"Applied Science, Faculty of"@en . "Materials Engineering, Department of"@en . "DSpace"@en . "UBCV"@en . "Ismay, Arnaldo Andre\u00CC\u0081s"@en . "2010-02-09T03:15:15Z"@en . "1976"@en . "Master of Applied Science - MASc"@en . "University of British Columbia"@en . "A study has been made of the oxidation of molybdenite in solutions of hypochlorite. The reaction was found to be first order in reagent concentration with a reaction rate constant of 1.90 x 10\u00E2\u0081\u00BB\u00C2\u00B2 min\u00E2\u0081\u00BB\u00C2\u00B9 cm\u00E2\u0081\u00BB\u00C2\u00B2 at pH 9 and 45\u00C2\u00B0C. The oxidation rate increases with increasing pH and later decreases if the pH is raised above 9.5. An activation energy of 6.3 \u00C2\u00B1 0.8 kcal/mole was observed for this reaction which was controlled\r\nby either chemical or mixed diffusion and chemical reactions. Other factors studied were the agitation, surface area, surface characteristics\r\nand effect of sulfates, chlorides, chlorites and chlorates.\r\nIt was observed that hypochlorite is capable of selectively leaching molybdenite from copper sulfides and positive results were obtained when applying this property to the extraction of molybdenite from copper rougher concentrates.\r\nThe formation of oxides during drying and/or leaching of copper sulfides was found to be detrimental to the process because they act as catalysts in the decomposition reaction of hypochlorite.\r\nRates of normal decomposition of the reagent were studied over the range 35 to 60\u00C2\u00B0C and pH 7 to 10 and found to be negligible as compared to the rates of oxidation of molybdenite.\r\nThe leaching of rougher concentrates with hypochlorite was found not to affect considerably the subsequent flotation operation.\r\n\r\nData of on-site hypochlorite generator plants and factors that affect production and decomposition, have been presented with the purpose of proposing a process using the information obtained in this work for the extraction of molybdenite in the Copper Concentration Plants."@en . "https://circle.library.ubc.ca/rest/handle/2429/19890?expand=metadata"@en . "SELECTIVE LEACHING OF MOLYBDENUM FROM MIXED COPPER-MOLYBDENUM SULFIDES by ARNALDO ANDRES ISMAY I n g . M e t a l u r g i c o , U n i v e r s i d a d T e c n o l d g i c a N a c i o n a l , A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF \u00E2\u0080\u00A2 MASTER IN APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d C o r d o b a , A r g e n t i n a , 1973 C t h e D e p a r t m e n t Me. nk**/ f*f\u00C2\u00A3. o f METALLURGY? THE UNIVERSITY OF BRITISH COLUMBIA September 1976 \u00C2\u00A7i) Arnaldo Andres Ismay SELECTIVE LEACHING OF MOLYBDENUM FROM MIXED OTPERHWBDENUM SULFIDES BY ARNALDO ANDRES ISMAY Ing. Metalurgico, Universidad Tecnologica Nacional, CordoBa, Argentina, ]973 A THESIS SUBMITTED IN PARTIAL FUlflLFENT OF THE FEQUIREMENTS FOR THE DEGREE OF MASTER IN APPLIED SCIENCE IN THE FACULTY OF GRADUATE STUDIES (DEPT. OF METALLURGY) We accept this thesis as conforming to the required standard \u00E2\u0080\u00A2 i i i \u00E2\u0080\u00A2 i i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 i i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i i i i i i \u00E2\u0080\u00A2 i i i i i i i i i i i i i i i i i i i i i \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i \u00E2\u0080\u00A2 i 11 i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i \u00E2\u0080\u00A2 i i i \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 > \u00E2\u0080\u00A2 THE UNIVERSITY OF BRITISH COLUMBIA SEPTEMBER 1976 Arnaldo Andres Ismay In p r e s e n t i n g 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 o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f Me>J*flurry The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1WS D a t e 0rf.4-m ABSTRACT A s t u d y has been made o f the o x i d a t i o n o f m o l y b d e n i t e i n s o l u t i o n s o f h y p o c h l o r i t e . The r e a c t i o n was found t o be f i r s t o r d e r i n r e a g e n t c o n c e n t r a t i o n w i t h a r e a c t i o n r a t e c o n s t a n t o f 1.90 x 1 0 \" 2 m i n - 1 c m - 2 . a t pH 9 and 45\u00C2\u00B0C. The o x i d a t i o n r a t e i n c r e a s e s w i t h i n c r e a s i n g pH and l a t e r d e c r e a s e s i f t h e pH i s r a i s e d above 9.5. An a c t i v a t i o n e n e r g y o f 6.3 \u00C2\u00B1 0.8 k c a l / m o l e was o b s e r v e d f o r t h i s r e a c t i o n which was con-t r o l l e d by e i t h e r c h e m i c a l o r mixed d i f f u s i o n and c h e m i c a l r e a c t i o n s . O t h e r f a c t o r s s t u d i e d were t h e a g i t a t i o n , s u r f a c e a r e a , s u r f a c e c h a r -a c t e r i s t i c s and e f f e c t o f s u l f a t e s , c h l o r i d e s , c h l o r i t e s and c h l o r a t e s . I t was o b s e r v e d t h a t h y p o c h l o r i t e i s c a p a b l e o f s e l e c t i v e l y l e a c h i n g m o l y b d e n i t e from c o p p e r s u l f i d e s and p o s i t i v e r e s u l t s were o b t a i n e d when a p p l y i n g t h i s p r o p e r t y t o t h e e x t r a c t i o n o f m o l y b d e n i t e from c o p p e r r o u g h e r c o n c e n t r a t e s . The f o r m a t i o n o f o x i d e s d u r i n g d r y i n g a nd/or l e a c h i n g o f copper s u l f i d e s was found t o be d e t r i m e n t a l t o t h e p r o c e s s because t h e y a c t as c a t a l y s t s i n t h e d e c o m p o s i t i o n r e a c t i o n o f h y p o c h l o r i t e . Rates o f normal d e c o m p o s i t i o n o f t h e r e a g e n t were s t u d i e d o v e r t h e range 35 t o 60\u00C2\u00B0C and pH 7 t o 10 and found t o be n e g l i g i b l e as compared t o t h e r a t e s o f o x i d a t i o n o f m o l y b d e n i t e . The l e a c h i n g o f ro u g h e r c o n c e n t r a t e s w i t h h y p o c h l o r i t e was found not t o a f f e c t c o n s i d e r a b l y t h e subsequent f l o t a t i o n o p e r a t i o n . i i Data o f o n - s i t e h y p o c h l o r i t e g e n e r a t o r p l a n t s and f a c t o r s t h a t a f f e c t p r o d u c t i o n and d e c o m p o s i t i o n , have been p r e s e n t e d w i t h t h e purpose o f p r o p o s i n g a p r o c e s s u s i n g the i n f o r m a t i o n o b t a i n e d i n t h i s work f o r t h e e x t r a c t i o n o f m o l y b d e n i t e i n t h e Copper C o n c e n t r a t i o n P l a n t s . i i i TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v i i i LIST OF FIGURES i x ACKNOWLEDGMENTS x i i Cha p t e r 1 INTRODUCTION 1 1.1 Ge n e r a l 1 1.2 P r o d u c t i o n o f M o l y b d e n i t e C o n c e n t r a t e s 2 1.3 P r o d u c t i o n o f Rhenium 7 1.4 A l t e r n a t i v e H y d r o m e t a l l u r g i c a l P r o c e s s 8 1.5 L i t e r a t u r e Review 10 2 SCOPE OF PRESENT INVESTIGATION 17 3 EXPERIMENTAL 19 3.1 M a t e r i a l s 19 3.2 A p p a r a t u s 22 3.3 P r o c e d u r e 23 3.4 Chemical A n a l y s i s 24 4 RESULTS AND OBSERVATIONS 26 4.1 O x i d a t i o n o f M o l y b d e n i t e by Sodium H y p o c h l o r i t e . ... 26 i v C h a p t e r Page 4.1.1 R e p r o d u c i b i l i t y 26 4.1.2 E f f e c t o f S t i r r i n g Rate 27 4.1.3 E f f e c t o f Temperature 27 4.1.4 E f f e c t o f S u r f a c e A r e a 33 4.1.5 MoS 2 C r y s t a l i n i t y and S u r f a c e C h a r a c t e r i s t i c s 33 4.1.6 Morphology o f MoS 2 L e a c h i n g 37 4.1.7 E f f e c t o f NaOCl C o n c e n t r a t i o n on the Rates o f Mo E x t r a c t i o n . 41 4.1.8 E f f e c t o f pH on t h e Rate o f R e a c t i o n 44 4.1.9 E f f e c t o f S u l f a t e C o n c e n t r a t i o n on t h e R e a c t i o n Rate . 44 4.1.10 E f f e c t o f NaCl on t h e R e a c t i o n Rate. ... 47 4.1.11 E f f e c t o f C10 2~ and C 1 0 3 = on the Rate o f R e a c t i o n 49 4.1.12 E f f e c t o f Mo l y b d a t e Ions on t h e Rates o f R e a c t i o n . 49 4.2 O x i d a t i o n o f C h a l c o p y r i t e by Sodium H y p o c h l o r i t e 53 4.2.1 L e a c h i n g o f C h a l c o p y r i t e C o n c e n t r a t e 53 4.2.2 L e a c h i n g o f M a s s i v e Specimens 54 4.2.3 C o m p a r a t i v e O x i d a t i o n and D i s s o l u t i o n o f MoS 2 and C u F e S 2 i n S o l u t i o n s o f NaOCl 57 4.2.4 E f f e c t o f C h a l c o p y r i t e on t h e Rates o f NaOCl Consumption and MoS 2 D i s s o l u t i o n . . 59 4.3 L e a c h i n g o f M o l y b d e n i t e from Copper Rougher C o n c e n t r a t e s 62 v C h a p t e r Page 4.3.1 I n f l u e n c e o f P a r t i c l e S i z e on t h e E x t r a c t i o n o f Molybdenum 95 4.3.2 Q u a n t i t y o f NaOCl R e q u i r e d f o r T o t a l Molybdenum E x t r a c t i o n 67 4.3.3 E f f e c t o f P r e t r e a t i n g the Rougher C o n c e n t r a t e w i t h S u l f u r i c A c i d ....... 67 4.3.4 E x t r a c t i o n o f M o l y b d e n i t e from \" I n - P u l p \" Rougher C o n c e n t r a t e . . . . . . . 68 4.3.5 F l o t a t i o n o f Leached Rougher C o n c e n t r a t e s 69 4.3.6 F l o t a t i o n o f \" I n - P u l p \" Rougher C o n c e n t r a t e s 73 4.3.7 S t a b i l i t y o f Sodium H y p o c h l o r i t e S o l u t i o n s 75 5 DISCUSSION 78 5.1 O x i d a t i o n o f M o l y b d e n i t e 78 5.2 O x i d a t i o n o f C h a l c o p y r i t e 87 5.3 L e a c h i n g o f M o l y b d e n i t e from Copper Rougher C o n c e n t r a t e s 89 5.4 F l o t a t i o n o f Leached Rougher C o n c e n t r a t e s 91 5.5 P r o d u c t i o n o f Sodium H y p o c h l o r i t e 91 5.6 K i n e t i c s o f Sodium H y p o c h l o r i t e D e c o m p o s i t i o n 94 5.6.1 E f f e c t o f E x c e s s C h l o r i d e on t h e D e c o m p o s i t i o n Rates 100 5.6.2 E f f e c t o f C a t i o n s on D e c o m p o s i t i o n Rates 100 5.6.3. C a t a l y t i c Agents i n H y p o c h l o r i t e D e c o m p o s i t i o n 101 5.7 H y p o c h l o r i t e L e a c h i n g P r o c e s s f o r the E x t r a c t i o n o f M o l y b d e n i t e From Copper Rougher C o n c e n t r a t e s 102 v i C h a p t e r Page 6 CONCLUSIONS 108 7 SUGGESTIONS FOR FUTURE WORK 110 REFERENCES I l l v i i LIST OF TABLES T a b l e Page 1 Comparison between P r o d u c t i o n from T o t a l A v a i l a b l e S o u r c e s and Copper P o r p h y r i e s 2 2 I n t e r n a t i o n a l Market Grade o f M o l y b d e n i t e C o n c e n t r a t e s 3 3 Copper, Molybdenum and Rhenium P r o d u c t P r i c e s 9 4 Chemical A n a l y s i s and X-ray D i f f r a c t i o n A n a l y s i s o f M o l y b d e n i t e C o n c e n t r a t e 20 5 Chemical C o m p o s i t i o n and X - r a y D i f f r a c t i o n P a t t e r n o f Copper Rougher C o n c e n t r a t e 21 6 Comparison o f S/Cu r a t i o s f o r Leached and N o n l e a c h e d C h a l c o p y r i t e . 56 7 V a l u e s f o r D e t e r m i n a t i o n o f S u r f a c e A r e a f o r M o l y b d e n i t e and C h a l c o p y r i t e 59 8 Oxide Copper C o n t e n t f o r D r i e d and I n - P u l p Rougher C o n c e n t r a t e s 93 9 Economic Assumptions f o r t h e E s t i m a t i o n o f C o s t s i n t h e O p e r a t i o n o f a H y p o c h l o r i t e G e n e r a t o r 107 10 Consumption o f A c i d f o r t h e R e d u c t i o n o f pH o f Molybdenum C o n t a i n i n g H y p o c h l o r i t e S o l u t i o n s v i i i LIST OF FIGURES F i g u r e Page 1 S i m p l i f i e d g e n e r a l f l o w s h e e t o f a c o p p e r - b y p r o d u c t m o l y b d e n i t e c o n c e n t r a t i o n p r o c e s s 4 2 R e p r o d u c i b i l i t y o f t h e r e s u l t s f o r t h e l e a c h i n g o f m o l y b d e n i t e p a r t i c l e s 27 3 E f f e c t o f s t i r r i n g on t h e r a t e o f o x i d a t i o n o f m o l y b d e n i t e 29 4 E f f e c t o f s t i r r i n g on t h e r a t e o f o x i d a t i o n , o f m o l y b d e n i t e ( r a t e v s . r.p.m.) 30 5 E f f e c t o f t e m p e r a t u r e on t h e o x i d a t i o n o f m o l y b d e n i t e 31 6 A r r h e n i u s p l o t o f t e m p e r a t u r e d a t a 32 7 E f f e c t o f s u r f a c e a r e a on t h e r a t e o f o x i d a t i o n o f m o l y b d e n i t e 34 8 L a y e r e d s t r u c t u r e o f m o l y b d e n i t e p a r t i c l e s 35 9 M o l y b d e n i t e s t r u c t u r e 36 10 View o f t h e \"FACE\" s u r f a c e o f m o l y b d e n i t e 38 11 M o l y b d e n i t e p a r t i c l e s o x i d i z e d o v e r i n c r e a s i n g p e r i o d s 39 12 M o l y b d e n i t e p a r t i c l e s a f t e r 10 minutes o f r e a c t i o n i n sodium h y p o c h l o r i t e . 40 i x F i g u r e Page 13 E f f e c t o f sodium h y p o c h l o r i t e on t h e r a t e o f o x i d a t i o n o f m o l y b d e n i t e 42 14 P l o t o f r e a c t i o n r a t e s v s . i n i t i a l h y p o c h l o r i t e c o n c e n t r a t i o n 43 15 E f f e c t o f pH on the r a t e o f o x i d a t i o n o f m o l y b d e n i t e 45 16 P l o t o f r e a c t i o n r a t e v s . pH 46 17 E f f e c t o f s u l f a t e s on the r a t e o f o x i d a t i o n o f m o l y b d e n i t e 48 18 E f f e c t o f c h l o r i t e s and c h l o r a t e s on the r a t e o f o x i d a t i o n o f m o l y b d e n i t e 50 19 E f f e c t o f molybdates-MoS 2 i n t e r a c t i o n 52 20 E x t r a c t i o n o f c o p p e r and consumption o f h y p o c h l o r i t e d u r i n g l e a c h i n g o f c h a l c o p y r i t e 55 21 S u r f a c e roughness o f m o l y b d e n i t e and c h a l c o p y r i t e 58 22 E x t r a c t i o n o f c o p p e r and molybdenum d u r i n g l e a c h i n g o f equal i n i t i a l s u r f a c e a r e a s o f m o l y b d e n i t e and c h a l c o p y r i t e 60 23 E f f e c t o f c h a l c o p y r i t e on t h e r a t e s o f m o l y b d e n i t e d i s s o l u t i o n . . . . . . . . 61 24 E x t r a c t i o n o f molybdenum and c o p p e r from a c o p p e r r o u g h e r c o n c e n t r a t e 63 25 E f f e c t o f p a r t i c l e s i z e on r a t e s o f e x t r a c t i o n o f molybdenum from r o u g h e r c o n c e n t r a t e s 65 x F i g u r e Page 26 Molybdenum e x t r a c t i o n and h y p o c h l o r i t e consumption f o r the l e a c h i n g o f ground and normal r o u g h e r c o n c e n t r a t e s 66 27 M o l y b d e n i t e d i s s o l u t i o n and h y p o c h l o r i t e consumption f o r the l e a c h i n g o f t r e a t e d and i n - p u l p r o u g h e r c o n c e n t r a t e s , 70 28 R e c o v e r y - g r a d e c u r v e s f o r t h e s e c o n d a r y f l o t a t i o n o f l e a c h e d r o u g h e r c o n c e n t r a t e s ( a f t e r t r e a t m e n t ) 72 29 R e c o v e r y grade c u r v e s f o r t h e s e c o n d a r y f l o t a t i o n o f l e a c h e d r o u g h e r c o n c e n t r a t e s ( s t o r e d i n - p u l p ) 74 30 E f f e c t o f pH on the d e c o m p o s i t i o n o f h y p o c h l o r i t e a t 60\u00C2\u00B0C 76 31 E f f e c t o f pH on the d e c o m p o s i t i o n o f h y p o c h l o r i t e a t 35\u00C2\u00B0C 77 32 H y p o c h l o r i t e and h y p o c h l o r o u s a c i d c o n c e n t r a t i o n s as a f u n c t i o n o f pH 80 33 E p o t e n t i a l o f m o l y b d e n i t e as a f u n c t i o n o f pH 82 34 L o g - l o g c u r v e o f r a t e s o f o x i d a t i o n v s . c o n c e n t r a t i o n o f h y p o c h l o r i t e . . 86 35 L o g - l o g c u r v e o f r a t e o f d e c o m p o s i t i o n o f h y p o c h l o r i t e v s . h y p o c h l o r i t e c o n c e n t r a t i o n 98 36 P o s i t i o n o f p r o p o s e d l e a c h i n g p r o c e s s i n t h e g e n e r a l c o p p e r c o n c e n t r a t i o n f l o w - s h e e t 103 37 Flow s h e e t o f t h e proposed method f o r e x t r a c t i n g m o l y b d e n i t e from c o p p e r r o u g h e r c o n c e n t r a t e s 104 x i ACKNOWLEDGMENTS I would l i k e t o e x p r e s s my g r a t i t u d e f o r t h e a d v i c e and encouragement o f my r e s e a r c h s u p e r v i s o r Dr. Ian H. Warren t h r o u g h o u t t h e c o u r s e o f t h i s r e s e a r c h p r o j e c t . Thanks a r e a l s o e x t e n d e d t o th e o t h e r members o f the department and f e l l o w g r a d u a t e s t u d e n t s f o r making t h i s p e r i o d b o t h u s e f u l and p l e a s a n t . The h e l p r e c e i v e d f r o m Dr. James King and t h e use o f f a c i l i t i e s a t the Re s e a r c h D i v i s i o n o f P l a c e r Development L i m i t e d f o r th e accomplishment o f p a r t s o f t h i s p r o j e c t a r e v e r y much a p p r e c i a t e d . A s p e c i a l thanks goes t o M i r t h a f o r a l l t h e n o n - t e c h n i c a l h e l p and p a t i e n c e . F i n a n c i a l a s s i s t a n c e r e c e i v e d from t h e Canadian I n d u s t r i e s L i m i t e d ( C I L ) i s g r a t e f u l l y acknowledged. x i i C h a p t e r 1 INTRODUCTION 1.1 Ge n e r a l M o l y b d e n i t e (MoS 2) i s o f t e n a s s o c i a t e d w i t h copper s u l f i d e m i n e r a l s such as c h a l c o p y r i t e ( C u F e S 2 ) and c h a l c o c i t e ( C u 2 S ) as a minor component o f many g i g a n t i c , low grade d i s s e m i n a t e d c o p p e r d e p o s i t s c a l l e d \" c o p p e r p o r p h y r i e s . \" The most v a l u a b l e components o f t h e s e d e p o s i t s a r e co p p e r and molybdenum. The e x t r a c t i o n o f g o l d and s i l v e r i s a l s o s i g n i f i c a n t . , Rhenium i s a by p r o d u c t o f p o r p h y r y p r o c e s s i n g and a l t h o u g h t o t a l w o r l d p r o d u c t i o n i s o n l y o f t h e o r d e r o f 7400 l b s . [ 1 , 2 ] , t h e m o l y b d e n i t e c o n c e n t r a t e o b t a i n e d from c o p p e r p o r p h y r i e s ' i s t h e s o l e s o u r c e o f t h i s m etal a t p r e s e n t . A t y p i c a l p o r p h y r y o r e m i g h t - c o n t a i n : ; Cu = 0.8% Au = 0.01-0.02 o z / t o n Re - 0.038% o f MoS 2 c o n c e n t r a t e Mo = 0.015% Ag = 0.05-0.1 o z / t o n Due t o t h e l a r g e tonnage o f p o r p h y r y m a t e r i a l p r o c e s s e d (540 x 10 6 t o n s i n 1973) t h e p r o d u c t i o n f i g u r e s f o r t h e molybdenum and rhenium 1 2 a r e v e r y s i g n i f i c a n t as shown i n T a b l e 1. Roughly 1-1.5 oz o f Au and 3-10 oz o f Ag can be r e c o y e r e d p er t o n o f co p p e r e x t r a c t e d . T a b l e 1 Comparison Between P r o d u c t i o n from T o t a l A v a i l a b l e S o u r c e s and Copper P o r p h y r i e s (based on 1973 s t a t i s t i c s ) Metal T o t a l World P r o d u c t i o n Output from Copper P o r p h y r i e s % Produced from Copper P r o p h y r i e s Cu 8,100,000 3,500,000 43% Mo 87,500 37,400 37% Re 3.7 3.7 100% From 1967 t o 1972 t h e p r o d u c t i o n o f MoS 2 as a b y p r o d u c t o f co p p e r p o r p h y r i e s i n the U.S.A. r o s e o v e r 42% [ 1 ] . I t has been e s t i m a t e d [ 3 ] t h a t t h e s e d e p o s i t s a c c o u n t f o r some 5.5 x 1 0 6 t o n s o f Mo, which r e p r e s e n t 17% o f the w o r l d ' s molybdenum r e s e r v e s . 1.2 P r o d u c t i o n o f M o l y b d e n i t e C o n c e n t r a t e s Molybdenum consumed i n i t s v a r i o u s end p r o d u c t s i s i n t h e form o f m o l y b d i c o x i d e ( 6 6 % ) , ferromolybdenum ( 2 0 % ) , ammonium and sodium molybdate ( 2 % ) , and o t h e r m a t e r i a l s ( 1 2 % ) . .To o b t a i n t h e s e , a m o l y b d e n i t e concen-t r a t e i s produced by f l o t a t i o n and th e n r o a s t e d t o o x i d i z e t h e MoS 2 t o Mo0 3, which i s t h e s t a r t i n g compound f o r a l l subsequent p r o d u c t s . 