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The decomposition of pyrite and other sulphide minerals by sulphur chloride McElroy, Roderick Owen 1972

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TEE DECOMPOSITION OF PYRITE AND OTHER SULPHIDE MINERALS BY SULPHUR CHLORIDE BY RODERICK OWEN McELROY B.Sc. (Honours C h e m i s t r y ) , U n i v e r s i t y o f A l b e r t a , 1965. M.Sc., MoHaster U n i v e r s i t y , 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department o f METALLURGY We a c c e p t t h i s t h e s i s as 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 THE UNIVERSITY OF BRITISH COLUMBIA March, 1972 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, 1 agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study . I f u r t h e r agree t h a t permiss ion fo r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or 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 ga in s h a l l not be a l lowed wi thout my w r i t t e n p e r m i s s i o n . Department o f Metallurgy  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date May 4, 1972 ABSTRACT The r e a c t i o n s o f p y r i t e CFeS^) and o t h e r s u l p h i d e m i n e r a l s w i t h l i q u i d s u l p h u r c h l o r i d e ( S 2 C 1 2 ) have been i n v e s t i g a t e d i n an a t t e m p t t o d e v e l o p a 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 e t a l s s u c h as Fe, Pb, Cu, Mo, e t c . from s u l p h i d e m i n e r a l s u s i n g S 2 C 1 2 ( w i t h or w i t h o u t d i s s o l v e d s u l p h u r ) as b o t h t h e s o l v e n t and r e a c t a n t . F o r t h i s p u r p o s e , f l o t a t i o n c o n c e n t r a t e s and s y n t h e t i c m i n e r a l powders o f v a r i o u s p a r t i c l e s i z e s were r e a c t e d a t temper-a t u r e s i n t h e r a n g e 40-150°C w i t h S 2 C 1 2 c o n t a i n i n g 0-40 w e i g h t p e r c e n t d i s s o l v e d s u l p h u r . P y r i t e , c h a l c o p y r i t e ( C u F e S 2 ) and g a l e n a (PbS) r e -a c t e d w i t h e x c e s s S 2 C 1 2 t o form s o l i d m e t a l c h l o r i d e s ( F e C l , C u C l , P b C l ) and d i s s o l v e d s u l p h u r . P y r i t e " 2 <-r e a c t s c o m p l e t e l y w i t h S 2 C 1 2 c o n t a i n i n g 25-40 wt % d i s s o l v e d s u l p h u r , b u t o n l y p a r t i a l l y w i t h S 2 C 1 2 o r S 2 C 1 2 c o n t a i n i n g 10 wt % o r l e s s o f d i s s o l v e d s u l p h u r . C h a l c o p y r i t e was f o u n d t o r e a c t c o m p l e t e l y w i t h S 2 C 1 2 s o l u t i o n s c o n t a i n i n g 40 wt % S. G a l e n a (PbS) r e a c t s c o m p l e t e l y w i t h d i s t i l l e d S 2 C 1 2 o r S 2 C 1 2 c o n t a i n i n g 10 wt % S, and t h i s r e a c t i o n was f o u n d t o be c a t a l y z e d by t h e n a t u r a l i m p u r i t i e s s i l v e r , a n t i m o n y , and b i s m u t h . P y r r h o t i t e ( F e S ) and a m a r m a t i t i c z i n c c o n c e n t r a t e were o n l y p a r t i a l l y decomposed by S 2 C 1 2 . A s e r i e s o f I n v e s t i g a t i o n s w i t h s p h a l e r i t e (ZnS) and m o l y b d e n i t e ( M oS 2) i n d i c a t e d t h a t t h e s e m i n e r a l s c o u l d n o t be s i g n i f i c a n t l y a t t a c k e d by S CI . - i i i -In a l l c a s e s , s u l p h u r p r o d u c e d i n t h e s e r e a c t i o n s can be c r y s t a l l i z e d i n s t o i c h i o m e t r i c y i e l d by c o o l i n g t h e s o l v e n t . A g e o m e t r i c model f o r t h e r e a c t i o n s o f p y r i t e , g a l e n a , and c h a l c o p y r i t e w i t h s u l p h u r c h l o r i d e has been used t o i n t e r p r e t t h e r e a c t i o n d a t a and t o c a l c u l a t e s p e c i f i c r a t e s and a c t i v a t i o n e n e r g i e s f o r the r e a c t i o n s c o n c e r n e d . On t h e b a s i s o f t h i s i n v e s t i g a t i o n , p o t e n t i a l p r o c e s s e s f o r t h e t r e a t m e n t o f p y r i t e , g a l e n a and m o l y b d e n i t e a r e p r o p o s e d . - i v -ACKNOWLEDGEMENTS The a u t h o r w i s h e s t o e x p r e s s h i s s i n c e r e t h a n k s t o Dr. E. P e t e r s f o r h i s i n t e r e s t and g u i d a n c e i n t h i s s t u d y . O t h e r members o f f a c u l t y , g r a d u a t e s t u d e n t s , and s t a f f have a s s i s t e d i n many a r e a s o f t h e s t u d y -t h e i r h e l p i s s i n c e r e l y a p p r e c i a t e d . F i n a n c i a l s u p p o r t from t h e N a t i o n a l R e s e a r c h C o u n c i l o f Canada t h r o u g h g r a n t s t o members o f t h e Department o f M e t a l l u r g y , 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 s g r a t e -f u l l y a c k n o w l e d g e d . - V -TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1 G e n e r a l . . 1 1.2 Methods o f P y r i t e T r e a t m e n t . 2 1.21 R o a s t i n g 2 1.22 C h l o r i d i z i n g R o a s t i n g 3 1.23 C h l o r i d i z i n g V o l a t i l i z a t i o n . . . 4 1.24 H y d r o m e t a l l u r g y o f P y r i t e . . . . 5 1.241 H y d r o m e t a l l u r g i c a l T r e a t m e n t o f P y r i t i c M a t e r i a l 5 1.242 Rate C o n t r o l i n H y d r o -m e t a l l u r g i c a l D e c o m p o s i t i o n o f S u l p h i d e s 6 1.25 C h l o r i n a t i o n P r o c e s s e s 8 1.26 Summary 10 1.3 B a c k g r o u n d t o t h e P r e s e n t I n v e s t i g a t i o n 11 1.31 Low T e m p e r a t u r e C h l o r i n a t i o n o f P y r i t e 11 1.32 P r o p e r t i e s o f S u l p h u r C h l o r i d e . 12 1.321 C h e m i c a l and P h y s i c a l P r o p e r t i e s o f S u l p h u r C h l o r i d e s 12 1.322 S u l p h u r - S u l p h u r C h l o r i d e S o l u t i o n s 14 1.323 P h y s i o l o g i c a l P r o p e r t i e s o f S u l p h u r C h l o r i d e . . . 15 1.33 Thermodynamics o f C h l o r i n a t i o n o f M e t a l S u l p h i d e s 15 - v i -Page 1.34 Thermodynamics o f O x i d a t i o n o f M e t a l C h l o r i d e s 15 1.4 O b j e c t i v e s 18 2. MATERIALS AND METHODS 19 2.1 M a t e r i a l s 19 2.11 N a t u r a l S u l p h i d e M i n e r a l s . . . . 19 2.12 S y n t h e s i s o f M i n e r a l s and C h e m i c a l s 19 2.13 O t h e r m a t e r i a l s 21 2.2 E x p e r i m e n t a l Methods and A p p a r a t u s . . . 21 2.21 Sample P r e p a r a t i o n 21 2.22 E x p e r i m e n t a l A p p a r a t u s and P r o c e d u r e 22 2.3 A n a l y t i c a l Methods 24 3. RESULTS AND DISCUSSION 27 3.1 D e c o m p o s i t i o n o f P y r i t e and R e l a t e d Compounds by S u l p h u r C h l o r i d e 27 3.11 R e a c t i o n o f P y r i t e w i t h S u l p h u r C h l o r i d e 27 3.12 R e a c t i o n o f P y r i t e w i t h S u l p h u r -S u l p h u r C h l o r i d e S o l u t i o n s . . . . 30 3.121 E f f e c t o f D i s s o l v e d S u l p h u r 30 3.122 E f f e c t o f S t i r r i n g on t h e R e a c t i o n Rate 32 3.123 A G e o m e t r i c Model o f t h e R e a c t i o n 32 , 3.124 R e s u l t s o f E x p e r i m e n t s on S u l l i v a n P y r i t e 35 - v i i -Page 3.125 The A c t i v a t i o n E n e r g y 42 3.126 R e a c t i o n o f P y r i t e f r o m a D i f f e r e n t S o u r c e . . . . 44 3.13 R e a c t i o n o f N a t u r a l and S y n t h e t i c P y r r h o t i t e 44 3.14 R e a c t i o n o f Anhydrous F e r r o u s C h l o r i d e w i t h S u l p h u r C h l o r i d e . 50 3.15 R e a c t i o n s o f M e t a l l i c I r o n w i t h S u l p h u r C h l o r i d e 51 3.16 Summary and D i s c u s s i o n o f E x p e r i m e n t s on I r o n Compounds . . 53 3.161 Summary o f O b s e r v a t i o n s . 53 3.162 The R e a c t i o n o f P y r i t e . . 57 3.163 The R e a c t i o n o f P y r r h o t i t e 58 3.164 The R e a c t i o n s o f M e t a l l i c I r o n 59 3.2 D e c o m p o s i t i o n o f O t h e r S u l p h i d e s by S u l p h u r C h l o r i d e 60 3.21 D e c o m p o s i t i o n o f G a l e n a 60 3.211 R e a c t i v i t y o f N a t u r a l and S y n t h e t i c G a l e n a 60 3.212 D e t e r m i n a t i o n o f C a t a l y s t s 60 3.213 R e s u l t s o f E x p e r i m e n t s on P i n e P o i n t G a l e n a . . . . 62 3.214 C a l c u l a t e d A c t i v a t i o n E n e r g i e s 66 3.215 M i s c e l l a n e o u s O b s e r v a t i o n s 68 3.22 D e c o m p o s i t i o n o f C h a l c o p y r i t e by S u l p h u r C h l o r i d e 68 3.221 R e s u l t s o f E x p e r i m e n t s on P h o e n i x C h a l c o p y r i t e . . . 68 - v i i i -Page 3.222 The C a l c u l a t e d A c t i v a -t i o n E n e r g y 73 3.223 Q u a l i t a t i v e O b s e r v a t i o n s on O t h e r Copper M i n e r a l s . 7 3 3.23 D e c o m p o s i t i o n o f Z i n c S u l p h i d e by S u l p h u r C h l o r i d e 73 3.24- D e c o m p o s i t i o n o f M o l y b d e n i t e by S u l p h u r C h l o r i d e 75 3.3 I n t e r p r e t a t i o n o f E x p e r i m e n t a l R e s u l t s 76 3.31 R e q u i r e m e n t s f o r a R e a c t i o n Me c h a n i s m 76 3.32 The R o l e o f S u l p h u r 77 3.33 S u r f a c e R e a c t i o n s 79 3.331 D i s s o c i a t i v e R e a c t i o n s o f S u l p h u r C h l o r i d e . . . . 79 3.332 A s s o c i a t i v e R e a c t i o n o f S u l p h u r C h l o r i d e . . . . 80 3.34 Models f o r M e t a l S u l p h i d e -S u l p h u r C h l o r i d e R e a c t i o n s . . . . 80 3,4- E l e m e n t a l S u l p h u r from C h l o r i n a t i o n o f M e t a l S u l p h i d e s 83 3.5 P o t e n t i a l M e t a l l u r g i c a l Uses f o r S u l p h u r C h l o r i d e 86 3.51 U s e f u l P r o p e r t i e s o f S u l p h u r C h l o r i d e 86 3.52 S p e c i f i c P o t e n t i a l Uses f o r S u l p h u r C h l o r i d e 87 3.521 P y r i t e 87 3 . 522 G a l e n a 87 3.523 M o l y b d e n i t e 89 3.53 P r o b l e m s i n t h e Use o f S u l p h u r C h l o r i d e 90 - i x -Page 4. CONCLUSIONS . 91 5. SUGGESTIONS FOR FURTHER WORK . 94 REFERENCES 95 APPENDICES 99 L I S T OF FIGURES F i g u r e Page 1 S c h e m a t i c D i a g r a m o f t h e E x p e r i m e n t a l A p p a r a t u s 23 2 R e a c t i o n o f P y r i t e w i t h Pure S u l p h u r C h l o r i d e a t 133°C 28 3 E f f e c t o f D i s s o l v e d S u l p h u r on t h e R e a c t i o n o f P y r i t e w i t h S u l p h u r C h l o r i d e a t 133°C (.Substrate: -70 + 100 mesh S u l l i v a n F eS 2> 31 4 E f f e c t o f S t i r r i n g on t h e R e a c t i o n o f F e S 2 w i t h 40 wt % S . S 2 C 1 2 33 5 R e a c t i o n o f -200 + 270 m S u l l i v a n F e S 2 w i t h 40 wt % S . S 2 C 1 2 36 1/3 6 P l o t o f r [ l - ( l - R ) ] vs Time f o r t h e o R e a c t i o n o f -200 + 270 m S u l l i v a n F e S 2 In 40 wt % S . S 2 C 1 2 . 37 7 R e a c t i o n o f -70 + 100 m S u l l i v a n F e S 2 w i t h 40 wt % S . S 2 C 1 2 39 8 A b s o r b e d E l e c t r o n Image M i c r o g r a p h s , M a g n i f i c a t i o n = 240 x . 41 9 A r r h e n i u s P l o t f o r t h e R e a c t i o n o f -70 + 100 m S u l l i v a n P y r i t e w i t h 40 wt % S . S 2 C 1 2 43 - x i -F i g u r e Page 10 P l o t o f r C l - ( l - R ) 1 I v s Time f o r -70 o + 100 m S u l l i v a n and Noranda P y r i t e s R e a c t e d w i t h 40 wt % S . S 2 C 1 2 a t 119.9°C 45 11 -70 + 100 m S u l l i v a n and Noranda P y r i t e s B e f o r e L e a c h i n g 46 12 R e a c t i o n o f -140 + 200 m S u l l i v a n FeS w i t h S 2 C 1 2 and 40 wt % S . S 2 C 1 2 48 13 R e a c t i o n o f Fe w i t h 40 wt % S . S 2 C 1 2 ( a ) and S 2 C 1 2 ( b ) a t 133°C 52 14 Growth o f FeS F i l m on I r o n R e a c t i n g w i t h S 2 C 1 2 54 15 R e a c t i o n o f -150 + 200 m P i n e P o i n t G a l e n a w i t h 10 wt % S . S 2 C 1 2 63 1/3 16 P l o t o f r [ 1 - C l - R ) ] vs Time f o r t h e o C a t a l y z e d R e a c t i o n o f -150 + 200 m P i n e P o i n t G a l e n a w i t h 10 wt % S . S 2 C 1 2 64 17 P l o t o f r [ 1 - ( 1 - R ) 1 / 3 ] vs Time f o r o U n c a t a l y z e d R e a c t i o n o f -150 t 200 m P i n e P o i n t G a l e n a w i t h 10 wt % S.S' CI 65 18 A r r h e n i u s P l o t s f o r C a t a l y z e d ( a ) and U n c a t a l y z e d ( b) R e a c t i o n s o f -150 + 200 m P i n e P o i n t G a l e n a and 10 wt % S . S 2 C 1 2 67 - x i i -F i g u r e Page 19 P e r c e n t R e a c t i o n vs Time f o r -100 + 140 m Phoenix C u F e S 2 i n 40 wt % S . S 2 C 1 2 70 20 P l o t o f r [ 1 - C l - R ) ' ] vs Time f o r o -100 + 140 m P h o e n i x C u F e S 2 i n 40 wt % S . S 2 C 1 2 . 71 21 A r r h e n i u s P l o t f o r R e a c t i o n o f -100 + 140 m P h o e n i x C u F e S 2 w i t h 40 wt % S . S 2 C 1 2 72 22 Models f o r t h e R e a c t i o n o f S u l p h u r C h l o r i d e w i t h M e t a l S u l p h i d e s 81 23 Rhombic S u l p h u r C r y s t a l s P r e c i p i t a t e d f r o m S.S-C1. S o l u t i o n 85 - x i i i -LIST OF TABLES T a b l e Page 1 E n t h a l p y and F r e e E n e r g y V a l u e s f o r R e a c t i o n s o f S e l e c t e d M e t a l S u l p h i d e s w i t h S 2 C 1 2 16 2 C a l c u l a t e d F r e e E n e r g y o f O x i d a t i o n f o r S e l e c t e d M e t a l C h l o r i d e s a t 70Q°K . . . . 17 3 R a t e s o f R e a c t i o n o f S u l l i v a n P y r i t e w i t h 40 wt % S. S 2 C 1 2 38 4 R e a c t i o n o f S y n t h e t i c FeS and F e C l 2 w i t h S . S 2 C 1 2 S o l u t i o n s 50 5 R e a c t i o n s o f F e S 2 , FeS, F e C l 2 and Fe w i t h S'CI 55 6 I n i t i a l and E x t e n d e d Time R e a c t i o n R a t e s f o r F e S 2 , FeS, F e C l 2 and Fe i n S 2 C 1 2 a n d 40 wt % S. S 2 C 1 2 . . • 56 7 E f f e c t o f V a r i o u s A d d i t i v e s on t h e Rate o f R e a c t i o n o f S y n t h e t i c PbS w i t h S 2 C 1 2 '. . 61 8 Rate o f R e a c t i o n o f 150 + 200 m P i n e P o i n t G a l e n a w i t h 10 wt %'S.S C l 2 . . . . 66 9 Rate o f R e a c t i o n ( P e n e t r a t i o n ) o f C u F e S 2 i n 40 wt % S . S 2 C 1 2 69 10 R e a c t i o n o f S p h a l e r i t e w i t h S 2 C 1 2 . . . . 