Open Collections will be undergoing maintenance Monday June 8th, 2020 11:00 – 13:00 PT. No downtime is expected, but site performance may be temporarily impacted.

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The interaction between xanthate and sulphur dioxide in the flotation of nickel-copper sulphide ores Peres, Antonio Eduardo Clark 1979

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1979_A1 P47.pdf [ 4.8MB ]
Metadata
JSON: 831-1.0081082.json
JSON-LD: 831-1.0081082-ld.json
RDF/XML (Pretty): 831-1.0081082-rdf.xml
RDF/JSON: 831-1.0081082-rdf.json
Turtle: 831-1.0081082-turtle.txt
N-Triples: 831-1.0081082-rdf-ntriples.txt
Original Record: 831-1.0081082-source.json
Full Text
831-1.0081082-fulltext.txt
Citation
831-1.0081082.ris

Full Text

THE INTERACTION BETWEEN XANTHATE AND SULPHUR DIOXIDE IN THE FLOTATION OF NICKEL-COPPER SULPHIDE ORES by ANTONIO EDUARDO CLARK PERES B . S c , UFMG, B r a z i l , 1968 M.Sc, UFMG, B r a z i l , 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of M i n e r a l Engineering) We accept t h i s t h e s i s as conforming to the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1979 © Antonio Eduardo C l a r k Peres, 1979 In present ing t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree a t the U n i v e r s i t y of B r i t i s h Co lumbia, I agree tha t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r re fe rence and s tudy. I f u r t h e r agree tha t permiss ion f o r ex tens ive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s en t a t i v e s . I t i s understood tha t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed wi thout my w r i t t e n pe rm iss i on . Department of MINERAL ENGINEERING The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P lace Vancouver, Canada V6T 1W5 D a t ^ J u l y , 1979 Research Supervisor: George W. P o l i n g , P r o f . & Head Dept. of M i n e r a l Engineering - i i -, , ABSTRACT El e c t r o c h e m i c a l methods and small s c a l e f l o t a t i o n t e s t s were used to study the e f f e c t s of sulphur d i o x i d e and potassium amyl xanthate on the f l o a t a b i l i t i e s of p e n t l a n d i t e , c h a l c o p y r i t e and n i c k e l i f e r o u s p y r r h o t i t e , at pH 5.5. Mixed p o t e n t i a l s of a l l three m i n e r a l systems were p o s i t i v e to the dixanthogen/xanthate redox couple, even i n the presence of aqueous S O 2 . Thus the existence of dixanthogen i s thermodynamically favoured i n a l l these systems. The t e s t s a l s o i n d i c a t e d that adsorption of xanthate by: ( i ) c h a l c o p y r i t e i s enhanced by S O 2 ; ( i i ) p e n t l a n d i t e i s impaired by S O 2 ; ( i i i ) p y r r h o t i t e i s unaffected by S O 2 ; Anodic p o l a r i z a t i o n curves, determined on mineral e l e c t r o d e s , suggested t h a t , i n xanthated systems, the c o l l e c t o r (probably dixanthogen) forms a f i l m on the e l e c t r o d e s . This f i l m i n h i b i t s the continued e l e c t r o n t r a n s f e r r e a c t i o n s on the surface. The p r o t e c t i v e character of the f i l m i s higher f o r c h a l c o p y r i t e (increased by S O 2 ) , than f o r p e n t l a n d i t e (decreased by S O 2 ) , than f o r p y r r h o t i t e (unaffected by S O 2 ) . Cathodic p o l a r i z a t i o n curves i n d i c a t e d that the cathodic process, on p e n t l a n d i t e and p y r r h o t i t e e l e c t r o d e s , i s c o n t r o l l e d by oxygen r e d u c t i o n . The r e d u c t i o n of o x i d i z e d species on the surface i s suggested as the con-t r o l l i n g mechanism on c h a l c o p y r i t e e l e c t r o d e s . Small s c a l e f l o t a t i o n t e s t s showed that the presence of S O 2 increases an already very high,recovery of c h a l c o p y r i t e ; decreases a h i g h recovery of p e n t l a n d i t e , and decreases f u r t h e r a very low recovery of p y r r h o t i t e . - i i i -TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i LIST OF FIGURES v i i ACKNOWLEDGEMENT x CHAPTER 1 - INTRODUCTION 1 CHAPTER 2 - LITERATURE REVIEW 3 2.1 Current M i l l i n g P r a c t i c e of Sulphide 3 Nickel-Copper Ores 2.2 Use of Sulphur Dioxide as a F l o t a t i o n Reagent 6 2.3 Level of Hydrophobicity at the Surface of 10 Minerals 2.4 Sulphur Dioxide Water Chemistry 12 2.5 Geology of N i c k e l Sulphide Ores 18 2.5.1 I d e n t i f i c a t i o n of Copper and N i c k e l 22 Sulphide M i n e r a l s 2.6 E l e c t r o p h y s i c a l P r o p e r t i e s of Sulphide 23 Minerals 2.7 E l e c t r o c h e m i s t r y of Sulphide Minerals 25 CHAPTER 3 - OBJECTIVES 34 CHAPTER 4 - EXPERIMENTAL METHODS AND APPARATUS 35 4.1 E l e c t r o c h e m i c a l Experiments 35 4.1.1 Rest P o t e n t i a l s on a Platinum 35 El e c t r o d e 4.1.2 Tests w i t h M i n e r a l E l e c t r o d e s 38 -. i v -Page 4.2 M i c r o f l o t a t i o n Tests 42 4.2.1 M o d i f i e d Hallimond Tube 42 4.2.2 Mo d i f i e d Smith-Partridge C e l l 44 CHAPTER 5 - MATERIALS 46 5.1 Sulphide M i n e r a l Samples 46 • 5.2 Chemical Reagents 49 5.3 Adsorption of Xanthate on Sulphide M i n e r a l s 51 CHAPTER 6 - RESULTS AND DISCUSSION 54 6.1 Rest P o t e n t i a l s on Platinum E l e c t r o d e 54 6.1.1 P r e l i m i n a r y Tests 54 6.1.2 Tests w i t h P e n t l a n d i t e 60 6.1.3 Tests w i t h C h a l c o p y r i t e 68 6.1.4 Tests w i t h P y r r h o t i t e 73 6.1.5 C o r r e l a t i o n between Redox Couples and 76 Experimental Results 6.2 Tests w i t h M i n e r a l Electrodes 81 6.2.1 P e n t l a n d i t e Electrode 81 6.2.2 C h a l c o p y r i t e Electrode 91 6.2.3 P y r r h o t i t e E l e c t r o d e 97 6.3 M i c r o f l o t a t i o n Tests 99 6.3.1 Tests w i t h P e n t l a n d i t e 99 6.3.2 Tests w i t h C h a l c o p y r i t e 105 6.3.3 Tests w i t h P y r r h o t i t e 105 6.4 D i s c u s s i o n of the E f f e c t of SO,, on the 106 Hydrophobicity L e v e l - v . -Page CHAPTER 7 - CONCLUSIONS 108 CHAPTER 8 - RECOMMENDATIONS FOR FUTURE WORK 110 REFERENCES 111 APPENDIX 1 118 APPENDIX 2 119 - v i -LIST OF TABLES Page I Reagents o f t e n used i n f l o t a t i o n of nickel-copper 6 sulphide ores (basic c i r c u i t ) . I I Sulphur d i o x i d e s o l u b i l i t y i n water at v a r i o u s 12 temperatures, at 1 atm of t o t a l pressure, a f t e r Schroeter (24). I l l The e f f e c t of pH on the conversion of 1 mg/1 of SO2 14 gas i n t o R^SOo, HSO3, and SO32-, a f t e r Kosherbaev and Sokolov (12). IV I n f r a r e d adsorption frequencies of aqueous SO^. 15 V M i n e r a l s i n the i r o n - n i c k e l - s u l p h u r system. 19 VI C o r r e l a t i o n between r e s t p o t e n t i a l s and the products 28 of i n t e r a c t i o n of sulphide minerals w i t h t h i o l c o l l e c t o r s , a f t e r A l l i s o n et a l . (72) and F i n k e l s t e i n and Goold (73). V I I Elemental d i s t r i b u t i o n of sulphide mineral samples 48 and corresponding i d e a l s t o i c h i o m e t r i c compounds. V I I I E l e c t r i c a l r e s i s t i v i t y of sulphide minerals ( i n Q, x cm). 49 IX Adsorption of xanthate on sulphide minerals. 52 X Standard p o t e n t i a l f o r the redox couple X^/X . 56 XI Rest p o t e n t i a l s measured w i t h c h a l c o p y r i t e e l e c t r o d e . 92 X I I Rest p o t e n t i a l s measured w i t h p y r r h o t i t e e l e c t r o d e . 98 X I I I R e sults of small s c a l e f l o t a t i o n t e s t s w i t h p e n t l a n d i t e . 104 XIV R e s u l t s of s m a l l s c a l e f l o t a t i o n t e s t s w i t h chalcopy- 105 r i t e . XV R e sults of small s c a l e f l o t a t i o n t e s t s w i t h p y r r h o t i t e . 106 - v i i -LIST OF FIGURES Page Figure 1. Flowsheet f o r Falconbridge M i l l , a f t e r 4 Boldt (2). Figure 2. Flowsheet f o r Copper C l i f f M i l l , a f t e r 5 Boldt (2). Figure 3. Flowsheet f o r Lynn Lake M i l l , a f t e r 7 Boldt (2). Figure 4. Oxidation s t a t e diagram f o r sulphur. 16 Figure 5. C e n t r a l p o r t i o n of the Fe-Ni-S t r i a n g u l a r 21 diagram a f t e r M i s r a and F l e e t (37). Figure 6. Eh - pH diagram f o r p e n t l a n d i t e and sulphur- 31 water system (a^n-t- = 10 -^) . Figure 7. Eh - pH diagram f o r p e n t l a n d i t e and sulphur 32 water system ( y t = 10"6; a ^ - = a R _ = 10 ). Figure 8. Current - p o t e n t i a l curves f o r oxygen r e d u c t i o n 33 on noble metal and sulphide mineral e l e c t r o d e s , at pH 1 and 9.06, a f t e r Rand (77). Figure 9. Schematic view of the apparatus f o r the measure- 37 ment of r e s t p o t e n t i a l s w i t h platinum e l e c t r o d e . Figure 10. Schematic view of the apparatus f o r t e s t s w i t h 40 mineral e l e c t r o d e s . Figure 11. Pr e p a r a t i o n of mineral e l e c t r o d e s . 41 Figure 12. M o d i f i e d Hallimond tube. 43 Figure 13. M o d i f i e d Smith-Partridge c e l l . 45 Figure 14. Test f o r semi c o n d u c t i v i t y type of a mineral 50 Figure 15. Rest p o t e n t i a l (on platinum el e c t r o d e ) versus 55 pH f o r 0.1N KC1 s o l u t i o n . Figure 16. Rest p o t e n t i a l (on platinum el e c t r o d e ) versus 57 lo g [X -] f o r KAmX s o l u t i o n s . - v i i i -Page Figure 17. Rest p o t e n t i a l (on platinum electrode) versus 59 pH f o r SO^ s o l u t i o n s . Figure 18. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 61 pH f o r SO^ - KAmX s o l u t i o n s . Figure 19. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 62 pH f o r p e n t l a n d i t e s l u r r y . F i g ure 20. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 64 pH f o r p e n t l a n d i t e s l u r r y - SC^. Figure 21. Rest p o t e n t i a l (on platinum electrode) versus 66 time f o r p e n t l a n d i t e s l u r r y - KAmX. Figure 22. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 67 time f o r p e n t l a n d i t e s l u r r y - SC^ - KAmX. Figure 23. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 69 pH f o r c h a l c o p y r i t e s l u r r y . Figure 24. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 70 time f o r c h a l c o p y r i t e s l u r r y - KAmX. Figure 25. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 71 time f o r c h a l c o p y r i t e s l u r r y - SC^ ~ KAmX. Figure 26. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 72 pH f o r p y r r h o t i t e s l u r r y . Figure 27. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 74 time f o r p y r r h o t i t e s l u r r y - KAmX. Figure 28. Rest p o t e n t i a l (on platinum e l e c t r o d e ) versus 75 time f o r p y r r h o t i t e s l u r r y - SO2 - KAmX Figure 29. Schematic p i c t u r e of the system SO2 ~ KAmX i n 77 terms of a c t i v a t i o n p o l a r i z a t i o n curves. Figure 30. Schematic p i c t u r e of the system p e n t l a n d i t e - 78 SO2 - KAmX i n terms of a c t i v a t i o n p o l a r i z a t i o n curves. Figure 31. Rest p o t e n t i a l (on p e n t l a n d i t e electrode) versus 82 ph f o r 0.1N KC1 and S0 2 s o l u t i o n s . Figure 32. Rest p o t e n t i a l (on p e n t l a n d i t e e l e c t r o d e ) versus 84 time f o r KAmX and S0„ - KAmX s o l u t i o n s . ^ ±x -Page Figure 33. P o l a r i z a t i o n curves of p e n t l a n d i t e e l e c t r o d e 86 i n 01N KC1 s o l u t i o n . F i g ure 34. P o l a r i z a t i o n curves of p e n t l a n d i t e e l e c t r o d e 87 i n KAmX s o l u t i o n . Figure 35. P o l a r i z a t i o n curves of p e n t l a n d i t e e l e c t r o d e 88 i n SC^ s o l u t i o n . Figure 36. P o l a r i z a t i o n curves of p e n t l a n d i t e e l e c t r o d e 89 i n SO^ - KAmX s o l u t i o n . Figure 37. P o l a r i z a t i o n curves of c h a l c o p y r i t e e l e c t r o d e 93 i n 0.1N KC1 s o l u t i o n . Figure 38. P o l a r i z a t i o n curves of c h a l c o p y r i t e e l e c t r o d e 94 i n KAmX s o l u t i o n . F i g ure 39. P o l a r i z a t i o n curves of c h a l c o p y r i t e e l e c t r o d e 95 i n SC^ s o l u t i o n . Figure 40. P o l a r i z a t i o n curves of c h a l c o p y r i t e e l e c t r o d e 96 i n SO2 - KAmX s o l u t i o n . F i g ure 41. P o l a r i z a t i o n curves of p y r r h o t i t e e l e c t r o d e 100 i n 0.1N KC1 s o l u t i o n . F i g ure 42. P o l a r i z a t i o n curves of p y r r h o t i t e e l e c t r o d e 101 i n KAmX s o l u t i o n . Figure 43. P o l a r i z a t i o n curves of p y r r h o t i t e e l e c t r o d e 102 i n SO2 s o l u t i o n . F i g ure 44. P o l a r i z a t i o n curves of p y r r h o t i t e e l e c t r o d e 103 i n S0„ - KAmX s o l u t i o n . - X -ACKNOWLEDGEMENT The sharp guidance and s i n c e r e f r i e n d s h i p of my research supervisor Dr. G. W. P o l i n g are g r a t e f u l l y acknowledged. My thanks are a l s o due to Dr. J . S. Forsyth, Dr. J . L e j a , P r o f . A. L. Mular, Dr. E. Peters and Dr. A. P. Watkinson f o r t h e i r u s e f u l suggestions and d i s c u s s i o n s . My g r a t i t u d e i s extended to P r o f . J . B. Evans f o r h i s encouragement and f r i e n d s h i p . The help from Mr. B.Y.K. Chow, Mrs. S. F i n o r a , Mr. D. T. Hornsby,. Mr. E. J . J i c k e l s , Mr. F. Schmidiger, Miss C. S. Velestuk and Mrs. 0. M. Weber i s f u l l y a ppreciated. The f i n a n c i a l support from CAPES and UFMG i s t h a n k f u l l y acknowledged. This t h e s i s i s dedicated to my wif e and daughters. CHAPTER 1 INTRODUCTION Canada i s the world's l e a d i n g producer of n i c k e l concentrates. The 1977 production of 232,500 t ^ " ^ of metal contained represented t h i r t y percent of the world t o t a l . Mining a c t i v i t i e s are p r e s e n t l y c a r r i e d out i n Ontario and Manitoba by two companies: INCO L i m i t e d and Falconbridge N i c k e l L i m i t e d . U n t i l i t s c l o s u r e i n 1976, S h e r r i t t Gordon's Lynn Lake m i l l , i n Manitoba, a c t i v e l y c o n t r i b u t e d to the Canadian production. Purchased concentrates, some of them imported, are now being used to feed t h e i r Fort Saskatchewan r e f i n e r y , i n A l b e r t a . N i c k e l concentrates produced i n Canada come from sulphide ores. P e n t l a n d i t e (and i t s a l t e r a t i o n products) and n i c k e l i f e r o u s p y r r h o t i t e are the n i c k e l bearing minerals. Most n i c k e l sulphide ores c o n t a i n copper as c h a l c o p y r i t e . G e n e r a l l y , c h a l c o p y r i t e and p e n t l a n d i t e are f l o a t e d i n a rougher stage, followed by a scavenger step to recover a c t -i v a t e d n i c k e l i f e r o u s p y r r h o t i t e . Nickel-copper s e p a r a t i o n i s e i t h e r a mineral processing or a p y r o m e t a l l u r g i c a l o p e r a t i o n . Obtaining a p e n t l a n d i t e - c h a l c o p y r i t e concentrate, w i t h l i t t l e pyrrho-t i t e , i s p o s s i b l e when the pulp i s a c i d i f i e d w i t h SO2 p r i o r to f l o t a t i o n w i t h a l k a l i metal xanthates. The mechanism of t h i s i n t e r a c t i o n i s p r e s e n t l y u n c l e a r . Sulphur d i o x i d e i s a reducing agent and the current theory s t a t e s that o x i d a t i o n of xanthate i s of t e n a requirement f o r f l o t a t i o n . The present i n v e s t i g a t i o n aims to c o n t r i b u t e to the understanding of the f l o t a t i o n behaviour of n i c k e l sulphide ores w i t h xanthates, i n the presence of sulphur d i o x i d e . This study was deemed worthwhile due to the importance of production of n i c k e l concentrates and the s c a r c i t y of info r m a t i o n concerning t h i s f l o t a t i o n system. 1 - 2 -S t a r t i n g from the current m i l l i n g p r a c t i c e of sulphide n i c k e l -copper ores, a n a t u r a l choice of t o p i c s to be reviewed i n c l u d e s u t i l i z -a t i o n of SC>2 as a r e g u l a t i n g reagent i n mineral p r o c e s s i n g , mechanisms of a c t i o n of modifying reagents, SO2 water chemistry, n i c k e l - c o p p e r ores, p r i n c i p a l minerals and t h e i r a s s o c i a t i o n s , e l e c t r o p h y s i c a l p r o p e r t i e s of these minerals and e l e c t r o c h e m i c a l i m p l i c a t i o n s r e l a t e d to f r o t h f l o t a t i o n . The main experimental techniques to be employed i n order to achieve the proposed o b j e c t i v e are e l e c t r o c h e m i c a l methods, such as determination of r e s t p o t e n t i a l s and p o l a r i z a t i o n curves, and small s c a l e f l o t a t i o n experiments. - 3 -CHAPTER 2 LITERATURE REVIEW 2.1 Current M i l l i n g P r a c t i c e of Sulphide Nickel-Copper Ores The conventional m i l l i n g p r a c t i c e of sulphide nickel - c o p p e r ores i n v o l v e s f i r s t f l o t a t i o n at a b a s i c pH to produce a bulk concentrate c o n t a i n i n g most of the p e n t l a n d i t e and c h a l c o p y r i t e . The t a i l i n g at t h i s stage i s composed c h i e f l y of the non-sulphide gangue minerals p l u s most of the p y r r h o t i t e . Magnetic s e p a r a t i o n can be combined w i t h f l o t a t i o n to produce a p y r r h o t i t e concentrate that i s e i t h e r added to the p e n t l a n d i t e f r a c t i o n or t r e a t e d s e p a r a t e l y i n an i r o n recovery p l a n t . The bulk n i c k e l - c o p p e r might f o l l o w one of two routes: ( i ) be shipped to a smelter, where a p y r o m e t a l l u r g i c a l s e p a r a t i o n of copper and n i c k e l i s performed. The 1966 flowsheet f o r the (2) Falconbridge m i l l (Falconbridge Mines L i m i t e d ) , presented i n Figure 1, i l l u s t r a t e s t h i s type of op e r a t i o n ; ( i i ) be separated i n t o n i c k e l and copper concentrates i n a s e l e c t i v e f l o t a t i o n step i n which p e n t l a n d i t e i s depressed, at pH 11 or 12, and c h a l c o p y r i t e i s f l o a t e d . The 1966 flowsheet (2) of the Copper C l i f f m i l l v (INCO L i m i t e d ) , shown i n Figure 2, i s an example of t h i s procedure. Some f l o t a t i o n reagents, f r e q u e n t l y used i n the conventional b a s i c c i r c u i t f l o t a t i o n of nic k e l - c o p p e r ores, are l i s t e d i n Table I . - 4 -M A G N E T I C \ S E P A R A T O R S a o Q Non-Magnetics i i ° r e r~n BINS ^pjj + 7/16" BAL  MIL  Ni-Cu Concentrate Tailng to Sand Fil Plant of Disposal . ************ -SCAVENGERS (2 Banks] Scalp Cone. To Pyrr.otie Treatment Plant SeconCary Ni-Cu C-0' ********* ROUGHERS _********-S C A L P F L O T A T I O N Non-Magnetics ^ BAL  MIL j Cyclone Ultra flues 0 NWWETIC SEFARtTOR Non-Mag, CLEANERS J 0 7.2% N i 6.8% Cu NICKELCOPPER CONCENTRATE TO SMELTER F igure 1. Flowsheet f o r Fa lconbr idge M i l l , a f t e r Bo ld t (2) - 5 -C O A R S E NICKEL-COPPER O R E F R O M MINES CONE C R U S H E R ^ ^ _ J _ ^ ^ N i - C u Concentrate S E P A R A T O R S Non-Mag . Water to To Sand Fill Reservoir Tail ings T o Mines D a m IRON C O N C E N T R A T E TO IRON ORE P L A N T INSIDE D R U M FILTERS 5% Ni NICKEL C O N C E N T R A T E TO S M E L T E R 30% Cu C O P P E R C O N C E N T R A T E TO S M E L T E R F igure 2. Flowsheet f o r Copper C l i f f M i l l , a f t e r Bo ld t (2) - 6 -TABLE I Reagents o f t e n used i n f l o t a t i o n of n i c k e l - c o p p e r sulphide ores (b a s i c c i r c u i t ) Function of „ , . _ , . _ ^ Stage of F l o t a t i o n Reagent c  Bulk Rougher Cu-Ni Separation Scavenger -gangue-dispersant - c o l l e c t o r - f r o t h e r -pH m o d i f i e r - a c t i v a t o r -depressant Sodium S i l i c a t e Xanthates various Lime Xanthates various Lime Lime* Xanthates v a r i o u s Copper Sulphate *Cyanide, d e x t r i n and o x i d i z i n g agents are a l s o used. 2.2 Use of Sulphur Dioxide as a F l o t a t i o n Reagent S h e r r i t t Gordon's Lynn Lake m i l l modified the conventional p r a c t i c e . Instead of operating a l l t h e i r f l o t a t i o n c e l l s i n the b a s i c range of pH, one a c i d i c step was introduced. The nickel-copper rougher concentrate was reground and conditioned w i t h sulphur