given in Chapter 7. 6.7 CONCLUSION

This pilot scale test confirmed that strong base ion exchange resins could be used effectively to remove free and complexed cyanide species from solutions of gold cyanidation tailings. This pilot scale test also proved that the oxidative acid elution is suitable for eluting mixed cyanide complexes from strong base resins. No net accumulation of copper or any other base metals was noticed. The H2O2 efficiency for oxidation of Cu^ to Cu^^ varied between 40% and 60%. The oxidation of cyanide by hydrogen peroxide in the presence of Cu^^ cations and the decomposition of hydrogen peroxide are thought to be the primary reasons for this low H2O2 efficiency for oxidation of copper.

The oxidative acid elution and the discharge solution from the two rinse steps produced a mildly acidic solution containing approximately 1 g/L of copper. This stream was deemed suitable as a feed for a base metal recovery circuit. The precious metals in the cyanide contaminated liquor were recovered by electro-winning as metallic gold and silver. Cyanide recovered from the contaminated liquor was detoxified in two stages. A fraction of the cyanide loaded on the resin was oxidised by H2O2 in the resin. The remainder of the cyanide was subsequently converted to NaCN and oxidised by the unused H2O2 in the spent eluent.

Strong discolouration, and a reduction of net operating capacity of the resin bed, suggested possible deterioration of resin. While the deterioration of the resin bed was not a major impediment in this operation, ongoing operation of this process would require regular replenishment of the resin bed. In conclusion, this pilot scale test confirmed that strong base ion exchange adsorption, when coupled with oxidative acid elution, is highly effective for the detoxification of cyanide contaminated liquors arising from gold cyanidation operations. The economic and environmental aspects of this novel cyanide detoxification process are discussed in Chapter 8. Evaluation of Resin Degradation During Oxidative Acid Elution

This chapter investigates the deterioration of resin, seen when oxidative acid elution is used to elute strong base resin loaded with mixed cyanide complexes. To gain further insight into the behaviour of metal cyanide complexes in the resin phase under oxidative acid elution conditions, deteriorated resin samples are examined using several characterisation techniques. Resin samples taken from the experimental work discussed in the preceding chapters are used in these studies. Characteristics of deteriorated resin are used to identify key factors contributing to the deterioration of ion exchange resin. This chapter concludes with a review of mechanisms which could lead to resin deterioration.

~~7.1 EVIDENCE OF RESIN DEGRADATION~~

The work reported in Chapter 5 indicated that the oxidative acid environment alone did not bring about a chemical or physical deterioration of strong base ion exchange resins. However, when metal cyanide species were repeatedly loaded and eluted, deterioration of loading capacity was detected along with discolouration of resin. The gradual reduction of strong base capacity caused by copper cyanide was attributed to either an accumulation of copper on resin, or a copper catalysed H2O2 oxidation of resin. When iron cyanide species were loaded and eluted from resin, a reduction of the net operating capacity was detected. This was attributed to the precipitation of copper hexacyanoferrates on the resin. A gradual deterioration of the net operating capacity of the ion exchange resin bed was also noted in the pilot scale testing (Chapter 6). As the concentration of non- WAD cyanide complexes in the loading solution were mostly below detection limits, the loss of net operating capacity could not be attributed to the formation of metal cyanide double sahs on the resin. The reduction of strong base capacity due to the oxidation of resin by hydrogen peroxide in the presence of copper was seen as one of the factors contributing to the deterioration, but other factors could not be ruled out.

~~7.2 CHARACTERISATION OF RESIN~~

Deteriorated Purolite A500 resin samples from the study on resin durability (Chapter 5) and pilot scale tests (Chapter 6) were selected for this study. A sample of fresh Purolite A500 resin was included in the study to benchmark the attributes of resin prior to deterioration. The total base capacities of resin samples were measured to see if a decrease in the total base capacity is responsible for the reduction of the net operating capacity in these resin samples. Following this, the rate of ion exchange in deteriorated resins were compared with that of fresh resin to determine if the reduction of the net operating capacity is caused by a reduction of mass transfer rate, instigated by physical changes in the resin structure. X-Ray Fluorescence Spectroscopy (XRFS), powder X-Ray Diffraction (XRD) and Diffuse Reflectance Spectroscopy techniques were used to identify any inorganic chemical species present in deteriorated resin. Finally, the microstructure of deteriorated resin samples were compared with that of fresh resin using Scanning Electron Microscopy (SEM) to investigate if any significant structural changes had occurred.

~~7.2.1 Sample Preparation~~

In addition to deteriorated resin selected for characterisation, samples of fresh resin and specimens of copper ferrocyanide and copper ferricyanide were used in this study. The specimens of copper ferricyanide and copper ferrocyanide were used to compare their reflectance spectra and X-Ray diffraction patterns with those of deteriorated resins. The pre-treatment and preparation of samples was performed as described below.

~~7.2.1.1 Fresh Resin~~

50 mL of Purolite A500 ion exchange resin was converted to sulphate form by contacting with three aliquots of 1000 mL of 50 g/L H2SO4 in an orbital shaker for 24 hours. The resin produced was rinsed twice with deionised water and stored in deionised water for characterisation tests.

~~7.2.1.2 Resin Samples from Studies on Resin Durability~~

Four resin samples from studies on resin durability (Chapter 5) were selected for characterisation. Each sample was subjected to 15 loading and oxidative acid elution cycles. All samples were loaded with a solution containing 1250 mg/L CNTOT matrix, at a pH of 12.1 to 12.2. The first of these samples did not have copper or iron in the loading solution. The loading solution used on the second sample had 950 mg/L copper. The third was loaded with a solution containing 25 mg/L iron as ferrocyanide and 950 mg/L copper. The last sample was loaded with a solution containing 50 mg/L of iron as ferrocyanide and 950 mg/L copper.

After each loading, these resin samples were subjected to identical oxidative acid elutions, using 200 mL of eluent containing 5 g/L H2O2 and 50 g/L H2SO4. Further details of the loading and elution conditions are given in Sections 5.1 and 5.2. After the last oxidative acid elution, these resin samples were rinsed and stored in deionised water for characterisation tests. 7.2.1.3 Resin Samples from Pilot Scale Tests In total, 14 loading and oxidative acid elution cycles were performed on the ion exchange resin bed during the pilot scale testing (Chapter 6). The resin samples for characterisation were taken after loading Cycles 4, 7, and 14. These samples were regenerated in the laboratory by eluting all base metals and precious metals using 0.125 M zinc tetracyanide, Na2Zn(CN)4 solution followed by the conversion to sulphate form with 50 g/L H2SO4 solution. The resin samples were then rinsed and stored in deionised water for characterisation tests.

7.2.1.4 Copper Ferrocyanide and Copper Ferricyanide Specimens Specimens of Cu2Fe(CN)6 and Cu3[Fe(CN)6]2 were synthesised by using a procedure described by Cola and colleagues (1977). To synthesise Cu2Fe(CN)6,100 mL of 89.5 mM solution of K4Fe(CN)6 (Chem Supply, Analytical Reagent) was added under gentle stirring to a 100 mL aliquot of 201 mM CUSO4 (UNILAB, Laboratory Reagent) solution. All reagents were prepared in deionised water. After mixing gently for 1 hour, the suspension was filtered using Whatman GF/C glass microfibre filter paper and the precipitate was dried at 60 ^C until constant weight. The clear filtrate was diluted to 500 mL and assayed for Iron and copper using a Varian VISTA AX CCD Simuhaneous Inductively Coupled Plasma Atomic Emission Spectroscope (ICP AES) unit. Cu3[Fe(CN)6]2 was synthesised by reacting 100 mL of 89.5 mM solution of K3Fe(CN)6 (UNIVAR, Analytical Reagent) with a 75 mL aliquot of 201 mM solution of CUSO4 (UNILAB, Laboratory Reagent). Mixing, filtering, drying, and analytical procedures were similar to those described above.

ICP AES analysis resuhs of the clear filtrate were used to calculate the elemental composition of copper and iron in the corresponding copper hexacyanoferrate compounds. This indicated that the copper ferrocyanide (Cu2Fe(CN)6) product had a Cu/Fe molar ratio of 1.93. The copper ferricyanide (Cu3[Fe(CN)6]2) product had a Cu/Fe molar ratio of 1.50. It is also likely that a small amount of K^ ions may have been included in the precipitate, but slight contamination of these specimens by K^ bearing hexacyanoferrates was deemed inconsequential for comparison of X-Ray Diffraction and UV-Visible absorption patterns of these compounds with those produced by resin samples. Appendix 13 gives the analytical resuhs and calculations associated with the synthesis of these compounds. Recoveries of dried compounds were somewhat less than the theoretical value due to the incomplete recovery from filtration of the precipitate. The precipitate recovered was stored in a desiccator for analysis.

~~7.2.1.5 Resin Samples from Pilot Scale Tests~~

In total, eight samples of resin and two copper hexacyanoferrate specimens were used in this study. In the ensuing discussion of experimental methods and procedures, resin samples are referred to by their abbreviated names. Table 7.1 gives the sample descriptions and abbreviated names of these resin samples.

Table 7.1 Resin Sample Specifications Resin Sample Description Abbreviated Sample Name Fresh resin R-Fresh Resin from studies on resin durability (Chapter 5) Resin samples loaded with 1250 mg/L CN solution R-OCu/OFe Resin after 15 loading elution cycles with 950 R-950Cu/0Fe mg/L copper and no iron Resin after 15 loading elution cycles with 950 R-950Cu/25Fe mg/L copper and 25 mg/L iron (Ferrocyanide) Resin after 15 loading elution cycles with 950 R-950Cu/50Fe mg/L copper and 50 mg/L iron (Ferrocyanide) Resin from pilot scale tests (Chapter 6) Resin after 4 adsorption cycles in the pilot plant R-PP04 Resin after 7 adsorption cycles in the pilot plant R-PP07 Resin after 14 adsorption cycles in the pilot plant R-PP14 7.2.2 Total Base Capacity Tests

The reduction of total base capacity of ion exchange columns when copper and iron cyanide complexes were introduced to the system was discussed in Chapter 5. The total base capacity of used resins was not measured during pilot scale tests (Chapter 6). The total base capacity is the key performance indicator of strong base ion exchange resins. A reduction in the total base capacity of a strong base macroporous resin indicates a loss of the quaternary ammonium functional groups available for ion exchange, or a restriction of access to functional groups due to restriction of resin pores. To document the change of total base capacities of resin, all deteriorated resin samples were re-analysed using a standard technique in this section.

~~7.2.2.1 Experimental~~

The total base capacity was measured using a technique prescribed by Harland (1994). Approximately 5 mL samples of resin were placed in a column with 10 mm inner diameter and regenerated by passing 100 mL of 1 M HCl (UNIVAR, Analytical Reagent) through the resin bed at 60 BV/hr (5 mL/min) flow rate. This ensured full conversion of the resin to CI" form. The resin was then rinsed with deionised water to remove any excess chloride from the resin. The rinsing continued until an aliquot of wash solution registered less than 0.2 mM CI" concentration, determined by titration with 10 mM AgNOs (UNIVAR, Analytical Reagent), using K2Cr04 (UNIVAR, Analytical Reagent) as the indicator. The resin samples were then transferred to a measuring cylinder and the volume in CI" form was measured and recorded.

After volume measurements were taken, the resin samples were placed back in the column and eluted with 200 mL of 0.5 M NaNOs solution (UNIVAR, Analytical Reagent) at 60 BV/hr (5 mL/min) flow rate to remove all adsorbed chloride ions from the resin. The resin was then rinsed with 200 mL of deionised water. The spent NaNOs solution and rinse solution was collected and diluted to 500 mL. An aliquot from this solution was titrated with 10 mM AgNOa using K2Cr04 as the indicator. The Cr concentration in solution as determined by titration was used to estimate the amount of CI" released from the ion exchange resin, which was taken as the total base capacity of resin.

~~7.2.2.2 Results and Discussion~~

Table 7.2 shows the total base capacity of resin samples on a wet settled volume basis. Further details and calculations pertaining to loading capacity tests are given in Appendix 14. It can be seen from Table 7.2 that the loading capacity of fresh resin agrees well with the manufacturer's specification of 1.15 mEq/mL. The loading capacity of resin, loaded with copper and eluted with the oxidative acid elution, has decreased by approximately 12%. This result is consistent with previous observations in Section 5.2. The loading capacity of resin samples loaded with mixed copper and iron cyanide species also show a similar decrease in total base capacity. The resin samples from the pilot scale tests (Chapter 6) show a significant reduction of the total base capacity. As can be seen in Table 7.1, resin subjected to seven loading/elution cycles lost approximately 23% of the total base capacity. After 14 cycles, the reduction is 40%.

~~Table 7.2 Total base capacity of resin samples Resin sample Loading capacity Relative (mEq/mL) deterioration~~

~~Fresh resin 1.12 ±0.02 - R-OCu/OFe 0.99 ± 0.02 12% R-950Cu/0Fe 0.97 ±0.01 13% R-950Cu/50Fe 0.98 ± 0.02 13% R-PP07 0.86 ±0.01 23% R-PP14 0.67 ± 0.02 40% 7.2.3 Ion Exchange Kinetics~~

As discussed in Section 3.2.3.4, kinetics of ion exchange is a combination of film diffusion, an intra-particulate diffusion, and a chemical reaction. In dilute solutions film diffusion is the rate controlling step while in concentrated solutions the intra- particulate diffusion controls the rate of ion exchange. In well agitated conditions, with relatively high concentration of counter-ions, the rate of ion exchange is predominately governed by the intra-particulate diffusion rate of ions. Properties of the resin such as the surface characteristics, the size of pores, and their interconnectivity, influence the intra-particulate diffusion rate of ions in macroporous resins. Therefore, a comparative assessment of physical properties of resin governing the intra-particulate ion diffusion rate could be made by observing the net ion exchange rates under well agitated conditions in relatively concentrated solutions.

~~7.2.3.1 Experimental~~

Approximately 5 mL samples of resin were converted to CI" form, as described in Section 7.2.2.1. After measuring the volume and draining all free water, the samples were carefully placed in a 500 mL flask containing 250 mL of 0.5 M KNO3 solution and agitated gently.

The Cr concentration in the solution was monitored constantly using a Radiometer PHM 250 Ion Analyser coupled to a Radiometer ISE25C1 chloride sensitive electrode and a Radiometer double junction REF 251 reference electrode. The temperature of the solution was monitored using a temperature probe. The temperature reading was used to automatically correct the CI" concentration reading of the PHM 250 Ion Analyser. The CI' readings were recorded at 5 second intervals using a desktop computer coupled to the ion analyser. Chloride concentration readings of the eluent were taken from the point of introducing the resin to the eluent, until a plateau of chloride concentration was detected. After a plateau was noted, a sample of the solution was analysed by titration with 10 mM AgNOs using K2Cr04 as the indicator. The result of titration was used to correct the CI" concentration readings of the ion selective electrode, eliminating errors introduced into the resuhs by any potential drifts in electrode response.

~~7.2.3.2 Results and Discussion~~

Figure 7.1 shows the CI" elution profiles of fresh resin and resin from studies on resin durability (Chapter 5). The CI" elution profiles of used resin from pilot scale tests are shown in Figure 7.2. It can be seen from Figure 7.1 that chloride ions in all resin samples are completely eluted within 10 minutes when brought into contact with the 500 mM NO3" eluent. The amount of CI" released from fresh resin, 1.11 mEq/mL, agrees well with the total base capacity resuhs seen previously (Table 7.2).

Regardless of the presence of iron in the loading solution, a reduction of the total base capacity is seen in resin samples from resin durability studies (Figure 7.1). These resuhs indicate a total base capacity of approximately 1.00 mEq/mL of resin, consistent with the resuhs in Table 7.2. In addition to the reduction of the total base capacity, these resin samples also show a small deviation in the CI" elution rates. The CI" release rate of resin sample R-950Cu/50Fe, which contains the highest copper and iron loading, appears to be lower than that of R-950Cuy0Fe. While this deviation is small, and may have resuhed from slight changes in experimental conditions, it could also indicate a small increase in the resistance to intra-particulate difftision rate of anions. If so, the restriction of pores in the resin caused by the precipitation of copper-iron cyanide species could explain this phenomenon. This is further explored using elemental analysis and X-Ray Diffraction, in Sections 7.2.4 and 7.2.5.

The resin samples from the pilot scale tests show a clear reduction of the loading capacity (Figure 7.2), which is consistent with the results in Table 7.2. An accurate comparison of ion exchange rates in these samples is not possible, due to the significant difference in total CI" loading capacities. However, no significant differences can be seen between the CI" elution rates of these samples; all samples reach equilibrium within 5-6 minutes of coming into contact with the KNO3 solution.

~~1.2~~

~~1.0 (0 £ E E 0.8 Q (A o •O o 0.6 0) v> E n = 0.4 £ S • R-Fresh o R-950Cu/0Fe 0.2 O + R-950Cu/25Fe - R-950Cu/50Fe 0.0 4 6 8 10 Time (min)~~

~~Fig. 7.1 Cr elution profiles of degraded resin after 15 loading/elution cycles~~

~~c '3 2 E 2 o (0 (0 c>~~

~~£ • R-Fresh O A R-PP07 X R-PP14~~

~~4 6 8 10 Time (min)~~

~~Fig. 7.2 cr elution profile of resin samples from the pilot scale tests 7.2.4 Elemental Loading on Resin~~

Elemental analysis of resin was performed to quantify the amount of metal loading on resin samples selected. The loading of a broad rage of elements in samples was analysed using X-Ray Fluorescence Spectroscopy.

~~7.2.4.1 Experimental~~

Accurately measured 5 mL samples of resin (wet settled volume, sulphate form) were dried at 60 ^C until constant weight. The wet settled volume before drying and the weight of dried resin was recorded. Then, dried resin samples were pulverised using a Rocklabs Vibratory Ringmill, in a chrome steel grinding ring. A sample (500 to 750 mg) of this crushed powder was then pressed into 38 mm discs using a 10 tonne press, over an inert H3BO3 (UNIVAR, Analytical Reagent) base. These pressed powder samples were analysed for a range of elements using a Philips PW 2404 XRF Spectrometer.

~~7.2.4.2 Results and Discussion~~

Generally, when dried at 60 ^C, each 5 mL sample of resin gave 1.50-1.65 g of dried resin. The elemental loading of resin (dry weight basis) is reported in Table 7.3. Of all the elements analysed, silver, gold, cobah, chromium, copper, and iron were seen in resin samples in varying quantities. Low levels of chromium were noted in all samples, including fresh resin. This is attributed to sample contamination, resulting from the attrition of the ring mill. Similarly, 0.2 mg/g of iron noted in the fresh resin is also ascribed to the attrition of the ring mill during the grinding of resin. As all samples were prepared using the same grinding procedure, it can be assumed that similar levels of chromium and iron have been introduced to all other samples. Table 7.3 Non-removable elemental loading in resin Sample Elemental loading on resin sample (mg/g) Ag Au Cd Co Cr Cu Fe Hg Mn Ni Pb V Zn R-Fresh <0.1 <0.1 <0.1 <0.1 0.04 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

~~R-OCu/OFe <0.1 <0.1 <0.1 <0.1 0.06 <0.1 0.3 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1~~

~~R-950Cu/0Fe (average of 3 repeats) <0.1 <0.1 <0.1 <0.1 0.09 <0.1 0.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1~~

~~R-950Cu/25Fe <0.1 <0.1 <0.1 <0.1 0.03 122 46.0 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1~~

~~R-950Cu/50Fe <0.1 <0.1 <0.1 <0.1 0.05 144 53.8 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1~~

~~R-PP07 <0.1 6.2 <0.1 0.96 0.16 <0.1 1.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1~~

R-PP14 0.12 19.7 <0.1 1.2 0.11 <0.1 0.8 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 As expected, both fresh resin and the resin sample loaded with a free cyanide solution had negligible levels of transition metals. The absence of copper contammation in the resin sample loaded with a copper cyanide loading solution is of interest, as this resin sample showed a 12% reduction of total base capacity (Table 7.1). Due to the peculiarity of this resuh, the initial analysis was repeated three times. All resuhs confirmed the absence of copper on resin, while the iron and chromium contamination changed slightly due to subtle changes in sample preparation. The resuh reported in Table 7.1 is the average resuh. The absence of appreciable levels of copper (or any other metal contamination) in this resin suggests that the reduction of total base capacity in resin is not a result of the loading of an anionic species or blockage of resin pores by copper cyanide.

The two resin samples loaded with mixed copper/iron cyanide solution showed significant levels of copper and iron loading. It can be seen that the copper/iron molar ratio in resin loaded with mixed copper and iron cyanide loading solution is approximately 2.3. This gives further evidence that the copper and iron in the resin is present as a copper hexacyanoferrate species, although the molar ratio of 2.3 does not directly correspond to the stoichiometry of any of the well known copper hexacyanoferrate compounds. However, it can be seen that the molar ratio of copper and iron on resin is closer to that of copper ferrocyanide than that of copper ferricyanide. The speciation of copper and iron on resin is further explored in Section 7.2.5 using Powder X-Ray Diffraction.

The resin samples from pilot scale tests had no detectable copper loading, while the iron loading was insignificant. However, these samples had significant gold loadings, as high as 2% w/w gold in the sample taken after Cycle 14. The extent of gold loading on resin, well above an order of magnitude more than the combined loading of other elements, implies that the gold loading on resin is not due to co-precipitation of gold with other metals. The nature of gold loading is further discussed in the ensuing sections of this chapter. 7.2.5 XRD and Diffuse Reflectance Spectroscopy

The elemental analysis of resin revealed that some deteriorated resin samples contained gold, while others contained copper and iron. Powder X-Ray Diffraction and Diffuse Reflectance Spectroscopy studies were carried out to gain an insight into the chemical speciation of these elements on deteriorated resin.

