THE INTERACTION BETWEEN XANTHATE AND SULPHUR DIOXIDE IN THE FLOTATION OF NICKEL-COPPER SULPHIDE ORES by ANTONIO EDUARDO CLARK PERES B.Sc, UFMG, Brazil, 1968 M.Sc, UFMG, Brazil, 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Mineral Engineering) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July, 1979 © Antonio Eduardo Clark Peres, 1979 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of MINERAL ENGINEERING The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Dat^July, 1979 Research Supervisor: George W. Poling, Prof. & Head Dept. of Mineral Engineering - ii - , , ABSTRACT Electrochemical methods and small scale flotation tests were used to study the effects of sulphur dioxide and potassium amyl xanthate on the floatabilities of pentlandite, chalcopyrite and nickeliferous pyrrhotite, at pH 5.5. Mixed potentials of all three mineral systems were positive to the dixanthogen/xanthate redox couple, even in the presence of aqueous SO2. Thus the existence of dixanthogen is thermodynamically favoured in all these systems. The tests also indicated that adsorption of xanthate by: (i) chalcopyrite is enhanced by SO2; (ii) pentlandite is impaired by SO2; (iii) pyrrhotite is unaffected by SO2; Anodic polarization curves, determined on mineral electrodes, suggested that, in xanthated systems, the collector (probably dixanthogen) forms a film on the electrodes. This film inhibits the continued electron transfer reactions on the surface. The protective character of the film is higher for chalcopyrite (increased by SO2), than for pentlandite (decreased by SO2), than for pyrrhotite (unaffected by SO2). Cathodic polarization curves indicated that the cathodic process, on pentlandite and pyrrhotite electrodes, is controlled by oxygen reduction. The reduction of oxidized species on the surface is suggested as the con• trolling mechanism on chalcopyrite electrodes. Small scale flotation tests showed that the presence of SO2 increases an already very high,recovery of chalcopyrite; decreases a high recovery of pentlandite, and decreases further a very low recovery of pyrrhotite. - iii - TABLE OF CONTENTS Page ABSTRACT ii LIST OF TABLES vi LIST OF FIGURES vii ACKNOWLEDGEMENT x CHAPTER 1 - INTRODUCTION 1 CHAPTER 2 - LITERATURE REVIEW 3 2.1 Current Milling Practice of Sulphide 3 Nickel-Copper Ores 2.2 Use of Sulphur Dioxide as a Flotation Reagent 6 2.3 Level of Hydrophobicity at the Surface of 10 Minerals 2.4 Sulphur Dioxide Water Chemistry 12 2.5 Geology of Nickel Sulphide Ores 18 2.5.1 Identification of Copper and Nickel 22 Sulphide Minerals 2.6 Electrophysical Properties of Sulphide 23 Minerals 2.7 Electrochemistry of Sulphide Minerals 25 CHAPTER 3 - OBJECTIVES 34 CHAPTER 4 - EXPERIMENTAL METHODS AND APPARATUS 35 4.1 Electrochemical Experiments 35 4.1.1 Rest Potentials on a Platinum 35 Electrode 4.1.2 Tests with Mineral Electrodes 38 -. iv - Page 4.2 Microflotation Tests 42 4.2.1 Modified Hallimond Tube 42 4.2.2 Modified Smith-Partridge Cell 44 CHAPTER 5 - MATERIALS 46 5.1 Sulphide Mineral Samples 46 • 5.2 Chemical Reagents 49 5.3 Adsorption of Xanthate on Sulphide Minerals 51 CHAPTER 6 - RESULTS AND DISCUSSION 54 6.1 Rest Potentials on Platinum Electrode 54 6.1.1 Preliminary Tests 54 6.1.2 Tests with Pentlandite 60 6.1.3 Tests with Chalcopyrite 68 6.1.4 Tests with Pyrrhotite 73 6.1.5 Correlation between Redox Couples and 76 Experimental Results 6.2 Tests with Mineral Electrodes 81 6.2.1 Pentlandite Electrode 81 6.2.2 Chalcopyrite Electrode 91 6.2.3 Pyrrhotite Electrode 97 6.3 Microflotation Tests 99 6.3.1 Tests with Pentlandite 99 6.3.2 Tests with Chalcopyrite 105 6.3.3 Tests with Pyrrhotite 105 6.4 Discussion of the Effect of SO,, on the 106 Hydrophobicity Level -v.- Page CHAPTER 7 - CONCLUSIONS 108 CHAPTER 8 - RECOMMENDATIONS FOR FUTURE WORK 110 REFERENCES 111 APPENDIX 1 118 APPENDIX 2 119 - vi - LIST OF TABLES Page I Reagents often used in flotation of nickel-copper 6 sulphide ores (basic circuit). II Sulphur dioxide solubility in water at various 12 temperatures, at 1 atm of total pressure, after Schroeter (24). Ill The effect of pH on the conversion of 1 mg/1 of SO2 14 gas into R^SOo, HSO3, and SO32-, after Kosherbaev and Sokolov (12). IV Infrared adsorption frequencies of aqueous SO^. 15 V Minerals in the iron-nickel-sulphur system. 19 VI Correlation between rest potentials and the products 28 of interaction of sulphide minerals with thiol collectors, after Allison et al. (72) and Finkelstein and Goold (73). VII Elemental distribution of sulphide mineral samples 48 and corresponding ideal stoichiometric compounds. VIII Electrical resistivity of sulphide minerals (in Q, x cm). 