d i o x i d e , before being cleaned. The i n s o l u b l e gangue and probably p y r r h o t i t e , l i b e r a t e d at the f i n e r s i z e s , were depressed, y i e l d i n g a cleaner n i c k e l - c o p p e r bulk f r a c t i o n that was next d i r e c t e d to a c o p p e r - n i c k e l s e p a r a t i o n c i r c u i t . Figure 3 presents (2) the flowsheet f o r the Lynn Lake m i l l , as i t was operated i n 1966. Another report of a Canadian nickel-copper operation to use S C ^as an a c i d i f y i n g agent i n t h e i r f l o t a t i o n c i r c u i t , came from INCO's Thompson m i l l , - 7 -j|» DISC FILTE DISC FILTER 130% Cu 10% Ni F igure 3. Flowsheet f o r Lynn Lake M i l l , a f t e r Bo ld t (2) - 8 -i n 1 9 7 4 ( 3 ) . The use of sulphur d i o x i d e as. a f l o t a t i o n reagent dates back at l e a s t to 1913, when t e s t s c a r r i e d out at Broken H i l l , A u s t r a l i a , showed that SC>2 (4) i n h i b i t e d the f l o t a t i o n of s p h a l e r i t e . Since that time depression of s p h a l e r i t e and marmatite by means of SC^ has been reported by s e v e r a l i n v e s t i g a t o r s ( 5 ) ' ( 6 ) ' ( 7 ) ' ( 8 ) ' ( 9 ) ' ( 1 0 ) ' " D i f f e r e n t r e s u l t s were obtained (12) by Kosherbaev and Sokolov . In t h e i r s m a l l - s c a l e l a b o r a t o r y experiments, 1 g samples of s p h a l e r i t e were t e s t e d i n a modified Hallimond tube, w i t h 5.00 mg of b u t y l xanthate as c o l l e c t o r and 6.25 mg of pine o i l as f r o t h e r . These authors concluded that the f l o a t a b i l i t y of ZnS, w i t h any length of treatment between 2 and 20 minutes, increased upon i n c r e a s i n g SO2 c o n c e n t r a t i o n . The e x p l a n a t i o n f o r t h i s apparently opposite a c t i o n of SO2 might be based on a d i f f e r e n t i a t i o n between depression and d e a c t i v a t i o n , as defined b e l o w ( 5 ) : -1'Activation i s a process whereby the surface of a mi n e r a l p a r t i c l e i s m odified so as to make i t r e a c t more r e a d i l y or more s t r o n g l y w i t h a c o l l e c t o r . — D e a c t i v a t i o n i s a process whereby an a c t i v a t i n g agent i s removed from the surface of a m i n e r a l , thereby rendering i t l e s s able to rea c t r e a d i l y and s t r o n g l y w i t h a c o l l e c t o r . —Depression i s a process whereby the surface of a p a r t i c l e i s modified i n such a way as to render i t more wettable by water". Sulphur d i o x i d e could be a d e a c t i v a t o r f o r copper-activated s p h a l e r i t e , but would not be a depressant f o r the unmodified m i n e r a l . A depressing a c t i o n of SO2 on the f l o a t a b i l i t y of galena was reported by s e v e r a l a u t h o r s ' and^"*""^ . Shimoiizaka et a l ^ " ^ s t a t e d that e i t h e r sodium s u l p h i t e or sulphur d i o x i d e depress the f l o t a t i o n of galena only when the surface of t h i s m i neral i s o x i d i z e d . Recent bench and p i l o t p l a n t s c a l e testwork c a r r i e d out by Arauco F. (14) et a l i n d i c a t e d that the depressing a c t i o n of SC^ increased over the f o l l o w i n g sequence of sulphide m i n e r a l s : c h a l c o p y r i t e < copper arseno sulphides < c h a l c o c i t e < c o v e l l i t e < galena < p y r i t e < marmatite < s p h a l e r i t e . T o t a l l y depressed minerals can o f t e n be rendered f l o a t a b l e by the a d d i t i o n of more xanthate c o l l e c t o r . Each mineral r e q u i r e s a c e r t a i n l e v e l of c o l l e c t o r to acquire the necessary f l o a t a b i l i t y . References to the u t i l i z a t i o n of SC^ as a modifying agent i n the f l o t a t i o n of p e n t l a n d i t e and r e l a t e d minerals are scarce and u s u a l l y b r i e f . C h a l c o p y r i t e i s claimed to be a c t i v a t e d by S C ^ " ^ ' ' ' w h i l e p y r r h o t i t e i s depressed . The f l o t a t i o n of s e v e r a l western A u s t r a l i a n p e n t l a n d i t e - p y r r h o t i t e ores was studi e d by Eltham and T i l y a r d ^ " ^ . B e t t e r n i c k e l recovery was obtained i n b a s i c c i r c u i t s , than when the pulp was a c i d i f i e d w i t h SC^. C l a r i d g e and Tenbergen , d e s c r i b i n g f l o t a t i o n d e v e l -opments f o r "Pipe ore" i n the Thompson m i l l of INCO L i m i t e d , c l a i m that p i l o t p l a n t work revealed that SC^ depressed p e n t l a n d i t e . The d e t a i l e d c o n d i t i o n s of these t e s t s were not s p e c i f i e d , however. A common problem a s s o c i a t e d w i t h the f l o t a t i o n of n i c k e l sulphide ores i s the presence of t a l c . T a lc i s a n a t u r a l l y f l o a t a b l e mineral which tends to end up i n the f l o t a t i o n concentrates, thereby d i l u t i n g t h e i r grades. The consequent hig h MgO content a l s o i n t e r f e r e s w i t h smelting processes. P r e f l o t a t i o n or depression are the two a v a i l a b l e routes to e l i m i n a t e t h i s t a l c d i l u t i o n . Even i n the absence of f r o t h e r , t a l c p a r t i c l e s can s t a b i l i z e - 10-a viscous f r o t h . Such a f r o t h tends to entrap both n i c k e l and copper sulphide p a r t i c l e s , which o f t e n r e s u l t s i n unacceptable l o s s e s when attempt-ing a t a l c - p r e f l o t a t i o n step. Sulphur d i o x i d e combined w i t h d e x t r i n ^ ^ ' (19) or Guartec has proved to be e f f e c t i v e i n t a l c depression during f l o t a t i o n of the copper and n i c k e l s u l p h i d e s . This i s the more normal route to f o l l o w i n t r e a t i n g t a l c o s e n i c k e l ores. (18) Recent work by P o l i n g i n d i c a t e d that SC^ can r e i n f o r c e the a c t i o n of d e x t r i n as a t a l c depressant. In a d d i t i o n he found that SC^ could enhance the f l o a t a b i l i t y of p e n t l a n d i t e and c h a l c o p y r i t e i n a p a r t i c u l a r ore from South A f r i c a . A review of the l i t e r a t u r e on u t i l i z a t i o n of SC^ as a sulphide f l o t -a t i o n modifying agent shows that very l i t t l e has been published about the mechanism of a c t i o n of t h i s compound. The i n f o r m a t i o n concerning i t s e f f e c t on n i c k e l - c opper ores i s even l e s s . Nickel-copper f l o t a t i o n i s a w e l l e s t a b l i s h e d p l a n t p r a c t i c e , but l i t t l e has been published about i t s fundamentals. 2.3 L e v e l of Hydrophobicity at the Surface of M i n e r a l s The s e l e c t i v i t y of f r o t h f l o t a t i o n i s based on the p r i n c i p l e t h a t , when a i r i s bubbled through a water suspension of mineral p a r t i c l e s , some species stay i n suspension w h i l e others adhere to the a i r bubbles and are buoyed to the s u r f a c e . A n e a r - i d e a l example of s e l e c t i v e f l o t a t i o n i s a system c o n t a i n i n g quartz and molybdenite p a r t i c l e s . The p r e f e r e n t i a l cleavage of molybdenite along '001 planes generates n a t u r a l l y hydrophobic surfaces on these planes. The M 0 S 2 p a r t i c l e s adhere to a i r bubbles and f l o a t . N a t u r a l l y h y d r o p h i l i c quartz i s wetted by water and i s not f l o a t e d . / Very few n a t u r a l systems are c o n s t i t u t e d of only two m i n e r a l s , one hydrophobic, the other h y d r o p h i l i c . Most minerals are h y d r o p h i l i c and have to be, at l e a s t p a r t i a l l y , coated w i t h a c o l l e c t o r to acquire the necessary degree of hydrophobicity r e q u i r e d f o r f l o t a t i o n . In many instances a c t i v a t i o n of the mineral surface must precede the a d d i t i o n of c o l l e c t o r . D e a c t i v a t i o n and depression are a l s o very common a c t i o n s i n mineral processing. The a c t i o n of modifying agents i s one of the f i e l d s i n which p r a c t i c a l achievements are f a r ahead of t h e o r e t i c a l c o n s i d e r a t i o n s . Among recent work i n t h i s area, s i g n i f i c a n t advances have been made by F i n k e l s t e i n and (20) (21) (22) (23) co-workers ' This work deals s p e c i f i c a l l y w i t h the m o d i f i c a t i o n of the surfaces of s p h a l e r i t e and c h a l c o p y r i t e . Many of t h e i r conclusions can be ex t r a p o l a t e d to other systems as discussed next. In systems c o n t a i n i n g s p h a l e r i t e and c h a l c o p y r i t e , depression i s due to the presence of i n s o l u b l e p r e c i p i t a t e s (mostly Zn(0H)2) and Zn(CN)2-These p r e c i p i t a t e s are weakly and n o n - s e l e c t i v e l y attached to the mineral p a r t i c l e s , through p h y s i c a l a d s o r p t i o n . D i f f e r e n c e s i n r e l a t i v e hydrophob-i c i t i e s of the d i f f e r e n t minerals are r e s p o n s i b l e f o r the s e l e c t i v i t y of t h i s depression. The concept of a hydrophobicity s c a l e i s introduced, i n c l u d i n g the f o l l o w i n g c o n t r i b u t i o n s : ( i ) "the hydrophobicity of the n a t u r a l mineral surface and.the change i n t h i s h ydrophobicity as a r e s u l t of a c t i v a t i o n of the surface; ( i i ) f u r t h e r c o n t r i b u t i o n to the o v e r a l l h y d r o p h o b i c i t y by the presence of f i l m s of a p a r t i c u l a r c o l l e c t o r r e a c t i o n product on the surface; ( i i i ) the h y d r o p h i l i c i t y of a depressant f i l m at the surface. A knowledge of the species present i n aqueous s o l u t i o n s of sulphur d i o x i d e might c o n t r i b u t e to the understanding of the e f f e c t of SO2 on the " l e v e l of hyd r o p h o b i c i t y " of sulphide m i n e r a l s . - 12 -2.4 Sulphur Dioxide Water Chemistry Most of the recent study i n the f i e l d of sulphur d i o x i d e water chemistry and e l e c t r o c h e m i s t r y r e f e r s to the c o r r o s i o n a c c e l e r a t i n g e f f e c t of SO2 on m e t a l l i c surfaces i n humid atmosphere. The o b j e c t i v e s of these s t u d i e s d i f f e r from those of the present i n v e s t i g a t i o n i n two major aspects: ( i ) the concentrations of S0£ i n v o l v e d are low compared w i t h those used i n f l o t a t i o n ; ( i i ) the s o l i d surfaces on which SO2 adsorbs are metals and not m e t a l l i c s u l p h i d e s . Sulphur d i o x i d e s o l u b i l i t y i n water decreases w i t h i n c r e a s i n g temperat-(24) ure, as shown i n Table I I , a f t e r Schroeter TABLE I I Sulphur d i o x i d e s o l u b i l i t y i n water at va r i o u s temperatures, at 1 atm of t o t a l pressure, a f t e r Schroeter(24) Temperature (°C) SO2(g/100 g of U2O) S0 2(moles/O 0 22.8 3.56 5 19.3 3.01 10 16.2 2.53 15 13.5 2.11 20 11.3 1.76 25 9.4 1.47 30 7.8 1.22 35 6.5 1.01 40 5.4 0.84 The l i s t of sulphur c o n t a i n i n g species e x i s t i n g when SO2 i s d i s s o l v e d (25) i n water i s c o n t r o v e r s i a l i n the l i t e r a t u r e . Duncan and Spedding 2~ - 2~ report SO2 (aq), H2SO3, HSO3, SO3 , HS2O5 and S2O5 as the main species (26) present i n aqueous s o l u t i o n s of SO2. Lyons and N i c k l e s s reported - 13 -molecular or so l v a t e d as the most abundant s p e c i e s , i n a d d i t i o n to 2- (27) l e s s abundant I^SO^, HSO^ and S20^ . F a l k and Guiguere repeatedly attempted to detect s t a b l e H2SO3 i n aqueous s o l u t i o n s of SO2, by i n f r a r e d spectrometry, w i t h no success. Sulphur d i o x i d e i n the molecular s t a t e and HSO3 and HS2O5 were the only species observed. E a r l y i n v e s t i g a t i o n ind i c a t e d that 50% of the SO2 present i n a 5% s o l u t i o n at 22 C was (28) (29) uncombined . Lynn et a l reported that a saturated s o l u t i o n of SO2 at normal pressure and temperature i s i o n i z e d approximately 11%,in c l o s e (27) agreement w i t h the 10% i o n i z a t i o n suggested by Fal k and Guiguere under the same c o n d i t i o n s . (12) Kosherbaev and Sokolov s t u d i e d the e f f e c t of pH on the conversion 2-of S0 2 (g) i n t o H 2S0 3, HSO3 and S0 3 . Table I I I , reproduced from t h e i r paper, i n d i c a t e s a complete transformation of SO2 i n t o these s p e c i e s . I t could be p o s s i b l e that the d i s t r i b u t i o n presented r e f e r s to the f r a c t i o n of SO2 which i s changed i n t o other s p e c i e s . I f t h i s i s t r u e , there i s no disagreement between these data and those i n d i c a t i n g a prevalence of molecular SO2, reported by other i n v e s t i g a t o r s . Table I I I i n d i c a t e s that HSO^ i s the most abundant sulphur c o n t a i n i n g i o n i c species of aqueous SO2 i n the pH range of t y p i c a l a c i d i c f l o t a t i o n c i r c u i t s (approximately pH 5.5) - 14 -TABLE I I I The e f f e c t of pH on the conversion of 1 mg/& of SC^ 2-gas i n t o H2SO3, HSO3 and SO^, a f t e r Kosherbaev and Sokolov pH H 2S0 3 (mg/l) HSO~ (mg/JO S0 2 _ (mg/£) 1 1.06 0.21 1.24 x 10-7 2 4.26 x 10 _ 1 0.84 4.96 X l O " 6 3 6.1 x 10~2 1.20 0.71 X i o - 5 4 6.4 x 10 - 3 1.26 7.48 X l O " 4 5 6.4 x 10"4 1.26 7.48 x 10"3 6 6.0 x 10 - 5 1.19 7.05 x i o " 2 7 8 4.0 x 10 - 6 9.1 x 10 - 8 0.64 0.17 4.67 1.06 X i o " 1 9 1.06 x 10 - 9 2.1 x l o " 2 1.25 10 1.06 x 1 0 - 1 1 2.1 x LO" 3 1.25 11 1.06 x 10" 1 3 2.1 x l o " 4 1.25 12 1.06 x 1 0 - 1 5 2.1 x l o " 5 1.25 13 1.06 x 1 0 - 1 7 2.1 x l O " 6 1.25 14 -19 1.06 x 10 2.1 x l O " 7 1.25 I n f r a r e d spectroscopy has been used f o r aqueous SO^ a n a l y s i s . E x p e r i -mentally determined absorption frequencies are l i s t e d i n Table IV. - 15 -TABLE IV I n f r a r e d a b s o r p t i o n frequencies of aqueous SC^ Reference Freq. (cm - 1) (27) (30) (31)* (32) v 2 527 523 517.5 v x 1152 1157 1148 1151 v 3 1334 1332 1338 1360 * pure l i q u i d SC^. Q u a n t i t a t i v e i n f r a r e d determination of aqueous SO2 (g) i s p o s s i b l e , i f the e x t i n c t i o n or absorption c o e f f i c i e n t i s known. Jones and M c L a r e n ^ 3 ^ 3 2 - 1 obtained a f i g u r e of approximately 0.8 x 10 cm g f o r the absorption c o e f f i c i e n t . a s s o c i a t e d w i t h the peak at 1157 cm ^ (NaCl prism). The common c h a r a c t e r i s t i c of the species present when i s d i s s o l v e d i n water i s that the o x i d a t i o n s t a t e of sulphur i s +4 i n each case. The u l t i m a t e product of d i s p r o p o r t i o n a t i o n of the p o s i t i v e o x i d a t i o n s t a t e s i s +6. The p o s s i b i l i t y of o x i d a t i o n to sulphate e x p l a i n s why sulphur d i o x i d e i s described i n the l i t e r a t u r e as a reducing agent. The thermodynamic s t a b i l i t y of sulphur species i n water can be v i s u a l i z e d w i t h the a i d of an o x i d a t i o n s t a t e diagram, as shown i n Figure 4. On t h i s f i g u r e , t h e o x i d a t i o n - r e d u c t i o n p o t e n t i a l of a couple formed by two species i s given by the gradient of the l i n e j o i n i n g the p o i n t s r e p r e s e n t i n g these species. A l a r g e p o s i t i v e gradient c h a r a c t e r i z e s a s t r o n g l y o x i d i z i n g couple and a l a r g e negative gradient i s a s s o c i a t e d w i t h a s t r o n g l y reducing couple. - 16 -0 2 4 OXIDATION STATE OF SULPHUR F igure 4. Ox ida t i on s t a t e diagram f o r su lphur - 17 -The diagram a l s o i n d i c a t e s t h a t , i f d i t h i o n a t e i s an intermediate i n the o x i d a t i o n of s u l p h i t e to sulphate, an excess of fr e e energy i s r e q u i r e d . A f i r s t mechanism f o r o x i d a t i o n of sulphur +4 to sulphur +6 was (33) proposed by Hayon et a l , and i n v o l v e s i n i t i a t i o n , propagation and termi n a t i o n steps: 2-I n i t i a t i o n S0„ + hv -> SC- + e (R-l) 3 3 aq S0 2~ + M1"*" ->• S 0 3 + M ( n _ 1 ) + (R-2) 5 0 3 + ° 2 ^ S 0 5 (R-5) iT"f" where hv represents a photon of i o n i z i n g r a d i a t i o n and M represents a metal c a t i o n s u s c e p t i b l e to a one e l e c t r o n o x i d a t i o n . 2- 2-Propagation SC>5 + SC>3 -»- S0 4 + SO^ (R-4) 50 4 + S0 2~ -s- S0 2~ + S0 3 (R-5) plus unknown termina t i o n steps f o r the species SO^, SO^ and SO^. Reaction (R-l) describes the s o - c a l l e d p h o t o x i d a t i o n of s u l p h i t e . Reaction (R-2) r e f e r s to thermal a u t o x i d a t i o n , when the photochemical i n i t i a t i o n i s replaced by a one-electron t r a n s f e r step i n v o l v i n g a metal c a t i o n . (34) Basset and Parker suggested a second mechanism f o r s u l p h i t e o x i d a t i o n . In the presence of f e r r i c or c u p r i c i o n s , s u l p h i t e forms a s u l p h i t e complex such as [Fe(S03)2] • This complex can be o x i d i z e d to e i t h e r sulphate or d i t h i o n a t e , according to the f o l l o w i n g r e a c t i o n s : 2 [ F e ( S 0 3 ) 2 ] + H 20 -> SO 2 - + 2H + + 2 F e 2 + + 3S0 2~ (R-6) 2[ F e ( S 0 3 ) 2 ] •> S 2 0 2 " + 2 F e 2 + + 2S0 2~ (R-7), Sev e r a l conclusions can be drawn from the l i t e r a t u r e review on sulphur d i o x i d e water chemistry. Approximately 10% of the t o t a l d i s s o l v e d species i s i o n i z e d . At pH 5.5 the most abundant i o n i z e d species i s HS0~. The - 18 -non-ionized p o r t i o n i s composed of. solyated and molecular S Q 2 • The concentration of hydrated molecules has been reported to be low, although a q u a n t i t a t i v e f i g u r e i s not a v a i l a b l e . The o x i d a t i o n s t a t e of sulphur i s +4 i n a l l the detected species of aqueous SO2, which shows the reducing character of these s o l u t i o n s . 2.5 Geology of N i c k e l Sulphide Ores The most important sulphide n i c k e l deposits of the world are l o c a t e d w i t h i n 25 miles of Sudbury, Ont a r i o . The orebodies are c o n s t i t u t e d of e i t h e r sulphides disseminated i n a host rock (two t h i r d s of the t o t a l ) (35) or i n c l u s i o n - b e a r i n g sulphide ores (one t h i r d of the t o t a l ) . The most common host rock i s n o r i t e , a b a s i c rock (igneous rocks are ranked as a c i d i c , n e u t r a l , b a s i c , u l t r a b a s i c , and a l k a l i n e according to decreasing s i l i c a c ontent). A l t e r a t i o n of the min e r a l assembly of n o r i t e to t a l c [Mg^Si^Oj^OH) i s p o s s i b l e but not very common. P y r r h o t i t e , c h a l c o p y r i t e and p e n t l a n d i t e account f o r 95 percent of the t o t a l sulphides i n Sudbury ores. The Sudbury D i s t r i c t provides most of the n i c k e l mined i n Canada, but (38) other deposits are economically s i g n i f i c a n t . K i l b u r n et a l discussed the Canadian n i c k e l sulphide ores r e l a t e d to u l t r a b a s i c rocks. The primary sulphide minerals a s s o c i a t e d w i t h u l t r a b a s i c rocks are p y r r h o t i t e , p e n t l a n d i t e , p y r i t e and c h a l c o p y r i t e . Most of the u l t r a b a s i c rocks are p a r t i a l l y or completely a l t e r e d to serpentine [Mg3Si20,_ (OH) ^] , c h l o r i t e [.