~~7.2.5.1 Experimental~~

As for X-Ray Fluorescence Spectroscopy (Section 7.2.4), selected resin samples were dried and pulverised before analysis. Powder X-Ray diffraction was performed with a Siemens D500 Diffractometer and CoKa radiation. Data were collected over the angular range 20 <85® with a step size of 0.05 degrees and an acquisition time of 10 seconds. Collected data were analysed using the diffraction pattern libraries of X'pert High Score software. Reflectance spectra in ultra-violet and visible range were collected on powder samples (5% in MgO) at ambient temperature using a Gary 500 Spectrophotometer equipped with a Labsphere Biconical accessory. Spectra collected were referenced to that of a Labsphere certified standard (Spectralon), and converted into Kubelka-Munk units, F(R) = (1-R)^/ 2 R (Wendlandt et al., 1966).

~~7.2.5.2 Results and Discussion~~

Figure 7.3 shows the X-Ray diffraction patterns of blank resin. As expected, there are no clear diffraction peaks. The X-Ray diffraction patterns seen in the resin samples from the pilot scale tests are shown in Figures 7.4 and 7.5. Although these samples contain a moderate gold loading, there are no clearly detectable peaks in the spectra. The lack of detectable diffraction peaks suggests that the gold in these samples is not likely to be present in a crystalline form, as most crystalline compounds produce clearly detectable X-Ray diffraction peaks at 2% concentration in an organic matrix. Counts

~~600-~~

~~400-~~

~~200-~~

~~0-1 I I I I I I I~~

~~Position niheta]~~

~~Fig. 7.3 Powder X-Ray diffraction patterns of fresh resin~~

~~Counts 800-~~

~~600-~~

~~400-~~

~~200-~~

~~30 40 50~~

~~Position [°2Theta]~~

~~Fig. 7.4 Powder X-Ray diffraction patterns of resin sample R-PP07 (Elemental loading on resin - Au: 6.2 mg/g) Counts~~

~~400-~~

~~200-~~

~~30 40~~

~~Position [°2Theta]~~

~~Fig. 7.5 Powder X-Ray diffraction patterns of resin sample R-PP14 (Elemental loading on resin - Au: 19.7 mg/g)~~

The XRD patterns of resin samples from process validation tests are shown in Figures 7.6 and 7.7. Lists of peaks produced by these samples are given in Tables 7.4 and 7.5 respectively. In Figures 7.7 and 7.8, all peaks identified by the software are indicated by a short red line placed on the top of the graph. The positions and intensities of peaks corresponding to copper ferrocyanide (Cu2Fe(CN)6), as available in the JCPDS library, have been superimposed on these X-Ray diffraction patterns in blue. As can be seen, there is agreement between the peaks produced by the resin sample and those for copper ferrocyanide, Cu2Fe(CN)6. Although this analysis indicates that the species found on the these resin samples is likely to be copper ferrocyanide, the presence of other forms of copper hexacyanoferrates cannot be ruled out due to the very close resemblance of X-Ray diffraction patterns of these species. On the other hand, the XRD patterns produced by these samples did not match any of the JCPDS library patterns for CuCN, confirming the absence of applicable levels of CuCN in crystalline form. Counts

~~500~~

~~Position [°2Theta]~~

~~Fig. 7.6 Powder X-Ray diffraction patterns of resin sample R-950Cu/25Fe (Elemental loading on resin - Cu: 122 mg/g and Fe: 46 mg/g)~~

Table 7.4 List of XRD peaks produced by resin sample R-950Cu/25Fe Pos. [°2Th.] Height [cts FWHM [°2Th.] d -spacing [A Rel. Int. [%] 17.8949 33.00 0.2952 5.75555 9.53 20.7160 346.15 0.1968 4.97867 100.00 29.3833 135.80 0.3936 3.52955 39.23 41.9991 105.45 0.3600 2.49611 30.46 Counts

~~1000-~~

~~500-~~

~~OH I I I I I I I I I 40~~

~~Position [°2Theta]~~

~~Fig. 7.7 Powder X-Ray diffraction patterns of resin sample R-950Cu/50Fe (Elemental loading on resin - Cu: 144 mg/g and Fe: 54 mg/g)~~

Table 7.5 List of XRD peaks produced by resin sample R-950Cu/50Fe Pos. [°2Th.] Height [cts] FWHM [°2Th.] d-spacing [A] Rel. Int. [% 17.8521 59.10 0.5904 5.76924 17.63 20.6831 335.33 0.2952 4.98650 100.00 29.4816 156.09 0.4920 3.51804 46.55 41.9383 92.50 0.2952 2.50137 27.58 47.3878 35.30 0.9600 2.22596 10.53 Almost all transition and post-transition metal hexacyanoferrates, commonly known as Prussian Blue analogous compounds, share a simple cubic framework. In these compounds, transition metal cations (M and M') form structures in which octahedral M'(CN)6]"" complexes are linked via octahedrally connected nitrogen bound M"^ ions (Kaye et al., 2005). X-Ray diffraction patterns of these compounds are relatively similar (Weiser et al., 1941). Hydration of these compounds varies depending on the precipitation conditions. As noted by Cola and colleagues (1977), the same compound could produce slightly different X-Ray diffraction patterns due to variation of hydration peaks. An analysis of powder X-Ray diffraction patterns of Cu2Fe(CN)6 and Cu3[Fe(CN)6]2 (synthesised in the laboratory) confirmed the difficulties in distinguishing powder X-Ray diffraction patterns of these two species.

Powder X-Ray diffraction patterns of Cu2Fe(CN)6 and Cu3[Fe(CN)6]2 prepared in the laboratory are shown in Appendix 16. These two specimens produced very similar powder X-Ray diffraction patterns. Further, some hydration peaks recorded in X-Ray diffraction pattern libraries are not seen in these figures, possibly due to differences in hydration caused by different drying conditions used.

For these reasons, although the X-Ray diffraction patterns of resin samples suggests that the compound on the resin is more likely to be copper ferrocyanide than copper ferricyanide, this evidence from X-Ray diffraction patterns alone is insufficient to make a positive identification between these species. Further, the possibility of the presence of both these compounds on the resin cannot be ruled out.

There have been some attempts to distinguish various transition-metal ferricyanides from ferrocyanides using I. R. and UV-Visible Spectra (Ghosh, 1974; Cola et al., 1977) and Diffuse Reflectance Spectroscopy in the UV-Visible range (Tacconi et al., 2003). A comparison of spectra from a resin sample with those of copper ferrocyanide and copper ferricyanide is shown in Figure 7.8. 0.8

~~B 0.6 c 3 c 3 0.4 (0 o n 3 0.2~~

~~200 300 400 500 600 700 800 900 1000 Wavelength (nm)~~

~~Fig. 7.8 Reflectance spectra in the 200-1000 nm range~~

The reflectance spectra of the resin sample R-950Cu/50Fe resemble that of copper ferrocyanide Cu2Fe(CN)6, more than that of copper ferricyanide Cu3[Fe(CN)6]2. In the visible section of the spectra (400 to 700 nm), where the effect of the resin matrix is negligible, there is good agreement between the spectra of Cu2Fe(CN)6 and that of resin sample R-950Cu/50Fe. In the UV range, in spite of the strong reflectance peak produced by fresh resin, the reflectance peak of resin sample F-950Cu/50Fe closely follows that of Cu2Fe(CN)6. However, these reflectance spectra do not confirm the absence of copper ferricyanide in resin. Hence, the presence of both species cannot be ruled out. Therefore, it can be concluded that the copper cyanide species found on these resin samples are most likely copper ferrocyanide, but may also contain appreciable levels of copper ferricyanide.

As the elemental analysis of resin from the pilot scale studies (Chapter 6) indicated that appreciable levels of iron and copper were not found in the resin, reflectance spectra of such resin samples were not investigated. 7.2.6 Optical and Electron Microscopy Imaging of Resin

Changes in the physical appearance were observed in deteriorated resin samples. A change in the colour of resin beads was the first and most obvious sign of deterioration. A significant shrinkage of particle size, when dried, was also noticeable in the resin from pilot scale tests. This section reports the study of changes in appearance in the macro and micro scales in the resin samples.

~~7.2.6.1 Experimental~~

Resin samples were photographed in wet settled form to document the changes in appearance. Following this, the resin samples were dried at 60 ^C and cracked to examine the microstructure of the fracture surfaces, using a JSM 6400 Scanning Electron Microscope.

~~7.2.6.2 Results and Discussion~~

Figure 7.9 shows the discolouration of resin seen in various columns of process validation tests (Chapter 5). Fresh resin was ivory in colour. The resin sample R- 950Cu/0Fe, which was subjected to 15 loading cycles with a solution containing 950 mg/L copper in a 1250 mg/L CNTQT at pH 12.2 showed brown/orange tinting, although elemental analysis indicated that there was no significant transition metal loading on this resin.

The resin samples loaded with mixed copper and iron cyanide species (R- 950Cu/25Fe and R-950Cu/50Fe) had a dark purple-brovm colour due to the presence of copper hexacyanoferrates. As discussed previously, the level of iron in the loading solution is not proportionally reflected in the discolouration of resin, although some difference in the two samples can be seen. These resin samples became lighter in colour as they were dried, but those loaded with copper and iron cyanide containing solution maintained a light brovm colour in the dry form. R-Fresh R-950Cu/0Fe R-950Cu/25Fe R-950Cu/50Fe

~~Fig. 7.9 Appearance of resin from resin durability tests~~

The appearance of resin from the pilot scale tests is shown in Figure 7.10. Gradual discolouration is seen in resin samples subjected to four, seven, and 14 loading/elution cycles. The uneven discolouration of resin from the pilot plant is of particular interest. While the bulk of the resin appears to have gradually moved toward a dark brown colour from its original ivory colour, some resin beads have turned dark brown after four loading/elution cycles. The fraction of dark brown resin to light brown resin appears to increase with the number of cycles on the resin bed. The resin sample after Cycle 14 has a significant number of dark brown resin beads. Unlike the resin samples loaded with copper and iron cyanide species, these resin samples increased in hue as they were dried.

~~R-Fresh R-PP04 R-PP07 R-PP14~~

Fig. 7.10 Appearance of resin from pilot plant tests Figure 7.11 gives a micrograph of fracture surface of a fresh resin bead, showing the macroporous structure of the resin interior. Macropores of resin are generally in the order of several hundred nanometers (nm), as reported in the literature (Harland, 1994). This structure was seen in the centre of the resin bead as well as close to the surface of the bead.

~~Fracture surface structure close to the surface Fracture surface structure close to the centre of the resin bead of the resin bead~~

~~Fig. 7.11 Fracture surface of fresh Purolite A500 strong base ion exchange resin~~

Figure 7.12 shows micrographs of fracture surfaces of resin taken from resin durability studies (Section 5.2). The microstructure in this resin sample appears to be swollen or bonded to some extent, especially closer to the surface of the resin bead. This sample had a copper and iron loading of 144 and 54 mg/g respectively, and these elements were present in the form of an insoluble copper hexacyanoferrate (Sections 7.2.4 and 7.2.5). This suggests that the structure with a swollen or bonded appearance close to the surface of the resin bead resuhs from the bridging of macropores by the copper hexacyanoferrate precipitate. However, the resin still appears to maintain some macroporosity, although the diffusion of counter-ions within the resin may be somewhat restricted. Fracture surface structure close to the surface Fracture surface structure close to the centre of the resin bead of the resin bead

~~Fig. 7.12 Fracture surface of resin sample R-950Cu/50Fe (Elemental loading on resin Cu: 144 mg/g and Fe: 54 mg/g)~~

The study of the microstructure of resin from the pilot scale tests was less conclusive. As wet settled resin, these resin beads displayed various shades of brown. When dried, some resin beads retained a light brown complexion, while others turned to various shades of dark brown or black. The dried light brown resin beads were approximately 0.5 mm in diameter, similar in size to dried fresh resin. The dark brown/black resin beads were visibly smaller. Resin beads as small as 0.2 mm were common. The darker the resin beads were, the smaller they appeared when dried.

These variations in resin size and colour presented a difficulty in finding representative resin beads to inspect the fracture surface microstructure. Therefore, resin samples taken from the pilot scale tests after Cycle 7 and Cycle 14, were visually segregated into light brown and dark brown beads. Fracture surfaces of various parts of the cross section of these resins were inspected to identify any patterns in the microstructure common to the majority of resin beads in a given sample. Fracture surface structure of light brown Fracture surface structure of dark brown resin resin beads beads

~~Fig. 7.13 Fracture surface of resin sample R-PP07 (Elemental loading on resin Au: 6.2 mg/g)~~

~~Fracture surface structure of light brown Fracture surface structure of dark brown resin resin beads beads~~

Fig. 7.14 Fracture surface of resin sample R-PP14 (Elemental loading on resin Au: 19.7 mg/g) Unlike resin samples from resin durability studies, no clear and consistent differences were identified between the fracture surface near the perimeter of beads and that closer to the centre of beads; i.e. the microstructure of resin appeared to be consistent throughout the cross section of these resin samples.

The fracture surfaces of resin taken after Cycle 7 from the pilot scale tests are shown in Figure 7.13. As can be seen in these micrographs, the microstructure of light brown resin appears to remain intact, with no clear sign of fusing. However, the microstructure of dark brown resins appears to have collapsed, losing most of its macroporosity. The fusion of macropores is even more evident in Figure 7.14, which shows the microstructure of a resin sample taken after loading Cycle 14 from the pilot plant.

It should be noted that the collapsed microstructure seen in the dark brown resin beads is not indicative of its microstructure in the water swollen form. The significant shrinkage taking place during drying hides any structural features in the resin microstructure in the hydrated form. As the ion exchange takes place in the water swollen form of the resin, the collapsed or fused microstructure of these resin samples, observed in the dry form, cannot be used to draw any direct inferences about the reason for the reduced ion exchange capacity. Nevertheless, the abnormally high shrinkage and the collapsed or fiised microstructure of the resin present an interesting phenomenon for ftirther study.

~~17S 7.3 REVIEW OF RESIN DETERIORATION~~

~~Resin characterisation studies in this chapter found that deteriorated resin would have one or more of the following properties:~~

1. reduction of total base capacity 2. reduction of ion exchange kinetics 3. precipitation of copper hexacyanoferrate on resin 4. loading of gold in a form not amenable to elution by Zn(CN)4^" eluent 5. discolouration 6. swollen, bonded or collapsed microstructure.

Factors contributing to resin deterioration can be identified by examining these results in light of the loading and elutions conditions of various resin samples. Consideration of the process chemistry of metal cyanide complexes on resin phase in the presence of oxidative acid eluent gives an insight into various modes of resin deterioration.

~~7.3.1 Factors Contributing to Resin Deterioration~~

When resin loaded with copper was eluted with the oxidative acid elution, a reduction of total base capacity and discolouration was noticed. Resin with no copper loading, when subjected to identical conditions, did not show these signs of degradation. The impact of copper is suggested as one factor leading to resin deterioration. Precipitation of copper hexacyanoferrates was seen in resin loaded with mixed copper and iron cyanide species. In addition to reduction of total base capacity, a slight reduction of ion exchange kinetics, swollen^onded microstructure and strong discolouration were also noted. The precipitation of copper hexacyanoferrates can be seen as another factor causing resin deterioration. The resin samples from pilot scale testing showed a significant reduction of total base capacity, along with discolouration and collapsed microstructure. Gold loading was seen on the resin, in a form not amenable to elution by Zn(CN)4^' eluent. The non-removable loading of gold is seen as another factor contributing to the diminished performance of resin.

~~7.3.2 Resin Deterioration Mechanisms~~

The impact of the oxidant on resin in the presence of copper, the precipitation of metal hexacyanoferrates, and the loading of gold to resin in a form not amenable to elution contribute to resin deterioration. While none of these processes produced a catastrophic failure of resin, a clear understanding of these processes allows prediction of resin inventory replenishment requirements in large scale operations.

~~7.3.2.1 The Effect of Copper on Resin Deterioration~~

The work in Section 5.1 demonstrated that repeated cycling between alkaline cyanide solutions and oxidative acid solutions (5 g/L H2O2 and 50 g/L H2SO4) does not affect the strong base or the total base capacity of strong base resins. However, when resins were repeatedly loaded with copper cyanide and eluted with the oxidative acid eluent, a reduction of total base capacity was observed. The reduction in the total loading of copper, the drift of breakthrough curves, and the gradual discolouration corroborated this deterioration. While some of these resuhs alluded to the possibility of copper accumulation in the resin, the XRF analysis of dried deteriorated resin proved that no net accumulation of copper had taken place. The absence of appreciable levels of copper (or any other metal contamination) suggested that the reduction of total base capacity in resin was not a result of the loading of an anionic species or blockage of resin pores by copper cyanide. As discussed in Chapter 5, the depletion of ftinctional groups due to the oxidation of resin by H2O2 in the presence of Cu^^ cations, i.e. Fenton reaction, remain as one of the more likely explanations for the observed reduction of total base capacity in these resins. 7.3.2.2 Resin Deterioration Due to the Precipitation of Hexacyanoferrates

When iron cyanide was present in the loading solution with copper, the formation of copper ferricyanide (Cu3[Fe(CN)6)]) and/or copper ferrocyanide (Cu2Fe(CN)6) on the resin was detected. Copper loading of up to 14% w/w and iron loading of up to 5% w/w were noted in some resin samples. A gradual reduction of the net operating capacity of resin beds (Table 5.7) was seen in columns loaded with affected resin. However, the total base capacity of these resin samples were similar to that of resin affected by repeated loading and elution of copper (Table 7.2). These resins also showed clear discolouration. The rate of CI" elution in these resins appeared to be slightly lower than that of resin with no metal contamination, while the micropores near the surface of these resin beads appeared to be somewhat congested.

These results led to the conclusion that the formation of copper hexacyanoferrates on resin is responsible for the reduction of the net operating bed capacity over time. However, this precipitate does not appear to affect the total base capacity of resin. The slight reduction of CI" elution rate and the congested microstructure suggests that the formation of this precipitate impacts on the ion exchange kinetics of resin, possibly due to the increased resistance to intra-particulate mass transfer. Such a gradual reduction of ion exchange rate gives rise to a reduction of the net operating bed capacity over time.

~~7.3.2.3 Resin Deterioration Due to Loading of Gold on Resin~~

Resin samples from pilot scale tests showed a significant reduction of loading capacity. Resin after 14 cycles of loading and eluting showed 40% reduction of strong base capacity, significantly more than the deterioration of resin expected from the effect of copper or iron cyanide species. X-Ray Fluorescence Spectroscopy of dry resin showed that there was no appreciable loading of copper or iron in these resins. However, a significant loading of gold was detected in these resin samples. Unlike the resin samples affected by copper and iron, no crystalline species were detected by X-Ray Diffraction. This suggested that the gold is loaded on resin in a non- crystalline form, leaving the possibilities of metallic, amorphous, or ionic forms for gold to remain on resin.

The cycling between high pH/low Eh conditions (during loading) and low pH/high Eh conditions (during oxidative acid elution) is not conducive to the precipitation of gold as metallic gold in the resin. In the remote scenario that Au(CN)2' adsorbed on the resin was reduced to metallic gold, it would have been re-dissolved and removed from the resin during the Zn(CN)4^' elution, as the Zn(CN)4^' eluent contained an appreciable level of excess cyanide and dissolved oxygen. Therefore, the presence of metallic gold on the resin can be ruled out.

As the resin is being subjected to repeated loading and oxidative acid elution cycles, gold could form some amorphous cyanide double salts with other cations. However, most cyanide double salts of alkali or alkaline earth elements are soluble. While most transition metal cyanide double salts are insoluble, the absence of any transition elements in appreciable quantities in the resin rules out the possibility of the presence of a transition metal gold cyanide double salt. Therefore, a non-removable gold loading on the resin, in the form of an amorphous complex, is an unlikely scenario.

Gold cyanide (Au(CN)2') is a non-WAD cyanide species. It is not reduced by cyanide, nor is it oxidised to its constituents by oxidants under normal conditions (Flynn and Haslem, 1995). In its anionic form, it is strongly bound to the resin, but is replaced by the highly polarised planer [Zn(CN)4)]^" ions, which have a higher affinity to resin. The elution of Au(CN)2' with zinc tetracyanide is an accepted practice, and its efficiency in removing gold from resin has been well documented (Tran et al., 2000). Therefore, the possibility of gold remaining on resin as Au(CN)2' is very unlikely.

Gold forms a cyanide complex in its trivalent oxidation state. This compound, tetracyanoaurate (Au(CN)4'), is not found in cyanidation plant liquors (Adams et al., 1992), but is formed when a strong oxidant, such as a halide, is introduced into a cyanide liquor containing Au(CN)2" (Smith et aL, 1965). Therefore, it is conceivable that when strong base ion exchange resins loaded with Au(CN)2' are brought into contact with H2O2, some of the gold loaded on the resin is oxidised to its trivalent state, forming Au(CN)4'. As it is a strong anion, Au(CN)4" could remain adsorbed on the resin as an anionic species, or could form a stable double salt with other metal cations such as copper, as discussed in Section 5.3. However, since no other elements were detected in significant quantities in these resins (Table 6.3), the possibility of the presence of a stable double salt of gold such as copper tetracynoaurate(III) (CU[AU(CN)4]2) in the resin, can be ruled out.