3 The t a s k o f p r o d u c i n g s p e c i f i c a t i o n MoS 2 c o n c e n t r a t e s [ T a b l e 2) from o r e s w i t h an aver a g e o f 150 ppm Mo i n which c o p e r and i r o n m i n e r a l s outweigh MoS 2 by r a t i o s o f about 140 t o 1 i s q u i t e f o r m i d a b l e . The p r o c e s s i s l o n g and t h e r e c o v e r i e s a r e low. T a b l e 2 I n t e r n a t i o n a l Market Grade o f M o l y b d e n i t e C o n c e n t r a t e s MoS 2 80% (min) Cu 0.5% (max).. Pb 0.3% (max) P, Sn, As 0.2% (max t o t a l ) A g e n e r a l i z e d d e s c r i p t i o n o f t h e common p r a c t i c e o f t r e a t i n g t h e s e o r e s i s p r e s e n t e d below w i t h t h e i n t e n t i o n o f showing why MoS 2 r e c o v e r y i s so low. A l t h o u g h t h e r e a r e v a r i a t i o n s i n t h e 30 p l a n t s f o r whi c h t h e r e i s a v a i l a b l e d a t a i t i s f e l t t h a t t h e y do not a f f e c t t h i s a n a l y s i s . F i g u r e 1 i s a s i m p l i f i e d f l o w s h e e t o f the method d e s c r i b e d , i n d i c a t i n g t h e e f f i c i e n c y o f the s u c c e s s i v e s t a g e s and t h e c u m u l a t i v e d r o p i n r e c o v e r y . MoS 2 i s f l o a t e d c o l l e c t i v e l y w i t h t h e Cu s u l f i d e s i n t o a r o u g h e r copper c o n c e n t r a t e which c o n t a i n s the bul k o f Cu and Mo. T h i s r o u g h e r c o n c e n t r a t e has a h i g h p r o p o r t i o n o f m i d d l i n g s and i s t h e r e f o r e s u b j e c t e d t o a c a r e f u l s i z e r e d u c t i o n i n o r d e r t o a v o i d t h e f o r m a t i o n o f s l i m e s because o f t h e ease w i t h which MoS 2 g r i n d s . I t i s t h e n r e f l o a t e d i n c l e a n e r and r e c l e a n e r c i r c u i t s t o produce a copper c o n c e n t r a t e which c o n t a i n s 25-50% Cu and 0.2-1% MoS 2. Run of Mine SIZE REDUCTION 80-85 70-75 >-z : UJ o u_ u_ LU I-< r r UJ o_ O 70 15% RQUBHER FLOTATION 1 Rougher 1 Concentrate 1 CYCLONE 8 REGRINDING 1 CLEANING a RECLEANING 1 25% >0.2% T Cu Flotation Concentrate <0.2% Mo THICKENING >-r r LU > o o LU ^ 33%. in in o LU > in in UJ r r o r r o_ 50% ROUGHER FLOTATION -\u00C2\u00BB\u00C2\u00BBMoS^ Rougher Concentrate CLEANING CYCLONE a REGRINDING RECLEANING MoS Flotation Concentrate 2 >0.5% Cu LEACHING THICKENING FILTERING S DRYING Cu Concentrate Mo Concentrate FIG. I- SIMPLIFIED GENERAL FLOWSHEET OF A COPPER BYPRODUCT MoS 2 CONCENTRATE PROCESS. 5 A t t h i s p o i n t MoS 2 i s s e p a r a t e d f r o m t h e Cu m i n e r a l s by s e l e c -t i v e f l o t a t i o n , e i t h e r d e p r e s s i n g t h e Cu and Fe m i n e r a l s and f l o a t i n g MoS 2 o r v i c e v e r s a . The p r o d u c t o f t h i s o p e r a t i o n i s a \"moly\" r o u g h e r c o n c e n t r a t e which i s th e n s u b j e c t e d t o r e g r i n d i n g and r e f l o a t i n g i n a c l o s e d - c o u n t e r c u r r e n t c l e a n i n g c i r c u i t to produce a MoS 2 c o n c e n t r a t e . I f t h i s p r o d u c t has i n e x c e s s o f 0.5% Cu i t must be f u r t h e r p r o c e s s e d by l e a c h i n g t o produce a m a r k e t a b l e c o n c e n t r a t e . The c u t o f f p o i n t f o r o p e r a t i n g a b y p r o d u c t MoS 2 f l o t a t i o n c i r c u i t i s c o n s i d e r e d e c o n o m i c a l l y t o be 0.2% MoS 2 i n t h e Cu c o n c e n t r a t e . However i n many c a s e s p l a n t s w i l l o n l y o p e r a t e i f t h e a s s a y i s above 0.7% MoS 2. Any Mo and Re not r e c o v e r e d by f l o t a t i o n a r e u n r e c o v e r a b l e i n t h e sub-sequent p y r o m e t a l l u g i c a l t r e a t m e n t . ' The f a c t o r s t h a t a f f e c t MoS 2 r e c o v e r y [ 4 ] a r e : 1. The p r i n c i p a l aim o f the o p e r a t i o n i s maximum Cu r e c o v e r y and t h i s may r e s u l t i n l e s s t h a n optimum c o n d i t i o n s f o r MoS 2 e x t r a c t i o n as may be seen i n t h e f o l l o w i n g examples: A. The a d d i t i o n o f l i m e which i s n e c e s s a r y t o d e p r e s s p y r i t e i n o r d e r to i n s u r e good Cu f l o t a t i o n may h i n d e r MoS 2 f l o t a t i o n by f l o c c u l a t i n g t h e gangue and t r a p p i n g t h e f i n e MoS 2 p a r t i c l e s . B. Hydrocarbon o i l s which r a i s e t h e MoS 2 r e c o v e r y a r e added o n l y t o t h e e x t e n t t h a t t h e r e i s no a d v e r s e e f f e c t on c o p p e r m i n e r a l s . The m i n e r a l i z a t i o n o f t h e o r e M i n e r a l i z a t i o n i s o f g r e a t e r s i g n i f i c a n c e i n MoS 2 f l o t a -t i o n t h a n i n o t h e r f l o t a t i o n o p e r a t i o n s due t o t h e v e r y low grade o f o r e as shown i n t h e next examples: A. Due t o t h e c h a r a c t e r i s t i c s o f copper p o r p h y r i e s i n which MoS 2 has a v e r y uneven d i s t r i b u t i o n , w h i l e t h e Cu grade o f the head may remain f a i r l y c o n s t a n t t h e MoS 2 g r a d e may be e r r a t i c and v a r y by s e v e r a l hundred p e r c e n t i n s h o r t p e r i o d s o f ti m e . B. MoS 2 can be p r e s e n t as w e l l formed c l e a n c r y s t a l s , o r as l e s s w e l l d e f i n e d m a t e r i a l w i t h v e r y a l t e r e d s u r f a c e s , w i t h o r w i t h o u t a t h i n o x i d e c o a t i n g . A l s o i t may o r may not be a s s o c i a t e d w i t h o t h e r h y d r o p h o b i c m a t e r i a l s such as g r a p h i t e , t a l c o r carbonaceous p r o d u c t s . C. M o l y b d e n i t e can a l s o be c o a t e d w i t h a c o l l o i d a l c h a l c o p y r i t e s l i m e which p r e v e n t s i t s f l o t a t i o n and causes a \"drop o u t \" i n t h e c l e a n e r c i r c u i t . D. T h e r e i s a s o - c a l l e d \"crowding o u t phenomena\" which can be e x p l a i n e d as a c o u n t e r e f f e c t on t h e d i f f e r e n t i a l f l o t a t i o n o f two m i n e r a l s p e c i e s produced by an e x t r a o r d i n a r y d i f f e r e n c e i n t h e number o f p a r t i c l e s o f each s p e c i e s . 7 3. C o s t o f Reagents The c o s t o f r e a g e n t s f o r d e p r e s s i n g t h e o t h e r m i n e r a l s p e c i e s impedes the e x t r a c t i o n o f MoS 2 from Cu c o n c e n -t r a t e s i n which Mo c o n t e n t i s v e r y low. A l t h o u g h c o n s i d e r a b l e r e s e a r c h has been d i r e c t e d towards s o l v i n g many of. t h e s e problems and i n c r e a s i n g t h e e f f i c i e n c y o f MoS 2 e x t r a c t i o n from c o p p e r p o r p h y r i e s s p r e s e n t t e c h n o l o g y does n o t a c h i e v e much more tha n 50% r e c o v e r y . T h i s means t h a t a p p r o x i m a t e l y 18,000 t o n s o f Mo r e p r e -s e n t i n g about 0.3% o f t h e i d e n t i f i e d r e s e r v e s o f Mo i n c o p p e r p o r p h y r i e s o f the w o r l d , a r e l o s t a n n u a l l y i n v a r i o u s p a r t s o f the p r o c e s s . 1.3 P r o d u c t i o n o f Rhenium To produce rhenium a MoS 2 c o n c e n t r a t e . i s r o a s t e d a t tempera-t u r e s between 540\u00C2\u00B0C and 650\u00C2\u00B0C and about 90% o f the Re i t c o n t a i n s i s v o l a t i l i z e d . The gases a r e s c r u b b e d u s i n g a c o m b i n a t i o n o f c y c l o n e s , e l e c t r o s t a t i c p r e c i p i t a t o r s and a h i g h energy V e n t u r i t y p e s c r u b b e r t o remove Re a l o n g w i t h some S 0 2 and s m a l l amounts o f Mo, Cu and Fe. By i n t e n s i v e r e c i r c u l a t i o n t h e p r e g n a n t s o l u t i o n i s c o n c e n t r a t e d t o 0.2 t o 0.5 g/1 o f Re. I t i s then c o n d i t i o n e d by a d d i n g C l 2 t o o x i d i z e Mo, Re and Fe v a l u e s and s u b s e q u e n t l y Fe and Cu a r e p r e c i p i t a t e d as c a r b o n a t e s . Re i s then a b s o r b e d i n ion-^exchange columns o r removed by s o l v e n t e x t r a c t i o n . . The e l u t r i a t i o n p r o d u c t i s t r e a t e d w i t h H2S. t o p r e c i p i -t a t e Re as ReS 2 which i s then t r e a t e d w i t h H 2 0 2 and.iNhU OH t o form a s o l u b l e p e r r h e n a t e which i s l a t e r c r y s t a l l i z e d . 8 A l t h o u g h t h e p r o c e s s i s r e l a t i v e l y s i m p l e i t has s e v e r a l d e f i c i e n c i e s which r e d u c e t h e t o t a l Re p r o d u c t i o n c a p a c i t y . These a r e : 1. R e d u c e d Re i n f e e d d u e t o l ow r e c o v e r i e s i n t h e p r e v i o u s M o S 2 c o n c e n t r a t i o n p r o c e s s 2 . P r o d u c t i o n o f S 0 2 3. L o s s e s o f Re i n t h e s c r u b b i n g o p e r a t i o n s The a v e r a g e r e c o v e r y o f rhenium from m o l y b e d e n i t e c o n c e n t r a t e s i s 60%. I f p r e s e n t t e c h n o l o g y c o n t i n u e s t o be used i n the f u t u r e t h i s would mean t h a t from t h e e s t i m a t e d 4.2 m i l l i o n l b s . o f Re r e s e r v e s c o n -t a i n e d i n copper p o r p h y r i e s o n l y 1.5 m i l l i o n can be c o n s i d e r e d r e c o v e r a b l e 1.4 A l t e r n a t i v e H y d r o m e t a l 1 u r g i c a l P r o c e s s A l i s t o f p r i n c i p a l commodities produced from c o p p e r p o r p h y r i e s and t h e i r r e s p e c t i v e p r i c e s i s p r e s e n t e d i n T a b l e 3. Any new p r o c e s s which a c h i e v e d g r e a t e r r e c o v e r i e s o f both molybdenum and rhenium c o u l d be o f s i g n i f i c a n t economic advantage s p e c i a l l y i n t h o s e c o p p e r p o r p h y r i e s i n which t h e Cu grade i s e x t r e m e l y low such as th e ones i n B r i t i s h Columbia. I f MoS 2 were p r e f e r e n t i a l l y l e a c h e d from copper s u l f i d e m a t e r i a l s t h e a p p l i c a t i o n o f a h y d r o m e t a l 1 u r g i c a l p r o c e s s t o an e a r l y s t a g e o f the co p p e r c o n c e n t r a t i o n c i r c u i t might r e s u l t i n a f a v o u r a b l e a l t e r n a t i v e t o t h e p r e s e n t t e c h n o l o g y . T h i s p r o c e s s c o u l d have t h e f o l l o w i n g a d v a n t a g e s : T a b l e 3 Copper, Molybdenum and Rhenium P r o d u c t s P r i c e s (1975) Copper P r i m a r y Cu .61 $ / l b R e f i n e d Cu . .64 $ / l b Rhenium a l l rhenium p r o d u c t s i n the range o f 1000-1200 $ / l b . Molybdenum MoS 2 C o n c e n t r a t e $ / l b . c o n t . Mo 2.20-.255 T e c h n i c a l Mo03 2.60 Mo0 3 B r i q u e t e s 2.65 F e r r o Molybdenum 2.30 Mo P e l l e t s 2.90 Mo Powder 3.10 10 1. H i g h e r M o S 2 r e c o v e r i e s 2. P r o d u c t i o n o f h i g h e r m a r k e t v a l u e p r o d u c t s , i . e . Mo s a l t s , Mo m e t a l p o w d e r 3. H i g h e r Re r e c o v e r y 4 . E l i m i n a t i o n o f t h e r o a s t i n g s t e p a n d t h u s p r o d u c t i o n o f Mo a n d Re w i t h o u t S 0 2 e m i s s i o n a n d w i t h o u t .^ c a p i t a l e x p e n d i t u r e o n r o a s t i n g e q u i p m e n t . Aqueous s u s p e n s i o n s o f MoS 2 must be o x i d i z e d t o produce molybdate i o n s t o e f f e c t T e a c h i n g ; ' a n d , depending on the p H , t h e s e ions\" w i l l e i t h e r be HMoOit\" o r MoO^ - [6 -9] . In s i m i l a r aqueous o x i d a t i o n , t h e s u l f i d e s o f Cu and Fe form c a t i o n s which under some c o n d i t i o n s o f pH, by h y d r o l y s i s , produce i n s o l u b l e o x i d e s o r h y d r o x i d e s . T h e r e f o r e t h e s e l e c t i v i t y o f a l e a c h i n g system might not o n l y depend on the r e l a t i v e o x i d a t i o n r a t e s o f m o l y b d e n i t e and the c o p p e r s u l f i d e s but on t h e s o l u b i l i t y o f the s p e c i e s formed, t he n a t u r e o f any s o l i d p r o d u c t s formed and t h e i r i n t e r a c t i o n w i t h t h e r e a g e n t employed. 1.5 L i t e r a t u r e Review S t u d i e s on the o x i d a t i o n o f aqueous s u s p e n s i o n s o f m o l y b d e n i t e have been r e p o r t e d as e a r l y as 1952. E.S. U s a t a y a et al. [11] i n v e s t i g a t e d t he e f f e c t o f a c i d s , b a s e s , s a l t s and o x i d i z i n g a g e n t s on MoS 2 c o n c l u d i n g t h a t t h e r a t e o f d e c o m p o s i t i o n i n c r e a s e s w i t h i n c r e a s i n g pH and t h a t s o l i d p r o t e c t i v e l a y e r s a r e formed i n the a c i d o r weakly a l k a l i n e r e g i o n s . The p r e s e n c e o f s t r o n g o x i d i z i n g a gents such as H 2 0 2 i n a s t r o n g a l k a l i n e s o l u t i o n was o b s e r v e d t o p r e v e n t the f o r m a t i o n o f such a c o a t i n g . D . M . Yukhtanov and K.D. L e o n t ' e v a [12] ( i n 1953) were t h e f i r s t t o use NaOCl a t normal and h i g h t e m p e r a t u r e s t o o x i d i z e MoS 2. 11 W.H. D r e s n e r et al. [7] i n 1956 s t u d i e d t h e k i n e t i c s o f MoS 2 l e a c h i n g i n a l k a l i n e s o l u t i o n s i n t h e t e m p e r a t u r e range o f 100-175\u00C2\u00B0C. They r e p o r t e d t h a t MoS 2 c o u l d l e a c h under moderate p r e s s u r e s o f oxygen (100-200 p . s . i . ) - The o v e r a l l r e a c t i o n b e i n g : MoS 2 + | 0 2 + 6 OH\" \u00E2\u0080\u00A2> Mo0 4 = + 2 S0.f + 3 H 2 0 (1) The end p r o d u c t s a f t e r complete o x i d a t i o n were MoOiT and S0iT~ i o n s . The p r e s e n c e o f S 2 0 3 ~ was d e t e c t e d o n l y as an i n t e r m e d i a t e u n s t a b l e s p e c i e s . G. Monev and S. M i r e v a [13] i n 1958 made t h e f i r s t a t t e m p t s t o e x t r a c t Mo from poor copper-molybdenum c o n c e n t r a t e s and o r e s u s i n g NaOCl s o l u t i o n s . H. Cox and A.K: S e h e l l i n g e r [8] i n 1958 s t u d i e d t h e l e a c h i n g o f Mo from low grade o r e s , c o p p e r c o n c e n t r a t e s and h i g h grade m o l y b d e n i t e c o n c e n t r a t e s u s i n g NaOCl. A l t h o u g h t h e y o b t a i n e d e x c e l l e n t e x t r a c t i o n s l ow g r a d e m o l y b d e n u m o r e ( 0 . 0 1 5 $ M o S 2 ) R e c o v e r y = 9 3 . 3 $ c o p p e r c o n c e n t r a t e ( 1 . 0 5 $ M o S 2 ) \" = 9 0 . 6 $ H i g h g r a d e m o l y b d e n u m c o n c e n t r a t e ( 9 9 . 9 $ MoS 2 .) \" = 9 9 . 9 $ t h e y d i d n o t p e r f o r m a s y s t e m a t i c s t u d y o f the v a r i a b l e s t h a t a f f e c t t h e r a t e o f o x i d a t i o n . The b e s t c o n d i t i o n s t h e y recommended f o r l e a c h i n g were: 3% NaOCl s o l u t i o n , room t e m p e r a t u r e and 30 m i n u t e s l e a c h i n g t i m e . The e q u a t i o n s u g g e s t e d by t h e s e i n v e s t i g a t o r s was: 7 Na 0C1 + MoS 2 + 4e\" + MoO^ + S 2 0 3 \" + 7 NaCl (2) 12 K.V. Ioardanov and A.N. Z e l i k m a n [14] made an e x t e n s i v e s t u d y o f the p h y s i c o - c h e m i c a l bases o f the o x i d a t i o n o f MoS 2 i n NaOCl s o l u t i o n s . They used pure MoS 2 p r e s s e d i n t o compact samples and f i n e l y ground m a t e r i a l . They assumed MoS 2 was o x i d i z e d a c c o r d i n g t o t h e r e a c t i o n : MoS 2 + 9 NaOCl + 6 NaOH -> Na 2 Mo0\u00E2\u0080\u009E + 2 N a 2 S 0 4 + 9 NaCl + 3 H 20 (3) The c o n c l u s i o n s r e a c h e d i n t h e i r s t u d y were: a ) T h e r a t e o f o x i d a t i o n i n c r e a s e s w i t h a n i n c r e a s e i n t e m p e r a t u r e a n d t h a t t h e r e a c t i o n i s d i f f u -s i o n c o n t r o l l e d . b) T h e r a t e i s d i r e c t l y p r o p o r t i o n a l t o t h e i n i t i a l c o n c e n t r a t i o n o f N a O C l . They proposed a mechanism f o r t h e o x i d a t i o n o f MoS 2. The f i r s t s t a g e i s the a d s o r p t i o n o f 0C1 i o n s on t h e s u r f a c e o f t h e MoS 2, th e second s t a g e i s the i n t e r a c t i o n o f the ad s o r b e d O C l\" and t h e s o l i d t o form an a c t i v e complex OCl ( s o l n ) \u00C2\u00AB- OCl (ads) (4) MoS 2 ( s o l i d ) + O C l ( a d s ) + |MoS2 + \u00E2\u0080\u00A2\u00E2\u0080\u00A2\u00E2\u0080\u00A2 + OCl\"] a c t i v e complex (5) Then t he f o r m a t i o n o f r e a c t i o n p r o d u c t s , oxygen r e p l a c i n g s u l f u r atoms and f o r m i n g i n t e r m e d i a t e compounds and c h l o r i d e i o n s . |MoS2 + ... + O C l - ] a c t > c o m p l e x + OCr + [ M O S 2 0 + + O C l - ] a c t > c o m p l e x + cr | M o S 2 0 + + O C T a c t > c o m p l e i ( + O C T -[MoS0 2 + -.. + O C T - | a 9 t . complex + C 1 \" + 5 [ M o S 0 2 + + 0 C l - ] a c t _ c o m p l e x + O C l \" -|Mo03 + \u00E2\u0080\u00A2*\u00E2\u0080\u00A2 + OCT\"] + C l \" + S [ M 0 O 3 + \u00E2\u0080\u00A2\u00E2\u0080\u00A2\u00E2\u0080\u00A2 + O C l \" ] 2 M 0 O 3 + O C l ~ and f i n a l l y M 0 O 3 + 2 OH~ ^ MOOL>= + H 20 The s u l f u r atoms a r e o x i d i z e d by O C l \" , a c c o r d i n g t o t h e r e a c t i o n s 2 S + 2 O C l \" 2 S 2 0 2 = + 2 C l \" 14 S 2 0 2 + 0C1 -\u00C2\u00AB- S 2 0 3 + C l (12) 3 OC1 ^ 2 SOk + 3C1 + H 20 (13) In an i n d e p e n d e n t s t u d y R.B. Bhappu et al. [6] d e t e r m i n e d t h a t t h e c o r r e c t m o l ar r a t i o between NaOCl and MoS 2, when the NaOCl i s i n excess, i s 9:1. They showed t h a t i f s u l f u r was formed d u r i n g t h e l e a c h i n g p r o c e s s by the e x c e s s o f OCT p r e s e n t such as would be t h e c a s e i n l e a c h i n g low gr a d e m a t e r i a l s would o x i d i z e i t t o SOi* as f o l l o w s : t h e r e f o r e i f OCT i s i n e x c e s s t h e o n l y s u l f u r s p e c i e s p r e s e n t i s SO^ -. By combining r e a c t i o n s (14) and (15) t h e y s u g g e s t e d t h e o v e r a l l r e a c t i o n i d e n t i c a l t o the one used by K.V. Ioardanov and A.N. Z e l i k m a n [ 1 4 ] , which a l s o a g r e e s w i t h t h e s t o i c h i o m e t r y o f the o x i d a t i o n o f MoS 2 i n aqueous K0H-0 2 systems [ 7 ] . R.B. Bhappu et al. [ 6 ] a l s o r e p o r t e d t h a t : a ) T h e r e i s p r a c t i c a l l y no c o n s u m p t i o n o f NaOC l by g a n g u e m a t e r i a l s ( q u a r t z a n d a p l i t e i n t h e i r e x p e r i m e n t s ) . b) T h e r e i s a d e c r e a s e i n t h e l e a c h i n g r a t e s b o t h i n c o n c e n t r a t e s a n d l a r g e r s p e c i m e n s o f 6 0C1 + MoS2 + 4 OH HoOk + S\u00C2\u00B0 + S0h + 6 C l \" + 2H 20 (14) 3 OCT + S\u00C2\u00B0 + H 20 1 SO^ + 3C1\" + 2H (15) 15 M o S 2 w h i c h t h e y a t t r i b u t e d t o d i s s o l u t i o n o f f i n e r p a r t i c l e s i n t h e f i r s t c a s e a n d t o c o n -c e n t r a t i o n p h e n o m e n a i n t h e s e c o n d . c ) Due t o e c o n o m i c c o n s i d e r a t i o n s i t was n e c e s s a r y t o p r o d u c e t h e NaOC l i n s i t u e i t h e r by c o m b i n i n g p u r c h a s e d c a u s t i c s o d a a n d c h l o r i n e o r by e l e c t r o l y s i s o f N a C I . F o r t h i s s e c o n d s y s t e m t h e y s u g g e s t e d t h e r e c y c l i n g o f l e a c h s o l u t i o n i n o r d e r t o r e u s e t h e NaCI p r o d u c e d i n r e a c t i o n \u00C2\u00A33), . K.A. S h a p i r o and B.B. Kulakeva [15] a p p l i e d NaOCl d i g e s t i o n t o l e a n i n t e r m e d i a t e p r o d u c t s c o n t a i n i n g 2-6% Mo formed i n t h e c o n c e n t r a t i o n o f d i s s e m i n a t e d o r e . No i n d i c a t i o n was g i v e n as t o t h e o t h e r m i n e r a l s i n t h o s e i n t e r m e d i a t e p r o d u c t s . They r e p o r t e d h a v i n g t o consume 400 and 500% t h e s t o i c h i o m e t r i c amount o f NaOCl f o r complete e x t r a c t i o n o f Mo. No e x p l a n a t i o n was g i v e n o f the cause* o f t h i s e x c e s s consumption. R.B. Bhappu et al. [16,17] s t u d i e d t h e d i s s o l u t i o n o f MoS 2 u s i n g s e v e r a l o x i d i z i n g a g e n t s ; NaOCl, ozone, o x y g e n - a l k a l i ; a c i d perman-g a n a t e , p e r s u l f a t e , a c i d - f e r r i c c h l o r i d e , n i t r i c a c i d , c h l o r i n e d i o x i d e , a c i d - c h l o r a t e , manganese d i o x i d e - s u l f u r i c a c i d and b a c t e r i a l l e a c h i n g . They r e p o r t e d t h a t NaOCl i n b a s i c s o l u t i o n s p r e s e n t e d t h e f a s t e s t r a t e o f l e a c h i n g and h i g h s e l e c t i v i t y towards MoS 2. The d i s a d v a n t a g e s i n d i c a t e d were i t s h i g h p r o d u c t i o n c o s t s , i t s i n s t a b i l i t y and i t s t r o u b l e -some r e g e n e r a t i o n . A c i d - N a C 1 0 3 a l s o l e a c h e s MoS 2 but n o t as f a s t as NaOCl. In com p a r i s o n NaC10 3 i s l e s s e x p e n s i v e and e a s i e r t o r e g e n e r a t e than NaOCl., but i s not as s e l e c t i v e . B . J . S c h e i n e r and R.E. L i n d s t r o m [18] i n v e s t i g a t e d t h e p o s s i b l i t y o f l e a c h i n g MoS 2 from low grade o r e s by an e l e c t r o o x i d a t i o n t e c h n i q u e t h a t c o n s i s t s o f g e n e r a t i n g NaOCl i n s i t u by e l e c t r o l y s i s o f a b r i n e - o r e s l u r r y . 