(MgjEe) ,-A12S1.J0^Q(0H)g] or t a l c . A l t e r a t i o n to serpentine i s by f a r the most widespread. A l t e r a t i o n to t a l c i s the most undesirable f o r e i t h e r mining or m i l l i n g operations. The e f f e c t s of t a l c on m i l l i n g were discussed i n s e c t i o n 2.2. I t s e f f e c t s on mining are r e l a t e d to the low mechanical st r e n g t h of the mi n e r a l . Planes of weakness i n t a l c can - 19 -somet imes c a u s e b l o c k f a i l u r e s due t o l u b r i c a t i n g a c t i o n . The a s s o c i a t i o n o f n i c k e l and i r o n s u l p h i d e s , and t h e p r e s e n c e o f c o p p e r m i n e r a l s , i s a c h a r a c t e r i s t i c o f n i c k e l - b e a r i n g d e p o s i t e . A l i s t o f more common m i n e r a l s i n t h e i r o n - n i c k e l - s u l p h u r s y s t e m i s p r e s e n t e d i n T a b l e V . Two c o p p e r - i r o n s u l p h i d e s a r e a l s o i n c l u d e d . N a t u r a l s p e c i m e n s u s u a l l y d e p a r t f r o m t h e i d e a l s t o i c h i o m e t r i c f o r m u l a . E l e m e n t a l s u b s t i t u t i o n i s common. C o b a l t i s f r e q u e n t l y f o u n d t o r e p l a c e i r o n and n i c k e l . TABLE V M i n e r a l s i n t h e i r o n - n i c k e l - s u l p h u r s y s t e m M i n e r a l I d e a l F o r m u l a C r y s t a l S y s t e m A w a r u i t e ( N i , F e ) C u b i c B r a v o i t e ( N i , F e ) S 2 C u b i c G e r s d o r f f i t e ( N i , F e ) A S S C u b i c G r e i g i t e F e 3 S 4 C u b i c H e a z l e w o o d i t e N i 3 S 2 H e x a g o n a l M a c k i n a w i t e FeS T e t r a g o n a l M a r c a s s i t e FeS2 O r t h o g o n a l M i l l e r i t e BN iS H e x a g o n a l P a r k e r i t e M 3 S 2 O r t h o g o n a l P e n t l a n d i t e ( N i , F e ) 9 S 8 C u b i c P o l y d y m i t e M 3 S 4 C u b i c P y r i t e FeS 2 C u b i c P y r r h o t i t e FeySg M o n o c l i n i c F e 9 S 1 0 H e x a g o n a l S m y t h i t e F e 3 S 4 H e x a g o n a l T r o i l i t e FeS H e x a g o n a l V a e s i t e N i S 2 C u b i c V i o l a r i t e ( N i , F e ) 3 S 4 C u b i c C h a l c o p y r i t e CuFeS2 T e t r a g o n a l C u b a n i t e C u F e 2 S 3 O r t h o g o n a l - 20 -The composition of the d i f f e r e n t phases present i n the i r o n -n i c k e l - s u l p h u r system can be b e t t e r v i s u a l i z e d i n a ternary phase diagram. The c e n t r a l p o r t i o n of such a diagram ( f o r the system at room temperature) i s shown i n Figure 5. The compositions described i n Table V and Figure 5 r e f e r to the bulk m i n e r a l . There i s i n d i c a t i o n that the surface s t o i c h i o m e t r y may d i f f e r from that i n the bulk due to u n s a t i s f i e d bonds and r e a c t i o n w i t h atmospheric or aqueous environment. The importance of surface s t o i c h -iometry towards the f l o a t i o n behaviour of sulphide minerals i s now recognized. Nevertheless, except f o r i n v e s t i g a t i o n s on the galena (37) surface , not much has been published on t h i s t o p i c . Not a l l the minerals l i s t e d i n Table V have i n d u s t r i a l importance. However, of the secondary minerals which deserve a t t e n t i o n , v i o l a r i t e p lays an important r o l e . This mineral has been reported as a common a l t e r a t i o n product of p e n t l a n d i t e - p y r r h o t i t e a s s o c i a t i o n s ^ 3 8 ^ ' ( ^ 9 ) , ( 4 0 ) , (41),(42)^ Eitham and T i l y a r d s u c c e s s f u l l y f l o a t e d samples of Western A u s t r a l i a n v i o l a r i t e using short chain xanthates as c o l l e c t o r s , without the need of any a c t i v a t o r . A tendency f o r v i o l a r i t e to slime during g r i n d i n g was the only f l o t a t i o n problem d i s c l o s e d . No reference was found i n the l i t e r a t u r e to m i l l i n g problems, i n the Canadian n i c k e l i n d u s t r y , a s sociated w i t h v i o l a r i t e . A review of Canadian n i c k e l ores i n d i c a t e s that the most important n i c k e l - b e a r i n g minerals are p e n t l a n d i t e and the s o - c a l l e d n i c k e l i f e r o u s p y r r h o t i t e . C h a l c o p y r i t e i s u s u a l l y a s s o c i a t e d w i t h these minerals. N i c k e l i f e r o u s p y r r h o t i t e i s a broad d e s i g n a t i o n which encompasses n i c k e l i n s o l i d s o l u t i o n and exsolved p e n t l a n d i t e as f i n e flames, s p i n d l e s , b l e b s , l e n s e s , granular aggregates or veins w i t h i n p y r r h o t i t e . - 2 1 -S Po r t i on represented i n the diagram Fe Ni • t r o i l i t e ( t r ) , p y r r h o t i t e (po) , smyth i te (smy), m i l l e r i t e (ml) o c o e x i s t i n g v i o l a r i t e ( v l ) and pen t l and i t e (pn) po lydymite (pm) a v i o l a r i t e ( v l ) not r e l a t e d to pen t l and i t e (pn) p y r i t e (py) and b r avo i t e (bv) F igure 5. Cent ra l p o r t i on o f the Fe-Ni-S t r i a n g u l a r d iagram, a f t e r M is ra and F l e e t^ 3 8 ^ - 22 -P y r o m e t a l l u r g i c a l s e p a r a t i o n of such n i c k e l i s u s u a l l y the only p r a c t i c a l recovery procedure. 2.5.1 I d e n t i f i c a t i o n of Copper and N i c k e l Sulphide M i n e r a l s Since p e n t l a n d i t e , c h a l c o p y r i t e and p y r r h o t i t e have been i d e n t i f i e d as the minerals r e l e v a n t to the present i n v e s t i g a t i o n , i t i s necessary to be able to i d e n t i f y them. O p t i c a l p r o p e r t i e s such as co l o u r and anisotropy are u s e f u l f o r micro-scopic i d e n t i f i c a t i o n of p o l i s h e d s e c t i o n s . Tables presented by (43) Uytenbogaart and Burke describe the three minerals under o i l immersion. P e n t l a n d i t e i s a l i g h t creamy or y e l l o w i s h c o l o u r , much l i g h t e r than p y r r h o t i t e , and i s o t r o p i c . C h a l c o p y r i t e i s ye l l o w , s l i g h t l y darker than p y r r h o t i t e , and the anisotropy i s weak but d i s t i n c t . P y r r h o t i t e i s cream w i t h a f a i n t p i n k i s h brown t i n t , and u s u a l l y very s t r o n g l y a n i s o t r o p i c . The i n t e n s i t y of anis o t r o p y depends on the c r y s t a l system and o r i e n t a t i o n . The ferromagnetic p r o p e r t i e s of monoclinic p y r r h o t i t e can be used to d i s t i n g u i s h i t from the hexagonal type, which i s paramagnetic. An e l e c t r o n microprobe i s very e f f e c t i v e f o r i d e n t i f i c a t i o n of min e r a l s . This method can provide q u a l i t a t i v e and q u a n t i t a t i v e i n f o r m a t i o n about the minerals present i n a sample, t h e i r a s s o c i a t i o n s and i m p u r i t i e s . Minerals present i n q u a n t i t i e s above a d e t e c t i o n l i m i t of u s u a l l y 5 to 10 percent, can be i d e n t i f i e d by X-ray d i f f r a c t i o n . The X-ray p a t t e r n f o r the mineral i s a very p r e c i s e i d e n t i f i c a t i o n method, p a r t i c u l -a r l y u s e f u l when other p r o p e r t i e s are s i m i l a r . L a s t , but not l e a s t , the c h a r a c t e r i z a t i o n of a mineral specimen r e q u i r e s elemental chemical a n a l y s i s . The importance of surface s t o i c h i o m e t r y of sulphide minerals was str e s s e d p r e v i o u s l y . A n a l y t i c a l techniques that d e a l s p e c i f i c a l l y w i t h surfaces have been known f o r decades. Recent improvements i n the f i e l d - 23 -i n c l u d e refinement of o l d e r methods, development of new techniques and production of i n s t r u m e n t a t i o n that i s e a s i e r to operate and l e s s expensive than the equipment that was a v a i l a b l e ten years ago. Techniques ( 4 4 ) such as AES (Auger E l e c t r o n Spectroscopy) , LEED (Low Energy E l e c t r o n D i f f r a c t i o n ) } ESCA ( E l e c t r o n Spectroscopy f o r Chemical A n a l y s i s ) ' ( 4 7 ) and ISS (Ion S c a t t e r i n g Spectrometry) , seem to be h e l p f u l i n e l u c i d a t i n g the surface s t o i c h i o m e t r y of sulphide m i n e r a l s . These techniques can a l s o be used to i d e n t i f y surface compounds formed a f t e r r e a c t i o n s w i t h c o l l e c t o r s and other reagents. A cautious i n t e r p r e t a t i o n of the r e s u l t s i s recommended when the operating c o n d i t i o n s (high vacuum or high temperature, f o r example) can change the surface of the sample under a n a l y s i s . 2.6 E l e c t r o p h y s i c a l P r o p e r t i e s of Sulphide M i n e r a l s P e n t l a n d i t e , p y r r h o t i t e and c h a l c o p y r i t e are a l l semiconducting m i n e r a l s . The mechanism of charge t r a n s f e r across a semiconductor-solution i n t e r f a c e i s a f f e c t e d by the c o n c e n t r a t i o n of charge c a r r i e r s . When t h i s c o n c e n t r a t i o n i s h i g h the behaviour of a m e t a l - s o l u t i o n i n t e r f a c e i s approached. In the case of lower c o n c e n t r a t i o n of c a r r i e r s , the space charge region of the s o l i d can i n f l u e n c e processes i n v o l v i n g charge t r a n s f e r . The r o l e of semiconductor p r o p e r t i e s on the f l o a t a b i l i t y of sulphide ( 4 8 ) ( 4 9 ) minerals was f i r s t discussed by P l a k s i n and Shafeev ' . T h e i r theory i s that n e g a t i v e l y charged xanthate ions cannot adsorb on n-type galena. F u r t h e r , they suggest that o x i d i z i n g agents can act as e l e c t r o n acceptors and convert galena i n t o a p-type semiconductor, c r e a t i n g the necessary c o n d i t i o n s f o r a d s o r p t i o n . Tolun and K i t c h e n e r s h o w e d that oxygen r a i s e s the e l e c t r o c h e m i c a l p o t e n t i a l of galena, a l l o w i n g xanthate to o x i d i z e to dixanthogen. A change from n- to p-type semi-- 24 _ c o n d u c t i v i t y was reported, but t h i s f a c t was not r e l a t e d to the adsorption of xanthate. S p r i n g e r c o n c l u d e d that the conduction type of p y r i t e , galena and c h a l c o p y r i t e does not p l a y a s i g n i f i c a n t r o l e i n the anodic o x i d a t i o n of these mine r a l s . (52) Z e v g o l i s and Cooke stud i e d the anodic p o l a r i z a t i o n of c h a l c o p y r i t e (n-type semiconductor). These i n v e s t i g a t o r s concluded that there i s a l i m i t i n g anodic current d e n s i t y . The value of t h i s current d e n s i t y i s determined by the c o n c e n t r a t i o n of h o l e s , which are the m i n o r i t y c a r r i e r s i n c h a l c o p y r i t e . The theory behind Z e v g o l i s and Cooke's work was i n t r o -(53) duced by B r a t t a i n and Garret , who s t u d i e d the germanium-electrolyte i n t e r f a c e . These i n v e s t i g a t o r s found out that a n o d i c a l l y biased n-type germanium i n an e l e c t r o l y t e s o l u t i o n behaves as a p-n j u n c t i o n . A p-n j u n c t i o n i s the i n t e r f a c e between a p-region and an n-region w i t h i n a s i n g l e c r y s t a l of a semiconductor. I t was proven that the s a t u r a t i o n of the current c r o s s i n g such an i n t e r f a c e i s due to the e f f e c t of d i f f u s i o n of the m i n o r i t y c a r r i e r s as a r a t e - l i m i t i n g step. The work of Z e v g o l i s and Cooke^"^ was c r i t i c i z e d by B i e g l e r ^ 4 ^ , w i t h respect to the i l l u m i n a t i o n technique and the wide range of anodic p o t e n t i a l s used (0-14V). I t i s questionable whether the c r i t i c i s m i s v a l i d i n terms of pure e l e c t r o c h e m i s t r y of s u l p h i d e s . As f a r as e l e c t r o -chemical i n f l u e n c e on f l o t a t i o n i s concerned, the l i m i t i n g current d e n s i t y was detected at a p o t e n t i a l too h i g h to be considered important (1.45 V anodic). B i e g l e r found no r e l a t i o n s h i p between the n- or p-type character of p y r i t e and k i n e t i c parameters f o r cathodic oxygen re d u c t i o n on p y r i t e e l e c t r o d e s . At present there i s no i n d i s p u t a b l e proof of the e f f e c t of semi-- 25 -c o n d u c t i v i t y type on the f l o t a t i o n of sulphide minerals w i t h xanthates. There i s an i n d i c a t i o n that the e f f e c t i s l e s s pronounced i n the case of more conductive m i n e r a l s . Less conductive m i n e r a l s , such as galena and s p h a l e r i t e , should have t h e i r response to f l o t a t i o n a f f e c t e d i n a stronger way by the semiconductivity type. The e l e c t r i c a l c o n d u c t i v i t y of sulphide minerals i s s t r o n g l y dependent on composition. Values from the l i t e r a t u r e f o r d i f f e r e n t samples of pent-l a n d i t e , p y r r h o t i t e and c h a l c o p y r i t e w i l l be presented i n s e c t i o n 5.1, t o -gether w i t h experimental data f o r the samples to be used i n the present i n v e s t i g a t i o n . 2.7 E l e c t r o c h e m i s t r y of Sulphide M i n e r a l s The use of an e l e c t r o c h e m i c a l approach to study sulphide minerals dates back to 1931, when K a m i e n s k i ^ " ^ i n v e s t i g a t e d the e f f e c t of pH on the e q u i l i -brium p o t e n t i a l s of galena. Most of the work on e l e c t r o c h e m i s t r y of sulphide minerals has been d i r e c t e d towards the l e a c h i n g of these minerals as a hydro-m e t a l l u r g i c a l s t e p ^ " ^ ' ' . The a p p l i c a t i o n of e l e c t r o c h e m i c a l methods (59) to f l o t a t i o n r esearch was introduced by Salamy and Nixon , who recognized the gap e x i s t i n g between p r a c t i c a l f l o t a t i o n developments and i t s fundamen-t a l s . Their pioneering work, presented i n 1953, brought f o r t h the suggestion that the r e a c t i o n between sulphide minerals and xanthates proceeds v i a an e l e c t r o c h e m i c a l mechanism. P r i o r to a d i s c u s s i o n of t h i s mechanism, i t i s p e r t i n e n t to review b r i e f l y the need- of a c o l l e c t o r f o r f l o t a t i o n of sulphide m i n e r a l s . Most of these minerals are only weakly h y d r o p h i l i c due p r i m a r i l y to t h e i r i n -a b i l i t y to form hydrogen b o n d s . Thus, f o r example, t h e i r n a t u r a l surfaces are l e s s s t r o n g l y hydrated than most oxide m i n e r a l s . The surface - 26 -of sulphide m i n e r a l p a r t i c l e s must be, p a r t i a l l y at l e a s t , coated w i t h c o l -l e c t o r s to provide c o n d i t i o n s f o r the attachment of a i r bubbles. There are exceptions to t h i s s i t u a t i o n , some of them r e l a t e d to i n d u s t r i a l l y important minerals. Molybdenite (MoS 2) i s one of the n a t u r a l l y hydrophobic m i n e r a l s . Recent i n v e s t i g a t i o n s have a l s o i n d i c a t e d the p o s s i b i l i t y of c o l l e c t o r l e s s f l o t a t i o n of copper-activated s p h a l e r i t e ^ " ^ and c h a l c o p y r i t e ^ 2 \ A complete review of the l i t e r a t u r e on the t o p i c of i n t e r a c t i o n between xanthates and sulphide minerals i s beyond the scope of t h i s work. The pre-sent s t a t e of knowledge may be summarized based on the i n f o r m a t i o n a v a i l a b l e _ ,. . _ (63),(64),(65),(66),(67),(68),(69),(70),(71),(54) i n recent p u b l i c a t i o n s ' ' ' ' ' ' ' The common mechanism of i n t e r a c t i o n between xanthates and sulphide minerals i s of an e l e c t r o c h e m i c a l nature. Xanthate ions are o x i d i z e d to e i t h e r dixanthogen or metal xanthate, according to the f o l l o w i n g r e -a c t i o n s : 2R0CSI -> (R0CS 2) 2 + 2e (R-8) MeS + 2R0CS2 Me (R0CS 2) 2 + S + 2e (R-9) 2MeS + 3H 20 + rROCSl + 2Me(R0CS 2) 2 + S 203~ + 6H + + 8e (R-10) Reaction (R-10) may be considered the r e s u l t of f u r t h e r o x i d a t i o n of elemental sulphur, produced i n r e a c t i o n (R-9), to t h i o s u l p h a t e . Geometrical c o n s i d e r a t i o n s suggest t h a t , at the surface, r e a c t i o n (R-9) i s u n r e a l i s t i c . The xanthate r a d i c a l i s l a r g e r than the metal r a d i c a l s . There i s i n s u f f i c i e n t space f o r two xanthate r a d i c a l s adjacent - 27 -to one metal c a t i o n at the sur f a c e . The evidence i n d i c a t e s the forma-t i o n of a f i r s t l a y e r of a mono-coordinated compound MeROCS2, which can be coated w i t h one or more l a y e r s of Me(ROCS 2) 2. Not a l l the steps that cause a p a r t i c l e to be hydrophobic i n a f l o t a t i o n environment have been completely e s t a b l i s h e d . - For example, the simple adsorption of xanthate on the surface may or may not be s u f f i c i e n t to give a hydrophobic character to a m i n e r a l : Surface + ROCS~ •> ROCS2 - Surface + e ( R - l l ) The r o l e played by elemental sulphur i n the f l o t a t i o n of sulphide minerals i s not yet c l e a r . Although sulphur i s a n a t u r a l l y f l o a t a b l e s p ecies, i t i s s t i l l c o n t r o v e r s i a l as to whether i t i s one of the hydro-phobic e n t i t i e s that render the p a r t i c l e s f l o a t a b l e . A r e l a t i o n s h i p appears to e x i s t between the product of o x i d a t i o n of t h i o l c o l l e c t o r s and the r e s t p o t e n t i a l of the system. Table V I , a f t e r (72) (73) A l l i s o n et a l . and F i n k e l s t e i n and Goold , shows t h a t , i f the r e s t p o t e n t i a l i s more p o s i t i v e than the r e v e r s i b l e p o t e n t i a l f o r oxida-t i o n of xanthate or d i t h i o c a r b o n a t e to dixanthogen or thiouram d i s u l p h i d e , r e s p e c t i v e l y , the l a t t e r compounds are formed. Metal t h i o l a t e s are formed when the r e s t p o t e n t i a l i s more negative than the e q u i l i b r i u m redox p o t e n t i a l f o r the t h i o l couple. Oxidation of xanthate on c o v e l l i t e does not f o l l o w t h i s r u l e . A p l a u s i b l e e x p l a n a t i o n f o r the d e t e c t i o n of both dixanthogen and cuprous xanthate i s that the p r e d i c t e d c u p r i c xanthate i s f i r s t formed and then r e a c t s producing cuprous xanthate and dixanthogen. Another exception to the "one o x i d a t i o n product" r u l e was (72) observed by A l l i s o n et a l . i n the case of molybdenite. A second o x i d a t i o n product of xanthate, which could not be i d e n t i f i e d , was detected i n a d d i t i o n to dixanthogen. - 28 -TABLE VI C o r r e l a t i o n between r e s t p o t e n t i a l s and the products of i n t e r -a c t i o n of sulphide minerals w i t h t h i o l c o l l e c t o r s (A) Potassium e t h y l xanthate (6.25 x 10 M^ at pH 7), from A l l i s o n et a l ( 7 2 ) . ( R e v e r s i b l e p o t e n t i a l f o r o x i d a t i o n to dixanthogen i s 0.13V versus NHE). M i n e r a l Rest P o t e n t i a l Product (V versus NHE) Arsenopyrite + 0.22 X2 P y r i t e + 0.22 X2 P y r r h o t i t e + 0.21 X2 Molybdenite + 0.16 x 2 Alabandite + 0.15 X 2 C h a l c o p y r i t e + 0.14 X 2 C o v e l l i t e + 0.05 X 2 B o r n i t e + 0.06 MX Galena + 0.06 MX (b) Sodium d i e t h y l d i t h i o c a r b a m a t e (100 ppm at pH 8 ) , from F i n k e l s t e i n and G o o l d ^ 3 . (Reversible p o t e n t i a l f o r o x i d a t i o n to thiouram d i s u l p h i d e i s 0.176V versus NHE). M i n e r a l Rest P o t e n t i a l (V versus NHE) Product P y r i t e + 0.475 (DTC) 2 C o v e l l i t e + 0.115 Cu(DTC) 2 C h a l c o p y r i t e + 0.095 Cu(DTC) 2 Molybdenite + 0.045 Mo(DTC) X Galena - 0.035 Pb(DTC) 2 B o r n i t e - 0.045 Cu(DTC) 2 C h a l c o c i t e - 0.115 Cu(DTC) 1 ? refers to unidentified oxidation product of xanthate - 29 -Whichever path the o x i d a t i o n of xanthates on sulphide minerals f o l l o w s , t h i s anodic process must be balanced by a cathodic r e a c t i o n . One of the im-portant r o l e s of oxygen i n xanthate-sulphide mineral systems i s to provide the balancing cathodic r e a c t i o n . The f i n a l product of oxygen r e d u c t i o n i n an aqueous environment can be e i t h e r H 2 O or OH , according to the r e a c t i o n s : 0 2 + 4H + + 4e -> 2H 20 (R-12) 0 2 + 2H 20 + 4e -* 40H~ (R-13) Reaction (R-12) i s more app r o p r i a t e to d e s c r i b e the process i n the a c i d i c range of pH (under the c a t a l y t i c a c t i o n of a mi n e r a l s u r f a c e ) . Reaction (R-13) i s more r e a l i s t i c i n the a l k a l i n e range. The high a c t i v a t i o n energy (117kcal/mol) r e q u i r e d f o r the breakage of the strong t r i p l e bonds i n the oxygen molecule (:0 0:) suggests that r e -a c t i o n s (R-12) and (R-13) represent only i n i t i a l and f i n a l s t a t e s . The formation of hydrogen