74 - x i v -T a b l e Page 11 C h l o r i n e C o n t e n t o f P r e c i p i t a t e d S u l p h u r 86 12 Summary o f R a t e s and A c t i v a t i o n E n e r g i e s 92 - 1 -1. INTRODUCTION 1.1 G e n e r a l P y r i t e ( F e S 2 ) o r e s and c o n c e n t r a t e s f r e q u e n t l y c o n -t a i n s i g n i f i c a n t q u a n t i t i e s o f n o n - f e r r o u s m e t a l s ( e . g . Cu, Pb, Zn, Co, Au, Ag) i n forms n o t amenable t o p h y s i c a l c o n -c e n t r a t i o n ( 1 ) . R e c o v e r y o f t h e s e m e t a l s r e q u i r e s c h e m i c a l t r e a t m e n t o f t h e e n t i r e p y r i t e c o n c e n t r a t e . P y r i t e i s a common m i n e r a l , f r e q u e n t l y f o u n d by i t s e l f ( 2) and a d j a c e n t . t o o r i n t e r s p e r s e d w i t h more v a l u -a b l e s u l p h i d e s (3) so i t i s r e a d i l y a v a i l a b l e i n l a r g e q u a n t i t i e s . P y r i t e i s t r e a t e d i n l a r g e q u a n t i t i e s (4) t o p r o d u c e s u l p h u r d i o x i d e (SO^) and i r o n o x i d e w h i c h i s used i n i r o n p r o d u c t i o n . N o n - f e r r o u s m e t a l s a s s o c i a t e d w i t h p y r i t e have been r e c o v e r e d by l e a c h i n g b e f o r e ( 5 ) or a f t e r (6,7) r o a s t i n g , o r by v o l a t i l i z a t i o n (4,8) o f n o n - f e r r o u s m e t a l c h l o r i d e s f r o m r o a s t e d m a t e r i a l s . A c o n s i d e r a b l e amount o f r e s e a r c h has been d i r e c t e d t o w a r d s improvement o f p r o c e s s e s c u r r e n t l y used f o r p y r i t e t r e a t m e n t and t o d e v e l o p m e n t o f new p r o c e s s e s . P r o d u c t i o n o f e l e m e n t a l s u l p h u r f r o m p y r i t e has been t h e s u b j e c t o f many o f t h e s e s t u d i e s ( 9 - 1 8 ) . - 2 -1.2 Methods o f P y r i t e T r e a t m e n t 1.21 R o a s t i n g R o a s t i n g , f o l l o w e d by a c i d l e a c h i n g , i s u s e d t o t r e a t l a r g e amounts o f p y r i t i c m a t e r i a l . R o a s t i n g decomposes s u l p h i d e s by o x i d a t i o n t o f o r m s u l p h u r d i o x i d e and m e t a l o x i d e s ( o r s u l p h a t e s ) i n t h e o v e r a l l r e a c t i o n s : (1) 2 F e S 2 + i | ° 2 F e 2 ° 3 + 4 S ° 2 (2) MS + | o + MO + S 0 2 (3) S 0 2 + j 0 2 t S 0 3 (4) MO + S 0 3 X MSO^ Dead r o a s t i n g f o r c o m p l e t e e l i m i n a t i o n o f s u l p h u r l e a d s t o f e r r i t e f o r m a t i o n ( 19 ) by t h e r e a c t i o n : (5) MO + Fe 0 -> MO.Fe Og F e r r i t e s - compounds o f t h e f o r m M 0 . F e 2 u 3 where M = Cu, Zn, e t c . , and u s u a l l y h a v i n g a s p i n e l s t r u c t u r e - a r e c o n v e n -t i o n a l l y t e r med a c i d i n s o l u b l e (more c o r r e c t l y t h e y a r e v e r y d i f f i c u l t t o d i s s o l v e ) and a r e an u n d e s i r a b l e p r o d u c t o f r o a s t i n g s i n c e any n o n - f e r r o u s m e t a l i n the f o r m o f f e r r i t e i s not r e c o v e r a b l e by c o n v e n t i o n a l a c i d l e a c h i n g and may make the l e a c h e d r e s i d u e u n s u i t a b l e f o r use as a raw m a t e r i a l i n i r o n p r o d u c t i o n . s u l p h u r e l i m i n a t i o n (M = Cu, Zn, e t c . ) s u l p h a t i o n - 3 -S u l p h a t i n g r o a s t i n g - s e l e c t i v e l y s u l p h a t i z i n g non-f e r r o u s m e t a l s w h i l e r e t a i n i n g i r o n as t h e form o f f e r r i c o x i d e - s o l u b i l i z e s more o f t h e n o n - f e r r o u s m e t a l s t h a n dead r o a s t i n g b u t a l s o s o l u b i l i z e s some o f t h e i r o n and f r e q u e n t l y l e a v e s some s u l p h i d e s u l p h u r i n t h e c a l c i n e . Thus, e x t e n s i v e p u r i f i c a t i o n o f t h e l e a c h l i q u o r may be r e q u i r e d , and t h e i r o n o x i d e r e s i d u e may be c o n t a m i n a t e d w i t h s u l p h u r . To p r e v e n t a g g l o m e r a t i o n , r o a s t i n g r e a c t i o n s a r e n o r m a l l y c a r r i e d o ut a t t e m p e r a t u r e s below t h e m e l t i n g p o i n t s o f t h e (.solid) r e a c t a n t s or p r o d u c t s . Thus, p r o -t e c t i v e o x i d e f i l m s may be formed and i n some c a s e s (20) r o a s t i n g r e a c t i o n s p r o c e e d s l o w l y , so l a r g e c a p a c i t y r e -a c t o r s a r e r e q u i r e d . A l s o , m a t e r i a l w h i c h has been r o a s t e d and l e a c h e d i n a f i n e l y d i v i d e d f o r m must be a g g l o m e r a t e d (by s i n t e r i n g o r p e l l e t i z i n g ) b e f o r e use i n c o n v e n t i o n a l i r o n p r o d u c t i o n . 1.22 C h l o r i d i z i n g R o a s t i n g C h l o r i d i z i n g r o a s t i n g (6,13,14) i s a l s o u s e d i n t h e t r e a t m e n t o f p y r i t e . In t h i s p r o c e s s , p y r i t e i s r o a s t e d f o r s u l p h u r e l i m i n a t i o n and t h e c a l c i n e i s t h e n r o a s t e d i n t h e p r e s e n c e o f sodium c h l o r i d e or o t h e r low c o s t s o u r c e o f c h l o r i n e . N o n - f e r r o u s m e t a l o x i d e s a r e c o n v e r t e d t o c h l o r i d e s and r e c o v e r e d by l e a c h i n g t h e c h l o r i d i z e d c a l c i n e . However, l e a c h i n g o f t h e s e c a l c i n e s has p r o v e n d i f f i c u l t ( 4 ) , - 4 -a g g l o m e r a t i o n o f t h e f i n e l e a c h r e s i d u e s i s r e q u i r e d i f t h e r e s i d u e i s t o be used f o r c o n v e n t i o n a l i r o n p r o d u c t i o n , and a complex l e a c h l i q u o r c o n t a i n i n g a m i x t u r e o f m e t a l c h l o r i d e s and sodium s u l p h a t e i s p r o d u c e d . 1.23 C h l o r i d i z i n g V o l a t i l i z a t i o n C h l o r i d i z i n g v o l a t i l i z a t i o n (4,8,21) i s a n o t h e r method used i n t h e t r e a t m e n t o f p y r i t e c a l c i n e . In a p r o -c e s s o f t h i s t y p e u s e d i n J a p a n ( 8 ) , p y r i t e c a l c i n e i s mixed w i t h c a l c i u m c h l o r i d e , p e l l e t i z e d , d r i e d , and h e a t e d i n a k i l n t o c h l o r i n a t e and v o l a t i l i z e t h e n o n - f e r r o u s m e t a l c o n t e n t o f t h e m a t e r i a l . T h i s p r o c e s s r e q u i r e s a h e a t i n g gas low i n h y d r o g e n t o m i n i m i z e h y d r o l y s i s o f c a l c i u m c h l o r i d e a t low t e m p e r a t u r e s where c h l o r i n a t i o n and v o l a t i l -i z a t i o n o f n o n - f e r r o u s m e t a l s w i l l n o t o c c u r . A l s o , t h i s p r o c e s s i s b e s t s u i t e d t o c a l c i n e s low i n s u l p h u r and a r s e n i c s i n c e t h e s e e l e m e n t s a r e o n l y p a r t i a l l y e l i m i n a t e d . A s u b s t a n t i a l l y d i f f e r e n t method o f c h l o r i n a t i n g and v o l a t i l i z i n g n o n - f e r r o u s m e t a l s from p y r i t e c a l c i n e i s i n use i n Germany ( 4 ) . T h i s p r o c e s s uses c h l o r i n e gas ( C l ^ ) t o remove n o n - f e r r o u s m e t a l s from p e l l e t i z e d p y r i t e c a l c i n e . In t h e most r e c e n t m o d i f i c a t i o n o f t h i s p r o c e s s , a s h a f t f u r n a c e w i t h t h r e e r e a c t i o n zones i s u s e d . In t h e f i r s t z o n e, g r e e n p e l l e t s a r e d r i e d and i n d u r a t e d by h o t combus-t i o n g a s e s . In t h e s e c o n d z o n e , n o n - f e r r o u s m e t a l s a r e removed by a s t r e a m o f a i r and c h l o r i n e , and i n t h e f i n a l - 5 -zone t h e p e l l e t s a r e a i r c o o l e d . Thus t h e n o n - f e r r o u s m e t a l s a r e e l i m i n a t e d i n a s m a l l , e a s i l y t r e a t a b l e volume o f g a s , g r e e n p e l l e t s , can be c h a r g e d t o the f u r n a c e , and s u l p h u r and a r s e n i c r e m o v a l i s n o t i n h i b i t e d by a d d i t i o n o f c a l c i u m t o t h e p e l l e t s . A l l r o a s t i n g p r o c e d u r e s have a common f e a t u r e - t h e y c o n v e r t t h e p y r i t i c s u l p h u r t o s u l p h u r d i o x i d e (SO ). T h i s p r o d u c t i s u s e f u l where a l o c a l market f o r s u l p h u r i c a c i d CH^SO^) e x i s t s . However, where m a r k e t s f o r t h e s u l p h u r p r o d u c t o f p y r i t e p r o c e s s i n g a r e f a r f r o m t h e p r o c e s s i n g s i t e , a more d e s i r a b l e p r o d u c t would be e l e m e n t a l s u l p h u r w h i c h Is more e a s i l y t r a n s p o r t e d t h a n s u l p h u r d i o x i d e or s u l p h u r i c a c i d , and i s r e a d i l y c o n v e r t e d t o o t h e r s u l p h u r compounds. 1.24 H y d r o m e t a l l u r g y o f P y r i t e 1.241 H y d r o m e t a l l u r g i c a l T r e a t m e n t o f P y r i t i c M a t e r i a l H y d r o m e t a l l u r g i c a l methods have been used t o l e a c h n o n - f e r r o u s s u l p h i d e m i n e r a l s i n t h e p r e s e n c e o f p y r i t e . C u p r i f e r o u s p y r i t e s have been heap l e a c h e d ( 5 ) f o r c o p p e r e x t r a c t i o n , and c o p p e r - , l e a d - , a n d z i n c s u l p h i d e s have been l e a c h e d by aqueous f e r r i c c h l o r i d e s o l u t i o n s w i t h o u t s i g n i f i c a n t a t t a c k on t h e p y r i t e p r e s e n t ( 2 3 , 2 4 ) . P y r i t e can be decomposed i n an aqueous e n v i r o n m e n t by l e a c h i n g under oxygen p r e s s u r e ( 1 8 ) , w i t h c h l o r i n e ( 2 5 , 2 6 , 2 7 ) , by b a c t e r i a l a c t i o n ( 2 8 ) , o r e l e c t r o l y t i c o x i d a t i o n ( 2 9 ) . - 6 -Up t o 50% o f t h e s u l p h u r c o n t e n t o f p y r i t e can be c o n v e r t e d t o t h e e l e m e n t a l f o r m by l e a c h i n g i n a c i d u n d e r oxygen p r e s -s u r e s , ' b u t a n o d i c o x i d a t i o n and b a c t e r i a l o r c h l o r i n e l e a c h i n g c o n v e r t s p y r i t i c s u l p h u r e n t i r e l y t o s u l p h u r ( V I ) ( s u l p h a t e o r b i s u l p h a t e ) . T h u s , p y r i t e can be decomposed i n aqueous s y s t e m s . F e r r i c s u l p h a t e s o l u t i o n s r e s u l t i n g f r o m o x i d i z i n g l e a c h i n g o f p y r i t e a r e u s e d i n dump o r i n - s i t u l e a c h i n g (28) but o t h e r w i s e t h e i r o n and s u l p h u r p r o d u c t s o f p y r i t e l e a c h i n g a r e d i f f i c u l t t o c o n v e r t t o c o m m e r c i a l l y u s e f u l f o r m s . The d i f f i c u l t y i n o x i d i z i n g p y r i t i c s u l p h u r t o t h e e l e m e n t a l f o r m i n an aqueous s y s t e m makes p y r i t e a l m o s t u n i q u e , s i n c e t h e s u l p h u r c o n t e n t o f o t h e r s u l p h i d e m i n e r a l s s u c h as p y r r h o t i t e ( F e S ) , c h a l c o p y r i t e ( C u F e S ^ ) , s p h a l e r i t e CZnS), g a l e n a (PbS) and n i c k e l - c o b a l t s u l p h i d e s can be c o n -v e r t e d t o e l e m e n t a l s u l p h u r by aqueous o x i d a t i o n w i t h s o l u -t i o n s c o n t a i n i n g f e r r i c i o n or c h l o r i n e ( 2 4 , 2 6 ) . In c o n -t r a s t , p y r i t i c s u l p h u r a p p a r e n t l y c a n n o t be c o m p l e t e l y c o n -v e r t e d t o t h e e l e m e n t a l form i n aqueous s y s t e m s . 1.242 Rate C o n t r o l i n H y d r o m e t a l l u r g i c a l D e c o m p o s i t i o n o f S u l p h i d e s The r a t e c o n t r o l l i n g s t e p s f o r aqueous d e c o m p o s i t i o n o f s u l p h i d e s can be g r o u p e d i n t o f i v e g e n e r a l c l a s s e s ( 3 0 ) : t r a n s f e r o f o x i d a n t from t h e gas t o t h e l i q u i d p h a s e , - 7 -t r a n s p o r t o f r e a c t a n t s or p r o d u c t s a c r o s s a d i f f u s i o n l a y e r , t r a n s p o r t o f r e a c t a n t s o r p r o d u c t s t h r o u g h an i n s o l u b l e f i l m , h e t e r o g e n e o u s r e a c t i o n a t t h e s u r f a c e , or a comb i n a -t i o n o f t h e s e . When t h e r a t e o f oxygen t r a n s f e r f r o m t h e gas phase i n t o a l e a c h i n g m i x t u r e i s r a t e c o n t r o l l i n g ( i . e . oxygen i s consumed as f a s t as i t can be t a k e n i n t o s o l u t i o n ) t h e n t h e r a t e o f t h e l e a c h i n g r e a c t i o n i s c o n s t a n t ( 3 1 ) . When t r a n s p o r t o f a r e a c t a n t or p r o d u c t a c r o s s a l i q u i d d i f f u s i o n l a y e r ( N e r n s t l a y e r ) i s r a t e c o n t r o l l i n g , l i n e a r k i n e t i c s a r e o b s e r v e d (26) and t h e r e a c t i o n i s u s u a l l y c h a r a c t e r i z e d by a low (^ 5 K c a l / m o l e ) a c t i v a t i o n e n e r g y , and a s t r o n g dependence o f r e a c t i o n r a t e on s t i r r i n g ( 3 0 ) . An example o f t h i s t y p e o f c o n t r o l i s t h e aqueous c h l o r i n a t i o n o f p y r i t e ( 2 5 ) . When a r e a c t i o n p r o d u c t i s i n s o l u b l e i n t h e l e a c h i n g s o l u t i o n , a p r o t e c t i v e l a y e r o f t h i s i n s o l u b l e p r o d u c t may be formed on t h e r e a c t i n g s u r f a c e . When t h i s o c c u r s , t h e r e a c t i o n can o n l y p r o c e e d by d i f f u s i o n t h r o u g h t h i s l a y e r . Such a d i f f u s i o n l a y e r has been r e p o r t e d (32) t o be the r a t e c o n t r o l l i n g mechanism f o r t h e d e c o m p o s i t i o n o f c h a l c o p y r i t e i n aqueous f e r r i c s u l p h a 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 r e a c t i o n d i s p l a y s p a r a b o l i c k i n e t i c s , and t h e r a t e i s i n s e n s i t i v e t o s t i r r i n g . R e a c t i o n s i n w h i c h t h e r a t e d e t e r m i n i n g s t e p i s a h e t e r o g e n e o u s s u r f a c e r e a c t i o n e x h i b i t h i g h 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 and a r e i n s e n s i t i v e t o s t i r r i n g ( 3 0 ) . - 8 -Mixed r e a c t i o n c o n t r o l o c c u r s when two s t e p s o f a r e a c t i o n p r o c e e d a t c o m p a r a b l e r a t e s a t a p a r t i c u l a r t e m p e r a t u r e . In t h i s c a s e , a change i n t e m p e r a t u r e can cau s e a change i n t h e r a t e d e t e r m i n i n g s t e p . F o r example, i n t h e aqueous c h l o r i n a t i o n o f g a l e n a (33) t h e r e a c t i o n r a t e i s t r a n s p o r t c o n t r o l l e d / a b o v e 4 5°C, but a t 20°C mixed c h e m i c a l and t r a n s p o r t c o n t r o l i s o b s e r v e d . 1.25 C h l o r i n a t i o n P r o c e s s e s A d i r e c t c h l o r i n a t i o n p r o c e s s f o r p y r i t e t r e a t m e n t has been d e v e l o p e d by Hohn e t a l . ( 9 ) . In t h i s p r o c e s s , p y r i t e i s r e a c t e d w i t h c h l o r i n e gas i n a f l u i d bed a t a t e m p e r a t u r e above the b o i l i n g p o i n t o f s u l p h u r . S u l p h u r i s e l i m i n a t e d by t h e r e a c t i o n : F e S 2 + C l 2 Cg) -*• F e C l 2 + | 5^ ( g ) , (x = 1-8) C h l o r i n a t i o n above t h e b o i l i n g p o i n t o f s u l p h u r and r e m o v a l o f s u l p h u r f r o m t h e s y s t e m as a gas e n s u r e s t h a t t h e r e a c t i o n c a n n o t be s t o p p e d by a l a y e r o f s o l i d o r l i q u i d s u l p h u r on t h e s u r f a c e o f t h e r e a c t i n g s u l p h i d e . The m e t a l c h l o r i d e p r o d u c t ' o f t h i s r e a c t i o n i s t h e n o x i d i z e d : 2 F e C l 2 + j 0 2 + F e 2 0 3 + 2 C 1 2 t o r e g e n e r a t e c h l o r i n e and p r o d u c e a m i x t u r e o f i r o n o x i d e - 9 -(Fe 0 ) and s o l u b l e n o n - f e r r o u s m e t a l c h l o r i d e s . The o n l y c h l o r i n e consumed by t h e p r o c e s s i s t h a t a s s o c i a t e d w i t h t h e n o n - f e r r o u s m e t a l s - t h e r e m a i n d e r r e c y c l e s w i t h i n t h e s y s t e m . P r o b l e m s i n t h i s p r o c e s s i n c l u d e t h e h a n d l i n g o f h i g h t e m p e r a t u r e s u l p h u r v a p o u r , p r e v e n t i o n o f back m i x i n g t h r o u g h t h e s y s t e m , and d u s t c o n t r o l . Thermodynamic s t u d i e s by P i l g r i m and Ingraham (34,35) have shown t h a t c h l o r i n a t i o n o f i r o n - , c o b a l t - , n i c k e l - , m a n g a n e s e - , l e a d - , a n d z i n c s u l p h i d e s by c h l o r i n e gas or f e r r i c c h l o r i d e i s t h e r m o d y n a m i c a l l y f a v o u r e d and t h a t s e l e c t i v e o x i d a t i o n of i r o n c h l o r i d e s t o i r o n o x i d e and c h l o r i n e i s t h e r m o d y n a m i c a l l y f e a s i b l e . R e f e r e n c e s t o o t h e r p r o c e s s e s i n v o l v i n g c h l o r i n a t i o n o f p y r i t e or o t h e r s u l p h i d e s w i t h c h l o r i n e gas o r f e r r i c c h l o r i d e a t t e m p e r a t u r e s below t h e b o i l i n g p o i n t o f s u l p h u r a r e f o u n d i n t h e l i t e r a t u r e ( 1 0 - 1 8 , 2 5 , 2 7 , 3 6 - 4 1 ) , but t h e p r o b l e m o f s e p a r a t i o n o f t h e v a r i o u s r e a c t i o n p r o d u c t s ap-p e a r s t o be u n r e s o l v e d i n many c a s e s . S u g g e s t e d methods o f s e p a r a t i o n i n c l u d e d i s t i l l a t i o n o f p r o d u c t s u l p h u r (36) o r f e r r i c c h l o r i d e (14) f r o m a s o l i d o r f u s e d mass o f m e t a l c h l o r i d e s , and c o m b u s t i o n o f p r o d u c t s u l p h u r ( 4 0 ) . D i s -t i l l a t i o n methods r e q u i r e s i g n i f i c a n t amounts o f h e a t i n p u t and may pose p r o b l e m s i n h e a t t r a n s f e r or c o n t a i n m e n t , and c o m b u s t i o n o f p r o d u c t s u l p h u r p r o d u c e s s u l p h u r d i o x i d e r a t h e r t h a n e l e m e n t a l s u l p h u r . - 10 -Where an a n h y d r o u s m e t a l c h l o r i d e p r o d u c t i s n o t r e q u i r e d , aqueous l e a c h i n g o f t h e s u l p h u r — m e t a l c h l o r i d e p r o d u c t s o f c h l o r i n a t i o n r e a c t i o n s has been s u g g e s t e d (15) and c h l o r i n a t i o n o f m e t a l s u l p h i d e s i n aqueous s o l u t i o n has been d e m o n s t r a t e d ( 2 5 - 2 7 , 3 3 , 3 8 , 3 9 ) . A n h y d r o u s l e a d c h l o r i d e can be p r o d u c e d by c h l o r i n a t i o n o f l e a d s u l p h i d e i n h o t a c i d c h l o r i d e s o l u t i o n s f o l l o w e d by c o o l i n g t o c r y s t a l l i z e l e a d c h l o r i d e ( 3 3 ) . However i n t h e c h l o r i n a t i o n o f p y r i t e , where the r e c o v e r y o f s u l p h u r , i r o n o x i d e , and c h l o r i n e i s d e s i r a b l e , t h e h i g h t e m p e r a t u r e p r o c e s s p r o p o s e d by Hohn e t a l . a p p e a r s t o p r e s e n t t h e most p r a c t i c a l a p p r o a c h t o the p r o b l e m o f s e p a r a t i o n o f p r o d u c t s . 