A Fundamental Study of the Reductive Leaching of Chalcopyrite Using Metallic Iron

A FUNDAMENTAL STUDY OF THE REDUCTIVE LEACHING OF CHALCOPYRITE USING METALLIC IRON by NED AM ABED B. Sc., Chemical Engineering, Jordan University of Science and Technology, Jordan, 1989 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Metals and Materials Engineering We accept this thesis as conforming to the,required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1999 ©Nedam Abed, 1999 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) ABSTRACT A fundamental study of the reductive leaching (decomposition) of chalcopyrite was performed in both sulfate and chloride media. This was done to understand the physical chemistry of the leaching reactions and the possibility of developing a process flowsheet. The main objective of reductive leaching is to achieve the enrichment of chalcopyrite by rejection of iron and sulfur. A chalcopyrite concentrate containing around 60% chalcopyrite and analyzing around 28% copper was leached under reducing conditions using metallic iron. Various parameters were studied to understand their effect on leaching kinetics, including : temperature, particle size, agitation, acid concentration, molar ratios, and others. The leaching data were analyzed to determine the leaching mechanism and develop a kinetic model. The leaching reaction was found to be rapid on fresh surfaces of the concentrate, but slows markedly in one hour, as a film of products, mainly chalcocite, forms on particle surfaces. Iron was also found to enter the leach solution as soluble ferrous ions and sulfur is released as hydrogen sulfide. The general leaching reaction may be written as : + 2+ 2CuFeS2(s) + Fe(s) + 6H (aq) ->' Cu2S(s) + 3Fe (aq) + 3H2S(g) The proposed mechanism is a series of reactions. It is envisaged to be composed of two parts : a corrosion mechanism, which is iron dissolution, and galvanic mechanism, which is chalcopyrite reduction. The kinetic analysis indicated that the leaching reaction, which is electrochemical in nature, follows the shrinking core model under product layer diffusion control, and the rate determining step is the transport of one or more of reaction species, through the product layer. The reaction was dependent on the initial acid concentration, chalcopyrite particle size and molar ratio of iron to chalcopyrite. Moreover, the reaction was independent of the rate of agitation beyond that required to provide a well-mixed reaction mixture. Under stoichiometric conditions, room temperature and atmospheric pressure, the conversion (decomposition of chalcopyrite to simpler copper sulfides) was always below 60%, unless the initial amount of the reductant was increased or very fine chalcopyrite particles were used. ii For the studied experimental conditions, the developed parabolic leaching model for sulfate media takes the form : -33,880" 2/3 l-3(l-Xb) + 2(l-Xb) 7 [FT] exp t R v RT J and for chloride media, The parabolic leaching behavior was confirmed from the successful estimation of the related thermodynamic and kinetic properties of the leaching systems. The analysis of temperature dependence indicated that leaching increases with increasing temperature up to 65 °C. The apparent activation energy for leaching in sulfate media was estimated to be ~33 kJ/mol, and for chloride media, ~26 kJ/mol under stoichiometric conditions, in the temperature range 25-65 °C. Chemical analysis was extensively used based on wet chemistry methods, which were capable of demonstrating the general reaction stoichiometry including the composition of the new solid phase. Further, qualitative analysis by SEM confirmed the findings of the kinetic and chemical analysis. The findings from the fundamental study show that conversion is preferred under high solid pulp density (SPD), and back reaction kinetics have essentially little or no adverse effect. In an attempt to improve the conversion and utilize the results for a possible flowsheet, the concentrate was leached in the presence of excess chloride content, at -35% SPD. Based on material balance calculations, at room temperature and under near stoichiometric conditions, greater than 80% of the added chalcopyrite can be decomposed to yield copper sulfides (chalcocite) by rejection of iron and sulfur, using size fractions smaller than 74 jam. As a result of these findings, a process flowsheet was developed and further investigation is required to demonstrate the viability of the proposed process. iii TABLE OF CONTENTS Abstract