peroxide as a s o l u b l e intermediate product i n oxygen r e d u c t i o n has been experimentally detected on some m e t a l l i c e l e c t r o d e s , as w e l l as on p y r i t e . There are a l s o i n d i c a t i o n s that peroxide formation i n v o l v e s two one-electron t r a n s f e r steps. The o v e r a l l process can be des-c r i b e d by the f o l l o w i n g r e a c t i o n s : 02 + e O 2 (R-14) 0l + 2H + + e -> H 20 2 (R-15) H 20 2 + 2H + + 2e -> 2H20 (R-l6) These equations may be a p p l i c a b l e i n r e p r e s e n t i n g the mechanism of oxygen r e d u c t i o n on other sulphide m i n e r a l s . At the present time i t i s c l e a r that an understanding of e l e c t r o -chemical p r i n c i p l e s i s important to. the explanation of the complex - 30 -mechanism of i n t e r a c t i o n between sulphide minerals and xanthates. Thermodynamics can be used as a f i r s t approach to study e l e c t r o d e r e a c t i o n s . A simple method of compiling thermodynamic i n f o r m a t i o n f o r (74) aqueous systems was proposed by Pourbaix . I t i s a g r a p h i c a l method i n which the e l e c t r o c h e m i c a l p o t e n t i a l , E^, i s p l o t t e d against pH. Figures 6 and 7 show - pH diagrams f o r p e n t l a n d i t e , combined w i t h the sulphur-water diagram. The a c t i v i t y of m e t a l l i c c a t i o n s was —6 taken as 10- f o r both diagrams. The a c t i v i t y of s u l p h u r - c o n t a i n i n g -2 i o n i c species was f i x e d at 10 f o r the p l o t shown i n Figure 6. U n i t a c t i v i t y was assumed unless otherwise s p e c i f i e d . The c a l c u l a t i o n s were (74) c a r r i e d out w i t h thermodynamic data from Pourbaix , except f o r the f r e e energy of formation of p e n t l a n d i t e , where the value presented by Abramov^ 7"^ was employed. The theory of k i n e t i c s of e l e c t r o d e r e a c t i o n s was e s t a b l i s h e d to e x p l a i n the c o r r o s i o n behaviour of m e t a l l i c systems. Many i n v e s t i g a t o r s i n the f i e l d of f r o t h f l o t a t i o n apply the same concepts. They assume that the surface of a sulphide mineral p a r t i c l e , i n a f l o t a t i o n e n v i r o n -ment , i s at a s i n g l e e q u i l i b r i u m p o t e n t i a l , the s o - c a l l e d mixed potent-i a l . Although t h i s may be true f o r c e r t a i n systems, there i s evidence f o r the e x i s t e n c e of both anodic and cathodic s i t e s on the surfaces of some sulphide m i n e r a l s . The published i n f o r m a t i o n on the e l e c t r o c h e m i c a l behaviour of the mineral p e n t l a n d i t e i s sparse. I I ' i n et a l reported the r e s t potent-i a l i n IN KC1 s o l u t i o n as +0.22V vs. NHE. Oxygen r e d u c t i o n on noble metal and sulphide mineral e l e c t r o d e s was s t u d i e d by Rand^ 7 7^. Some of h i s r e s u l t s , reproduced i n Figure 8, show that the a c t i v i t y of pentland-i t e f o r oxygen r e d u c t i o n i s h i g h and approaches that of noble metals. The high oxygen r e d u c t i o n a c t i v i t y suggests a low requirement f o r oxygen i n f l o t a t i o n . - 31 -- 32 -- 33 -Eh (V) F igure 8. Cu r r en t - po t en t i a l curves f o r oxygen reduc t i on on noble metal and su lph ide minera l e l e c t r o d e s , a t phf1 1 and 9.06, a f t e r Rand (77 ) - 34 -CHAPTER 3 OBJECTIVES The main o b j e c t i v e of the present i n v e s t i g a t i o n i s to study the mechanism of i n t e r a c t i o n between xanthate c o l l e c t o r and the minerals p e n t l a n d i t e , p y r r h o t i t e and c h a l c o p y r i t e , i n the presence of sulphur d i o x i d e as a r e g u l a t i n g reagent. The pH of the t e s t s was sel e c t e d as 5.5 to provide an a c i d i c c o n d i t i o n and yet avoid r a p i d decomposition of the xanthate at lower pH. Most researchers now agree that the f l o a t a b i l i t y of unoxidized sulphide minerals w i t h xanthates i s a s s o c i a t e d w i t h the o x i d a t i o n of xanthate i on to dixanthogen or metal xanthate. Sulphur d i o x i d e should have s u f f i c i e n t reducing power to prevent such o x i d a t i o n of xanthate i o n . Nevertheless, s u c c e s s f u l f l o t a t i o n of p e n t l a n d i t e and c h a l c o p y r i t e w i t h xanthates has been reported, i n the presence of SO2. At present, only guesses can be made as to the hydrophobic e n t i t y . I t could be elemental sulphur, dixanthogen, metal xanthate or s e v e r a l other hydrophobic surface species. Other aspects s t i l l unclear are the e f f e c t of SO2 towards o x i d i z e d species at the surface of the minerals and the relevance of these species to f l o a t a b i l i t y . An explanation and experimental v e r i f i c a t i o n of t h i s i n t e r a c t i o n would f i l l a gap i n the fundamental understanding of f l o t a -t i o n . During the course of the present work, emphasis w i l l be placed on the mi n e r a l p e n t l a n d i t e , s i n c e i t i s the most important n i c k e l - b e a r i n g sulphide m i n e r a l . - 35 -CHAPTER 4 EXPERIMENTAL METHODS AND APPARATUS Two main l i n e s of experimentation were pursued i n order to achieve the proposed o b j e c t i v e : ( i ) e l e c t r o c h e m i c a l experiments; ( i i ) m i c r o f l o t a t i o n t e s t s . 4.1 E l e c t r o c h e m i c a l Experiments The e l e c t r o c h e m i c a l experiments were set up i n i t i a l l y , to monitor the behaviour of each i n d i v i d u a l component of the system under i n v e s t i g -a t i o n , namely potassium amyl xanthate, sulphur d i o x i d e and the three sulphide minerals ( p e n t l a n d i t e , c h a l c o p y r i t e and p y r r h o t i t e ) , and subsequently to study t h e i r i n t e r a c t i o n . The t e s t s were d i v i d e d i n t o two groups: ( i ) r e s t p o t e n t i a l s on a platinum e l e c t r o d e ; ( i i ) t e s t s w i t h mineral e l e c t r o d e s . 4.1.1 Rest P o t e n t i a l s on a Platinum E l e c t r o d e This s e r i e s of t e s t s was c a r r i e d out i n a c y l i n d r i c a l pyrex c e l l , provided w i t h a l i d c o n t a i n i n g four o r i f i c e s . Three of the o r i f i c e s were used f o r i n s e r t i o n of e l e c t r o d e s : platinum, calomel reference and standard combination. The remaining o r i f i c e was employed f o r feeding reagents and mineral sample to the system. The platinum and calomel reference e l e c t r o d e s were connected to a F i s h e r Accumet pH-meter, model 210, operated i n the * 700 mV s c a l e . The combination e l e c t r o d e was connected - 36 to a Beckmarm Zeromatic I I pH-meter, operated i n the pH mode. The calomel reference and standard combination e l e c t r o d e s were from F i s h e r and the platinum from Corning. The c e l l was supported by a p l e x i g l a s s frame and placed on a mag-n e t i c s t i r r e r . A schematic view of the set up i s presented i n Figure 9. The working volume of the c e l l was 750 ml. A 0.1 N KC1 s o l u t i o n was used as supporting e l e c t r o l y t e i n a l l t e s t s , to ensure good e l e c t r i c a l c o n d u c t i v i t y . D i l u t e s o l u t i o n s of NaOH and HC1 were employ-ed f o r pH adjustment. In the p r e l i m i n a r y t e s t s without mineral s l u r r i e s , and those w i t h p e n t l a n d i t e s l u r r i e s , SO2 was added as a gas, by means of a gas d i s p e r s i o n tube. I t was found that i t was e a s i e r to c o n t r o l pH i f a water s o l u t i o n of SO2 was added to the system, i n s t e a d of the gas. This procedure was then adopted i n the t e s t s w i t h c h a l c o p y r i t e and p y r r h o t i t e s l u r r i e s . S l u r r i e s c o n t a i n i n g 1% (by weight) s o l i d s were used i n a l l t e s t s . The t e s t s were c a r r i e d out at pH 5.5 to avoid r a p i d decomposition of the xanthate at lower pH. The h a l f - l i f e f o r decom-p o s i t i o n of amyl xanthate decreases from 989 minutes at pH 5.6 to 11.8 (78) minutes at pH 3.4 . A l l t e s t s were c a r r i e d out at room temperature. A j u s t i f i c a t i o n f o r the choice of a platinum e l e c t r o d e f o l l o w s . I r r e s p e c t i v e of the p a r t i c u l a r metal being used as a r e s t p o t e n t i a l i n d i c a t o r e l e c t r o d e , poisoning of the e l e c t r o d e must always be a major concern of the researcher. The use of platinum e l e c t r o d e s f o r p o t e n t i a l (97) measurements has been e x t e n s i v e l y studied by Natarajan and Iwasaki , (80),(81),(82),(83) _ . , .... . , r / » \ /»v /_ These authors t e s t e d d i f f e r e n t methods f o r - 37 -Calomel e l e c t r ode Pt e l e c t r ode pH meter K A Reagents Combination e l e c t r ode pH meter Magnetic S t i r r e r F igure 9. Schematic view of the apparatus f o r the measurement o f r e s t p o t e n t i a l s w i th p la t inum e l e c t r ode - 3.8 -c l e a n i n g poisoned platinum e l e c t r o d e s and concluded that mechanical p o l i s h i n g i s the most adequate technique to r e a c t i v a t e an e l e c t r o d e . Although they appreciated the f a c t that platinum e l e c t r o d e s were not i n e r t i n a simulated f l o t a t i o n environment, i t was impossible f o r them to recommend an e l e c t r o d e that could present b e t t e r performance under these c o n d i t i o n s . A d i s c u s s i o n of the p o s s i b l e d i f f e r e n c e s between a mineral e l e c t r o d e and a platinum e l e c t r o d e being s t r u c k by p a r t i c l e s of the same mineral i s presented i n s e c t i o n 6.2.1. In the present work the platinum e l e c t r o d e was p o l i s h e d on a wet 600 g r i t paper immediately before each t e s t . The e l e c t r o d e was always stored i n a sealed tube c o n t a i n i n g d i s t i l l e d water. 4.1.2 Tests w i t h M i n e r a l E l e c t r o d e s A round glass f l a s k , w i t h m u l t i p l e o r i f i c e s , was u t i l i z e d f o r these i n v e s t i g a t i o n s . O r i f i c e s were provided f o r : a working e l e c t r o d e ( m i n e r a l ) ; an a u x i l i a r y or counter e l e c t r o d e (platinum); a Luggin c a p i l l a r y probe; a microprobe combination e l e c t r o d e (pH); a gas i n l e t and o u t l e t and a thermometer. The counter e l e c t r o d e was i n s e r t e d i n t o a g lass tube w i t h a f r i t t e d g l a s s bottom that permitted a p h y s i c a l s e p a r a t i o n between anode and cathode compartments, to prevent cross contamination. The Luggin c a p i l l a r y was connected to the reference e l e c t r o d e (saturated calomel electrode) v i a a s a l t b r i d g e . The e l e c t r o c h e m i c a l c e l l was complete when the e l e c t r o d e s i n the glass f l a s k were connected to a Wenking p o t e n t i o s t a t , model 68TS10. P r e l i m i n a r y testwork showed that the r e s i s t a n c e of the working e l e c t r o d e and the impedance of the semi-conducting connection to the c i r c u i t could be neglected. Because of t h i s f a c t , a f our-wire system was not r e q u i r e d . The pH e l e c t r o d e was - 39 -connected to a Beckmann Zeromatic I I pH-meter. The f l a s k was mounted s i t t i n g on a magnetic s t i r r e r . The c e l l i s s c h e m a t i c a l l y represented i n Figure 10. The working volume of the c e l l was 1250 ml. A l l t e s t s were c a r r i e d out i n 0.1 N KC1 supporting e l e c t r o l y t e , at room temperature. NaOH and HC1 were employed when pH adjustment was necessary. A b u f f e r s o l u t i o n (potassium hydrogen phthalate - sodium hydroxide b u f f e r ) , pH 5.5, was employed to keep the pH constant during the p o l a r i z a t i o n t e s t s . Sulphur d i o x i d e was added i n the form of an aqueous s o l u t i o n . P o t e n t i o s t a t i c p o l a r i z a t i o n curves were determined according to the f o l l o w i n g procedure. A f t e r the system had reached a s t a b l e r e s t p o t e n t i a l , a p o t e n t i a l 10 to 20 mV anodic or cathodic w i t h respect to the r e s t p o t e n t i a l was a p p l i e d to the system. A reading of the current between working and counter e l e c t r o d e was taken one minute l a t e r . The p o t e n t i a l was then immediately s h i f t e d by 10 mV, to i t s next value, the current again being read a f t e r a one minute i n t e r v a l . This procedure was repeated u n t i l the curve had been determined. The mineral e l e c t r o d e s were prepared according to the f o l l o w i n g technique. Pieces of the minerals were mounted i n "quick mount" p l a s t i c (2.54 cm i n diameter and l e s s than 0.5 cm i n t h i c k n e s s ) , ground and p o l i s h e d to a l y f i n i s h using diamond compound. The mineral p a r t i c l e was exposed at both faces of the sample. One face was s e l e c t e d to be exposed to the e l e c t r o l y t e and the other face was coated w i t h gold i n a vacuum b e l l j a r device. A copper w i r e was connected to the gold coated face by means of s i l v e r conducting cement. A glass tube was bent and mounted i n "quick mount" as shown i n Figure 11(a). The copper wire was i n s e r t e d i n t o the glass tube and the two p l a s t i c pieces were - 40 -gas o u t l e t and o r i f i c e P o t en t i o s t a t Magnetic S t i r r e r F igure 10. Schematic view of the apparatus f o r t e s t s w i th minera l e l e c t r odes - 41 -* Glass tube Quick mount r e s i n (a) * Glass tube "* Copper w i re Gold coa t i ng r e s i n '(b) F igure 11. P repara t i on of M inera l E lec t rodes - 4 2 -glued together w i t h f a s t d r y i n g epoxy r e s i n . The f i n a l arrangement of the e l e c t r o d e i s shown i n Figure 11(b). In a l l t e s t s the mineral e l e c t r o d e was p o l i s h e d on wet 600 g r i t paper and immediately i n s e r t e d i n t o the c e l l . The aim of t h i s procedure was to generate surface c o n d i t i o n s s i m i l a r to those i n an a c t u a l f l o t a t i o n environment, where a f r e s h surface i s produced by wet g r i n d i n g . 4.2 M i c r o f l o t a t i o n Tests Small s c a l e f l o t a t i o n t e s t s were c a r r i e d out i n two types of c e l l : ( i ) modified Hallimond tube; ( i i ) modified Smith-Partridge c e l l . 4.2.1 Modified Hallimond Tube This c e l l i s a f u r t h e r m o d i f i c a t i o n of the v e r s i o n of the Hallimond tube presented by Fuerstenau et al^^ . The tube i s i l l u s t r a t e d i n Figure 12. The important f e a t u r e s are a f r i t t e d g l a s s d i s k f o r a i r d i s p e r s i o n , a magnetic s t i r r e r , and a ground glass j o i n t that s i m p l i f i e s h a n d l ing. The working volume was 125 ml. A i r was s u p p l i e d by the exhaust of a vacuum pump and went through a flow meter that was set to provide a constant flow r a t e of 50 ml/min. The pH of the s l u r r y was adjusted w i t h a b u f f e r s o l u t i o n (borax b u f f e r ) , pH 9.18, p r i o r to any SO2 a d d i t i o n . Sulphur d i o x i d e was always added as an aqueous s o l u t i o n . Potassium hydrogen phthalate - sodium hydroxide b u f f e r s o l u t i o n was used to keep the pH at a constant value of 5.5 during the f l o t a t i o n t e s t s . A f t e r the a d d i t i o n of e i t h e r SO^ or potassium amyl xanthate, a c o n d i t i o n i n g p e r i o d of 2 minutes was allowed. S l u r r i e s c o n t a i n i n g 1% (by weight) s o l i d s were used i n a l l t e s t s . - 43 -water l e v e l Magnetic S t i r r e r • path of f l o a t e d mate r i a l f r i t t e d g lass d i s k a i r F igure 1 2 . Mod i f i ed Hal l imond tube 4.2.2 M o d i f i e d Smith-Partridge C e l l This c e l l , shown i n Figure 13, i s a f u r t h e r m o d i f i c a t i o n of the (85) o r i g i n a l Smith-Partridge c e l l , that had been p r e v i o u s l y changed by F i n k e l s t e i n and S t e w a r t . The main features are a f r i t t e d g l a s s d i s k f o r a i r d i s p e r s i o n and a mechanical s t i r r e r . The advantage of the mechanical i m p e l l e r over the magnetic s t i r r e r i s obvious when a ferromagnetic mineral ( l i k e p y r r h o t i t e ) i s t e s t e d . Except f o r minerals i n that c l a s s , both s t i r r i n g mechanisms are adequate. The major advantage i n favour of the Hallimond tube i s the ease i n handling. The working volume of the c e l l was 125 ml. The a i r flow r a t e employed was 75 ml/min. The i m p e l l e r speed was 100 rpm. A i r supply and t e s t c o n d i t i o n s were the same as those described f o r the Hallimond tube. - 45 -F igure 13. Mod i f i ed Sm i th -Pa r t r i dge c e l l - 46 -CHAPTER 5 MATERIALS The m a t e r i a l s used i n the present i n v e s t i g a t i o n can be d i v i d e d i n t o two groups: ( i ) sulphide mineral samples; ( i i ) chemical reagents. 5.1 Sulphide M i n e r a l Samples A massive matrix of n i c k e l i f e r o u s p y r r h o t i t e from Sudbury, Ontar i o , c o n t a i n i n g i n c l u s i o n s of p e n t l a n d i t e , was purchased from Ward's Labora-to r y . INCO s u p p l i e d a sample of high grade p e n t l a n d i t e concentrate, pro-duced by f l o t a t i o n i n t h e i r Thompson m i l l . High grade c h a l c o p y r i t e and n i c k e l - f r e e p y r r h o t i t e , o r i g i n a t i n g from S h i v a t a k i and Kawagama, i n Japan, r e s p e c t i v e l y , were obtained. Thompson p e n t l a n d i t e was employed i n t e s t s i n v o l v i n g s l u r r i e s ( r e s t p o t e n t i a l on a platinum e l e c t r o d e and f l o t a t i o n ) . The sample was care-f u l l y washed i n d i - e t h y l - e t h e r , to remove c o l l e c t o r that could have been l e f t from the previous concentration. The m a t e r i a l , as r e c e i v e d , was below 65 mesh and was wet screened at 325 mesh. The f i n e s were d i s -carded. P e n t l a n d i t e e l e c t r o d e s were prepared by c u t t i n g , w i t h a mini c u t - o f f saw, v i s u a l l y s e l e c t e d p o r t i o n s from the massive b l o c k , precut w i t h a diamond saw. C h a l c o p y r i t e from S h i v a t a k i , Japan, was used as e l e c t r o d e and s l u r r y . The sample f o r s l u r r i e s was ground to minus 65 mesh w i t h mortar and p e s t l e and the f r a c t i o n below 325 mesh was discarded. P o r t i o n s of the Sudbury sample, v i s u a l l y s e l e c t e d f o r being low i n p e n t l a n d i t e , c o n s t i t u t e d the source of n i c k e l i f e r o u s p y r r h o t i t e . The e l e c t r o d e s were prepared d i r e c t l y from these p o r t i o n s . M a t e r i a l f o r - 47 -s l u r r i e s was f u r t h e r cleaned from p e n t l a n d i t e by magnetic s e p a r a t i o n . A hand magnet and a Frantz Isodynamic Separator were used i n t h i s opera-t i o n . From t h i s point on, any n i c k e l i f e r o u s p y r r h o t i t e sample w i l l be r e f e r r e d to simply as p y r r h o t i t e , ( unless otherwise s p e c i f i e d . The n i c k e l - f r e e p y r r h o t i t e sample from Kawagama, Japan, was u t i l i z -ed as an e l e c t r o d e . The chemical composition of these mineral samples i s l i s t e d i n Table V I I . Before being mounted as e l e c t r o d e s , the samples were submitted to a l i n e scan w i t h the e l e c t r o n microprobe. A summary of the r e s u l t s f o l l o w s . Although the p e n t l a n d i t e sample was f u l l of cracks, due to the extreme b r i t t l e n e s s of t h i s m i n e r a l , the a n a l y s i s of f l a t surface regions suggest-ed that n i c k e l , i r o n and sulphur were uniformly d i s t r i b u t e d along the sample. Scans along the n i c k e l i f e r o u s p y r r h o t i t e showed f a i r l y even d i s -t r i b u t i o n f o r i r o n and sulphur, the n i c k e l content being v a r i a b l e along the sample. This p a t t e r n was an i n d i c a t i o n that most of the n i c k e l was present as very f i n e grains of p e n t l a n d i t e i n the p y r r h o t i t e m atrix. The n i c k e l - f r e e p y r r h o t i t e and the c h a l c o p y r i t e samples were very pure, as shown by uniform d i s t r i b u t i o n of a l l elements. The c h a r a c t e r i z a t i o n of the samples i n c l u d e d the experimental d e t e r -mination of e l e c t r o p h y s i c a l p r o p e r t i e s . For e l e c t r i c a l c o n d u c t i v i t y measurements, both exposed faces of the mounted speciments were immersed i n mercury. The a p p l i e d voltage and r e s u l t i n g current f l o w i n g across the sample were measured by means of a d i g i t a l multimeter. The r e s u l t s , expressed as r e s i s t i v i t y , are presented i n Table V I I I . Data published by Parasnis , K e l l e r and Frischknecht , Parkhomenko and Shuey are a l s o included i n the t a b l e . TABLE V I I Elemental d i s t r i b u t i o n of sulphide mineral samples and corresponding i d e a l s t o i c h i o m e t r i c compounds M i n e r a l O r i g i n Elemental D i s t r i b u t i o n N i Fe Cu Co S. T o t a l P e n t l a n d i t e Con* Thompson 33.8 31.3 0.03 0.50 32.7 98.33 P e n t l a n d i t e Sudbury 33.6 32.4 0.27 0.76 33.9 100.93 S t o i c h . Fe, _ N i , r S n 4.5 4.5 8 34.22 32.55 - - 33.23 100.00 P y r r h o t i t e * * Sudbury 4.35 57.5 0.06 - 38.8 100.71 P y r r h o t i t e * * * Sudbury 4.45 55.5 0.14 0.09 40.9 101.08 P y r r h o t i t e Kawagama - 60.9 0.38 - 35.9 97.18 S t o i c h . Fe_S Q / o - 60.38 - - 39.62 100.00 C h a l c o p y r i t e S h i v a t a k i - 30.9 33.9 - 34.8 99.60 S t o i c h . CuFeS 2 — 30.43 34.62 — 34.95 100.00 * A n a l y s i s provided by Inco, Thompson. The other samples were analysed i n the Department of M i n e r a l Engineering, U.B.C, by atomic absorption (sulphur was analysed g r a v i m e t r i c a l l y ) . Samples were submitted i n d u p l i c a t e and the confidence i n t e r v a l i s ± 2%. * This represents the matrix surrounding p e n t l a n d i t e . * Same as above, a f t e r magnetic c l e a n i n g . - 49 -TABLE V I I I E l e c t r i c a l r e s i s t i v i t y of sulphide minerals ( i n Q x cm) Source P e n t l a n d i t e .Chalcopyrite P y r r h o t i t e (86) - 10~ 2 - 7x10" -2 -3 -3 10 3 - 5x10 J (87) -4 10 - 1.1x10 1.5xl0~ 2 - 9x10" -1 2 x l 0 ~ 4 - 1.6xl0~ 2 (88) - 10" 2 - 7x10" •2 6.5xl0~ 4 - 4 . 