16 T h i s method had been p r e v i o u s l y used i n t r e a t i n g c a r b o n a c e o u s g o l d o r e s [19,20] and f o r r e c o v e r i n g mercury from c i n n a b a r o r e s [ 2 1 ] . They c l a i m e d a 90-99% e x t r a c t i o n o f molybdenum, good s e l e c -t i v i t y o f Mo o v e r Cu and a power consumption o f 16-24 kwh/lb o f Mo e x t r a c t e d from a low grade MoS 2 o r e . However i n a r e c e n t p u b l i s t i o n D.S. B a r r et al. [22] i n d i c a t e d t h a t the p r o d u c t i o n o f b y p r o d u c t NaC10 3 d u r i n g the e l e c t r o o x i d a t i o n , i n t e r f e r e s w i t h t h e r e c o v e r y o f molybdenum and c o n s e q u e n t l y h i n d e r s t h e economics o f the p r o c e s s . To m i n i m i z e NaC10 3 p r o d u c t i o n t h e s e a u t h o r s s u g g e s t e d l e a c h i n g a t a low pH (4.0-5.0) and low t e m p e r a t u r e (<30\u00C2\u00B0C). The use o f NaOCl as an o x i d i z i n g - l e a c h i n g r e a g e n t has a l s o been r e p o r t e d f o r s t i b n i t e [ 2 3 ] , s p h a l e r i t e [24] and c h a l c o p y r i t e [ 2 5 ] . D. Stump and Y. Berube [26] c l a i m e d t h a t t h e o x i d a t i o n r a t e s o f c h a l c o p y r i t e and m o l y b d e n i t e i n an a l k a l i n e medium a r e s i m i l a r and t h a t i t i s u n l i k e l y t h a t s e l e c t i v e l e a c h i n g o f molybdenum from c o p p e r con-c e n t r a t e s c o u l d be a c c o m p l i s h e d . C h a p t e r 2 SCOPE OF PRESENT INVESTIGATION The r e s e a r c h r e p o r t e d i n t h i s t h e s i s i s p r i m a r i l y aimed a t s t u d y i n g t h e p o s s i b i l i t i e s o f e x t r a c t i n g molybdenum from low g r a d e - c o p p e r s u l f i d e c o n t a i n i n g m a t e r i a l s by a d i r e c t l e a c h i n g o p e r a t i o n u s i n g sodium h y p o c h l o r i t e as r e a g e n t . The p r e v i o u s work on t h i s s u b j e c t s u g g e s t e d t h a t a p h y s i c o -c h e m i c a l s t u d y was r e q u i r e d i n o r d e r t o d e t e r m i n e t h e f a c t o r s t h a t govern t he o x i d a t i o n and d i s s o l u t i o n o f MoS 2 i n s o l u t i o n s o f NaOCl. The v a r i a b l e s s e l e c t e d f o r s t u d y were: a g i t a t i o n r a t e , t e m p e r a t u r e , pH, NaOCl c o n c e n t r a t i o n , s u r f a c e a r e a , n e u t r a l s a l t s , C 1 0 2~ and C10 3~ a d d i t i o n . A c o m p a r a t i v e s t u d y was made f o r l e a c h i n g r a t e s and t o t a l l e a c h i n g time between C u F e S 2 and MoS 2 under i d e n t i c a l e x p e r i m e n t a l con-d i t i o n s t o d e t e r m i n e i f s e l e c t i v e l e a c h i n g u s i n g NaOCl was p o s s i b l e . T h i s b e i n g s a t i s f a c t o r y i t was i n t e n d e d t o d e s i g n a s i m p l e f l o w s h e e t which would d e s c r i b e t h e p r a c t i c a l a p p l i c a t i o n o f t h i s t e c h n i q u e and a t th e same ti m e p r o v i d e a p r e l i m i n a r y economic b a s i s on which t o j u d g e t h e f e a s i b i l i t y o f the p r o c e s s . As a l r e a d y o u t l i n e d , p r e v i o u s workers had e s t a b l i s h e d t h e r e q u i r e m e n t o f p r o d u c i n g NaOCl i n - s i t u t o r e n d e r t h e p r o c e s s e c o n o m i c a l l y 17 18 competent, t h e r e f o r e t h e s e l e c t i o n o f a d i r e c t NaOCl l e a c h f o r o u r s t u d y , i n s t e a d o f a s i m u l t a n e o u s e l e c t r o o x i d a t i o n p r o c e d u r e , meant t h a t a v a i l a b l e d a t a on NaOCl g e n e r a t i n g systems would have t o be c o l l e c t e d . A n o t h e r s p e c i f i c o b j e c t i v e was t o e s t a b l i s h i f s o l u t i o n s o f NaOCl were s t a b l e under l e a c h i n g c o n d i t i o n s and i f any o f t h e m a t e r i a l s used o r p r o d u c t s o f r e a c t i o n formed c o u l d c a t a l y z e t h e d e c o m p o s i t i o n o f t h i s r e a g e n t . C h a p t e r 3 EXPERIMENTAL The e x p e r i m e n t a l work can be d i v i d e d i n t o f o u r s e c t i o n s : A. D e t e r m i n a t i o n o f t h e k i n e t i c s o f d i s s o l u t i o n o f m o l y b d e n i t e and c h a l c o p y r i t e i n NaOCl . s o l u t i o n s . B. Study o f the l e a c h i n g o f m o l y b d e n i t e from r o u g h e r c o p p e r c o n c e n t r a t e s . C. D e t e r m i n a t i o n o f the f l o t a t i o n c h a r a c t e r i s t i c s o f l e a c h e d r o u g h e r c o n c e n t r a t e s . D. E s t a b l i s h m e n t o f the s t a b i l i t y o f NaOCl s o l u t i o n s and f a c t o r s t h a t cause i t s d e c o m p o s i t i o n . 3.1 M a t e r i a l s a. M o l y b d e n i t e With a few e x c e p t i o n s , m o l y b d e n i t e used i n s e c t i o n A c o n s i s t e d o f a c l e a n e d m o l y b d e n i t e c o n c e n t r a t e (Brenda M i n e s ) . The c h e m i c a l a n a l y s i s o f t h e MoS 2 c o n c e n t r a t e i s g i v e n i n T a b l e 4. To p r e p a r e t h i s m a t e r i a l , t h e c o a r s e s t p a r t o f the MoS 2 c o n c e n t r a t e was s e p a r a t e d , washed i n a c e t o n e t o remove t h e o r g a n i c r e a g e n t s l e f t from t h e f l o t a t i o n o p e r a -t i o n , d r y e d a t 80\u00C2\u00B0C and wet s c r e e n e d t o the s i z e -70 + 140 mesh. 19 20 T a b l e 4 Chemical A n a l y s i s o f M o l y b d e n i t e C o n c e n t r a t e Element Weight % Element Weight % T o t a l Molybdenum 52.57 Lead 0.02 Molybdenum ( o x i d e ) Mo0 3 0.099 I r o n 0.90 S u l f u r 37.37 C a l c i u m 0.19 Copper 0.59 Alumin a 0.65 S i 0 2 3.80 X-ray D i f f r a c t i o n P a t t e r n o f t h e M o l y b d e n i t e C o n c e n t r a t e o I/I i -- S p e c i e s I n d e n t i f i e d L i n e dA MoS 2 C u F e S 2 Mg 3 S n O i o ( O H ) 2 1 9.35 100 2 6.75 u n i d e n t i f i e d 3 6.18 100 4 4.67 30 5 3.11 80 6 3.06 100 7 2.73 10 8 2.60 30 9 2.72 20 10 2.05 20 11 1.86 80 12 1.82 25 13 1.54 60 80 14 1.34 20 15 1.23 5 16 1.08 30 17 1.03 20 Large specimens o f MoS 2 were p u r c h a s e d from David-New M i n e r a l s Providence, Utah and c o n s i s t e d o f l e a f y f ragments a d h e r i n g t o q u a r t z r o c k from which t h e y were e a s i l y s e p a r a t e d and i n some e x p e r i m e n t s ground t o f i n e powder o f c o m p o s i t i o n 99.8% MoS 2. 21 b. Copper Rougher C o n c e n t r a t e T h i s m a t e r i a l was s u p p l i e d by P l a c e r Development Inc. and was o b t a i n e d from the normal o u t p u t o f t h e r o u g h e r f l o t a t i o n o p e r a t i o n a t G i b r a l t a r ( B . C . ) . Chemical and x - r a y a n a l y s i s a r e p r e s e n t e d i n T a b l e 5. T a b l e 5(a) Chemical C o m p o s i t i o n o f Copper Rougher C o n c e n t r a t e T o t a l Copper 12.40% Molybdenum 9.3 % \" S u l f u r 21.89% I r o n 32.29% \" CaO 0.21% T a b l e 5(b) X-ray D i f f r a c t i o n P a t t e r n o f the Rougher C o n c e n t r a t e L i n e o dA I/I i - S p e c i e s I d e n t i f i e d C u F e S 2 F e S 2 1 3.43 40 2 3.40 u n i d e n t i f i e d 3 3.03 100 4 2.70 100 5 2.42 25 6 2.31 20 7 1.91 15 8 1.87 40 9 1.85 70 10 1.75 40 11 1.59 40 60 12 1.50 5 13 1.07 u n i d e n t i f i e d 22 c. C h a l c o p y r i t e The p a r t i c u l a t e m a t e r i a l was a Phoenix c o n c e n t r a t e c o n s i s t i n g a l m o s t e n t i r e l y o f c h a l c o p y r i t e . No p r e p a r a t i o n t r e a t m e n t was r e q u i r e d . Some e x p e r i m e n t s i n v o l v e d u s i n g m a s s i v e c h a l c o p y r i t e f o r which samples were c u t and mounted i n Quik-mount and then p o l i s h e d . d. Sodium H y p o c h l o r i t e The sodium h y p o c h l o r i t e used i n a l l e x p e r i m e n t s was s u p p l i e d by Chernetics I n t e r n a t i o n a l and was produced i n an e x p e r i m e n t a l membrane t y p e h y p o c h l o r i t e g e n e r a t o r . The v a r i o u s b a t c h e s o b t a i n e d v a r i e d o v e r a wide range o f c o n c e n t r a t i o n s o f both NaOCl and NaCI. In a l l c a s e s t h e pH was o v e r 12. 3. O t h e r M a t e r i a l s A l l o t h e r c h e m i c a l s used were r e a g e n t grade q u a l i t y . 3.2 A p p a r a t u s A l l d i s s o l u t i o n e x p e r i m e n t s were done i n a 1 I. g l a s s v e s s e l e q u i p p e d w i t h f o u r T e f l o n b a f f l e s f i x e d t o t h e w a l l o f the r e a c t o r a t e q u a l s p a c i n g s . A g i t a t i o n was p r o v i d e d by a f o u r b l a d e r a d i a l f l o w t u r b i n e . Both v e s s e l and a g i t a t o r d i m e n s i o n s were d e t e r m i n e d u s i n g g e o m e t r i c a l r e l a t i o n s t h a t c o r r e s p o n d t o S t a n d a r d Tank C o n f i g u r a t i o n [ 2 7 ] . S t i r r i n g r a t e was c o n t r o l l e d w i t h a F i s h e r Dyna-Mix. The v e l o c i t y o f t h e t u r b i n e was measured u s i n g a T e c l o c k hand tachometer. 23 Temperature u n i f o r m i t y was o b t a i n e d by p l a c i n g t h e r e a c t o r i n a water bath heated e l e c t r i c a l l y and c o n t r o l l e d by a Thermistemp YSI Model 71 t e m p e r a t u r e c o n t r o l l e r . The t e m p e r a t u r e was m a i n t a i n e d w i t h i n \u00C2\u00B10.5\u00C2\u00B0C o f the r e q u i r e d v a l u e . 3.3 P r o c e d u r e E x p e r i m e n t s i n s e c t i o n s A.and B were done i n t h e f o l l o w i n g way: A r e q u i r e d volume o f c o n c e n t r a t e d s t o c k NaOCl was added t o a p p r o x i m a t e l y 800 ml o f H 20 and t h e pH lowered t o t h e r e q u i r e d v a l u e f o r t h e p a r t i c u l a r e x p e r i m e n t . A weighed amount o f b u f f e r components (Na 2C0 3/NaHC0 3) was i n t r o d u c e d and t h e s o l u t i o n made up t o 1000 ml. The NaOCl s o l u t i o n was t r a n s f e r r e d t o the r e a c t o r and i n t r o -duced i n t h e wa t e r b a t h , slow a g i t a t i o n was i n d u c e d u n t i l t h e r e a g e n t r e a c h e d t h e e x p e r i m e n t t e m p e r a t u r e . A t t h i s t ime a g i t a t i o n was i n c r e a s e d , the f i r s t sample e x t r a c t e d f o r NaOCl a n a l y s i s and b l a n k s f o r molybdenum and copper a n a l y s i s . , t h e MoS 2 sample t o be l e a c h e d i n t r o d u c e d and t h e chronometer s t a r t e d . Samples were withdrawn from t he r e a c t o r w i t h a p i p e t t e and f i l t e r e d u s i n g a f r i t t e d g l a s s tube o r a f i l t e r paper. The pH was measured u s i n g an Expandomatic pH-meter. For t h e c o m p a r a t i v e l e a c h i n g e x p e r i m e n t s w i t h c h a l c o p y r i t e and m o l y b d e n i t e , both m i n e r a l s were wet s c r e e n e d t o a s i z e f r a c t i o n -140 + 200 mesh and examined m i c r o s c o p i c a l l y t o d e t e r m i n e t h e i r shape and s u r f a c e c o n d i t i o n s . Based on t h i s i n f o r m a t i o n a shape f a c t o r was s e l e c t e d and u s i n g a nomogram f o r t he D e t e r m i n a t i o n o f S p e c i f i c S u r f a c e s [28] t h e i r s u r f a c e a r e a was d e t e r m i n e d . 24 E x p e r i m e n t s i n s e c t i o n C were done a t P l a c e r Development and c o n s i s t e d o f s t a n d a r d f l o t a t i o n t e s t s on samples o f l e a c h e d r o u g h e r con-c e n t r a t e s t o d e t e r m i n e t h e i r f l o t a b i l i t y and r e a g e n t consumption. 3.4 Ch e m i c a l A n a l y s i s a. Molybdenum Molybdenum was d e t e r m i n e d by a c o l o r i m e t r i c method [29] u s i n g the brown-red H 2 Mo02(CNS) 3 complex. The o p t i c a l d e n s i t y was measured u s i n g a Beckman Model B S p e c t r o p h o t o m e t e r s e t a t a w a v e l e n g t h o f 460 my. The c o n c e n t r a t i o n o f Mo was r e a d d i r e c t l y f r o m a c a l i b r a t i o n c u r v e p r e p a r e d by u s i n g s t a n d a r d molybdenum s o l u t i o n s . When copper b e a r i n g m a t e r i a l s were l e a c h e d s i m u l t a n e o u s l y t he a n a l y s i s o f molybdenum was done by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y u s i n g a wa v e l e n g t h o f 313.3 nm. To overcome any i n t e r f e r e n c e sample s o l u t i o n s were made up t o be 10% i n aluminum c h l o r i d e and 5% i n ammonium c h l o r i d e . b. Copper Copper i n l e a c h i n g s o l u t i o n s was d e t e r m i n e d by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y u s i n g t he l i n e o f wa v e l e n g t h 324.7 nm. In a n a l y z i n g s o l i d m a t e r i a l s t h e d e t e r m i n a t i o n o f c o p p e r was done e l e c t r o g r a v i m e t r i c a l l y i n which c a s e t h e i n t e r f e r e n c e o f molybdenum was n u l l i f i e d by a r e d o p o s i -t i o n o f c o p p e r . The d i s s o l u t i o n o f m o l y b d e n i t e , c h a l c o p y r i t e and c o p p e r r o u g h e r c o n c e n t r a t e s f o r t h e purpose o f a n a l y s i s , was found t o be com p l e t e 25 f o l l o w i n g t r e a t m e n t w i t h a m i x t u r e o f c o n c e n t r a t e d n i t r i c a c i d and p o t a s s i u m c h l o r a t e a t low t e m p e r a t u r e . . c. Sodium H y p o c h l o r i t e D e t e r m i n a t i o n o f sodium h y p o c h l o r i t e was done u s i n g the KI-T h i o s u l f a t e method a c c o r d i n g t o ASTM-D-62-T [ 3 0 ] . P o t a s s i u m i o d i d e was added i n e x c e s s t o an a c i d i f i e d sample and t h e h y p o c h l o r i t e i m m e d i a t e l y t i t r a t e d u s i n g a 0.1 N N a 2 S 2 0 3 s o l u t i o n u n t i l t h e d i s a p p e a r a n c e o f t h e s t a r c h b l u e c o l o u r as e n d - p o i n t . T h i s method does not d i f f e r e n t i a t e between ( i n - i o n i z e d NaOCl and i o n i z e d h y p o c h l o r i t e O C l \" , nor c h l o r i n e d i o x i d e C 1 0 2 . T h e r e f o r e a p o t e n t i o m e t r i c method was used f o r some e x p e r i m e n t s t h a t r e q u i r e d more p r e c i s e d a t a . T h i s method [31] i s based on d i f f e r e n t r e d u c i n g r a t e s o f h y p o c h l o r i t e , and c h l o r i t e by a r s e n i t e . The r e a c t i o n w i t h c h l o r i t e i s slow and may be d e l i b e r a t e l y a c c e l e r a t e d by a d d i t i o n o f OsO.* which works as a c a t a l y s t . C h l o r a t e i s d e t e r m i n e d on the same sample by b r o m a t o m e t r i c t i t r a t i o n and c h l o r i d e may be t i t r a t e d u s i n g AgN0 3. I t was t h e r e f o r e p o s s i b l e t o d e t e r m i n e t h e c o n c e n t r a t i o n o f O C l _ + HC10 by h o l d i n g the sample o f pH 12 and then d r o p p i n g the pH t o 8.5 t o d e t e r m i n e t h e c o n c e n t r a t i o n o f C 1 0 2 . C h a p t e r 4 RESULTS AND OBSERVATIONS 4.1 O x i d a t i o n o f M o l y b d e n i t e by Sodium H y p o c h l o r i t e 4.1.1 R e p r o d u c i b i l i t y The f a c t o r s t h a t c o u l d a f f e c t t h e r e p r o d u c i b i l i t y were: a ) R e a c t i v i t y o f r e a c t o r m a t e r i a l t o NaOC l s o l u t i o n s . b ) A n a l y t i c a l p r o c e d u r e s f o r Mo a n d N a O C l . To t e s t i f any o f t h e r e a c t o r m a t e r i a l s ( b a f f l e s o f T e f l o n and T i s t i r r e r c o v e r e d w i t h a f i l m o f M i c r o s t o p ) r e a c t e d w i t h NaOCl a run was made o f 40\u00C2\u00B0C u s i n g a s o l u t i o n w i t h an i n i t i a l c o n c e n t r a t i o n o f 5 g/1 b u f f e r e d a t pH 9.3. Four samples were removed e v e r y 30 m i n u t e s and a n a l y z e d f o r NaOCl. The c o n c e n t r a t i o n o f NaOCl remained c o n s t a n t d u r i n g t h e e n t i r e run i n d i c a t i n g t h a t t h e m a t e r i a l s used n e i t h e r r e a c t n o r c a t a l y t i c a l l y decompose t h e r e a g e n t . The c o n s i s t e n c y o f sample e x t r a c t i o n and a n a l y s i s were t e s t e d by r u n n i n g two e x p e r i m e n t s under i d e n t i c a l c o n d i t i o n s . The m o l y b d e n i t e used i n t h e s e e x p e r i m e n t s was t h e pure m a t e r i a l o b t a i n e d by g r i n d i n g the m a s s i v e specimens. The r e s u l t s o f Mo d i s s o l u t i o n and NaOCl consumption a r e shown i n F i g u r e 2 showing good agreement f o r both r u n s . 26 o o run I * * run 2 5 8 10 TIME (min) 15 FIG- 2 - REPRODUCIBILITY OF THE RESULTS FOR THE LEACHING OF MOLYBDENITE PARTICLES. 28 4.1.2 E f f e c t o f S t i r r i n g Rate I t was e s t a b l i s h e d i n p r e l i m i n a r y e x p e r i m e n t s t h a t t h e r a t e o f r e a c t i o n between MoS 2. and NaOCl s o l u t i o n s was dependent on t h e a g i t a t i o n . F i n a l l y a b a f f l e d v e s s e l was made and e x p e r i m e n t s were c a r r i e d o u t v a r y i n g t h e r a t e o f t h e t u r b i n e a g i t a t o r w h i l e m a i n t a i n i n g c o n s t a n t t h e o t h e r v a r i a b l e s . Runs were made a d d i n g 0.3 g o f MoS 2 c o n c e n t r a t e t o 1000 ml o f a s o l u t i o n c o n t a i n i n g 5.1 g/1 o f NaOCl b u f f e r e d a t pH 9.6 by a 0.1 N Na 2C0 3-0.1 N NaHC0 3 s o l u t i o n . The t e m p e r a t u r e o f a l l e x p e r i m e n t s was 35\u00C2\u00B0C \u00C2\u00B1 0.5\u00C2\u00B0C. R e s u l t s o f t h e e x t r a c t i o n r a t e s o f molybdenum i n t o s o l u t i o n a r e p r e s e n t e d i n F i g u r e 3 f o r 5 a g i t a t i o n s peeds. I t was c o n c l u d e d from the above r e s u l t s t h a t t h e r e a c t i o n r a t e was ind e p e n d e n t o f s t i r r i n g above 750 rpm ( F i g u r e 4 ) . 4.1.3 E f f e c t o f Temperature The r e a c t i o n was s t u d i e d o v e r t h e t e m p e r a t u r e range 9-70\u00C2\u00B0C. The e x p e r i m e n t a l c o n d i t i o n s f o r t h e s e t e s t s were: pH o f b u f f e r e d s o l u t i o n = 9; s t i r r i n g r a t e = 780 r.p.m. C o n c e n t r a t i o n .of NaOCl = 8 . 3 5 g/1; amount o f MoS 2 c o n c e n t r a t e added = 0.3g. The e x t r a c t i o n c u r v e s a r e p r e s e n t e d i n \ F i g u r e 5. An A r r h e n i u s p l o t t a k e n f o r a c o n c e n t r a t i o n o f 15 mg/1 Mo was c o n s t r u c t e d . The s l o p e o f t h i s l i n e ( F i g u r e 6) was found t o be l i n e a r o v e r t h e e n t i r e t e m p e r a t u r e range, and t h e e x p e r i m e n t a l a c t i v a t i o n e n e r g y was c a l c u l a t e d t o be 6.3 \u00C2\u00B1 0.8 k c a l / m o l e . 29 5 10 15 20 TIME (MIN) FIG-3- EFFECT OF AGITATION ON THE RATE OF OXIDATION-30 w , 1 1 1 5 6 7 8 RPM x 100 FIG- 4- EFFECT OF AGITATION ON THE RATE OF OXIDATION OF MOLYBDENITE-31 FIG. 5 - EFFECT OF TEMPERATURE ON THE OXIDATION OF MOLYBDENITE . 32 1.2 2.9 3.1 33 35 l/T(\u00C2\u00B0K) x IOOO FIG. 6 - ARRHENIUS PLOT OF TEMPERATURE DATA. 33 T h i s v a l u e f o r t h e a c t i v a t i o n energy i s i n good agreement w i t h t h e e x p e r i m e n t s done by Ioardanov and Z e l i k m a n [14] u s i n g compressed MoS 2 powder specimens i n the t e m p e r a t u r e range 20-80\u00C2\u00B0C g i v i n g a v a l u e o f 5.25 k c a l / m o l e . 4.1.4 E f f e c t o f S u r f a c e A r e a Two e x p e r i m e n t s were done v a r y i n g t h e amount o f MoS 2 p a r t i c l e s o n l y and m a i n t a i n i n g c o n s t a n t t h e o t h e r p a r a m e t e r s . As shown i n F i g u r e 7 t h e r a t e o f e x t r a c t i o n o f m o l y b d e n i t e was found t o v a r y d i r e c t l y w i t h t h e s u r f a c e a r e a . T h i s i n d i c a t e s t h a t t h e r a t e o f l e a c h i n g i s c o n t r o l l e d by a heterogeneous r e a c t i o n on t h e s u r f a c e o f t h e MoS 2 o r by d i f f u s i o n o f t h e h y p o c h l o r i t e o r molybdate i o n s t h r o u g h t h e s o l u t i o n boundary l a y e r on t h e s u r f a c e o f t h e MoS 2. 