Scavenging Flotation Tailings using a Continuous Centrifugal Gravity Concentrator by Hassan Ghaffari B.A.Sc. & M.A.Sc. Department of Mining Engineering, Technical Faculty Tehran University, Iran, 1990 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF MINING ENGINEERIG THE UNIVERSITY OF BRITISH COLUMBIA We accepted this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August 2004 © Hassan Ghaffari, 2004 THE UNIVERSITY OF BRITISH COLUMBIA FACULTY OF GRADUATE STUDIES Library Authorization In presenting this thesis in partial fulfillment 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. H ASS A A/ GrMFFAR I 31 ,o%2t>4 Name of Author (please print) Date (dd/mm/yyyy) Title of Thesis: Degree: /l/l-A S C Year: Department of The University of British Columbiumbia ^ u c/ Vancouver, BC Canada grad.ubc.ca/forms/?formlD=THS page 1 of 1 last updated: 31-Aug-04 11 Summary A study was conducted to evaluate the Knelson Continuous Variable Discharge (CVD) concentrator as a scavenger for coarse middling particles from flotation tailings. The goal was to recover a product of suitable grade for recycling to the grinding circuit to improve liberation and aid subsequent recovery in flotation. Such a hybrid flotation- gravity circuit would result in improved metal recoveries, product grades and potentially lead to lower grinding costs. Froth flotation, a physico-chemical process, is the most commonly used process for treating base metal sulphides. Since separation is achieved on the basis of the surface hydrophobicity, mixed-phased particles or middlings are not efficiently treated by froth flotation. The coarser fractions in flotation feeds contain heavy and valuable liberated and non liberated minerals that cannot be floated efficiently. There is a top limit for particle size floatability which varies for different ores. The specific gravity of these particles plays an important role which causes decreasing the flotation performance. This study is based on the premise that the middling particles in tailings can be recovered efficiently by size enhanced density separation. The ability of gravity separators to treat fine particles has been limited by the lack of particle inertia relative to the surface drag forces. Particle inertia can be enhanced by the application of a centrifugal field. The Knelson CVD is a relatively new technology as a continuous centrifugal concentrator that recovers particles based primarily on density but also on size. Tailing samples from two mines were subjected to characterization, batch gravity and pilot scale CVD testing. Table 1 shows the specifications of the analyzed samples. Ill Table 1. Specification of the Analyzed Samples Grade Mine Sample Au (ppm) S% Ni% Eskay Creek (Barrick) Low Grade Tails (LGT) l.l 1.0 N/A High Grade Tails (HGT) 1.9 1.2 N/A Birchtree (INCO Thompson) Rougher-Scavenger Tails (AS-4) <1 3.0 0.2 Cleaner-Scavenger Tails (SC-4) <1 4.2 0.5 The sample characterization of the both Eskay Creek and INCO Thompson samples indicated that there is potential to upgrade gold and nickel in the coarsest fractions. A preliminary assessment of gold and nickel recovery was obtained using a batch Knelson concentrator and the results were similar to those predicted from the characterization results. Based on the characterization and batch gravity tests, there appeared to be a greater opportunity to recover a recyclable product from the LGT and the SC-4, samples than the HGT and AS-4 samples. They were therefore selected for pilot scale tests using the CVD6 separator. The objective was to produce a concentrate with a low mass yield and high gold and nickel upgrade ratios. Products from these tests were subjected to size/assay analysis. The results for Eskay Creek sample show that the gold distributions are significantly higher than sulphur and arsenic distributions, which indicates that free gold or gold associated with poorly floated minerals is being recovered. The best result was obtained from Test 3 in which 28% of the gold was recovered in a concentrate grading 12.5 ppm Au representing 3.3% of the feed mass. This represents a gold upgrade ratio of 8.7. The results for INCO Thompson show that the gold distributions are significantly higher than nickel and sulphur distributions, which indicates that free gold is being recovered. The best result was obtained from Test 3 in which 12.9% of the nickel was recovered in a concentrate grading 0.85% Ni representing 6.7% of the feed mass. It is iv worth noting that the Mg grade is decreased dramatically in the concentrate products. The Mg distribution in concentrate was just 1.7%. This is a good indication that the centrifugal concentrator can also remove the magnesium bearing minerals such as talc. In the case of gold, remarkable results