1 x l 0 " 2 (89) - 10~ 2 - 1* 2 x l d ~ 4 - 1 . 6 x l 0 ~ 2 This work 8.2xl0~ 2 4 . 5 x l 0 - 1 1 . 2 x l 0 - 1 - 9 . 9 x l 0 _ 1 * * * range of most incidence i n a histogram. ** 1.2 x 10 x f o r n i c k e l i f e r o u s p y r r h o t i t e ; 9.9 x 10 1 f o r n i c k e l - f r e e p y r r h o t i t e . The type of s e m i c o n d u c t i v i t y of each mineral specimen was q u a l i t a t i v e -l y determined. The technique employed was based on the Seebeck e f f e c t , and the experimental set up i s i l l u s t r a t e d i n F i g u r e 14. The f o l l o w i n g r e s u l t s were obtained: ( i ) the c h a l c o p y r i t e sample i s s t r o n g l y n-type. A f t e r 2 minutes immersion i n xanthate s o l u t i o n there i s a s l i g h t decrease i n the n-type character; ( i i ) the p e n t l a n d i t e sample i s weakly n-type, and does not seem to be a f f e c t e d by xanthate; ( i i i ) both p y r r h o t i t e samples are weakly p-type and are unaffected by xanthate. 5.2 Chemical Reagents A l l t e s t s were c a r r i e d out i n s i n g l e d i s t i l l e d water. The f o l l o w i n g chemicals ( a n a l y t i c a l reagent grade) were s u p p l i e d by F i s h e r : KC1; NaOH; - 50 -F igure 14. Test f o r sem i conduc t i v i t y type of a minera l - 51 -HC1; b u f f e r s a l t s of pH 4.01 (potassium hydrogen p h t h a l a t e ) , pH 7.41 (potassium phosphate monobasic - sodium phosphate d i b a s i c ) and pH 9.18 (borax). B u f f e r s o l u t i o n , pH 5.5, was prepared from potassium hydrogen phthalate and NaOH. Anhydrous SO2 was u t i l i z e d . The b u f f e r s o l u t i o n s employed were test e d f o r t h e i r p o s s i b l e e f f e c t s on the systems under i n v e s t i g a t i o n . The r e s t p o t e n t i a l s and p o l a r i z a t i o n curves were the same i n buff e r e d systems as i n those which pH was c o n t r o l l -ed by NaOH or HC1 only. Methyl i s o b u t y l c a r b i n o l (MIBC) was u t i l i z e d as a f r o t h e r i n the f l o t a t i o n t e s t s . The dosage employed was 32 mg/1, which corresponds to 6.4 l b s of f r o t h e r per ton of miner a l . This l e v e l i s u n r e a l i s t i c , as f a r as p l a n t p r a c t i c e i s concerned, but the f r o t h generated was considered adequate f o r the present purposes. The xanthate used i n a l l t e s t s was potassium amyl xanthate from Hoechst (92% pure according to UV a n a l y s i s ) . From now on, the word xanthate w i l l be used to mean t h i s potassium amyl d i t h i o c a r b o n a t e , unless otherwise s p e c i f i e d ; KAmX and X w i l l be used as a b b r e v i a t i o n s f o r the s a l t and anion; X2 w i l l represent the o x i d a t i o n product, di-amyl dixanthogen. -4 The c o n c e n t r a t i o n of a l l xanthate s o l u t i o n s was 0.74 x 10 M. The choice was based on the f o l l o w i n g reasoning. A r e a l i s t i c p i c t u r e from p l a n t p r a c t i c e of m i l l i n g n i c k e l ores i n d i c a t e d t h a t , f o r an ore c o n t a i n i n g 1% N i , the xanthate consumption i s about 0.1 l b s per ton of ore processed. The sample i n t h i s work assayed 30% N i and 1% wt s l u r r i e s were used i n the t e s t s . This l e d to 15 mg of xanthate per l i t e r of s o l u t i o n , or 0.74 x -4 10 M (assuming that both xanthates added i n the m i l l and used i n t h i s i n v e s t i g a t i o n are 100% pure). 5.3 Adsorption of Xanthate on Sulphide M i n e r a l s The c h a r a c t e r i z a t i o n of the m a t e r i a l s used i n the present work . - 52 -included an i n v e s t i g a t i o n of the adsorption of xanthate on p e n t l a n d i t e and c h a l c o p y r i t e . S l u r r i e s c o n t a i n i n g 1% (by weight) of these minerals were kept under a g i t a t i o n by means of a magnetic s t i r r e r . Xanthate was added to -4 the system so that the i n i t i a l c o n c e n t r a t i o n was 0.74 x 10 M. A c e r t a i n c o n d i t i o n i n g time was allowed, immediately a f t e r which the s l u r r y was f i l t e r e d . The f i l t r a t e was analysed, by UV spectrophotometry, f o r xanthate i o n . The adsorption of UV r a d i a t i o n by the OCSS chromophore, 3 -1 -1(71) at 301 my, w i t h an e x t i n c t i o n c o e f f i c i e n t of 17.7 x 10 1. mol cm was the property u t i l i z e d . The percentage of xanthate not adsorbed on the mineral p a r t i c l e s i s l i s t e d i n Table IX, f o r t e s t c o n d i t i o n s there s p e c i f i e d . In the systems i n v o l v i n g S02> a c o n d i t i o n i n g time of 2 minutes was allowed p r i o r to xanthate a d d i t i o n . TABLE IX Adsorption of xanthate on sulphide minerals System C o n d i t i o n i n g time (sec) % xanthate not adsorbed P e n t l a n d i t e 5 55 P e n t l a n d i t e 15 21 P e n t l a n d i t e 60 19 P e n t l a n d i t e - S 0 2 15 28 C h a l c o p y r i t e 5 71 C h a l c o p y r i t e 15 61 C h a l c o p y r i t e 60 44 Chalcopyrite-S02 15 not deti - 53 -The r e s u l t s reported i n Table IX show that SC^ enhanced the adsorp-t i o n of xanthate on c h a l c o p y r i t e and s l i g h t l y hindered the adsorption on p e n t l a n d i t e . The a c t u a l s p e c i f i c area of the samples was not determined. There was an i n d i c a t i o n that the p e n t l a n d i t e samples had l a r g e r s p e c i f i c areas than those of c h a l c o p y r i t e . This f a c t prevented any conc l u s i o n being drawn, r e l a t e d to the apparently l a r g e r amount of xanthate adsorbed on p e n t l a n d i t e . CHAPTER 6 RESULTS AND DISCUSSION 6.1 Rest P o t e n t i a l s , oii Platinum E l e c t r o d e A l l p o t e n t i a l s i n the present i n v e s t i g a t i o n were measured w i t h respect to the calomel reference e l e c t r o d e . The r e s u l t s were then converted to the normal hydrogen e l e c t r o d e s c a l e , assuming that the calomel reference i s at 224 mV anodic on the hydrogen s c a l e . 6.1.1 P r e l i m i n a r y Tests A. 0.1N KC1 s o l u t i o n The f i r s t experiments were conducted to i n v e s t i g a t e the i n f l u e n c e of pH on the r e s t p o t e n t i a l of the 0.1N KC1 s o l u t i o n , used as supporting e l e c t r o -l y t e . The r e s u l t s are shown i n Figure 15. A l e a s t squares f i t * a p p l i e d to the data gi v e s the f o l l o w i n g r e l a t i o n s h i p between Eh and pH: Eh = -53.0 pH + 872 ( E - l ) r 2 = 0.9993 where Eh = p o t e n t i a l converted to the normal hydrogen e l e c t r o d e s c a l e , i n mV r = c o e f f i c i e n t of c o r r e l a t i o n (see Appendix 1 f o r confidence i n t e r v a l s of r e g r e s s i o n l i n e s ) P o t e n t i a l s c a l c u l a t e d using equation E - l were s l i g h t l y p o s i t i v e compared to the t h e o r e t i c a l e q u i l i b r i u m p o t e n t i a l of platinum i n aqueous s o l u t i o n , given by equations R-17 and E-2 below: P t ( 0 H ) 2 + 2H + + 2e~ = 2H 20 + Pt (R-17) Eh = -59.1 pH + 980 (E-2)** ( a l l thermodynamic data are from r e f . (74), unless otherwise s p e c i f i e d ) * A least squares fit of data was used in obtaining a l l the linear equations present in this chapter. ** The standard electrode potential relates to the standard free energy of reaction and equilibrium constant as.'follows: E°h = -LG°/(nP) = (RT/F) InK F igure 15. Rest p o t en t i a l (on p la t inum e lec t rode) versus pH f o r 0.1N KC1 s o l u t i o n - 56 -B. KAmX s o l u t i o n s A next step was the measurement of r e s t p o t e n t i a l s of KAmX so l u t i o n s . A p l o t of the v a r i a t i o n of p o t e n t i a l w i t h xanthate molar co n c e n t r a t i o n i s presented i n Figure 16. The r e l a t i o n s h i p between the two v a r i a b l e s i s expressed by: Eh = -59.6 l o g [X _] -193 (E-3) r 2 = 0.9997 The l i n e a r behaviour and the value of the slope are i n agreement w i t h the redox p o t e n t i a l a s s o c i a t e d with the r e a c t i o n : X 2 + 2e = 2X~ (R-18) Eh = -59.1 l o g [X~] + E°h (E-4) where u n i t a c t i v i t y of X^ i s assumed. The standard p o t e n t i a l f o r the redox couple X^/X has been d e t e r -mined i n t h i s study and by other i n v e s t i g a t o r s , as shown i n Table X. TABLE X Standard p o t e n t i a l f o r the redox couple X /X E°h(mV) Author Method -160 / / T O N Majima and Takeda p o t e n t i o s t a t i c -158 Winter and Woods^ 9°^ p o t e n t i o s t a t i c -140 D u R i e t z ^ 9 1 ^ i o d i n e t i t r a t i o n -193 present work p o t e n t i o s t a t i c The use of commercial xanthate, as opposed to pure synthesized reagents, probably accounts f o r the discrepancy between the f i g u r e o b t a i n -ed i n t h i s work and r e s u l t s from other i n v e s t i g a t o r s . However, due to - 58 -the f a c t that r e l a t i v e p o t e n t i a l s are compared i n the present i n v e s t i g a -t i o n , a constant s h i f t does not i n t e r f e r e w i t h the i n t e r p r e t a t i o n of r e s u l t s . C. SC^ s o l u t i o n s The pH of s o l u t i o n s c o n t a i n i n g the supporting e l e c t r o l y t e was i n i -t i a l l y r a i s e d w i t h NaOH to values between 9 . 0 and 10.5. Gaseous S0^ was then sl o w l y bubbled i n t o the system. The amount of SO2 i n j e c t e d was not q u a n t i t a t i v e l y monitored. A q u a l i t a t i v e i n d i c a t i o n was given by the pH of the s o l u t i o n . Sulphur d i o x i d e a d d i t i o n r e s u l t e d i n a reducing character being imparted to the system, as shown i n F i g u r e 17. In the pH range between 5 and 8, a l i n e a r r e l a t i o n s h i p between p o t e n t i a l and pH i s expressed by: Eh = -27 . 3 pH + 569 (E-5) r 2 = 0.6747 The poor c o r r e l a t i o n between the data could be explained by a l a c k of adequate c o n t r o l of SO2 a d d i t i o n and to the f a c t that the r e s u l t s r e f e r to s e v e r a l i n d i v i d u a l t e s t s . The use of a constant amount of a p a r t i c u l a r b u f f e r s o l u t i o n i s a b e t t e r method of a d j u s t i n g the i n i t i a l pH. This procedure was adopted i n l a t e r t e s t s . The o x i d a t i o n s t a t e diagram f o r sulphur, at pH 7, i n d i c a t e s that when SO2 ( o x i d a t i o n s t a t e of sulphur = +4) i s added to a system, the f o l l o w i n g e q u i l i b r i u m should occur: S o 0 ~ + 2 H + + 2 e = 2 H S 0 ~ (R-19) 2 6 3 Eh = -59.1 pH + 455 + 29.6 l o g [ a g Q 2 ~ / ( a H S ( f ) 2 ] (E-6) 2 6 3 The discrepancy between equations E-5 and E-6 suggests that redox 2 -couples other than S „0 , / H S 0 „ play an important r o l e i n S 0 o water chemistry. z t> j i. 5 6 7 8 9 10 pH F igure 17. Rest p o t en t i a l (on p lat inum e l e c t rode ) versus pH f o r S0 2 s o l u t i o n s - 60 -D. S0 2 - KAmX s o l u t i o n s Xanthate added to SO2 s o l u t i o n s caused a p o t e n t i a l d r i f t i n the negative d i r e c t i o n , towards the p o t e n t i a l f o r the X^/X couple, as i l l u s -t r a t e d i n Figure 18. P o t e n t i a l i s expressed as a f u n c t i o n of pH, as f o l l o w s : Eh = -24.3 pH + 237 (E-7) r 2 = 0.8551 The most s i g n i f i c a n t aspect of these r e s u l t s i s that the r e s t poten-t i a l of the system i s s t i l l p o s i t i v e w i t h respect to that of the X^/X couple, at concentrations s i m i l a r to those employed i n p l a n t p r a c t i c e . This i n d i c a t e s that the o x i d a t i o n of xanthate i o n to dixanthogen i s thermodynamically favoured under a l l these c o n d i t i o n s . I n f r a r e d s p e c t r o -scopy might be used to confirm the presence of dixanthogen adsorbed on the platinum e l e c t r o d e . Attenuated t o t a l r e f l e c t a n c e i s probably an appropriate technique f o r d e t e c t i o n of adsorbed species on a f l a t p l a t i -num surface. 6.1.2 Tests w i t h P e n t l a n d i t e A. P e n t l a n d i t e s l u r r i e s F i g ure 19 shows the v a r i a t i o n of p o t e n t i a l as a f u n c t i o n of pH f o r a 1% (by weight) p e n t l a n d i t e s l u r r y . The p o i n t s on the curve presented i n F i g ure 19 were determined from lower to higher pH values. The curve e x h i b i t s two l i n e a r r e g i o n s , one between pH 4.0 and 5.0, and the other between pH 6.1 and 8.7. In the intermediate r e g i o n there i s a d i s t i n c t minimum. The two l i n e a r p o r t i o n s are represented by: Eh = -61.2 ph + 774 (pH 4.0 - 5.0) (E-8) r 2 = 0.9983 F igure 19. Rest p o t en t i a l (on p la t inum e l ec t rode) versus pH f o r pen t l and i t e s l u r r y - 63 -Eh = -49.2 pH + 773 (pH 6.1 - 8.7) (E-9) r 2 = 0.9984 The slopes of' the s t r a i g h t l i n e regions and the general aspect of the curve e x h i b i t e d good r e p r o d u c i b i l i t y . The depth of the minimum seems to be a f f e c t e d by the r a t e of pH change. The Eh - pH diagram f o r the p e n t l a n d i t e and sulphur-water system, Figure 7, p r e d i c t s that the o x i d a t i o n of p e n t l a n d i t e should be independent of pH, i n the pH range between 4.1 and 5.6, due to formation of elemental sulphur as one of the o x i d a t i o n products. A c o r r e l a t i o n between t h i s . mechanism and the minimum i n the experimental curve i s a p o s s i b i l i t y . The minimum could represent a metastable s i t u a t i o n , and as e q u i l i b r i u m i s approached i t would change i n t o a h o r i z o n t a l l i n e . The l i n e a r r e gion at lower pH values suggests that the cathodic r e a c t i o n , namely oxygen r e d u c t i o n , d i c t a t e s the slope of the curve. A d i s c u s s i o n of the r e l e v a n t anodic and cathodic r e a c t i o n s that c o n t r i b u t e to the experimentally determined r e s t p o t e n t i a l w i l l be pre-sented i n s e c t i o n 6.1.5. At t h i s point i t i s p e r t i n e n t to s t a t e t h a t , i n systems i n v o l v i n g sulphide minerals and xanthate, oxygen r e d u c t i o n plays a major r o l e as a cathodic r e a c t i o n . B. P e n t l a n d i t e s l u r r i e s - SO2 The e f f e c t of a d d i t i o n of SO2 to p e n t l a n d i t e s l u r r i e s i s i l l u s t r a t e d i n Figure 20. P r i o r to SO2 i n j e c t i o n , the pH of the system was adjusted, i n a l l t e s t s , w i t h NaOH, to a value between 9 and 10. The presence of SO2 proved to have a reducing e f f e c t on the m i n e r a l , as compared w i t h only a pH change using HC1. The p o t e n t i a l versus pH r e l a t i o n s h i p , f o r the s l u r r y a c i d i f i e d w i t h S09 to a pH between 4.3 and 6.8, obeys the - 65 -equation: Eh = -48.8 pH +554 (E-10) r 2 = 0.8364 The r e s t p o t e n t i a l a f t e r SO^ i n j e c t i o n i s p o s i t i v e w i t h respect to that of the X^/X couple. These c o n d i t i o n s i n d i c a t e that the o x i d a t i o n of xanthate i o n to dixanthogen i s again thermodynamically favoured. C. P e n t l a n d i t e s l u r r i e s - KAmX The a d d i t i o n of xanthate to a p e n t l a n d i t e s l u r r y caused an i n i t i a l f a s t d r i f t of p o t e n t i a l i n the negative d i r e c t i o n . A minimum i n the p o t e n t i a l versus time curve was reached, and then the p o t e n t i a l s t a r t e d moving i n the p o s i t i v e d i r e c t i o n , tending to r e s t o r e the p o t e n t i a l of the system to i t s i n i t i a l value before xanthate a d d i t i o n . Figure 21 i l l u s -t r a t e s the change of p o t e n t i a l w i t h time f o r one t e s t . The minimum i n the curve occurred 30 seconds a f t e r xanthate a d d i t i o n . The general shape of the curve and time of the minimum were r e p r o d u c i b l e , and were not pH dependent. The minimum i n the p o t e n t i a l versus time curve can be explained as f o l l o w s . When xanthate was added to the system the p o t e n t i a l d r i f t e d towards i t s e q u i l i b r i u m p o s i t i o n , a t a more negative value. Before the expected r e s t p o t e n t i a l was reached, the almost complete e x t r a c t i o n of xanthate from s o l u t i o n , due to adsor p t i o n on the mineral p a r t i c l e s , r e s t o r e d the p o t e n t i a l of the system to i t s i n i t i a l c o n d i t i o n (before xanthate a d d i t i o n ) . D. P e n t l a n d i t e s l u r r i e s - SO2 - KAmX A p l o t of p o t e n t i a l versus time f o r t h i s system, as shown i n F i g u r e 22, r e v e a l s s i m i l a r features to those obtained i n the absence of SO2 (Figure 21). The major d i f f e r e n c e i s that the minimum i n the curve i s Eh mV 500 Eh mV - 68 -now d i s p l a c e d to 2.5 minutes. This f a c t suggests that SC^ slowed down the adsorption of xanthate by the mineral p a r t i c l e s . The present r e s u l t s i n d i c a t e t h i s delay, but do not provide any clue to i t s i n t e r -p r e t a t i o n . 