4.1.5 MoS 2 C r y s t a l i n i t y and S u r f a c e C h a r a c t e r i s t i c s L e a c h i n g o f MoS 2 p a r t i c l e s would be e x p e c t e d t o be a n i s o t r o p i c s i n c e t h e y c o n s i s t o f a l a y e r e d s t r u c t u r e ( F i g u r e 8 ) . In each l a y e r Mo(IV) atoms a r e s u r r o u n d e d by s i x S atoms f o r m i n g a t r i a n g u l a r p r i s m c o n f i g u r a t i o n s h a r i n g v e r t i c a l edges w i t h one a n o t h e r t o form S-Mo-S p l a n e s normal t o the c - a x i s . The r e p e t i t i o n o f t h e s e complete l a y e r s a c c o r d i n g t o r e q u i r e m e n t s o f hexagonal c l o s e p a c k i n g r e s u l t s i n a MoS 2 c r y s t a l ( F i g u r e 9 ) . The bonding w i t h i n each l a y e r i s about 80% c o v a l e n t and t h e m e t a l l i c l u s t e r i t has, i s a t t r i b u t e d t o some m e t a l l i c bonding [ 3 2 ] . 34 NoOCI = 5 g/l T= 30\u00C2\u00B0 C pH= 8.5 \u00C2\u00A3 Q UJ I-O < or X U J 200} I0C4 0.6 g. \u00E2\u0080\u00A2 \u00E2\u0080\u0094 0.3 g. TIME (min) FIG. 7 - EFFECT OF SURFACE AREA ON THE RATE OF OXIDATION OF MOLYBDENITE. 35 FIG. 9 - MOLYBDENITE STRUCTURE 37 The l a y e r s a r e h e l d t o g e t h e r by Van der-Waal bonds y i e l d i n g l a r g e S-S i n t e r l a y e r d i s t a n c e s and p e r m i t t i n g t h e d i s t i n c t i v e c l e a v a g e a l o n g t h e (0001) p l a n e . T h e r e f o r e MoS 2 p a r t i c l e s have two t y p e s o f s u r f a c e s each w i t h d i f f e r e n t c h e m i c a l a c t i v i t y . Those formed from r u p t u r e o f Van der-Waal bonds a r e c a l l e d \" f a c e s \" . t h e y a r e h y d r o p h o b i c and a r e c o n s i d e r e d i n a c t i v e and t h e ones formed from b r e a k i n g S-Mo c o v a l e n t bonds, c a l l e d edges, which a r e h y d r o p h i l i c and c h e m i c a l l y a c t i v e . However e x a m i n a t i o n o f t h e \" f a c e s \" o f a r e c e n t l y c l e a v e d MoS 2 p a r t i c l e w i t h t h e S.E.M. r e v e a l s a s u r f a c e which has m u l t i p l e s t e p l i k e hexagonal p i t s as shown i n F i g u r e 10, i n d i c a t i n g t h a t t h e \" a c t i v e \" s u r f a c e which can c o n t r i b u t e t o l e a c h i n g i s much g r e a t e r than t h e s u r r o u n d i n g \"edge\" s u r f a c e o f t h e p a r t i c l e s . 4.1.6 Morphology o f MoS 2 L e a c h i n g C o a r s e m o l y b d e n i t e c o n c e n t r a t e (-70 + 140 mesh) was l e a c h e d a t room t e m p e r a t u r e (26\u00C2\u00B0C) i n a s o l u t i o n o f 5 g/1 NaOCl and s o l i d s were removed a f t e r 5, 10, 15, 20 and 30 m i n u t e s . A comparison between t h e s u r f a c e o f t h e p a r t i c l e s l e a c h e d f o r d i f f e r e n t p e r i o d s i s p r e s e n t e d i n F i g u r e 11. The u n l e a c h e d p a r t i c l e s a r e smooth and do not p r e s e n t t h e p i t s o f a normal MoS 2 p a r t i c l e such as shown i n F i g u r e 10, t h i s i s l i k e l y t o be due t o the g r i n d i n g a c t i o n d u r i n g s i z e r e d u c t i o n . However, i m m e d i a t e l y a f t e r l e a c h i n g b e g i n s t h e appearance o f such a c t i v e s i t e s i s o b s e r v e d and t h e y c o n t r i b u t e l a r g e l y t o t h e r e a c t i o n as can be o b s e r v e d a t a h i g h e r m a g n i f i c a t i o n i n F i g u r e 12. I t can a l s o be o b s e r v e d t h a t a f t e r FIG. 10- VIEW OF THE \"FACE\" SURFACE MoS 2 39 FIG. 12 - MoS 2 PARTICLES AFTER 10 MIN. OF REACTION IN NaOCl . 41 30 minutes o f l e a c h i n g under moderate c o n d i t i o n s o f c o n c e n t r a t i o n and te m p e r a t u r e , MoS 2 p a r t i c l e s have d i s s o l v e d a l m o s t c o m p l e t e l y . The r e a c t i o n o f h y p o c h l o r i t e on MoS 2 o c c u r s t h e r e f o r e n o t o n l y on t h e \"edges\" o f t h e p a r t i c l e s but a l s o on t h e s t e p s o f hexagonal p i t s formed on t h e \" f a c e s \" o f t h e p a r t i c l e s and i s a i d e d by a f r e e f l o w o f r e a g e n t deep i n t o t h e MoS 2 p a r t i c l e s t h r o u g h i n t e r l a y e r s p a c i n g s u c h as can be o b s e r v e d i n F i g u r e 12c. M o l y b d e n i t e may have up t o a p p r o x i m a t e l y 5% Mo0 3 on i t s s u r f a c e due t o d r y o x i d a t i o n . Under a l k a l i n e c o n d i t i o n s o n l y , Mo0 3 and o t h e r non-s t o i c h i o m e t r i c o x i d e s a r e s o l u b l e . I t has been r e p o r t e d [ 3 3 ] t h a t some Mo0 2 may a l s o be p r e s e n t on t h e MoS 2 s u r f a c e i n v e r y s m a l l amounts and i s not s o l u b l e under a l k a l i n e c o n d i t i o n s . 4.1.7 E f f e c t o f NaOCl C o n c e n t r a t i o n on t h e Rates o f Mo E x t r a c t i o n Samples o f m o l y b d e n i t e were l e a c h e d a t 45\u00C2\u00B0C i n s o l u t i o n s o f NaOCl b u f f e r e d w i t h Na 2C0 3-NaHC0 3 a t pH 9 o f d i f f e r e n t i n i t i a l c o n c e n t r a -t i o n s . The e x t r a c t i o n c u r v e s a r e p l o t t e d i n F i g u r e 13 and i n d i c a t e t h a t t h e r e a c t i o n r a t e s i n c r e a s e w i t h h i g h e r i n i t i a l NaOCl c o n c e n t r a t i o n s . A p l o t o f r e a c t i o n r a t e s a t 15 mg / l t Mo a g a i n s t i n i t i a l NaOCT c o n c e n t r a t i o n ( F i g u r e 14) g i v e s a s t r a i g h t l i n e o f s l o p e 2 one i n d i c a t i n g t h a t t h e r e a c t i o n between MoS 2 and NaOCl i s f i r s t o r d e r w i t h r e s p e c t t o sodium h y p o c h l o r i t e . T h i s i s i n agreement w i t h p r e v i o u s work r e p o r t e d by Ioardanov and Z e l i k m a n [14] and Bhappu et al. [ 6 ] . 5 10 15 20 TIME (min) Fl G 13 - EFFECT OF NoOCI CONCENTRATION ON THE OXIDATION OF MOLYBDENITE \u00E2\u0080\u00A2 INITIAL NaOCl CONCENTRATION (g/1) FIG. 14 - PLOT OF REACTION RATES VS. INITIAL HYPOCHLORITE CONCENTRATION . 44 4.1.8 E f f e c t o f pH on the Rate o f R e a c t i o n The e f f e c t o f [ H + ] on the r a t e o f the r e a c t i o n between MoS 2 and NaOCl was s t u d i e d o v e r t h e pH range o f 6.7 t o 12. T h i s range was s e l e c t e d on t h e b a s i s t h a t NaOCl s o l u t i o n s a r e s t o r e d a t a pH o f 12 t o p r e v e n t any d e c o m p o s i t i o n and t h a t t h e y a r e s t a b l e o n l y i n a l k a l i n e s o l u t i o n s . In t h e s e e x p e r i m e n t s t h e pH was m a i n t a i n e d e i t h e r by p r e p a r i n g a b u f f e r s o l u t i o n ( h i g h e r pH's) o r by a d d i n g N a 2 C 0 3 t o t h e s o l u t i o n s a t i n t e r v a l s i n o r d e r t o keep t he s o l u t i o n s w i t h i n a narrow pH r e g i o n . I t was o b s e r v e d t h a t MoS 2 d i s s o l v e s f a s t e r w i t h i n c r e a s i n g pH up t o a p p r o x i m a t e l y pH 8.5 and t h a t t h e r a t e s d e c r e a s e f o r pH's above 10 ( F i g u r e 15). A p l o t o f r e a c t i o n r a t e s a g a i n s t pH o f t h e s o l u t i o n ( F i g u r e 16) i n d i c a t e s a peak between pH 8.3 and 9.8 i n which t he r e a c t i o n r a t e i s a maximum. T h i s o b s e r v a t i o n has n o t been r e p o r t e d by p r e v i o u s w orkers a l t h o u g h t h e same r e g i o n o f pH was s e l e c t e d f o r working p r o b a b l y due t o t h e s t a b i l i t y o f the NaOCl a t t h i s pH. Ioardanov and Z e l i k m a n [ 1 4] r e p o r t e d f i n d i n g no e f f e c t on t h e r a t e o f o x i d a t i o n when the c o n c e n t r a t i o n o f NaOH was above t h e t h e o r e t i c a l l y r e q u i r e d amount. 4.1.9 E f f e c t o f S u l f a t e C o n c e n t r a t i o n on t h e R e a c t i o n Rate When t h e r e i s s u f f i c i e n t h y p o c h l o r i t e a l l t h e s u l f u r i n the MoS 2 w i l l be o x i d i z e d t o S0i+~. T h e r e f o r e t h e e f f e c t o f s u l f a t e on t h e r e a c t i o n r a t e was i n v e s t i g a t e d . 5 10 15 20 TIME (min) FIG. 15 - EFFECT OF pH ON THE RATE OF OXIDATION OF MOLYBDENITE. 46 FIG. 1 6 - PLOT OF REACTION RATES VS. pH. 47 E x p e r i m e n t s were s e t up m a i n t a i n i n g i d e n t i c a l r e a c t i o n c o n d i -t i o n s by a d d i n g an e x c e s s amount o f Na2S04. t o t h e s o l u t i o n b e f o r e i n t r o d u c -i n g the\"MoS 2. Two runs w i t h one and t e n ti m e s t h e s t o i c h i o m e t r i c amount o f SOtr t o be produced a r e compared i n F i g u r e 17 w i t h an e x t r a c t i o n c u r v e n o t c o n t a i n i n g any i n i t i a l SOir \u00E2\u0080\u00A2 The s l i g h t v a r i a t i o n o f r e a c t i o n r a t e s a r e w i t h i n e x p e r i m e n t a l e r r o r and t h e i n c r e a s e i n [SOi^] can be r e g a r d e d as h a v i n g no e f f e c t on t h e r e a c t i o n . S i n c e t h e [ S C \ = ] examined i s much l a r g e r t h a n what would be produced i n a MoS2 l e a c h , i t may be c o n c l u d e d t h a t t h e Na 2S0it formed i n the c o u r s e o f t h e r e a c t i o n i s a l s o w i t h o u t e f f e c t . 4.1.10 E f f e c t o f NaCl on the R e a c t i o n Rate Sodium c h l o r i d e i s always p r e s e n t i n s o l u t i o n s o f NaOCl i n g r e a t e r o r s m a l l e r c o n c e n t r a t i o n s a c c o r d i n g t o the method used t o g e n e r a t e i t , and t h e s a l t u t i l i z a t i o n i f i t i s produced by NaCl e l e c t r o l y s i s . I t i s a l s o formed as a p r o d u c t o f t h e r e a c t i o n between NaOCl and MoS 2 and i t was t h e r e f o r e c o n s i d e r e d i m p o r t a n t t o e s t a b l i s h i t s e f f e c t i f any upon t h e r e a c t i o n r a t e . To t h i s end an e x p e r i m e n t was c o n d u c t e d a d d i n g 50 g o f NaCl t o a s o l u t i o n o f 7.9 g/1 NaOCl a l r e a d y c o n t a i n i n g 70 g/1 o f NaCl. MoS 2 c o n c e n t r a t e was l e a c h e d i n t h i s s o l u t i o n and compared t o a run under i d e n t i c a l c o n d i t i o n s w i t h no NaCl-added:. No e f f e c t w hatsoever was d e t e c t e d on t h e r e a c t i o n r a t e . 5 10 15 20 TIME (min) FIG. 17 - EFFECT OF SULFATES ON THE OXIDATION OF MOLYBDENITE \ 49 4.1.11 E f f e c t o f C102 and C10 3 on t h e Rate o f R e a c t i o n S o l u t i o n s o f sodium h y p o c h l o r i t e a r e u n s t a b l e t o a c e r t a i n d e gree even i n t h e a l k a l i n e r e g i o n and decompose i n t o sodium c h l o r a t e and sodium c h l o r i d e . Most o f t h e mechanisms proposed t o e x p l a i n i t s d e c o m p o s i t i o n show the f o r m a t i o n o f C 1 0 2 i o n s as an i n t e r m e d i a t e s t e p . E x p e r i m e n t s were done t o e s t a b l i s h i f t h e s e s p e c i e s have any e f f e c t on t h e r a t e o f o x i d a t i o n o f MoS 2 by NaOCl. S o l u t i o n s o f NaOCl o f 8.0 g/1 were p r e p a r e d and b u f f e r e d a t pH 9 and d i f f e r e n t amounts o f NaC10 2 and N a 2 C 1 0 3 were added and the r a t e s o f e x t r a c t i o n compared. The i n f o r m a t i o n o b t a i n e d was p l o t t e d i n F i g u r e 18. I t can be o b s e r v e d t h a t C 10 2~ i o n s have no e f f e c t on t h e r a t e s o f e x t r a c t i o n o f Mo. The p r e s e n c e o f C10 3~ however lowers t h e r a t e o f Mo e x t r a c t i o n . In both c a s e s t h e amounts added were f a r i n e x c e s s o f what would be e x p e c t e d from t h e normal d e c o m p o s i t i o n o f NaOCl under t h e c o n d i t i o n s o f o u r l e a c h i n g s t u d i e s and t h e r e f o r e t h e e f f e c t s o b s e r v e d would not h i n d e r t h e l e a c h i n g r e a c t i o n . The p r e s e n c e o f c h l o r a t e would be hazardous o n l y i n the c a s e i n which s o l u t i o n s o f NaOCl had been s t o c k e d f o r l o n g p e r i o d s o f time under u n f a v o u r a b l e c o n d i t i o n s . 4.1.12 E f f e c t o f Molybdate Ions on t h e Rates o f R e a c t i o n Two e x p e r i m e n t s a re r e p o r t e d i n t h i s s e c t i o n . In the f i r s t one the e f f e c t o f [ M o O ^ ] on t h e r a t e o f r e a c t i o n was d e t e r m i n e d a t a f i x e d pH v a l u e . In t h e second, t h e e f f e c t o f MoS 2 p a r t i c l e s on-the [ M o 0 4 _ ] was e s t a b l i s h e d f o r d i f f e r e n t 0H~ c o n c e n t r a t i o n s . ( 5 0 5 10 15 20 TIME (min) FIG. 18- EFFECT OF CHLORITE AND CHLORATE ON THE OXIDATION OF MOLYBDENITE. 51 As mentioned i n 1.5, i t has been r e p o r t e d t h a t i n the p r e s e n c e o f e x c e s s o x i d i z i n g agent i n a l k a l i n e s o l u t i o n s t h e Mo(IV) i n MoS 2 i s e n t i r e l y o x i d i z e d t o (VI) i n t h e MoCV - i o n s . I t was t h e r e f o r e d e c i d e d t o i n v e s t i g a t e i f t h e p r e s e n c e o f l a r g e r c o n c e n t r a t i o n s o f MoO^ a f f e c t e d t h e r e a c t i o n . A run was made u s i n g a b u f f e r e d s o l u t i o n (pH 9.5) o f 7.5 g/1 NaOCl a t 35\u00C2\u00B0C, l e a c h i n g 0.3 g MoS 2 c o a r s e p a r t i c l e s i n t h e p r e s e n c e o f an i n i t i a l [M0O4. ] f i v e t i m e s t h e amount t h a t would be produced by t h e t o t a l r e a c t i o n o f t h e MoS 2 employed. The., d i s s o l u t i o n c u r v e s were th e n compared t o an i d e n t i c a l run w i t h no i n i t i a l MoO^ - p r e s e n t . In t h i s e x p e r i m e n t MoOi*- i o n s e v i d e n t l y had no e f f e c t on t h e l e a c h i n g r e a c t i o n . From the s t o i c h i o m e t r y o f r e a c t i o n (3) i t c o u l d be e x p e c t e d t h a t t h e r a t e o f t h e r e a c t i o n s h o u l d depend on the c o n c e n t r a t i o n o f h y d r o x i d e ; however e x p e r i m e n t s r e p o r t e d i n 4.1.8 i n d i c a t e an i n c r e a s e i n r a t e s o f e x t r a c t i o n up t o pH 8.5 but a d e c r e a s e i n the r e a c t i o n r a t e s when t h e pH exceeds 10.5. C o n s e q u e n t l y i t was d e c i d e d t o examine i f t h e r e was any r e a c t i o n between Mo04~ i o n s and MoS2 p a r t i c l e s which would d e c r e a s e the molybdate c o n c e n t r a t i o n a t h i g h e r pH's. T h r e e runs were made w i t h s o l u t i o n s o f 10 g/1 Na 2Mo0i f a t 26\u00C2\u00B0C w i t h t h e pH c o n t r o l l e d a t 8.5, 10.5 and 11.5. In a l l c a s e s 50 g o f MoS2 f i n e c o n c e n t r a t e were added. In F i g u r e 19 i t can be o b s e r v e d t h a t w h i l e t h e [MO0L>~] remains c o n s t a n t a f t e r 60 min. a t the lower pH, t h e runs a t pH 10.5 and 11.5 i n d i c a t e a d e c r e a s e i n t h e [MoOiT] i n t h e f i r s t 20 min. and th e n t h e c o n c e n t r a t i o n remains c o n s t a n t . The o c c u r r e n c e o f a r e a c t i o n was a l s o P 8 + o Si or h-LU O O o 5{ _ A o o pH 8.5 * ^ 10.5 \u00E2\u0080\u00A2 \u00E2\u0080\u0094 . . \u00E2\u0080\u009E 5 T = 2 6 \u00C2\u00B0 C 10 20 30 TIME (min) -A \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 40 50 60 FIG. 19 - EFFECT OF MOLYBDATES - MoS2 INTERACTION 53 o b s e r v a b l e when an a d d i t i o n a l run was made w i t h an i n i t i a l pH o f 10.5 and t he s o l u t i o n was n o t b u f f e r e d . T h e r e was a d e c r e a s e i n t h e pH i n th e f i r s t 30 min. o f r e a c t i o n . No d i f f e r e n c e i n the s u r f a c e o f the MoS 2 p a r t i c l e s were o b s e r v e d a f t e r t h e r e a c t i o n ; the o b s e r v a t i o n s i n t h i s s e c t i o n however, i n d i c a t e t h a t t h e r e i s some i n t e r a c t i o n between t h e Mo0 4 i n s o l u t i o n and the MoS 2 p a r t i c l e s a t h i g h e r 0H~ c o n c e n t r a t i o n s which r e s u l t s i n a d e c r e a s e o f t h e [MoG\ =]. 4.2 O x i d a t i o n o f C h a l c o p y r i t e by Sodium H y p o c h l o r i t e S i n c e c h a l c o p y r i t e was t h e major copper m i n e r a l i n t h e r o u g h e r c o n c e n t r a t e and because a p p a r e n t l y i t was an i m p o r t a n t c o n t r i b u t o r t o t h e e x c e s s consumption o f h y p o c h l o r i t e as d e t e r m i n e d from p r e l i m i n a r y l e a c h i n g e x p e r i m e n t s o f t h e r o u g h e r c o n c e n t r a t e , i t was d e c i d e d t o i n v e s t i g a t e t h e e x t e n t o f i t s r e a c t i o n w i t h s o l u t i o n s o f sodium h y p o c h l o r i t e . 4.2.1 L e a c h i n g o f C h a l c o p y r i t e C o n c e n t r a t e Samples o f a Phoenix c h a l c o p y r i t e ground t o -200 mesh were l e a c h e d i n s o l u t i o n s o f sodium h y p o c h l o r i t e under s i m i l a r c o n d i t i o n s as t h o s e f o r t h e b e s t e x t r a c t i o n from m o l y b d e n i t e c o n c e n t r a t e s . In each run t h e c o n c e n t r a t i o n o f c o p p e r i o n s and sodium h y p o c h l o r i t e was d e t e r m i n e d . In a l l c a s e s i t was o b s e r v e d t h a t t h e r e a c t i o n was accompanied by a d e c r e a s e i n t h e [ H + ] . Some runs were then r e p e a t e d m a i n t a i n i n g t h e pH c o n s t a n t by b u f f e r i n g t h e s o l u t i o n s . 54 The r e s u l t s o f one run a r e p r e s e n t e d i n F i g u r e 20. I t can be o b s e r v e d t h a t t h e c o n c e n t r a t i o n o f Cu i n c r e a s e d r a p i d l y and t h e n remained c o n s t a n t t h r o u g h t h e e n t i r e e x p e r i m e n t . In c o n t r a s t the c o n c e n t r a t i o n o f NaOCl d e c r e a s e d c o n t i n u o u s l y a l m o s t r e a c h i n g z e r o a f t e r 24 h o u r s . In t h i s run t h e pH had d e c r e a s e d i n the l a s t 12 hours and t h e d e c r e a s e i n h y p o c h l o r i t e c o n c e n t r a t i o n may have been i n f l u e n c e d by t h e h i g h e r H + c o n c e n t r a t i o n . As was o b s e r v e d i n a l l o t h e r l e a c h i n g e x p e r i m e n t s u s i n g c h a l c o p y r i t e , i t s s u r f a c e was s l i g h t l y darkened by t h e r e a c t i o n . T h i s a p p a r e n t c o a t i n g was e a s i l y removed by d i l u t e s u l f u r i c a c i d . 4.2.2 L e a c h i n g o f M a s s i v e Specimens To i n v e s t i g a t e i f t h e consumption o f NaOCl was due t o any t o p o t a c t i c r e a c t i o n w i t h i n t h e c h a l c o p y r i t e p a r t i c l e s , l a r g e C u F e S 2 specimens were l e a c h e d and t h e i r c r o s s - s e c t i o n s l a t e r examined u s i n g t h e e l e c t r o n m i c r o p r o b e . In p r e p a r a t i o n f o r t h e s e t e s t s t h e C u F e S 2 specimens were p r e -v i o u s l y p o l i s h e d and a r e a s f r e e o f f o r e i g n i m p u r i t i e s s p e c i a l l y F e S 2 were d e t e c t e d and marked. They were t h e n immersed i n s o l u t i o n s o f NaOCl f o r d i f f e r e n t p e r i o d s and e x p e r i m e n t a l c o n d i t i o n s and f i n a l l y s e c t i o n e d t h r o u g h the marked a r e a s . A s i m i l a r t a r n i s h i n g o f t h e s u r f a c e was o b s e r v e d as i n t h e c a s e o f the f i n e p a r t i c l e s . The C u F e S 2 a r e a s a f t e r l e a c h i n g were brown and t r a n s p a r e n t w h i l e the F e S 2 a r e a s formed a b l a c k - o p a q u e c o a t i n g . 54 cn O O o 4 i E \u00C2\u00A925 e - A A\u00E2\u0080\u0094Theor. NaOCl consumption. ^-Experim. II T- 26\u00C2\u00B0C CuFeS - 10g pH - 9.2 10 30 TIME (min) 50 to \u00E2\u0080\u0094- 8 3 \u00E2\u0080\u00A2 o .4,2 FIG. 20 - EXTRACTION OF COPPER AND CONSUMPTION OF HYPOCHLORITE DURING LEACHING OF CHALCOPYRITE. 