1.26 Summary In g e n e r a l , p r o c e s s e s f o r t r e a t m e n t o f p y r i t e a r e d e s i g n e d t o r e c o v e r a l l t h e v a l u a b l e components o f the m i n e r a l i n c o m m e r c i a l l y u s e f u l f o r m s . The d e s i r e d p r o d u c t s a r e : i r o n o x i d e ( f r e e f r o m h a r m f u l i m p u r i t i e s ) , a c o n c e n -t r a t e o f n o n - f e r r o u s m e t a l s i n a f o r m s u i t a b l e f o r f u r t h e r p r o c e s s i n g , and s u l p h u r i n an e c o n o m i c a l l y u s e f u l f o r m . F o r f u t u r e p y r i t e p r o c e s s i n g p l a n t s , p r o d u c t i o n o f e l e m e n t a l s u l p h u r ( f r o m p y r i t e ) may be d e s i r a b l e , s i n c e e l e m e n t a l s u l p h u r i s e a s i l y t r a n s p o r t a b l e and can be r e a d i l y c o n v e r t e d i n t o o t h e r f o r m s . D e c o m p o s i t i o n o f p y r i t e ( o r s o l u b i l i z a t i o n o f n o n - f e r r o u s m e t a l s ) a t a f a s t e r r a t e t h a n - 11 -t h a t a t t a i n a b l e w i t h p r e s e n t r o a s t i n g methods would a l s o be d e s i r a b l e . A l l t h e p r o c e s s e s d e s c r i b e d above a r e u s e f u l i n the p r o d u c t i o n o f s u l p h u r ( o r I t s d e r i v a t i v e s ) and m e t a l s f r o m p y r i t e . However, most o f t h e s e p r o c e s s e s have p r o b l e m s a s s o c i a t e d w i t h them. 1.3 B a c k g r o u n d t o t h e P r e s e n t I n v e s t i g a t i o n 1.31 Low T e m p e r a t u r e C h l o r i n a t i o n o f P y r i t e An a p p e a l i n g r o u t e t o t h e p r o d u c t i o n o f e l e m e n t a l s u l p h u r , i r o n o x i d e , and a n o n - f e r r o u s m e t a l c o n c e n t r a t e from p y r i t e seemed t o be v i a low t e m p e r a t u r e c h l o r i n a t i o n o f p y r i t e t o m e t a l c h l o r i d e s and (low t e m p e r a t u r e ) s e p a r a -t i o n o f s u l p h u r . The s e c o n d s t a g e o f s u c h a p r o c e s s would be s e l e c t i v e o x i d a t i o n o f i r o n c h l o r i d e s t o i r o n o x i d e and c h l o r i n e f o r r e c y c l e . N o n - f e r r o u s m e t a l c h l o r i d e s would n o t be o x i d i z e d and c o u l d be s e p a r a t e d from i r o n o x i d e by v o l a t i l i z a t i o n o r l e a c h i n g . C h l o r i n a t i o n o f p y r i t e i n aqueous s o l u t i o n c o n v e r t s t h e e n t i r e s u l p h u r c o n t e n t o f t h e m i n e r a l t o s u l p h u r ( V I ) (26) so use o f a non-aqueous s o l v e n t seemed a p p r o p r i a t e . I n i t i a l l y , samples o f a p y r i t e f l o t a t i o n c o n c e n t r a t e were r e a c t e d w i t h c h l o r i n e d i s s o l v e d i n c a r b o n t e t r a c h l o r i d e (CC1 ). T h i s work showed t h a t p y r i t e i s r e a c t i v e t o c h l o r i n e a t low t e m p e r a t u r e s i n a non-aqueous e n v i r o n m e n t , b u t t h e p y r i t i c s u l p h u r was c o n v e r t e d t o s u l p h u r c h l o r i d e - 12 -(S^Cl^) r a t h e r t h a n e l e m e n t a l s u l p h u r . The p r o p e r t i e s of s u l p h u r c h l o r i d e Ccf. n e x t s e c t i o n ) s u g g e s t e d t h a t t h i s m a t e r i a l m ight be a good s o l v e n t and r e a c t a n t f o r t h e d e s i r e d r e a c t i o n - c o n v e r s i o n o f p y r i t e i n t o m e t a l c h l o r i d e s and e l e m e n t a l s u l p h u r . 1.32 P r o p e r t i e s o f S u l p h u r C h l o r i d e s 1.321 C h e m i c a l and P h y s i c a l P r o p e r t i e s o f S u l p h u r C h l o r i d e s S u l p h u r C h l o r i d e ( S 2 C I 2 ) i s c o n v e n i e n t l y p r e p a r e d by c o n t a c t i n g c h l o r i n e gas and e l e m e n t a l s u l p h u r : Sg + 4 C 1 2 + U S 2 C 1 2 and may be p u r i f i e d by f r a c t i o n a l d i s t i l l a t i o n ( 4 2 ) . Some p h y s i c a l p r o p e r t i e s o f s u l p h u r c h l o r i d e (42,43) a r e : m e l t i n g p o i n t - 8 2 ° C , b o i l i n g p o i n t 138°C, s p e c i f i c g r a v i t y (20°C) 1.6733, h e a t o f v a p o r i z a t i o n 64.6 c a l / g , s u r f a c e t e n -s i o n ( 2 2 ° C ) 40.78 dynes/cm, v i s c o s i t y (18°C) 2.015 c p s . In t h e v a p o u r p h a s e , s u l p h u r c h l o r i d e has t h e s t r u c -t u r e C l - S - S - C l ( 4 4 ) . The S-S and S - C l bond l e n g t h s a r e 2.5A., and 1.99A. The S - S - C l a n g l e i s 103° and t h e mole-c u l e i s t w i s t e d o ut o f p l a n e g i v i n g i t a s t r u c t u r e s i m i l a r t o t h a t o f h y d r o g e n p e r o x i d e . S u l p h u r C h l o r i d e i s r e p o r t e d (45) t o r e a c t w i t h m e t a l o x i d e s : - 13 -2M0 + 2 S 2 C 1 2 2MC1 2 + S 0 2 + 3S and s u l p h - l d e s : ZnS + S 2 C 1 2 Z n C l 2 + 3S and I s r e a d i l y h y d r o l y z e d (.44) t o s u l p h u r , s u l p h u r d i o x i d e , and h y d r o g e n c h l o r i d e , b u t i s m i s c i b l e w i t h n o n p o l a r s o l v e n t s s u c h as c a r b o n t e t r a c h l o r i d e and e t h y l e n e c h l o r i d e . S u l p h u r c h l o r i d e forms a t l e a s t one a d d u c t w i t h a Lewis a c i d -A l C l g . 2 S 2 C 1 2 but t h i s m a t e r i a l decomposes on h e a t i n g t o A1C1 .SCI ( 4 6 ) . R e a c t i o n o f s u l f a n e s (HS H) w i t h s u l p h u r o z n c h l o r i d e (42) p r o d u c e s c h l o r o s u l p h a n e s ( S ^ C l , ^ , n = 3-8) by r e a c t i o n s o f t h e form: 2 S 0 C 1 „ + HS H ->- C l - S -CI + 2HC1 2 2 n n+4 These c h l o r o s u l p h a n e s a r e u n s t a b l e and s e n s i t i v e t o i m p u r -i t i e s . C h l o r i n a t i o n o f s u l p h u r c h l o r i d e p r o d u c e s s u l p h u r d i c h l o r i d e - S C 1 2 . Impure s u l p h u r d i c h l o r i d e i s u n s t a b l e even a t room t e m p e r a t u r e w i t h r e s p e c t t o d e c o m p o s i t i o n t o s u l p h u r c h l o r i d e and c h l o r i n e but i t can be d i s t i l l e d a t 59.5°C (760mm Hg) a f t e r a d d i n g 0.5% p h o s p h o r u s p e n t a c h l o r i d e t o t h e impure m i x t u r e ( 4 2 ) . S u l p h u r d i c h l o r i d e forms a v a r i e t y o f compounds w i t h - 14 -—"" Lewis a c i d s - e.g. A1C1 _-SCl„ , F e C l -SC1_ , S b C l - S C l - ( 4 6 ) . o 2 a 2 D 2 The s u g g e s t e d s t r u c t u r e o f t h e s e compounds i s o f t h e t y p e S C 1 + A l C l ^ - . A d d i t i o n o f c h l o r i n e t o s u l p h u r d i c h l o r i d e a t low t e m p e r a t u r e p r o d u c e s y e l l o w c r y s t a l s o f s u l p h u r t e t r a c h l o r i d e ( S C l ^ ) which decompose d i s s ' o c i a t i v e l y above -31°C ( 4 4 ) . 1.322 S u l p h u r - S u l p h u r C h l o r i d e S o l u t i o n s S u l p h u r i s m i s c i b l e w i t h s u l p h u r c h l o r i d e a t temper-a t u r e s above t h e m e l t i n g p o i n t o f s u l p h u r and e x t e n s i v e l y s o l u b l e below t h i s t e m p e r a t u r e . The s o l u b i l i t y o f s u l p h u r i n s u l p h u r c h l o r i d e i n the t e m p e r a t u r e r a n g e 0°C-119.5°C ( d e t e r m i n e d by A t e n ( 4 7 ) ) i s shown i n A p p e n d i x H. E x p e r i -ments u s i n g l a b e l l e d ( r a d i o a c t i v e ) s u l p h u r (48) have shown t h a t above 100°C t h e r e i s a s i g n i f i c a n t amount o f exchange o f s u l p h u r between d i s s o l v e d s u l p h u r and s u l p h u r c h l o r i d e . However, the i n s t a b i l i t y o f c h l o r o s u l p h a n e s (42) ( c f . p r e -v i o u s s e c t i o n ) s u g g e s t s t h a t t h e s p e c i e s i n s o l u t i o n a r e p r i m a r i l y m o l e c u l e s o f s u l p h u r ( S g ) and s u l p h u r c h l o r i d e . A l s o , f r o m the i d e a l s o l u t i o n model o f G l a s s t o n e (49) when the s o l u t i o n i s t r e a t e d as c o n s i s t i n g o n l y o f S_C1 and S m o l e c u l e s t h e p r e d i c t e d s o l u b i l i t y ( A p p e n d i x 2 2 a H) i s s u f f i c i e n t l y c l o s e t o t h e e x p e r i m e n t a l v a l u e s t o j u s t i f y t r e a t i n g t h e s y s t e m as e s s e n t i a l l y i d e a l . In c a l -c u l a t i n g t h e i d e a l s o l u b i l i t y o f s u l p h u r i n s u l p h u r c h l o r i d e the thermodynamic d a t a o f Meyer (50) were u s e d . The - 15 -p h y s i c a l p r o p e r t i e s o f t h e v a r i o u s f orms o f e l e m e n t a l s u l -p h ur a r e q u i t e complex and a r e f u l l y d i s c u s s e d by Meyer ( 5 0 ) . 1.32-3 P h y s i o l o g i c a l P r o p e r t i e s o f S u l p h u r C h l o r i d e S u l p h u r c h l o r i d e and s u l p h u r d i c h l o r i d e b o t h have r e v o l t i n g o d o u r s and a r e c l a s s i f i e d as a c u t e r e s p i r a t o r y i r r i t a n t s ( 5 1 ) . The maximum p e r m i s s i b l e l e v e l o f e x p o s u r e t o s u l p h u r c h l o r i d e v a p o u r i s 1 ppm o v e r e i g h t h o u r s . 1.33 Thermodynamics o f C h l o r i n a t i o n o f Metal. S u l p h i d e s T a b l e 1 summarizes t h e c a l c u l a t e d e n t h a l p y and f r e e e n e r g y changes ( a t 25 ° C ) f o r t h e r e a c t i o n s o f common s u l -p h i d e m i n e r a l s w i t h s u l p h u r c h l o r i d e . 1.34 Thermodynamics o f O x i d a t i o n o f M e t a l C h l o r i d e s S e l e c t i v e o x i d a t i o n o f i r o n c h l o r i d e s t o i r o n o x i d e and c h l o r i n e ( w i t h o u t c o n v e r s i o n o f n o n - f e r r o u s m e t a l c h l o r -i d e s t o o x i d e s ) i s an i n t e g r a l p a r t o f t h e scheme p r o p o s e d i n 1.31. - 16 -T a b l e 1: E n t h a l p y and F r e e E n e r g y V a l u e s f o r R e a c t i o n s o f S e l e c t e d M e t a l S u l p h i d e s w i t h S C I R e a c t i o n A H ° ( K c a l ) A F ° ( K c a l ) F e S 2 ! S 2 C 1 2 - F e C l 3 + 5S -32 . 7 -31. 7 FeS + r S 2 C 1 2 • * F e C l 3 + 4S -5 2 . 5 -58 . 5 CuS + s 2 c i 2 - C u C l 2 + 3S -26 . 3 -24 . 4 PbS + s 2 c i 2 - P b C l 2 + 3S -48 . 9 -47 . 0 ZnS + s 2 c i 2 •> Z n C l 2 + 3S -36 . 5 -35 . 0 A g 2 S + s 2 c i 2 + 2 A g C l + 3S -38 . 7 -36 . 9 MoS 2 + T S 2 C 1 2 -* • M o C l c b + 7S + 0 . 7 + 4. 0 ft V a l u e s c a l c u l a t e d f r o m d a t a o f L a t i m e r (52) a t 25°C . F r e e e n e r g y v a l u e s and e q u i l i b r i u m c o n s t a n t s f o r t h e r e a c t i o n s o f f e r r i c c h l o r i d e and o t h e r m e t a l c h l o r i d e s w i t h oxygen a t 700°K have been c a l c u l a t e d u s i n g t h e d a t a o f G l a s s n e r ( 5 3 ) . (Note t h a t a t t e m p e r a t u r e s up t o about 900°K f e r r i c c h l o r i d e v a p o u r c o n s i s t s p r e d o m i n a n t l y o f the dimer F e 2 C l g ( 5 4 ) ) . The c a l c u l a t e d v a l u e s a r e p r e s e n t e d i n T a b l e 2. - 1 7 -T a b l e 2: C a l c u l a t e d F r e e E n e r g y o f O x i d a t i o n f o r S e l e c t e d M e t a l C h l o r i d e s a t 70Q°K" R e a c t i o n A F ° 0 Q ( K c a l ) l ° g 1 0 K F E 2 C 1 6 Cg) + 3 2 ° 2 -> F 6 2 ° 3 + 3 C 1 2 - 3 1 + 9 . 6 C u C l 2 • 1 ° 2 -> -«- CuO + C 1 2 + 5 - 1 . 5 5 P b C l 2 • k ° 2 -> -«- PbO + C 1 2 + 28 -8 . 7 Z n C l 2 • k ° 2 ZnO + C 1 2 + 9 - 2 . 8 N i C l 2 • 7 ° 2 -> -<- NiO + c i 2 + 3 -0 . 9 V a l u e s c a l c u l a t e d f r o m t h e d a t a o f G l a s s n e r ( 5 3 ) a t 7 0 0 ° K , F o r t h e r e a c t i o n o f f e r r i c c h l o r i d e , K _ F E 2 ° 3 C 1 2 _ 1 0 9 . 6 F E 2 C 1 6 ° 2 I f P n i s a r b i t r a r i l y s e t a t 0 . 0 1 ( c o r r e s p o n d i n g t o 1 % I E 2 6 c a r r y o v e r o f f e r r i c c h l o r i d e i n a c o n t i n u o u s p r o c e s s ) , t h e c a l c u l a t e d e q u i l i b r i u m P ( a t P = 1 a t m o s p h e r e ) i s 2 2 -5 0 7 1 0 ' . Thus v e r y l i t t l e oxygen w i l l be i n t r o d u c e d i n t o t h e c h l o r i n a t i o n r e a c t i o n s , and t h e h i g h P v a l u e w i l l C 1 2 s u p p r e s s o x i d a t i o n o f n o n - f e r r o u s m e t a l c h l o r i d e s . E x p e r i m e n t s p e r f o r m e d by Hohn e t a l . ( 9 ) have - 18 -q u a l i t a t i v e l y c o n f i r m e d t h e p r e d i c t e d e q u i l i b r i u m i n t h e o x i d a t i o n o f f e r r i c c h l o r i d e and shown t h e r e a c t i o n t o be f a s t a t 7 0 0 ° K - 8 0 0 ° K . 1.4 O b j e c t i v e s L i q u i d s u l p h u r c h l o r i d e has n e v e r been s e r i o u s l y i n v e s t i g a t e d as a p r o c e s s r e a g e n t f o r e x t r a c t i v e m e t a l l u r g y . The main p u r p o s e o f t h i s s t u d y was t o d e t e r m i n e c o n d i t i o n s under w h i c h th e p r o p e r t i e s o f sulphur c h l o r i d e as a s u l p h u r s o l v e n t and c h l o r i n a t i n g a g e n t c o u l d be u s e d i n p r o c e s s i n g s u l p h i d e concentrates f o r t h e e x t r a c t i o n o f m e t a l s and s u l p h u r . In p a r t i c u l a r , i t was d e s i r e d t o f i n d c o n d i t i o n s under w h i c h s p e c i f i c m i n e r a l s c o u l d be c o m p l e t e l y decomposed by s u l p h u r c h l o r i d e , t o c o l l e c t and i n t e r p r e t r e a c t i o n r a t e d a t a , and t o d e t e r m i n e t h e n a t u r e o f t h e m e t a l c h l o r i d e and s u l p h u r p r o d u c t s o f s u c h r e a c t i o n s . O t h e r s p e c i f i c o b j e c t i v e s were: t o d e t e r m i n e t h e e f f e c t o f p a r t i c l e s i z e on r e a c t i o n r a t e s , the e f f e c t C i f any) o f m i n e r a l i m p u r i t i e s on the r a t e and e x t e n t o f r e a c t i o n , t h e r e l a t i v e r e a c t i v i t i e s o f m i n e r a l s o f d i f f e r e n t g e o g r a p h i c a l o r i g i n a n d / o r c h e m i c a l c o m p o s i t i o n , and t h e e f f e c t o f r e a c t i o n p r o d u c t s on t h e r a t e and e x t e n t o f r e a c t i o n . The d e t e r m i n a t i o n o f r e a c t i o n p a t h s was n o t a p r i m a r y aim o f t h i s s t u d y . - 19 -2. MATERIALS AND METHODS 2.1 M a t e r i a l s 2.11 N a t u r a l S u l p h i d e M i n e r a l s W i t h a few e x c e p t i o n s , t h e e x p e r i m e n t s t o be d e s c r i b e d were done on n a t u r a l s u l p h i d e m i n e r a l s i n t h e f o r m o f f l o t a -t i o n c o n c e n t r a t e s . The n a t u r a l m i n e r a l s w h i c h have been s t u d i e d a r e p y r i t e ( F e S 2 ) , p y r r h o t i t e ( F e S ) , c h a l c o p y r i t e ( C u F e S j ) , g a l e n a ( P b S ) , s p h a l e r i t e (ZnS) and m o l y b d e n i t e ( M o S 2 ) . The s o u r c e s and c h e m i c a l a n a l y s e s o f t h e s e m i n e r -a l s a r e p r e s e n t e d i n A p p e n d i x A. N a t u r a l m i n e r a l s were u s e d f o r two r e a s o n s : any i n -d u s t r i a l a p p l i c a t i o n o f t h e methods d e v e l o p e d i n t h i s s t u d y would i n v o l v e t r e a t m e n t o f n a t u r a l m i n e r a l s ( p r o b a b l y i n t h e f o r m o f f l o t a t i o n c o n c e n t r a t e s ) , and n a t u r a l m i n e r a l s f r e q u e n t l y d i f f e r i n r e a c t i v i t y f r o m s y n t h e t i c s s i n c e t h e l a t t e r have n o t been a n n e a l e d o v e r g e o l o g i c t i m e p e r i o d s ( 3 2 ) . 