6.1.3 Tests w i t h c h a l c o p y r i t e The v a r i a t i o n of p o t e n t i a l as a f u n c t i o n of pH, f o r a c h a l c o p y r i t e s l u r r y , i s presented i n Figure 23. The features of the curve are very s i m i l a r to those f o r p e n t l a n d i t e . There are two l i n e a r r e g i o n s , separat ed by a minimum. Between pH 4.2 and 5.6 the curve f o l l o w s the equation: Eh = -67.7 pH + 858 ( E - l l ) r 2 = 0.9998 In the pH range between 7.1 and 9.5 the r e s u l t s f i t the equation : Eh = -54.0 pH + 827 (E-12) r 2 = 0.9986 Figure 23 a l s o shows one point that represents the e f f e c t of SO2 added to a c h a l c o p y r i t e s l u r r y , o r i g i n a l l y at pH = 9.35. The reducing character of SO2 i s evident. Figure 24 i s a p l o t of the v a r i a t i o n of p o t e n t i a l w i t h time, f o r a c h a l c o p y r i t e s l u r r y t r e a t e d w i t h xanthate. A minimum can be seen at time = 1.5 minutes. The same type of p l o t i s i l l u s t r a t e d i n Figure 25, w i t h the d i f f e r e n c e that the s l u r r y was a c i d i f i e d w i t h S02> p r i o r to xanthate a d d i t i o n . The minimum s t i l l e x i s t s , but now i t has been s h i f t e to 30 seconds. Assuming that the minimum i s associated w i t h xanthate being adsorbed on the m i n e r a l , these t e s t s r e v e a l that SO2 speeds up the xanthate adsorption mechanism on c h a l c o p y r i t e . This e f f e c t seems to be due to the reducing a c t i o n of S02» towards o x i d i z e d species on the sur-face of c h a l c o p y r i t e . Thermodynamically the steps i n o x i d a t i o n of c h a l -c o p y r i t e are q u i t e d i f f e r e n t from those of p e n t l a n d i t e . At pH 5.5 pent-2+ 2+ l a n d i t e o x i d i z e s producing Fe and N i . The o x i d a t i o n of chalcopy-500 r -400 300 h-F igure 24. Rest p o t en t i a l (on p la t inum e l ec t rode) versus time f o r c ha l c opy r i t e s l u r r y - KAmX - 72 -r i t e proceeds v i a c o v e l l i t e , c h a l c o c i t e , copper and copper oxides and hydroxides . 6.1.4 Tests w i t h p y r r h o t i t e The p o t e n t i a l of a p y r r h o t i t e s l u r r y v a r i e s w i t h pH as shown i n Figure 26. Again the curve e x h i b i t s two s t r a i g h t l i n e p o r t i o n s . In the pH range between 4.25 and 5.45 the equation followed i s : Eh = -60.5 pH + 798 (E-13) r 2 = 0.9995 At higher pH v a l u e s , between 7.1 and 9.7, the r e s u l t s f i t : Eh = -57.2 pH + 851 (E-14) r 2 = 0.9998 The e f f e c t of SO2 a d d i t i o n , . o n a p y r r h o t i t e s l u r r y i n i t i a l l y at pH -• 9.7, i s als o featured i n Figure 26. The behaviour of p y r r h o t i t e s l u r r i e s i n the presence of xanthate was i n v e s t i g a t e d next. The r e s u l t s are reported i n Figure 27 (xanthate a d d i t i o n only) and Figure 28 (SO^ i n j e c t e d p r i o r to xanthate a d d i t i o n ) . Both p l o t s are very s i m i l a r , a minimum i n the p o t e n t i a l versus time curve being found 1 minute a f t e r xanthate was introduced. The r e s u l t s do not i n d i c a t e any important e f f e c t of SO2 on the adsorption of xanthate by unactivated p y r r h o t i t e . Elemental sulphur i s supposed to be formed r e a d i l y on the surface of p y r r h o t i t e , as an o x i d a t i o n product. The p r e d i c t e d e f f e c t of SO2 i s to c o n t r i b u t e to i t s f u r t h e r o x i d a t i o n to t h i o s u l p h a t e , rendering the surface l e s s hydrophobic, i n the absence of xanthate. The r e s t p o t e n t i a l from the platinum e l e c t r o d e t e s t s n e i t h e r confirmed nor denied t h i s hypo-t h e s i s . Eh mV 450 0 10 20 30 40 time (min.) 50 F igure 28. Rest p o t en t i a l (on p la t inum e lec t rode) versus time f o r p y r r h o t i t e s l u r r y - S 0 2 - KAmX - 76 -One aspect that has to be kept i n mind, regarding p y r r h o t i t e , i s that adhesion of mi n e r a l p a r t i c l e s to the s t i r r i n g magnet i n t e r f e r e d w i t h the a c t u a l s l u r r y d e n s i t y , and could have a f f e c t e d the r e s u l t s . 6.1.5 C o f r e l a t i o n between Redox Couples arid Experimental Results This s e c t i o n c o n s i s t s of an attempt to c o r r e l a t e the experimental r e -s u l t s , at pH 5.5, w i t h the redox couples that are supposed to be re l e v a n t to the system. T a f e l behaviour i s assumed f o r a l l couples, w i t h constant (93) T a f e l slope (see Appendix 2 f o r the Butler-Volmer equation •;) . The ab-s c i s s a a x i s i s not to s c a l e . The i n i t i a l v alue of the exchange current d e n s i t y f o r the i n d i v i d u a l redox couples was a r b i t r a r i l y f i x e d . Figure 29 deals w i t h systems not i n v o l v i n g m i neral s l u r r i e s . F i g ure 30 i s an attempt to d e s c r i b e the i n t e r a c t i o n between p e n t l a n d i t e s l u r r i e s , xanthate and SO2. The model created seems to agree w i t h the r e s t p o t e n t i a l s that were measured. When only one anodic and one cathodic r e a c t i o n are s i g n i f i c a n t to the system under i n v e s t i g a t i o n , the r e s t p o t e n t i a l l i e s at the i n t e r -s e c t i o n of the cathodic curve f o r the anodic redox couple and the anodic curve f o r the cathodic redox couple. An example of t h i s s i t u a t i o n i s the r e s t p o t e n t i a l f o r SO2 s o l u t i o n , presented i n Figure 29. The r e s t poten-t i a l of 419 mV i s determined by the point at which the oxygen r e d u c t i o n curve i n t e r c e p t s the curve f o r o x i d a t i o n of hydrogen s u l p h i t e to d i t h i o -nate. When more redox couples are involved i n the determination of poten-t i a l , e q u i l i b r i u m occurs at the i n t e r s e c t i o n of the net anodic curve and the net cathodic curve. The system p e n t l a n d i t e s l u r r y - SO2 - KAmX, shown i n Figure 30, i l l u s t r a t e s t h i s s i t u a t i o n . The anodic curve f o l l o w s the o x i d a t i o n of p e n t l a n d i t e , from the redox p o t e n t i a l f o r the couple " p e n t l a n d i t e / o x i d a t i o n products" to the redox p o t e n t i a l f o r the X2/X couple. At t h i s p o t e n t i a l there i s a h o r i z o n t a l s h i f t towards l a r g e r F igure 29. Schematic p i c t u r e of the system S0 2 - KAmX i n terms of a c t i v a t i o n p o l a r i z a t i o n curves F igure 30. Schematic p i c t u r e o f the system pen t l and i t e - S02-KAmX i n terms o f a c t i v a t i o n p o l a r i z a t i o n curves - 79 -current d e n s i t i e s and, then, the curve f o l l o w s the o x i d a t i o n of xanthate i o n to dixanthogen. The cathodic curve f o l l o w s oxygen r e d u c t i o n at more anodic p o t e n t i a l s , s h i f t s to l a r g e r current d e n s i t i e s at the redox poten-2- -t i a l f o r S„0, /HSCL and then f o l l o w s d i t h i o n a t e r e d u c t i o n . The expect-z o J ed r e s t p o t e n t i a l of 55 mV i s at the i n t e r s e c t i o n of the net curves. A l i s t of the r e a c t i o n s that are l i k e l y to determine the experimen-t a l l y measured r e s t p o t e n t i a l s f o l l o w s : A. 0.1N KC1 s o l u t i o n s Anodic r e a c t i o n : R = 0 + + e (R-20) where R and 0 + r e f e r to unknown reduced and o x i d i z e d species Cathodic r e a c t i o n : Pt(0H)2.+ 2H + + 2e = Pt + 2H 20 (R-17) Er experimental = Eh^ = 581 mV B. KAmX s o l u t i o n s Anodic r e a c t i o n : 2X~ = X 2 + 2e (R-18) Cathodic r e a c t i o n : C>2 + 4H + + 4e = 2H 20 (R-12) Er experimental = Eh 2 = 53 mV C. S0 2 s o l u t i o n s 2- + Anodic r e a c t i o n : 2HS0„ = S o0, + 2H + 2e (R-19) 3 Z o Cathodic r e a c t i o n : 0 2 + 4H + + 4e = 2H 20 (R-12) Er experimental = Eh^ = 419 mV D. S0 2 - KAmX s o l u t i o n s Anodic r e a c t i o n : 2X~ = X 2 + 2e (R-18) Cathodic r e a c t i o n s : 0 2 + 4H + + 4e = 2H 20 (R-12) S o0, 2~ + 2H + + 2e = 2HS0~ (R-19) Z o j Er experimental = Eh^ = 103 mV - 80 -E. P e n t l a n d i t e s l u r r i e s Anodic r e a c t i o n : (Fe, Ni) S = 5 N i 2 + + 4 F e 2 + + 8S° + 18e (R-21) Cathodic r e a c t i o n : 0 2 + 4H + + 4 e = 2H 20 (R-12) Er experimental = Eh,- = 460 mV F. P e n t l a n d i t e s l u r r i e s - SO,, Anodic r e a c t i o n s : (Fe, N i ) g S g = 5 N i 2 + + 4 F e 2 + + 8S° + 18e (R-21) 2HS0~ = S O 2 " + 2H + + 2e (R-19) Cathodic r e a c t i o n : 0 2 + 4H + + 4e = 2H 20 (R-12) Er experimental = Eh^ = 285 mV G. P e n t l a n d i t e s l u r r i e s - KAmX Anodic r e a c t i o n s : (Fe, N i ) _ S Q = 5 N i 2 + + 4 F e 2 + + 8S° + 18e (R-21) y o 2X" = X 2 + 2e (R-18) Cathodic r e a c t i o n : 0 2 + 4H + + 4e = 2H 20 (R-12) Er expected •= Eh^ = 40 mV (expected p o t e n t i a l i f exhaustion of xanthate, due to ads o r p t i o n , had not occurred). Er experimental = Eh = 354 mV (at the minimum i n the p o t e n t i a l v e r -o sus time curve). H. P e n t l a n d i t e s l u r r i e s - S0 2 - KAmX Anodic r e a c t i o n s : (Fe, N i ) n S D = 5 N i 2 + + 4 F e 2 + + 8S° + 18e (R-21) y o 2X~ = X 2 + 2e (R-18) Cathodic r e a c t i o n s : 0 2 + 4H + + 4e = 2H 20 (R-12) S o 0 2 ~ + 2H + + 2e = 2 HS0~ (R-19) 2 6 3 Er expected = Eh Q = 55 mV y Er experimental = E h ^ = 168 mV In systems c o n t a i n i n g p e n t l a n d i t e and S0 2, elemental sulphur w i l l tend to d i s s o l v e i n S0 2 s o l u t i o n s , according to the r e a c t i o n s : - 81 -H S 0 3 + S° = H S 2 0 3 (pH <3) ( R - 2 2 ) H S 0 3 + S° = S 2 0 3 2 - + R + ( 3 < p R < ? ) ( R _ 2 3 ) S 0 3 2 " + S° = S 2 0 3 2 " (pH >7) ( R - 2 4 ) T h i s mechan ism l e a d s t o t he p o s s i b i l i t y o f an a d d i t i o n a l a n o d i c r e a c t i o n , i n c a s e s F and H: " ~ O I _1 2" ~T~ ( F e , N i ) _ S + 8HS0„ = 5 N i + 4Fe + 8 S „ 0 „ + 8H + 18e (R -25 ) y o 3 Z 3 T h i s method o f i n t e r p r e t a t i o n o f r e s u l t s i s o m i t t e d i n t h e c a s e o f t h e m i n e r a l s c h a l c o p y r i t e and p y r r h o t i t e f o r two r e a s o n s . The e m p h a s i s o f t h i s i n v e s t i g a t i o n i s on p e n t l a n d i t e , and a l s o , no m a j o r change i s e x p e c t e d i n t h e above p a t t e r n f o r t h e c h a l c o p y r i t e and p y r r h o t i t e s y s t e m s . 6 . 2 T e s t s w i t h M i n e r a l E l e c t r o d e s 6 . 2 . 1 P e n t l a n d i t e E l e c t r o d e A . R e s t p o t e n t i a l s The e f f e c t o f changes o f pH on t h e r e s t p o t e n t i a l o f t h e p e n t l a n d i t e e l e c t r o d e i s shown i n F i g u r e 3 1 . F o r a s y s t e m c o n s i s t i n g o f a 0 . 1 N KC1 s o l u t i o n t h e r e l a t i o n s h i p be tween p o t e n t i a l and pH i s g i v e n b y : Eh = - 3 7 . 2 pH + 608 ( E - 1 5 ) r 2 = 0 . 9 9 9 5 The p r e s e n c e o f S 0 2 c a u s e d a s h i f t o f p o t e n t i a l i n t h e n e g a t i v e d i r e c t i o n . The r e s u l t s f i t t h e e q u a t i o n : Eh = - 3 3 . 4 pH + 551 ( E - 1 6 ) r 2 = 0 . 9 4 8 8 R e s t p o t e n t i a l s , measured on a p l a t i n u m e l e c t r o d e , f o r p e n t l a n d i t e s l u r r y and p e n t l a n d i t e s l u r r y - S 0 2 s y s t e m s ( f r om F i g u r e 2 0 ) , were i n c l u d e d i n F i g u r e 3 1 . One p o i n t r e p r e s e n t i n g t h e p o t e n t i a l o f a p e n t l a n d i t e mV O 0.1 N KC1 s o l u t i o n (pen t l and i t e e l e c t r ode ) © S0 2 s o l u t i o n (pen t l and i t e e l e c t rode ) • pen t l and i t e s l u r r y (pen t l and i t e e l e c t rode ) 450 CD 0 \ Eh = -33.4 pH + 5 5 1 -r 2 = 0.9488 pen t l and i t e s l u r r y ^ " v ^ p l a t i n u m e l e c t r ode ) 350 CD > ^ pen t l and i t e s l u r r y - S 0 2 (p la t inum e l ec t rode) Eh = -37.2 pH + 608 r 2 = 0.9995 250 *~ 1 i : i i ^ i i i 4 5 6 7 8 9 pH F igure 31. Rest p o t en t i a l (on pen t l and i t e e l ec t rode) versus pH f o r 0.1 N KC1 and S0 2 s o l u t i o n s - 83 -s l u r r y measured w i t h a p e n t l a n d i t e e l e c t r o d e , i s a l s o featured. A d i f f e r e n c e i n behaviour between the platinum e l e c t r o d e being s t r u c k by mineral p a r t i c l e s and the r e s p e c t i v e mineral e l e c t r o d e i s evident. The f a c t that minerals from d i f f e r e n t sources were used as an elec t r o d e and i n the s l u r r y d i d not account f o r the d e v i a t i o n . The d i f f e r e n c e s reported i n Figure 31 were a l s o observed i n systems c o n t a i n -i n g the minerals c h a l c o p y r i t e and p y r r h o t i t e , i n which case samples from the same source were used i n both sets of experiments. A much l a r g e r surface area was one of the c h a r a c t e r i s t i c s that made the t e s t s w i t h mineral s l u r r i e s d i f f e r e n t from those w i t h mineral e l e c t r o d e s . A l s o , a platinum e l e c t r o d e being s t r u c k by p a r t i c l e s has been considered as equivalent to a mi n e r a l e l e c t r o d e , but t h i s statement r e q u i r e s f u r t h e r c o n f i r m a t i o n . A simple s e r i e s of* t e s t s was c a r r i e d out, i n which the r e s t p o t e n t i a l of 1% s l u r r i e s of p e n t l a n d i t e , chalco-p y r i t e and p y r r h o t i t e , i n 0.1N KC1 e l e c t r o l y t e , was measured w i t h both platinum and the r e s p e c t i v e mineral e l e c t r o d e s . The p o t e n t i a l on a platinum e l e c t r o d e was, i n a l l cases, approximately 120 mV p o s i t i v e w i t h respect to that measured on the mineral e l e c t r o d e . These r e s u l t s i n d i -cate e i t h e r poisoning of one of the e l e c t r o d e s , or a d i f f e r e n c e i n mechanism between the two systems. The magnetic s t i r r e r provided a very gentle a g i t a t i o n , j u s t enough to keep the p a r t i c l e s i n suspension. In a d d i t i o n , a very low pulp d e n s i t y was used. I t i s p o s s i b l e that the platinum e l e c t r o d e was not s u f f i c i e n t l y bombarded by the p a r t i c l e s , and the r e f o r e i t d i d not behave as the mineral e l e c t r o d e . P o t e n t i a l versus time p l o t s f o r xanthate s o l u t i o n s , i n the presence and absence of SO^, are presented i n Figure 32. In both cases there was an i n i t i a l drop of p o t e n t i a l , which, then, s t a b i l i z e d at a constant Eh mV F igure 32. Rest p o t en t i a l (on pen t l and i t e e l e c t rode) versus time f o r KAmX and S0 2 - KAmX so l u t i o n s - 85 -value. This p o t e n t i a l was much higher than the e q u i l i b r i u m p o t e n t i a l f o r X 2/X , as measured w i t h a platinum e l e c t r o d e . I t i s not c l e a r yet i f t h i s e f f e c t i s due to the mineral e l e c t r o d e i t s e l f , or to the f a c t that the e l e c t r o d e i s l i k e l y coated w i t h a xanthate species (probably dixanthogen). B. P o l a r i z a t i o n curves Anodic and cathodic p o l a r i z a t i o n curves, as measured w i t h a pent-l a n d i t e working e l e c t r o d e , are presented i n the next four f i g u r e s , f o r the f o l l o w i n g systems: ( i ) 0.1N KC1 s o l u t i o n , i n Figure 33, ( i i ) KAmX s o l u t i o n , i n Figure 34, ( i i i ) SC^ s o l u t i o n , i n Figure 35, ( i v ) S0 2 - KAmX s o l u t i o n , i n Figure 36. In Figures 33 through 44 two symbols were adopted: ( i ) Y = l o g [I/A] = loga r i t h m to base 10 of the absolute value of the a p p l i e d current d e n s i t y , 2 ( i i ) K = p o t e n t i a l i n t e r c e p t at current d e n s i t y = 1 yA/cm (no p h y s i c a l meaning i s a t t r i b u t e d to K). I t i s w e l l understood that l i n e a r p o r t i o n s shorter than one decade, i n a p p l i e d current d e n s i t y , i n the p o t e n t i a l versus l o g current d e n s i t y curve, do not n e c e s s a r i l y c h a r a c t e r i z e T a f e l behaviour. Nevertheless there i s a p o s s i b i l i t y that these p o i n t s do represent a region under a c t i v a t i o n c o n t r o l , and t h i s r e g i o n does not extend any f u r t h e r due to a change i n mechanism. A l e a s t square f i t was a p p l i e d to a l l regions that seemed to be reasonably l i n e a r . Eh) mV| G o ° o 700 500 •100 Er 3 0 0 1 — °° °o ioo|— J I I I I L o o 0 Eh = 185 Y+ K Eh = 274 Y + K • o 0 o Eh = -168 Y+K Y = log |I/A 2 5 10 20 50 100 200 500 |I/A| (uA/cm 2) F igure 33. P o l a r i z a t i o n curves of pen t l and i t e e l ec t rode i n 0.1N KC1 s o l u t i o n Eh f mV 700h S00[ 3001 e Er Eh = 152 Y+K Eh = 661 Y+K 100L Eh = -140 Y+K •100r 10 20 50 100 200 500 | I /A|(yA/cm 2 ) F i gu re 34. P o l a r i z a t i o n curves of pen t l and i t e e l e c t r ode i n KAmX so l u t i o n Eh i mV 700h— 500 Er 300 100 -100h" J L Eh = 108 Y+K Eh = 248 Y+K Eh = -116 Y+K 10 20 50 100 200 500 | I/A| (uA/cm 2) F i gu re 35. P o l a r i z a t i o n curves of pen t l and i t e e l e c t rode i n S0 2 s o l u t i o n Eh, mV 700 0 © 0 ' Eh = 164 Y+K 500 Eh = 596 Y+K 300L_ 100 Er Eh = -158 Y+K •ioor~ J_ 2 5 10 20 50 100 200 500 | I/A | (jjA/cm 2) F igure 36. P o l a r i z a t i o n curves of pen t l and i t e e l e c t rode i n S0 2 - KAmX s o l u t i o n - 90 -B l . Anodic p o l a r i z a t i o n A l l curves present two l i n e a r p o r t i o n s . The f i r s t r egion s t a r t s at p o t e n t i a l s ca. 100 mV above the r e s t p o t e n t i a l . The second l i n e a r r e g i o n s t a r t s ca. Eh = 750 mV and extends to the highest p o t e n t i a l used i n the present i n v e s t i g a t i o n . Between p o t e n t i a l s 650 and 750 mV (lower i n Figure 36) there i s an i n f l e c t i o n that seems to be associated w i t h a change i n the o x i d a t i o n mechanism. Further o x i d a t i o n of elemental sulphur i s one of the r e a c t i o n s that could a f f e c t the anodic curve. The p o l a r i z a t i o n curves do not i n d i c a t e the o x i d a t i o n of xanthate i o n to dixanthogen as being part of the anodic process. This r e a c t i o n probably occurred p r i o r to the measurement of the curve. This would confirm the thermodynamic p r e d i c t i o n that dixanthogen was the hydrophobic species i n t h i s system. I t might be p o s s i b l e to i d e n t i f y dixanthogen adsorbed on the surface of sulphide minerals by means of i n f r a r e d s p e c t r o -scopy (attenuated t o t a l r e f l e c t a n c e ) . The e f f e c t of xanthate seems to have been the formation of a pro-t e c t i v e or i n h i b i t o r - l i k e f i l m of dixanthogen on the e l e c t r o d e surface. This f i l m increased the r e s i s t a n c e to anodic d i s s o l u t i o n . The anodic mechanism would s t i l l have been c o n t r o l l e d by the o x i d a t i o n of the m i n e r a l , but i t s r a t e was decreased due to the presence of the f i l m . The decrease i n d i s s o l u t i o n r a t e was l a r g e r i n the absence of S02» than i n i t s presence. This e f f e c t could be due to e i t h e r a change i n the extent of surface coverage or a change i n the s t r e n g t h of the f i l m -surface bond. Another a c t i o n of SO2 was to generate a second i n f l e c t i o n (not as pronounced, and at a lower p o t e n t i a l than the f i r s t ) on the p o l a r i z a t i o n curve. The mechanism a s s o c i a t e d w i t h i t i s unexplained i n the l i g h t of the present r e s u l t s . B2. Cathodic P o l a r i z a t i o n A l l four curves e x h i b i t T a f e l behaviour f o r about one decade, followed by a c o n c e n t r a t i o n p o l a r i z a t i o n e f f e c t . B i e g l e r et a l ^ ^ concluded that the mechanism of oxygen r e d u c t i o n on a p y r i t e e l e c t r o d e i n v o l v e s a rate-determining f i r s t step: 0 2 + e = Oz (R-14) Assuming a symmetry f a c t o r B of 0.5 i n the Butler-Volmer equation, t h i s mechanism leads to a T a f e l slope of 120 mV/decade. T a f e l slopes ranging from 168 to 116 mV/decade were measured i n the present work. I f these slopes are as s o c i a t e d w i t h 8 values ranging from 0.36 to 0.52, i t can be stated that these r e s u l t s are c o n s i s t e n t w i t h the above mechanism. The existence of a l i m i t i n g current d e n s i t y a l s o favours the hypothesis ( 94') that the cathodic r e a c t i o n was oxygen r e d u c t i o n . Fontana and Greene suggested that i n a i r - s a t u r a t e d non-agitated s o l u t i o n s , the l i m i t i n g d i f f u s i o n current f o r oxygen r e d u c t i o n i s approximately 100 uA/cm2. The present r e s u l t s are i n good agreement w i t h t h e i r f i n d i n g . Sulphur d i o x i d e seems to have s h i f t e d the l i m i t i n g c urrent d e n s i t y to a l a r g e r v a l u e . The e f f e c t was not very pronounced. A p o s s i b l e i n f l u e n c e 2 — of SO2 on the cathodic process i s by r e a c t i o n w i t h O2, l e a d i n g to S2O6 . D i t h i o n a t e i s e l e c t r o c h e m i c a l l y a c t i v e and i t s r e d u c t i o n may be f a s t e r than oxygen r e d u c t i o n because of p o t e n t i a l l y higher c o n c e n t r a t i o n s . 