56 U s i n g t h e x ^ r a y . e n e r g y a n a l y z e r o f t h e SEM on t h e l e a c h e d C u F e S 2 a r e a s i t was p o s s i b l e t o d e t e r m i n e a d e c r e a s e i n the s u l f u r - c o p p e r r a t i o when compared t o u n t r e a t e d C u F e S 2 . An example o f t h e s e o b s e r v a t i o n s i s p r e s e n t e d i n T a b l e 6. I t was a l s o o b s e r v e d t h a t t h e S/Cu r a t i o d i d not change s i g n i f i c a n t l y w i t h t h e d u r a t i o n o f l e a c h i n g t h e specimens. T a b l e 6 Comparison o f S/Cu R a t i o s f o r ^ L e a c h e d and Nonleached C h a l c o p y r i t e Leaching Conditions NaOCl = 15g/l Temp = 31\u00C2\u00B0C pH = 9.6 ( c o n t r o l l e d ) Time = 4 hours S/Cu r a t i o u n t r e a t e d C u F e S 2 = .79 \" l e a c h e d \" = .37 T h i s r e d u c t i o n i n t h e S/Cu r a t i o c o u l d be i n t e r p r e t e d as an o x i d a t i o n o f t h e C u F e S 2 s u r f a c e . However as t h e r e was s u l f u r r e m a i n i n g a f t e r t h e r e a c t i o n , a l t h o u g h t h e r e was an e x c e s s o f o x i d i z i n g r e a g e n t i n s o l u t i o n , t h i s p r o c e d u r e c o u l d n o t d i s c r i m i n a t e between an i n c o m p l e t e o x i d a t i o n o f the CuF e S 2 s u r f a c e and t h e i n t e r f e r e n c e o f l o w e r ' C u F e S 2 l a y e r s e x c i t e d by t h e x - r a y beam p e n e t r a t i o n . The m i c r o p r o b e a n a l y s i s o f l e a c h e d c r o s s - s e c t i o n s i n d i c a t e d t h a t a l i m i t e d t o p o t a c t i c r e a c t i o n had o c c u r r e d . The s u r f a c e o f t h e C u F e S 2 was a l t e r e d o n l y t o a maximum de p t h o f 20 m i c r o n s and i t was n o t p o s s i b l e t o d e t e r m i n e t h e e x t e n t o f t h e r e a c t i o n between the NaOCl and th e C u F e S 2 w i t h i n t h i s depth because o f the e r r a t i c s i g n a l s f o r Cu and S o r i g i n a t i n g from t he e m i s s i o n o f d i f f r a c t e d beams from t h e uneven edge o f the specimen. 5\"7 These l a s t o b s e r v a t i o n s d e m o n s t r a t e t h a t t h e r e a c t i o n between NaOCl and C u F e S 2 o c c u r r e d o n l y a t t h e s u r f a c e f o r m i n g a p r o t e c t i v e l a y e r c o n s i s t i n g a t l e a s t i n p a r t by some form o f o x i d e o r h y d r o x i d e o f c o p p e r I I . I t was r e a s o n a b l e t o s p e c u l a t e t h e r e f o r e , t h a t t h e f u r t h e r d e c r e a s e i n [NaOCl] was due t o some d e c o m p o s i t i o n r e a c t i o n which i s c a t a l y z e d by th e a l t e r e d C u F e S 2 s u r f a c e . 4.2.3 Comparative O x i d a t i o n and D i s s o l u t i o n o f MoS 2 and C u F e S 2 i n S o l u t i o n s o f NaOCl In a r o u g h e r c o n c e n t r a t e t h e w e i g h t r a t i o between C u F e S 2 and MoS 2 i s a p p r o x i m a t e l y 80. I t i s t h e r e f o r e c o n v e n i e n t t o d e t e r m i n e how each o f them behave when e x p o s i n g equal s u r f a c e a r e a s i n s o l u t i o n s o f NaOCl under t h e c o n d i t i o n s o f p r e v i o u s e x p e r i m e n t s . T h i s c o u l d then e s t a b l i s h i f s e l e c t i v e l e a c h i n g i s p o s s i b l e . MoS 2 and C u F e S 2 o f the same s c r e e n e d s i z e (-140 + 200 mesh) were examined u s i n g t h e SEM t o d e t e r m i n e t h e s u r f a c e r o u g h n e s s . Examples o f each a r e p r e s e n t e d i n F i g u r e 21. I t was o b s e r v e d t h a t t h e p r e s e n c e o f m u l t i p l e s t e p s and edges on t h e m o l y b d e n i t e p a r t i c l e s i n c r e a s e d i t s s u r f a c e a r e a . The s p e c i f i c a r e a was d e t e r m i n e d u s i n g a nomogram [28] on t h e b a s i s o f p a r t i c l e d i a m e t e r , shape f a c t o r and the m a t e r i a l s d e n s i t y . T h i s method o f s u r f a c e a r e a d e t e r m i n a t i o n i s not as a c c u r a t e as any o f the a d s o r p t i o n methods but i t was c o n s i d e r e d t o be adequate f o r c o m p a r a t i v e p u r p o s e s i n t h e l e a c h i n g e x p e r i m e n t . 58 FfG. 21 - SURFACE ROUGHNESS OF MoS2 AND CuFeS2 59 T a b l e 7 V a l u e s f o r D e t e r m i n a t i o n o f S u r f a c e A r e a f o r M o l y b d e n i t e and C h a l c o p y r i t e M a t e r i a l Average P a r t i c l e d i a m e t e r -(urn) Shape F a c t o r D e n s i t y S p e c i f i c S u r f a c e - -m2/g MoS 2 C u F e S 2 100 ll 5 4 4.8 5.1 .06 m 2/g .02 m 2/g Samples o f m o l y b d e n i t e and c h a l c o p y r i t e p a r t i c l e s c o r r e s p o n d i n g t o equal s u r f a c e a r e a s were l e a c h e d t o g e t h e r i n a s o l u t i o n o f NaOCl. The e x t r a c t i o n c u r v e s f o r molybdenum and co p p e r a r e shown i n F i g u r e 22. I t was p o s s i b l e t o o b s e r v e t h a t t h e r e l a t i v e d i s s o l u t i o n between t h e s e m i n e r a l s f a v o r s m o l y b d e n i t e by a t l e a s t a r a t i o 100:1 and t h a t t h e r e a c t i o n o f MoS 2 was complete. T h e r e f o r e t h e s e l e c t i v e l e a c h i n g o f MoS 2 from C u F e S 2 s h o u l d be p o s s i b l e . 4.2.4 E f f e c t o f C h a l c o p y r i t e on t h e Rates o f NaOCl Consumption and MoS 2 D i s s o l u t i o n Runs i n t h i s s e c t i o n were made by a d d i n g p r o g r e s s i v e l y g r e a t e r amounts o f C u F e S 2 t o l e a c h i n g e x p e r i m e n t s i n which t h e i n i t i a l m o l y b d e n i t e and c o n c e n t r a t i o n o f sodium h y p o c h l o r i t e were i d e n t i c a l . R e s u l t s f o r m o l y b d e n i t e d i s s o l u t i o n a r e p r e s e n t e d i n F i g u r e 23. I t was o b s e r v e d t h a t g r e a t e r amounts o f c h a l c o p y r i t e ( s e v e r a l t i m e s t h e w e i g h t and s u r f a c e a r e a o f m o l y b d e n i t e ) d i d not have a s i g n i f i c a n t e f f e c t on t h e d i s s o l u t i o n r a t e s s i n c e t i m e s f o r t o t a l e x t r a c t i o n remained unchanged. .601 Q UJ I-O < or h-x LU .40 ,20 [NaOCl] = 7.2 g/1 pH =9 T =30\u00C2\u00B0C Mo = 100 % extracted o o 30 TIME (min) a UJ I-< r r h-x UJ \u00E2\u0080\u00A23 V .006 004 \u00E2\u0080\u00A2.002 FIG. 22 - EXTRACTION OF Cu AND Mo DURING LEACHING OF MoS2 AND CuFeS2 OF EQUAL INITIAlO SURFACE AREAS. 10 30 50 TIME (hr) FIG. 2 3 - E F F E C T OF CHALCOPYRITE ON THE RATE OF MOLYBDENITE DISSOLUTION. 62 4.3 L e a c h i n g o f M o l y b d e n i t e from Copper Rougher C o n c e n t r a t e s U s i n g t h e optimum l e a c h i n g c o n d i t i o n s e s t a b l i s h e d w i t h pure MoS 2, e x p e r i m e n t s were performed t o e x t r a c t molybdenum from c o p p e r m i l l p r o d u c t s . Some i n i t i a l e x p e r i m e n t s u s i n g a c o p p e r o r e showed e r r a t i c r e s u l t s which were a t t r i b u t e d t o t h e e x t r e m e l y low grade (<.01% Mo) o f t h e o r e sample. I t was then d e c i d e d t o use a co p p e r r o u g h e r c o n c e n t r a t e , which was d r i e d i n an oven a t 110-120\u00C2\u00B0C, w i t h the purpose o f e l i m i n a t i n g most o f t h e a t t a c h e d f l o t a t i o n r e a g e n t s . The r e s u l t s o f p r e l i m i n a r y e x p e r i m e n t s u s i n g a c o n c e n t r a t i o n o f sodium h y p o c h l o r i t e up t o 10 t i m e s t h a t t h e o r e t i c a l l y r e q u i r e d t o o x i d i s e a l l t h e m o l y b d e n i t e p r e s e n t t o Mo0 4~ and SQk~ showed as was e x p e c t e d , t h a t t he e x t r a c t e d Mo/Cu r a t i o was v e r y h i g h . However some Cu was p r e s e n t i n t h e s o l u t i o n and the consumption o f NaOCl was f a r i n e x c e s s o f the t h e o r e t i c a l l y c a l c u l a t e d amount. The r e s u l t o f one such e x p e r i m e n t i s r e p o r t e d i n F i g u r e 24. The % e x t r a c t e d Mo and Cu r e f e r t o t h e t o t a l o f each i n t h e i n i t i a l sample. I t can be o b s e r v e d t h a t t h e r a t e s o f moybdenum e x t r a c t i o n a r e v e r y h i g h i n th e i n i t i a l p a r t (50% r e a c t e d i n 8 m i n u t e s ) but d e c r e a s e r a p i d l y t o z e r o a f t e r 40 m i n u t e s . A t t h i s time t h e c o n c e n t r a t i o n o f NaOCl had d e c r e a s e d t o z e r o and t h e t o t a l e x t r a c t i o n o f Mo was o n l y 83%. The d i s s o l u t i o n o f c o p p e r was o b s e r v e d t o go t h r o u g h a maximum and l a t e r remain c o n s t a n t a f t e r t h e NaOCl c o n c e n t r a t i o n r e a c h e d z e r o . In t h i s run t h e maximum Cu d e t e c t e d i n s o l u t i o n was 1.2%. In no c a s e d i d t h e Cu e x t r a c t i o n exceed 3%. I t i s assumed t h a t i n t h e p r e s e n c e o f an e x c e s s [NaOCl] the r e a c t i o n between c h a l c o p y r i t e and sodium h y p o c h l o r i t e w i l l have t h e f o l l o w i n g s t o i c h i o m e t r y : 63 NaOCl = 5.3 T=29\u00C2\u00B0C pH = 8.9 FIG. 24 - EXTRACTION OF Mo AND Cu FROM A COPPER ROUGHER CONCENTRATE , 64 2 C u F e S 2 + 17 NaOCl + 8 NaOH + H 20 -\u00C2\u00BB\u00E2\u0080\u00A2 2 C u ( O H ) 2 + 2 F e ( 0 H ) 3 + 4 Na 2 SO* + 17 Na C l In the l e a c h i n g o f the r o u g h e r c o n c e n t r a t e , t h e a n a l y s i s o f [NaOCl] measured even i n t h e f i r s t samples i n d i c a t e d t h a t t h e consumption o f r e a g e n t was much g r e a t e r t h a n t h e o r e t i c a l l y r e q u i r e d t o c o m p l e t e l y o x i d i z e a l l t h e Mo and t h e Cu d i s s o l v e d a t t h o s e s t a g e s . As i n t h e c a s e o f l e a c h i n g C u F e S 2 , c l e a r f i l t e r e d s o l u t i o n s from t h e r o u g h e r c o n c e n t r a t e l e a c h were o b s e r v e d t o form a b l a c k f i n e p r e c i p i t a t e . I t was not p o s s i b l e t o c o l l e c t s u f f i c i e n t o f t h i s m a t e r i a l f o r NaOCl d e c o m p o s i t i o n s t u d i e s . 4.3.1 I n f l u e n c e o f P a r t i c l e S i z e on t h e E x t r a c t i o n o f Molybdenum The i n f l u e n c e o f p a r t i c l e s i z e was i n v e s t i g a t e d by s e p a r a t i n g two s i z e f r a c t i o n s o f t h e r o u g h e r c o n c e n t r a t e and s u b j e c t i n g them t o i d e n t i c a l l e a c h i n g e x p e r i m e n t s . The r e s u l t s a r e p r e s e n t e d i n F i g u r e 25. I t was o b s e r v e d t h a t t h e sample w i t h g r e a t e r s u r f a c e a r e a p r e s e n t e d a h i g h e r e x t r a c t i o n r a t e but the t o t a l m o l y b d e n i t e l e a c h e d was l o w e r . The r e a s o n f o r t h i s was b e l i e v e d t o be a f a s t e r d e c r e a s e i n NaOCl s t r e n g t h . T h i s was c o n f i r m e d i n t h e f o l l o w i n g e x p e r i m e n t s i n which a f i n e l y ground r o u g h e r c o n c e n t r a t e sample was l e a c h e d . A c o mparison o f t h e e x t r a c t i o n r a t e s and NaOCl consumption i s p r e s e n t e d i n F i g u r e 26, between the l e a c h i n g o f t h e \"as r e c e i v e d \" r o u g h e r c o n c e n t r a t e and t h e ground sample. A l t h o u g h the c o n c e n t r a t i o n o f NaOCl 65 Co ioot o UJ h-V < or h-X LU \u00E2\u0080\u0094 o o (- 4 0 + 70) MESH \u00E2\u0080\u0094 * * (- 140) \u00E2\u0080\u00A2 A. O 30 TIME (min) 50 FIG. 25 - EFFECT OF PARTICLE SIZE ON THE RATES OF Mo EXTRACTION FROM Cu ROUGHER CONCEN TRATES. 66 . 26 - Mo EXTRACTION AND NaOCl CONSUMPTION IN THE LEACHING OF GROUND AND NORMAL ROUGHER CONCENTRATES. 67 was o v e r t h r e e t i m e s t h e t h e o r e t i c a l l y r e q u i r e d t o l e a c h a l l the m o l y b d e n i t e p r e s e n t i t d e c r e a s e d t o z e r o i n l e s s than 10 m i n u t e s a t which time o n l y 46% o f Mo had been e x t r a c t e d from the ground sample. Equal c o n d i t i o n s e x t r a c t e d 84% o f t h e c o a r s e r c o n c e n t r a t e . 4.3.2 Q u a n t i t y o f NaOCl R e q u i r e d f o r T o t a l Molybdenum E x t r a c t i o n S e v e r a l runs were per f o r m e d i n c r e a s i n g t h e c o n c e n t r a t i o n o f sodium h y p o c h l o r i t e w i t h the purpose o f d e t e r m i n i n g the minimum q u a n t i t y t h a t would e x t r a c t a l m o s t a l l the molybdenum. The e x p e r i m e n t a l c o n d i t i o n s were s e t a t : i n i t i a l pH 9.5, t e m p e r a t u r e 30\u00C2\u00B0C. I t was d e t e r m i n e d t h a t f o r the complete e x t r a c t i o n o f MoS 2 from t h e r o u g h e r c o n c e n t r a t e used, t h e q u a n t i t y o f NaOCl r e q u i r e d was e q u i v a l e n t t o 4.2 t i m e s the t h e o r e t i c a l l y needed t o c o m p l e t e l y o x i d i z e t h e molybdenum and s u l f u r i n t h e sample. 4.3.3 E f f e c t o f P r e t r e a t i n g t h e Rougher C o n c e n t r a t e w i t h S u l f u r i c A c i d With the i n t e n t i o n o f e l i m i n a t i n g any o x i d e s p r e s e n t w i t h t h e c o p p e r s u l f i d e m i n e r a l s i n the r o u g h e r c o n c e n t r a t e which c o u l d be i n c r e a s i n g t h e NaOCl consumption, a p o r t i o n o f t h e c o n c e n t r a t e was l e a c h e d i n a d i l u t e s o l u t i o n o f s u l f u r i c a c i d (0.5%) and l a t e r l e a c h e d w i t h sodium h y p o c h l o r i t e under s i m i l a r c o n d i t i o n s as the u n t r e a t e d r o u g h e r c o n c e n t r a t e . I t was o b s e r v e d t h a t t h i s p r e t r e a t m e n t had a r e m a r k a b l e e f f e c t on t h e sodium h y p o c h l o r i t e consumption. C o n s e q u e n t l y s e v e r a l runs were perf o r m e d as i n s e c t i o n 4.3.2 and i t was d e t e r m i n e d t h a t t o t a l m o l y b d e n i t e 68 e x t r a c t i o n was o b t a i n e d u s i n g a s o l u t i o n o f NaOCl w i t h an i n i t i a l c oncen-t r a t i o n e q u i v a l e n t t o 1.5 t o 1.8 t i m e s the t h e o r e t i c a l l y r e q u i r e d t o d i s s o l v e t h e MoS 2 p r e s e n t . 4.3.4 E x t r a c t i o n o f M o l y b d e n i t e from \" I n - P u l p \" Rougher C o n c e n t r a t e The e x p e r i m e n t s i n s e c t i o n 4.3.3 were per f o r m e d s i m u l t a n e o u s l y w i t h the F l o t a t i o n s t u d i e s r e p o r t e d below. The r e s u l t s o f b o t h i n d i c a t e d t h a t the r o u g h e r c o n c e n t r a t e used c o u l d have an e x c e s s o f c o p p e r o x i d e as compared t o t h e u n p r e p a r e d \" i n - p u l p \" r o u g h e r c o n c e n t r a t e o b t a i n e d i n t h e p r i m a r y f l o t a t i o n c i r c u i t . T h i s was c o n f i r m e d by c h e m i c a l a n a l y s i s as i n d i c a t e d i n Tabe 8. T a b l e 8 Oxide Copper C o n t e n t f o r D r i e d and I n - P u l p Rougher C o n c e n t r a t e s G i b r a l t a r R.C. washed and d r i e d f o r L e a c h i n g E x p e r i m e n t s Oxide Copper = 1.26% G i b r a l t a r R.C. u n t r e a t e d \" \" = 0.52% The c a u s e o f t h e e x c e s s c o p p e r o x i d e was a t t r i b u t e d t o h i g h t e m p e r a t u r e s o f the d r y i n g p r o c e s s used i n p r e p a r i n g the samples f o r l e a c h i n g e x p e r i m e n t s and s t o r i n g t h e d r i e d r o u g h e r c o n c e n t r a t e i n c o n t a c t w i t h a i r f o r l o n g p e r i o d s o f time. C o n s e q u e n t l y a new b a t c h o f r o u g h e r c o n c e n t r a t e was o b t a i n e d from G i b r a l t a r Mines and m a i n t a i n e d as a dense p u l p . The a d d i t i o n o f r o u g h e r c o n c e n t r a t e t o the l e a c h i n g e x p e r i m e n t s r e p o r t e d i n t h i s s e c t i o n was by measured volumes a f t e r s t i r r i n g t h e p u l p o n e - h a l f hour. 69 S e v e r a l runs were performed w i t h t h e u n t r e a t e d r o u g h e r c o n c e n t r a t e u s i n g s i m i l a r c o n d i t i o n s as i n s e c t i o n 4.3 and 4.3.2 w i t h t h e purpose o f d e t e r m i n i n g t h e e f f e c t o f the exc e s s c o p p e r o x i d e on t h e e x t r a c t i o n r a t e s o f m o l y b d e n i t e and the consumption o f r e a g e n t . The r e s u l t s o f one run a r e p r e s e n t e d i n F i g u r e 27. A l s o p l o t t e d i s t h e e x t r a c t i o n c u r v e s o f the l e a c h i n g o f a t r e a t e d r o u g h e r c o n c e n t r a t e . I t i s not p o s s i b l e t o compare the a p p r o x i m a t e r e a c t i o n r a t e s from t h e s e two c u r v e s because o f the d i f f e r e n c e i n t h e i n i t i a l c o n c e n t r a t i o n o f the r e a g e n t . F u r t h e r m o r e t h e d e t e r m i n a t i o n o f r e a c t i o n r a t e s i n t h i s r e a c t i o n would have r e q u i r e d a more s o p h i s t i c a t e d s a m p l i n g t e c h n i q u e which was not ju d g e d c o n v e n i e n t f o r t h e purpose o f t h i s s t u d y . F o r t h e purpose o f a p r a c t i c a l a p p l i c a t i o n i t i s p o s s i b l e t o say t h a t t h e r e was no s i g n i f i c a n t change e i t h e r i n t h e r e a c t i o n r a t e s nor i n t h e t o t a l l e a c h i n g times between t h e s e two c o n c e n t r a t e s . However t h e NaOCl consumption was n o t i c e a b l y d i f f e r e n t . By u s i n g t h e p r o c e d u r e o f l e a c h i n g w i t h i n c r e a s i n g i n i t i a l NaOCl c o n c e n t r a t i o n and f o l l o w i n g the Mo e x t r a c t i o n u n t i l t o t a l NaOCl consumption i t was p o s s i b l e t o d e t e r m i n e t h a t 98% o f t h e MoS 2 i n t h e u n t r e a t e d r o u g h e r con-c e n t r a t e was e x t r a c t e d w i t h a NaOCl s o l u t i o n w i t h an i n i t i a l c o n c e n t r a t i o n 1.6 times t he t h e o r e t i c a l l y r e q u i r e d t o o x i d i z e a l l MoS 2 t o MoOiT and S 0 H = . 4.3.5 F l o t a t i o n o f Leached Rougher C o n c e n t r a t e s To compare t h e e f f e c t o f l e a c h i n g on t h e f l o t a b i l i t y o f r o u g h e r c o n c e n t r a t e s , t e s t s were per f o r m e d u s i n g t h r e e m a t e r i a l s : 70 T = 30\u00C2\u00B0 C pH = 9r.5 10 30 TIME (min) FIG. 2 7 - MOLYBDENITE DISSOLUTION AND HYPOCHLORITE CONSUMPTION IN THE LEACHING TREATED AND IN PULP ROUGHER CONCENTRATES 71 A . T r e a t e d R o u g h e r C o n c e n t r a t e d i r e c t l y l e a c h e d i n a s o l u t i o n o f NaOC l ( c o m p l e t e e x t r a c t i o n o f mo I y b d e n i t e ) . B. T r e a t e d R o u g h e r C o n c e n t r a t e p r e v i o u s l y l e a c h e d i n a \% H2S0^ a t 2 5 \u00C2\u00B0 C f o r o n e h o u r a n d l a t e r l e a c h e d i n a s o l u t i o n o f NaOC l ( c o m p l e t e e x t r a c t i o n o f M o S 2 ) . C . T r e a t e d R o u g h e r C o n c e n t r a t e n o t l e a c h e d t o s e r v e a s c o m p a r i s o n . In a l l c a s e s the s t a n d a r d t e c h n i q u e f o r t h e p r e f e r e n t i a l f l o -t a t i o n o f c h a l c o p y r i t e was used, c a r e f u l l y c o n t r o l l i n g the pH a t which t h e s e v e r a l f l o t a t i o n and c l e a n i n g s t a g e s were p e r f o r m e d . Z200 was used as the c o l l e c t o r h a v i n g t h e p r o p e r t y o f s e l e c t i v i t y o f c h a l c o p y r i t e o v e r p y r i t e . The r e c o v e r y grade r e l a t i o n s h i p has been p l o t t e d i n F i g u r e 28. I t was o b s e r v e d t h a t the f l o t a b i l i t y o f t h e l e a c h e d r o u g h e r c o n c e n t r a t e was i n f e r i o r t o t h e u n l e a c h e d m a t e r i a l . In c o n t r a s t t h e r o u g h e r concen-t r a t e which r e c e i v e d t h e same NaOCl l e a c h but had been p r e v i o u s l y t r e a t e d w i t h a d i l u t e HzSOk had a s l i g h t l y b e t t e r f l o t a b i l i t y . In a l l c a s e s the consumption o f c o l l e c t o r was f a r i n e x c e s s o f the normal q u a n t i t i e s employed f o r the s e c o n d a r y f l o t a t i o n o f t h e r o u g h e r c o n c e n t r a t e s i n the normal c o p p e r c o n c e n t r a t i o n p r o c e s s and i t was s u s p e c t e d t h a t the s u r f a c e o f t h e m i n e r a l s c o u l d have been a l t e r e d d u r i n g the d r y i n g p r o c e s s i n p r e p a r a t i o n f o r l e a c h i n g , and t h a t t h i s c o n d i t i o n was r e s p o n s i b l e t o a l a r g e r degree f o r t h e poor f l o t a b i l i t y than any changes produced on the m i n e r a l s u r f a c e d u r i n g l e a c h i n g w i t h NaOCl. 72 PROGRESSIVE GRADE (% Cu) FIG. 28 - RECOVERY - GRADE CURVES FOR THE SECONDARY FLOTATION OF LEACHED ROUGHER CONCENT. 