2.12 S y n t h e s i s o f M i n e r a l s and C h e m i c a l s In the c o u r s e o f t h i s s t u d y some c h e m i c a l s ( s u l p h u r c h l o r i d e and a n h y d r o u s f e r r o u s c h l o r i d e ) and s y n t h e t i c - 20 -m i n e r a l s ( l e a d s u l p h i d e and l o w - s u l p h u r p y r r h o t i t e ) were p r e p a r e d i n t h e l a b o r a t o r y . The methods o f p r e p a r a t i o n and c h e m i c a l a n a l y s e s o f t h e s e m a t e r i a l s a r e d i s c u s s e d below. The s u l p h u r c h l o r i d e u s e d i n t h i s s t u d y was p r e p a r e d by p a s s i n g c h l o r i n e gas t h r o u g h a g l a s s d i f f u s e r i n t o s u l p h u r - s u l p h u r c h l o r i d e m i x t u r e s . P u r i f i c a t i o n was done by d i s t i l l a t i o n a t 137 (.- 1)°C. A s m a l l amount o f f o r e - r u n ( a t t h e d i s t i l l a t i o n t e m p e r a t u r e ) was d i s c a r d e d f r o m each b a t c h . The a v e r a g e c o m p o s i t i o n o f s e v e r a l l o t s o f t h i s m a t e r i a l was 4-7.5 w e i g h t p e r c e n t (wt %) s u l p h u r and 52.4 wt % c h l o r i n e . These r e s u l t s a r e i n good agreement w i t h t h e t h e o r e t i c a l c o m p o s i t i o n o f 47.4 wt % S and. 52.6 wt % C I . F o r e x p e r i m e n t s u s i n g s u l p h u r - s u l p h u r c h l o r i d e (S.S C l ^ ) s o l u t i o n s , w e ighed q u a n t i t i e s o f s u l p h u r and s u l p h u r c h l o r -i d e were mixed and h e a t e d t o d i s s o l v e t h e s u l p h u r . A nhydrous f e r r o u s c h l o r i d e ( F e C l ^ ) was u s e d t o i n -v e s t i g a t e t h e p o s s i b i l i t y t h a t f e r r o u s c h l o r i d e might be an i n t e r m e d i a t e p r o d u c t i n t h e r e a c t i o n o f i r o n s u l p h i d e m i n e r -a l s w i t h s u l p h u r c h l o r i d e . T h i s m a t e r i a l ( F e C l 2 ) was p r e p a r e d by h e a t i n g r e a g e n t g r a d e h y d r a t e d f e r r o u s c h l o r i d e ( F e C l 2 . 4 H 2 0 ) t o 400°C i n a s t r e a m o f d r i e d h y d r o g e n c h l o r i d e g a s . The p r o d u c t c o n t a i n e d 46.0. wt % Fe and 53.8 wt % CI (vs t h e o r e t i c a l v a l u e s o f 46.1 wt % Fe and 53.9 wt % C I ) . S y n t h e t i c l e a d s u l p h i d e (PbS) - u s e d t o s t u d y t h e r e a c t i o n s o f l e a d s u l p h i d e i n t h e a b s e n c e o f i m p u r i t i e s f o u n d i n t h e n a t u r a l m i n e r a l - was p r e p a r e d by h e a t i n g - 21 -powdered t e s t l e a d and e x c e s s s u l p h u r a t 500°C i n a m u f f l e f u r n a c e . The c o v e r e d c r u c i b l e c o n t a i n i n g t h e l e a d - s u l p h u r m i x t u r e was p a c k e d w i t h c h a r c o a l i n a l a r g e r c r u c i b l e t o m i n i m i z e o x i d a t i o n o f t h e c h a r g e . The a n a l y s i s o f t h e p r o d u c t was 87.0 wt % Pb and 12.9 wt % S ( v s t h e o r e t i c a l v a l u e s o f 86.7 wt % Pb and 13.3 wt % S ) . A l o w - s u l p h u r a r t i f i c a l p y r r h o t i t e ( F e S ) was p r e -p a r e d by p a s s i n g h y d r o g e n gas t h r o u g h a sample o f S u l l i v a n p y r i t e ( A p p e n d i x A) f o r two h o u r s a t 550°C. The s o l i d r e s i d u e f r o m t h i s t r e a t m e n t c o n t a i n e d 60.5 wt % Fe and 35.7 wt % S (vs t h e o r e t i c a l v a l u e s o f 63.5 wt % Fe and 36.5 wt % S i n s t o i c h i o m e t r i c , p u r e F e S ) . 2.13 O t h e r M a t e r i a l s O t h e r m a t e r i a l s - c h e m i c a l s , m e t a l s , and s o l v e n t s -used i n t h i s s t u d y a r e l i s t e d a c c o r d i n g t o g r ade i n Appen-d i x B. 2.2 E x p e r i m e n t a l Methods and A p p a r a t u s 2.21 Sample P r e p a r a t i o n M i n e r a l c o n c e n t r a t e s were c a r e f u l l y s i z e d by s c r e e n i n g b e f o r e u s e . P y r r h o t i t e ( b o t h n a t u r a l and s y n t h e t i c ) was d r y - s c r e e n e d t o m i n i m i z e s u r f a c e o x i d a t i o n . A l l o t h e r m i n e r a l s were s c r e e n e d wet and d r y t o e l i m i n a t e f i n e m a t e r -i a l . A f t e r s i z i n g , t h e m i n e r a l samples were washed i n a c e t o n e and a i r d r i e d . To o b t a i n r e p r o d u c i b l e r e s u l t s w i t h g a l e n a , i t was n e c e s s a r y t o wash e a c h sample w i t h hot sodium - 22 -c h l o r i d e s o l u t i o n ( f o l l o w e d by water and a c e t o n e ) b e f o r e l e a c h i n g . O t h e r m i n e r a l s showed no d i f f e r e n c e i n r e a c t i v -i t y a f t e r l o n g p e r i o d s o f a i r e x p o s u r e . 2.22 E x p e r i m e n t a l A p p a r a t u s and P r o c e d u r e L e a c h i n g e x p e r i m e n t s were done i n t h e a p p a r a t u s shown s c h e m a t i c a l l y i n F i g u r e 1. A c o v e r e d 250 c c p y r e x e l e c t r o -l y t i c b e a k e r c o n t a i n e d t h e r e a c t i o n m i x t u r e and a T e f l o n c o a t e d m a g n e t i c s t i r r i n g b a r . A g i t a t i o n and b a s a l h e a t i n g were p r o v i d e d by a C o r n i n g h e a t e r - s t i r r e r (model PC 3 5 1 ) . T e m p e r a t u r e c o n t r o l was m a i n t a i n e d by a Thermistemp temper-a t u r e c o n t r o l l e r and p r o b e ( Y e l l o w S p r i n g s I n s t r u m e n t Co. models 71 and 403 r e s p e c t i v e l y ) . A s m a l l i n d e n t a t i o n was made i n t h e l i p o f t h e b e a k e r t o a l l o w t h e p r o b e t o be p a r t i a l l y immersed i n t h e r e a c t i o n m i x t u r e . V a r i a b l e h e a t i n g was done by an i n f r a r e d lamp c o n n e c t e d v i a a v o l t a g e r e g u l a t o r t o a r e l a y i n t h e t e m p e r a t u r e c o n t r o l l e r . A l l l e a c h i n g e x p e r i m e n t s were done i n a fume hood t o p r e v e n t s u l p h u r c h l o r i d e v a p o u r from e n t e r i n g t h e l a b o r a t o r y a r e a . F o r e x p e r i m e n t s t o t e s t t h e e f f e c t o f more v i o l e n t a g i t a t i o n on r e a c t i o n r a t e s , s t i r r i n g was done by a 1 1/4 i n c h d i a m e t e r s t a i n l e s s s t e e l i m p e l l e r mounted on a v a r i a b l e s p e e d e l e c t r i c motor, and two 1/2 i n c h r a d i a l b a f f l e s were i n s e r t e d a t o p p o s i t e s i d e s o f t h e b e a k e r . F o r an i n d i v i d u a l e x p e r i m e n t , t h e s o l v e n t ( u s u a l l y 300 g) was b r o u g h t t o t e m p e r a t u r e and a s m a l l ( u s u a l l y 1-2 g) - 2 3 -Figure 1: S c h e m a t i c Diagram o f the E x p e r i m e n t a l A p p a r a t u s A. Heater -magnetic s t i r r e r . B. Covered 250 cc e l e c t r o l y t i c beaker containing the reaction mixture and a s t i r r i n g bar. C. Temperature probe. D. Temperature controller,. E. Power s u p p l y f o r h e a t i n g lamp. F. I n f r a r e d h e a t i n g lamp. - 2 4 -sample o f s o l i d s was added. When the p r e - d e t e r m i n e d t i m e had e l a p s e d , t h e b e a k e r was l i f t e d o f f t h e h o t p l a t e and l e t s t a n d f o r f i f t e e n s e c o n d s t o s e t t l e t h e s o l i d s . E x c e s s s o l v e n t was t h e n d e c a n t e d ( s e l e c t e d samples b e i n g r e t a i n e d f o r a n a l y s i s ) and t h e r e s i d u e washed i n t h e b e a k e r w i t h c a r b o n t e t r a c h l o r i d e , c a r b o n d i s u l p h i d e , a c e t o n e , and w a t e r . F i n a l l y , t h e s o l i d s were t r a n s f e r r e d t o a s i n t e r e d g l a s s c r u c i b l e , r i n s e d w i t h a c e t o n e , d r i e d b r i e f l y i n an oven a t 80°C, and w e i g h e d . G a l e n a s a m p l e s r e q u i r e d a d o u b l e wash w i t h h o t s a l t s o l u t i o n t o remove p r o d u c t l e a d c h l o r i d e , b u t a l l o t h e r r e s i d u e s were washed c l e a n by t h e s o l v e n t s e q u e n c e g i v e n . The c a r b o n t e t r a c h l o r i d e wash c h i l l e d t h e r e s i d u e t o room t e m p e r a t u r e and d i l u t e d t h e s u l p h u r c h l o r i d e i n t h e r e s i d u e , c a r b o n d i s u l p h i d e removed e l e m e n t a l s u l p h u r and any r e m a i n i n g s u l p h u r c h l o r i d e ; a c e t o n e and w a t e r removed m e t a l c h l o r i d e s , and t h e f i n a l a c e t o n e r i n s e f a c i l i t a t e d d r y i n g o f the r e s i d u e s . I r o n m e t a l and monel a l l o y were t r e a t e d w i t h s u l p h u r c h l o r i d e s o l u t i o n s t o i n v e s t i g a t e t h e i r r e a c t i v i t i e s i n t h e s e s o l u t i o n s . S o l i d m e t a l s p e c i m e n s were s u s p e n d e d i n the s o l u t i o n by a n i c k e l p l a t e d t e s t - t u b e h o l d e r o r s u p p o r t e d on a b e n t g l a s s r o d . 2.3 A n a l y t i c a l Methods In t h e c o u r s e o f t h e i n v e s t i g a t i o n i t was n e c e s s a r y t o d e v e l o p a n a l y t i c a l methods f o r s u l p h u r and c h l o r i n e i n - 2 5 -s u l p h u r c h l o r i d e , and f o r c h l o r i n e i n low c o n c e n t r a t i o n s i n s u l p h u r . C h l o r i n e i n S> 2C1 2 and i n s u l p h u r was d e t e r m i n e d by d i s s o l v i n g a w e ighed sample o f t h e unknown i n C S 2 , a d d i n g aqueous sodium a c e t a t e CNaOAc) s o l u t i o n and h e a t i n g t o b o i l o f f t h e C S 2 and h a s t e n t h e h y d r o l y s i s o f S - C l compounds. When t h e C S 2 had e v a p o r a t e d , t h e m i x t u r e was f i l t e r e d , t h e s u l p h u r b r o k e n up and washed. The c y c l e was r e p e a t e d t o e n s u r e c o m p l e t e e x t r a c t i o n o f c h l o r i d e i n t o t h e aqueous p h a s e . The r e s u l t i n g s o l u t i o n - b u f f e r e d by NaOAc a t pH 7 - was d i l u t e d t o volume and a l i q u o t s were t i t r a t e d w i t h 0.1 or 0.001 N s i l v e r n i t r a t e s o l u t i o n s u s i n g a drop o f s a t u r a t e d p o t a s s i u m chromate s o l u t i o n as i n d i c a t o r . S u l p h u r i n S 2 C 1 2 was d e t e r m i n e d by d i s s o l v i n g a weighed sample o f t h e unknown i n c h l o r i n e s a t u r a t e d C C l ^ and h y d r o l y z i n g t h i s s o l u t i o n w i t h d i l u t e sodium h y d r o x i d e . C h l o r i n e was added i n e x c e s s t o e n s u r e c o m p l e t e c o n v e r s i o n o f s u l p h u r t o s u l p h a t e . The r e s u l t i n g aqueous s o l u t i o n was a c i d i f i e d and b o i l e d . S u l p h a t e was p r e c i p i t a t e d w i t h b a r i u m c h l o r i d e s o l u t i o n , f i l t e r e d , i g n i t e d , and weighed as b a r i u m s u l p h a t e . L o s s o f s u l p h u r or c h l o r i n e d u r i n g a n a l y s i s was f o u n d t o be n e g l i g i b l e s i n c e %S + %C1 v a l u e s t o t a l l e d 100 - 0.4% i n a l l c a s e s where b o t h e l e m e n t s were d e t e r m i n e d . F e r r o u s and t o t a l i r o n d e t e r m i n a t i o n s were done by t i t r a t i o n w i t h s t a n d a r d c e r i u m ( I V ) s u l p h a t e s o l u t i o n u s i n g - 26 -( 1 , 1 0 ) - o - p h e n a n t h r o l i n e i n d i c a t o r . R e d u c t i o n o f f e r r i c i r o n f o r t o t a l i r o n d e t e r m i n a t i o n was done by b o i l i n g t h e sample w i t h t e s t l e a d In h y d r o c h l o r i c a c i d s o l u t i o n . - 27 -3. RESULTS AND DISCUSSION 3.1 D e c o m p o s i t i o n o f P y r i t e and R e l a t e d Compounds by S u l p h u r C h l o r i d e 3.11 R e a c t i o n o f P y r i t e w i t h S u l p h u r C h l o r i d e The 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 o f p y r i t e w i t h d i s t i l l e d s u l p h u r c h l o r i d e was d e t e r m i n e d (See A p p e n d i x C - l ) t o be: 2FeS. + 3 S . C 1 0 -* 2 F e C l + 10S 2 2 2 3 However, as shown i n F i g u r e 2, t h i s r e a c t i o n does n o t go u n i f o r m l y t o c o m p l e t i o n . The e x t e n t t o w h i c h t h e r e a c t i o n o c c u r s ( i n a c o n s t a n t w e i g h t o f s u l p h u r c h l o r i d e ) was f o u n d t o be d e p e n d e n t on t h e s i z e o f t h e i n i t i a l p y r i t e sample a t t e m p e r a t u r e s up t o t h e b o i l i n g p o i n t o f p u r e s u l p h u r c h l o r -i d e . A p r o t e c t i v e l a y e r o f p r o d u c t f e r r i c c h l o r i d e on t h e m i n e r a l s u r f a c e was s u s p e c t e d t o be t h e ca u s e o f t h e incom-p l e t e - ' r e a c t i o n . The p r e s e n c e o f a n h y d r o u s f e r r i c c h l o r i d e fa (added as r e a g e n t or as t h e p r o d u c t o f a p r e v i o u s r e a c t i o n ) was f o u n d t o d e c r e a s e t h e e x t e n t o f r e a c t i o n . The r e s u l t s - 28 -TIME (MINUTES) Figure 2: Reaction of P y r i t e with Pure Sulphur Chloride at 133°C. (a) 1 g FeS 2 i n 300 g S 2C1 2 (b) 2 g FeS 2 i n 300 g S 2 C l 2 - 29 -o f t h e s e e x p e r i m e n t s were q u i t e n o n - r e p r o d u c i b l e , but t h e e x t e n t o f r e a c t i o n when f e r r i c c h l o r i d e was p r e s e n t i n t h e i n i t i a l r e a c t i o n m i x t u r e was a l w a y s l e s s t h a n t h a t w i t h pure s u l p h u r c h l o r i d e . No f e r r i c c h l o r i d e f i l m c o u l d be v i s u a l l y d e t e c t e d on t h e s u r f a c e o f m a s s i v e p o l i s h e d p y r i t e s p e c i m e n s a f t e r r e a c t i o n i n s u l p h u r c h l o r i d e s i n c e any s o l -v e n t w h i c h removed t h e a d h e r i n g l i q u i d l a y e r l e f t a c l e a n s u l p h i d e s u r f a c e . The p o s s i b i l i t y o f a p r o t e c t i v e l a y e r o f f e r r o u s c h l o r i d e Ca p o s s i b l e r e a c t i o n i n t e r m e d i a t e ) on t h e s u l p h i d e s u r f a c e was i n v e s t i g a t e d by d e t e r m i n i n g t h e amount o f f e r r o u s i r o n i n t h e ( d i l u t e ) a c i d s o l u b l e m a t e r i a l a s s o c i a t e d w i t h the s o l i d r e a c t i o n r e s i d u e . No s i g n i f i c a n t amount o f i r o n ( I I ) was f o u n d , i n d i c a t i n g t h a t no s u b s t a n t i a l amount o f i r o n ( I I ) c h l o r i d e i s a s s o c i a t e d w i t h t h e m i n e r a l s u r f a c e . The i n c o m p l e t e r e a c t i o n o f p y r i t e i n p u r e s u l p h u r c h l o r i d e i s d i s c u s s e d i n r e l a t i o n t o t h e r e a c t i o n s o f o t h e r m a t e r i a l s i n S e c t i o n 3.162. S i n c e I t was d e s i r e d t o f i n d c o n d i t i o n s u n d e r w h i c h p y r i t e c o u l d be c o m p l e t e l y decomposed, t h e r e a c t i o n c o n d i -t i o n s were changed by a d d i t i o n o f s u l p h u r t o t h e s u l p h u r c h l o r i d e r e a c t a n t . The o r i g i n a l p u r p o s e o f t h i s a d d i t i o n was t o r a i s e t h e b o i l i n g p o i n t o f t h e r e a c t i o n m i x t u r e , t h u s e x t e n d i n g t h e t e m p e r a t u r e r a n g e a v a i l a b l e w i t h o u t u s i n g a p r e s s u r i z e d r e a c t o r . However, t h e p r e s e n c e o f d i s s o l v e d s u l p h u r i n s u l p h u r c h l o r i d e was f o u n d t o have a s t r o n g e f f e c t - 30 -on t h e r e a c t i o n o f s u l p h u r c h l o r i d e w i t h p y r i t e a t a l l t e m p e r a t u r e s i n v e s t i g a t e d C l l Q - 1 5 0 ° C ) . T h i s e f f e c t i s d i s -c u s s e d below. 