AU(CN)4' ions have a planer geometry, similar to [Zn(CN)4]^" anions used to elute gold from the resin. However, Au(CN)4' ions have a higher oxidation state in the central metal atom and an overall lower valency than [Zn(CN)4]^' ions. Therefore, ion exchange resins could be expected to show a higher affinity to Au(CN)4' than [Zn(CN)4]^' ions. The preference of activated carbon to Au(CN)4' over Au(CN)2' has been documented by Adams and colleagues (1992). This also suggests that Au(CN)4" would be more difficult to elute from resin than Au(CN)2' using [Zn(CN)4)]^" ions.

~~Therefore, it can be suggested that if Au(CN)2" loaded on the resin is oxidised to~~

AU(CN)4' by the oxidant, the oxidised gold complex is likely to remain on the resin after the [Zn(CN)4]^" elution. In other words, the gold loading seen in these resin samples could be due to the presence of gold as Au(CN)4" species.

~~The gold loading in anionic form on resin could contribute to the reduction of loading capacity seen in these resins, as some of the loading sites are occupied by~~

AU(CN)4". It also explains the absence of X-Ray diffraction pattern peaks. Further, since the gold loading on resin in Au(CN)4" form does not require the presence of other transition or post transition elements, the absence of other elements in the resin, as seen in the X-Ray Fluorescence Spectroscopy analysis, can also be explained. This hypothesis could be tested by conducting a Mossbauer Spectroscopic investigation on resin samples, which would reveal the valency of gold in the resin. If a significant level of trivalent gold is found by Mossbauer Spectroscopy, the gold loading on the resin in the tetracyanoaurate form could be confirmed. Although this could be a matter of high scientific interest, it falls outside the scope of this thesis and therefore has not been further addressed. If it could be confirmed that some

AU(CN)2' loaded on to the resin is oxidised to Au(CN)4" by the oxidant, a key area for further research would be to develop an elution technique to release the gold from resin. If the resin could be stripped of gold and regenerated to an acceptable level, the lifespan of the ion exchange bed could be extended, while averting the requirement to incinerate the resin to recover the gold. This area has also been identified for further research.

~~7.4 CONCLUSION~~

Work reported in this chapter identified three possible modes of resin deterioration taking place when an oxidative acid eluent is used repeatedly to elute strong base ion exchange resins loaded with mixed cyanide complexes. It was seen that resins lose some of the strong base capacity when exposed to repeated loading of copper cyanide and elution by the oxidative acid eluent, irrespective of the presence of non- WAD cyanide species. The depletion of functional groups due to the oxidation of resin by H2O2 in the presence of Cu^"^ cations, i.e. Fenton reaction, remain as one of the more likely explanations for the observed reduction of total base capacity.

It was also noted that the presence of iron cyanide species in the loading solution leads to a precipitation of copper hexacyanoferrates on the resin. The macropores of affected resin were somewhat restricted due to the precipitation of copper hexacyanoferrates. This did not lead to a reduction of strong base capacity of resin. A reduction of the rate of ion exchange in these resins was seen, most likely due to the congestion or blocking of resin macropores. This reduction of ion exchange rate was attributed to the reduction of net operating capacity of columns containing affected resin.

Used resin samples from the pilot scale tests showed a clear reduction of total base capacity. The resin sample after the fmal loading cycle (Cycle 14) had only 60% of its original total base capacity. This resin had a significant loading of gold (approximately 2% w/w gold in the resin taken after the last cycle). It was suggested that the gold on this resin is loaded as tetracyanoaurate ions (Au(CN)4"). This hypothesis could be tested by conducting a Mossbauer Spectroscopic investigation on resin samples, which would reveal the valency of gold in the resin.

In conclusion, the deteriorated resin displayed a reduction of total base capacity and/or a reduction of ion exchange kinetics. The extent of loss of net operating capacity was approximately 1-3% per loading/elution cycle. This is not prohibitive to the application of oxidative acid elution to elute mixed cyanide complexes from resin, provided that resin deterioration is taken into consideration, and the replenishment of a small fraction of the resin inventory is incorporated into plant operating procedures. Environmental Impact and Operating Costs

This chapter presents a critical assessment of the environmental impact of the overall cyanide detoxification process developed and tested in the preceding chapters. Also presented in this chapter are the reagent consumption figures and estimated operating costs, as observed from the pilot scale testing program reported in Chapter 6.

~~8.1 ENVIRONMENTAL IMPACT~~

A critical outcome of the successful demonstration of the process, from the mine rehabilitation point of view, was the treatment and disposal of the low-grade liquor. At the end of the pilot scale testing program, all of this low-grade liquor was detoxified. The site was left with approximately 14,000 m^ of water, suitable for use as process water or for dust suppression. Hence, the cyanide detoxification process met its primary objective; the remediation of cyanide contaminated solutions from gold mining operations.

Further, the pilot plant testing program demonstrated that there were no other significant environmental impacts of this process. This is evident when the environmental impacts of the discharge streams are assessed individually. The key discharge from the plant, in terms of volume, was the detoxified liquor. As can be seen in Table 6.2, CNTQT levels in the treated liquor emerging from the plant were consistently less than 2.5 mg/L in all cycles. At the end of ion exchange resin treatment (May 2000), the combined treated liquor accumulated in the tailings dam averaged 1.5 mg/L CNTQT. This treated liquor was held in a detoxified liquor dam for natural degradation of the remaining cyanide. Over a period of approximately 4 months, this cyanide concentration reduced gradually to 0.1 mg/L. These resuhs are shown in Figure 8.1. Appendix 17 gives the total cyanide concentration in the tailings dam during the period of natural degradation. The detoxified liquor was not contaminated with other chemicals. As such, after being subjected to natural degradation, it was suitable for discharge into the environment, or for reuse. In this case, it was used for dust suppression in other rehabilitation work being carried out in the mine site.

~~2.0~~

~~o 3 1.5~~

~~T3 O "S 1.0 3 G) o E T3 C 0.5 OH z o 0.0~~

~~01-Jun-00 01-Jul-00 31-Jul-OO 30-Aug-00 29-Sep-OO~~

~~Time subjected to natural degradation~~

~~Fig. 8.1 Natural degradation of cyanide in the treated liquor~~

The other liquid discharge from the plant was the neutralised mixture of spent eluent and scrubber solution. This solution was a weakly acidic (pH 3-4) CUSO4 solution containing 1 to 1.5 g/L copper and some decomposing CNO", resulting from the oxidation of cyanide. Under acidic conditions, CNO" is not stable in solution and decomposes to N2 and CO2 over time (Smith and Mudder, 1991). The environmental impact of CNO" in this stream was not given further consideration due to the short Hved nature of CNO" in low pH environments. In the absence of an SX/EW facility, which would have enabled the recovery of copper from this solution, it was dispersed over the leaching vats, which contained cement agglomerated ore. As this acidic solution came into contact with the agglomerated ore, it was neutralised by the cement, immobilising the copper in the alkaline ore matrix.

In conclusion, the cyanide contaminated liquor at the site was successfully detoxified, without generating any other toxic waste products, or introducing other toxic chemicals into the treated liquor. This is a significant advantage over most cyanide detoxification processes used in the mining industry today, which unlike this ion exchange process, remove cyanide contamination at the cost of introducing other chemicals (SO2, chlorine, or iron compounds) into the tailing stream or producing other forms of toxic waste (Mishra, 2002).

~~8.2 OPERATING COST AND REAGENT CONSUMPTION~~

The cyanide contaminated liquor at May Day mine was in many ways typical of cyanidation tailings produced from large cyanidation operations. Nevertheless, the presence of precious metals in the liquor gave an unusual economic advantage. In spite of substantial overhead costs, typical to pilot scale tests, the precious metals recovered from the liquor led to a net positive bottom line for the pilot plant test program. As the presence of precious metals in appreciable quantities is an unlikely scenario in other cyanide decontamination operations, the revenue from precious metals and the reagent/utility costs associated with precious metal recovery, has not been taken into consideration in the proceeding discussion of operating costs. Reagents and utility consumption figures for a basic cyanide detoxification cycle, consisting of loading, oxidative acid elution, and cyanide oxidation, are shown in Table 8.1. Table 8.1 Pilot plant costs for the treatment of cyanide contaminated solution Item Amount needed for treating Cost per Item 1000 m^ of solution unit* Cost* Reagent costs H2S04(97%) 650 kg $0.25 per kg $162.50 H202(50%w/v) 120 kg $0.90 per kg $108.00 NaOH (50% w/v) 1000 kg $0.24. per kg $240.00 Total reagent costs $510.50

~~Utilities Electricity 1400 kWh $0.12 per kWh $168.00 Process water 70 m^ $0.20 per m^ $14.00 Total utilities cost $ 182.00~~

~~Ion exchange resin (due to loss of 60 L 5.00 per liter $300.00 loading capacity )~~

~~Total estimated cost for treatment of 1000 m^ of liquor $992.50~~

* Approximate cost in AUD (Australian Dollars) quoted in late 2003.

The cost of ion exchange resins was a significant cost of this operation. As discussed in Chapter 6, the loading capacity of resin reduced by approximately 40% over the course of 14 cycles. This, in effect, equates to a total loss of 800 L of resin, or approximately 60 L of resin per loading/oxidative acid elution cycle. This amounted to approximately a third of the total cost of a cycle. As seen in Chapter 7, the loss of loading capacity could be attributed to the deterioration of resin due to the effect of the oxidant in the presence of Cu^^ ions and the loading of gold onto the resin in a form not amenable to elution by Zn(CN)4 " ions.

Therefore, the presence of gold in the liquor is seen as a 'mixed blessing'. Subject to the concentration of gold in the liquor requiring detoxification, the recovery of gold could offset the full cost of cyanide detoxification (as in the case of this pilot scale study), while increasing the rate of ion exchange resin deterioration. With the exception of ion exchange resin costs, the total cost of reagents was approximately AUD 0.50 per m^ of liquor treated. This cost, although not directly proportional, is a function of the CNWAD concentration in the feed liquor.

This process does not have highly power consuming operations such as heating, cooling, or evaporation. Most of the power consumption was associated with pumping liquor from the feed liquor dam through the plant to the discharge liquor dam. As such, the power consumption is subject to the configuration of the feed and discharge liquor reservoirs in relation to the processing plant. The cost of electricity in this project was estimated based on peak power consumption figures observed during the loading cycle. The cost of process water, although a very small component in the total cost of the operation, was abnormally high in this project, due to its remote locality.

Overall, a total reagent, resin and utility cost of AUD 1.00 per m^ of liquor treated (2003 dollars) is not economically prohibitive for cyanide detoxification. This would be further reduced at low CNWAD concentrations.

~~8.3 CONCLUSIONS~~

In this pilot scale test, some 14,000 m^ of cyanide contaminated liquor was treated. The precious metals found in the cyanide contaminated liquor proved to be a windfall and effectively covered all expenses of the project, but also contributed to resin deterioration. The loss of resin efficiency was equivalent to the loss of 60 L of strong base ion exchange resin (or 3% of total capacity) per loading/elution cycle. Despite this impediment, the pilot scale test program was completed successfully, treating all the cyanide contaminated liquor at the mine site, preparing it for further rehabilitation. The process produced no additional toxic wastes as byproducts of cyanide treatment. In comparison to other cyanide detoxification processes available to the mining industry today, the ability to produce a detoxified liquor stream, which is not contaminated with other chemicals, is a key environmental advantage. The reagent cost of detoxification was approximately AUD 0.50 for 1 m^ of liquor. The cost associated with the loss of resin was a large component of costs, and amounted to be almost AUD 0.30 per 1 m^ of liquor.

The process has numerous advantages over conventional cyanide detoxification techniques. The rapid processing rate, the potential for scavenging precious metals, and economically recovering base metals such as copper and zinc, and the ability to produce environmentally acceptable detoxified liquor are some of the key benefits of this process.

The environmental impact and operating costs of this pilot scale test, when taken together with the process results reported in Chapter 6, confirm that this novel cyanide detoxification process is technically feasible, environmentally sound, and economically viable for the detoxification of cyanide contaminated liquors arising from gold cyanidation operations. Conclusions

This project explored the behaviour of metal cyanide complexes under oxidative acid conditions in ion exchange systems, with the objective of developing an ion exchange based cyanide detoxification process suitable for gold cyanidation operations.

The work described in Chapter 4 investigated the behaviour of metal cyanide complexes on ion exchange resin in the presence of oxidative acid conditions. It was seen that an oxidative acid eluent, comprised of H2O2 and H2SO4, is capable of eluting all copper cyanide species from strong base anion exchange resins, provided that stoichiometric requirements of hydrogen peroxide are available in the eluent. The rate of elution depended on the hydrogen peroxide concentration. Cyanide recovery was also found to depend on hydrogen peroxide concentration, with reduced yields at high oxidant concentrations. Loading of mixed cyanide complexes on strong base ion exchange resins confirmed that precious metals and base metals are loaded indiscriminately to the resin. Testing of the oxidative acid elution on ion exchange resin beds loaded with mixed cyanide species proved that it is capable of completely removing all major base metals from strong base resins. The elemental concentration profiles gave clear evidence that copper and other base metals could be eluted at separate stages if required, with little cross contamination. None of the precious metals (gold and silver) loaded on resin were removed during the oxidative acid elution. The effect of aggressive oxidative acidic conditions on the durabihty of standard commercially available strong base ion exchange resins were explored in Chapter 5. This study confirmed that there were no significant deleterious effects on resin caused by the long term exposure to H2O2 in an acidic environment. However, resin deterioration was seen when metals such as copper and iron were introduced to the system. When resin was repeatedly loaded with copper cyanide and eluted with the oxidative acid eluent, a gradual reduction of total base capacity was observed. When iron cyanide was present in the loading solution, a reduction of the net operating capacity of the resin bed was detected. Other non-WAD cyanide species, such as those of cobah and chromium, were assumed to be capable of producing a similar affect.

~~The pilot scale testing of the cyanide detoxification process developed was reported in Chapter 6. During the pilot scale testing program, some 14,000 m^ of cyanide~~

contaminated liquor was treated. On average, CNTOT contamination in the liquor was reduced from approximately 50 mg/L in the feed, to approximately 1.5 mg/L in the final discharge. The precious metals found in the cyanide contaminated liquor were recovered. The revenue from precious metals was used to offset the cost of cyanide detoxification. A loss of ion exchange bed efficiency was noticeable after a number of loading/elution cycles. The loss of loading capacity of resin equated to 1-3% reduction in total base capacity per loading/elution cycle. A byproduct of the process was a mildly acidic CUSO4 solution, which was deemed suitable for an SX/EW circuit for recovery of copper. All cyanide recovered from the contaminated liquor was destroyed within the processing cycle, without needing additional unit operations or reagents. The process produced no additional toxic waste forms as byproducts of cyanide treatment. The reagent cost of detoxification was approximately AUD 0.50 for a 1 m^ of liquor.

This process has numerous advantages over conventional cyanide detoxification techniques. The rapid processing rate, the potential for scavenging precious metals, the potential for economical recovery of base metals such as copper and zinc, and the ability to produce environmentally acceptable detoxified liquor, are some of the key benefits of this process. Environmental impacts and operating costs of the process were reported in Chapter 8.

A study of resin deterioration was presented in Chapter 7. Three modes of ion exchange resin deterioration were identified. Repeated loading of resin with copper cyanide and elution with the oxidative acid eluent appeared to give a gradual reduction of the total base capacity of resin. The deterioration of resin due to the oxidation by H2O2 catalysed by Cu^^ cations, i.e. Fenton reaction, is the most likely explanation for this deterioration. Copper hexacyanoferrate precipitate was detected in resin samples loaded with a mixed copper and iron cyanide solution. This did not appear to affect the total base capacity of resin. However, it impacted on the ion exchange kinetics of resins, possibly due to the increased resistance to intra- particulate mass transfer. The reduction of loading capacity of the resin from the pilot scale tests was confirmed using total base capacity measurements. At the end of the pilot scale testing program, the total base capacity of the resin had reduced to 60% of its original capacity. Elemental analysis of dry resin samples showed the presence of significant levels of gold in this resin. The loading of gold to the resin in tetracyanoaurate form (Au(CN)4") was presented as the most likely explanation for this phenomenon.

The extent of resin deterioration was found to be approximately 1-3% per loading/elution cycle. This level of deterioration is not prohibitive to the application of oxidative acid elution to elute mixed cyanide complexes from resin, provided that resin deterioration is taken into consideration and the replenishment of a small fraction of the resin inventory is incorporated into plant operating procedures.

In conclusion, this operationally driven research project explored the reactions of metal cyanide complexes in the presence of oxidative acid conditions in ion exchange systems. The understanding of the behaviour of metal cyanide complexes under oxidative conditions has been enhanced as a result of this work. From this study, a novel cyanide detoxification process was developed. This novel process was shown to have significant environmental and economic advantages over conventional cyanide detoxification processes used in the treatment of cyanidation tailings. Recommendations for Further Research

Several areas requiring further research were identified in the research work presented in this thesis. Some of these areas were of direct relevance to the cyanide detoxification process presented herein. A better understanding of such issues could lead to improvements in process performance and economics of the process. Several other issues identified were not directly related to the cyanide detoxification process, but are of scientific interest. The ensuing section lists all such areas identified for further research.

~~10.1 THE IMPACT OF THE OXIDANT ON RESIN IN THE PRESENCE OF COPPER~~

The work in Section 5.1 demonstrated that repeated cycling between alkaline cyanide solution and an oxidative acid solution (5 g/L H2O2 and 50 g/L H2SO4) does not affect the strong base or the total base capacity of strong base ion exchange resins. However, as seen in Section 5.2, when resin was repeatedly loaded with copper cyanide and eluted with the oxidative acid eluent, a reduction of total base capacity was observed over 15 cycles. While reduction in the total loading of copper, the drift of breakthrough curves, and the gradual discolouration, seen together with the reduction of total base capacity alluded to the possibility of copper accumulation in the resin, the X-Ray Fluorescence Spectroscopy analysis of dried deteriorated resin proved that no net accumulation of copper had taken place. The absence of appreciable levels of copper, or any other metal contamination, suggested that the reduction of total base capacity is not a result of the loading of an anionic species, or blockage of resin pores by copper cyanide. The depletion of functional groups due to the oxidation of resin by H2O2 catalysed by Cu^^ cations, i.e. Fenton reaction, was put forward as the most likely explanation for the observed reduction of total base capacity in these resins. Further research is needed to explore this phenomenon.

~~10.2 THE EFFECT OF OTHER NON-WAD CYANIDE SPECIES~~

It was suggested in Section 5.3 that other non-WAD cyanide species such as tetracynoaurate(III) (Au(CN)4'), hexacyanocobaltate(III) (Co(CN)6^'). and hexacyanochromate(III) (Cr(CN)6^"), could produce a double salt with copper and other base metals, if these non-WAD cyanide species were in the loading solution. The formation of these stable double salts such as copper tetracynoaurate(III) (CU[AU(CN)4]2), copper hexacyanocobaltate (Cu3[Co(CN)6]2), and copper hexacyanochromate (Cu3[Cr(CN)6]2), would produce a reduction of the net operating capacity, similar to that produced by the ferricyanide and ferrocyanide species. It is recommended that this phenomenon be investigated experimentally, by co-loading these cyanide species with other base metals such as copper, followed by subjecting resin beds to oxidative acid elutions, as described in Section 5.2.

~~10.3 THE NATURE OF GOLD LOADING ON RESIN~~

Elemental analysis of the dry resin samples obtained from the pilot plant tests indicated significant levels of gold loading. Approximately 2% w/w gold, which was not amenable to elution by zinc tetracyanide (Zn(CN)4^') ions, was seen in the resin sample taken after the last loading cycle. X-Ray Diffraction indicated that there were no clearly detectable crystalline species on the resin. Therefore, the presence of gold on the resin in tetracyanoaurate form (Au(CN)4") was suggested. It is recommended that this hypothesis be tested by conducting a Mossbauer Spectroscopic investigation on resin samples. The Mossbauer resonance effect of gold can be measured using the 113 keV gamma photons produced by Pt-197 isotope, as described by Adams and colleagues (1991).