73 4.3.6 F l o t a t i o n o f \" I n - P u l p \" Rougher C o n c e n t r a t e s F l o t a t i o n s t u d i e s r e p o r t e d i n t h i s s e c t i o n were pe r f o r m e d on t h e G i b r a l t a r c o p p e r r o u g h e r c o n c e n t r a t e kept as \" i n - p u l p . \" Samples o f t h i s m a t e r i a l were l e a c h e d w i t h o u t any p r e t r e a t m e n t i n s o l u t i o n s o f NaOCl and then f l o a t e d as i n 4.3.5. A sample o f u n l e a c h e d m a t e r i a l was f l o a t e d f o r c o m p a r i s o n . A l t h o u g h a s o l i d s / l i q u i d s e p a r a t i o n was used a f t e r l e a c h i n g , c a r e was t a k e n t o p r e v e n t the r e s i d u e from d r y i n g o r e x c e s s i v e c o n t a c t w i t h a i r . The same f i l t e r i n g p r o c e d u r e was a p p l i e d t o t h e u n l e a c h e d m a t e r i a l and t i m e s between S / l s e p a r a t i o n and f l o t a t i o n were a p p r o x i m a t e l y t h e same f o r both m a t e r i a l s . The r e c o v e r y - g r a d e r e l a t i o n s h i p was p l o t t e d i n F i g u r e 29. I t i s p o s s i b l e t o o b s e r v e t h a t t h i s r e l a t i o n s h i p i s s i m i l a r f o r both r o u g h e r c o n c e n t r a t e s . On the b a s i s o f r e a g e n t consumption i t was d e t e r m i n e d t h a t t h e f l o t a b i l i t y o f the l e a c h e d r o u g h e r c o n c e n t r a t e i s lower t h a n t h e u n t r e a t e d m a t e r i a l , i . e . the f l o t a t i o n r e c o v e r y i s l o w e r a l t h o u g h t h e c o n c e n t r a t e grade i s h i g h e r f o r i d e n t i c a l r e a g e n t consumption. I t i s l i k e l y t h a t t h e r e c o v e r y o f the l e a c h e d r o u g h e r c o n c e n t r a t e c o u l d be i n c r e a s e d by a d j u s t i n g t h e r e a g e n t s e i t h e r by i n c r e a s i n g t h e dosage o f the one used i n our e x p e r i m e n t s o r u s i n g a d i f f e r e n t t y p e . The d e t e r m i n a t i o n o f t h e a p p r o p r i a t e f l o t a t i o n p r o c e d u r e would have r e q u i r e d many more e x p e r i m e n t s and was n o t i n t h e scope o f t h i s p r o j e c t . However the i n f o r m a t i o n g a t h e r e d i s s u f f i c i e n t t o i n d i c a t e t h a t t h e l e a c h i n g o f a c o p p e r r o u g h e r c o n c e n t r a t e w i t h sodium h y p o c h l o r i t e does not d e c r e a s e 74 100 3 804 or w 6 0 O o or 8 4 0 3 O 2 0 - \u00E2\u0080\u0094 o Rougher Con. Not L e a c h e d Leached \u00E2\u0080\u0094 A \u00C2\u00A3k H= ' \u00E2\u0080\u0094=\u00C2\u00B1r 4 z+? 1 rA= 1 =h- 1-16 20 2'4 28 32 \"^6 PROGRESSIVE GRADE (% Cu) FIG. 2 9 - RECOVERY- GRADE CURVES FOR THE SECONDARY FLOTATION OF LEACHED ROUGHER CONCENTRATES. 75 t o a g r e a t e x t e n t t he f l o t a b i l i t y o f the m a t e r i a l and t h a t t he a d d i t i o n a l c o s t s o f f l o t a t i o n r e a g e n t s i f a l e a c h i n g c i r c u i t were i n t r o d u c e d t o a c o n v e n t i o n a l c o n c e n t r a t i o n p r o c e s s might not be s i g n i f i c a n t . 4.3.7 S t a b i l i t y o f Sodium H y p o c h l o r i t e S o l u t i o n s S e v e r a l e x p e r i m e n t s were per f o r m e d t o d e t e r m i n e t h e s t a b i l i t y o f NaOCl under t he c o n d i t i o n s used i n t h e l e a c h i n g s t u d i e s . The r e g i o n o f pH i n f l u e n c e s t u d i e d was between 12 a t which NaOCl i s g e n e r a l l y s t o r e d f o r minimum d e c o m p o s i t i o n and 7 a t which t h e r e a c t i o n t o H0C1 i s r a p i d l y f a v o r e d . Two t e m p e r a t u r e s were s e l e c t e d f o r comparison o v e r t he same range as i n v e s t i g a t e d i n t h e m o l y b d e n i t e d i s s o l u t i o n , and t h e i n i t i a l c o n c e n t r a t i o n o f NaOCl was s i m i l a r i n a l l r u n s . [NaOCl] as used i n t h i s s e c t i o n i s a measure o f the t o t a l a c t i v e c h l o r i n e s p e c i e s , t h a t i s O C l \" , H0C1 and C10 2~. R e s u l t s f o r some runs have been p l o t t e d i n F i g u r e 30 and 31. The d e t r i m e n t a l e f f e c t o f both h i g h e r t e m p e r a t u r e s and lower pH a r e o b s e r v e d . A t lower t e m p e r a t u r e s t h e r e i s no me a s u r a b l e d e c r e a s e i n t h e c o n c e n t r a t i o n o f NaOCl a t a hydrogen i o n c o n c e n t r a t i o n i n which t h e f a s t e s t r a t e s o f m o l y b d e n i t e d i s o l u t i o n were o b s e r v e d . In two runs, samples were a n a l y z e d u s i n g t he p o t e n t i o m e t r i c t e c h n i q u e w i t h t he purpose o f d i s t i n g u i s h i n g C 1 0 2 \" from O C l \" and HC10. No C 1 0 2 was o b s e r v e d a t h i g h pH and the c o n c e n t r a t i o n was v e r y s m a l l and e r r a t i c a t pH 7 o b s t r u c t i n g any q u a n t i t a t i v e a n a l y s i s . 76 ~ 12 pH 7 1 1 h 2 3 4 TIME (hs) FIG. 3 0 - EFFECT OF pH ON THE DECOMPOSITION OF HYPOCHLORITE AT 60\u00C2\u00B0 C. 77 12 FIG. 31- EFFECT OF pH ON THE DECOMPOSITION OF HYPOCHLORITE AT 35\u00C2\u00B0 C. C h a p t e r 5 DISCUSSION 5.1 O x i d a t i o n o f M o l y b d e n i t e The r e s u l t s o f the d i s s o l u t i o n e x p e r i m e n t s i n d i c a t e t h a t t he r e a c t i o n between m o l y b d e n i t e and aqueous s o l u t i o n s o f sodium h y p o c h l o r i t e goes t o c o m p l e t i o n v e r y r a p i d l y under t h e c o n d i t i o n s used i n t h i s s t u d y . T h i s was found t o be t r u e both w i t h a h i g h grade m o l y b d e n i t e c o n c e n t r a t e and c o p p e r r o u g h e r c o n c e n t r a t e s i n which t he MoS 2 c o n t e n t i s v e r y s m a l l . T o t a l d i s s o l u t i o n o f MoS 2 from d i l u t e p u l p s was o b t a i n e d i n a l l c a s e s w i t h i n 45 minutes l e a c h i n g t i m e . The o v e r a l l s t o i c h i o m e t r y o f t h e r e a c t i o n as d e t e r m i n e d by [6,14] i s : MoS 2 + 9 NaOCl + 6 NaOH -*\u00E2\u0080\u00A2 NazMoO^ + 2 N a 2 S 0 4 \u00E2\u0080\u00A2+ 9 NaCI + 3 H 20 (3) which i s v a l i d i n t h e c a s e s i n which NaOCl i s i n e x c e s s and t h e r e f o r e both Mo and S can be assumed t o be o x i d i z e d t o t h e i r h i g h e s t s t a t e . T h i s r e a c t i o n was found t o a c c u r a t e l y r e p r e s e n t a l l t h e e x p e r i m e n t s u s i n g t h e MoS 2 c o n c e n t r a t e and a t l e a s t t h e i n i t i a l s t a g e s i n the d i s s o l u t i o n o f MoS 2 from t h e r o u g h e r c o n c e n t r a t e s . No attempts have been r e p o r t e d o f 78 79 e s t a b l i s h i n g t h e s t o i c h i o m e t r y o f t h e r e a c t i o n when M0S2 i s i n e x c e s s , as would be t h e c a s e i n t h e f i n a l s t a g e s o f t h e r o u g h e r c o n c e n t r a t e d i s s o l u t i o n when t h e [NaOCl] i s v e r y low, and was not a t t e m p t e d i n t h i s s t u d y because o f t h e c o m p l e x i t i e s o f p a r a l l e l r e a c t i o n s and c a t a l y z e d d e c o m p o s i t i o n o f the r e a g e n t . The A6\u00C2\u00B0of r e a c t i o n (3) was c a l c u l a t e d as -670 k c a l , which p r e d i c t s t h e h i g h l y f a v o r a b l e thermodynamic tendency o f d i s s o l u t i o n o f MoS 2. A l i n e a r dependence was o b s e r v e d between t h e r a t e s o f d i s s o l u -t i o n o f MoS 2 and t h e s u r f a c e a r e a i n d i c a t i n g a heterogeneous r e a c t i o n . The a p p a r e n t a c t i v a t i o n e n e r g y o f t h e r e a c t i o n (6.3 k c a l / m o l e ) i s on the b o r d e r o f t h e r e g i o n c h a r a c t e r i s t i c o f d i f f u s i o n c o n t r o l l e d r e a c t i o n s . T h e r e f o r e t h e r a t e d e t e r m i n i n g s t e p c o u l d be e i t h e r under e x c l u s i v e c h e m i c a l o r p o s s i b l y mixed c h e m i c a l and d i f f u s i o n c o n t r o l . I t i s c o n s i d e r e d t h a t t h e a c t i v a t i o n energy o f 6.3 k c a l / m o l e o b t a i n e d i n t h i s work i s i n c l o s e agreement w i t h t h e v a l u e o f 5.25 k c a l / mole o b t a i n e d by [14] u s i n g compressed specimens o f h i g h grade MoS 2. I t - h a s been o b s e r v e d i n t h i s s t u d y , t h a t t h e r e a c t i o n between C u F e S 2 and NaOCl produces a p r o t e c t i v e c o a t i n g which p r e v e n t s f u r t h e r d i s s o l u t i o n . The r e a c t i o n o f NaOCl w i t h ZnS has a l s o been s t u d i e d [24] and t h e o b s e r v a -t i o n o f a z i n c h y d r o x i d e and z i n c f e r r i t e l a y e r on t h e s u r f a c e o f s p h a l e r i t e was c o n s i d e r e d t o be t h e cause o f t h e d e c r e a s e i n t h e r e a c t i o n r a t e . The a p p a r e n t a c t i v a t i o n e n e r g i e s have been measured i n both c a s e s ; 5 k c a l f o r t h e r e a c t i o n w i t h C u F e S 2 and 4.6 k c a l f o r the r e a c t i o n w i t h ZnS. 80 The s i m i l a r v a l u e s o f a c t i v a t i o n energy f o r r e a c t i o n s i n which the r e a c t i o n p r o d u c t s a r e e n t i r e l y d i f f e r e n t i n n a t u r e would s u p p o r t the c o n c e p t t h a t the r a t e c o n t r o l l i n g s t e p i s t h e d i f f u s i o n o f NaOCl t h r o u g h t h e boundary l a y e r . S i n c e NaOCl has a h i g h s o l u b i l i t y i t can be e x p e c t e d t h a t most o f i t . . i s i o n i z e d i n a l k a l i n e s o l u t i o n s even a t low t e m p e r a t u r e s . The q u a n t i t y o f O C T i o n s however w i l l be d e t e r m i n e d by t h e pH o f t h e s o l u t i o n s i n c e t h e r e e x i s t s an e q u i l i b r i u m between O C T and m o l e c u l a r H0C1 which i s i n f l u e n c e d d i r e c t l y by t h e [ H + ] as r e p r e s e n t e d by r e a c t i o n (17) Ka 0C1\" + H + H0C1 (17) The p r o p o r t i o n o f each s p e c i e s has been p l o t t e d a g a i n s t pH i n F i g u r e 32. F i g . 32. H y p o c h l o r i t e and h y p o c h l o r o u s a c i d c o n c e n t r a t i o n s as a f u n c t i o n o f pH. 81 A l t h o u g h i t has been r e p o r t e d t h a t t h e o x i d i z i n g power o f t h e i o n i z e d and m o l e c u l a r s p e c i e s o f h y p o c h l o r i t e a r e s i m i l a r [34] i t was o b s e r v e d i n t h i s work t h a t t h e r a t e s o f o x i d i a t i o n o f MoS 2 i n c r e a s e w i t h i n c r e a s i n g pH u n t i l a maximum i s o b t a i n e d i n the r e g i o n pH 8.5-9.5 i n which a l l h y p o c h l o r i t e e x i s t s as 0C1~ i o n s s u g g e s t i n g t h a t i t i s t h e O C T i o n which p l a y s t h e major r o l e i n t h e o x i d a t i o n r e a c t i o n . The i n f l u e n c e o f [ H + ] on t h e r a t e s o f o x i d a t i o n i s complex as shown i n F i g u r e 10. I t would be e x p e c t e d from r e a c t i o n (3) t h a t any i n c r e a s e i n the [OH ] would f a v o r t h e f o r m a t i o n o f MoOt,-. T h i s was o b s e r v e d i n l e a c h i n g e x p e r i m e n t s v a r y i n g t h e pH from 7 t o 9.5. But any i n c r e a s e o v e r t h i s r e g i o n r e s u l t e d i n a d e c r e a s e o f t h e r e a c t i o n r a t e s . These r e s u l t s d i f f e r from t h e work o f Ioardanov [14] who r e p o r t e d t h a t t h e r a t e o f o x i d a t i o n i s not i n c r e a s e d by an i n c r e a s e i n f r e e sodium base above t h e t h e o r e t i c a l l y r e q u i r e d . A l t h o u g h most o f t h e o t h e r i n v e s t i g a -t i o n s on t h i s r e a c t i o n [6,8] have worked i n the h i g h a l k a l i n e r e g i o n i t i s f e l t t h a t t h i s was s e l e c t e d o n l y on t h e b a s i s o f r e a g e n t s t a b i l i t y . To e x p l a i n t h e d e c r e a s e i n the r a t e s o f o x i d a t i o n above pH 10 i t was c o n s i d e r e d t h a t t h e r e c o u l d e x i s t c o m p e t i t i o n between 0C1 a d s o r p -t i o n and some o t h e r s p e c i e s which d e c r e a s e d t h e c o n c e n t r a t i o n o f o x i d a n t on t h e s u r f a c e o f the MoS 2. The z e t a p o t e n t i a l o f m o l y b d e n i t e i n t h e absence o f any c o l l e c t o r s i s shown i n F i g u r e 33 i n d i c a t i n g an i n c r e a s e i n t h e n e g a t i v e v a l u e o f \u00C2\u00A3 f o r both h i g h e r a c i d and h i g h e r a l k a l i n e s o l u t i o n s . S: Chander and D.W. F u e r s t e n a u [ 3 3 ] i n s t u d y i n g t h e n a t u r a l f l o t a b i l i t y o f m o l y b d e n i t e were a b l e t o o b s e r v e t h a t on a d d i t i o n o f MoO^ 82 ' 4 5 6 7 8 9 10 II 12 pH F i g . 33. E, p o t e n t i a l o f m o l y b d e n i t e as a f u n c t i o n o f pH. i o n s i n a l k a l i n e s o l u t i o n s t h e z e t a p o t e n t i a l was even more n e g a t i v e and s u g g e s t e d t h a t MoOV i o n s a r e s t r o n g l y s p e c i f i c a l l y a b s o r b e d on m o l y b d e n i t e . I t seems l i k e l y then t h a t i n a l k a l i n e s o l u t i o n s an i n c r e a s e i n the pH r e s u l t s i n some p r e f e r e n t i a l a d s o r p t i o n o f Mo0 4~ and p o s s i b l y OH\" i n s t e a d o f O C l \" . In the l e a c h i n g e x p e r i m e n t s performed a t h i g h e r pH's i t was o b s e r v e d t h a t lower r a t e s o f d i s s o l u t i o n o f MoS 2 were o b t a i n e d when M o 0 4 -i o n s were i n t e n t i o n a l l y added t o the h y p o c h l o r i t e s o l u t i o n s . Under t h e s e c o n d i t i o n s t h e lower r a t e s o f m o l y b d e n i t e d i s s o l u t i o n can be e x p l a i n e d i f i t assumed t h a t some MoS 2 s i t e s a d s o r b Mo0 4~ i o n s and r e a c t f o r m i n g an i n s o l u b l e porous o x i d e t h r o u g h which t he OCl\" must p e n e t r a t e i n o r d e r t o r e a c t w i t h t h e MoS 2 and t h a t t h e d i f f u s i o n t h r o u g h i t r e t a r d s the v e l o c i t y o f d i s s o l u t i o n . 83 The p o s s i b l e r e a c t i o n s a r e : 7 Mo0\ = + MoS 2 + 4 OH\" 2 Mo^On + 2 S 0 4 = + 2 H 20 (18) MoOiT + MoS 2 2 Mo0 2 + 2 S (19) Th e r e a p p e a r s t o be g r e a t d i s c r e p a n c y between t he r e s u l t s o b t a i n e d i n t h i s s t u d y and t h o s e o b t a i n e d w i t h e l e c t r o o x i d a t i o n l e a c h i n g o f m o l y b d e n i t e . In t h e i r f i r s t r e p o r t B.J. S c h e i n e r and R.E. L i n d s t r o n [18] d e t e r m i n e d t h e pH f o r optimum e x t r a c t i o n as b e i n g i n the range o f 6-8. L a t e r work on the c o n t r o l o f c h l o r a t e f o r m a t i o n d u r i n g e l e c t r o o x i d a -t i o n l e a d D.S. B a r r , R.E. L i n d s t r o n and J.T. H e n d r i x [ 2 2] t o s u g g e s t t h a t maximum m o l y b d e n i t e d i s s o l u t i o n i s o b t a i n e d a t a pH between 4- and 5. In t h e i r s t u d y t h e y o b s e r v e d a d e c r e a s e i n t h e r a t e o f m o l y b d e n i t e d i s -s o l u t i o n when i n c r e a s i n g t h e pH from 5.5 t o 8. I t i s i m p o s s i b l e t o compare both p r o c e s s e s d i r e c t l y as t h e r e i s no me n t i o n o f any s p e c i f i c r a t e s . However i t i s p o s s i b l e t o o b s e r v e i n [22] t h a t f o r equal c o n c e n t r a t i o n s o f h y p o c h l o r i t e , t h e e l e c t r o o x i d a t i o n p r o c e s s produces a t l e a s t 50 t i m e s more c h l o r a t e than a normal h y p o c h l o r i t e c o n t a i n i n g s o l u t i o n r e g a r d l e s s o f t h e pH. C o n t r a r y t o t h e b e l i e f t h a t because C 1 0 3 ~ i s s t a b l e i t does not a f f e c t t h e m o l y b d e n i t e d i s s o l u t i o n , i t was o b s e r v e d i n t h i s work ( F i g u r e 12) t h a t t h e p r e s e n c e o f C 1 0 3 \" d e c r e a s e s the r e a c t i o n r a t e s . In t h i s s t u d y t h e l o w e s t pH a t which d i s s o l u t i o n o f MoS 2 was performed was 7 and i n t h e s e s o l u t i o n s , as can be o b s e r v e d from F i g u r e 33, 84 HC10 a c i d p r e d o m i n a t e s o v e r 0C1 . The r e a s o n s f o r not s t u d y i n g t h e e f f e c t s below t h i s r e g i o n a r e two: f i r s t as a l r e a d y p o i n t e d o u t , t h e r e i s e v i d e n c e t h a t i t i s the 0C1~ i o n s which p a r t i c i p a t e m o s t l y i n t h e d i s s o l u t i o n o f MoS 2 and second r e g a r d l e s s o f the ty p e o f mechanism adop t e d t o e x p l a i n h y p o c h l o r i t e d e c o m p o s i t i o n t o c h l o r a t e (which w i l l be d e a l t w i t h b e l o w ) , i t i s g e n e r a l l y a c c e p t e d t h a t i t i s s t r o n g l y dependent on HC10 a c i d and t h e r e f o r e from 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 i t would be e x p e c t e d t h a t t h e l o s s e s o f h y p o c h l o r i t e due t o d e c o m p o s i t i o n would p r o h i b i t i t s a p p l i c a t i o n . The s l o p e o f the s t r a i g h t l i n e i n the p l o t r e a c t i o n r a t e s f o r o x i d a t i o n o f MoS 2 a g a i n s t i n i t i a l h y p o c h l o r i t e c o n c e n t r a t i o n i s a p p r o x i -m a t e l y one i n d i c a t i n g a f i r s t o r d e r dependence on the r e a g e n t . T h i s i s i n agreement w i t h t h e work o f Ioardanov and Z e l i k m a n [14] and on e x t r a p o l a -t i o n o f Bhappu et al. [6] d a t a . I f i t i s assumed t h a t i n the pH r e g i o n 7-8.5 t h e c o n c e n t r a t i o n o f OH\" i o n s does not a f f e c t t h e r a t e o f r e a c t i o n d i r e c t l y but t h r o u g h t h e a v a i l a b i l i t y o f 0C1~ as d e s c r i b e d i n r e a c t i o n (17) and t h a t i n t h e pH r e g i o n 8.5-9.5 t h e r a t e s a're inde p e n d e n t o f [0H~] then't'he r e a c t i o n between MoS 2 and NaOCl can be d e s c r i b e d as a second o r d e r r e a c t i o n , t h e r e f o r e , Rate o f O x i d a t i o n o f MoS 2 = d = k i [ M o S 2 ] [NaOCl] (20) The e x p e r i m e n t a l r a t e c o n s t a n t k i was d e t e r m i n e d u s i n g t h e d a t a i n F i g u r e 7 o b t a i n e d from l e a c h i n g e x p e r i m e n t s i n which t he i n i t i a l s u r f a c e a r e a o f m o l y b d e n i t e was i d e n t i c a l , by p l o t t i n g a d o u b l e l o g a r i t h m i c 85 c u r v e o f the r a t e s o f MoO^ - appearance a g a i n s t c o n c e n t r a t i o n o f NaOCl, F i g u r e 34. A c t u a l l y t h e v a r i a t i o n w i t h r e s p e c t t o [NaOCl] i s o n l y con-s i d e r e d , i n the form o f i u j o o * : - k 2 [ N a 0 C i ] but as the s u r f a c e a r e a was i d e n t i c a l a t t h e s t a r t o f e v e r y e x p e r i m e n t and r a t e s were o b t a i n e d o n l y i n t h e i n i t i a l s t a g e i t i s p o s s i b l e t o i n c l u d e t h e v a r i a t i o n w i t h r e s p e c t t o MoS 2 i n t h e e m p i r i c a l c o n s t a n t k 2 The v a l u e o f k 2 was d e t e r m i n e d as 2.29 m i n \" 1 . As t h e s u r f a c e a r e a was c a l c u l a t e d as 120 cm 2 the s p e c i f i c r a t e c o n s t a n t k 2 = 1.90 x 1 0 \" 2 m i n \" 1 T h e r e e x i s t s no d a t a on r e a c t i o n r a t e c o n s t a n t s f o r t h i s system w i t h which t o compare t h i s r e s u l t . The upper l i m i t o f a r e a c t i o n r a t e i n a d i f f u s i o n c o n t r o l l e d r e a c t i o n i s r e a c h e d when i t i s assumed t h a t t h e c h e m i c a l r e a c t i o n i s i n s t a n t a n e o u s , i n which c a s e t h e c o n c e n t r a t i o n a t t h e i n t e r f a c e i s z e r o T h e r e f o r e d[NaQCl] = D.A.C. d t 6 i n which: D = D i f f u s i o n c o e f f i c i e n t o f h y p o c h l o r i t e i n aqueous media = 1.84 x 1 0 \" 5 cm 2/sec [35] A = S u r f a c e a r e a o f m o l y b d e n i t e = 120 cm 2 C = C o n c e n t r a t i o n i n g/1 o f h y p o c h l o r i t e = 16 g/1 6 = d i f f u s i o n l a y e r t h i c k n e s s f o r an i n t e n s e l y a g i t a t e d system = 10\" 3 cm [36] I I I 1 I I 1 1 I 1 1 I I I 1\u00E2\u0080\u0094 0 .2 .4 .6 .8 1.0 1.2 1.4 Log NaOCl (g/l) 34 - LOG - LOG CURVE OF THE RATES OF OXIDATION VS. [NaOCl] . 87 and t h e maximum r a t e o f h y p o c h l o r i t e consumption f o r t h e s e c o n d i t i o n s i s : d(NaOCl) _ 9 , 9 . . jj\u00C2\u00A3 2.12 g/rmn S i n c e t h e s t o i c h i o m e t r y o f t h e r e a c t i o n d i c a t e s a consumption o f 9 moles o f NaOCl p e r mole o f m o l y b d e n i t e , t h e maximum r a t e o f molybdate a p p e a r a n c e was c a l c u l a t e d a s : d(MoO i t =) cnr. / \u00E2\u0080\u00A2 ^ ' = 505 mg/min The e x p e r i m e n t a l r a t e f o r t h e s e c o n d i t i o n s was measured, and: dCMoOO c \u00E2\u0080\u009E , . d t P = m g / m i n The c a l c u l a t e d d i f f u s i o n r a t e b e i n g t e n ti m e s f a s t e r t h a n t h e o b s e r v e d r a t e would s u g g e s t c h e m i c a l c o n t r o l o f t h e l e a c h i n g . However, t h e low a c t i v a t i o n energy and t h e marked dependency o f the l e a c h r a t e on a g i t a -t i o n c o u l d f a v o r t h e c o n c e p t o f mixed d i f f u s i o n and c h e m i c a l c o n t r o l o f th e l e a c h i n g r a t e b e i n g o p e r a t i v e . 