3.12 R e a c t i o n o f P y r i t e w i t h S u l p h u r - S u l p h u r C h l o r i d e S o l u t i o n s 3.121 E f f e c t o f D i s s o l v e d S u l p h u r The e x t e n t t o w h i c h p y r i t e r e a c t s w i t h s u l p h u r c h l o r -i d e was f o u n d t o be s t r o n g l y a f f e c t e d by t h e p r e s e n c e o f d i s s o l v e d s u l p h u r i n t h e s u l p h u r c h l o r i d e . E x p e r i m e n t a l r e s u l t s C F i g u r e 3) showed t h a t i n c r e a s i n g the d i s s o l v e d s u l p h u r c o n t e n t o f s u l p h u r c h l o r i d e l e a d s t o more c o m p l e t e r e a c t i o n and t h a t i n 25 wt % s u l p h u r - 7 5 wt % s u l p h u r c h l o r -i d e C25 wt % S . S 2 C 1 2 ) and 40 wt % S . S 2 C 1 2 s o l u t i o n s , t h e r e a c t i o n goes u n i f o r m l y t o c o m p l e t i o n . From t h e r e s u l t s o f F i g u r e 3, i t a p p e a r s t h a t t h e r e i s a c r i t i c a l l e v e l ( i n t h e r a n g e o f 10-25 wt %) o f d i s s o l v e d s u l p h u r above w h i c h the r e a c t i o n goes t o c o m p l e t i o n , and t h a t i n t h e c o m p o s i t i o n r a n g e 25-40 wt % S . S 2 C 1 2 t h e r a t e and e x t e n t o f t h e r e a c t i o n a r e n o t s i g n i f i c a n t l y a f f e c t e d by t h e amount o f d i s s o l v e d s u l p h u r . The s o l v e n t c o m p o s i t i o n c h o s e n f o r f u r t h e r work on p y r i t e d e c o m p o s i t i o n was 40 wt % S . S 2 C 1 2 , i n w h i c h p y r i t e was f o u n d t o r e a c t u n i f o r m l y t o c o m p l e t i o n . T h i s s o l u t i o n has a h i g h e r b o i l i n g p o i n t t h a n 25 wt % S . S 2 C 1 2 ( t h u s e x t e n d -i n g t h e t e m p e r a t u r e r a n g e a v a i l a b l e w i t h o u t p r e s s u r e above a t m o s p h e r i c ) , and has a l o w e r v a p o u r p r e s s u r e t h a n p u r e - 3 1 -Figure 3: i 10 20 30 40 TIME (MINUTES) E f f e c t of Dissolved Sulphur on the Reaction of P y r i t e with Sulphur Chloride a t 133°C C S u b s t r a t e ; -70 + 10Q m e s h . (a) 1 g FeS 2 i n 300 g S 2C1 2 (b) 1 g FeS 2 i n 300 g 10 wt % S.S 2C1 2 S u l l i v a n F e S 2 ) (c) 1 g FeS 2 i n 300 25 or 40 wt % S . S 2 C l 2 - 32 -s u l p h u r c h l o r i d e . A l s o , i n an i n d u s t r i a l a p p l i c a t i o n o f s u l p h u r c h l o r i d e d e c o m p o s i t i o n o f s u l p h i d e s , a h i g h l e v e l o f d i s s o l v e d s u l p h u r would be d e s i r a b l e t o m i n i m i z e t h e amount o f c o o l i n g n e c e s s a r y t o c r y s t a l l i z e p r o d u c t s u l p h u r . F o r t h e s m a l l p y r i t e s a m p l e s u s e d i n t h e s e e x p e r i m e n t s , t h e c o m p o s i t i o n C S : C 1 r a t i o ) o f t h e s o l v e n t i s e s s e n t i a l l y c o n -s t a n t s i n c e .complete r e a c t i o n o f t h e s u b s t r a t e i n t h e q u a n t i t y (3QQ g) o f s o l v e n t u s e d changed t h e c h l o r i n e c o n -t e n t o f t h e s o l v e n t by l e s s t h a n 1 % . 3 . 1 2 2 E f f e c t o f S t i r r i n g on t h e R e a c t i o n Rate E x p e r i m e n t s w i t h v a r i o u s r a t e s o f s t i r r i n g i n t h e a p p a r a t u s shown i n F i g u r e 1 showed t h a t t h e r a t e o f r e a c t i o n o f p y r i t e i n 40 wt % S . S 2 C I 2 was i n d e p e n d e n t o f t h e s t i r r e r s p e e d once a l l s o l i d s were i n s u s p e n s i o n . To t e s t t h e e f f e c t o f more v i o l e n t a g i t a t i o n , t h e a p p a r a t u s o f F i g u r e 1 was m o d i f i e d by t h e i n s e r t i o n o f b a f f l e s and t h e use o f a v a r i a b l e s p e e d i m p e l l e r . The r e s u l t s ( F i g u r e 4 ) show t h e same l i m i t i n g r a t e as w i t h m a g n e t i c s t i r r i n g and t h e same r e q u i r e m e n t f o r c o m p l e t e s u s p e n s i o n o f the p a r t i c l e s t o r e a c h t h i s l i m i t i n g r a t e . 3.123 A G e o m e t r i c Model o f t h e R e a c t i o n M i c r o s c o p i c e x a m i n a t i o n o f t h e p y r i t e c o n c e n t r a t e (.Figure 8) I n d i c a t e d t h a t t h e i n d i v i d u a l p a r t i c l e s were (.roughly) e q u i a x e d , and t h e f o r m o f the p l o t o f p e r c e n t - 33 -2 20 O < LLI tr. U l o tr UJ o. g O < UJ tr o cr ui GL 1 2 3 4 STIRRER SPEED 0 100 200 300 IMPELLER SPEED (RPM) Figure 4: The E f f e c t of S t i r r i n g on the Rate of Reaction of FeS,, with 40 wt. % S.S 2C1 2- ("S t i r r e r Speed" refe r s to control d i a l setting.) A. A g i t a t i o n by Magnetic S t i r r i n g P e l l e t . A l l Solids Suspended at S t i r r e r Speed = 1. B. Ag i t a t i o n by Impeller with B a f f l e s . A l l Solids Suspended at Impeller Speed = 100 rpm. C o n d i t i o n s : T - 126.2°C, s u b s t r a t e : - 7 0 + 100 m S u l l i v a n F e S 2 R e a c t i o n t i m e = 10 m i n u t e s i n a l l c a s e s - 3 4 -r e a c t i o n v s . time a p p e a r e d t o be c o n s i s t e n t w i t h a c o n s t a n t r a t e o f d e c o m p o s i t i o n ( p e r u n i t a r e a ) o f t h e p a r t i c l e s . An e q u a t i o n d e s c r i b i n g t h e r e a c t i o n o f an e q u i a x e d p a r t i c l e when t h e i n t e r f a c e v e l o c i t y o f t h e r e a c t i n g s u r f a c e s i s c o n s t a n t can be d e r i v e d as f o l l o w s : C o n s i d e r a r o u g h l y e q u i a x e d p a r t i c l e h a v i n g a volume 3 ar where r i s t h e i n i t i a l r a d i u s and a i s a c o n s t a n t , o o I f t h e p a r t i c l e r e a c t s a t a r a t e w h i c h i s c o n s t a n t p e r u n i t o f s u r f a c e a r e a , t h e n —TT = k o r r = r - k t dt o i f t h e f r a c t i o n o f t h e p a r t i c l e r e a c t e d a t time t i s R t h e n 3 r - k t , v - t - q C l - R ) = t f r a c t i o n unreacted) = i £ — = (-2 = ( 1 - i H ) d 3 r r ar o o o therefore C l - R ) 1 7 3 = 1 - — or r [ 1 - ( 1 - R ) 1 / 3 ] = k t . r o o ^ 1 / 3 I f a p l o t o f t h e f u n c t i o n r [ 1 - ( . 1 - R ) ] v s . time i s l i n e a r , t h i s i n d i c a t e s t h a t t h e r e a c t i o n r a t e i s c o n s t a n t p e r u n i t o f s u r f a c e a r e a . The f u n c t i o n can be us e d f o r a s i n g l e p a r t i c l e or a group o f e q u a l l y s i z e d p a r t i c l e s . In t h i s c a s e i t i s us e d f o r a group o f n a r r o w l y s i z e d p a r t i c l e s (between two s c r e e n s i z e s ) . V a l u e s o f r were c a l c u l a t e d f o r each s c r e e n s i z e o - 35 -f r a c t i o n . F o r a p a r t i c u l a r s i z e f r a c t i o n , t h e v a l u e o f r Q c a l c u l a t e d by s e v e r a l methods C55) v a r i e s by < 4%. The e x p e r i m e n t a l d a t a were t h e n p l o t t e d i n t h e f o r m 1/3 r [ 1 - C l - R ) ] vs t . The v a l u e s o f r were c a l c u l a t e d f r o m o o t h e g e o m e t r i c mean o f t h e s c r e e n d i m e n s i o n s . ( A p p e n d i x D-4) 3.124 R e s u l t s o f E x p e r i m e n t s on S u l l i v a n P y r i t e Samples o f S u l l i v a n p y r i t e ( A p p e n d i x A) o f v a r i o u s s c r e e n s i z e s were r e a c t e d i n 40 wt % S . S 2 C I 2 o v e r a r a n g e o f t i m e s and t e m p e r a t u r e s . R e p r e s e n t a t i v e p l o t s o f p e r -c e n t r e a c t i o n vs t i m e f o r t h e s e r e a c t i o n s a r e shown i n F i g u r e 5 . The e x p e r i m e n t a l d a t a were t h e n p l o t t e d i n t h e f o r m 1/3 r ^ C l - d - R ) ] vs t i m e . F i g u r e 6 shows a r e p r e s e n t a t i v e sample o f s u c h p l o t s f o r t h e r e a c t i o n o f S u l l i v a n p y r i t e w i t h 40 wt % S . S 2 C I 2 . S i n c e t h e s t a r t i n g m a t e r i a l had a r a n g e o f s i z e s , i t i s t o be e x p e c t e d t h a t a f t e r 65 % r e a c -t i o n t h e s m a l l e s t o f t h e o r i g i n a l p a r t i c l e s w i l l have r e -a c t e d c o m p l e t e l y . T h i s e f f e c t i s shown i n F i g u r e 5 ( p l o t f o r 1 2 9 ° C ) . No a t t e m p t was made t o compute a shape f a c t o r , so t h e 1/3 r a t e s c a l c u l a t e d f r o m t h e s l o p e s pf r [ l - ( l - R ) ] vs time o w i l l be s u b j e c t t o some c o r r e c t i o n f a c t o r t o be a c c u r a t e i n a b s o l u t e t e r m s . T a b l e 3 summarizes t h e r e s u l t s o f t h e s e e x p e r i m e n t s i n terms o f t h e c a l c u l a t e d i n t e r f a c e v e l o c i t i e s ( r a t e s o f - 36 -TIME (MINUTES) Figure 5: Reaction of -200 + 270 m S u l l i v a n FeS with 40 wt. % S.S CI - 37 -TIME (MINUTES) 1/3 F i g u r e 6: P l o t o f r [ l - ( l - R ) ] vs Time f o r t h e R e a c t i o n o of -200 + 270 m S u l l i v a n F e S 2 i n 40 wt % S.S 2C1 - 38 -T a b l e 3: R a t e s o f R e a c t i o n o f S u l l i v a n P y r i t e w i t h 40 wt % S.S 2^x2 ( r e a c T l o n r a t e s e x p r e s s e d as r a t e o f p e n e t r a t i o n o f t h e s o l i d (cm mm x 1 0 5 ) ) S c r e e n S i z e -70 + F r a c t i o n s T ( ° C ) * 100m r a t e -200 T ( ° C ) + 270m r a t e -270 + T(°C ) 325 m r a t e 113.0 2 . 01 113 . 0 1. 29 120.0 3 .14 119 . 7 1.86 119 . 9 2 . 15 126.2 5.38 129 . 0 4 . 49 133.0 8.70 139 . 7 12 . 6 139 . 7 10 . 2 146 . 9 19 . 2 S m a l l v a r i a t i o n s i n measured t e m p e r a t u r e s a r e due t o d r i f t o f the t e m p e r a t u r e c o n t r o l l e r o v e r the p e r i o d o f e x p e r i -m e n t a t i o n . p e n e t r a t i o n ) f o r t h r e e s c r e e n s i z e f r a c t i o n s o f t h e S u l l i v a n p y r i t e c o n c e n t r a t e . These r a t e s were c a l c u l a t e d f r o m the s l o p e s o f p l o t s o f the f o r m o f F i g u r e 6. I t i s s u g g e s t e d t h a t t h e d i f f e r e n t r a t e s f o r the v a r i o u s s i z e f r a c t i o n s a t t h e same t e m p e r a t u r e may be due t o d i f f e r e n t shape f a c t o r s o r d i f f e r e n t p a r t i c l e s i z e d i s -t r i b u t i o n s w i t h i n t h e s c r e e n f r a c t i o n s , o r t o c r e v i c e c o r r o s i o n ( F i g u r e 7) w hich e x p o s e s more a r e a t o a t t a c k and - 39 -Absorbed Electron Image Micrographs, 240 x Magnification. - 40 -may o c c u r t o a g r e a t e r e x t e n t i n the c o a r s e r p a r t i c l e s . In a d d i t i o n i t may be p o s s i b l e t h a t i n t h e c o a r s e r f r a c t i o n , i n d i v i d u a l p a r t i c l e s may c o n t a i n more t h a n one g r a i n , and t h a t i n t e r g r a n u l a r a t t a c k e x p o s e s more s u r f a c e a r e a , c a u s i n g t h e h i g h e r c a l c u l a t e d r e a c t i o n r a t e s . F i g u r e 8 shows u n l e a c h e d samples o f -70 + 100 mesh and -200 + 270 mesh S u l l i v a n p y r i t e . F i g u r e 7 shows p y r i t e a f t e r v a r i o u s amounts of l e a c h -i n g i n 40 wt % S . S ^ C l ^ s o l u t i o n s . A l t h o u g h e t c h p i t s o r c h a n n e l s a r e e v i d e n t i n the l e a c h e d m a t e r i a l , t h e s i z e o f the l e a c h e d p a r t i c l e s d e c r e a s e s w i t h o u t f a c e t i n g or o t h e r e v i d e n c e o f a n i s o t r o p i c d i s s o l u t i o n . To I n v e s t i g a t e t h e p o s s i b i l i t y t h a t any o f t h e common t r a c e i m p u r i t i e s i n s u l p h i d e o r e s might c a t a l y z e o r i n h i b i t t h e r e a c t i o n o f p y r i t e w i t h 40 wt % S . S 2 C I 2 s o l u t i o n s , a sample o f P i n e P o i n t g a l e n a c o n c e n t r a t e c o n t a i n i n g a l a r g e v a r i e t y o f I m p u r i t i e s was c o m p l e t e l y c h l o r i n a t e d i n 40 wt % S . S 2 C I 2 . A sample o f -70 + 100 mesh S u l l i v a n p y r i t e was t h e n i n t r o d u c e d i n t o t h e r e a c t i o n m i x t u r e and t r e a t e d f o r 10 m i n u t e s at 133°C. The e x t e n t o f r e a c t i o n ( 22%) was t h e same as w i t h f r e s h s o l v e n t , i n d i c a t i n g t h a t a t low c o n c e n -t r a t i o n s i n t h e s o l v e n t none o f t h e i m p u r i t i e s i n t h i s mix-t u r e have a s i g n i f i c a n t e f f e c t on t h e r a t e o f r e a c t i o n o f p y r i t e w i t h 40 wt % S.S.C1 . - 4 1 Figure 8 : Absorbed Electron Image Micrographs, Magnification = 240 x A -70 + 100 m S u l l i v a n FeS 2 B -200 + 270 m S u l l i v a n FeS„. - 42 -To i n v e s t i g a t e t h e e f f e c t o f a l a r g e v a r i a t i o n i n t h e i n i t i a l r a t i o o f p y r i t e t o S . S ^ C l ^ s o l u t i o n on t h e t o t a l r e a c t i o n , a r e l a t i v e l y l a r g e s c a l e e x p e r i m e n t was done w i t h 40 g o f -70 + 200 mesh S u l l i v a n p y r i t e and 500 g o f 25 wt % S . S 2 C I 2 . The s o l v e n t was h e a t e d t o 130°C and p y r i t e was added g r a d u a l l y o v e r a p e r i o d o f 5 m i n u t e s t o a v o i d b o i l i n g due t o t h e h e a t o f t h e r e a c t i o n . The m i x t u r e was t h e n h e l d f o r 5 m i n u t e s a t 1 5 0 ° C , c o o l e d t o 1 00°C, and t h e s o l i d p r o d u c t s a l l o w e d t o s e t t l e . The c l e a r s u p e r n a t a n t l i q u i d was d e c a n t e d and t h e r e s i d u e a n a l y z e d . A n a l y s i s o f the r e a c t i o n p r o d u c t s showed t h a t 99% o f t h e p y r i t e was decom-p o s e d . The s o l i d , w a t e r i n s o l u b l e r e s i d u e c o n s i s t e d o f t h e z i n c s u l p h i d e C Z n S ) , s i l i c a and m a g n e t i t e (Fe 0 ) c o n t e n t o f t h e c o n c e n t r a t e ( s e e A p p e n d i x C - 3 ) . 3.125 The A c t i v a t i o n E n e r g y The r a t e s o f r e a c t i o n o f t h e -70 + 100 mesh f r a c t i o n o f S u l l i v a n p y r i t e w i t h 40 wt % S . S 2 C I 2 were u s e d t o c o n s t r u c t an A r r h e n i u s p l o t ( F i g u r e 9 ) . T h i s s i z e f r a c t i o n was u s e d b e c a u s e s m a l l e r p a r t i c l e s a r e n e a r l y c o m p l e t e l y r e a c t e d i n s h o r t t i m e s a t h i g h t e m p e r a t u r e s . The s l o p e o f t h e A r r h e n i u s . p l o t i n d i c a t e s an a c t i v a -t i o n e n e r g y o f 21.7 - 2 K c a l / m o l e . T h i s a c t i v a t i o n e n e r g y v a l u e , t h e l a c k o f e f f e c t o f s t i r r i n g (.beyond t h a t n e c e s s a r y t o s u s p e n d the p a r t i c l e s i n - 4 3 -T f C ) -3-6 146 9 1397 1330 1262 120 0 1130 £ -3-8 E ill < cr -4-0h ? -4-2 h g O < LU rr -4*4 h o Q -4-6 -4*8 2-35 2-40 245 250 255 ' ° 3/T°K 2-60 F i g u r e 9 : A r r h e n i u s P l o t f o r t h e R e a c t i o n o f - 7 Q t 1 0 0 m S u l l i v a n P y r i t e w i t h 4 0 w t % S . S 2 C 1 2 - 44 -t h e S . S ^ C l ^ s o l u t i o n ) on t h e r e a c t i o n r a t e , and t h e l i n e a r -1/3 i t y o f t h e p l o t s o f r [ l - ( l - R ) ] vs t i m e i n d i c a t e t h a t t h e r a t e l i m i t i n g f a c t o r i s a c h e m i c a l phase b o u n d a r y r e a c t i o n ( 5 6 ) . 3.126 R e a c t i o n o f P y r i t e f r o m a D i f f e r e n t S o u r c e P y r i t e samples from Noranda Mines L t d . ( A p p e n d i x A) were r e a c t e d under the same c o n d i t i o n s as S u l l i v a n m a t e r i a l t o compare the r a t e s o f r e a c t i o n . The Noranda p y r i t e r e a c t s ^ 5 0 % s l o w e r t h a n th e S u l -l i v a n p y r i t e , but w i t h th e same s t o i c h i o m e t r y . The r e s u l t s were l i n e a r i n b o t h c a s e s when p l o t t e d i n t h e f o r m 1/3 r [ l - ( l - R ) ] vs t i m e ( F i g u r e 1 0 ) . F i g u r e 11 shows samples o f -70 + 100.mesh S u l l i v a n and Noranda p y r i t e s b e f o r e l e a c h -i n g . I t a p p e a r s t h a t t h e s u r f a c e s o f t h e Noranda m a t e r i a l a r e r e l a t i v e l y s m oother — t h u s p r e s e n t i n g l e s s e f f e c t i v e a r e a f o r c h e m i c a l a t t a c k . I t i s s u g g e s t e d t h a t t h i s d i f f e r -ence i n s u r f a c e r o u g h n e s s i s a t l e a s t p a r t i a l l y r e s p o n s i b l e f o r t h e d i f f e r e n c e i n r e a c t i v i t y between the two m a t e r i a l s . 