~~10.4 REGENERATION OF DETERIORATED RESIN~~

The loading of copper and iron as copper hexacyanoferrates, and the loading of gold in a form not amenable to elution by Zn(CN)4 " ions, were identified as factors continuing to the deterioration of resin. It is recommended that a suitable elution technique be developed to elute these species from resin. This would enable the recovery of gold and the regeneration of the resin to an acceptable level, extending the useful lifespan of the ion exchange resin bed. It is recommended that an elution with strong ammonia solution be studied for eluting copper hexacyanoferrates from deteriorated resin, as ammonia effectively complexes both copper and iron, decomposing the copper hexacyanoferrate double salt. References

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~~Table Al.l Mass balance calculation for loading of Amberlite IRA 900 RF resin~~

~~Dry weight of Amberlite IRA 900 RF resin: 100.0 g Loading duration 6 hrs Loading solution specifications:~~

~~Volume: 160 mL Cu concentration: 0.894 M~~

~~CNTOT concentration 2.71 M Spent Loading solution specifications~~

~~Volume: 160 mL~~

~~Cu concentration: 8.0 E-5 M~~

~~CNTOT concentration 0.31 M~~

~~Calculated total copper loading to resin 0.894 moles~~

~~9.09 g 90.9 mg/g~~

~~Calculated total cyanide loading to the resin 0.386 moles~~

~~9.94 g 99 mg/g APPENDIX 2~~

Table A2.1 Elution of Copper from Amberlite IRA 900 RF resin Test Time Weight Resin Cu Total initial Cu Cu conc. in Solution Cu wt in Elution of No. of resin loading in resin solution volume solution Cu from (min) (g) (mg/g) (mg) (mg/L) (L) (mg) resin 0 5.01 90.9 455.4 <0.1 1 0.0 0%

~~28 5.01 90.9 455.4 2.4 1 2.4 1%~~

~~45 5.01 90.9 455.4 7.6 1 7.6 2%~~

~~60 5.01 90.9 455.4 9.6 1 9.6 2%~~

~~80 5.01 90.9 455.4 20.5 1 20.5 5%~~

~~100 5.01 90.9 455.4 28.7 1 28.7 6%~~

~~150 5.01 90.9 455.4 59.7 1 59.7 13%~~

~~180 5.01 90.9 455.4 76.9 1 76.9 17%~~

~~2 0 5.00 90.9 454.5 <0.1 1 0.0 0%~~

~~2 15 5.00 90.9 454.5 28.6 1 28.6 6%~~

~~2 30 5.00 90.9 454.5 48.3 1 48.3 11%~~

~~2 45 5.00 90.9 454.5 57.2 1 57.2 13%~~

~~2 60 5.00 90.9 454.5 81.3 1 81.3 18%~~

~~2 90 5.00 90.9 454.5 114.4 1 114.4 25%~~

~~2 120 5.00 90.9 454.5 141.7 1 141.7 31%~~

~~2 150 5.00 90.9 454.5 177.3 1 177.3 39%~~

~~2 180 5.00 90.9 454.5 184.3 1 184.3 41%~~

~~3 0 5.00 90.9 454.5 <0.1 1 0.0 0%~~

~~3 12 5.00 90.9 454.5 43.2 1 43.2 10%~~

~~3 27 5.00 90.9 454.5 95.3 1 95.3 21%~~

~~3 42 5.00 90.9 454.5 110.5 1 110.5 24%~~

~~3 57 5.00 90.9 454.5 143.6 1 143.6 32%~~

~~3 87 5.00 90.9 454.5 182.9 1 182.9 40%~~

~~3 124 5.00 90.9 454.5 234.4 1 234.4 52%~~

3 180 5.00 90.9 454.5 249.1 1 249.1 55% Table A2.2 Elution of Copper from Amberlite IRA 900 RF resin (Contd.) Test No. Time Weight Resin Cu Total initial Cu Cu conc. in Solution Cu wt in Elution of of resin loading in resin solution volume solution Cu from (min) (g) (mg/g) (mg) (mg/L) (L) (mg) resin 4 0 5.00 90.9 454.5 <0.1 1 0.0 0%

~~4 15 5.00 90.9 454.5 81.8 1 81.8 18% 4 30 5.00 90.9 454.5 140.9 1 140.9 31% 4 45 5.00 90.9 454.5 186.3 1 186.3 41% 4 60 5.00 90.9 454.5 222.7 1 222.7 49%~~

~~4 93 5.00 90.9 454.5 281.8 1 281.8 62% 4 120 5.00 90.9 454.5 313.6 1 313.6 69% 4 180 5.00 90.9 454.5 354.5 1 354.5 78%~~

~~5 0 5.00 90.9 454.5 <0.1 1 0.0 0%~~

~~5 25 5.00 90.9 454.5 160.0 1 160.0 35%~~

~~5 55 5.00 90.9 454.5 254.6 1 254.6 56% 5 85 5.00 90.9 454.5 331.4 1 331.4 73%~~

~~5 115 5.00 90.9 454.5 370.8 1 370.8 82% 5 180 5.00 90.9 454.5 405.1 1 405.1 89%~~

~~6 0 4.99 90.9 453.6 <0.1 1 0.0 0%~~

~~6 17 4.99 90.9 453.6 159.9 1 159.9 35% 6 37 4.99 90.9 453.6 254.5 1 254.5 56%~~

~~6 57 4.99 90.9 453.6 331.3 1 331.3 73%~~

~~6 97 4.99 90.9 453.6 370.7 1 370.7 82% 6 180 4.99 90.9 453.6 406.2 1 406.2 90%~~

~~7 0 5.00 90.9 454.5 <0.1 1 0.0 0%~~

~~7 16 5.00 90.9 454.5 265.0 1 265.0 58% 7 31 5.00 90.9 454.5 354.5 1 354.5 78%~~

~~7 61 5.00 90.9 454.5 409.1 1 409.1 90%~~

~~7 121 5.00 90.9 454.5 422.9 1 422.9 93% 94% 7 180 5.00 90.9 454.5 426.7 1 426.7 APPENDIX 3~~

Table A3.1 Recovery of cyanide from Amberlite IRA 900 RF resin over 24 hours Test No. Weight of Resin CN" Total initial CN" Total initial CN' Total CN" CN' recovery resin loading in resin in resin recovered efficiency (g) (mg/g) (mg) (moles) (moles) (%) 1 5.01 99 496 0.019 0.0192 101%

~~2 5.00 99 495 0.019 0.0191 101%~~

~~3 5.00 99 495 0.019 0.0180 95%~~

~~4 5.00 99 495 0.019 0.0184 97%~~

~~5 5.00 99 495 0.019 0.0193 102%~~

~~6 4.99 99 494 0.019 0.0187 99%~~

~~7 5.00 99 495 0.019 0.0176 93%~~

Table A3.2 Elution of Cu ^^ from Amberlite IRA 900 RF resin over 24 hours Time Resin Resin Cu Total Cu Cu conc. in Solution Cu wt in Cu eluted from weight loading taken solution volume solution resin (g) (mg/g) (mg) (mg/L) (L) (mg) (%) 0.00 5.00 90.9 454.5 0.0 1 0.0 0%

~~0.20 5.00 90.9 454.5 374.9 1 374.9 82%~~

~~0.45 5.00 90.9 454.5 385.3 1 385.3 85%~~

~~0.97 5.00 90.9 454.5 401.6 1 401.6 88%~~

~~1.45 5.00 90.9 454.5 409.7 1 409.7 90%~~

~~1.95 5.00 90.9 454.5 412.0 1 412.0 91%~~

~~15.77 5.00 90.9 454.5 416.7 1 416.7 92%~~

~~18.77 5.00 90.9 454.5 417.8 1 417.8 92%~~

Table A3.3 Elution of CN" from Amberlite IRA 900 RF resin over 24 hours Time Resin Resin CN- Total CN" Free CN' conc. in Solution CN' wt in Elution ofCN' weight loading taken solution volume solution from resin (g) (mg/g) (mg) (mg/L) (L) (mg) (%) 0.25 5.00 99 495 8.1 2 16.2 3.3%

~~0.50 5.00 99 495 15.7 2 31.5 6.4%~~

~~0.75 5.00 99 495 26.2 2 52.3 10.6%~~

~~1.00 5.00 99 495 37.8 2 75.5 15.3%~~

~~2.00 5.00 99 495 98.6 2 197.1 39.8% 61.1% 4.00 5.00 99 495 151.2 2 302.4 460.4 93.0% 24.00 5.00 99 495 230.2 2 APPENDIX 4~~

~~Table A4.1 Adsorption of mixed metal cyanide species on Purolite A500 resin: Cycle 1 Sample Au Ag Cu Fe Zn Total CN" pH (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)~~

~~Feed 1.23 13.40 356.0 0.52 8.55 420 12.1 Composite Discharge <0.01 2.12 21.1 0.12 0.18 61 11.5 Spot samples~~

~~30 min <0.01 0.03 0.7 0.01 0.12 -~~

~~60 min <0.01 0.16 2.7 0.03 0.06 -~~

~~90 min <0.01 0.02 0.2 0.01 0.06 -~~

~~120 min <0.01 0.05 0.3 0.01 0.06 -~~

~~150 min <0.01 0.15 0.9 0.02 0.06 -~~

~~180 min <0.01 0.45 2.4 0.03 0.06 -~~

~~210 min <0.01 1.65 8.6 0.09 0.08 -~~

~~240 min 0.01 4.30 28.5 0.22 0.12 -~~

~~270 min 0.04 8.41 82.9 0.47 0.24 -~~

~~300 min 0.07 11.10 153.0 0.63 0.40 -~~

~~Table A4.2 Sample Au Ag Cu Fe Zn Total CN" pH (mg/L) (mg/L) (mg/L) (mgA.) (mg/L) (mg/L)~~

~~Feed 1.23 13.40 356.0 0.52 8.55 480 12.4 Composite Discharge 0.02 3.53 26.1 0.19 0.20 78 11.3 Spot samples~~

~~30 min <0.01 0.34 6.5 0.05 0.22 -~~

~~60 min <0.01 0.24 0.9 0.04 0.06 -~~

~~90 min <0.01 0.36 1.3 0.05 0.06 -~~

~~120 min <0.01 0.46 1.5 0.05 0.07 - 150 min <0.01 0.82 3.3 0.07 0.07 -~~

~~180 min <0.01 1.68 7.9 0.11 0.08 -~~

210 min 0.02 3.57 19.7 0.18 0.11 - 240 min 0.05 6.64 41.9 0.33 0.15 - 270 min 0.11 11.60 86.1 0.60 0.23 - 300 min 0.19 15.50 159.0 0.85 0.36 - Table A4.3 Sample Au Ag Cu Fe Zn Total CN- pH (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)

~~Feed 1.23 13.40 356.0 0.52 8.55 450 12.3 Composite Discharge 0.07 5.66 33.0 0.30 0.23 73 11.8 Spot samples~~

~~30 min <0.01 0.44 15.0 0.05 0.19 -~~

~~60 min <0.01 0.40 1.1 0.02 0.07 -~~

~~90 min <0.01 0.66 1.9 0.06 0.06 -~~

~~120 min <0.01 1.19 5.9 0.12 0.07 -~~

~~150 min 0.01 1.41 4.2 0.10 0.07 -~~

~~180 min 0.02 2.66 0.7 0.15 0.08 -~~

~~210 min 0.06 6.16 20.9 0.34 0.11 -~~

~~240 min 0.15 12.90 57.2 0.68 0.17 -~~

~~270 min 0.28 19.80 130.0 1.12 0.30 -~~

~~300 min 0.40 23.00 212.0 1.28 0.45 -~~

~~Table A4.4 Adsorption of mixed metal cyanide species on Purolite A500 resin: Cycle 4 Sample Au Ag Cu Fe Zn Total CN" pH (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)~~

~~Feed 1.01 9.08 272.0 0.31 5.10 458 12.3 Composite Discharge 0.05 3.77 18.4 0.11 <0.01 60 11.5 Spot samples~~

~~30 min <0.01 <0.01 <0.1 <0.01 <0.01 -~~

~~60 min <0.01 0.05 <0.1 <0.01 <0.01 -~~

~~90 min 0.01 0.75 10.6 <0.01 <0.01 -~~

~~120 min <0.01 0.44 <0.1 <0.01 <0.01 -~~

~~150 min <0.01 0.58 <0.1 <0.01 <0.01 -~~

~~180 min <0.01 0.99 0.2 <0.01 <0.01 -~~

~~210 min 0.02 2.47 4.7 0.03 <0.01 -~~

~~240 min 0.05 4.69 10.8 0.08 <0.01 -~~

~~270 min 0.13 9.48 34.8 0.29 <0.01 -~~

~~300 min 0.26 15.70 91.6 0.64 0.02 - Table A4.5 Adsorption of mixed metal cyanide species on Purolite A500 resin: Cycle 5 Sample Au Ag Cu Fe Zn Total CN- PH (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)~~

~~Feed 1.18 10.20 302.0 0.41 6.02 430 12.1 Composite Discharge 0.07 4.67 15.0 0.10 <0.01 58 11.4 Spot samples~~

30 min <0.01 <0.1 <0.01 <0.01 <0.01 60 min <0.01 0.03 <0.01 <0.01 <0.01 90 min 0.01 0.57 6.52 <0.01 <0.01 120 min 0.02 1.02 10.4 <0.01 <0.01 150 min <0.01 0.71 0.3 <0.01 <0.01 180 min 0.01 1.32 1.1 <0.01 <0.01 210 min 0.03 2.68 2.0 <0.01 <0.01 240 min 0.05 4.51 6.8 0.05 <0.01 270 min 0.14 10.10 23.2 0.23 <0.01 300 min 0.30 18.90 59.8 0.60 <0.01

~~Table A4.6 Adsorption of mixed metal cyanide species on Purolite A500 resin: Cycle 6 Sample Au Ag Cu Fe Zn Total CN" pH (mg/L) (mg/L) (mg/L) {mg/L) (mg/L) (mg/L)~~

Feed 1.21 10.30 313.0 0.44 6.07 425 12.2 Composite Discharge 0.16 7.91 27.7 0.18 <0.01 66 11.4 Spot samples 30 min <0.01 <0.01 <0.1 <0.01 <0.01 60 min <0.01 0.11 2.4 <0.01 <0.01 90 min 0.01 0.59 2.8 <0.01 <0.01 120 min 0.01 0.67 <0.1 <0.01 <0.01 150 min 0.01 1.46 0.2 <0.01 <0.01 180 min 0.03 2.96 2.4 <0.01 <0.01 210 min 0.07 4.86 6.9 0.03 <0.01 240 min 0.15 9.36 20.8 0.17 <0.01 270 min 0.31 17.50 48.0 0.46 <0.01 300 min 0.55 26.20 101.0 0.95 <0.01 Table A4.7 Sample Au Ag Cu Fe Zn Total CN" pH (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)

~~Feed 17.40 7.98 245.0 0.27 4.47 320 12.0 Composite Discharge 0.08 1.41 <0.1 <0.01 <0.01 11 11.2 Spot samples~~

30 min <0.01 <0.1 <0.01 <0.01 <0.01 60 min 0.02 0.20 14.60 <0.01 <0.01 90 min <0.01 0.11 <0.01 <0.01 <0.01 120 min <0.01 0.20 <0.01 <0.01 <0.01 150 min 0.01 0.37 <0.01 <0.01 <0.01 180 min 0.01 0.77 <0.01 <0.01 <0.01 210 min 0.02 1.11 <0.01 <0.01 <0.01 240 min 0.05 1.50 <0.01 <0.01 <0.01 270 min 0.11 2.30 <0.01 <0.01 <0.01 300 min 0.26 4.36 2.15 <0.01 <0.01 APPENDIX 5

Table A5.1 Loading/oxidative acid elution cycle specifications Cycles 1 to 30 Resin column volume 10 mL Column orientation Vertical Total run duration 120 min Flow rate of feed, eluent and flush solutions 5 mL/min

~~Loading: Composition, Cu 0 mg/L Composition, CN" 1250 mg/L Composition, Fe (All species) 0 mg/L Composition, NaOH 400 mg/L Solution pH 11.9 units Duration 60 min Flow direction Upwards Volume 300 mL~~

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H:0; 5.0 g/L Composition, H;S04 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL Table A5.2 Strong base capacity measurements Sample Description Test No. Resin volume NO3" Eluent Eluent Cr Resin loading Standard loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result Fresh resin 1 10 500 21.95 1.10 2 10 500 22.28 1.11 3 10 500 22.61 1.13 Average 1.11 0.02

~~Resin after 6 loading 1 10 500 21.67 1.08 /oxidative acid elution 2 10 500 22.14 1.11 cycles 3 10 500 22.42 1.12 Average 1.10 0.02~~

~~Resin after 12 loading 1 10 500 21.86 1.09 /oxidative acid elution 2 10 500 22.19 1.11 cycles 3 10 500 22.47 1.12 Average 1.11 0.02~~

~~Resin after 18 loading 1 10 500 21.81 1.09 /oxidative acid elution 2 10 500 22.28 1.11 cycles 3 10 500 22.56 1.13 Average 1.11 0.02~~

~~Resin after 24 loading 1 10 500 21.95 1.10 /oxidative acid elution 2 10 500 22.38 1.12 cycles 3 10 500 22.61 1.13 Average 1.12 0.02~~

Resin after 30 loading 1 10 500 21.63 1.08 /oxidative acid elution 2 10 500 21.91 1.10 cycles 3 10 500 22.14 1.11 Average 1.09 0.01 Table A5.3 Sample Description Test No. Resin volume NOB" Eluent Eluent Cr Resin loading Standard loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result Fresh resin 1 10 500 21.97 1.10 2 10 500 22.27 1.11 3 10 500 22.22 1.11 Average 1.11 0.01

~~Resin after 6 loading 1 10 500 22.78 1.14 /oxidative acid elution 2 10 500 22.48 1.12 cycles 3 10 500 22.22 1.11 Average 1.12 0.01~~

~~Resin after 12 loading 1 10 500 21.77 1.09 /oxidative acid elution 2 10 500 22.43 1.12 cycles 3 10 500 21.67 1.08 Average 1.10 0.02~~

~~Resin after 18 loading 1 10 500 22.32 1.12 /oxidative acid elution 2 10 500 21.67 1.08 cycles 3 10 500 22.07 1.10 Average 1.10 0.02~~

~~Resin after 24 loading 1 10 500 21.87 1.09 /oxidative acid elution 2 10 500 22.38 1.12 cycles 3 10 500 22.07 1.10 Average 1.11 0.01~~

~~Resin after 30 loading 1 10 500 22.07 1.10 /oxidative acid elution 2 10 500 22.38 1.12 cycles 3 10 500 22.48 1.12 Average 1.12 0.01 APPENDIX 6~~

~~Table A6.1 Column A - Cycle specifications Cycles 1 to 15 Resin column volume 10 mL Column orientation Vertical Total run duration 120 min Flow rate of feed, eluent and flush solutions 5 mL/min~~

~~Loading: Composition, Cu 950 mg/L Composition, CN" 1250 mg/L Composition, Fe (All species) 0 mg/L Composition, NaOH 400 mg/L Solution pH 12.2 units Duration 60 min Flow direction Upwards Volume 300 mL~~

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H2O2 5.0 g/L Composition, H2SO4 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

~~2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL~~

Table A6.2 Column A - Loading results Cycle Comp. discharge (mg/L) Loading on resin Loading on resin Loading (mg) (milli Moles) (mEq/mL) Cu Fe Cu Fe Cu Fe Cu Fe 1 86 <0.1 259 <0.1 4.1 0.815 2 72 <0.1 263 <0.1 4.1 0.829 3 86 <0.1 259 <0.1 4.1 0.815 4 86 <0.1 259 <0.1 4.1 0.815 5 72 <0.1 263 <0.1 4.1 0.829 6 115 <0.1 250 <0.1 3.9 0.788 7 101 <0.1 255 <0.1 4.0 0.802 8 101 <0.1 255 <0.1 4.0 0.802 9 101 <0.1 255 <0.1 4.0 0.802 10 115 <0.1 250 <0.1 3.9 0.788 11 130 <0.1 246 <0.1 3.9 0.775 12 115 <0.1 250 <0.1 3.9 0.788 13 130 <0.1 246 <0.1 3.9 0.775 14 115 <0.1 250 <0.1 3.9 0.788 15 130 <0.1 246 <0.1 3.9 0.775 Table A6.3 Column A - Composite solution from elution, and rinse Cycle Element in solution H2O2 concentration in Elution of element Mass balance for cycle (mg/L) solution (mg) Cu Fe (g/L) Cu Fe Cu Fe 1 860 <0.1 2.6 258 N/A 0% N/A 2 802 <0.1 2.5 241 N/A 9% N/A 3 860 <0.1 2.6 258 N/A 0% N/A 4 826 <0.1 2.5 248 N/A 4% N/A 5 826 <0.1 2.5 248 N/A 6% N/A 6 814 <0.1 2.4 244 N/A 3% N/A 7 814 <0.1 2.4 244 N/A 4% N/A 8 837 <0.1 2.5 251 N/A 1% N/A 9 826 <0.1 2.4 248 N/A 3% N/A 10 802 <0.1 2.4 241 N/A 4% N/A 11 814 <0.1 2.4 244 N/A 1% N/A 12 802 <0.1 2.4 241 N/A 4% N/A 13 872 <0.1 2.3 262 N/A -6% N/A 14 814 <0.1 2.4 244 N/A 3% N/A 15 791 <0.1 2.4 237 N/A 4% N/A

Table A6.4 Column A - Statistical analysis of resin copper loading and elution Cycle Loading Elution Average between loading Standard Deviation between loading (mg) (mg) and elution (mg) and elution (mg) 1 259 258 259 1 2 263 241 252 16 3 259 258 259 1 4 259 248 253 8 5 263 248 256 11 6 250 244 247 4 7 255 244 249 7 8 255 251 253 3 9 255 248 251 5 10 250 241 246 7 11 246 244 245 1 12 250 241 246 7 13 246 262 254 11 14 250 244 247 4 15 246 237 242 6 Table A6.5 Column A - Breakthrough curve data Time Flow Cycle 1 Cycle 5 (min) BV Discharge concentration Discharge concentration

Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 <0.1 3 <0.1 10 5.0 <1 <0.1 9 <0.1 15 7.5 <1 <0.1 14 <0.1 20 10.0 14 <0.1 14 <0.1 25 12.5 28 <0.1 29 <0.1 30 15.0 42 <0.1 29 <0.1 35 17.5 56 <0.1 57 <0.1 40 20.0 84 <0.1 71 <0.1 45 22.5 140 <0.1 100 <0.1 50 25.0 182 <0.1 157 <0.1 55 27.5 238 <0.1 214 <0.1 60 30.0 308 <0.1 286 <0.1