5.2 O x i d a t i o n o f C h a l c o p y r i t e Both c h a l c o p y r i t e and p y r i t e were o b s e r v e d t o r e a c t . w i t h sodium h y p o c h l o r i t e but t h e e x t e n t o f t h e r e a c t i o n s a r e v e r y s m a l l i n comparison w i t h m o l y b d e n i t e . A l t h o u g h t h e f a s t e l i m i n a t i o n o f t h e c o a t i n g formed on C u F e S 2 u s i n g d i l u t e H2SO4 s u g g e s t e d t h a t i t was an o x i d e , o b s e r v a t i o n s of t h e 88 p r e c i p i t a t i o n o f c o p p e r out o f s o l u t i o n when the c o n c e n t r a t i o n o f NaOCl d e c r e a s e d i n d i c a t e d t h a t t h e n a t u r e o f the p r o d u c t s formed on t h e s u r f a c e o f C u F e S 2 was complex. I t i s r e p o r t e d i n the l i t e r a t u r e [37] t h a t Cu p r e c i p i t a t e s f r o m a l k a l i n e s o l u t i o n s as compounds which a r e p r o b a b l y s o l i d s o l u t i o n s o f CuO and C u ( 0 H ) 2 , t h e appearance b e i n g s i m i l a r t o t h e p r e c i p i t a t e s o b t a i n e d from t h e l e a c h i n g o f C u F e S 2 and r o u g h e r c o n c e n t r a t e s . Both s p e c i e s a r e t h e r m o d y n a m i c a l l y s t a b l e i n t h i s pH r e g i o n . T h i s c o a t i n g formed on C u F e S 2 e f f e c t i v e l y i n h i b i t s any f u r t h e r r e a c t i o n and t h e r e s u l t s from m i c r o p r o b e a n a l y s i s on c r o s s s e c t i o n s o f l e a c h e d p a r t i c l e s d e m o n s t r a t e s t h a t t h e d i s t r i b u t i o n o f e l e m e n t s i n the n e x t t o s u r f a c e l a y e r s i s u n a l t e r e d . The c o n t i n u e d consumption o f r e a g e n t i s t h e r e f o r e e x c l u s i v e l y o f a d e c o m p o s i t i o n n a t u r e . The r a t e o f f o r m a t i o n o f t h e o x i d e c o a t i n g i s d i f f i c u l t t o c a l c u l a t e from the d a t a o b t a i n e d s i n c e no r e d i s s o l u t i o n e x p e r i m e n t s were pe r f o r m e d . The o b s e r v a t i o n s o f t h e l e a c h i n g time e f f e c t on t h e S/Cu r a t i o change on t h e C u F e S 2 s u r f a c e i n d i c a t e s t h a t the f o r m a t i o n o f t h e o x i d e l a y e r i s f a s t e r t h a n t h e d i s s o l u t i o n o f c o p p e r i n t h e l e a c h s o l u t i o n . T h e r e f o r e i t i s p r o b a b l e t h a t the o x i d a t i o n r a t e o f C u F e S 2 i s s i m i l a r t o t h e o x i d a t i o n r a t e s o f MoS 2 when equal s u r f a c e a r e a s a r e exposed. T h i s s i m i l a r i t y o f t h e o x i d a t i o n r a t e s o f t h e s e two m i n e r a l s was a l s o s u g g e s t e d by B\-Stump and Y. Berube [26] working w i t h a d i s s o l v e d o x y g e n - c a u s t i c system. However t h e i r c o n c l u s i o n t h a t because o f t h e s i m i l a r o x i d a t i o n r a t e s , p r e f e r e n t i a l l e a c h i n g cannot be a c h i e v e d i s not s u p p o r t e d by t h i s work. 89 The p r i n c i p a l d i f f e r e n c e between t h e o x i d a t i o n o f C u F e S 2 and MoS 2 i s t h a t w h i l e t h e f i r s t forms a v e r y e f f e c t i v e p r o t e c t i v e l a y e r , t h e l a t e r forms a r e a d i l y s o l u b l e i o n i c s p e c i e s i m m e d i a t e l y e x p o s i n g f r e s h s u r f a c e . T h i s was c o n f i r m e d by l e a c h i n g e q u a l s u r f a c e a r e a s o f C u F e S 2 and MoS 2 i n a s o l u t i o n w i t h a g r e a t e x c e s s o f NaOCl, F i g u r e 22. The f a v o r a b l e d i s s o l u t i o n o f m o l y b d e n i t e i n t h i s e x p e r i m e n t d e m o n s t r a t e s t h a t i f a m a t e r i a l which c o n s i s t s m a i n l y o f t h e s e two m i n e r a l s i s ground t o i t s l i b e r a t i o n s i z e and a g i t a t e d v i g o r o u s l y i n a s o l u t i o n o f NaOCl t h e p r e f e r -e n t i a l e x t r a c t i o n o f molybdenum s h o u l d be p o s s i b l e . F u r t h e r m o r e t h e r e s u l t s p l o t t e d i n F i g u r e 23 i n d i c a t e t h a t a l t h o u g h t h e p r e s e n c e o f C u F e S 2 l o w e r s t h e MoS 2 d i s s o l u t i o n r a t e s s l i g h t l y , t h e r e i s not a g r e a t v a r i a t i o n i n t h e t o t a l l e a c h i n g t i m e s . T h i s f a c t w i l l be i m p o r t a n t i n t h e d e s i g n o f the c a p a c i t y o f l e a c h i n g equipment as t h e r e a r e c o n t i n u e d v a r i a t i o n s < i n t h e MoS 2 c o n t e n t . o f r o u g h e r c o n c e n t r a t e s . 5.3 L e a c h i n g o f M o l y b d e n i t e from Copper Rougher C o n c e n t r a t e s The r e s u l t s o f t h e e x c e s s i v e consumption o f h y p o c h l o r i t e when l e a c h i n g r o u g h e r c o n c e n t r a t e s was a t t r i b u t e d i n l a t e r e x p e r i m e n t s t o be due p r i n c i p a l l y t o t h e h i g h c o n t e n t o f c o p p e r o x i d e produced i n i t s p r e p a r a t i o n f o r e x p e r i m e n t s . The p r o c e s s o f d r y i n g t h e ro u g h e r c o n c e n t r a t e i n o r d e r t o e l i m i n a t e f l o t a t i o n r e a g e n t s and t o c o n v e n i e n t l y add mass samples t o t h e e x p e r i m e n t s , was u n d e r t a k e n w i t h o u t much c o n s i d e r a t i o n o f t h e change i t would produce i n i t s r e a c t i v i t y . N e i t h e r was i t known 90 a t t h i s s t a g e , t h a t t h e o x i d e s o f some heavy m e t a l s a c t e d c a t a l y t i c a l l y on t h e d e c o m p o s i t i o n o f h y p o c h l o r i t e s . T h e r e f o r e t h e d a t a o b t a i n e d from l e a c h i n g e x p e r i m e n t s o f the p r e t r e a t e d r o u g h e r c o n c e n t r a t e i s o f l i t t l e s i g n i f i c a n c e t o t h e g e n e r a l aim o f t h i s t h e s i s , and the most u s e f u l i n f o r m a t i o n d e r i v e d from i t , i s t h a t s p e c i a l p r e c a u t i o n s would have t o be ta k e n i n a p r a c t i c a l p r o c e s s i n o r d e r t o m a i n t a i n a low c o n t e n t o f o x i d i z e d c o p p e r m i n e r a l s i n the f e e d . In t h e s e e x p e r i m e n t s w i t h a c o n t e n t a v e r a g i n g 1.6% CuO i t was o b s e r v e d t h a t complete e x t r a c t i o n o f MoS 2 c o u l d o n l y be o b t a i n e d w i t h a consumption o f a t l e a s t 400% t h e t h e o r e t i c a l l y r e q u i r e d . S i m i l a r h y p o c h l o r i t e consumption was r e p o r t e d by K .A . S h a p i r o et al. [ 9 ] f o r the l e a c h i n g o f a low molybdenum i n t e r m e d i a t e c o n c e n t r a t e . No e x p l a n a t i o n was g i v e n o f t h i s e x c e s s i v e c o n s u m p t i o n , however t he c o n c e n t r a t e r e c e i v e d a d r y i n g p r o c e s s s i m i l a r t o t h e one used i n t h i s work. The e x p l a n a t i o n o f t h i s g r e a t NaOCl consumption i s t h a t t h e co p p e r o x i d e formed on the s u r f a c e o f CuF e S 2 d u r i n g d r y i n g a c t s as a c a t a l y s t i n t h e d e c o m p o s i t i o n o f t h e reagent, a c c e l e r a t i n g t h e r a t e o f d e c o m p o s i t i o n t o a v a l u e s i m i l a r t o the r a t e o f MoS 2 o x i d a t i o n . The r e s u l t o f m a i n t a i n i n g t h e r o u g h e r c o n c e n t r a t e i n a p u l p t o m i n i m i z e c o n t a c t w i t h t h e a i r , r e d u c e d t h e h y p o c h l o r i t e consumption con-s i d e r a b l y . In the e x p e r i m e n t s w i t h a c o p p e r o x i d e c o n t e n t o f 0.52%, t o t a l r e c o v e r y was o b t a i n e d w i t h o n l y 150% o f the t h e o r e t i c a l l y r e q u i r e d h y p o c h l o r i t e . I f a l e a c h i n g p r o c e s s i s i n c o r p o r a t e d i m m e d i a t e l y a f t e r t h e p r i m a r y f l o t a t i o n , i t s h o u l d be p o s s i b l e t o c o n t r o l t h e o x i d e c o n t e n t below 0.5% s e c u r i n g t h e low r e a g e n t consumptions o b t a i n e d i n t h e s e b a t c h e x p e r i m e n t s . 91 5.4 F l o t a t i o n o f Leached Rougher C o n c e n t r a t e s As the s u r f a c e s o f t h e component m i n e r a l s ( n o t i c e a b l y C u F e S 2 and F e S 2 ) i n the c o p p e r r o u g h e r c o n c e n t r a t e a r e o x i d i z e d d u r i n g t h e h y p o c h l o r i t e l e a c h i n g o f m o l y b d e n i t e , i t was n e c e s s a r y t o d e t e r m i n e i f t h e r o u g h e r c o n c e n t r a t e c o u l d be r e f l o a t e d e c o n o m i c a l l y i n t h e s e c o n d a r y f l o t a t i o n i n o r d e r t o o b t a i n t h e f i n a l c o n c e n t r a t e . The r e s u l t s shown i n F i g u r e 29 i n d i c a t e t h a t the l e a c h e d r o u g h e r c o n c e n t r a t e s t i l l has a s i m i l a r r e c o v e r y - g r a d e c o r r e s p o n d e n c e as t h e non-l e a c h e d m a t e r i a l , the d i f f e r e n c e i s i n t h e consumption o f c o l l e c t o r . In t h e s e e x p e r i m e n t s i n which the same c o l l e c t o r was used f o r both m a t e r i a l s , t h e net a d d i t i o n f o r the s e c o n d a r y f l o t a t i o n would be 2 kgms/ton o f concen-t r a t e . The c o s t o f the e x t r a c o l l e c t o r dosage i s v e r y s m a l l compared t o t h e molybdenum r e c o v e r e d [ 3 8 ] . I t i s a l s o n e c e s s a r y t o i n d i c a t e t h a t e x p e r i m e n t a t i o n w i t h o t h e r r e a g e n t s more s p e c i f i c t o o x i d i z e d s u l f i d e s u r f a c e s c o u l d d e c r e a s e t h i s c o s t even more. The i n f o r m a t i o n g a t h e r e d i s s u f f i c i e n t t o i n d i c a t e t h a t t h e l e a c h i n g o f copper r o u g h e r c o n c e n t r a t e s w i t h NaOCl does n o t d e c r e a s e t o a g r e a t e x t e n t t h e f l o t a b i l i t y and t h a t t h e a d d i t i o n a l c o s t s o f f l o t a t i o n r e a g e n t s i f a l e a c h i n g c i r c u i t were i n t r o d u c e d t o a c o n v e n t i o n a l c o n c e n t r a -t i o n p r o c e s s might n o t be s i g n i f i c a n t . 5.5 P r o d u c t i o n o f Sodium H y p o c h l o r i t e A p r o c e s s d e s i g n e d to e x t r a c t molybdenum from c o p p e r r o u g h e r c o n c e n t r a t e u s i n g NaOCl would r e q u i r e t h a t the r e a g e n t be produced i n - s i t u . P u r c h a s i n g , t r a n s p o r t i n g and s t o r i n g e i t h e r sodium h y p o c h l o r i t e o r t h e 92 r e a g e n t s r e q u i r e d f o r i t s d i r e c t p r o d u c t i o n , c h l o r i n e and c a u s t i c most l i k e l y would r e n d e r t he p r o c e s s u n e c o n o m i c a l . Not c o n s i d e r i n g any s i d e r e a c t i o n s nor d e c o m p o s i t i o n o f sodium h y p o c h l o r i t e , t h e consumption o f t h i s r e a g e n t as i n d i c a t e d by s t o i c h i o m e t r y o f t h e r e a c t i o n between MoS 2 and NaOCl i s 7 kg per kg o f Mo e x t r a c t e d . The p r i c e o f pu r c h a s e d NaOCl i s between 20 and 32 c e n t s p er kg which would a l l o w a narrow margin under t h e p r i c e o f c o n t a i n e d Mo which i s a p p r o x i m a t e l y 3 $/kg. Sodium h y p o c h l o r i t e i s produced by r e a c t i n g c h l o r i n e and sodium h y d r o x i d e , both t h e s e r e a g e n t s a r e g e n e r a t e d s i m u l t a n e o u s l y by e l e c t r o l y z -i n g a sodium c h l o r i d e b r i n e . T h e r e a r e two a l t e r n a t i v e s i n t h e s e l e c t i o n o f e l e c t r o c h e m i c a l c e l l s f o r o n - s i t e g e n e r a t i o n o f sodium h y p o c h l o r i t e based on t h e s e p a r a -t i o n o f t h e a n o d i c and c a t h o d i c compartments. They a r e t h e diaphragm and t h e membrane c e l l s . Diaphragm c e l l t e c h n o l o g y has been employed f o r many y e a r s i n the p r o d u c t i o n o f c h l o r i n e w h i l e t h e membrane t e c h n o l o g y has been c o m m e r c i a l l y proven o n l y i n s m a l l s c a l e . T h e r e a r e no s i g n i f i c a n t d i f f e r e n c e s i n c u r r e n t e f f i c i e n c y between t h e s e two p r o c e s s e s [48]. The advantages o f t h e membrane c e l l a r e a h i g h e r c o n c e n t r a t i o n o f NaOCl and b e t t e r s a l t u t i l i z a t i o n . In b o t h c a s e s t h e c h l o r i n e formed a t t h e anode i s s e p a r a t e d from t h e d e p l e t e d b r i n e and hydrogen i s removed from t he c a u s t i c formed i n th e c a t h o d e compartment. C h l o r i n e and c a u s t i c i m m e d i a t e l y combine i n the r e a c t o r t o form sodium h y p o c h l o r i t e f o l l o w i n g t h e r e a c t i o n 2 NaOH + C l 2 \u00E2\u0080\u00A2* NaOCH NaCI + H 20 (23) 93 The p o s s i b i l i t y o f f o r m i n g NaOCl d i r e c t l y i n t h e c e l l s by c a r e f u l l y c o n t r o l l i n g c o n d i t i o n s t o m a i n t a i n some s e c o n d a r y r e a c t i o n s t h a t p roduce NaOCl i s not e c o n o m i c a l l y p r a c t i c a l because s o l u t i o n s p r o d u c e d t h i s way have a low c o n c e n t r a t i o n o f NaOCl and the e l e c t r i c a l e f f i c i e n c y i s low. The o p e r a t i n g c o s t s o f a h y p o c h l o r i t e g e n e r a t o r depend p r i n c i p a l l y on the s a l t u t i l i z a t i o n and t h e power consumption. The t h e o r e t i c a l consumption o f NaCl i s 1.6 Kg per kg o f NaOCl produced. In membrane c e l l s s a l t u t i l i z a t i o n can r e a c h 80% o f t h e t o t a l NaCl f e d t o the p r o c e s s . The minimum v a l u e s f o r c u r r e n t and v o l t a g e a r e 755 amp hr per kg o f c h l o r i n e and 2.15 v o l t s p e r c e l l . Data from o p e r a t i n g o n - s i t e g e n e r a t o r s o f h y p o c h l o r i t e f o r t h e t r e a t m e n t o f water [39] i n d i c a t e s a consumption o f 3.52 Kwh and 2.1 kg o f NaCl per kg o f NaOCl produced. P r o j e c t e d c o s t s f o r a p l a n t p r o d u c i n g NaOCl a t a r a t e o f o v e r 500 kg/day w i t h the assumptions s t a t e d i n T a b l e 9 i s about 12tt/kg which i s between 1/2 and 1/3 o f t h e p u r c h a s e d p r i c e . T a b l e 9 Economic Assumptions f o r t h e E s t i m a t i o n o f C o s t s i n the O p e r a t i o n o f a H y p o c h l o r i t e G e n e r a t o r [39] 1) power c h a r g e i n c l u d i n g demand charge = 2.8it/Kwh 2) s a l t ( s t a n d a r d g r a d e ) b u l k d e l i v e r y = 15$/Ton 3) p r o c e s s water - n e g l i g i b l e 4) l a b o r = 5.71 $/hr 5) l e n g t h o f a m o r t i z a t i o n 20 y e a r s 6) i n t e r e s t 5% 94 I t i s p o s s i b l e t o compare t h e power consumption between t h i s p r o c e s s and the e x t r a c t i o n o f m o l y b d e n i t e by e l e c t r o o x i d a t i o n , a l t h o u g h t h e d a t a f o r the l a t e r was o b t a i n e d from l e a c h i n g a low grade m o l y b d e n i t e o r e i n which t h e c o n t e n t o f Cu was o n l y 0.01% and t h e r e f o r e t h e consump-t i o n o f h y p o c h l o r i t e due t o c a t a l y t i c d e c o m p o s i t i o n s h o u l d be e x p e c t e d t o be n e g l i g i b l e . To a r r i v e a t t h e power consumption o f t h i s p r o c e s s i t has been e s t i m a t e d t h a t t o t a l r e c o v e r y f r o m a c o p p e r r o u g h e r c o n c e n t r a t e can be a c h i e v e d w i t h 160% o f t h e t h e o r e t i c a l amount o r 11.2 kg NaOCl/kg o f Mo and t h a t the power r a t i o i s 3.52 kwh/kg o f NaOCl. T h e r e f o r e : Power consumption e s t i m a t e d f o r t h i s p r o c e s s = 40 kwh/kg molybdenum Power consumption o b t a i n e d i n e l e c t r o o x i d a t i o n p r o c e s s = 53 kwh/kg molybdenum 5.6 K i n e t i c s o f Sodium H y p o c h l o r i t e D e c o m p o s i t i o n The p r o c e s s by which sodium h y p o c h l o r i t e s o l u t i o n s decompose has been s t u d i e d e x t e n s i v e l y . I t i s known t h a t t h e r e a c t i o n can be spontaneous and c a t a l y z e d even i n s l i g h t l y a l k a l i n e s o l u t i o n s . The p r o d u c t s o f r e a c t i o n a r e c h l o r i d e s , c h l o r a t e and oxygen. However t h e mechanisms remain c o n t r o -v e r t i a l p r i n c i p a l l y due t o a n a l y t i c a l d i f f i c u l t i e s . The r e a c t i o n s t h a t most g e n e r a l y d e s c r i b e t h e d e c o m p o s i t i o n o f NaOCl s o l u t i o n s a r e : HC10 + 2 0C1\" + C 1 0 3 \" + 2 . G l \" + H + (24) 95 2 HC10 + OCT -> C10 3 + 2 Cl + 2H (25) HCIO + OCl' 2 C l + 0 2 + H (26) R e a c t i o n s (24) and (25) r e p r e s e n t t h e same p r o c e s s , when the s o l u t i o n i s a l k a l i n e O C l \" pr e d o m i n a t e s and i t w i l l f o l l o w ( 2 4 ) , when the s o l u t i o n i s a c i d i f i e d i t f o l l o w s ( 2 5 ) . As t h e r e was no .agreement w i t h r e s p e c t t o t h e o r d e r o f t h e r e a c t i o n n o r w i t h r e g a r d t o r a t e c o n s t a n t s , i t was not p o s s i b l e t o d e t e r m i n e t h e o r e t i c a l l y the r a t e o f d e c o m p o s i t i o n . . f o r v a r i a t i o n s i n such v a r i a b l e s as pH and t e m p e r a t u r e . T h e r e f o r e a few e x p e r i m e n t s on d e c o m p o s i t i o n were pe r f o r m e d t o e s t a b l i s h t h e r e g i o n i n which t h e r e a g e n t c o u l d be used s a f e l y . The NaOCl used was t h e same as t h a t used i n some l e a c h i n g e x p e r i m e n t s , i t had been g e n e r a t e d i n t h e same e x p e r i m e n t a l c e l l as a l l t h e NaOCl s o l u t i o n s used i n t h i s work and c o u l d d i f f e r from o t h e r b a t c h e s i n t h e c o n c e n t r a t i o n o f c h l o r i d e . No p u r i f i c a t i o n was per f o r m e d b e f o r e t h e d e c o m p o s i t i o n r e a c t i o n s . The r a t e s o b t a i n e d from F i g u r e 32 were p l o t t e d on a d o u b l e l o g a r i t h m i c p l o t , l o g r a t e o f d e c o m p o s i t i o n i n mg/l/min v s . l o g c o n c e n t r a -t i o n o f NaOCl i n g/1. The r e s u l t s were a good f i t t i n g s t r a i g h t l i n e w i t h a s l o p e o f 2.5. T h i s o r d e r i s s i m i l a r t o the t h i r d o r d e r r e p o r t e d by s e v e r a l o t h e r w o r k e r s . As i t i s not the i n t e n t i o n o f t h i s work t o s t u d y t he mechanism o f NaOCl d e c o m p o s i t i o n a b r i e f summary o f some o f the most common pap e r s i n t h i s s u b j e c t i s p r e s e n t e d t o i n d i c a t e t h e wide v a r i a t i o n s i n r e s u l t s and i n t e r p r e t a t i o n s . 96 1. N.V.S. Knibbs and H. Pa l f r e e m a n [40] s u g g e s t e d t h a t the r a t e d HftC 1 = K [ H C 1 0 ] 2 [OCT'] (27 and t h a t c h l o r a t e formed by th e r e a c t i o n 0C1\" + 2 H0C1 C 1 0 3 \" + 2 H + + 2 C l \" (25 wi t h a f a s t r e f o r m a t i o n o f H0C1 by 2 0C1\" + 2 H + + 2 C l \" -> 2 HOC! + 2 C l \" (28 2. M.W. L i s t e r [41] and B.P. N i k o l s k i i et al. [ 4 2 ] . Both a g r e e t h a t i t i s a second o r d e r r e a c t i o n and c o r r o b o r a t e e a r l i e r work by F. F o e r s t e r [50] t h a t t h e r e a c t i o n goes t h r o u g h t h e i n t e r m e d i a t e f o r m a t i o n o f c h l o r i t e , t h e r e f o r e C 1 0 3 ~ i s formed i n a l k a l i n e s o l u t i o n s by the r e a c t i o n s HC10 + CIO\" + C1 0 2 \" + C l \" + H + C 1 0 2 \" + CIO\" + C I O 3 \" + C l \" HC10 + 2 CIO\" + C I O 3 \" + 2C1\" + H + (29 3. J . D'ans and H.E. Freund [43] d e s c r i b e the f o r m a t i o n o f c h l o r a t e v i a the f o r m a t i o n o f a complex o f two moles o f HC10 and one mole o f 0C1~ f o l l o w e d by the r e a r r a n g e m e n t o f t h e complex a c c o r d i n g t o 97 a f i r s t o r d e r r a t e c o n t r o l l i n g r e a c t i o n t o form c h l o r a t e . No c h l o r i t e was f o u n d i n t h e i r work which shows t h a t i t i s a t h i r d o r d e r r e a c t i o n . 