6.2.2 C h a l c o p y r i t e E l e c t r o d e A. Rest P o t e n t i a l R e s t . p o t e n t i a l s , measured w i t h a c h a l c o p y r i t e working e l e c t r o d e , immersed i n d i f f e r e n t s o l u t i o n s , at pH = 5.5, are reported i n Table XI. - 92 -TABLE XI Rest p o t e n t i a l s measured w i t h c h a l c o p y r i t e e l e c t r o d e S o l u t i o n Eh (mV) 0.1N KC1 398 372 KAmX 169 S0 2 - KAmX 134 These r e s u l t s r e v e a l the same trend as those f o r the p e n t l a n d i t e e l e c t r o d e . The o x i d a t i o n of xanthate to dixanthogen i s thermodynamically favoured. In the presence of SO^ and xanthate, the c h a l c o p y r i t e e l e c t r o d e seems to be c a t h o d i c a l l y p o l a r i z e d to a greater extent than the p e n t l a n -d i t e e l e c t r o d e . B. P o l a r i z a t i o n curves Anodic and cathodic p o l a r i z a t i o n curves, as measured w i t h a chalco-p y r i t e working e l e c t r o d e , are presented i n the next four f i g u r e s , f o r the f o l l o w i n g systems: ( i ) 0.1N KC1 s o l u t i o n , i n Figure 37, ( i i ) KAmX s o l u t i o n , i n Figure 38, ( i i i ) SC>2 s o l u t i o n , i n Figure 39, ( i v ) S0 2 _ KAmX s o l u t i o n , i n Fi g u r e 40. B l . Anodic p o l a r i z a t i o n A l l curves show two l i n e a r p o r t i o n s , separated by an i n f l e c t i o n , that r e f l e c t s a change i n the o x i d a t i o n mechanism. The very high i n i t i a l slope of the systems i n v o l v i n g xanthate suggests that the e l e c t r o d e was Eh I l o * mV 0o 7 0 0 L _ „ G ° o°° Eh = 251 Y+K © soor- 0 0 ° G o ° ° Er 300 » Q J | | | | | | _ I 2 5 TO 215 515 rUD 21515 515 o ° 0 Eh = 141 Y+K 1001— ° ° 0 O °© 0 Eh = -237 Y+K X = " 1 0 ° h \ ' % Eh = -403 Y+K S015 |I/A| (uA/cm 2) F igure 37'.' P o l a r i z a t i o n curves of c h a l c opy r i t e e l e c t rode i n 0.1N KC1 s o l u t i o n Eh mV 700 500 300 © Er 100 •100 _L JL V ± Eh = 152 Y+K Eh = 1102 Y+K Eh = -194 Y+K Eh = -342 Y+K 2 5 10 20 50 100 200 500 | I /A|(yA/cm 2 ) F igure 38. P o l a r i z a t i o n curves of c h a l c opy r i t e e l ec t rode i n KAmX s o l u t i o n Eh mV 700 .0 o , 0 9 500 o o Er Eh = 224 Y+K Eh = 203 Y+K 300 Q 100 0 O V •100 Eh = -206 Y+K Eh = -434 Y+K J L J L 5 10 20 50 100 200 500 | I /A|(uA/cm 2 ) F igure 39. P o l a r i z a t i o n curves of c ha l c opy r i t e e l e c t rode i n KAmX s o l u t i o n F igure 40. P o l a r i z a t i o n curves o f c h a l c o py r i t e e l ec t rode i n S0 2 - KAmX s o l u t i o n - 97 -coated w i t h a f i l m (probably dixanthogen). The p r o t e c t i v e character of the f i l m was more pronounced i n the presence of SO^. This f a c t seems to be as s o c i a t e d w i t h the reducing a c t i o n of SO^ towards o x i d i z e d species on the surface of the e l e c t r o d e . The removal of some of these species i s l i k e l y to f a c i l i t a t e the adsorption of c o l l e c t o r . In the t e s t w i t h SO^ s o l u t i o n there was a l i m i t i n g current d e n s i t y at low current that i s yet to be explained. B2. Cathodic p o l a r i z a t i o n A l l curves presented a l i m i t i n g current d e n s i t y at very low current 2 ( l e s s than 10 yA/cm ), followed by two l i n e a r regions. The slopes were, i n a l l but one case, much higher than the expected T a f e l slope f o r oxygen red u c t i o n . There was no i n d i c a t i o n of a l i m i t i n g current d e n s i t y around 2 100 yA/cm . These f a c t s suggest that the cathodic mechanism c o n s i s t e d of the r e d u c t i o n of o x i d i z e d species on the surface of the e l e c t r o d e , i n s t e a d of oxygen r e d u c t i o n . This assumption i s supported by the f a c t s discussed above, under anodic p o l a r i z a t i o n . On the other hand, the presence of SO2 does not seem to have i n t e r f e r e d w i t h the aspect of the cathodic curves. The i n d i c a t i o n i s t h a t , even under these circumstances, enough o x i d i z e d species were l e f t on the el e c t r o d e surface to prevent the cathodic process from being under oxygen r e d u c t i o n c o n t r o l . 6.2.3 P y r r h o t i t e e l e c t r o d e A. Rest p o t e n t i a l Rest p o t e n t i a l s , measured w i t h a n i c k e l i f e r o u s p y r r h o t i t e working e l e c t r o d e , immersed i n d i f f e r e n t s o l u t i o n s , at pH = 5.5, are reported i n Table X I I . The r e s t p o t e n t i a l , measured i n a 0.1N KC1 s o l u t i o n , of a n i c k e l - f r e e p y r r h o t i t e e l e c t r o d e , i s included i n the t a b l e . - 98 -TABLE X I I Rest p o t e n t i a l s measured w i t h p y r r h o t i t e e l e c t r o d e s S o l u t i o n Eh (mV) 0.1N KC1 376 S0 2 340 KAmX 264 S0 2 - KAmX 267 NF py* i n 0.1 NKC1 344 *NF py = n i c k e l - f r e e p y r r h o t i t e . These r e s u l t s are s i m i l a r to those f o r p e n t l a n d i t e and c h a l c o p y r i t e e l e c t r o d e s . They r e v e a l that the need of an a c t i v a t o r f o r the f l o t a t i o n of p y r r h o t i t e i n i n d u s t r i a l p r a c t i c e i s not due to the thermodynamic con-d i t i o n s of the system being unfavourable f o r the presence of dixanthogen. The r e s t p o t e n t i a l i n a l l t e s t s was p o s i t i v e to the e q u i l i b r i u m p o t e n t i a l f o r the X 2/X redox couple. Microprobe a n a l y s i s proved that the n i c k e l i f e r o u s p y r r h o t i t e e l e c -trode c o n s i s t e d of very f i n e l y disseminated p e n t l a n d i t e i n a p y r r h o t i t e matrix. The r e s t p o t e n t i a l of t h i s e l e c t r o d e , i n 0.1N KC1 s o l u t i o n , d i d not d i f f e r d r a s t i c a l l y from that of a n i c k e l - f r e e p y r r h o t i t e e l e c t r o d e . B. P o l a r i z a t i o n curves Anodic and cathodic p o l a r i z a t i o n curves, as measured w i t h a pyrrho-t i t e working e l e c t r o d e , are presented i n the next four f i g u r e s , f o r the f o l l o w i n g systems: - 99 -( i ) 0.1N KC1 s o l u t i o n , i n Figure 41, ( i i ) KAmX s o l u t i o n , i n Figure 42, ( i i i ) SC>2 s o l u t i o n , i n Figure 43, ( i v ) SC^ - KAmX s o l u t i o n , i n Figure 44. B l . Anodic p o l a r i z a t i o n A l l curves present three l i n e a r r e g i o n s , the slope of each one decreasing w i t h i n c r e a s i n g p o t e n t i a l . The p y r r h o t i t e systems c o n t a i n i n g KAmX e x h i b i t smaller slopes than those obtained i n the t e s t s w i t h pent-l a n d i t e and c h a l c o p y r i t e e l e c t r o d e s . This f a c t i n d i c a t e s that the xanthate species f i l m was weaker on the p y r r h o t i t e e l e c t r o d e s than i t was on the other two. The presence of SG^ d i d not seeem to i n t e r f e r e w i t h the s t a b i l i t y of the f i l m . B2. Cathodic p o l a r i z a t i o n A l l curves d i s p l a y . a T a f e l behaviour r e g i o n f o r approximately one decade, followed by a l i m i t i n g c u r r e n t d e n s i t y . The l i m i t i n g c urrent d e n s i t y i s c o n s i s t e n t w i t h that f o r oxygen re d u c t i o n . I f a symmetry f a c t o r 3 as low as 0.27 i s acceptable, the experimental T a f e l slopes are i n agreement w i t h that f o r oxygen re d u c t i o n . 6.3 M i c r o f l o t a t i o n Tests 6.3.1 Tests w i t h P e n t l a n d i t e R e s u l t s of small s c a l e f l o t a t i o n t e s t s , using p e n t l a n d i t e , i n a modified Smith-Partridge c e l l and a modified Hallimond tube, are present-ed i n Table X I I I . These t e s t s were c a r r i e d out at pH 5.5. The concen--4 t r a t i o n of c o l l e c t o r was 0.74 x 10 M. Eh mV Q O O o o ° Eh = 114 Y+K 700 0 G O O G ' , G G 500 Er 0 o G O G O © O 300 ° 3 O 100r O Or 'Or. O Or 'O, Jo, O, 'O, •100k X J I 1 L Eh = 199 Y+K Eh = 328 Y+K Eh = -226 Y+K 5 T5 20 : 50 100 200 500 I I/A I(yA/cm 2) F igure 41. P o l a r i z a t i o n curves of p y r r h o t i t e e l ec t rode i n 0.1N KC1 s o l u t i o n - 101 -Eh mV o 0 o © w Eh = 127 Y+K 700 Eh = 238 Y+K 500 300 G Er o Eh = 256 Y+K -TOOL Eh = -152 Y+K 1001 J L 10 20 50 100 200 500 |I/A| (yA/cm 2) F igure 43 . P o l a r i z a t i o n curves of p y r r h o t i t e e l e c t rode in S0 2 s o l u t i o n Eh mV 700 500 300 Er 0 -e 144 Y+K Eh = 193 Y+K Eh = 504 Y+K -100h— 100 Eh = -194 Y+K J L 10 20 50 100 200 500 |I/A| (yA/cm 2) F igure 44. P o l a r i z a t i o n curves of p y r r h o t i t e e l ec t rode i n S0 2 - KAmX s o l u t i o n - 104 -TABLE X I I I Results of small s c a l e f l o t a t i o n t e s t s w i t h p e n t l a n d i t e Conditions F l o t a t i o n Time(min) %F - %NF SD ; No. of t e s t s Smith P a r t r i d g e c e l l KAmX 3 82 18 1.80 4 SO -KAmX 2; 3 70 30 3.91 4 KAmX 1 69 31 5.07 4 S02-KAmX 1 61 39 5.10 4 Hallimond tube KAmX 3 91 9 1.22 4 S02-KAmX 3 85 15 2.17 4 KAmX 1 74 26 5.92 4 S02-KAmX 1 53 47 5.07 4 * %F = % f l o a t e d (mean v a l u e ) , %NF = standard d e v i a t i o n . % not f l o a t e d (mean v a l u e ) , SD = These r e s u l t s i n d i c a t e c l e a r l y that S0 2 had a d e l e t e r i o u s e f f e c t on the f l o a t a b i l i t y of p e n t l a n d i t e w i t h KAmX. Thus these data confirmed the p r e d i c t i o n s from the e l e c t r o c h e m i c a l testwdrk. Neither of the minerals under i n v e s t i g a t i o n showed any si g n of n a t u r a l f l o a t a b i l i t y . This means t h a t , i f elemental sulphur were present on the - 105 -surface, i t d i d not impart the necessary hydrophobicity r e q u i r e d f o r f l o -t a t i o n under the c o n d i t i o n s t e s t e d . 6.3.2 Tests w i t h c h a l c o p y r i t e Tests w i t h the modified Smith-Partridge c e l l , i n the presence or absence of S O 2 , revealed that 1 minute f l o t a t i o n time was enough f o r a l l the min e r a l p a r t i c l e s to f l o a t . A q u a l i t a t i v e observation was made that f l o t a t i o n was f a s t e r i n the presence of S0 2. One hundred percent f l o t a t i o n was a l s o reported f o r the 3 minute t e s t s i n the modified Hallimond tube. Results f o r 1 minute t e s t s i n t h i s apparatus are presented i n Table XIV. TABLE XIV Results o f s m a l l s c a l e f l o t a t i o n t e s t s w i t h c h a l c o p y r i t e F l o t a t i o n Conditions Time (min) %F %NF SD No. of Tests Hallimond tube KAmX 1 61 39 1.09 4 S02-KAmX 1 84 16 4.74 4 The above r e s u l t s show t h a t , according to the p r e d i c t i o n from the ele c t r o c h e m i c a l experiments, the f l o a t a b i l i t y of c h a l c o p y r i t e w i t h KAmX was enhanced by previous c o n d i t i o n i n g of the mineral w i t h S O 2 . 6.3.3 Tests w i t h P y r r h o t i t e The magnetic s t i r r e r a g i t a t i o n i n the modified Hallimond tube was not compatible w i t h the ferromagnetic character of p y r r h o t i t e , thus only the Smith-Partridge c e l l was used. - 106 -Only n e g l i g i b l e amounts of the mineral could be f l o a t e d i n 1 minute t e s t s i n the modified Smith-Partridge c e l l . R e s u lts f o r 3 minute t e s t s are presented i n Table XV. TABLE XV Results of sm a l l s c a l e f l o t a t i o n t e s t s w i t h p y r r h o t i t e Conditions F l o t a t i o n %F %NF SD No. of t e s t s Time (min). Smith-Partridge c e l l KAmX 3 18 82 5.24 4 SO -KAmX 3 11 89 3.64 4 These r e s u l t s i n d i c a t e that SO^ acted as a depressant on the f l o t a t i o n of p y r r h o t i t e w i t h KAmX. The amount f l o a t e d i n e i t h e r case was so small that no major s i g n i f i c a n c e could be a t t r i b u t e d to the depressing a c t i o n . 6.4 D i s c u s s i o n of the E f f e c t of SO^ on the Hydrophobicity L e v e l In the present i n v e s t i g a t i o n SO^ was the only modifying agent employed, and i t was always i n j e c t e d before the a d d i t i o n of -xanthate. Results of f l o t a t i o n t e s t s w i t h p e n t l a n d i t e i n d i c a t e that the presence of SO^ caused a decrease i n the r a t e of f l o t a t i o n . A p o s s i b l e e x p l a n a t i o n f o r t h i s e f f e c t could l i e i n the a c t i o n of SO^ towards elemental sulphur at the surface.of the p a r t i c l e s . In the absence of SO^ the f i l m of c o l l e c t o r (probably dixanthogen) and elemental sulphur c o n t r i b u t e to the o v e r a l l hydro-p h o b i c i t y . In the presence o f . S 0 2 , elemental sulphur r e a c t s to thdosxilphate;, the surface moves to a lower p o s i t i o n i n the hydr o p h o b i c i t y s c a l e . - 107 -The a d d i t i o n of SO^ enhanced the f l o a t a b i l i t y of c h a l c o p y r i t e w i t h xanthate. The surface of t h i s m i neral i s l i k e l y to be coated w i t h one or more l a y e r s of h y d r o p h i l i c compounds, such as hydroxides. Sulphur d i o -x i d e would reduce these species and decrease the n a t u r a l l e v e l of hydro-p h i l i c i t y at the surface. Another p o s s i b i l i t y , that r e q u i r e s f u r t h e r c o n f i r m a t i o n , i s that the r e a c t i o n product between the surface and c o l l e c t o r confers a higher l e v e l of hydrophobicity i f the surface i s at a more reduced s t a t e . Results of f l o t a t i o n t e s t s w i t h p y r r h o t i t e r e v e a l that an a c t i v a t o r i s r e q u i r e d i n order to achieve h i g h f l o t a t i o n r a t e s . The s l i g h t decrease i n f l o a t a b i l i t y due to S0^ could be a t t r i b u t e d to the same reasons pre-sented i n the d i s c u s s i o n f o r p e n t l a n d i t e . One aspect, that does not a r i s e from the present set of r e s u l t s , but should be regarded as a f e a s i b l e mechanism of a c t i o n of SO^j i s the p h y s i c a l adsorption of SO^ molecules to the surface. The review on S0^ water chemistry showed that approximately 90% of S0 2 i n s o l u t i o n i s con-s t i t u t e d of molecular or s o l v a t e d species. Sulphur d i o x i d e , being a p o l a r molecule, should decrease the degree of hydrophobicity of the minerals. -.108 -CHAPTER 7 CONCLUSIONS 1. The e f f e c t of SO^ on 0 . 1 N KC1 s o l u t i o n s and 1% wt s l u r r i e s of pent-l a n d i t e , c h a l c o p y r i t e and p y r r h o t i t e was to s h i f t the r e s t p o t e n t i a l of the systems i n the negative d i r e c t i o n , i . e . i t acted as a reducing agent. 2. For a l l systems i n v e s t i g a t e d (SO2 s o l u t i o n , KAmX s o l u t i o n , pentland-i t e , c h a l c o p y r i t e or p y r r h o t i t e s l u r r i e s and combinations of these) the measured r e s t p o t e n t i a l was always p o s i t i v e w i t h respect to that f o r the ^ / X redox couple. This f a c t i n d i c a t e s that dixanthogen should be the hydrophobic e n t i t y r e s p o n s i b l e f o r f l o t a t i o n of these three minerals. 3 . The curve f o r the v a r i a t i o n of r e s t p o t e n t i a l on a platinum e l e c t r o d e versus time elapsed a f t e r xanthate a d d i t i o n , f o r s l u r r i e s of the three minerals, i n the presence and absence of S02> shows a minimum. The e f f e c t of SO2 was to s h i f t the minimum towards longer times i n systems c o n t a i n i n g p e n t l a n d i t e , and towards sh o r t e r times i n systems c o n t a i n i n g c h a l c o p y r i t e . The presence of SO2 d i d not change the p o s i t i o n of the minimum i n p y r r h o t i t e systems. UV a n a l y s i s of the f i l t r a t e from s l u r r i e s conditioned w i t h KAmX revealed that the presence of SO2 increased the amount of non-adsorbed xanthate i n s o l u t i o n i n the p e n t l a n d i t e systems and decreased i t i n the chalcopy-r i t e systems. I t i s suggested that the minimum i s a s s o c i a t e d w i t h the adsorption of xanthate on the surface of mineral p a r t i c l e s . - 109 -The anodic p o l a r i z a t i o n curves f o r p e n t l a n d i t e , c h a l c o p y r i t e and p y r r h o t i t e e l e c t r o d e s ' a r e determined by the o x i d a t i o n of the miner a l . The a c t i o n of KAmX i s towards the formation of an i n h i b i t o r - l i k e f i l m on the surface of the e l e c t r o d e . This e f f e c t was stronger f o r c h a l c o p y r i t e (enhanced by SO^) than f o r p e n t l a n d i t e (weakened by SO^) and f o r p y r r h o t i t e (unaffected by SC^)• The cathodic p o l a r i z a t i o n curves f o r the p e n t l a n d i t e a n d p y r r h o t i t e e l e c t r o d e s show a one-electron t r a n s f e r T a f e l behaviour, followed by a concentration p o l a r i z a t i o n e f f e c t s t a r t i n g at current d e n s i t i e s 2 j u s t l a r g e r than 100 uA/cm . I t i s suggested that the cathodic mechanism on these two electro d e s was oxygen r e d u c t i o n . The cathodic p o l a r i z a t i o n curves f o r the c h a l c o p y r i t e e l e c t r o d e present two l i n e a r r e g i o n s , that seem to be associated w i t h the r e d u c t i o n of ox i d i z e d species on the surface of the el e c t r o d e . Small s c a l e f l o t a t i o n t e s t s , w i t h KAmX used as a c o l l e c t o r , revealed very good f l o a t a b i l i t y of c h a l c o p y r i t e (enhanced by SO2); good f l o a t -a b i l i t y of p e n t l a n d i t e (impaired by SO^); and very poor f l o a t a b i l i t y of p y r r h o t i t e (impaired by S0„). - 110 -CHAPTER 8 RECOMMENDATIONS FOR FUTURE WORK A b e t t e r understanding of SO^ water chemistry and the i n t e r a c t i o n between SQ^ and the mineral p a r t i c l e s i s d e s i r a b l e . E l e c t r o c h e m i c a l techniques such as r a p i d g a l v a n o s t a t i c and c y c l i c voltammetry should shed some l i g h t on the mechanism of xanthate i o n o x i d a t i o n and adsorption. A n a l y t i c a l techniques that deal s p e c i f i c a l l y w i t h surfaces should provide u s e f u l i n f o r m a t i o n on the surface compounds i n the presence of SO^ and/or xanthate. S p e c i f i c a l l y , i n f r a r e d spectroscopy (attenuated t o t a l r e f l e c t a n c e ) might be an adequate technique f o r i d e n t i f i c a t i o n of dixanthogen or metal xanthate on the surface of e i t h e r sulphide minerals or platinum. The i n t e r a c t i o n between SO2, xanthate and a c t i v a t i n g agents, such as copper sulphate, should be i n v e s t i g a t e d , s p e c i a l l y i n r e l a t i o n to p y r r h o t i t e . D i f f e r e n t sequences of a d d i t i o n of these reagents should c o n t r i b u t e to the understanding of t h e i r e f f e c t i v e a c t i o n . - I l l -REFERENCES 1. ANDREWS, P.W., "The Canadian m i n e r a l i n d u s t r y : review and outlook", Canadian Mining J o u r n a l , 100, no. 2, Feb. 1979, pp.16-30. 2. BOLDT, J r . J.R., "The winning of n i c k e l " , Longmans Canada L i m i t e d , Toronto, 196 7. 3. "The I n t e r n a t i o n a l N i c k e l Company of Canada, L i m i t e d . Manitoba D i v i s i o n " , M i n e r a l I n d u s t r i e s i n Western Canada, The Tenth Commonwealth Mining and M e t a l l u r g i c a l Congress, The Canadian I n s t i t u t e of Mining and M e t a l l u r g y , 1974, pp.1-28. 4. A u s t r a l i a n Patent 11253, i n Froth F l o t a t i o n 50th Anniversary Volume, AIME, New York, 1962, p.44. 5. FINKELSTEIN, N.P and ALLISON, S.A., "The chemistry of a c t i v a t i o n , d e a c t i v a t i o n and depression i n the f l o t a t i o n of z i n c s u l p h i d e : a review", F l o t a t i o n A.M. Gaudin Memorial Volume, volume 1, AIME, New York, 1976, pp.414-457. 