Table A6.6 Column A - Breakthrough curve data (Contd.) Time Flow Cycle 10 Cycle 15 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 <0.1 <1 <0.1 10 5.0 9 <0.1 <1 <0.1 15 7.5 14 <0.1 <1 <0.1 20 10.0 29 <0.1 <1 <0.1 25 12.5 43 <0.1 29 <0.1 30 15.0 58 <0.1 43 <0.1 35 17.5 86 <0.1 86 <0.1 40 20.0 130 <0.1 158 <0.1 45 22.5 201 <0.1 259 <0.1 50 25.0 259 <0.1 360 <0.1 55 27.5 360 <0.1 446 <0.1 60 30.0 432 <0.1 518 <0.1 Table A6.7 Column A - Total base capacity measurements Sample Description Test No. Resin volume NO3" Eluent Eluent CI" Resin loading Standard loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result Fresh resin 1 10 500 22.62 1.13 2 10 500 22.72 1.14 3 10 500 23.48 1.17 Average 1.15 0.02

~~Resin after 12 loading 1 10 500 20.18 1.01 /oxidative acid elution 2 10 500 20.49 1.02 cycles 3 10 500 20.74 1.04 Average 1.02 0.01~~

~~Resin after 15 loading 1 10 500 19.63 0.98 /oxidative acid elution 2 10 500 19.88 0.99 cycles 3 10 500 20.28 1.01 Average 1.00 0.02 APPENDIX 7~~

~~Table A7.1 Cycles 1 to 15 Resin column volume 10 mL Column orientation Vertical Total run duration 120 min Flow rate of feed, eluent and flush solutions 5 mL/min~~

Loading: Composition, Cu 950 mg/L Composition, CN" 1250 mg/L Composition, Fe (Ferrocyanide) 50 mg/L Composition, NaOH 400 mg/L Solution pH 12.1 units Duration 60 min Flow direction Upwards Volume 300 mL

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H2O2 5.0 g/L Composition, H2SO4 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

~~2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL~~

Table A7.2 Column B - Loading results Cycle Comp, discharge Loading on resin Loading on resin Loading on resin (mg/L) (mg) (milli Moles) (milli Moles) Cu Fe Cu Fe Cu Fe Cu Fe 1 139 23.0 243 8.1 3.8 0.15 0.766 0.058 2 222 33.8 218 4.9 3.4 0.09 0.687 0.035 3 278 37.8 202 3.6 3.2 0.07 0.635 0.026 4 319 39.2 189 3.2 3.0 0.06 0.595 0.023 5 347 39.2 181 3.2 2.8 0.06 0.569 0.023 6 403 43.3 164 2.0 2.6 0.04 0.517 0.015 7 403 41.9 164 2.4 2.6 0.04 0.517 0.017 8 417 41.9 160 2.4 2.5 0.04 0.504 0.017 9 403 40.5 164 2.8 2.6 0.05 0.517 0.020 10 444 43.3 152 2.0 2.4 0.04 0.477 0.015 0.04 0.504 11 417 41.9 160 2.4 2.5 0.017 2.4 0.04 0.477 12 444 43.3 152 2.0 0.015 2.4 0.04 0.477 0.015 13 444 43.3 152 2.0 2.3 0.03 0.451 0.012 14 472 44.6 143 1.6 1.6 2.2 0.03 0.438 0.012 15 486 44.6 139 Table A7.3 Column B - Composite solution from elution, and rinse Cycle Element in solution H2O2 concentration Elution of element Mass balance for cycle (mg/L) in solution (mg) Cu Fe (g/L) Cu Fe Cu Fe 1 758 <0.1 2.8 228 N/A 7% N/A 2 736 <0.1 2.9 221 N/A -1% N/A 3 613 <0.1 2.9 184 N/A 9% N/A 4 602 <0.1 2.8 181 N/A 5% N/A 5 558 <0.1 2.9 167 N/A 8% N/A 6 535 <0.1 2.9 161 N/A 2% N/A 7 513 <0.1 3.0 154 N/A 6% N/A 8 546 <0.1 3.0 164 N/A -2% N/A 9 539 <0.1 3.0 162 N/A 2% N/A 10 513 <0.1 3.0 154 N/A -1% N/A 11 480 <0.1 3.0 144 N/A 10% N/A 12 468 <0.1 2.8 141 N/A 7% N/A 13 446 <0.1 3.2 134 N/A 12% N/A 14 468 <0.1 3.0 141 N/A 2% N/A 15 457 <0.1 2.9 137 N/A 1% N/A

Table A7.4 Column B - Statistical analysis of resin copper loading and elution Cycle Loading Elution Average between loading Standard Deviation between loading (mg) (mg) and elution (mg) and elution (mg) 1 243 228 235 11 2 218 221 220 2 3 202 184 193 12 4 189 181 185 6 5 181 167 174 10 6 164 161 162 3 7 164 154 159 7 8 160 164 162 3 9 164 162 163 2 10 152 154 153 2 11 160 144 152 11 12 152 141 146 8 13 152 134 143 13 14 143 141 142 2 15 139 137 138 1 Table A7.5 Column B -Breakthrough curve data Time Flow Cycle 1 Cycle 5 (min) BV Discharge concentration Discharge concentration

Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 3.0 54 12.0 10 5.0 <1 3.0 95 22.0 15 7.5 27 5.0 162 33.0 20 10.0 40 10.0 230 39.0 25 12.5 67 14.0 311 46.0 30 15.0 107 22.0 419 49.0 35 17.5 148 30.0 460 50.0 40 20.0 201 35.0 514 51.0 45 22.5 255 41.0 527 51.0 50 25.0 309 46.0 554 51.0 55 27.5 376 50.0 554 50.0 60 30.0 416 51.0 581 51.0

Table A7.6 Column B -Breakthrough curve data (Contd.) Time Flow Cycle 10 Cycle 15 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 69 15.0 83 17.0 10 5.0 111 24.0 181 29.0 15 7.5 208 37.0 264 37.0 20 10.0 319 45.0 361 44.0 25 12.5 417 49.0 458 48.0 30 15.0 514 52.0 542 49.0 35 17.5 583 53.0 611 52.0 40 20.0 639 54.0 694 55.0 45 22.5 666 54.0 708 55.0 50 25.0 694 54.0 736 53.0 55 27.5 694 54.0 750 55.0 60 30.0 736 56.0 764 56.0 Table A7.7 Column B - Total base capacity measurements Sample Description Test No. Resin volume NO," Eluent Eluent Cr Resin loading Standard loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result Fresh resin 1 10 500 22.06 1.10 2 10 500 22.42 1.12 3 10 500 23.02 1.15 Average 1.13 0.02

~~Resin after 12 loading 1 10 500 19.63 0.98 /oxidative acid elution 2 10 500 20.03 1.00 cycles 3 10 500 20.33 1.02 Average 1.00 0.02~~

~~Resin after 15 loading 1 10 500 18.82 0.94 /oxidative acid elution 2 10 500 19.27 0.96 cycles 3 10 500 19.78 0.99 Average 0.96 0.02 APPENDIX 8~~

~~Table A8.1 Column C - Cycle specifications Cycles 1 to 15 Resin column volume 10 mL Column orientation Vertical Total run duration 120 min Flow rate of feed, eluent and flush solutions 5 mL/min~~

Loading: Composition, Cu 950 mg/L Composition, CN" 1250 mg/L Composition, Fe (Ferricyanide) 50 mg/L Composition, NaOH 400 mg/L Solution pH 12.1 units Duration 60 min Flow direction Upwards Volume 300 mL

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H2O2 5.0 g/L Composition, H2SO4 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

~~2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL~~

Table A8.2 Column C - Loading results Cycle Comp, discharge Loading on resin Loading on resin Loading (mg/L) (mg) (milli Moles) (mEq/mL) Cu Fe Cu Fe Cu Fe Cu Fe 1 140 22.3 243 8.3 3.8 0.15 0.765 0.045 2 210 33.4 222 5.0 3.5 0.09 0.699 0.027 3 294 37.6 197 3.7 3.1 0.07 0.620 0.020 4 350 40.3 180 2.9 2.8 0.05 0.567 0.016 5 378 41.7 172 2.5 2.7 0.04 0.540 0.013 6 392 41.7 168 2.5 2.6 0.04 0.527 0.013 7 406 41.7 163 2.5 2.6 0.04 0.514 0.013 8 434 43.1 155 2.1 2.4 0.04 0.488 0.011 9 434 41.7 155 2.5 2.4 0.04 0.488 0.013 10 434 41.7 155 2.5 2.4 0.04 0.488 0.013 11 462 43.1 147 2.1 2.3 0.04 0.461 0.011 12 481 29.2 141 6.2 2.2 0.11 0.443 0.034 0.03 0.435 0.009 13 490 44.5 138 1.6 2.2 2.2 0.03 0.448 0.009 14 476 44.5 142 1.6 2.2 0.03 0.435 0.009 15 490 44.5 138 1.6 Table A8.3 Column C - Composite solution from eiution, and rinse Cycle Element in solution H2O2 concentration Elution of element Mass balance for cycle (mg/L) in solution (mg) Cu Fe (g/L) Cu Fe Cu Fe 1 768 <0.1 2.8 230 N/A 5% N/A 2 688 <0.1 2.7 206 N/A 7% N/A 3 630 <0.1 2.8 189 N/A 4% N/A 4 596 <0.1 2.9 179 N/A 1% N/A 5 585 <0.1 2.9 175 N/A -2% N/A 6 585 <0.1 2.9 175 N/A -5% N/A 7 516 <0.1 3.0 155 N/A 5% N/A 8 527 <0.1 3.0 158 N/A -2% N/A 9 493 <0.1 2.9 148 N/A 5% N/A 10 470 <0.1 3.0 141 N/A 9% N/A 11 481 <0.1 3.0 144 N/A 1% N/A 12 470 <0.1 2.9 141 N/A 0% N/A 13 493 <0.1 2.9 148 N/A -7% N/A 14 436 <0.1 2.9 131 N/A 8% N/A 15 458 <0.1 2.9 138 N/A 0% N/A

Table A8.4 Column C - Statistical analysis of resin copper loading and elution Cycle Loading Elution Average between loading Standard Deviation between loading (mg) (mg) and elution (mg) and elution (mg) 1 243 230 237 9 2 222 206 214 11 3 197 189 193 5 4 180 179 179 1 5 172 175 174 3 6 168 175 171 6 7 163 155 159 6 8 155 158 157 2 9 155 148 151 5 10 155 141 148 10 11 147 144 145 1 12 141 141 141 0 13 138 148 143 7 14 142 131 136 8 15 138 138 138 0 Table A8.5 Column C - Breakthrough curve data Time Flow Cycle 1 Cycle 5 (mm) BV Discharge concentration Discharge concentration

Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 <0.1 69 16.4 10 5.0 14 <0.1 111 26.0 15 7.5 27 1.3 194 35.5 20 10.0 41 2.6 264 41.0 25 12.5 55 7.8 347 45.1 30 15.0 96 19.0 403 46.5 35 17.5 123 25.8 472 47.8 40 20.0 178 34.0 528 50.6 45 22.5 233 42.1 555 50.6 50 25.0 288 47.6 583 51.9 55 27.5 370 50.3 611 51.9 60 30.0 411 51.6 611 51.9

Table A8.6 Column C - Breakthrough curve data (Contd.) Time Flow Cycle 10 Cycle 15 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 70 15.1 57 <0.1 10 5.0 113 23.4 143 26.9 15 7.5 211 34.4 257 39.6 20 10.0 324 42.6 357 43.9 25 12.5 422 46.7 471 49.5 30 15.0 507 49.5 557 50.9 35 17.5 591 52.2 628 52.4 40 20.0 634 52.2 686 55.2 45 22.5 662 52.2 714 55.2 50 25.0 690 53.6 743 55.2 55 27.5 718 55.0 771 58.0 60 30.0 718 53.6 785 58.0 Table A8.7 Column C - Total base capacity measurements Sample Description Test No. Resin volume NOs" Eluent Eluent Cr Resin loading Standard loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result Fresh resin 1 10 500 22.06 1.10 2 10 500 22.42 1.12 3 10 500 22.62 1.13 Average 1.12 0.01

~~Resin after 12 loading 1 10 500 19.47 0.97 /oxidative acid elution 2 10 500 20.13 1.01 cycles 3 10 500 20.38 1.02 Average 1.00 0.02~~

~~Resin after 15 loading 1 10 500 19.47 0.97 /oxidative acid elution 2 10 500 19.78 0.99 cycles 3 10 500 20.44 1.02 Average 0.99 0.02 APPENDIX 9~~

~~Table A9.1 Column D - Cycle specifications Cycle 1 to 15 Resin column volume 10 mL Column orientation Vertical Total run duration 120 mm Flow rate of feed, eluent and flush solutions 5 mL/min~~

Loading: Composition, Cu 950 mg/L Composition, CN" 1250 mg/L Composition, Fe (Ferrocyanide) 25 mg/L Composition, NaOH 400 mg/L Solution pH 12.1 units Duration 60 min Flow direction Upwards Volume 300 mL

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H2O2 5.0 g/L Composition, H2SO4 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

~~2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL~~

Table A9.2 Column D - Loading results Cycle Comp, discharge Loading on resin Loading on resin Loading (mg/L) (mg) (milli Moles) (mEq/mL) Cu Fe Cu Fe Cu Fe Cu Fe 1 157 12.9 238 3.6 3.7 0.07 0.748 0.026 2 143 14.3 242 3.2 3.8 0.06 0.762 0.023 3 157 15.7 238 2.8 3.7 0.05 0.748 0.020 4 172 17.2 234 2.4 3.7 0.04 0.735 0.017 5 227 20.0 217 1.5 3.4 0.03 0.683 0.011 6 234 18.6 215 1.9 3.4 0.03 0.676 0.014 7 257 20.0 208 1.5 3.3 0.03 0.654 0.011 8 231 20.0 216 1.5 3.4 0.03 0.679 0.011 9 272 20.0 203 1.5 3.2 0.03 0.640 0.011 10 270 20.0 204 1.5 3.2 0.03 0.642 0.011 11 329 22.9 186 0.6 2.9 0.01 0.586 0.005 12 315 20.0 191 1.5 3.0 0.03 0.600 0.011 0.02 13 325 21.5 188 1.1 3.0 0.590 0.008 14 358 22.9 178 0.6 2.8 0.01 0.559 0.005 2.9 0.02 0.573 0.008 15 343 21.5 182 1.1 Table A9.3 Column D - Composite solution from elution, and rinse Cycle Element in solution H2O2 concentration Elution of element Mass balance for cycle (mg/L) in solution (mg) Cu Fe (g/L) Cu Fe Cu Fe 1 835 <0.1 2.7 250 N/A -5% N/A 2 847 <0.1 2.7 254 N/A -5% N/A 3 835 <0.1 2.7 250 N/A -5% N/A 4 787 <0.1 2.7 236 N/A -1% N/A 5 738 <0.1 2.7 221 N/A -2% N/A 6 738 <0.1 2.7 221 N/A -3% N/A 7 726 <0.1 2.7 218 N/A -5% N/A 8 738 <0.1 2.7 221 N/A -3% N/A 9 702 <0.1 2.7 211 N/A -3% N/A 10 714 <0.1 2.7 214 N/A -5% N/A 11 617 <0.1 2.7 185 N/A 1% N/A 12 629 <0.1 2.7 189 N/A 1% N/A 13 653 <0.1 2.7 196 N/A -5% N/A 14 617 <0.1 2.7 185 N/A -4% N/A 15 629 <0.1 2.7 189 N/A -4% N/A

Table A9.4 Column D - Statistical anlalysi s of resin copper loading and elution Cycle Loading Elution Average between loading Standard Deviation between loading (mg) (mg) and elution (mg) and elution (mg) 1 238 250 244 9 2 242 254 248 8 3 238 250 244 9 4 234 236 235 2 5 217 221 219 3 6 215 221 218 5 7 208 218 213 7 8 216 221 219 4 9 203 211 207 5 10 204 214 209 7 11 186 185 186 1 12 191 189 190 1 13 188 196 192 6 14 178 185 181 5 15 182 189 185 5 Table A9.5 Column D - Breakthrough curve data Time Flow Cycle 1 Cycle 5 (min) BV Discharge concentration Discharge concentration

Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 <0.1 10 4.2 10 5.0 <1 <0.1 17 5.7 15 7.5 <1 1.4 57 7.2 20 10.0 <1 2.9 86 8.0 25 12.5 29 7.2 143 12.6 30 15.0 86 12.9 215 18.7 35 17.5 157 18.6 315 24.4 40 20.0 243 22.9 400 28.1 45 22.5 315 25.7 458 32.9 50 25.0 400 27.2 515 34.3 55 27.5 458 28.6 558 34.3 60 30.0 486 27.2 601 34.3

Table A9.6 Column D - Breakthrough curve data (Contd.) Time Flow Cycle 10 Cycle 15 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 13 4.3 7 2.9 10 5.0 43 5.7 14 2.9 15 7.5 72 7.2 29 4.3 20 10.0 114 10.0 86 8.6 25 12.5 172 15.7 172 17.2 30 15.0 257 21.5 329 28.6 35 17.5 358 28.6 458 34.3 40 20.0 458 32.9 615 38.6 45 22.5 543 35.8 672 38.6 50 25.0 615 35.8 729 38.6 55 27.5 637 35.8 758 37.2 60 30.0 658 35.8 758 35.8 APPENDIX 10

~~Table AlO.l Column E - Cycle specifications Cycle 1 to 15 Resin column volume 10 mL Column orientation Vertical Total run duration 120 min Flow rate of feed, eluent and flush solutions 5 mL/min~~

Loading: Composition, Cu 950 mg/L Composition, CN" 1250 mg/L Composition, Fe (Ferricyandie) 25 mg/L Composition, NaOH 400 mg/L Solution pH 8.5 units Duration 60 min Flow direction Upwards Volume 300 mL

~~1st rinse Duration 5 min Flow direction Upwards Volume 25 mL~~

~~Elution Duration 40 min Composition, H2O2 5.0 g/L Composition, H2SO4 50 g/L Solution pH <1 units Flow direction Upwards Volume 200 mL~~

~~2nd rinse Duration 15 min Flow direction Upwards Volume 75 mL~~

Table A10.2 Column E - Loading results Cycle Comp, discharge Loading on resin Loading on resin Loading (mg/L) (mg) (milli Moles) (mEq/mL) Cu Fe Cu Fe Cu Fe Cu Fe 1 94 9.1 257 4.8 4.0 0.09 0.808 0.034 2 188 16.9 229 2.4 3.6 0.04 0.719 0.017 3 242 18.2 212 2.0 3.3 0.04 0.669 0.015 4 282 19.5 200 1.7 3.2 0.03 0.631 0.012 5 228 18.2 216 2.0 3.4 0.04 0.681 0.015 6 255 18.2 208 2.0 3.3 0.04 0.656 0.015 7 296 20.8 196 1.3 3.1 0.02 0.618 0.009 8 296 19.5 196 1.7 3.1 0.03 0.618 0.012 0.04 9 282 18.2 200 2.0 3.2 0.631 0.015 3.2 0.03 0.631 0.012 10 282 19.5 200 1.7 2.9 0.02 0.580 0.009 11 336 20.8 184 1.3 2.8 0.02 0.567 0.009 12 349 20.8 180 1.3 3.0 0.02 0.592 0.009 13 322 20.8 188 1.3 2.8 0.02 0.567 0.009 14 349 20.8 180 1.3 1.3 2.9 0.02 0.580 0.009 15 336 20.8 184 Table A10.3 Column E - Composite solution from elution, I'^and rinse Cycle Element in solution H2O2 concentration Elution of element Mass balance for cycle (mg/L) in solution (mg) Cu Fe (g/L) Cu Fe Cu Fe 1 816 <0.1 2.9 245 N/A 5% N/A 2 749 <0.1 2.8 225 N/A 2% N/A 3 715 <0.1 2.8 215 N/A -1% N/A 4 682 <0.1 3.0 205 N/A -2% N/A 5 715 <0.1 2.8 215 N/A 1% N/A 6 715 <0.1 3.0 215 N/A -3% N/A 7 671 <0.1 3.0 201 N/A -2% N/A 8 663 <0.1 2.9 199 N/A -1% N/A 9 674 <0.1 2.8 202 N/A -1% N/A 10 685 <0.1 2.9 206 N/A -3% N/A 11 596 <0.1 2.9 179 N/A 3% N/A 12 652 <0.1 2.9 196 N/A -9% N/A 13 618 <0.1 2.9 185 N/A 2% N/A 14 629 <0.1 3.0 189 N/A -5% N/A 15 607 <0.1 3.0 182 N/A 1% N/A

~~Table A10.4 Column E - Statistical analysis of resin copper loading and elution Cycle Loading Elution Average between loading Standard Deviation between loading~~

1 257 245 251 9 2 229 225 227 3 3 212 215 214 2 4 200 205 202 3 5 216 215 216 1 6 208 215 211 4 7 196 201 199 3 8 196 199 198 2 9 200 202 201 1 10 200 206 203 4 11 184 179 181 4 12 180 196 188 11 13 188 185 187 2 14 180 189 184 6 15 184 182 183 2 Table A10.5 Column E - Breakthrough curve data Time Flow Cycle 1 Cycle 5 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 <1 1.3 26 10.4 10 5.0 <1 2.6 46 13.0 15 7.5 13 2.6 80 13.0 20 10.0 27 2.6 159 16.9 25 12.5 40 5.2 199 19.5 30 15.0 53 5.2 239 20.8 35 17.5 80 9.1 292 22.1 40 20.0 107 11.7 345 23.4 45 22.5 133 14.3 371 23.4 50 25.0 187 18.2 411 23.4 55 27.5 254 20.8 451 24.7 60 30.0 307 23.4 477 26.0