3.13 R e a c t i o n o f N a t u r a l and S y n t h e t i c P y r r h o t i t e The r e a c t i o n s o f n a t u r a l ( S u l l i v a n — A p p e n d i x A) and low s u l p h u r s y n t h e t i c p y r r h o t i t e w i t h ( i n i t i a l l y ) p u r e S 2 C 1 and 40 wt % S . S 2 C 1 2 have been s t u d i e d . The o b s e r v e d s t o i c h i o m e t r y o f t h e l i m i t e d r e a c t i o n w h i c h o c c u r r e d was f o u n d (.Appendix C-4) t o be: - 45 -Noranda P y r i t e s Reacted with 40 wt. % S.S CI at 119.9°C. - 46 -A B 11: -70 + 100 m S u l l i v a n and Noranda Pyrites Before Leaching. A, B Kimberley FeS 2; C,D Noranda FeS 2 A,C,D Absorbed Electron Image Micrographs, 240 x B Backscattered Electron Image Micrograph, 240 x. _ i+7 -2FeS + 3S C1 •> 2 F e C l + 8S The e f f e c t s o f t e m p e r a t u r e , s o l v e n t c o m p o s i t i o n , and sample s i z e on t h e r e a c t i o n o f S u l l i v a n p y r r h o t i t e w i t h s u l p h u r c h l o r i d e a r e shown i n F i g u r e 12. The a b r u p t d e c r e a s e i n r e a c t i o n r a t e a f t e r p a r t i a l r e a c t i o n and t h e d e c r e a s e d e x t e n t o f r e a c t i o n w i t h i n c r e a s e d sample s i z e i n d i c a t e t h a t t h e r e a c t i o n i s s t i f l e d by some p r o d u c t . In c o n t r a s t t o t h e r e s u l t s o f e x p e r i m e n t s on p y r i t e , t h e p r e s e n c e o f a l a r g e amount (40 wt %) o f s u l p h u r i n t h e i n i t i a l s o l u t i o n had no s i g n i f i c a n t e f f e c t on t h e e x t e n t o f r e a c t i o n . A d d i t i o n o f f e r r i c c h l o r i d e t o t h e i n i t i a l r e a c t i o n m i x t u r e d e p r e s s e d t h e e x t e n t o f r e a c t i o n o f p y r r h o t i t e b u t , as was f o u n d t o be t h e c a s e w i t h p y r i t e , t h e r e s u l t s were not r e p r o d u c i b l e . F o r m a t i o n o f an i n h i b i t i n g f i l m o f f e r r o u s or f e r r i c c h l o r i d e a t t h e s u l p h i d e s u r f a c e seemed t o be a p r o b a b l e cause o f t h e s t i f l i n g o f t h e r e a c t i o n , b u t such a f i l m c o u l d n o t be p o s i t i v e l y i d e n t i f i e d . S o l v e n t s such as c a r b o n t e t r a c h l o r i d e , c a r b o n d i s u l p h i d e , or dichloroethane w h i c h removed a d h e r i n g s o l v e n t f r o m t h e m i n e r a l s u r f a c e a l s o r e -moved f e r r i c c h l o r i d e , so the e x t e n t ( i f any) t o w h i c h f e r r i c c h l o r i d e f ormed a f i l m on t h e r e a c t i n g s u r f a c e c o u l d n o t be d e t e r m i n e d . A t t e m p t s t o d e t e c t a f i l m of f e r r o u s c h l o r i d e on t h e r e a c t i n g s u r f a c e by t i t r a t i o n o f w a t e r s o l u b l e i r o n ( I I ) i n the s o l i d r e a c t i o n p r o d u c t were c o m p l i c a t e d by the 90 - 4 8 80 L / 70 60 r A / ^ 50 o i -u < U J UJ o cr UJ Q_ 40 30 20 10 0 o40%SS 2 CI 2 I33°C. -• 4 0 % S S C L I33°C 2 2 4 0 % S S 0 CI 0 I I3 °C 2 2 -o S2CI2 I I3 °C o 2g.FeS • 4g.FeS \- cr 10 20 30 40 TIME (MINUTES) Figure 12: Reaction of -140 + 200 m S u l l i v a n FeS with S 2C1 2 and 40 wt. % S•S 12• 4 50 60 - 49 -t e n d e n c y o f t h e s u l p h i d e t o d i s s o l v e i n a s l i g h t l y a c i d wash s o l u t i o n . H i g h and e r r a t i c i r o n C l I ) t i t r a t i o n b l a n k s (wash s o l u t i o n p a s s e d t h r o u g h u n l e a c h e d s o l i d s ) were ob-t a i n e d , b u t t h e r e was no i n d i c a t i o n o f any s u b s t a n t i a l f e r -r o u s c h l o r i d e f i l m on t h e s u r f a c e o f l e a c h e d m a t e r i a l . To i n v e s t i g a t e t h e e f f e c t o f t h e m i n e r a l c o m p o s i t i o n on t h e r e a c t i o n o f p y r r h o t i t e , low s u l p h u r s y n t h e t i c p y r r h o t i t e was a l s o t r e a t e d w i t h 40 wt % S . S 2 C 1 2 . The e x p e r i m e n t a l r e s u l t s a r e summarized i n T a b l e 4. T h i s m a t e r i a l a p p e a r s t o r e a c t i n t h e same way as t h e n a t u r a l m i n e r a l e x c e p t t h a t t h e e x t e n t o f r a p i d r e a c t i o n a t a p a r -t i c u l a r t e m p e r a t u r e , e.g. 1 1 3 ° C , was f o u n d t o be g r e a t e r w i t h 40 wt % S . S 2 C 1 2 t h a n w i t h S 2 C 1 2 > These r e s u l t s a r e d i f f i c u l t t o e x p l a i n i n terms o f the r o l e o f d i s s o l v e d s u l p h u r i n the s o l v e n t . - 50 -T a b l e 4: R e a c t i o n o f S y n t h e t i c FeS and F e C l 2 w i t h S.S 2C1 S o l u t i o n s S o l v e n t S u b s t r a t e Time T°C % Reac- mg Fe m i n u t e s t i o n r e a c t e d 40 wt % s. s 2 c i 2 FeS (2 g) 5 113 . 0 47 284 I I II 10 II 50 302 I I n 20 I I 52 314. s 2 c i 2 FeS (2 g) 5 113 . 0 28 169 I I it 10 II 30 181 I I II 20 ' it 32 . 5 193 s 2 c i 2 FeS (1 g) 5 113 . 0 30 90 I I it 10 I I 32 95 40 wt % s. s 2 c i 2 F e C l 2 (1 g) 5 113 . 0 95 . 3 395 I I it (3 g) 5 II 88 1241 s 2 c i 2 F e C l 2 (1 g) 5 113 . 0 80 . 5 358 I I I I 60 II 78. 7 350 In 300 g o f s o l v e n t . 3.14 R e a c t i o n o f Anhydrous F e r r o u s C h l o r i d e w i t h S u l p h u r C h l o r i d e As has been m e n t i o n e d p r e v i o u s l y , f e r r o u s c h l o r i d e i s c o n s i d e r e d t o be a p l a u s i b l e i n t e r m e d i a t e i n the r e a c t i o n o f i r o n s u l p h i d e s w i t h s u l p h u r c h l o r i d e . To t e s t t h e s t a b i l i t y o f f e r r o u s c h l o r i d e under c o n d i t i o n s i n w h i c h s u l p h i d e s r e a c t , s a m p l e s o f t h i s m a t e r i a l ( b r o k e n under n i t r o g e n t o p a s s a 70 mesh s c r e e n ) were t r e a t e d w i t h - 51 -S 2 C 1 2 and 40 wt % S . S ^ ^ . The e x p e r i m e n t a l p r o c e d u r e was v a r i e d s l i g h t l y f o r t h e s e t e s t s : the s o l i d r e a c t i o n r e s i -dues were washed w i t h d i e t h y l e t h e r i n s t e a d o f w a t e r , and oven d r y i n g o f t h e r e s i d u e was o m i t t e d . The e x p e r i m e n t a l r e s u l t s a r e summarized i n T a b l e 4. In S 2 C 1 2 , f e r r o u s c h l o r i d e r e a c t e d p a r t i a l l y t o f o r m f e r r i c c h l o r i d e . However, t h e amount o f i r o n ( I I ) c o n v e r t e d t o f e r r i c c h l o r i d e was q u i t e d i f f e r e n t f r o m t h e amount r e a c t i n g f r o m p y r r h o t i t e u nder t h e same c o n d i t i o n s . In 40 wt % S . S 2 C 1 2 , f e r r o u s c h l o r i d e was c o n v e r t e d r a p i d l y and n e a r l y c o m p l e t e l y t o f e r r i c c h l o r i d e . 3.15 R e a c t i o n s o f M e t a l l i c I r o n w i t h S u l p h u r C h l o r i d e The r e a c t i o n s o f m e t a l l i c i r o n w i t h s u l p h u r c h l o r i d e and s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s were a l s o i n v e s t i -g a t e d . T h i s was done i n o r d e r t o e x p l o r e t h e p o s s i b i l i t y t h a t knowledge o f t h e s e r e a c t i o n s might l e a d t o a more com-p l e t e u n d e r s t a n d i n g o f t h e r e a c t i o n s o f i r o n s u l p h i d e s . A l s o , l a r g e f l a t s p e c i m e n s were r e a d i l y a v a i l a b l e , and i t was e x p e c t e d t h a t s u c h s u r f a c e s would s i m p l i f y the d e t e c t i o n o f s u r f a c e f i l m s i f s u c h f i l m s e x i s t e d . S t r i p s o f m e t a l l i c i r o n were t r e a t e d w i t h S 2 C 1 2 and 40 wt % S.Sg-Cl . The b e h a v i o u r o f i r o n i n t h i s s y s t e m i s more complex t h a n t h a t o f t h e i r o n s u l p h i d e s . R e s u l t s o f the e x p e r i m e n t s a r e summarized i n F i g u r e 13. I t was o b s e r v e d t h a t a f i l m f ormed on t h e s u r f a c e o f - 52 -0 60o[ \/ T I M E 4 6 CM . o 500 ro 2 4 0 0 ll_ • MG. vs. T IME 2i o MG. vs. N/TIME 8 10 T r Q o 0 2 0 4 0 6 0 8 0 T I M E ( M I N U T E S ) 100 Figure 13: Reaction of Fe with 40 wt. % S.S 2C1 2 (a) and S 2C1 2 (b) at 133°C. - 53 -i r o n t r e a t e d w i t h S 2 C 1 2 < The f i l m was i n s o l u b l e i n a c e t o n e o r w a t e r b ut r e a d i l y s o l u b l e i n d i l u t e a c i d . When th e f i l m was d i s s o l v e d i n a c i d , a h y d r o g e n s u l p h i d e s m e l l was n o t e d , so i t was c o n c l u d e d t h a t t h e s u r f a c e f i l m was i r o n s u l p h i d e . The f i l m grew i n a s t r e a k y f o r m u n t i l i t a p p e a r e d t o c o v e r the e n t i r e s u r f a c e o f t h e s p e c i m e n . The growth o f t h i s f i l m i s shown i n F i g u r e 14. When i r o n was t r e a t e d w i t h 40 wt % S . S 2 C 1 2 , a p a l e g r e e n f i l m formed on t h e s u r f a c e . T h i s f i l m was i n s o l u b l e i n a c e t o n e b u t s o l u b l e i n w a t e r and was d e t e r m i n e d t o be f e r r o u s c h l o r i d e . (See A p p e n d i x C-5) The f o r m o f the p l o t o f w e i g h t o f i r o n r e a c t e d v s . t i m e ( F i g u r e 13) i n d i c a t e s t h a t t h e f e r r o u s c h l o r i d e f i l m g r a d u a l l y t h i c k e n s and s l o w s the r e a c t i o n by f o r m i n g a b a r r i e r t o d i f f u s i o n o f r e a c t a n t s a n d / o r p r o d u c t s . F i g u r e 13 a l s o shows p l o t s o f w e i g h t o f i r o n r e a c t e d v s . Ct) ' f o r i r o n i n S 2 C 1 2 and 40 wt % S . S 2 C 1 2 . These p l o t s a r e a p p r o x i m a t e l y l i n e a r , t h u s p r o v i d i n g a d d i t i o n a l e v i d e n c e t h a t f i l m f o r m a t i o n a f f e c t s t h e r a t e o f r e a c t i o n . 3.16 Summary and D i s c u s s i o n o f E x p e r i m e n t s on I r o n Compounds 3.161 Summary o f O b s e r v a t i o n s I t was o b s e r v e d t h a t i r o n , t h e i r o n s u l p h i d e s , and f e r r o u s c h l o r i d e a l l behave somewhat d i f f e r e n t l y i n t h e i r r e a c t i o n s w i t h s u l p h u r c h l o r i d e . The p o s s i b l e c h e m i c a l r e a c t i o n s i n t h e s e s y s t e m s a r e l i s t e d i n T a b l e 5 w i t h some - 54 -Figure 14: Growth of FeS Film on Iron Reacting with S2CI a before reaction b t = 5 minutes c t = 10 minutes d t = 20 minutes - 55 -a p p r o p r i a t e o b s e r v a t i o n s . T a b l e 6 shows t h e i n i t i a l and e x t e n d e d t i m e r e a c t i o n r a t e s f o r t h e s e s y s t e m s . T a b l e 5: R e a c t i o n s o f F e S 2 , FeS, F e C l 2 and Fe w i t h S 2 C 1 2 R e a c t i o n O b s e r v a t i o n s 1) F e S 2 + S 2 C 1 2 -> F e C l 2 ' + 4S 2) F e C l 2 + j S 2 C 1 2 F e C 1 3 + S F e C l 2 was n o t o b s e r v e d but i s a p o s s i b l e r e a c -t i o n i n t e r m e d i a t e 3) = 1) + 2) F e S 2 + | S 2 C 1 2 F e C l 3 + 5S O b s e r v e d s t o i c h i o m e t r y . The r e a c t i o n i s i n c o m -p l e t e u n l e s s t h e s o l v e n t c o n t a i n s >10 wt. % S. 4) FeS +' S 2 C 1 2 F e C l 2 + 3S 5) FeS + | S 2 C 1 2 F e C 1 3 + 4 S F e C l 2 was n o t o b s e r v e d , O b s e r v e d s t o i c h i o m e t r y , The e x t e n t o f r e a c t i o n i s d e p e n d e n t on sample s i z e . 6) Fe + n S . S 2 C l 2 -»- F e C l 2 (n+2)S 7) Fe + j S 2 C 1 2 -»• F e C l g + 3S ) 4Fe + j S 2 C 1 2 3 F e S + ; F e C 1 3 9) F e C l 2 + ± S 2 C 1 2 F e C l g + S An F e C l 2 l a y e r was formed i n 40 wt s . s 2 c i 2 F e C l g i s t h e f i n a l p r o d - . u c t o f S 2 C 1 2 a t t a c k on Fe An FeS f i l m was o b s e r v e d i n r e a c t i o n w i t h ( i n i t i a l l y ) 100% S 2 C 1 2 . F a s t b u t i n c o m p l e t e i n S 2 C 1 0 . F a s t and v i r t u -a l l y c o m p l e t e i n 40 wt % s . s 2 c i 2 - 56 -T a b l e 6: I n i t i a l and E x t e n d e d Time R e a c t i o n R a t e s f o r FeS FeS, F e C l 2 and Fe i n S 2 C 1 2 and 40 wt % S . S 2 C 1 2 . S u b s t r a t e T°C S o l v e n t I n i t i a l r a t e Rate a f t e r / -2 . -1, e x t e n d e d t i m e Cg cm mm ) _ 2 (g cm min ) F e S 2 113 s 2 c i 2 > 8 X I C T * < 1 X 10 -5 ti 133 40 wt % s . s 2 c i 2 4.2 X l O " 4 4 . 2 X 10 -4 FeS 113 . 5 s 2 c i 2 ^2.1 X l O ' 4 < 1 X 10 -5 II 113 . 5 40 wt % s . s 2 c i 2 6 X l O " 4 1 X 10 -5 Fe 133 s 2 c i 2 1.7 X l O " 4 8.5 X 10 -6 it 133 40 wt % s . s 2 c i 2 5 .1 X l O " 4 1 X 10 -4 F e C l . 113 . 5 s 2 c i X 0 . 1 X ( a r e a n o t known) ft 113 . 5 40 wt % s . s 2 c i 2 v e r y f a s t I t was o b s e r v e d t h a t t h e i n i t i a l r e a c t i o n s o f p y r i t e , p y r r h o t i t e and f e r r o u s c h l o r i d e w i t h s u l p h u r c h l o r i d e a r e f a s t b u t t h a t t h e s e r a t e s d e c r e a s e c o n s i d e r a b l y b e f o r e t h e r e a c t i o n i s c o m p l e t e ( T a b l e 6 ) . The e x t e n t o f t h e f a s t r e a c t i o n was f o u n d t o be d e p e n d e n t on sample s i z e . S i n c e t hermodynamic c a l c u l a t i o n s p r e d i c t t h a t f e r r i c c h l o r i d e s h o u l d be t h e f i n a l r e a c t i o n p r o d u c t , i t may be s u p p o s e d t h a t i n t h e s e s y stems t h e f a s t r e a c t i o n c o n t i n u e s o n l y u n t i l t h e s u b s t r a t e s u r f a c e i s e f f e c t i v e l y c o v e r e d by an i n h i b i t i n g f i l m o f f e r r i c c h l o r i d e . The amount o f f e r r i c c h l o r i d e - 57 -r e q u i r e d t o s t i f l e t h e f a s t r e a c t i o n a p p e a r s t o be a f u n c -t i o n o f t h e f o r m and c o m p o s i t i o n o f t h e s u b s t r a t e . In the c a s e o f m e t a l l i c i r o n i n s u l p h u r c h l o r i d e , a f i l m o f i r o n s u l p h i d e was formed on t h e s u r f a c e and t h e r e a c t i o n became e q u i v a l e n t t o t h a t o f p y r r h o t i t e . 