were produced and the metallurgical balances showed gold recoveries ranging from 12.6 to 67.3% and gold grades from 1.4 to 10.0 ppm. Size partition curves were obtained for all tests, which demonstrated that the CVD operates as a size classifier as well as a density separator (size enhanced density separation). For the Eskay sample (Tests 3 and 6) and the INCO sample (Test 7), the cut size was about 300 microns. In conclusion, the pilot scale testing indicated that the CVD was effective at recovering gold, gold bearing sulfides and nickel bearing sulfides from the coarse particles of the flotation tailings and also at de-sliming. The nickel and gold recovered were primarily in the coarse size fractions, which would likely contain middling particles (sulfides + silicates). The results showed that the CVD is capable of rejecting the Mg bearing minerals as well. These results support the application of continuous centrifugal concentrators into hybrid flotation-gravity circuits that could lead to improved metallurgical performance. Plant trials testing are recommended to confirm the results and potential benefits. V TABLE OF CONTENTS Summary ii Table of Contents v List of Figures vii List of Tables x Acknowledgements xiii CHAPTER 1 Introduction 1 1.1. Background 1 1.2. Methodology 2 CHAPTER 2 Literature Review 4 2.1. Introduction 4 2.2. Relationship between Mineral Recovery and Particle Size 4 2.3. Enhanced Gravity Separation Process Technologies 7 2.4. Continuous Centrifugal Gravity Concentrators 8 2.4.1. Types 8 2.4.2. Applications 14 2.5. Conclusion 22 CHAPTER 3 Experimental Program 23 3.1. Analyzed Samples 23 3.1.1 Eskay Creek 23 3.1.2. INCO Thompson 24 3.2. Sample Characterization 25 3.2.1. Sample Preparation 25 3.2.2. Size/Assay Analysis 26 3.2.3. Mineralogical characterization 26 3.2.4. Density Fractionation 26 3.3. Batch Tests 28 3.4. Pilot Scale Tests 29 3.4.1. Products Characterization 3 0 3.4.2. Concentrate Density Fractionation Tests 31 3.4.3. Flotation Test and Proposed Flowsheet 31 CHAPTER 4 Results and Discussion 32 4.1. Eskay Creek Samples 32 4.1.1. Introduction 32 vi 4.1.2. Results and Discussion 33 4.1.3. Conclusion and Recommendation 47 4.2. INCO Thompson sample 49 4.2.1. Introduction 49 4.2.2. Results and Discussion 50 4.2.3. Conclusion and Recommendation 70 CHAPTER 5 Conclusions and Recommendations 73 5.1. Conclusions 73 5.2. Recommendations 75 REFERENCES 76 APPENDICES 81 Appendix I - Eskay Creek 81 Appendix IA Sample Characterization 82 Appendix IB Batch Tests 86 Appendix IC Pilot Scale Test Conditions and Results 87 Appendix ID Mineralogical Analysis 101 Appendix IE Flotation Test 104 Appendix II - INCO Thompson 105 Appendix IIA Sample Characterization 106 Appendix IIB Batch Tests 117 Appendix IIC Pilot Scale Test Conditions and Results 118 Appendix IID Density Fractionation Test Results 132 Appendix HE Flotation Test 141 List of Figures Figure2.1 Dependence of flotation efficiency on particle size for several ores 6 Figure2.2 Typical grinding throughput, product size and flotation Recovery relationship for a base metal concentrator 7 Figure2.3 Continuous Centrifugal Gravity Concentrators 9 Figure 3.1 Eskay Creek Flotation Circuit Sample Point 23 Figure 3.2 Birchtree Flotation Circuit Sample Points 24 Figure 3.3 Sampling procedure of wet tailing samples 25 Figure 3.4 Batch Knelson test procedure 28 Figure 4.1 Au Grade Distributions, LGT & HGT 34 Figure 4.2 S Grade Distributions, LGT & HGT 34 Figure 4.3 Au Grade Distributions in Concentrate and Tailing of Test 3, LGT 38 Figure 4.4 S Grade Distributions in Concentrate and Tailing of Test 3, LGT 39 Figure 4.5 Mass Yield and Au Recovery versus Pinch Valve Closed Time, LGT 40 Figure 4.6 Au Grade/Recovery versus Mass Yield, LGT 41 Figure 4.7 Au Upgrade Ratio/Recovery versus Mass Yield, LGT 41 Figure 4.8 Size Separation Partition Curves, LGT 42 Figure 4.9 Au Recovery versus Size, LGT 43 Figure 4.10 S Recovery versus Size, LGT 44 Figure 4.11 Au Recovery versus S Recovery, LGT 44 Figure 4.12 Proposed Flowsheet, Eskay Creek 46 Figure 4.13 Ni Grade for each Size Fraction, SC-4 & AS-4 51 Vlll Figure 4.14 Mg Grade for each Size Fraction, SC-4 & AS-4 52 Figure 4.15 S Grade for each Size Fraction, SC-4 & AS-4 52 Figure 4.16 Ni Grade for each Size Fraction of Concentrate & Tailing of Test 3, SC-4 56 Figure 4.17 Mg Grade for each Size Fraction of Concentrate & Tailing of Test 3, SC-4 57 Figure 4.18 S Grade for each Size Fraction of Concentrate & Tailing of Test 3, SC-4 57 Figure 4.19 Au Grade for each Size Fraction of Concentrate & Tailing of Test 3, SC-4 58 Figure 4.20 Mass Pull, Ni Grade/Recovery versus Pinch Valve Closed Time, SC-4 59 Figure 4.21 Ni Upgrade and Mg Downgrade Ratios versus Mass Pull, SC-4 60 Figure 4.22 Ni Grade/Recovery versus Cone.