Table A10.6 Column E - Breakthrough curve data (Contd.) Time Flow Cycle 10 Cycle 15 (min) BV Discharge concentration Discharge concentration (mg/L) (mg/L) Cu Fe Cu Fe 0 0.0 <1 <0.1 <1 <0.1 5 2.5 27 7.8 40 9.1 10 5.0 54 10.4 54 11.7 15 7.5 94 13.0 81 14.3 20 10.0 148 15.6 188 16.9 25 12.5 215 18.2 242 19.5 30 15.0 282 20.8 336 22.1 35 17.5 349 23.4 417 23.4 40 20.0 417 24.7 484 24.7 45 22.5 484 26.0 578 27.3 50 25.0 537 27.3 632 28.6 55 27.5 578 28.6 685 29.9 60 30.0 618 28.6 712 29.9 APPENDIX 11

Table All.l Cycle 1 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.78 mg/L Ag 8.42 mg/L Cu 56 mg/L Fe <0.01 mg/L Zn 0.14 mg/L CNTOT 48 mg/L Solution pH 11.2 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 mVhr Base metal elution Duration 3.5 hrs Composition, H2O2 1.86 g/L Composition, H2SO4 20.9 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 1 hrs Flow direction Upwards Flow rate 10 m^/hr

~~Table A11.2 Pilot Plant breakthrough curve data - Cycle 1 Time Flow Concentration in discharge (mg/L)~~

(hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 <0.01 <0.01 <0.1 <0.1 <0.1 1 25 <0.01 <0.01 <0.1 <0.1 <0.1 2 50 <0.01 <0.01 <0.1 <0.1 <0.1 3 75 <0.01 <0.01 <0.1 <0.1 <0.1 4 100 <0.01 <0.01 <0.1 <0.1 <0.1 5 125 <0.01 <0.01 <0.1 <0.1 <0.1 6 150 <0.01 <0.01 <0.1 <0.1 <0.1 7 175 <0.01 <0.01 <0.1 <0.1 <0.1 8 200 <0.01 <0.01 <0.1 <0.1 <0.1 9 225 <0.01 <0.01 <0.1 <0.1 <0.1 10 250 <0.01 <0.01 <0.1 <0.1 <0.1 11 275 <0.01 <0.01 <0.1 <0.1 <0.1 12 300 <0.01 <0.01 <0.1 <0.1 <0.1 13 325 <0.01 <0.01 <0.1 <0.1 <0.1 14 350 <0.01 <0.01 <0.1 <0.1 <0.1 15 375 <0.01 <0.01 <0.1 <0.1 <0.1 16 400 <0.01 0.10 <0.1 <0.1 <0.1 <0.1 <0.1 17 425 <0.01 0.28 <0.1 <0.1 <0.1 18 450 <0.01 0.50 <0.1 <0.1 <0.1 <0.1 19 475 <0.01 0.82 <0.1 <0.1 <0.1 20 500 <0.01 1.17 <0.1 <0.1 1.03 Composite <0.01 0.14 <0.1 Table Al 1.3 Base metal elution and rinse solution specifications - Cycle 1 Time* Eluent Feed concentration Discharge concentration (min) flow H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (BV) (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 - <0.01 <0.1 <0.1 <0.1 <0.1 <0.01 <0.1 10 0.8 - - <0.01 <0.1 <0.1 <0.1 <0.1 <0.01 <0.1 20 1.7 - - <0.01 <0.1 <0.1 <0.1 <0.1 <0.01 <0.1 30 2.5 2.30 19.6 <0.01 2.4 <0.1 <0.1 <0.1 <0.01 <0.1 40 3.3 2.25 21.2 <0.01 2.8 400 0.4 <0.1 0.10 0.6 50 4.2 2.20 20.4 <0.01 3.6 760 1.8 <0.1 0.15 0.8 60 5.0 1.95 19.2 <0.01 3.6 1220 12.2 29.7 0.10 6.4 70 5.8 1.70 18.8 <0.01 4.3 2640 8.8 38.0 0.05 12.8 80 6.7 1.70 19.2 <0.01 6.8 2810 6.9 34.4 0.05 14.4 90 7.5 1.80 20.4 <0.01 10.4 2930 5.7 29.2 0.10 15.6 100 8.3 1.85 21.6 <0.01 8.7 3020 4.9 24.1 0.05 17.2 110 9.2 1.75 21.2 <0.01 12.8 3110 4.2 20.9 0.05 17.6 120 10.0 1.65 21.2 <0.01 16.9 3100 3.7 18.8 0.10 19.6 130 10.8 1.65 20.8 <0.01 12.9 2920 3.2 16.8 0.10 20.0 140 11.7 1.65 20.8 <0.01 4.4 2600 2.9 15.0 0.15 20.0 150 12.5 1.70 21.2 <0.01 16.2 2190 2.7 13.4 0.40 20.4 160 13.3 1.75 21.2 <0.01 9.1 1800 <0.1 12.0 0.80 20.4 170 14.2 1.80 21.6 <0.01 0.8 1530 2.7 10.2 0.90 22.0 180 15.0 1.80 21.6 <0.01 2.7 1230 2.6 8.8 1.15 20.8 190 15.8 1.90 22.0 <0.01 3.5 832 2.4 8.0 1.30 20.8 200 16.7 1.80 22.0 <0.01 4.3 554 2.4 6.8 1.30 21.2 210 17.5 1.90 21.6 <0.01 5.3 334 2.2 5.8 1.40 21.2 220 18.3 1.95 21.6 <0.01 2.9 206 1.8 5.1 1.45 21.2 230 19.2 2.00 22.0 <0.01 3.5 133 0.9 4.5 1.60 21.6 240 20.0 - - <0.01 2.0 89 0.6 3.8 1.65 21.6 250 20.8 - - <0.01 0.4 51 0.5 2.8 1.20 18.4 260 21.7 - - <0.01 0.2 31 0.4 2.2 0.70 10.0 270 22.5 - - <0.01 0.1 18 0.3 1.7 0.35 7.2 280 23.3 - - <0.01 <0.1 11 0.2 1.4 0.20 5.2 290 24.2 - - <0.01 <0.1 7 0.2 1.2 0.10 4.0 300 25.0 - - <0.01 <0.1 4 0.1 0.9 0.08 3.0

~~Table A11.4 Calculation of elution performance - Cycle 1 rinse Base metal elution 2nd rinse Total elution~~

Duration (hrs) 0.50 3.50 1.00 5.00 Flow rate (m^/hr) 10 10 10 10 Volume (m^) 5.0 35.0 10.0 50.0 Average H2O2 in feed (g/L) 0.00 1.86 0.00 1.30 Average H2SO4 in feed (g/L) 0.0 20.9 0.0 14.6 Total H2O2 in feed (kg) 0 65 0 65 Total H2SO4 in feed (kg) 0 732 0 732 Average H2O2 in discharge (g/L) 0.00 0.54 0.70 0.52 Average H2SO4 in discharge (g/L) 0.0 15.9 11.1 13.4 Average Cu in discharge (g/L) 0.00 1.63 0.03 1.15 Total H2O2 in discharge (kg) 0 19 7 26 111 668 Total H2SO4 in discharge (kg) 0 558 Total Cu in discharge (kg) 0 57 0 58 -7 Total H2O2 consumption (kg) 0 46 39 174 -111 64 H2SO4 consumption (kg) 0 0 Cu eluted from resin (kg) 0 57 58 Table Al 1.5 Pilot Plant operating conditions and results - Cycle 2 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.85 mg/L Ag 9.41 mg/L Cu 55.7 mg/L Fe <0.01 mg/L Zn 0.02 mg/L

CNTOT 45.9 mg/L Solution pH 11.0 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 2.75 hrs Composition, H2O2 1.8 g/L Composition, H2SO4 20.6 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 1.75 hrs Flow direction Upwards Flow rate 10 m^/hr

Table A11.6 Pilot Plant breakthrough curve data - Cycle 2 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 <0.01 0.03 <0.1 0.04 3 1 25 <0.01 0.33 <0.1 <0.1 <0.1 2 50 <0.01 0.26 <0.1 <0.1 <0.1 3 75 <0.01 0.31 <0.1 <0.1 <0.1 4 100 <0.01 0.31 <0.1 <0.1 <0.1 5 125 <0.01 0.30 <0.1 <0.1 <0.1 6 150 <0.01 0.33 <0.1 <0.1 <0.1 7 175 <0.01 0.34 <0.1 <0.1 <0.1 8 200 <0.01 0.34 <0.1 <0.1 <0.1 9 225 <0.01 0.34 <0.1 <0.1 <0.1 10 250 <0.01 0.36 <0.1 <0.1 <0.1 11 275 <0.01 0.42 <0.1 <0.1 <0.1 <0.1 12 300 <0.01 0.53 <0.1 <0.1 <0.1 <0.1 13 325 <0.01 0.68 <0.1 <0.1 <0.1 14 350 <0.01 0.94 <0.1 <0.1 <0.1 <0.1 15 375 <0.01 0.13 <0.1 <0.1 <0.1 16 400 <0.01 1.79 <0.1 <0.1 <0.1 17 425 <0.01 2.33 <0.1 <0.1 <0.1 18 450 <0.01 3.15 <0.1 <0.1 <0.1 19 475 <0.01 4.33 4.24 <0.1 <0.1 <0.1 20 500 <0.01 1.04 <0.1 0.002 0.14 1.8 Composite <0.01 Table Al 1.7 Base metal elution and rinse solution Eluent Feed concentration Time Discharge concentration flow (min) H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 - <0.01 <0.1 <0.1 <0.1 <0.1 <0.01 <0.1 15 1.3 - 0.10 8.0 2.0 0.5 0.2 <0.01 <0.1 30 2.5 1.90 21.2 <0.01 5.3 <0.1 0.2 <0.1 <0.01 <0.1 45 3.8 1.80 20.0 <0.01 1.0 <0.1 1.5 <0.1 <0.01 0.8 60 5.0 1.60 20.0 <0.01 6.8 840 16.7 31.4 <0.01 6.0 75 6.3 1.65 20.8 <0.01 4.0 2880 6.3 26.7 <0.01 14.4 90 7.5 1.65 20.4 <0.01 3.9 3240 3.7 18.3 <0.01 18.0 105 8.8 1.60 20.8 <0.01 8.7 3140 2.8 12.8 <0.01 19.2 120 10.0 1.60 20.8 <0.01 10.0 2960 2.6 9.5 <0.01 18.8 135 11.3 1.45 20.4 <0.01 16.8 2670 2.3 7.4 <0.01 19.6 150 12.5 1.70 20.4 <0.01 11.0 2260 2.2 5.3 0.2 20.0 165 13.8 2.10 20.8 <0.01 9.9 1800 2.0 3.7 0.55 19.6 180 15.0 2.05 20.8 <0.01 <0.1 1030 1.9 1.7 1.35 20.8 195 16.3 - <0.01 2.5 294 1.9 0.1 1.85 20.0 210 17.5 - <0.01 1.6 122 3.2 1.4 1.8 18.8 225 18.8 - <0.01 <0.1 64.0 0.9 <0.1 0.8 12.8 240 20.0 - <0.01 <0.1 28.0 0.4 <0.1 0.3 6.2 255 21.3 - <0.01 0.1 19.0 0.4 0.4 0.1 4.2 270 22.5 - <0.01 <0.1 8.0 0.9 0.2 <0.01 3.0 285 23.8 - <0.01 <0.1 4.0 0.2 0.1 <0.01 2.2 300 25.0 - <0.01 <0.1 1.0 0.1 0.1 <0.01 1.8

Table Al 1.8 Calculation of elution performance - Cycle 2 1st rinse Base metal elution 2nd rinse Total elution Duration (hrs) 0.50 2.75 1.75 5.00 Flow rate (m^/hr) 10 10 10 10 Volume (m^) 5.0 27.5 17.5 50.0 Average H2O2 in feed (g/L) 0.00 1.74 0.00 0.96 Average H2SO4 in feed (g/L) 0.0 20.6 0.0 11.3 Total H2O2 in feed (kg) 0 48 0 48 Total H2SO4 in feed (kg) 0 566 0 566 Average H2O2 in discharge (g/L) 0.00 0.19 0.69 0.35 Average H2SO4 in discharge (g/L) 0.0 14.3 9.6 11.2 Average Cu in discharge (g/L) 0.01 1.89 0.08 1.07 Total H2O2 in discharge (kg) 0 5 12 17 Total H2SO4 in discharge (kg) 0 393 168 561 Total Cu in discharge (kg) 0 52 1 53 Total H2O2 consumption (kg) 0 43 -12 30 H2SO4 consumption (kg) 0 173 -168 5 Cu eluted from resin (kg) 0 52 1 53 Table Al 1.9

Cycle 3 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.84 mg/L Ag 9.16 mg/L Cu 54.6 mg/L Fe <0.01 mg/L Zn 0.01 mg/L CNTOT 44.8 mg/L Solution pH 11.5 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 2.75 hrs Composition, H2O2 1.78 g/L Composition, H2SO4 18.8 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 1.75 hrs Flow direction Upwards Flow rate 10 m^/hr

Table All.lO Pilot Plant breakthrough curve data - Cycle 3 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 <0.01 0.13 0.9 0.1 2.5 1 25 <0.01 0.26 <0.1 <0.1 <0.1 2 50 <0.01 0.13 <0.1 <0.1 <0.1 3 75 <0.01 0.14 <0.1 <0.1 <0.1 4 100 <0.01 0.15 <0.1 <0.1 <0.1 5 125 <0.01 0.15 <0.1 <0.1 <0.1 6 150 <0.01 0.15 <0.1 <0.1 <0.1 7 175 <0.01 0.14 <0.1 <0.1 <0.1 8 200 <0.01 0.16 <0.1 <0.1 <0.1 9 225 <0.01 0.18 <0.1 <0.1 <0.1 10 250 <0.01 0.24 <0.1 <0.1 <0.1 11 275 <0.01 0.35 <0.1 <0.1 <0.1 12 300 <0.01 0.53 <0.1 <0.1 <0.1 13 325 <0.01 0.76 <0.1 <0.1 <0.1 14 350 <0.01 0.95 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 15 375 <0.01 1.42 2.14 <0.1 <0.1 <0.1 16 400 <0.01 2.86 <0.1 <0.1 <0.1 17 425 <0.01 3.89 <0.1 <0.1 <0.1 18 450 <0.01 4.96 <0.1 <0.1 <0.1 19 475 <0.01 6.03 <0.1 <0.1 <0.1 20 500 <0.01 0.04 0.00 0.12 Composite <0.01 1.23 1.5 Table All.11 Base metal eiution and rinse solution specifications - Cycle 3 Time Eluent Feed concentration Discharge concentration (min) flow H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (BV) (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 0.50 12.5 20 2.4 1.0 <0.01 <0.1 15 1.3 - - 0.20 13.1 <0.1 0.5 <0.1 <0.01 <0.1 30 2.5 2.50 16.8 0.20 9.3 <0.1 0.1 <0.1 <0.01 <0.1 45 3.8 2.05 20.6 <0.01 1.6 <0.1 0.3 <0.1 <0.01 <0.1 60 5.0 2.30 20.4 <0.01 2.2 788 1.5 1.7 <0.01 4.8 75 6.3 1.65 17.8 <0.01 0.3 2073 0.8 2.0 <0.01 10.8 90 7.5 1.45 17.6 <0.01 0.2 3241 0.5 1.5 <0.01 14.0 105 8.8 1.60 18.8 <0.01 0.2 4066 0.4 1.2 <0.01 16.0 120 10.0 1.65 18.4 <0.01 0.3 4038 0.2 0.9 <0.01 16.8 135 11.3 1.55 18.4 <0.01 0.1 3385 0.2 0.7 0.40 16.8 150 12.5 1.60 19.2 <0.01 0.1 2814 0.2 0.5 0.50 17.6 165 13.8 1.60 18.8 <0.01 0.1 1200 0.2 0.4 0.70 18.4 180 15.0 1.65 19.6 <0.01 0.1 621 0.2 0.2 0.90 18.4 195 16.3 - - 0.10 3.0 782 2.0 3.0 1.15 18.4 210 17.5 - - 0.10 1.9 417 2.1 2.0 1.30 19.4 225 18.8 - - 0.10 2.8 158 1.6 1.4 1.20 18.4 240 20.0 - - <0.01 2.6 80 0.6 1.0 0.25 7.4 255 21.3 - - <0.01 2.4 123 0.4 0.4 0.10 4.2 270 22.5 - - <0.01 1.8 27 0.2 0.3 0.03 2.8 285 23.8 - - <0.01 1.1 49 0.2 0.1 <0.01 2.0

~~300 25.0 - - <0.01 1.8 43 0.2 0.1 <0.01 1.6~~

Table Al 1.12 Calculation of eiution performance - Cycle 3 V^ rinse Base metal eiution rinse Total eiution Duration (hrs) 0.50 2.75 1.75 5.00 Flow rate (m^/hr) 10 10 10 10 Volume (m^) 5.0 27.5 17.5 50.0 Average H2O2 in feed (g/L) 0.00 1.78 0.00 0.98 Average H2SO4 in feed (g/L) 0.0 18.8 0.0 10.3 Total H2O2 in feed (kg) 0 49 0 49 Total H2SO4 in feed (kg) 0 516 0 516 Average H2O2 in discharge (g/L) 0.00 0.23 0.58 0.33 Average H2SO4 in discharge (g/L) 0.0 12.1 10.4 10.3 Average Cu in discharge (g/L) 0.10 2.02 0.23 1.19 Total H2O2 in discharge (kg) 0 6 10 16 Total H2SO4 in discharge (kg) 0 334 182 516 Total Cu in discharge (kg) 0 56 4 60 Total H2O2 consumption (kg) 0 43 -10 33 -182 H2SO4 consumption (kg) 0 182 0 Cu eluted from resin (kg) 0 56 4 59.7 Table All.13 Cycle 4 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.85 mg/L Ag 8.27 mg/L Cu 50.7 mg/L Fe <0.01 mg/L Zn <0.01 mg/L CNTOT 63.3 mg/L Solution pH 11.1 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 2.75 hrs Composition, H2O2 1.81 g/L Composition, H2SO4 20.7 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 1.75 hrs Flow direction Upwards Flow rate 10 m^/hr

Table A11.14 Pilot Plant breakthrough curve data - Cycle 4 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 0.01 0.20 <0.1 <0.1 <0.1 1 25 0.02 0.32 <0.1 <0.1 <0.1 2 50 0.02 0.26 <0.1 <0.1 <0.1 3 75 0.02 0.26 <0.1 <0.1 <0.1 4 100 0.02 0.26 <0.1 <0.1 <0.1 5 125 0.02 0.26 <0.1 <0.1 <0.1 6 150 0.02 0.27 <0.1 <0.1 <0.1 7 175 0.02 0.29 <0.1 <0.1 <0.1 8 200 0.02 0.35 <0.1 <0.1 <0.1 9 225 0.02 0.47 <0.1 <0.1 <0.1 10 250 0.03 0.66 <0.1 <0.1 <0.1 11 275 0.03 0.95 <0.1 <0.1 <0.1 12 300 0.04 1.42 <0.1 <0.1 <0.1 13 325 0.04 2.04 <0.1 <0.1 <0.1 14 350 0.05 2.95 <0.1 <0.1 <0.1 15 375 0.06 4.12 <0.1 <0.1 <0.1 16 400 0.07 5.38 <0.1 <0.1 <0.1 17 425 0.08 6.84 <0.1 <0.1 <0.1 18 450 0.09 8.63 <0.1 <0.1 <0.1 19 475 0.11 10.30 <0.1 <0.1 <0.1 20 500 10.12 12.10 <0.1 <0.1 <0.1 Composite 0.52 2.78 <0.1 <0.1 <0.1 1.5 Table A11.15 Base metal elution and rinse solution specifications - Cycle 4 Eluent Feed concentration flow (min) H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (BV) (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 0.80 16.5 29 2.6 0.8 <0.01 <0.1 15 1.3 - - 0.60 18.5 10 1.4 0.3 <0.01 <0.1 30 2.5 1.05 20.4 0.40 15.8 4.0 0.5 0.1 <0.01 <0.1 45 3.8 1.25 19.6 0.70 19.8 <0.1 3.6 <0.1 <0.01 <0.1 60 5.0 1.45 20.0 0.30 3.4 500 11.6 14.3 <0.01 3.4 75 6.3 1.75 20.4 0.30 8.1 2367 6.0 10.7 <0.01 10.2 90 7.5 2.00 20.4 0.40 5.2 3177 3.5 8.2 <0.01 12.4 105 8.8 2.20 20.8 0.40 10.0 3321 2.6 6.7 0.01 15.6 120 10.0 1.95 21.6 0.30 12.0 3519 2.2 6.0 0.20 17.2 135 11.3 1.70 21.6 0.30 13.5 3051 2.2 4.7 0.20 18.4 150 12.5 2.05 21.2 0.30 11.2 2304 1.9 2.5 0.45 19.6 165 13.8 2.35 20.8 0.30 14.3 1800 1.8 1.3 0.95 19.6 180 15.0 2.20 20.8 0.20 7.2 1120 1.7 <0.1 1.60 20.0 195 16.3 - - 0.10 7.4 223 2.1 1.0 2.00 20.0 210 17.5 - - 0.10 8.1 47 2.7 0.6 2.15 18.6 225 18.8 - - 0.10 6.7 28 1.7 0.4 1.60 15.6 240 20.0 - - 0.10 4.2 23 1.0 0.2 0.55 9.2 255 21.3 - - <0.01 4.6 17 0.7 0.1 0.30 6.0 270 22.5 - - <0.01 5.3 11 0.5 <0.1 0.10 4.5 285 23.8 - - <0.01 2.4 6.0 0.4 <0.1 0.06 3.0