ii List of Tables vi . List of Figures ix Acknowledgment xiii Section 1 Introduction 1 Section 2 Literature Survey : 8 2.1 Thermodynamics of Chalcopyrite Leaching 8 2.2 Oxidative Leaching of Chalcopyrite 30 2.3 Non-oxidative Leaching of Chalcopyrite 37 2.4 Reductive Leaching of Chalcopyrite 38 2.5 Halide Media Leaching of Chalcopyrite 50 Section 3 Objectives 52 Section 4 Proposed Leaching Mechanism with Metallic Iron 53 Section 5 Experimental Methods 57 5.1 Materials 57 5.2 Methods 59 5.2.1 The Kinetic Study 59 5.2.2 The Process Study 62 5.2.3 Analysis Techniques 64 5.2.4 Reaction Product Characterization 64 5.3. Calculations 65 Section 6 Results and Discussion 67 6.1 Analysis of Reaction Kinetics 67 6.1.1 Effect of Agitation 79 iv 6.1.2 Effect of Temperature 83 6.1.3 Effect of Particle Size 92 6.1.4 Effect of Initial Acid Concentration 100 6.1.5 Effect of Metallic Iron Addition 109 6.1.6 Effect of Chalcopyrite Addition 114 6.1.7 Effect of Solid Pulp Density (SPD) 119 6.1.8 Leaching Rates of Chalcopyrite Particles 121 6.2 Schematic Representation of the Leaching Process 126 6.3 Concluding Remarks 138 6.4 Process Development 139 6.4.1 Leaching 139 6.4.1.1 Acid Effect 139 6.4.1.2 Ferrous Chloride Effect 142 6.4.1.3 Metallic Iron Effect 142 6.4.1.4 Particle Size Effect 144 6.4.2 Solid / Liquid Separation 148 6.4.3 Iron Removal 148 6.4.4 Solid Washing Unit 148 6.4.5 Hydrogen Sulfide Collection Unit 149 6.4.6 Process Advantages 149 6.5 Hydrogen Sulfide Treatment 151 Section 7 Conclusions 156 Section 8 Recommendations for Future Research 158 Bibliography 162 Appendix I : Leaching Kinetics Models 172 Appendix II : Chemical Analysis 183 v LIST OF TABLES Table 1.1 : Common copper minerals 3 Table 1.2 : Electronic and structural properties of selected sulfide and oxide minerals 6 Table 2.1 : Summary of physical and chemical properties of group 11 (IB) metals 9 Table 2.2 : Selected solubility data for copper and related species 10 Table 2.3 : Thermodynamic values for some common species and reactions in copper aqueous chemistry 13 Table 2.4 : Reactions and thermodynamic equations used in constructing the Eh-pH diagrams 16 Table 2.5 : Selected heat capacity values for different species 21 Table 2.6 : Standard thermodynamic data for different species 22 Table 2.7 : Selected physical constants for copper and other species 23 Table 2.8 : The oxidative leaching of chalcopyrite in sulfate media 30 Table 2.9 : Reduction potentials of some metals and minerals at standard conditions 40 Table 2.10 : Summary of reviewed research on chalcopyrite reductive leaching 49 Table 5.1 : Detailed chemical analysis of the tested chalcopyrite concentrate 57 Table 5.2 : The mineralogical composition of the tested chalcopyrite concentrate 57 Table 5.3 : Particle size distribution of the concentrate 58 Table 6.1 : Sample experimental leaching data for selecting a leaching model by Wen's method (sulfate media, stoichiometric run, 25 °C) 69 Table 6.2 : Sample experimental leaching data for selecting a leaching model by Wen's method (chloride media, stoichiometric run, 65 °C) 70 Table 6.3 : Agitation speed effect on reaction kinetics (stoichiometric runs, sulfate media, 25 °C) 80 Table 6.4 : Agitation speed effect on reaction kinetics (stoichiometric runs, chloride media, 25 °C). 80 Table 6.5 : Temperature effect on reaction kinetics (0.1 M H2S04 solution, stoichiometric runs, 25-85 °C) 84 Table 6.6 : Temperature effect on reaction kinetics (0.1 M HC1 solution, stoichiometric runs, 25-85 °C) 85 Table 6.7 : Temperature dependence of reaction rates and related thermodynamic values for sulfate and chloride media 89 Table 6.8 : Particle size effect on reaction kinetics (sulfate media, stoichiometric runs, 25 °C) 93 Table 6.9 : Particle size effect on reaction kinetics (chloride media, stoichiometric runs, 25 °C) 94 Table 6.10 : Particle size dependence of reaction rates for sulfate and chloride media 94 Table 6.11 : Acid concentration effect on reaction kinetics (sulfate media, constant CuFeS2 and Fe additions, 25 °C) 101 Table 6.12 : Acid concentration effect on reaction kinetics (chloride media, constant CuFeS2 and Fe additions, 25 °C) 101 Table 6.13 : Hydrogen ion dependence of reaction rates (sulfate media) 104 Table 6.14 : Hydrogen ion dependence of reaction rates (chloride media) 107 Table 6.15 : Metallic iron effect on reaction kinetics (sulfate media, constant CuFeS2 and H2S04 additions, 25 °C) 110 Table 6.16 : Metallic iron effect on reaction kinetics

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