3.162 The R e a c t i o n o f P y r i t e I t has been o b s e r v e d t h a t t h e r e a c t i o n o f p y r i t e w i t h i n i t i a l l y p u r e s u l p h u r c h l o r i d e i s i n h i b i t e d by t h e p r e s e n c e o f f e r r i c c h l o r i d e b u t t h a t p y r i t e r e a c t s u n i f o r m l y t o com-p l e t i o n when e x p o s e d t o e x c e s s s u l p h u r c h l o r i d e c o n t a i n i n g 25-40 wt % d i s s o l v e d s u l p h u r . F o r t h e c a s e o f p y r i t e r e a c t i n g i n 25-40 wt % S . S 2 C I 2 J r e a c t i o n 2 (.Table 5) would be s u p p r e s s e d a t t h e r e a c t i n g s u r f a c e i f t h e l o c a l c o n c e n t r a t i o n o f s u l p h u r f r o m r e a c t i o n 1 p l u s t h e h i g h i n i t i a l l e v e l o f d i s s o l v e d s u l p h u r were h i g h enough t o d e p r e s s t h e c h l o r i n e a c t i v i t y a t t h e s u l p h i d e s u r f a c e below t h e l e v e l o f d e c o m p o s i t i o n o f f e r r i c c h l o r i d e . F e r r o u s c h l o r i d e p r o d u c e d a t t h e s u l p h i d e s u r f a c e may t h e n be t r a n s p o r t e d away f r o m t h e s u r f a c e (as a s u s p e n d e d s o l i d ) by t h e m o t i o n o f the l i q u i d b e f o r e c o n v e r -s i o n t o f e r r i c c h l o r i d e . Any f e r r i c c h l o r i d e formed away from the r e a c t i n g s u r f a c e would not f o r m a p r o t e c t i v e l a y e r on t h e s u r f a c e . An e f f e c t i n t e r p r e t a b l e i n t h i s way i s o b s e r v e d i n an aqueous s y s t e m when n i c k e l - i r o n a l l o y i s l e a c h e d i n ammonia-ammonium c a r b o n a t e s o l u t i o n ( 5 7 ) . At a - 58 -h i g h s o l u t i o n o x i d i z i n g p o t e n t i a l , i r o n i s o x i d i z e d t o i r o n ( H I ) a t or n e a r t h e s u r f a c e and forms a l a y e r o f h y d r o u s f e r r i c o x i d e w h i c h s l o w s o r s t o p s th e r e a c t i o n . In t h e c a s e o f p y r i t e r e a c t i n g w i t h 40 wt % S . S 2 C I 2 5 t h e r e i s no i n d i c a -t i o n t h a t an i n i t i a l f e r r o u s c h l o r i d e p r o d u c t i s s o l u b l e , but i t i s p o s s i b l e t h a t f e r r o u s c h l o r i d e i s f ormed as a f i n e l y d i v i d e d s u s p e n d e d s o l i d w h i c h does n o t a d h e r e t o t h e r e a c t i n g p y r i t e s u r f a c e , and i s c h l o r i n a t e d t o f e r r i c c h l o r -i d e a t a p o i n t remote from the s u l p h i d e s u r f a c e . F e r r o u s c h l o r i d e p r o d u c e d i n t h i s s y s t e m would be f i n e l y d i v i d e d b e c a u s e i t i s b e l i e v e d t o be i n s o l u b l e i n t h e s o l v e n t and t h u s i n c a p a b l e o f r e c r y s t a l l i z i n g by the s o l u t i o n - p r e c i p i -t a t i o n mechanism w h i c h i s p o s s i b l e f o r f e r r i c c h l o r i d e . However, t h i s h y p o t h e s i s i s n o t c o n s i s t e n t w i t h t h e o b s e r v a -t i o n t h a t the r e a c t i o n r a t e i s i n d e p e n d e n t o f t h e s t i r r i n g s p e e d . The o b s e r v e d k i n e t i c s o f t h e r e a c t i o n o f p y r i t e w i t h 4Q wt % S . S 2 C I 2 a r e a l s o c o n s i s t e n t w i t h r a t e c o n t r o l by d i f f u s i o n t h r o u g h a s u r f a c e f i l m o f c o n s t a n t t h i c k n e s s , but no a n a l y t i c a l e v i d e n c e o f s u c h a f i l m was f o u n d . 3.163 The R e a c t i o n o f P y r r h o t i t e The f a i l u r e o f p y r r h o t i t e t o r e a c t c o m p l e t e l y a t m e a s u r a b l e r a t e s i n S 2 C I 2 and 40 wt % S . S j C ^ s o l u t i o n i s presumed t o be due t o s u p p r e s s i o n o f t h e r e a c t i o n by f e r r i c c h l o r i d e p r o d u c t w h i c h i s formed or d e p o s i t e d on t h e s u l p h i d e - 59 -s u r f a c e . There i s no way o f d i s t i n g u i s h i n g between a f i l m o f f e r r i c c h l o r i d e f ormed on t h e s u r f a c e and one t h a t has d e p o s i t e d f r o m s o l u t i o n . The o b s e r v a t i o n i s t h a t t h e r e a c -t i o n i s i n h i b i t e d by f e r r i c c h l o r i d e . . 3.164 The R e a c t i o n s o f M e t a l l i c I r o n When m e t a l l i c i r o n was t r e a t e d w i t h 40 wt % S . S 2 C I 2 , a f i l m o f f e r r o u s c h l o r i d e was f ormed on the s u r f a c e . T h i s o b s e r v a t i o n would seem t o be i n c o n s i s t e n t w i t h th e o b s e r v a -t i o n t h a t powdered f e r r o u s c h l o r i d e r e a c t s r a p i d l y w i t h 40 wt % S . S 2 C I 2 at a l o w e r t e m p e r a t u r e . However, i t i s p o s s i b l e t h a t a t h i n f i l m o f f e r r o u s c h l o r i d e g r o w i n g f r o m a s u b s t r a t e might be s t a b l e u nder c o n d i t i o n s i n w h i c h a f i n e l y d i v i d e d s u s p e n d e d powder i s v e r y r e a c t i v e . I t i s a l s o somewhat s u r p r i s i n g • t h a t no v i s i b l e l a y e r o f i r o n s u l -p h i d e was formed on i r o n i n 40 wt % S . S 2 C I 2 , but an e x t r e m e l y t h i n l a y e r o f s u l p h i d e may be p r e s e n t between the i r o n and f e r r o u s c h l o r i d e l a y e r s . Such a f i l m would be c o n t i n u o u s l y decomposed by s u l p h u r c h l o r i d e d i f f u s i n g t h r o u g h t h e f e r r o u s c h l o r i d e l a y e r , b u t a h i g h l o c a l s u l p h u r c o n c e n t r a t i o n a t t h i s i n t e r f a c e may p r e v e n t th e f o r m a t i o n o f i n h i b i t i n g f e r r i c c h l o r i d e a t t h e r e a c t i n g s u r f a c e . In S 2 C I 2 , when i r o n s u l p h i d e i s formed Con i r o n ) i t i s p r e s u m a b l y p r o t e c t e d by an i n h i b i t i n g l a y e r o f f e r r i c c h l o r i d e and t h u s d e t e c t a b l e as a l a y e r on t h e s u r f a c e . - 60 -3.2 D e c o m p o s i t i o n o f O t h e r S u l p h i d e s by S u l p h u r C h l o r i d e 3.21 D e c o m p o s i t i o n o f G a l e n a 3.211 R e a c t i v i t y o f N a t u r a l and S y n t h e t i c G a l e n a The r e a c t i o n o f g a l e n a (PbS) w i t h s u l p h u r c h l o r i d e was s t u d i e d i n i t i a l l y u s i n g a P i n e P o i n t g a l e n a c o n c e n t r a t e ( A p p e n d i x A ) . The 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 was d e t e r -mined ( A p p e n d i x C-6) t o be: PbS + S 2 C 1 2 -»• P b C l 2 + 3S but t h e e x p e r i m e n t a l r a t e d a t a were v e r y e r r a t i c . To e l i m i n a t e the p o s s i b l e e f f e c t o f c h e m i c a l i m p u r -i t i e s on t h e r e a c t i o n r a t e , a s y n t h e t i c l e a d s u l p h i d e was p r e p a r e d . T h i s m a t e r i a l d i d n o t r e a c t a t a u s e f u l r a t e w i t h p u r e s u l p h u r c h l o r i d e or s u l p h u r — s u l p h u r c h l o r i d e s o l u t i o n s . I t d i d , however, r e a c t s l o w l y when s m a l l amounts of n a t u r a l ( P i n e P o i n t ) g a l e n a were added t o the r e a c t i o n m i x t u r e . From t h i s o b s e r v a t i o n , i t was i n f e r r e d t h a t some i m p u r i t y i n t h e n a t u r a l g a l e n a might have c a t a l y z e d t h e r e a c t i o n o f g a l e n a w i t h s u l p h u r c h l o r i d e . 3.212 D e t e r m i n a t i o n o f C a t a l y s t s . The c a t a l y t i c e f f e c t o f v a r i o u s c h e m i c a l s on t h e r e a c t i o n o f s y n t h e t i c l e a d s u l p h i d e w i t h s u l p h u r c h l o r i d e was i n v e s t i g a t e d i n i t i a l l y by a d d i n g s m a l l q u a n t i t i e s (^ 0.1 g) o f c h e m i c a l s - c o r r e s p o n d i n g t o a l l t h e i m p u r i t i e s p r e s e n t - 61 -i n t h e n a t u r a l m i n e r a l - t o a r e f l u x i n g m i x t u r e o f s u l p h u r c h l o r i d e and s y n t h e t i c l e a d s u l p h i d e . Complete r e a c t i o n o f t h e l e a d s u l p h i d e was o b s e r v e d i n t h i s e x p e r i m e n t , so i n s u c c e e d i n g t e s t s v a r i o u s c h e m i c a l s were o m i t t e d u n t i l i n c o m -p l e t e r e a c t i o n o f t h e l e a d s u l p h i d e was o b s e r v e d . By t h i s t r i a l and e r r o r method the a c t i v e c a t a l y s t c o m b i n a t i o n s were f o u n d t o be s i l v e r - b i s m u t h and s i l v e r - a n t i m o n y . Data on the e f f e c t o f m a t e r i a l s f o u n d t o be c a t a l y t i c a l l y a c t i v e i n t h i s s y s t e m a r e p r e s e n t e d i n T a b l e 7. T a b l e 7: E f f e c t o f V a r i o u s A d d i t i v e s on t h e Rate o f R e a c t i o n o f S y n t h e t i c PbS w i t h S C I M a t e r i a l added S o l v e n t Time T°C % R e a c t i o n C 0.1 g o f e a c h ( m i n u t e s ) ( o f 1 g sample) c h e m i c a l ) n i l S 2 C 1 2 2 0 135-40 0.5 A g 2 S " . » 8 A s 2 S 3 , S b 2 S 3 , B i 2 S 3 » « » 4 A g 2 S , A s 2 S 3 » " » 12 A g 2 S , S b 2 S 3 » » " 75 A g 2 S , B i 2 S 3 " » » 94 The r e a s o n f o r t h e c a t a l y t i c e f f e c t i s n o t known, but two p o s s i b i l i t i e s a r e s u g g e s t e d . Antimony and b i s m u t h c h l o r i d e s f o r m c o m p l e x e s w i t h t h e g e n e r a l f o r m u l a M + + B i C l ~ o r M + + S b C l ~ ( 5 8 ) . Complexes o f t h i s t y p e may be - 62 -i n v o l v e d i n t h e t r a n s p o r t o f p r o d u c t l e a d c h l o r i d e f r o m the r e a c t i n g s u r f a c e . I f t h i s I s t h e i r r o l e t h e n t h e r e q u i r e -ment f o r s i l v e r I s u n e x p l a i n e d . A l t e r n a t i v e l y , f o r m a t i o n o f s u c h compounds may s t a b i l i z e or s o l u b i l i z e s i l v e r C l I ) c h l o r i d e . S i l v e r ( I I ) i s a s t r o n g o x i d a n t (59) and might be an i n t e r m e d i a t e i n t h e r e a c t i o n o f l e a d s u l p h i d e w i t h s u l p h u r c h l o r i d e . 3.213 R e s u l t s o f E x p e r i m e n t s on P i n e P o i n t G a l e n a R e p r e s e n t a t i v e s e t s o f d a t a f o r t h e r e a c t i o n o f P i n e P o i n t g a l e n a w i t h s u l p h u r c h l o r i d e ( w i t h and w i t h o u t added c a t a l y s t ) a r e shown i n F i g u r e 15. F o r measurements on t h e c a t a l y z e d r e a c t i o n , c a t a l y t i c m a t e r i a l was added t o t h e s y s t e m by c o m p l e t e l y c h l o r i n a t i n g a one gram sample o f t h e m i n e r a l a t h i g h t e m p e r a t u r e ( ^ 1 0 0 ° C ) and c o o l i n g t h i s m i x t u r e t o t h e d e s i r e d r e a c t i o n t e m p e r a t u r e b e f o r e a d d i n g a w e i ghed sample o f f r e s h m i n e r a l . T h i s method was f o u n d t o g i v e much more r e p r o d u c i b l e r e s u l t s t h a n a d d i t i o n o f c a t a -l y s t i n t h e f o r m o f r e a g e n t c h e m i c a l s . The d a t a f o r u n c a t a l y z e d r e a c t i o n was o b t a i n e d by r e a c t i n g t h e n a t u r a l m i n e r a l i n i n i t i a l l y p u r e s o l v e n t . The i n i t i a l r a t e s o f r e a c t i o n o b t a i n e d i n t h i s way i n d i c a t e t h e r a t e o f r e a c t i o n when o n l y a s m a l l amount o f a c t i v e c a t a l y s t i s p r e s e n t i n the m i x t u r e . O b v i o u s l y as t h e e x t e n t o f r e a c t i o n i n c r e a s e s t h e r e w i l l be an I n c r e a s i n g c a t a l y t i c e f f e c t on t h e r e a c t i o n . - 63 -35 TIME (MINUTES) Figure 15: Reaction of -150 + 200 m Pine Point Galena with 10 wt. % S.S2C1 a Catalyzed reaction at 40°C. b Uncatalyzed reaction at 70°C. - 64 -TIME (MINUTES) 1/3 F i g u r e 16 - P l o t of r [ l - ( l - R ) ] vs Time f o r t h e C a t a l y z e d R e a c t i o n o f -150 + 200 m P i n e P o i n t G a l e n a w i t h 10 wt % S . S 0 C 1 0 - 65 -eure 17: P l o t of r [ l - ( l - R ) ] vs Time f o r U n c a t a l y z e d ° o R e a c t i o n o f -150 + 200 m P i n e P o i n t G a l e n a w i t h 10 wt % S . S 0 C 1 0 - 66 -The r a t e o f r e a c t i o n o f P i n e P o i n t g a l e n a w i t h s u l -phur c h l o r i d e was f o u n d t o be I n d e p e n d e n t o f t h e s t i r r i n g r a t e once a l l s o l i d s were s u s p e n d e d . In f i g u r e s 16 and 17, d a t a f o r t h e c a t a l y z e d and un-1/3 c a t a l y z e d r e a c t i o n s a r e p l o t t e d i n t h e f o r m r Q [ l - C l - R ) ] v s . t i m e . R e a c t i o n r a t e s c a l c u l a t e d f r o m t h e s l o p e s o f p l o t s o f t h i s f o r m a r e summarized i n T a b l e 8. T a b l e 8: Rate o f R e a c t i o n w i t h 10 wt % S.S o f 150 2 c i 2 + 200 m P i n e P o i n t G a l e n a U n c a t a l y z e d R e a c t i o n C a t a l y z e d R e a c t i o n T°C Rate T°C Rate —1 5 Ccm min x 10 ) . (cm min 1 x 10^) 90 3.32 80 1.77 70 0.83 60 0.43 6 0 . 1.55 50 0.89 40 0.36 30 0.19 3.214 C a l c u l a t e d A c t i v a t i o n E n e r g i e s The r e a c t i o n r a t e s p r e s e n t e d i n T a b l e 8 were us e d t o c o n s t r u c t A r r h e n i u s p l o t s ( F i g u r e 18) f o r t h e c a t a l y z e d and u n c a t a l y z e d r e a c t i o n s . The a c t i v a t i o n e n e r g y f o r t h e un-c a t a l y z e d r e a c t i o n was c a l c u l a t e d t o be 17.6 - 2 K c a l mole A s i m i l a r v a l u e o f 15.4 - 2 K c a l mole 1 was c a l c u l a t e d f o r t h e c a t a l y z e d r e a c t i o n . F i g u r e 18: A r r h e n i u s P l o t s f o r C a t a l y z e d ( a ) and U n c a t a l y z e d (b) R e a c t i o n s o f -150 + 200 m P i n e P o i n t G a l e n a and 10 wt % S.S„C1„. - 68 -T hese a c t i v a t i o n e n e r g y v a l u e s , t h e l a c k o f e f f e c t o f s t i r r i n g on t h e r e a c t i o n r a t e , and t h e l i n e a r i t y o f t h e 1/3 p l o t s o f r [ 1 - C l - R ) ] v s . t i m e i n d i c a t e t h a t t h e r a t e d e t e r m i n i n g s t e p i s a c h e m i c a l phase b o u n d a r y r e a c t i o n i n b o t h c a s e s . 3.215 M i s c e l l a n e o u s O b s e r v a t i o n s Q u a l i t a t i v e o b s e r v a t i o n s made on t h e r a t e o f r e a c t i o n o f t h e v a r i o u s c h e m i c a l s added d u r i n g t h e c a t a l y s i s e x p e r i -ments were: a r s e n i c , a n t i m o n y and b i s m u t h s u l p h i d e s r e a c t e d on c o n t a c t w i t h s u l p h u r c h l o r i d e l e a v i n g no s o l i d r e s i d u e . A l e a d s u l p h i d e matte b a s e d on P i n e P o i n t g a l e n a w i t h g o l d and s i l v e r v a l u e s added was a l s o r e a c t e d w i t h s u l p h u r c h l o r i d e . More t h a n 90% o f t h e g o l d and s i l v e r c o n t e n t o f t h e matte were f o u n d i n t h e s o l i d r e a c t i o n r e s i d u e . 3.22 D e c o m p o s i t i o n o f C h a l c o p y r i t e by S u l p h u r C h l o r i d e 3.221 R e s u l t s o f E x p e r i m e n t s on P h o e n i x C h a l c o p y r i t e C h a l c o p y r i t e ( CuFeS^) was f o u n d t o r e a c t r a p i d l y and c o m p l e t e l y w i t h 40 wt % S.S2CI2. 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 was d e t e r m i n e d ( A p p e n d i x C-7) t o be: 2 C u F e S 0 + 5S„C1 •> 2FeCl„ + 2CuCl + 14S The b e s t a v a i l a b l e c h a l c o p y r i t e i n a f o r m s u i t a b l e f o r t h i s s t u d y c o n t a i n e d a s i g n i f i c a n t amount o f p y r i t e ( s e e A p p e n d i x A) but a t t h e low t e m p e r a t u r e s u s e d f o r c h a l c o p y r i t e - 69 -d e c o m p o s i t i o n t h e p y r i t e was n o t s i g n i f i c a n t l y a t t a c k e d . A n a l y s i s o f t h e r e s i d u e f r o m a c h a l c o p y r i t e sample l e a c h e d f o r 90 m i n u t e s a t 7Q°C showed t h a t t h e w a ter i n s o l u b l e r e s i -due c o n t a i n e d 90% o f t h e o r i g i n a l p y r i t e but no s i g n i f i c a n t amount of c o p p e r . R e p r e s e n t a t i v e p l o t s o f p e r c e n t r e a c t i o n v s . t i m e f o r P h o e n i x c h a l c o p y r i t e r e a c t i n g w i t h 40 wt % S . S ^ C l ^ s o l u t i o n a r e shown i n F i g u r e 19. These d a t a a r e p l o t t e d i n t h e f o r m 1/3 r [ l - ( l - R ) ] v s . t i m e i n F i g u r e 20. In t h e r a n g e o f 30-70% r e a c t i o n , t h e s e p l o t s a r e l i n e a r . The r e a s o n f o r t h e i n i t i a l p e r i o d o f f a s t r e a c t i o n i s n o t known. The s t i r r i n g r a t e - above t h a t r e q u i r e d t o s u s p e n d the p a r t i c l e s i n t h e l i q u i d - had no a p p a r e n t e f f e c t on t h e r a t e o f r e a c t i o n . U s i n g the s t r a i g h t s e c t i o n s (30-70% r e -a c t i o n ) o f t h e p l o t s o f F i g u r e 20, r a t e s o f r e a c t i o n ( p e n e t r a t i o n ) were c a l c u l a t e d f o r v a r i o u s t e m p e r a t u r e s and summarized i n T a b l e 9. T a b l e 9: Rate o f 40 wt % R e a c t i o n s . s 2 c i 2 ( P e n e t r a t i o n ) o f C u F e S 2 " i n T°C P e n e t r a t i o n (cm min x Rate i o 5 ) 80 70 60 50 10 . 6 5 . 4 2 . 