~~300 25.0 - - <0.01 2.5 3.0 0.3 <0.1 <0.01 2.0~~

Table A11.16 Calculation of elution performance - Cycle 4 1st rinse Base metal elution 2nd rinse Total elution Duration (hrs) 0.50 2.75 1.75 5.00 Flow rate (m^/hr) 10 10 10 10 Volume (m^) 5.0 27.5 17.5 50.0 Average H2O2 in feed (g/L) 0.00 1.81 0.00 1.00 Average H2SO4 in feed (g/L) 0.0 20.7 0.0 11.4 Total H2O2 in feed (kg) 0 50 0 50 Total H2SO4 in feed (kg) 0 569 0 569 Average H2O2 in discharge (g/L) 0.00 0.31 0.97 0.51 Average H2SO4 in discharge (g/L) 0.0 12.4 11.0 10.7 Average Cu in discharge (g/L) 0.20 1.92 0.05 1.08 Total H2O2 in discharge (kg) 0 9 17 25 Total H2SO4 in discharge (kg) 0 341 192 533 Total Cu in discharge (kg) 1 53 1 54 Total H2O2 consumption (kg) 0 41 -17 24 -192 36 H2SO4 consumption (kg) 0 228 Cu eluted from resin (kg) 1 53 1 54 Table A11.17 Cycle 5 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.8 mg/L Ag 7.81 mg/L Cu 48.4 mg/L Fe <0.01 mg/L Zn <0.01 mg/L CNTOT 50.7 mg/L Solution pH 11.4 units Duration 20 hrs Flow direction Downwards Flow rate 50 mVhr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 2.75 hrs Composition, H2O2 1.74 g/L Composition, H2SO4 19.8 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 mVhr 2nd rinse Duration 1.75 hrs Flow direction Upwards Flow rate 10 mVhr

Table All.18 Pilot Plant breakthrough curve data - Cycle 5 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 0.03 0.21 <0.1 <0.1 0.2 1 25 0.04 0.33 <0.1 <0.1 <0.1 2 50 0.03 0.25 <0.1 <0.1 <0.1 3 75 0.04 0.26 <0.1 <0.1 <0.1 4 100 0.04 0.26 <0.1 <0.1 <0.1 5 125 0.04 0.27 <0.1 <0.1 <0.1 6 150 0.04 0.29 <0.1 <0.1 <0.1 7 175 0.04 0.34 <0.1 <0.1 <0.1 8 200 0.05 0.41 <0.1 <0.1 <0.1 9 225 0.05 0.56 <0.1 <0.1 <0.1 10 250 0.06 0.80 <0.1 <0.1 <0.1 11 275 0.06 1.16 <0.1 <0.1 <0.1 12 300 0.07 1.76 <0.1 <0.1 <0.1 13 325 0.08 2.63 <0.1 <0.1 <0.1 14 350 0.09 3.68 <0.1 <0.1 <0.1 15 375 0.10 4.77 <0.1 <0.1 <0.1 <0.1 <0.1 16 400 0.11 5.76 <0.1 <0.1 <0.1 <0.1 17 425 0.13 6.81 <0.1 <0.1 <0.1 18 450 0.14 8.52 <0.1 <0.1 <0.1 19 475 0.15 9.59 <0.1 <0.1 <0.1 20 500 0.16 10.90 <0.1 <0.1 <0.1 1.9 Composite 0.07 2.84 Table A11.19 Base metal elution and rinse solution specifications - Cycle 5 Time Eluent Feed concentration nischarpe ronrpntratinn (min) flow H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (BV) (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 - - 1.30 19.4 21 <0.1 <0.1 <0.01 <0.1 15 1.3 - - 0.50 18.1 <0.1 0.2 <0.1 <0.01 <0.1 30 2.5 1.80 18.8 0.30 13.3 <0.1 <0.1 <0.1 <0.01 <0.1 45 3.8 1.65 19.2 0.10 28.5 <0.1 1.0 <0.1 <0.01 <0.1 60 5.0 1.60 19.6 0.10 21.3 480 15.1 3.5 <0.01 2.8 75 6.3 1.70 19.2 0.00 29.1 1724 13.4 6.0 <0.01 12.0 90 7.5 1.75 20.0 0.10 34.7 2858 9.7 5.2 <0.01 16.2 105 8.8 1.85 20.2 0.10 51.2 3164 7.0 4.3 <0.01 17.6 120 10.0 1.85 20.4 0.10 42.2 3164 5.4 3.0 0.05 18.0 135 11.3 1.80 20.4 0.10 34.8 2880 4.6 1.5 0.20 18.0 150 12.5 1.75 20.6 0.10 28.6 2326 4.4 <0.1 0.60 19.0 165 13.8 1.75 20.0 <0.01 16.3 1699 4.0 <0.1 0.85 19.0 180 15.0 1.65 19.6 <0.01 13.3 1341 3.8 <0.1 1.20 19.6 195 16.3 - - 0.30 17.6 597 3.4 1.1 1.60 19.2 210 17.5 - - 0.20 16.7 338 3.2 0.2 1.70 19.5 225 18.8 - - 0.20 17.2 216 1.5 <0.1 1.10 13.2 240 20.0 - - 0.10 16.9 137 0.6 <0.1 0.35 6.8 255 21.3 - - 0.10 7.9 93 0.4 <0.1 0.05 4.2 270 22.5 - - 0.10 10.7 31 0.3 <0.1 0.05 2.6 285 23.8 - - 0.10 9.8 41 0.2 <0.1 <0.01 1.9 300 25.0 - - <0.01 6.1 27 0.2 <0.1 <0.01 1.6

Table A11.20 Calculation of elution performance - Cycle 5 1st rinse Base metal elution 2nd rinse Total elution Duration (hrs) 0.50 2.75 1.75 5.00 Flow rate (mVhr) 10 10 10 10 Volume (m^) 5.0 27.5 17.5 50.0 Average H2O2 in feed (g/L) 0.00 1.74 0.00 0.96 Average H2SO4 in feed (g/L) 0.0 19.8 0.0 10.9 Total H2O2 in feed (kg) 0 48 0 48 Total H2SO4 in feed (kg) 0 545 0 545 Average H2O2 in discharge (g/L) 0.00 0.26 0.69 0.39 Average H2SO4 in discharge (g/L) 0.0 12.9 9.6 10.5 Average Cu in discharge (g/L) 0.11 1.78 0.21 1.06 Total H2O2 in discharge (kg) 0 7 12 19 Total H2SO4 in discharge (kg) 0 356 169 524 Total Cu in discharge (kg) 1 49 4 53 Total H2O2 consumption (kg) 0 41 -12 29 H2SO4 consumption (kg) 0 190 -169 21 Cu eluted from resin (kg) 1 49 4 53 Table Al 1.21 Cycle 6 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.81 mg/L Ag 7.94 mg/L Cu 53.4 mg/L Fe <0.01 mg/L Zn <0.01 mg/L CNTOT 58.0 mg/L Solution pH 11.4 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 3.5 hrs Composition, H2O2 1.63 g/L Composition, H2SO4 20.0 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 1.5 hrs Flow direction Upwards Flow rate 10 m^/hr

Table A11.22 Pilot Plant breakthrough curve data - Cycle 6 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CNTOT 0 0 <0.01 <0.01 <0.1 <0.1 <0.1 1 25 0.07 0.42 <0.1 <0.1 <0.1 2 50 0.07 0.42 <0.1 <0.1 <0.1 3 75 0.07 0.41 <0.1 <0.1 <0.1 4 100 0.06 0.40 <0.1 <0.1 <0.1 5 125 0.06 0.38 <0.1 <0.1 <0.1 6 150 0.06 0.42 <0.1 <0.1 <0.1 7 175 0.07 0.49 <0.1 <0.1 <0.1 8 200 0.08 0.63 <0.1 <0.1 <0.1 9 225 0.08 0.81 <0.1 <0.1 <0.1 10 250 0.08 1.12 <0.1 <0.1 <0.1 11 275 0.11 1.80 <0.1 <0.1 <0.1 12 300 0.12 2.56 <0.1 <0.1 <0.1 13 325 0.13 3.65 <0.1 <0.1 <0.1 14 350 0.15 5.26 <0.1 <0.1 <0.1 15 375 0.18 7.03 <0.1 <0.1 <0.1 16 400 0.20 8.99 <0.1 <0.1 <0.1 17 425 0.23 10.90 <0.1 <0.1 <0.1 18 450 0.27 13.00 <0.1 <0.1 <0.1 19 475 0.32 15.90 <0.1 <0.1 <0.1 20 500 0.36 17.40 <0.1 <0.1 <0.1 Composite 0.13 4.38 <0.1 <0.1 <0.1 1.2 Table A11.23 Base metal elution and rinse solution specifications - Cycle 6 Eluent Feed concentration Discharee concentration flow (min) H2O2 H2SO4 Au Ag Cu Fe Zn H2O2 H2SO4 (BV) (g/L) (g/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (g/L) (g/L) 0 0.0 - 1.20 17.4 36 0.4 <0.1 <0.01 <0.1 15 1.3 - - 1.00 21.3 10 2.7 <0.1 <0.01 <0.1 30 2.5 2.02 18.8 0.70 19.2 5.0 1.3 <0.1 <0.01 <0.1 45 3.8 1.55 17.8 0.80 35.7 2.0 1.3 <0.1 <0.01 <0.1 60 5.0 1.20 18.0 0.40 10.6 78 16.4 10.0 <0.01 1.6 75 6.3 1.10 18.4 <0.01 14.6 1652 11.2 10.3 <0.01 11.0 90 7.5 1.60 22.4 <0.01 11.5 2022 6.3 5.4 <0.01 15.0 105 8.8 1.75 21.4 <0.01 9.1 2722 4.5 4.7 <0.01 19.2 120 10.0 1.55 20.0 <0.01 11.2 2884 3.8 3.9 <0.01 19.2 135 11.3 1.60 19.6 <0.01 12.3 2430 3.0 1.2 <0.01 18.4 150 12.5 1.80 19.8 <0.01 20.7 2430 2.8 0.6 0.10 18.8 165 13.8 1.70 20.4 <0.01 16.6 2313 2.7 <0.1 0.20 18.8 180 15.0 1.30 20.6 <0.01 16.7 1724 2.8 <0.1 0.50 19.4 195 16.3 1.50 21.4 <0.01 14.6 855 2.7 <0.1 0.80 20.8 210 17.5 1.95 20.8 <0.01 11.2 242 2.6 <0.1 1.30 20.8 225 18.8 2.15 21.2 0.10 4.9 38 2.4 <0.1 1.80 20.8 240 20.0 - - 0.10 8.0 23 2.4 <0.1 2.00 20.6 255 21.3 - - 0.10 5.7 16 2.4 <0.1 2.10 20.6 270 22.5 - - 0.10 5.0 14 1.8 <0.1 1.45 16.2 285 23.8 - - <0.01 2.7 12 0.1 <0.1 1.35 9.0 300 25.0 - - <0.01 4.0 11 0.5 <0.1 1.25 4.8 315 26.3 - - <0.01 2.2 11 0.3 <0.1 0.05 3.0

~~330 27.5 - - <0.01 1.3 8.0 0.2 <0.1 <0.01 1.8~~

~~Table A11.24 Calculation of elution performance - Cycle 6 rinse Base metal elution 2nd rinse Total elution~~

Duration (hrs) 0.50 3.50 1.50 5.50 Flow rate (mVhr) 10 10 10 10 Volume (m^) 5.0 35.0 15.0 55.0 Average H2O2 in feed (g/L) 0.00 1.63 0.00 1.04 Average H2SO4 in feed (g/L) 0.0 20.0 0.0 12.8 Total H2O2 in feed (kg) 0 57 0 57 Total H2SO4 in feed (kg) 0 702 0 702 Average H2O2 in discharge (g/L) 0.00 0.34 1.37 0.59 Average H2SO4 in discharge (g/L) 0.0 14.6 12.4 12.6 Average Cu in discharge (g/L) 0.23 1.39 0.01 0.89 Total H2O2 in discharge (kg) 0 12 21 32 Total H2SO4 in discharge (kg) 0 510 186 695 Total Cu in discharge (kg) 1 48 0 49 Total H2O2 consumption (kg) 0 45 -21 25 192 -186 7 H2SO4 consumption (kg) 0 0 49 Cu eluted from resin (kg) 1 48 Table A11.25 Pilot Plant operating conditions and results - Cycle 7 Cycle Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: Composition Au 0.88 mg/L Ag 9.56 mg/L Cu 62.7 mg/L Fe <0.01 mg/L Zn <0.01 mg/L

CNTOT 51.0 mg/L Solution pH 11.1 units Duration 20 hrs Flow direction Downwards Flow rate 50 m^/hr 1st rinse Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Precious metal elution Duration 90 Hrs Composition, Na2Zn(CN)4 0.15 M Composition, NaOH 0.1 M Solution pH >12.5 Flow direction Upwards Flow rate 10 m^/hr 2nd rinse Duration 6 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution Duration 3.5 hrs Composition, H2O2 1.8 g/L Composition, H2SO4 21.2 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr rinse Duration 6 hrs Flow direction Upwards Flow rate 10 m^/hr Table A11.26 Pilot Plant breakthrough curve data - Cycle 7 Time Flow Concentration in discharge (mg/L) (hrs) (BV) Au Ag Cu Fe Zn CN TOT 0 0 0.10 0.24 2.3 <0.1 0.2 1 25 0.11 0.36 <0.1 <0.1 <0.1 2 50 0.11 0.36 <0.1 <0.1 <0.1 3 75 0.11 0.39 <0.1 <0.1 <0.1 4 100 0.11 0.38 <0.1 <0.1 <0.1 5 125 0.11 0.42 <0.1 <0.1 <0.1 6 150 0.11 0.46 <0.1 <0.1 <0.1 7 175 0.12 0.56 <0.1 <0.1 <0.1 8 200 0.12 0.71 <0.1 <0.1 <0.1 9 225 0.13 0.99 <0.1 <0.1 <0.1 10 250 0.14 1.39 <0.1 <0.1 <0.1 11 275 0.16 2.00 <0.1 <0.1 <0.1 12 300 0.18 2.83 <0.1 <0.1 <0.1 13 325 0.20 3.79 <0.1 <0.1 <0.1 14 350 0.22 5.01 <0.1 <0.1 <0.1 15 375 0.25 6.48 <0.1 <0.1 <0.1 16 400 0.28 7.99 <0.1 <0.1 <0.1 17 425 0.31 9.75 <0.1 <0.1 <0.1 18 450 0.39 12.2 <0.1 <0.1 <0.1 19 475 0.45 14.4 <0.1 <0.1 <0.1 20 500 0.50 16.0 <0.1 <0.1 <0.1 Composite 0.20 4.13 0.1 <0.1 <0.1 2.2

Table A11.27 Precious metal elution profile - Cycle 7 Time Feed to the column Discharge from the column Spent solution from EW cell (hr) Au Ag Au Ag Au Ag (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) 1 16.75 360 31.95 772 25.50 332 5 48.80 1313 59.10 1596 50.65 603 9 42.75 673 57.80 846 41.70 289 13 29.30 242 44.80 321 19.40 89.7 17 22.30 86.7 34.05 111 15.86 34.3 21 18.05 37.6 25.95 46.9 15.73 16.4 25 15.10 20.1 22.15 11.5 13.50 8.60 33 13.75 10.8 15.35 7.70 11.96 7.10 37 11.02 7.00 13.23 6.70 11.04 6.30 41 10.08 5.10 12.32 5.20 10.52 4.90 45 9.33 4.60 11.51 4.90 9.82 4.30 49 9.07 3.90 10.45 3.90 9.40 3.70 53 8.94 3.40 10.30 3.60 9.02 3.20 57 8.33 3.40 9.90 3.00 9.31 2.90 61 7.89 3.10 9.00 2.50 8.41 2.50 65 7.45 2.20 8.68 2.50 7.81 2.10 69 7.07 1.80 8.29 2.10 7.64 1.90 73 6.95 1.50 7.85 1.60 7.32 1.60 77 6.53 1.40 7.53 1.40 6.78 1.50 81 6.43 1.30 7.24 1.30 6.68 1.40 85 6.29 1.30 7.06 1.10 6.58 1.20 89 6.20 1.10 6.72 1.20 6.24 1.20 APPENDIX 12

Table A12.1 Cycle 8-14 Resin column volume 2000 L Column orientation Vertical Total run duration 25 hrs Loading: (all cycles) Solution pH 10.8-11.5 units Duration 20 hrs Flow direction Downwards Flow rate 50 m'/hr rinse (all cycles) Duration 0.5 hrs Flow direction Upwards Flow rate 10 m^/hr Base metal elution (cycles 8-13) Duration 3.5 hrs Composition, H2O2 1.7 g/L Composition, H2SO4 20.1 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 2nd rinse (cycles 8-13) Duration 1 hrs Flow direction Upwards Flow rate 10 m^/hr Precious metal elution (cycle 14 only) Duration 90 Hrs Composition, Na2Zn(CN)4 0.15 M Composition, NaOH 0.1 M Solution pH >12.5 Flow direction Upwards Flow rate 10 m^/hr Base metal elution (cycles 14 only) Duration 3.5 hrs Composition, H2O2 1.6 to 2.1 g/L Composition, H2SO4 17 to 22 g/L Solution pH <1 Units Flow direction Upwards Flow rate 10 m^/hr 3'^'' rinse (cycle 14 only) Duration 6 hrs Flow direction Upwards Flow rate 10 m^/hr Table A12.2 Average grade of feed liquor - Cycles 8-14 Cycle Concentration in feed(mg/L)

Au Ag Cu Fe Zn CNTOT 8 0.82 8.95 68.0 <1.0 <0.01 56 9 0.86 8.72 58.1 <1.0 <0.01 49 10 0.81 9.31 66.3 <1.0 <0.01 52 11 0.82 9.11 56.9 <1.0 <0.01 50 12 0.79 8.37 63.4 <1.0 <0.01 47 13 0.85 8.97 60.2 <1.0 <0.01 45 14 0.84 8.74 58.8 <1.0 <0.01 35

~~Table A12.3 Average grade of discharge liq uor - Cycles 8-14 Cycle Concentration in discharge (mg/L)~~

Au Ag Cu Fe Zn CNTOT 8 0.04 1.85 <0.01 <1.0 <0.01 0.8 9 0.08 2.01 <0.01 <1.0 <0.01 1.0 10 0.09 3.54 <0.01 <1.0 <0.01 1.6 11 0.16 5.69 <0.01 <1.0 <0.01 2.5 12 0.21 5.84 <0.01 <1.0 <0.01 2.5 13 0.28 5.87 0.04 <1.0 <0.01 2.4 14 0.31 6.15 0.12 <1.0 <0.01 3.2 APPENDIX 13

Table A13.1 Synthesis of Cu2Fe(CN)6 and Cu3[Fe(CN)6]7 Synthesis ofCujFeíCN)« Molarity of Potassium Ferrocyanide solution 0.0895 M Volume of Potassium Ferrocyanide solution 0.1 L Moles of Potassium Ferrocyanide 0.00895 moles Molarity of Copper Sulphate solution 0.201 M Volume of Copper Sulphate solution taken 0.1 L Moles of Potassium Ferrocyanide 0.0201 moles Reaction Temperature Ambient Reaction pH -6.0 Reaction duration 6 hrs Total volume of fíltrate

~~(After filtration of the precipitate by Whatman GF/C glass microfíber filter paper) 0.522 L Elemental concentration in the filtrate~~

~~Cu 334 mg/L Fe 0 mg/L Moles of Cu^^ reacted 0.01736 moles Moles of Ferricyanide reacted 0.0895 moles Cu/Fe molar ratio in the precipitate 1.93~~

Table A13.2 Synthesis of Cu3[Fe(CN)6]2 Molarity of Potassium Ferricyanide solution 0.0895 M Volume of Potassium Ferricyanide solution 0.1 L Moles of Potassium Ferricyanide 0.00895 moles Molarity of Copper Sulphate solution 0.201 M Volume of Copper Sulphate solution taken 0.075 1 Moles of Potassium Ferricyanide 0.015075 moles Reaction Temperature Ambient Reaction pH -6.0 Reaction duration 6 hrs Total volume of fíltrate (After fíltration of the precipitate by Whatman GF/C glass microfíber fílter paper) 0.5 L Elemental concentration in the fíltrate Cu 207 mg/L Fe 0 mg/L

~~Moles of Cu^^ reacted 0.0134 moles Moles of Ferricyanide reacted 0.0895 moles Cu/Fe molar ratio in the precipitate 1.50 APPENDIX 14~~

Table A14. Sample Description Test No. Resin volume Eluent Eluent Cr Resin loading Standard ID loaded with CI" volume concentration capacity Deviation (mL) (mL) (mM) (mEq/mL) of result SlOl Fresh resin in sulphate 1 5 500 11.22 1.12 form 2 5 500 11.45 1.14 3 5 500 10.98 1.10 4 5 500 11.22 1.12 Average 1.12 0.02