4. H. Imagama et al. [44] a l s o i n d i c a t e s a t h i r d o r d e r r e a c t i o n , however the mechanism proposed i s t h a t HC10 r e a c t s w i t h C 1 0 2 _ l i b e r a t i n g c h l o r i n e d i o x i d e i n the f i r s t s t e p f o l l o w e d by a r e a c t i o n between C 1 0 2 and OCl t o form c h l o r a t e . In such a complex system i t i s d i f f i c u l t t o e x p l a i n t h e 2.5 o r d e r o b t a i n e d i n t h i s work, but as t h e e x p e r i m e n t s were pe r f o r m e d w i t h t h e r e a g e n t i n the same c o n d i t i o n s as was used i n the l e a c h i n g e x p e r i m e n t s , the r a t e c o n s t a n t s o b t a i n e d here a r e u s e f u l f o r comparing w i t h r a t e c o n s t a n t s f o r the l e a c h i n g o f MoS 2. From the i n t e r c e p t o f t h e l i n e s on F i g u r e 35 a t l o g NaOCl = 0 i t i s p o s s i b l e t o o b t a i n the d e c o m p o s i t i o n s r e a c t i o n s r a t e c o n s t a n t s k 3 f o r t h e d i f f e r e n t pH's a t 50\u00C2\u00B0C. From t h i s d a t a i t i s p o s s i b l e t o d e t e r m i n e t h e e f f e c t o f pH on the d e c o m p o s i t i o n r a t e s . A t pH 8 t h e r a t e i s 13 t i m e s the v e l o c i t y a t pH9, and a t pH 7 t h e r a t e i s 60 t i m e s f a s t e r than a t pH 9. An A r r h e n i u s c u r v e was p l o t t e d u s i n g the r a t e s from the decom-p o s i t i o n a t pH 7 a t t h e two t e m p e r a t u r e s e x p e r i m e n t e d (60\u00C2\u00B0 and 3 5 \u00C2\u00B0 C ) . The r e s u l t s show an a c t i v a t i o n e n e r g y o f a p p r o x i m a t e l y 20 k c a l . With the i n f o r m a t i o n o f the a c t i v a t i o n energy and t h e r a t e c o n s t a n t s f o r t h e d e c o m p o s i t i o n r e a c t i o n i t i s p o s s i b l e t o c a l c u l a t e t h e l o s s e s o f h y p o c h l o r i t e due t o d e c o m p o s i t i o n f o r a wide range o f o p e r a t i n g v a r i a b l e s . 98 .2 .4 .6 .8 1.0 1.2 Log [NaOCl] (g/1) FIG. 35 - LOG-LOG CURVES OF RATE OF DECOMPOSITION OF NaOCl VS. [NaOCl] . 99 The d e c o m p o s i t i o n r a t e c o n s t a n t was c a l c u l a t e d f o r the o p e r a t i n g c o n d i t i o n s a t which t h e r o u g h e r c o n c e n t r a t e was l e a c h e d , t h a t i s pH = 9 and T = 30\u00C2\u00B0C. The v a l u e o f k 3= 4.89 x 1 0 - 3 ( m i n - 1 ) - H i g h e r t e m p e r a t u r e s o f l e a c h i n g c o u l d be ex p e r i m e n t e d i n the f u t u r e as i t was o b s e r v e d t h a t the maximum r a t e s o f d e c o m p o s i t i o n o f t h e r e a g e n t a t t h e s e h i g h pH's a r e slow i n com p a r i s o n t o the r a t e s o f consumption o f NaOCl i n t h e r e a c t i o n w i t h MoS 2. One example i s p r e s e n t e d i n which t h e f o l l o w i n g c o n d i t i o n s have been s e t : . I n i t i a l C o n c e n t r a t i o n o f NaOC l = 50 g / l W e i g h t o f M o S 2 l e a c h e a b l e w i t h t h i s a m o u n t o f NaOC l = 3 . 6 g I f c o m p o s e d o f p a r t i c l e s - 7 0 + 140 mesh t h e s u r f a c e a r e a = 1432 c m 2 O p e r a t i n g pH = 9 O p e r a t i n g T e m p e r a t u r e = 5 0 \u00C2\u00B0 C V o l u m e o f R e a g e n t = 1000 c m 3 To c a l c u l a t e t h e d e c o m p o s i t i o n r a t e : m ^ M = k 3 [ N a O C l ] 2 \" 5 a t pH 9 and 50\u00C2\u00B0C k 3 = 0.0251 4^ -d-^CU= 0.0251 ( 1 5 ) 2 - 5 = 218.7 mg/l/min The r e a c t i o n r a t e i s c a l c u l a t e d a s : 100 d(NaOCl) D x A x C (Max) = LNaOCl d t 6 x v d(NaOCl) _ 2 x 10 ~ 5 x 1432 x 15 x 60 _ ?t- 7 A n / 1 / m,_ dt 10-3 x 103 25.78 g / l / m i n From t h i s , i t i s p o s s i b l e t o o b s e r v e t h a t t h e r a t e o f consump-t i o n o f NaOCl w i l l be a p p r o x i m a t e l y lOOx f a s t e r i n t h e r e a c t i o n s t e p t h a n i n t h e d e c o m p o s i t i o n one even a t t h i s h i g h t e m p e r a t u r e . However t h e s e r e s u l t s must be t a k e n w i t h c a r e as t h e y do not r e p r e s e n t the i n f l u e n c e o f the c a t a l y s i s o f the c o p p e r o x i d e p r e s e n t i n r e a l s i t u a t i o n s . 5.6.1 E f f e c t o f E x c e s s C h l o r i d e on t h e D e c o m p o s i t i o n Rates The i n c r e a s e i n the r a t e o f d e c o m p o s i t i o n o f NaOCl w i t h i n c r e a s e s o f the C l - c o n c e n t r a t i o n i s now c o n s i d e r e d t o be due t o the i n c r e a s e i n i o n i c s t r e n g t h . o f the s o l u t i o n s and not any d i r e c t p a r t i c i p a t i o n o f t h e c h l o r i d e i o n i n t h e r e a c t i o n [41,42,43]. A l t h o u g h [ C l - ] was n o t measured i n t h e NaOCl s o l u t i o n s used, the i n f l u e n c e o f t h i s v a r i a b l e i s s m a l l compared t o t h e ones a l r e a d y c o n s i d e r e d and as a l r e a d y mentioned t h e same s o l u t i o n s were used f o r l e a c h i n g e x p e r i m e n t s and d e c o m p o s i t i o n e x p e r i m e n t s . 5.6.2 E f f e c t o f C a t i o n s on D e c o m p o s i t i o n Rates The d e c o m p o s i t i o n r a t e depends c o n s i d e r a b l y on t h e c a t i o n o f t h e a l k a l i n e s o l u t i o n . The o r d e r o f s t a b i l i t y o f h y p o c h l o r i t e s o l u t i o n s o f d i f f e r e n t base has been found t o be [ 4 6 ] . 101 NaOCl > K0C1 > C a ( 0 C l ) 2 5.6.3 C a t a l y t i c Agents i n H y p o c h l o r i t e D e c o m p o s i t i o n When a NaOCl s o l u t i o n has been p u r i f i e d from c a t a l y t i c a g e n t s , r e a c t i o n s (24) o r (25) c o n t r i b u t e much more th a n r e a c t i o n (26) i n t h e d e c o m p o s i t i o n o f t h e s o l u t i o n . The p l a t i n u m group m e t a l s have been r e p o r t e d t o c a t a l y z e both r e a c t i o n s and t h e mechanism o f d e c o m p o s i t i o n i n t h e p r e s e n c e o f m e t a l l i c c a t a l y s t s has been c l a i m e d t o be i d e n t i c a l t o t h e spontaneous r e a c t i o n [ 4 5 ] . Ox i d e s o f heavy m e t a l s (Co, Cu and N i ) a r e a l s o known t o c a t a l y z e NaOCl d e c o m p o s i t i o n . I t has been shown t h a t c o pper o x i d e does not a f f e c t t h e r e a c t i o n s l e a d i n g t o C10 3~ f o r m a t i o n , i n s t e a d c o p p e r and n i c k e l o x i d e s s t r o n g l y c a t a l y z e r e a c t i o n (26) a c c e l e r a t i n g t h e f o r m a t i o n o f oxygen [ 4 1 ] . N o r m a l l y t h e f o r m a t i o n o f oxygen and c h l o r a t e t a k e p l a c e i n p a r a l l e l [46,47] and i t was found t h a t t h e amount o f C10 3~ formed i n c r e a s e s w i t h t h e amount o f oxygen e v o l v e d . The maximum e v o l u t i o n was o b s e r v e d i n an a c i d medium [ 4 7 ] . A g a i n t h i s p o i n t i s c o n t r a d i c t o r y and M.W. L i s t e r [41] and I.E. F l i s et al. [47] found t h a t s u b s t a n c e s t h a t produce g r e a t i n c r e a s e s i n 0 2 p r o d u c t i o n do n o t i n c r e a s e C 10 3~ f o r m a t i o n . In t h i s a r e a t h e work p e r f o r m e d was l i m i t e d t o t h e o b s e r v a t i o n t h a t i n the p r o c e s s o f l e a c h i n g w i t h h y p o c h l o r i t e s o l u t i o n s , c o p p e r m i n e r a l s f o r m a c o a t i n g which c o n s i s t s o f c o p p e r o x i d e and t h a t t h i s compound was r e s p o n s i b l e f o r e x c e s s i v e l o s s e s due to- i t s c a t a l y t i c a c t i o n . No attempt was made o f e s t a b l i s h i n g a q u a n t i t a t i v e i n f l u e n c e . 102 5.7 H y p o c h l o r i t e L e a c h i n g P r o c e s s f o r t h e E x t r a c t i o n o f M o l y b d e n i t e From Copper Rougher C o n c e n t r a t e s The e x p e r i m e n t a l work has e s t a b l i s h e d t h a t m o l y b d e n i t e can be s e l e c t i v e l y l e a c h e d from copper r o u g h e r c o n c e n t r a t e s w i t h o u t s i g n i f i c a n t changes i n the f l o t a t i o n p r o p e r t i e s o f t h e c o p p e r s u l f i d e m i n e r a l s . On t h i s b a s i s , a p r o c e s s i s proposed f o r the a p p l i c a t i o n o f t h i s t e c h n i q u e t o t h e e x t r a c t i o n o f molybdenum. The f l o w - s h e e t i n F i g u r e 36 shows the p o s i t i o n o f the l e a c h i n g p r o c e s s i n t h e c o p p e r c o n c e n t r a t i o n p l a n t . The molybdenum e x t r a c t i o n s h o u l d be i n c l u d e d i m m e d i a t e l y a f t e r t h e p r i m a r y f l o t a t i o n o p e r a t i o n . T h i s w i l l e n s u r e t h a t no more th a n 15% o f t h e t o t a l Mo i n t h e o r e w i l l be l o s t and p r e v e n t o x i d a t i o n o f t h e c o p p e r m i n e r a l s . The l e a c h e d r o u g h e r c o n c e n t r a t e i s washed and r e t u r n s t o the c o p p e r f l o t a t i o n c i r c u i t b e f o r e t h e r e g r i n d i n g s t a g e i n p r e p a r a t i o n f o r t h e s e c o n d a r y c l e a n i n g f l o t a t i o n . A s c h e m a t i c f l o w - s h e e t f o r the molybdenum e x t r a c t i o n p r o c e s s i s p r e s e n t e d i n F i g u r e 37. The fundamental u n i t o p e r a t i o n s a r e : 1) H y p o c h l o r i t e g e n e r a t o r 2 ) L e a c h i n g 3) S/L S e p a r a t i o n 4) M o l y b d e n u m r e c o v e r y Sodium h y p o c h l o r i t e s h o u l d be o f h i g h c o n c e n t r a t i o n (20-30 g/1) when emerging from the h y p o c h l o r i n a t o r s i n c e i t w i l l be d i l u t e d when c o n t a c t e d w i t h t he c o n c e n t r a t e s l u r r y . Due t o the h i g h v e l o c i t y o f the 103 Cu-Mo Ore SIZE REDUCTION PRIMARY FLOTATION Cu ROUGHER CONCENTRATE. HYPOCHLORITE LEACHING PROCESS REGRINDING Molybdenum 81 Rhenium SECONDARY FLOTATION Copper Concentrate FIG. 36 - POSITION OF PROPOSED LEACHING PROCESS IN THE GENERAL Cu CONCENTRATION FLOWSHEET. I Cu circuit \u00E2\u0080\u009E.Cu rougher concentrate j <40% solids-pH 8.0 104 THICKENING pH control LEACHING >50% solids-pH 9.5 NaOCl S/L leached Cu rougher concentrate pH adjustm. Cu circuit recycle H 2 REDUCTION IV l 0 FINAL TREATMENT Mo Products HYPOCHLORINATOR r \u00E2\u0080\u0094 f Cl 2 NaOH anodic cothodic NaCI H 0 recycled 2 I NaOH/ H 2 separator EVAPORATOR H, SO^ REMOVAL \u00E2\u0080\u00A2NoCI feed s o : 4 effluent FIG. 37 - FLOWSHEET OF THE PROPOSED METHOD FOR EXTRACTING MoS^ FROM COPPER ROUGHER CONCENTRATES. 105 l e a c h i n g r e a c t i o n , t h e r e a g e n t w i l l be added d i r e c t l y t o t h e l e a c h i n g r e a c t o r s . The a d d i t i o n o f c a u s t i c f o r pH c o n t r o l w i l l a l s o be added t o th e r e a c t o r s . R e s i d e n c e time i n t h e l e a c h s e c t i o n f o r a 40% s l u r r y was d e t e r m i n e d e x p e r i m e n t a l l y as 7-10 m i n u t e s , and t h e amount o f a l k a l i needed f o r m a i n t a i n i n g t he pH i n t h e narrow r e g i o n 9.5 t o 8.5 was between 3.0 and 3.5 g/1 when t h e r o u g h e r c o n c e n t r a t e has 0.3% Mo. A r e c y c l e c i r c u i t i s i n c l u d e d i n o r d e r t o b u i l d up t h e con-c e n t r a t i o n o f molybdenum. The amount o f c y c l e s w i l l be d e t e r m i n e d by t h e maximum t o l e r a n c e o f S 0 H ~ i n t h e e l e c t r o l y t i c c e l l s . C a l c i u m , magnesium and s u l f a t e i o n s a r e d e t r i m e n t a l i n t h e b r i n e e l e c t r o l y t i c c e l l as t h e y p r e c i p i t a t e on t h e diaphragm o r membrane [ 4 8 ] . I t w i l l be n e c e s s a r y t o i n c l u d e a S 0 4 ~ removal o p e r a t i o n i n any r e c y c l e c i r c u i t . The s o l u t i o n c o n t a i n i n g NaCl f r e e o f MoO^ - and S 0 4 _ must be c o n c e n t r a t e d i n o r d e r t o be r e c y c l e d as an a n o l y t e . T h i s would r e q u i r e an e v a p o r a t i o n s t a g e . The economics o f r e c y c l i n g t h e l e a c h i n g s o l u t i o n t o m i n i m i z e s a l t consumption r e q u i r e s f u r t h e r s t u d y . F o r c o s t e s t i m a t e s o f t h e p r o c e s s , t o t a l s a l t has been c o n s i d e r e d w i t h o u t any r e c y c l i n g . A major problem o f t h i s p r o c e s s i s t h e molybdenum r e c o v e r y from s o l u t i o n . The c o n c e n t r a t i o n o f MO0L>~ would be low due t o t h e r e c y c l i n g problems a l r e a d y o u t l i n e d . I n s t e a d c h l o r i d e s and s u l f a t e s w i l l be h i g h . T h i s s u b j e c t w i l l have t o be s t u d i e d i n f u t u r e i n v e s t i g a t i o n s . The i d e a l p r o c e s s would r e q u i r e t h a t molybdenum be removed from a l k a l i n e s o l u t i o n s . A l i t e r a t u r e s e a r c h has shown t h a t a l m o s t a l l molybdenum r e c o v e r y p r o c e s s e s u s i n g e i t h e r s o l v e n t e x t r a c t i o n o r i o n 106 exchange a r e worked on a c i d s o l u t i o n s . T h i s would be u n d e s i r a b l e i n t h e pr o p o s e d f l o w s h e e t because o f t h e a c i d consumed i n t h e pH ad j u s t m e n t f o r e x t r a c t i o n and a l k a l i a d d i t i o n f o r r e c y c l e . I t has been r e p o r t e d t h a t A l i q u a t 336, a q u a t e r n a r y amine i s c a p a b l e o f e x t r a c t i n g Mod* - i o n s from a l k a l i n e s o l u t i o n s a l t h o u g h w i t h a d e c r e a s e d l o a d i n g c a p a c i t y [ 4 9 ] . However t h i s r e a g e n t would not be a p p r o p r i a t e t o t h e p r o c e s s because i t s l o a d i n g c a p a c i t y i s d e c r e a s e d by the p r e s e n c e o f C l \" i o n s i n a l k a l i n e s o l u t i o n s . A few at t e m p t s were made ( i n our work) o f r e d u c i n g MOOL, i o n s i n a l k a l i n e s o l u t i o n s w i t h o u t s u c c e s s . The r e d u c i n g a g e n t s e x p e r i m e n t e d were sodium d i t h i o n a t e , sodium f o r m a l d e h i d e s u l f o x y l a t e and . h y d r a z i n e . From the p r e s e n t i n f o r m a t i o n i t appea r s t h a t Mo would have t o be r e c o v e r e d from a c i d s o l u t i o n s . T h i s a l t e r n a t i v e can be a c c o m p l i s h e d e i t h e r by i o n exchange, s o l v e n t e x t r a c t i o n o r hydrogen r e d u c t i o n . On t h e b a s i s o f s i m p l i c i t y o f o p e r a t i o n and a v a i l a b i l i t y o f hydrogen from t h e e l e c t r o l y t i c c e l l t h e l a t e r o p t i o n has been s e l e c t e d and i n c l u d e d i n t h e f l o w s h e e t w i t h t h e c o n s i d e r a t i o n t h a t f u r t h e r s t u d i e s a r e r e q u i r e d . The d i s a d v a n t a g e t h a t hydrogen r e d u c t i o n has o v e r t h e o t h e r two o p t i o n s i s t h e d i f f i c u l t y i n s e p a r a t i n g rhenium, which because o f i t s c h e m i c a l s i m i l a r i t y w i l l l i k e l y f o l l o w molybdenum i n t h e e x t r a c t i o n . The consumption o f a c i d - was measured by a d d i n g s u l f u r i c a c i d t o s o l u t i o n s o f sodium h y p o c h l o r i t e a t an i n i t i a l pH o f 9.5 and l o w e r i n g t h e pH t o 4 and 3. I t was o b s e r v e d t h a t t h e r e was a d i f f e r e n c e o f con-sumption i n r e l a t i o n t o the c o n c e n t r a t i o n o f molybdate i o n s . T h e r e f o r e two c o n c e n t r a t i o n s were used a t 1 and 4 g/1 o f Mo. The i n f o r m a t i o n i s p r e s e n t e d i n T a b l e 10. 107 T a b l e 10 Consumption o f A c i d i n t h e R e d u c a t i o n o f pH o f Molybdenum C o n t a i n i n g H y p o c h l o r i t e S o l u t i o n s Consumption o f A c i d (as c o n c e n t r a t e d H2S0it) Reduced t o pH 4 Reduced t o pH 3 1 g/1 Mo-pH 9 .41 ml/1000 ml .50 ml/1000 ml 4 g/1 Mo-pH 9 1.54 ml/1000 ml 1.81 ml/1000 ml C h a p t e r 6 CONCLUSIONS 1. The r e a c t i o n between MoS 2 and. NaOCl. i s - f i r s t o r d e r i n h y p o c h l o r i t e . 2. The a p p a r e n t a c t i v a t i o n e n e r g y i s 6.3 k c a l / m o l e . 3. T h i s r e a c t i o n was p r o b a b l y c o n t r o l l e d i n t h e s e e x p e r i m e n t s by e i t h e r c h e m i c a l o r mixed d i f f u s i o n and c h e m i c a l r e a c t i o n s . 4. The r e a c t i o n r a t e c o n s t a n t was e s t i m a t e d as 1.90 x 10 \" 2 m i n - 1 c m - 2 at.pH9 and 4 5 \u00C2\u00B0 . 5. Sodium h y p o c h l o r i t e i s c a p a b l e o f s e l e c t i v e l y l e a c h i n g m o l y b d e n i t e from c h a l c o p y r i t e . 6. M i n e r a l s accompaning m o l y b d e n i t e i n t h e c o p p e r r o u g h e r c o n c e n t r a t e s form p r o t e c t i v e c o a t i n g s which p r e v e n t any s i g n i f i c a n t d i s s o l u t i o n . In t h e c a s e o f C u F e S 2 , t h i s l a y e r was d e s c r i b e d as a s o l i d s o l u t i o n o f CuO - C u ( 0 H ) 2 . 7. The p r e s e n c e o f CuO i s u n d e s i r a b l e i n t h e f e e d t o t h e h y p o c h l o r i t e l e a c h i n g system because i t i s a c a t a l y s t i n t h e decomposi-t i o n r e a c t i o n o f t h i s r e a g e n t . 108 109 9. The r a t e s o f d e c o m p o s i t i o n o f NaOCl a r e n e g l i g i b l e when compared w i t h t h e r a t e o f r e a c t i o n w i t h m o l y b d e n i t e when the s o l u t i o n i s a t pH 9 and ambient t e m p e a t u r e s . 10. The consumption o f NaOCl from c o p p e r r o u g h e r c o n c e n t r a t e s can be kept as low as 1.6 t i m e s t h e s t o i c h i o m e t r i c consumption o f t h e m o l y b d e n i t e p r e s e n t i f t h e c o n c e n t r a t e i s not a l l o w e d t o o x i d i z e b e f o r e l e a c h i n g . 11. With t h e i n f o r m a t i o n g a t h e r e d a f l o w s h e e t has been proposed f o r t h e a p p l i c a t i o n o f t h i s method. The g e n e r a l c o n c e p t i s t h a t l e a c h i n g o f m o l y b d e n i t e be a c c o m p l i s h e d i m m e d i a t e l y a f t e r t h e p r i m a r y f l o t a t i o n i n t h e c o p p e r c o n c e n t r a t i o n p l a n t , u s i n g NaOCl as t h e r e a g e n t which has been p r o d u c e d by an o n - s i t e g e n e r a t o r and t h a t molybdenum be r e c o v e r e d by a hydrogen r e d u c t i o n p r o c e d u r e . C h a p t e r 7 SUGGESTIONS FOR FUTURE WORK T h i s s t u d y has opened up s e v e r a l a r e a s o f work t h a t c o u l d be u s e f u l l y p e r s u e d : 1) Hydrogen r e d u c t i o n o f molybdenum from s o l u t i o n s w i t h h i g h c o n c e n t r a t i o n s o f c h l o r i d e s and s u l f a t e s such as would be o b t a i n e d from t h e h y p o c h l o r i t e l e a c h i n g o p e r a t i o n . 2) R e c i r c u l a t i o n o f l o a d e d s o l u t i o n t h r o u g h the e l e c t r o l y t i c c e l l t o o b t a i n b e t t e r s a l t u t i l i z a t i o n . T h i s s t u d y would a l s o d e t e r m i n e t h e a l l o w a b l e c o n c e n t r a t i o n o f d e t r i m e n t a l i o n s and what t y p e o f p r e -t r e a t m e n t i s r e q u i r e d . 3) F l o t a t i o n o f c o p p e r c o n c e n t r a t e s from r o u g h e r c o n c e n t r a t e s w h ich have been s l i g h t l y o x i d i z e d by h y p o c h l o r i t e . 110 REFERENCES 1. 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F l i s , I.E., Z h u r n a l P r i k l a d n o i K h i m i i , V o l . 41, No. 10 (1968). 114 48. Payer, S. and B. S t r a s s e r , C h l o r i n e B i c e n t e n n i a l Symposium, T.C. J e f f e r y and P.A. (ed s . ) (1974), 133. 49. Lewis, C . J . and J . E . House, T r a n s . AIME, 220 (1961), 359. 50. F o e r s t e r , F. and P. D o l c h , Z. E l e k t r o c h e m , 23: 137 (1917). "@en . "Thesis/Dissertation"@en . "10.14288/1.0078787"@en . "eng"@en . "Materials Engineering"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "Selective leaching of molybdenum mixed copper-molybdenum sulfides"@en . "Text"@en . "http://hdl.handle.net/2429/19890"@en .