49 IX Adsorption of xanthate on sulphide minerals. 52 X Standard potential for the redox couple X^/X . 56 XI Rest potentials measured with chalcopyrite electrode. 92 XII Rest potentials measured with pyrrhotite electrode. 98 XIII Results of small scale flotation tests with pentlandite. 104 XIV Results of small scale flotation tests with chalcopy- 105 rite. XV Results of small scale flotation tests with pyrrhotite. 106 - vii - LIST OF FIGURES Page Figure 1. Flowsheet for Falconbridge Mill, after 4 Boldt (2). Figure 2. Flowsheet for Copper Cliff Mill, after 5 Boldt (2). Figure 3. Flowsheet for Lynn Lake Mill, after 7 Boldt (2). Figure 4. Oxidation state diagram for sulphur. 16 Figure 5. Central portion of the Fe-Ni-S triangular 21 diagram after Misra and Fleet (37). Figure 6. Eh - pH diagram for pentlandite and sulphur- 31 water system (a^n-t- = 10-^) . Figure 7. Eh - pH diagram for pentlandite and sulphur 32 water system (yt = 10"6; a^- = aR _ = 10 ). Figure 8. Current - potential curves for oxygen reduction 33 on noble metal and sulphide mineral electrodes, at pH 1 and 9.06, after Rand (77). Figure 9. Schematic view of the apparatus for the measure- 37 ment of rest potentials with platinum electrode. Figure 10. Schematic view of the apparatus for tests with 40 mineral electrodes. Figure 11. Preparation of mineral electrodes. 41 Figure 12. Modified Hallimond tube. 43 Figure 13. Modified Smith-Partridge cell. 45 Figure 14. Test for semiconductivity type of a mineral 50 Figure 15. Rest potential (on platinum electrode) versus 55 pH for 0.1N KC1 solution. Figure 16. Rest potential (on platinum electrode) versus 57 log [X-] for KAmX solutions. - viii - Page Figure 17. Rest potential (on platinum electrode) versus 59 pH for SO^ solutions. Figure 18. Rest potential (on platinum electrode) versus 61 pH for SO^ - KAmX solutions. Figure 19. Rest potential (on platinum electrode) versus 62 pH for pentlandite slurry. Figure 20. Rest potential (on platinum electrode) versus 64 pH for pentlandite slurry - SC^. Figure 21. Rest potential (on platinum electrode) versus 66 time for pentlandite slurry - KAmX. Figure 22. Rest potential (on platinum electrode) versus 67 time for pentlandite slurry - SC^ - KAmX. Figure 23. Rest potential (on platinum electrode) versus 69 pH for chalcopyrite slurry. Figure 24. Rest potential (on platinum electrode) versus 70 time for chalcopyrite slurry - KAmX. Figure 25. Rest potential (on platinum electrode) versus 71 time for chalcopyrite slurry - SC^ ~ KAmX. Figure 26. Rest potential (on platinum electrode) versus 72 pH for pyrrhotite slurry. Figure 27. Rest potential (on platinum electrode) versus 74 time for pyrrhotite slurry - KAmX. Figure 28. Rest potential (on platinum electrode) versus 75 time for pyrrhotite slurry - SO2- KAmX Figure 29. Schematic picture of the system SO2 ~ KAmX in 77 terms of activation polarization curves. Figure 30. Schematic picture of the system pentlandite - 78 SO2 - KAmX in terms of activation polarization curves. Figure 31. Rest potential (on pentlandite electrode) versus 82 ph for 0.1N KC1 and S02 solutions. Figure 32. Rest potential (on pentlandite electrode) versus 84 time for KAmX and S0„ - KAmX solutions. ^ ±x - Page Figure 33. Polarization curves of pentlandite electrode 86 in 01N KC1 solution. Figure 34. Polarization curves of pentlandite electrode 87 in KAmX solution. Figure 35. Polarization curves of pentlandite electrode 88 in SC^ solution. Figure 36. Polarization curves of pentlandite electrode 89 in SO^ - KAmX solution. Figure 37. Polarization curves of chalcopyrite electrode 93 in 0.1N KC1 solution. Figure 38. Polarization curves of chalcopyrite electrode 94 in KAmX solution. Figure 39. Polarization curves of chalcopyrite electrode 95 in SC^ solution. Figure 40. Polarization curves of chalcopyrite electrode 96 in SO2 - KAmX solution. Figure 41. Polarization curves of pyrrhotite electrode 100 in 0.1N KC1 solution. Figure 42. Polarization curves of pyrrhotite electrode 101 in KAmX solution. Figure 43. Polarization curves of pyrrhotite electrode 102 in SO2 solution. Figure 44. Polarization curves of pyrrhotite electrode 103 in S0„ - KAmX solution. - X - ACKNOWLEDGEMENT The sharp guidance and sincere friendship of my research supervisor Dr. G. W. Poling are gratefully acknowledged. My thanks are also due to Dr. J. S. Forsyth, Dr. J. Leja, Prof. A. L. Mular, Dr. E. Peters and Dr. A. P. Watkinson for their useful suggestions and discussions. My gratitude is extended to Prof. J. B. Evans for his encouragement and friendship. The help from Mr. B.Y.K. Chow, Mrs. S. Finora, Mr. D. T. Hornsby,. Mr. E. J. Jickels, Mr.