~~S102 Resin after 15 loading 1 4.8 500 9.38 0.98 elution cycles with 950 2 4.8 500 9.69 1.01 mg/L Cu 3 4.8 500 9.34 0.97 4 4.8 500 9.48 0.99 Average 0.99 0.02~~

~~S103 Resin after 15 loading 1 5 500 9.62 0.96 elution cycles with 950 2 5 500 9.87 0.99 mg/L Cu and 25 mg/L Fe 3 5 500 9.55 0.95 (Ferrocyanide) 4 5 500 9.73 0.97 Average 0.97 0.01~~

~~S104 Resin after 15 loading 1 4.8 500 9.39 0.98 elution cycles with 950 2 4.8 500 9.67 1.01 mg/L Cu and 50 mg/L Fe 3 4.8 500 9.21 0.96 (Ferrocyanide) 4 4.8 500 9.51 0.99 Average 0.98 0.02~~

S105 Resin after 7 adsorption 1 5 500 8.55 0.86 cycles in the pilot plant, 2 5 500 8.74 0.87 regenerated with 3 5 500 8.39 0.84 Na2Zn(CN)4 and oxidative 4 5 500 8.65 0.86 acid base metal elution Average 0.86 0.01

S106 Resin after 14 adsorption 1 4.9 500 6.50 0.66 cycles in the pilot plant. 2 4.9 500 6.76 0.69 regenerated with 3 4.9 500 6.39 0.65 Na2Zn(CN)4 and oxidative 4 4.9 500 6.76 0.69 acid base metal elution Average 0.67 0.02 APPENDIX 15

~~Table A15.1 CI" selective electrode measurements~~

Time Fresh resin Resin with 15 Resin with 15 Resin with 15 Resin from pilot Resin from pilot (s) loading/elution loading/elution loading/elution plant tests after 7 plant tests after 7 cycles with 950 cycles with 950 cycles with 950 loading and loading and mg/L Cu and no mg/L Cu and 25 mg/L Cu and 50 elution cycles elution cycles Fe mg/L Fe^* mg/L Fe^'

Sample: 5 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.8 mL cr in cr cr in ci- CI" in cr cr in cr cr in cr cr in cr eluent release eluent release eluent release eluent release eluent release eluent release rate rate rate rate rate rate (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5 1.40 0.07 1.24 0.06 1.35 0.07 1.22 0.06 1.25 0.07 2.72 0.14 10 4.15 0.21 3.30 0.17 3.44 0.18 3.13 0.16 3.62 0.19 3.91 0.20 15 5.86 0.29 5.05 0.26 5.06 0.26 4.16 0.22 5.13 0.27 4.74 0.24 20 7.13 0.36 6.18 0.32 6.07 0.32 4.97 0.26 6.30 0.33 5.31 0.27 25 8.02 0.40 7.11 0.37 6.95 0.36 5.68 0.30 7.12 0.37 5.94 0.30 30 8.80 0.44 7.81 0.41 7.66 0.40 6.85 0.36 7.88 0.41 6.39 0.33 35 9.47 0.47 8.55 0.45 8.31 0.43 7.52 0.39 8.49 0.44 6.76 0.34 40 10.14 0.51 9.21 0.48 8.83 0.46 8.09 0.42 9.07 0.47 7.17 0.37 45 10.64 0.53 9.69 0.50 9.33 0.49 8.59 0.45 9.59 0.50 7.41 0.38 50 11.23 0.56 10.19 0.53 9.77 0.51 9.04 0.47 10.09 0.53 7.60 0.39 55 11.73 0.59 10.63 0.55 10.24 0.53 9.44 0.49 10.50 0.55 8.15 0.42 60 12.23 0.61 11.05 0.58 10.63 0.55 9.89 0.52 10.92 0.57 8.48 0.43 65 12.65 0.63 11.47 0.60 11.03 0.57 10.17 0.53 11.29 0.59 8.84 0.45 70 13.07 0.65 11.89 0.62 11.32 0.59 10.53 0.55 11.60 0.60 9.11 0.46 75 13.40 0.67 12.20 0.64 11.62 0.61 10.90 0.57 11.95 0,62 9.38 0.48 80 13.82 0.69 12.52 0.65 11.91 0.62 11.18 0.58 12.29 0.64 9.66 0.49 85 14.16 0.71 12.94 0.67 12.21 0.64 11.45 0.60 12.52 0.65 9.87 0.50 90 14.49 0.72 13.15 0.68 12.50 0.65 11.73 0.61 12.87 0.67 10.10 0.52 95 14.83 0.74 13.47 0.70 12.80 0.67 12.00 0.62 13.10 0.68 10.29 0.52 100 15.16 0.76 13.78 0.72 12.99 0.68 12.27 0.64 13.33 0.69 10.50 0.54 105 15.41 0.77 13.99 0.73 13.29 0.69 12.55 0.65 13.56 0.71 10.65 0.54 110 15.67 0.78 14.31 0.75 13.49 0.70 12.73 0.66 13.90 0.72 10.84 0.55 115 15.92 0.80 14.52 0.76 13.68 0.71 12.92 0.67 14.01 0.73 10.98 0.56 120 16.25 0.81 14.73 0.77 13.98 0.73 13.19 0.69 14.24 0.74 11.14 0.57 125 16.42 0.82 14.94 0.78 14.18 0.74 13.47 0.70 14.47 0.75 11.28 0.58 130 16.67 0.83 15.15 0.79 14.37 0.75 13.65 0.71 14.70 0.77 11.42 0.58 135 16.92 0.85 15.36 0.80 14.57 0.76 13.83 0.72 14.82 0.77 11.54 0.59 140 17.09 0.85 15.57 0.81 14.77 0.77 14.02 0.73 15.05 0.78 11.69 0.60 145 17.34 0.87 15.67 0.82 14.96 0.78 14.20 0.74 15.16 0.79 11.79 0.60 150 17.51 0.88 15.89 0.83 15.06 0.78 14.38 0.75 15.28 0.80 11.88 0.61 155 17.68 0.88 15.99 0.83 15.26 0.79 14.56 0.76 15.51 0.81 11.97 0.61 160 17.84 0.89 16.20 0.84 15.46 0.80 14.75 0.77 15.62 0.81 12.09 0.62 165 18.01 0.90 16.31 0.85 15.55 0.81 14.93 0.78 15.74 0.82 12.17 0.62 170 18.26 0.91 16.52 0.86 15.75 0.82 15.02 0.78 15.85 0.83 12.25 0.63 175 18.43 0.92 16.62 0.87 15.85 0.83 15.21 0.79 15.97 0.83 12.32 0.63 180 18.51 0.93 16.73 0.87 15.95 0.83 15.30 0.80 16.20 0.84 12.41 0.63 185 18.68 0.93 16.83 0.88 16.14 0.84 15.48 0.81 16.31 0.85 12.47 0.64 190 18.85 0.94 17.04 0.89 16.24 0.85 15.66 0.82 16.31 0.85 12.55 0.64 195 19.02 0.95 17.15 0.89 16.34 0.85 15.76 0.82 16.43 0.86 12.61 0.64 200 19.18 0.96 17.25 0.90 16.44 0.86 15.85 0.83 16.54 0.86 12.68 0.65 205 19.27 0.96 17.36 0.90 16.54 0.86 15.94 0.83 16.66 0.87 12.72 0.65 210 19.44 0.97 17.46 0.91 16.64 0.87 16.12 0.84 16.66 0.87 12.80 0.65 215 19.52 0.98 17.46 0.91 16.74 0.87 16.21 0.84 16.77 0.87 12.86 0.66 220 19.69 0.98 17.57 0.92 16.83 0.88 16.31 0.85 16.89 0.88 12.90 0.66 225 19.77 0.99 17.67 0.92 16.93 0.88 16.49 0.86 16.89 0.88 12.92 0.66 230 19.85 0.99 17.78 0.93 17.03 0.89 16.58 0.86 17.00 0.89 12.96 0.66 235 19.94 1.00 17.88 0.93 17.13 0.89 16.67 0.87 17.12 0.89 13.02 0.66 240 20.11 1.01 17.88 0.93 17.23 0.90 16.76 0.87 17.12 0.89 13.06 0.67 245 20.19 1.01 17.99 0.94 17.33 0.90 16.85 0.88 17.23 0.90 13.08 0.67 Table A15.1 CI" selective electrode measurements (Contd.) Time Fresh resin Resin with 15 Resin with 15 Resin with 15 Resin from pilot Resin from pilot is) loading/elution loading/elution loading/elution plant tests after 7 plant tests after 7 cycles with 950 cycles with 950 cycles with 950 loading and loading and mg/L Cu and no mg/L Cu and 25 mg/L Cu and 50 elution cycles elution cycles Fe mg/L Fe^* mg/L Fe^'

Sample: 5 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.9 mL CI" in Cl" cr m CI" CI" in cr CI" in cr Cl" in cr cr in cr eluent release eluent release eluent release eluent release eluent release eluent release rate rate rate rate rate rate (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) 250 20.27 1.01 18.09 0.94 17.42 0.91 16.95 0.88 17.23 0.90 13.12 0.67 255 20.36 1.02 18.20 0.95 17.52 0.91 17.04 0.89 17.23 0.90 13.16 0.67 260 20.44 1.02 18.20 0.95 17.52 0.91 17.13 0.89 17.35 0.90 13.19 0.67 265 20.52 1.03 18.30 0.95 17.62 0.92 17.22 0.90 17.35 0.90 13.22 0.67 270 20.61 1.03 18.30 0.95 17.72 0.92 17.31 0.90 17.46 0.91 13.26 0.68 275 20.69 1.03 18.30 0.95 17.72 0.92 17.40 0.91 17.46 0.91 13.28 0.68 280 20.78 1.04 18.41 0.96 17.82 0.93 17.50 0.91 17.58 0.92 13.30 0.68 285 20.78 1.04 18.52 0.96 17.82 0.93 17.59 0.92 17.58 0.92 13.32 0.68 290 20.86 1.04 18.52 0.96 17.92 0.93 17.68 0.92 17.58 0.92 13.34 0.68 295 20.94 1.05 18.52 0.96 18.01 0.94 17.68 0.92 17.58 0.92 13.36 0.68 300 21.03 1.05 18.62 0.97 18.01 0.94 17.77 0.93 17.69 0.92 13.36 0.68 305 21.11 1.06 18.62 0.97 18.11 0.94 17.86 0.93 17.69 0.92 13.38 0.68 310 21.20 1.06 18.62 0.97 18.11 0.94 17.86 0.93 17.69 0.92 13.38 0.68 315 21.20 1.06 18.73 0.98 18.21 0.95 17.95 0.94 17.69 0.92 13.38 0.68 320 21.28 1.06 18.73 0.98 18.21 0.95 18.05 0.94 17.81 0.93 13.38 0.68 325 21.28 1.06 18.73 0.98 18.21 0.95 18.14 0.94 17.81 0.93 13.38 0.68 330 21.36 1.07 18.73 0.98 18.31 0.95 18.14 0.94 17.81 0.93 13.38 0.68 335 21.36 1.07 18.83 0.98 18.31 0.95 18.14 0.94 17.81 0.93 13.51 0.69 340 21.45 1.07 18.83 0.98 18.41 0.96 18.14 0.94 17.81 0.93 13.51 0.69 345 21.45 1.07 18.83 0.98 18.41 0.96 18.23 0.95 17.81 0.93 13.51 0.69 350 21.53 1.08 18.83 0.98 18.41 0.96 18.32 0.95 17.81 0.93 13.51 0.69 355 21.53 1.08 18.83 0.98 18.51 0.96 18.41 0.96 17.81 0.93 13.51 0.69 360 21.53 1.08 18.94 0.99 18.51 0.96 18.41 0.96 17.81 0.93 13.51 0.69 365 21.53 1.08 18.94 0.99 18.61 0.97 18.41 0.96 17.81 0.93 13.51 0.69 370 21.61 1.08 18.94 0.99 18.61 0.97 18.50 0.96 17.81 0.93 13.51 0.69 375 21.70 1.08 18.94 0.99 18.61 0.97 18.50 0.96 17.92 0.93 13.51 0.69 380 21.70 1.08 18.94 0.99 18.61 0.97 18.50 0.96 17.92 0.93 13.51 0.69 385 21.70 1.08 18.94 0.99 18.70 0.97 18.60 0.97 17.92 0.93 13.51 0.69 390 21.70 1.08 18.94 0.99 18.70 0.97 18.60 0.97 17.92 0.93 13.51 0.69 395 21.70 1.08 18.94 0.99 18.70 0.97 18.60 0.97 17.92 0.93 13.51 0.69 400 21.78 1.09 18.94 0.99 18.80 0.98 18.69 0.97 17.92 0.93 13.51 0.69 405 21.78 1.09 18.94 0.99 18.80 0.98 18.69 0.97 17.92 0.93 13.51 0.69 410 21.78 1.09 18.94 0.99 18.80 0.98 18.69 0.97 17.92 0.93 13.51 0.69 415 21.87 1.09 19.04 0.99 18.80 0.98 18.69 0.97 17.92 0.93 13.51 0.69 420 21.87 1.09 18.94 0.99 18.80 0.98 18.78 0.98 17.92 0.93 13.51 0.69 0.93 13.65 0.70 425 21.87 1.09 18.94 0.99 18.90 0.98 18.78 0.98 17.92 17.92 0.93 13.51 0.69 430 21.87 1.09 18.94 0.99 18.90 0.98 18.78 0.98 0.98 17.92 0.93 13.51 0.69 435 21.87 1.09 18.94 0.99 18.90 0.98 18.78 18.78 0.98 17.92 0.93 13.51 0.69 440 21.87 1.09 19.04 0.99 18.90 0.98 18.78 0.98 17.92 0.93 13.51 0.69 445 21.87 1.09 19.04 0.99 18.90 0.98 18.87 0.98 17.92 0.93 13.51 0.69 450 21.95 1.10 18.94 0.99 18.90 0.98 0.98 18.87 0.98 17.92 0.93 13.51 0.69 455 21.95 1.10 18.94 0.99 18.90 0.98 18.87 0.98 17.81 0.93 13.51 0.69 460 21.95 1.10 18.94 0.99 18.90 0.99 18.87 0.98 17.81 0.93 13.51 0.69 465 21.95 1.10 18.94 0.99 19.00 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 470 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 475 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 480 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 485 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 490 21.95 1.10 18.94 0.99 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 495 21.95 1.10 18.94 Table A15.1 CI selective electrode measurements (Contd.) Time Fresh resin Resin with 15 Resin with 15 Resin with 15 Resin from pilot Resin from pilot (s) loading/elution loading/elution loading/elution plant tests after 7 plant tests after 7 cycles with 950 cycles with 950 cycles with 950 loading and loading and mg/L Cu and no mg/L Cu and 25 mg/L Cu and 50 elution cycles elution cycles Fe mg/L Fe^* mg/L Fe^'

Sample: 5 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.8 mL Sample: 4.9 mL cr in cr cr in Cl" CI" in Cl" cr in CI" cr in cr cr in cr eluent release eluent release eluent release eluent release eluent release eluent release rate rate rate rate rate rate (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/mL) (mM) (mEq/m(mEq/mLl ) 500 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 505 21.95 1.10 18.94 0.99 19.00 0.99 18.96 0.99 17.81 0.93 13.51 0.69 510 21.95 1.10 18.94 0.99 19.10 0.99 19.05 0.99 17.81 0.93 13.51 0.69 515 21.95 1.10 18.83 0.98 19.00 0.99 19.05 0.99 17.81 0.93 13.51 0.69 520 21.95 1.10 18.83 0.98 19.00 0.99 19.05 0.99 17.81 0.93 13.51 0.69 525 21.95 1.10 18.83 0.98 19.10 0.99 19.05 0.99 17.81 0.93 13.51 0.69 530 21.95 1.10 18.83 0.98 19.00 0.99 19.14 1.00 17.69 0.92 13.51 0.69 535 21.95 1.10 18.83 0.98 19.10 0.99 19.05 0.99 17.69 0.92 13.51 0.69 540 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 545 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 550 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 555 21.95 1.10 18.83 0.98 19.00 0.99 19.14 1.00 17.69 0.92 13.51 0.69 560 21.95 1.10 18.83 0.98 19.10 0.99 19.05 0.99 17.69 0.92 13.51 0.69 565 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 570 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 575 21.95 1.10 18.83 0.98 19.10 0.99 19.14 1.00 17.69 0.92 13.51 0.69 580 21.95 1.10 18.83 0.98 19.00 0.99 19.14 1.00 17.69 0.92 13.51 0.69 585 21.87 1.09 18.83 0.98 19.00 0.99 19.14 1.00 17.58 0.92 13.51 0.69 590 21.87 1.09 18.83 0.98 19.10 0.99 19.05 0.99 17.58 0.92 13.51 0.69 595 21.87 1.09 18.83 0.98 19.10 0.99 19.05 0.99 17.58 0.92 13.51 0.69 600 21.87 1.09 18.83 0.98 19.10 0.99 19.05 0.99 17.58 0.92 13.51 0.69 605 21.87 1.09 18.83 0.98 19.10 0.99 19.05 0.99 17.58 0.92 13.51 0.69 610 21.87 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 615 21.78 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 620 21.78 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 625 21.78 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 630 21.78 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 635 21.78 1.09 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 640 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 645 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 650 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 655 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 660 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 665 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 670 21.70 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 675 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 680 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 685 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 690 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 695 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 700 21.61 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 705 21.53 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 710 21.53 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 715 21.53 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 720 21.53 1.08 18.83 0.98 19.10 0.99 19.14 1.00 17.58 0.92 13.51 0.69 APPENDIX 16

~~Powder X-Ray diffraction patterns of Cu2Fe(CN)6~~

~~Counts S22427~~

~~2000-~~

~~1000-~~

~~Position [°2Theta]~~

Powder X-Ray diffraction patterns of Cu2Fe(CN)6 synthesised in laboratory. Peaks identified by the software are indicated by a short red line placed on the top of the graph. Locations and intensities of peaks corresponding to Cu2Fe(CN)6, as available in the library, have been superimposed on the XRD pattern.

Table A16.1 List of peaks produced by Cu2Fe(CN)6 Pos. [°2Th.] Height [cts] FWHM [°2Th.] d-spacing [A] Rel. Int. \%] 10.3410 45.23 0.9840 9.93295 2.04 17.6429 364.46 0.2952 5.83710 16.45 17.9474 347.38 0.1476 5.73886 15.68 20.6346 2215.46 0.4920 4.99808 100.00 29.2952 1602.75 0.3444 3.53993 72.34 34.4508 271.43 0.2952 3.02282 12.25 41.9795 904.94 0.4428 2.49903 40.85 47.1602 371.79 0.3444 2.23771 16.78 51.9956 236.19 0.6888 2.04216 10.66 55.4785 67.40 0.4920 1.92321 3.04 60.8632 181.00 0.6888 1.76730 8.17 64.9910 154.25 0.3936 1.66623 6.96 69.0076 161.74 0.8856 1.58026 7.30 72.7195 34.01 0.7872 1.50991 1.54 76.6353 25.91 1.2000 1.44270 1.17 Powder X-Ray diffraction patterns of Cu3[Fe(CN)6];

~~Counts S22428~~

~~8000-~~

~~6000 H~~

~~4000-~~

~~2000-~~

~~0^ jL, .j ^ , jLJl irrrtrr? 10 20 30 40 50 60 70 80~~

~~Position [°2Theta]~~

Powder X-Ray diffraction patterns of Cu3[Fe(CN)6]2 synthesised in laboratory. Peaks identified by the software are indicated by a short red line placed on the top of the graph. Locations and intensities of peaks corresponding to Cu3[Fe(CN)6]2, as available in the library, have been superimposed on the XRD pattern.

Table A16.2 List of peaks produced by Cu3[Fe(CN)6]: Pos. [°2Th. Height [cts] FWHM r°2Th. d-spacing [A] 10.3389 26.17 0.5904 9.93492 0.30 17.7365 761.95 0.1968 5.80653 8.60 20.5165 8861.20 0.2460 5.02655 100.00 29.1354 4572.32 0.2460 3.55892 51.60 34.2671 538.93 0.2460 3.03854 6.08 35.8837 54.65 0.2952 2.90586 0.62 41.6334 3057.94 0.2460 2.51887 34.51 45.5529 87.80 0.2952 2.31224 0.99 46.7819 1749.63 0.2952 2.25478 19.74 51.5257 649.28 0.3444 2.05949 7.33 54.9435 165.50 0.1968 1.94045 1.87 60.2420 650.50 0.3936 1.78379 7.34 63.3119 127.14 0.1968 1.70565 1.43 64.3834 618.89 0.3444 1.68024 6.98 68.2253 645.09 0.2952 1.59615 7.28 72.1060 120.01 0.3936 1.52099 1.35 75.8144 95.07 0.1968 1.45699 1.07 79.5543 286.08 0.6000 1.39809 3.23 APPENDIX 17

~~Table A17.1 Cyanide concentration in the treated liquor dam~~

~~Sample date Total Cyanide (CNJOT) Weak Acid Dissociable Cyanide (CNWAD) (mg/L) (mg/L)~~

~~2/06/2000 1.41 N/A 23/06/2000 1.20 1.24 31/07/2000 0.8 0.76 22/08/2000 0.30 0.20 27/09/2000 0.1 N/A NOTES H/~~