6. LEWIS, F.M. and MORRIS, T.M., "Operating data from a sulphide f l o t a t i o n p l a n t , the London M i l l " , F r o t h F l o t a t i o n 50th  Anniversary Volume, AIME, New York, 1962, pp.455-481. 7. DAVEY, J.M. and SLAUGHTER, P.J., "Changes i n the l e a d - z i n c f l o t a t i o n p r a c t i c e a t Mount I s a Mines L i m i t e d " , AIME World Symposium  on Mining and M e t a l l u r g y of Lead and Zi n c , volume 1, AIME, New York,- 1970, pp. 401-427. 8. NEUMANN, G.W. and SCHNARR, J.R., "Concentrator o p e r a t i o n at Brunswick Mining and Smelting Corporation, L i m i t e d -No. 12 mine", AIME  World Symposium on Mining and M e t a l l u r g y of Lead and Zin c " , volume 1, AIME, New York, 1970, pp.500-525. 9. MATHEWS, F.W. and RAICEVIC, D., "Sulphur d i o x i d e as a replacement f o r sodium s u l p h i t e i n sulphide f l o t a t i o n " , CIM B u l l e t i n , 55, no. 600, 1962, pp.256-258. 10. MANSER, R.M. and ANDREWS, P.R.A., "The use of a new m o d i f i e r , Kr6D i n d i f f e r e n t i a l sulphide f l o t a t i o n " , I n t e r n a t i o n a l J o u r n a l of  M i n e r a l Processing, _2, 1975, pp.207-218. 11. SCHRANZ, H. et a l . , "The s e l e c t i v e f l o t a t i o n of copper p y r i t e s and s p h a l e r i t e w i t h sulphur d i o x i d e " , Bergbauwissen, 1, 1954, i n IMM A b s t r a c t s , 5_, no. 1, Oct-Nov. 1954, pp.32. 12. KOSHERBAEV, K.T. and S0K0L0V, M.A., "The e f f e c t s of S0 2 on the f l o t a t i o n of sulphide m i n e r a l s " , Vestnik Akademii Nauk  Kazackstanskoj SSR, 21, no. 3, 1965, pp..66-71. - 112 -13. SHIMOIIZAKA, J . et a l . , "Depression of galena f l o t a t i o n by s u l p h i t e or chromate i o n " , F l o t a t i o n A.M. Gaudin.Memorial Volume, volume 1, AIME, New York, 1976, pp.393-413. 14. ARAUCO, F.H.C. et a l . , "The use of SO as a f l o t a t i o n reagent", Avances en F l o t a c i o n , volume 3, Universidad de Concepcion, Concepcion, 1977, pp.87-110. 15. ELTHAM, J.A. and T1LYARD, P.A., "An approach to the f l o t a t i o n of Western A u s t r a l i a n n i c k e l , ores", The A u s t r a l a s i a n IMM, Western A u s t r a l i a Conference, 1973. 16. CLARIDGE, P.G. and TENBERGEN, R.A., "Pipe ore processing developments i n the Thompson M i l l " , Proceedings of the 7th Annual Meeting of  CMP, Ottawa, 1975, pp.269-299. 17. McLACHLAN, C.G., "The m i l l i n g of copper, c o p p e r - n i c k e l , copper-zinc and z i n c ores",. The m i l l i n g of Canadian ores, Toronto, 1957, pp.204-205. 18. POLING, G.W., p r i v a t e communication. 19. McLACHLAN, C.G., "The m i l l i n g of copper, c o p p e r - n i c k e l , copper-zinc and z i n c ores", The m i l l i n g of Canadian ores, Toronto, 1957, pp.265-266. 20. FINKELSTEIN, N.P. and ALLISON, S.A., "A fundamental i n v e s t i g a t i o n i n t o the depression of copper-activated s p h a l e r i t e " , N a t i o n a l  I n s t i t u t e f o r M e t a l l u r g y . Report n. 1953,,Randburg, 1978. 21. FINKELSTEIN, N.P. et a l . , "Some thermodynamic aspects of systems r e l e v a n t to the f l o t a t i o n of s p h a l e r i t e " , N a t i o n a l I n s t i t u t e f o r  M e t a l l u r g y . Report no. 1785, Johannesburg, 1976. 22. FINKELSTEIN, N.P. et a l . , "A p r e l i m i n a r y i n v e s t i g a t i o n i n t o the mech-anism of depression i n the f l o t a t i o n of sulphide minerals at the P r i e s k a copper mine", N a t i o n a l I n s t i t u t e , f o r M e t a l l u r g y . Report  no. 1721, Johannesburg, 1975. 23. FINKELSTEIN, N.P. et a l . , " D e a c t i v a t i o n of copper-activated s p h a l e r i t e w i t h cyanide", N a t i o n a l I n s t i t u t e f o r M e t a l l u r g y . Report no.  1613, Johannesburg, 1974. 24. SCHROETER, L.C., "Sulphur d i o x i d e " , Pergamon Press, Oxford, 1966. 25. DUNCAN, J.R. and SPEDDING, D.J., " I n i t i a l r e a c t i o n s of SO a f t e r a dsorption on to metals", C o r r o s i o n Science, 13, 19/3, pp.881-889. 26. LYONS, D. and NICKLESS, G., "Inorganic sulphur c h e m i s t r y " , E l s e v i e r , Amsterdam, 1968. 27. FALK, M. and GUIGUERE, P.A., "On the nature of sulphurous a c i d " , Canadian J o u r n a l of Chemistry, 36, 1958, pp.1121-1125. - 113 -28. CAMPBELL, W.B. and MAASS, 0., " E q u i l i b r i a i n sulphur d i o x i d e s o l u t i o n s " , Canadian J o u r n a l of Research. 2, 1930, pp.42-64. 29. LYNN, S. et a l . , "Absorption s t u d i e s i n the l i g h t of the p e n e t r a t i o n theory", Chemical Engineering Science, 4_,. A p r i l 1955, pp.49-57., 30. JONES, L.H. and McLAREN, E., " I n f r a r e d absorption s p e c t r a of S 0 2 and CO i n aqueous s o l u t i o n " , J o u r n a l of Chemical P h y s i c s , 28, 1958, p.T995. 31. MAYBURY, R.H. et a l . , " I n f r a r e d s p e c t r a of l i q u i d anhydrous hydrogen f l u o r i d e , l i q u i d sulphur d i o x i d e , and hydrogen f l u o r i d e - s u l p h u r d i o x i d e s o l u t i o n s " , J o u r n a l of Chemical P h y s i c s , 23, 1955, pp.1277-1281. 32. M0RCILL0, J . and HERRANZ, J . , " i n t e n s i t i e s , of the fundamental v i b r a t i o n -r o t a t i o n bands of sulphur d i o x i d e . I . Experimental determination", P u b l i c a c i o n e s d e l I n s t i t u t o de Quimica F i s i c a , 10, 1956, pp.162, i n Chemical A b s t r a c t s , 51, 16098f, 1957. 33. HAYON, E. et a l . , " E l e c t r o n i c s p e c t r a , photochemistry and a u t o x i d a t i o n mechanism of the s u l p h i t e - b i s u l p h i t e - p y r o s u l p h i t e systems. The S0^, S0~, S OT and S0= r a d i c a l s " , J o u r n a l of American Chemical S o c i e t y , 94, 1972, pp.47-57. 34. BASSET, H. and PARKER, W.G., "The o x i d a t i o n of sulphurous a c i d " , J o u r n a l of.Chemical S o c i e t y , London, 1951, pp.1540-1560. 35. S0UCH, B.E. and P0D0LSKY, T., "The sulphide ores of Sudbury: t h e i r p a r t i c u l a r r e l a t i o n s h i p to a d i s t i n c t i v e i n c l u s i o n - b e a r i n g f a c i e s of the n i c k e l i r r u p t i v e " , Magmatic ore deposits - A  Symposium, Lancaster Press, Lancaster, 1969, pp.252-261. 36. KILBURN, L.C. et a l . , " N i c k e l sulphide ores r e l a t e d to u l t r a b a s i c i n t r u s i o n s i n Canada", Magmatic ore deposits - A Symposium, Lancaster Press, Lancaster, 1969, pp.276-293. 37. RICHARDSON, P.E. and MAUST J r . E.E., "Surface s t o i c h i o m e t r y of galena i n aqueous e l e c t r o l y t e s and i t s e f f e c t on xanthate i n t e r a c t i o n s " , F l o t a t i o n A.M. Gaudin Memorial Volume, volume 1, AIME, New York, 1976, pp.364-392. 38. MISRA, K.C. and FLEET, M.E., "Chemical composition and s t a b i l i t y of v i o l a r i t e " , Economic Geology, 69, 1974, pp. 391-403. 39. BIRD, W.H., "A note on the occurance of v i o l a r i t e , Copper King Mine, Boulder Country, Colorado", Economic Geology, 64, 1969, pp.91-94. 40. NICKEL, E.H., " V i o l a r i t e - a key mineral i n the supergene a l t e r a t i o n of n i c k e l sulphide ores", The A u s t r a l a s i a n . IMM, Western A u s t r a l i a Conference, 19 73. 41. MICHENER, C.E. and YATES, A.B., "Oxidation of primary n i c k e l s u l p h i d e s " , Economic Geology, 39, 1944, pp.506-514. - 114 -42. HUDSON, D.R. and GROVES, D.I.,. "The composition of v i o l a r i t e c o e x i s t i n g w i t h v a e s i t e , p y r i t e and m i l l e r i t e " , Economic.Geology, 69, 1974, pp.1335-1340. 43. UYTENBOGAARDT, W. and BURKE, E.A.J., "Tables f o r microscopic i d e n t i -f i c a t i o n of ore min e r a l s " , E l s e v i e r , Amsterdam, 1971. 44. WEBER, R.E., "Auger e l e c t r o n spectroscopy f o r t h i n f i l m a n a l y s i s " , Research/Development.23, Oct. 1972, pp.22-28. 45. MacRAE, A.U., "Low-energy e l e c t r o n d i f f r a c t i o n " , Science, 139, Feb. 1963, pp.379-388. 46. RIGGS, W.M., "How ESCA pays i t s way", CHEM TECH, .5, 1975, pp.652-659. 47. KARASEK, F.W., "Surface a n a l y s i s by ISS and ESCA", Research/Development, 24, Jan. 1973, pp.25-30. 48. PLAKSIN, I.N. and SHAFEEV, R.Sh., "A study of the i n f l u e n c e of some surface s e m i c o n d u c t i v i t y p r o p e r t i e s on the i n t e r a c t i o n between potassium butyl-xanthates and sulphide m i n e r a l s " , Proceedings  I I I I n t e r n a t i o n a l Congress on surface a c t i v i t y , Cologne, 1960, pp.104-109. 49. PLAKSIN, I.N. and SHAFEEV, R.Sh., "Influence of surface p r o p e r t i e s of sulphide minerals on a d s o r p t i o n of f l o t a t i o n reagents", Transcations IMM, 72, 1963, pp.715-722. 50. TOLUN, R. and KITCHENER, J.A., " E l e c t r o c h e m i c a l study of the galena-xanthate-oxygen f l o t a t i o n system", Transactions IMM, 73, 1964, pp.313-322. 51. SPRINGER, G., "Observations on the e l e c t r o c h e m i c a l r e a c t i v i t y of semi-conducting m i n e r a l s " , Transactions IMM, 79, 1970, pp.Cll-C14. 52. ZEVGOLIS, E.N. and COOKE, S.R.B., "El e c t r o c h e m i c a l p r o p e r t i e s of the semiconductor mineral c h a l c o p y r i t e " , Proceedings XI IMPC, 1975, C a g l i a r i , pp.449-465. 53. BRATTAIN, W.H. and GARRETT, C.G.B., "Surface p r o p e r t i e s of semi-conduc-t o r s " , P h y s i c a , 20, 1954, pp.885-892. 54. BIEGLER, T., "Oxygen r e d u c t i o n on sulphide m i n e r a l s . P a r t I I . R e l a t i o n between a c t i v i t y and semiconducting p r o p e r t i e s of p y r i t e e l e c t r o d e s " , J o u r n a l of E l e c t r o a n a l y t i c a l Chemistry, 70, 1976, pp.265-275. 55. KAMIENSKI, B., " S o - c a l l e d f l o t a t i o n " , Przemysl Chemiczny, 15, 1931, pp. 201-202, i n L e j a (67). 56. PETERS, E., "The e l e c t r o c h e m i s t r y of sulphide m i n e r a l s " Trends i n e l e c t r o c h e m i s t r y , Plenum Press, New York, 1977, pp.267-298. - 115 -57. PETERS, E. and MAJIMA, H., "Electrochemical, r e a c t i o n s of p y r i t e i n a c i d p e r c h l o r a t e s o l u t i o n s " , . Canadian M e t a l l u r g i c a l Q u a r t e r l y , 7_, 1968, pp.111-117. 58. BRODIE, J.B., " E l e c t r o c h e m i c a l d i s s o l u t i o n of galena", M.Sc. Thesis, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, 1968. 59. SALAMY, S.G. and.NlXON, J . C , "The a p p l i c a t i o n of e l e c t r o c h e m i c a l methods to f l o t a t i o n research", Recent Developments i n M i n e r a l  Dressing, IMM, London, 1953, pp.503-516. 60. FINKELSTEIN, N.P. et a l . , " N a tural and induced h y d r o p h o b i c i t y i n sulphide mineral systems", AlChE Symposium s e r i e s , 71, no. 150, 1975, pp.165-175. 61. FINKELSTEIN, N.P. and STEWART, B.V., "A p r e l i m i n a r y i n v e s t i g a t i o n of the f l o t a t i o n of copper-activated s p h a l e r i t e without the use of c o l l e c t o r s " , N a t i o n a l I n s t i t u t e f o r Metallurgy, Report no. 1587, Johannesburg, 1973. 62. TRAHAR, W., " C o l l e c t o r l e s s f l o t a t i o n of c h a l c o p y r i t e " , Seminar pre-sented a t the Department of M i n e r a l Engineering, U n i v e r s i t y of B r i t i s h Columbia, 1977. 63. MAJIMA, H. and TAKEDA, M., "El e c t r o c h e m i c a l s t u d i e s of the xanthate-dixanthogen system on p y r i t e " , Transcations AIME, 241, 1968, pp.431-436. 64. TOPERI, D. and TOLUN, R., "El e c t r o c h e m i c a l study and thermodynamic e q u i l i b r i a of the galena-oxygen-xanthate f l o t a t i o n system", Transactions IMM, 78, 1969, pp. C191-C197. 65. WOODS, R., "The o x i d a t i o n of e t h y l xanthate on platinum, g o l d , copper, and galena e l e c t r o d e s . R e l a t i o n to the mechanism of min e r a l f l o t a t i o n " , J o u r n a l of P h y s i c a l Chemistry, 75, 1971, pp.354-362. 66. WOODS, R., "E l e c t r o c h e m i s t r y of sulphide f l o t a t i o n " , Proceedings of A u s t r a l a s i a n IMM, no. 241, March 1971, pp.53-61. 67. LEJA, J . , "Some e l e c t r o c h e m i c a l and chemical s t u d i e s r e l a t e d to f r o t h f l o t a t i o n w i t h xanthates", M i n e r a l s Science and Engineering, 5_, NO. 4, Oct. 1973, pp.278-286. 68. POMIANOWSKI, A. and CZARNECKI, J . , "Mixed p o t e n t i a l s and l o c a l c e l l s i n f l o t a t i o n systems", Journa l of C o l l o i d and I n t e r f a c e Science, 47, no. 2, May 1974, pp.315-321. 69. WOODS, R., "El e c t r o c h e m i s t r y of sulphide f l o t a t i o n " , F l o t a t i o n AM Gaudin Memorial Volume, volume 1, AIME, New York, 1976, pp.298-333. - 116 -70. BIEGLER, T. e t a l . , "Oxygen r e d u c t i o n on sulphide m i n e r a l s . Part 1. K i n e t i c s and mechanism at r o t a t e d p y r i t e e l e c t r o d e " , J o u r n a l of E l e c t r o a n a l y t i c a l Chemistry, 60, 1975, pp.151-162. 71. POLING, G.W., "Reactions between t h i o l reagents and sulphide m i n e r a l s " , F l o t a t i o n AM Gaudin Memorial Volume, volume 1,.AIME, New York, 1976, pp.334-363. 72. ALLISON, S.A. et a l . , "A determination of the products of r e a c t i o n between various sulphide minerals andaq.ueous xanthate s o l u t i o n , and a c o r r e l a t i o n of the products w i t h e l e c t r o d e r e s t p o t e n t i a l s " , M e t a l l u r g i c a l Transactions, 3, 1972, pp.2613-2618. 73. FINKELSTEIN, N.P. and GOOLD, L.A., "The r e a c t i o n of sulphide minerals w i t h t h i o l compounds", N a t i o n a l I n s t i t u t e f o r M e t a l l u r g y . Report no. 1439, Johannesburg, 1973. 74. POURBAIX, M., " A t l a s of e l e c t r o c h e m i c a l e q u i l i b r i a " , G a u t h i e r s — V i l l a r s , P a r i s , 1963. 75. ABRAMOV, A.A. et a l . , "Surface s t a t e i n sulphide minerals during f l o -t a t i o n " , Tsvetnye M e t a l l y , no. 3, 1975, pp.83-88. 76. I l ' i n , Yu.T. e t a l . , " E l e c t r o c h e m i c a l p r o p e r t i e s of n a t u r a l e l e c t r o n conductors", Uchebnyie Z a p i s k i Leningradskogo Gosudarstviennogo  U n i v e r s i t e t a S e r i a F i z i c h e s k o - Geologichnych Nauk, 1970, no 356, pp.139-152. ' 77. RAND, D.A.J., "Oxygen r e d u c t i o n on sulphide minerals. P a r t I I I . Com-pa r i s o n of a c t i v i t i e s of va r i o u s copper, i r o n , lead and n i c k e l m i n eral e l e c t r o d e s " , J o u r n a l of E l e c t r o a n a l y t i c a l Chemistry, 83, 1977, pp.19-32. 78. KLASSEN, V.I. and M0KR0US0V, V.A., "An i n t r o d u c t i o n to the theory of f l o t a t i o n " , Butterworths, London, 1963, p.238. 79. NATARAJAN, K.A. and IWASAKI, I . , " E f f e c t of poisoning of platinum e l e c t r o d e s on Eh measurements", Transactions AIME, 254, 1973, pp.23-28. 80. NATARAJAN, K.A. and IWASAKI, I . , "Behaviour of platinum electrodes as redox p o t e n t i a l i n d i c a t o r s i n some systems of m e t a l l u r g i c a l i n t e r e s t " , Transactions AIME, 247, 1970, pp.317-324. 81. NATARAJAN, K.A. and IWASAKI, I . , " S i g n i f i c a n c e of mixed p o t e n t i a l s i n Eh measurements w i t h platinum e l e c t r o d e s " , Transactions AIME, 255, 1974, pp.82-86. 82. NATARAJAN, K.A. and IWASAKI, I . , " P r a c t i c a l i m p l i c a t i o n s of Eh measure-ments i n sulphide f l o t a t i o n c i r c u i t s " , Transactions AIME, 254, 1973, pp.323-328 - 117 -83. NATARAJAN, K.A. and IWASAKI, I.,. "Eh-pH response of noble metal and sulphide mineral e l e c t r o d e s " , Transactions AIME, 252, 1972, 437-439. 84. FUERSTENAU, D.W. et a l . , "How to use t h i s modified Hallimond tube", Engineering and.Mining J o u r n a l , 158, March 1957, pp.93-95. 85. PARTRIDGE, A.C. and SMITH, G.W., "Small-sample f l o t a t i o n t e s t i n g : a new c e l l " , Transactions IMM, 80, 1971, pp.C199-C200. 86. PARASNIS, D.S., "The e l e c t r i c a l r e s i s t i v i t y of some sulphide and oxide minerals and t h e i r ores", Geophysical P r o s p e c t i n g , 4_, 1956, pp. 249-278. 87. KELLER, G.V. and FRISCHKNECHT, F.C., " E l e c t r i c a l methods i n geophysical p r o s p e c t i n g " , Pergamoni: Press, Oxford, 1966, p; 5. 88. PARKOMENKO, E.I., " E l e c t r i c a l p r o p e r t i e s of rocks", Plenum Press, New York, 1967, p. 88. 89. SHUEY, R.T., "Semiconducting ore mi n e r a l s " , E l s e v i e r , Amsterdam, 1975, p. 243 and p. 292. 90. WINTER, G. and WOODS, R., "The r e l a t i o n of c o l l e c t o r redox p o t e n t i a l to f l o t a t i o n e f f i c i e n c y : monothio-carbonates", Separation  Science, 8, no. 2, 1973, pp. 261-267. 91. DuRIETZ, C., Svensk. Kern. T i d s k r . , 69, 1957, pp.310-327, i n Majima and Takeda (59). 92. PETERS, E., " D i r e c t l e a c h i n g of s u l p h i d e s : chemistry and a p p l i c a t i o n s " , M e t a l l u r g i c a l Transactions AIME, 7B, no. 4, December 1976, pp. 505-517. 93. BOCKRIS, J . 0,*M. and REDDY, A.K.N., "Modern electrochemistry",volume 2, Plenum Press, New York, 1970. 94. FONTANA, M.G. and GREENE, N.D., "Corrosion engineering", McGraw H i l l , New York, 1967. - 118 -APPENDIX 1 CONFIDENCE INTERVALS OF REGRESSION LINES Y = a 4- bx ± 2 ( s / / — ) v n where 2(s/ ;—) = confidence i n t e r v a l vn S = v a r i a n c e of Y = z ,, 1 7 " " Ze i/(n-2) n = number of observations e. = Y , - (a + bx) i measured Equation Confidence i n t e r v a l (±mV) E-1 2 E-3 1 E-5 5 E-7 5 E-8 1 E-9 2 E-10 10 E-11 1 E-12 1 E-13 1 E-14 1 E-15 1 E-16 4 - 119 -. APPENDIX 2 THE BUTLER-VOLMER EQUATION E l e c t r o n t r a n s f e r r e a c t i o n s at the i n t e r f a c e between an ele c t r o d e and an e l e c t r o l y t i c s o l u t i o n obey the b a s i c e l e c -t r o d i c equation: the Butler-Volmer equation. When the over p o t e n t i a l i s nu m e r i c a l l y l a r g e (>100 mV) the s o - c a l l e d h i g h -f i e l d approximation i s a p p l i c a b l e , and the equation reduces . (l-S)Fn/RT 1 = 1 e o where i = net current d e n s i t y i ^ = exchange current d e n s i t y 3 = symmetry f a c t o r F = Faraday constant n = o v e r p o t e n t i a l R = gas constant T = absolute temperature In a loga r i t h m form, the equation can be arranged t o : n = <x l n _ i -i o RT where « = n~a\v  = T a f e l slope LIST OF PUBLICATIONS PERES, A . E . C . , PITELLA, C . F . , FONSECA, F.V. and WERNECK, R .A .F . , "Vacuum R e f i n i n g o f Copper-Z inc A l l o y s " * , M e t a l u r g i a , 25 , 138, 1969, pp. 351-360. PERES, A . E . C . , "Mathemat ica l Mode l l i ng o f B i na ry M e t a l l i c Systems P re sen t i ng M i s c i b i l i t y Gap", M.Sc. T h e s i s , UFMG, B r a z i l , 1973. PERES, A .E .C . and CAMPOS, V . F . , "Thermodynamic Study o f Lead-Z inc and Aluminum-Indium Systems" , Metal u r g i a , 30, 194, 1974, pp. 13-18. PERES, A . E . C . , GOMES, M.R. and MATOS, M., " P r epa ra t i on o f Aluminum Ch l o r i d e f o r i the E x t r a c t i o n o f the M e t a l : Thermodynamic Behav iour o f the Aluminum-Chlor ine-Oxygen-Carbon System", M e t a l u r g i a , 3 1 , 208, 1975, pp. 147-150. COELHOg E.M., OLIVEIRA, L . J . and PERES, A . E . C . , " P o s s i b i l i t y o f T a b l i n g and F l o t a t i o n o f Z i n c Ore from Vazan te " , M e t a l u r g i a , 3 1 , 206, 1975, pp. 23-28. MATOS, M.,. PERES, A .E .C . and GODOY, J . M . , "Removal o f Impu r i t i e s f rom Chromite and from Ox i d i z ed Z i n c Ores by Su l ph i d a t i o n R o a s t i n g " , M e t a l u r g i a , 32 , 218, 1976, pp. 11-17. OLIVEIRA, J . B . , GODOY, J . M . , CAMPOS, V . F . and PERES, A . E . C . , "Recovery o f Z i n c from Ox i d i z ed Ores v i a Carbothermic Reduc t i on " ,** M e t a l u r g i a , 34, 252, 1978, pp. 773-777. R e c i p i e n t o f the "oxigenio do B r a s i l " Annual Award f o r the best on a p p l i c a t i o n s o f n i t r o g e n and argon, ( i n B r a z i l ) . R e c i p i e n t o f the "Metal Leve" Annual Award f o r the best paper oi p r o d u c t i o n o f non-ferrous metals ( i n B r a z i l ) . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0081082/manifest

Comment

Related Items