7 1.3 -100 + 140 mesh P h o e n i x CuFeS 801 - 70 -40 wt. % S.S 2C1 2-0 10 20 30 40 50 60 70 80 TIME (MINUTES) 1/3 Figure 20; Plot of r Q [ l - ( l - R ) ' ] vs. Time for -100 + 140 m Phoenix CuFeS 2 i n 40 wt. % S.S 2C1 2. - 73 -3.222 The C a l c u l a t e d A c t i v a t i o n E n e r g y The r a t e s summarized i n T a b l e 9 were u s e d t o c o n s t r u c t an A r r h e n i u s p l o t ( F i g u r e 21) f o r t h e r e a c t i o n . The s l o p e o f t h i s p l o t c o r r e s p o n d s t o an a c t i v a t i o n e n e r g y o f 16.4 ±2 K c a l mole ^. T h i s v a l u e , and t h e l a c k o f e f f e c t o f s t i r r i n g on t h e r e a c t i o n r a t e a g a i n i n d i c a t e t h a t t h e r a t e i s c o n t r o l l e d by a c h e m i c a l phase b o u n d a r y r e a c t i o n . 3.223 Q u a l i t a t i v e O b s e r v a t i o n s on O t h e r Copper M i n e r a l s Q u a l i t a t i v e e x p e r i m e n t s on u n c h a r a c t e r i z e d samples o f b o r n i t e (Cu^-FeS^), c o v e l l i t e ( C u S ) , and c h a l c o c i t e ( C u 2 S ) i n d i c a t e d t h a t t h e s e m i n e r a l s r e a c t a t l e a s t as f a s t as c h a l c o p y r i t e i n 40 wt % S . S 2 C 1 2 . Copper m e t a l i s a l s o a t t a c k e d by 40 wt % S . S 2 C 1 2 . 3.23 D e c o m p o s i t i o n o f Z i n c S u l p h i d e by S u l p h u r C h l o r i d e To i n v e s t i g a t e t h e r e a c t i v i t y o f z i n c s u l p h i d e i n s u l p h u r c h l o r i d e , samples o f two z i n c c o n c e n t r a t e s - a r e l a t i v e l y p u r e s p h a l e r i t e f r o m P i n e P o i n t Mines L t d . , and a m a r m a t i t i c or h i g h i r o n z i n c c o n c e n t r a t e f r o m t h e S u l l i v a n Mine ( f o r a n a l y s e s , see A p p e n d i x A) - were t r e a t e d w i t h s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s . The e x t e n t o f r e a c t i o n o f t h e c o n c e n t r a t e s under v a r i o u s c o n d i t i o n s o f t e m p e r a t u r e and s u l p h u r c o n c e n t r a t i o n i s summarized i n T a b l e 10. _ 74 -T a b l e 10: R e a c t i o n o f S p h a l e r i t e w i t h S CI S u b s t r a t e R e a c t i o n C o n d i t i o n s % R e a c t i o n ( w e i g h t l o s s ) P i n e P o i n t ZnS 40 wt % S.S_C1 0 0 . 8 C-150 + 200 m) 2 2 10 min a t 146°C tt 40 wt % S . S 2 C 1 2 30 min a t 146°C 0 . 9 tt ioo% s 2 c i 2 10 min a t 133°C 0 . 8 S u l l i v a n ZnS 100% S 0 C 1 0 31.3" (-70 + 140 m) 10 min a t 133°C tt 40 wt % S . S 2 C 1 2 40 min a t 150°C 3 2.4" R e s i d u e a s s a y (60. 5% Zn , 0.4% Pb, 4.5% Fe ) showed 18 (-1)% o f Zn i n o r i g i n a l sample was s o l u b i l i z e d . From t h e t a b l e i t i s a p p a r e n t t h a t t h e r e l a t i v e l y p u r e ( P i n e P o i n t ) m a t e r i a l i s v i r t u a l l y u n r e a c t i v e t o s u l -phur c h l o r i d e d e s p i t e t h e f a v o u r a b l e c a l c u l a t e d f r e e e n e r g y ( T a b l e 1) f o r t h e r e a c t i o n ZnS + S 2 C 1 2 -»•• Z n C l 2 + 3S I t seems p r o b a b l e t h a t a p r o t e c t i v e l a y e r o f z i n c c h l o r i d e i s f ormed on t h e s u l p h i d e s u r f a c e , and a c t s as a b a r r i e r t o f u r t h e r r e a c t i o n . The S u l l i v a n z i n c c o n c e n t r a t e c o n t a i n s an a p p r e c i a b l e - 75 -amount (9 . 0 % ) o f i r o n i n s o l i d s o l u t i o n and as p y r r h o t i t e n o t removed i n f l o t a t i o n . The w a t e r i n s o l u b l e , s o l i d r e s i d u e a f t e r t r e a t m e n t o f S u l l i v a n z i n c c o n c e n t r a t e w i t h s u l p h u r c h l o r i d e c o n t a i n e d o n l y 4.5% I r o n . The r a t i o o f z i n c t o i r o n i n t h e m a t e r i a l decomposed was 1.3:1. I t i s s u g g e s t e d t h a t i n t h e c a s e o f t h e S u l l i v a n z i n c c o n c e n t r a t e ( w h i c h c o n t a i n e d 9.0% i r o n ) t h e f o r m a t i o n o f a p r o t e c t i v e f i l m o f z i n c c h l o r i d e a t t h e m i n e r a l s u r f a c e i s h i n d e r e d by s i m u l t a n e o u s r e a c t i o n s o f i r o n s u l p h i d e i n s o l i d s o l u t i o n i n t h e z i n c m i n e r a l . 3.24 D e c o m p o s i t i o n o f M o l y b d e n i t e by S u l p h u r C h l o r i d e The r e a c t i v i t y o f m o l y b d e n i t e (MoS^) i n s u l p h u r c h l o r -i d e s o l u t i o n s was s t u d i e d by t r e a t i n g samples o f a molybden-i t e c o n c e n t r a t e ( A p p e n d i x A) w i t h S 2 C 1 2 a t 1 3 6 ° C , 40 wt % S . S 2 C 1 2 a t 1 5 0 ° C , and c h l o r i n e s a t u r a t e d - S 2C1 a t 60°C. In no c a s e was any s i g n i f i c a n t amount o f m o l y b d e n i t e r e a c t e d (as p r e d i c t e d by thermodynamic c a l c u l a t i o n s - T a b l e 1 ) . The s m a l l ( 1%) but c o n s i s t e n t w e i g h t l o s s o b s e r v e d i n t h e s e e x p e r i m e n t s c a n be e x p l a i n e d by r e a c t i o n o f t h e c o p p e r m i n e r a l c o n t e n t ( 0 . 4 % Cu) o f t h e c o n c e n t r a t e - the samples gave n e g a t i v e q u a l i t a t i v e t e s t s f o r c o p p e r a f t e r t r e a t m e n t w i t h s u l p h u r c h l o r i d e . From t h e s e r e s u l t s , i t i s a p p a r e n t t h a t m o l y b d e n i t e i s u n a t t a c k e d by s u l p h u r c h l o r i d e u nder a wide r a n g e o f c o n -d i t i o n s . Thus, i t i s p o s s i b l e t o s e l e c t i v e l y decompose - 76 -o t h e r s u l p h i d e s s u c h as p y r i t e , c h a l c o p y r i t e o r g a l e n a i n t h e p r e s e n c e o f m o l y h d e n i t e . 3.3 I n t e r p r e t a t i o n o f E x p e r i m e n t a l R e s u l t s 3.31 R e q u i r e m e n t s f o r a R e a c t i o n Mechanism The mechanism o f t h e r e a c t i o n o f s u l p h u r c h l o r i d e w i t h a m e t a l s u l p h i d e w i l l i n v o l v e at l e a s t t h r e e s t e p s : i . A s u r f a c e r e a c t i o n i n w h i c h s u l p h u r c h l o r i d e or a d i s -s o c i a t i o n p r o d u c t o f s u l p h u r c h l o r i d e forms bonds d i r e c t l y t o t h e m i n e r a l s u r f a c e , i i . The g e n e r a t i o n o f i n t e r m e d i a t e p r o d u c t s ( p o s s i b l y t r a n s -i t o r y i n n a t u r e ) s u c h as S n ( n = 1 - 4 ) , f r e e r a d i c a l s s u c h as •CI o r - S - S - C l , or mixed s u l p h u r - c h l o r i n e compounds o f t h e m e t a l c o m p o n e n t ( s ) o f t h e m i n e r a l , i i i . E s t a b l i s h m e n t o f a s o l i d d e p o s i t o f r e a c t i o n p r o d u c t s a t t h e m i n e r a l s u r f a c e a n d / o r t h e d i s s o l u t i o n and d i f -f u s i o n o f r e a c t i o n p r o d u c t s t h r o u g h a b o u n d a r y l a y e r . B e s i d e s i n c o r p o r a t i n g t h e t h r e e s t e p s m e n t i o n e d above, any p r o p o s e d mechanism f o r t h e r e a c t i o n s s t u d i e d s h o u l d be c o n s i s t e n t w i t h t h e f o l l o w i n g o b s e r v a t i o n s : i . The a c t i v a t i o n e n e r g i e s c a l c u l a t e d f r o m e x p e r i m e n t a l r a t e d a t a a r e i n t h e r a n g e o f.16-22 K c a l / m o l e . These v a l u e s a r e c o n s i s t e n t w i t h r a t e c o n t r o l by c h e m i c a l r e a c t i o n ( s ) and a r e h i g h e r t h a n v a l u e s e x p e c t e d f o r r a t e c o n t r o l by d i f f u s i o n i n t h e l i q u i d s t a t e ( 5 6 ) . A l s o , t h e l a c k o f a s i g n i f i c a n t s t i r r i n g e f f e c t i n t h e r e a c t i o n s - 7 7 -o f p y r i t e , g a l e n a and c h a l c o p y r i t e i n d i c a t e s t h a t d i f -f u s i o n i n a l i q u i d b o u n d a r y l a y e r i s n o t r a t e c o n t r o l -l i n g . i i . E v i d e n c e i n d i c a t i n g t h e f o r m a t i o n o f s t a b l e f i l m s o f s o l i d r e a c t i o n p r o d u c t s was o b t a i n e d i n t h e r e a c t i o n s o f s p h a l e r i t e , p y r r h o t i t e , and p y r i t e ( i n p u r e S ^ C l ^ ) . In t h e r e a c t i o n o f m e t a l l i c i r o n w i t h s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s d e f i n i t e e v i d e n c e o f s u r f a c e f i l m f o r m a t i o n was o b t a i n e d i n t h e f o r m o f p a r a b o l i c r e a c t i o n k i n e t i c s and v i s i b l e d e p o s i t s on t h e m e t a l s u r f a c e . 1/3 i i i . The l i n e a r i t y o f t h e p l o t s o f r [ l - ( l - R ) ] v s . t i m e f o r t h e r e a c t i o n s o f p y r i t e , g a l e n a , and c h a l c o p y r i t e i n d i c a t e t h a t the r e a c t i o n mechanism f o r t h e s e m a t e r i a l s must be c o n s i s t e n t w i t h a c o n s t a n t i n t e r f a c e v e l o c i t y i n t h e r e a c t i o n s . 3.32 The R o l e o f S u l p h u r In c o n s i d e r i n g mechanisms a p p l i c a b l e t o t h e r e a c t i o n s i n v e s t i g a t e d , t h e r o l e o f s u l p h u r - e i t h e r p r e s e n t i n i t i a l l y i n t h e s o l v e n t o r formed as a p r o d u c t - s h o u l d be c o n s i d e r e d . I t i s r e a s o n a b l e t o assume t h a t s m a l l S (n = 1-4) n m o l e c u l e s a r e i n t e r m e d i a t e s i n the r e a c t i o n s o f s u l p h u r c h l o r i d e w i t h s u l p h i d e m i n e r a l s . These S m o l e c u l e s w i l l n p o l y m e r i z e and may f o r m a s i g n i f i c a n t f r a c t i o n o f l o n g c h a i n ^ > y ^ p o l y m e r s i n s t e a d o f S g r i n g s . Long c h a i n s u l p h u r m o l e c u l e s a r e known t o be i n s o l u b l e i n c a r b o n d i s u l p h i d e and - 78 -may t h e r e f o r e have a p o o r s o l u b i l i t y i n p u r e s u l p h u r c h l o r -i d e w h i l e t h e i r s o l u b i l i t y may be I n c r e a s e d by t h e p r e s e n c e o f a l a r g e f r a c t i o n o f S m o l e c u l e s i n s o l u t i o n i n t h e s u l p h u r c h l o r i d e . T hus, f a c t o r s d e t e r m i n i n g t h e r e a c t i o n r a t e c o u l d be d i s s o l u t i o n o f l o n g c h a i n s u l p h u r m o l e c u l e s a t a phase b o u n d a r y , d i f f u s i o n o f s u l p h u r c h l o r i d e t h r o u g h a v i s c o u s b o u n d a r y l a y e r o f p r o d u c t s u l p h u r o r c o n v e r s i o n o f S m o l e c u l e s t o t h e e q u i l i b r i u m S c o n f i g u r a t i o n a t a IN O b o u n d a r y . T h i s would i m p l y a mixed mechanism i n w h i c h l o n g c h a i n s u l p h u r m o l e c u l e s a r e formed by r e a c t i o n a t t h e min-e r a l s u r f a c e , t h e n d i s s o l v e i n t h e s o l v e n t . The s t e a d y s t a t e t h i c k n e s s o f an S„ f i l m f ormed by s u c h a r e a c t i o n N would depend on t h e r e l a t i v e r a t e s o f : s u l p h u r r e m o v a l , d i f f u s i o n o f s u l p h u r c h l o r i d e t h r o u g h a v i s c o u s b o u n d a r y l a y e r , and t h e s u r f a c e r e a c t i o n . T h i s p r o c e s s would be a s s o c i a t e d w i t h h i g h a c t i v a t i o n e n e r g i e s and c o n s t a n t i n t e r f a c e v e l o c i t i e s o f t h e r e a c t i o n s as o b s e r v e d e x p e r i m e n t a l l y . A n o t h e r p o s s i b l e r o l e f o r d i s s o l v e d s u l p h u r i n t h e r e a c t i o n s s t u d i e d i s In t h e r e m o v a l o f s o l i d r e a c t i o n p r o d -u c t s f r o m th e m i n e r a l s u r f a c e - t h u s p r e v e n t i n g t h e b u i l d u p o f a p a s s i v e ( o r i n h i b i t o r y ) f i l m , o f s o l i d m e t a l c h l o r i d e on t h e m i n e r a l s u r f a c e . In t h e c a s e o f p y r i t e , s u l p h u r may a c c o m p l i s h t h i s f u n c t i o n by e i t h e r i n c r e a s i n g t h e s o l u b i l i t y o f p r o d u c t f e r r i c c h l o r i d e so t h a t r e m o v a l by a d i s s o l u t i o n - p r e c i p i t a -t i o n r e a c t i o n can o c c u r r a p i d l y enough t o m a i n t a i n a c l e a n - 7 9 -r e a c t i n g s u r f a c e o r by f o r m i n g u n s t a b l e or t r a n s i t i o n a l com-p l e x e s w i t h m e t a l c h l o r i d e r e a c t i o n p r o d u c t s so t h a t m e t a l c h l o r i d e p r e c i p i t a t i o n o c c u r s away f r o m t h e r e a c t i n g s u r -f a c e . A l t e r n a t i v e l y , s u l p h u r might p r e v e n t f o r m a t i o n o f a c o h e r e n t l a y e r o f m e t a l c h l o r i d e p r o d u c t by p r e f e r e n t i a l l y w e t t i n g t h e m i n e r a l s u r f a c e so t h a t m e t a l c h l o r i d e p r o d u c t w i l l n o t a d h e r e t o t h e s u r f a c e . 3.33 S u r f a c e R e a c t i o n s The s u l p h u r c h l o r i d e m o l e c u l e can r e a c t w i t h a m i n e r a l or m e t a l s u r f a c e i n one o f two ways: by d i s s o c i a t i o n i n t o a c t i v e s p e c i e s s u c h as c h l o r i n e atoms w h i c h t h e n a t t a c k t h e s u r f a c e o r by f o r m i n g M-Cl bonds v i a an a s s o c i a t i v e mechan-ism w i t h an or - S - S - C l m o l e c u l e b e i n g formed as a remnant o f t h e s u l p h u r c h l o r i d e m o l e c u l e . 3.331 D i s s o c i a t i v e R e a c t i o n s of S u l p h u r C h l o r i d e A v e r a g e bond e n e r g y v a l u e s Cat 2 5 ° C ) have been c a l -c u l a t e d C60) f o r S-S and S - C l bonds. These v a l u e s a r e r e s p e c t i v e l y 51 and 60 K c a l p e r mole o f b o n d s . From t h e s e v a l u e s i t a p p e a r s most u n l i k e l y t h a t t h e o b s e r v e d r e a c t i o n s p r o c e e d by a p u r e d i s s o c i a t i o n Cor S ^ l ) t y p e o f mechanism s i n c e t h e c a l c u l a t e d a c t i v a t i o n e n e r g i e s (16-22 K c a l ) a r e s i g n i f i c a n t l y l o w e r t h a n t h o s e r e q u i r e d f o r bond r u p t u r e . - 80 -3.332 A s s o c i a t i v e R e a c t i o n o f S u l p h u r C h l o r i d e The a l t e r n a t i v e t o a d i s s o c i a t i v e mechanism i s an a s s o c i a t i v e mechanism In w h i c h t h e s u l p h u r c h l o r i d e m o l e c u l e I n t e r a c t s w i t h t h e m i n e r a l s u r f a c e t o form a t l e a s t a tempo-r a r y S..C1..M bond b e f o r e the s u l p h u r - c h l o r i n e bond i s com-p l e t e l y b r o k e n . In t h i s c a s e a s u r f a c e i n t e r m e d i a t e c o u l d be a s u l p h o c h l o r i d e ( m e t a l - s u l p h u r - c h l o r i n e compound), w i t h p o s s i b l e r e s i d u a l S - C l bonds. However s u c h compounds a r e not d e s c r i b e d i n t h e t e c h n i c a l l i t e r a t u r e and under th e e x p e r i m e n t a l c o n d i t i o n s o f t h i s s t u d y a r e u n s t a b l e w i t h r e s p e c t t o d e c o m p o s i t i o n t o c r y s t a l l i n e m e t a l c h l o r i d e s and s u l p h u r . The s m a l l ( S ^ , n = 1-4) s u l p h u r m o l e c u l e s r e m a i n i n g a f t e r t h e c h l o r i n a t i o n r e a c t i o n w i l l p o l y m e r i z e ( t o S or o S^j, N >> 8) l e a v i n g m e t a l c h l o r i d e s w hich may o r may not adhere t o the r e a c t i n g s u r f a c e . 3.34 M o d els f o r M e t a l S u l p h i d e - S u l p h u r C h l o r i d e R e a c t i o n s Some p o s s i b l e modes of r e a c t i o n o f s u l p h u r c h l o r i d e w i t h m e t a l s u l p h i d e s (as d i s c u s s e d i n the p r e v i o u s s e c t i o n s ) a r e p r e s e n t e d i n F i g u r e 22. Scheme A o f F i g u r e 22 r e p r e s e n t s t h e f o r m a t i o n o f a s t e a d y s t a t e l a y e r o f p o l y m e r i c S^ m o l e c u l e s on t h e s u r f a c e . In t h i s c a s e , r a t e c o n t r o l may be by d i f f u s i o n o f s u l p h u r c h l o r i d e t h r o u g h the v i s c o u s s u l p h u r f i l m , by the r e a c t i o n A . MS S,CL / S f l 2 2 8 to=0 B. MS SCI / S 2 2 8 to =0 MS S /MCI N n SCI / S /MCI 2 2 8 n t, >0 MS MCI ni S 2 CI 2 /S 8 ->• MS MCI n MCI n s,cu/s oo t— 1 t,>0 to»0 J C . MS s 2ci 2/s 8 to = 0 MS S 2 C I 2 / S 8 / MCI„ t, >0 Figure 22: Models for the Reaction of Sulphur Chloride with Metal Sulphides (see text, Section 3.34) - 82 -a t t h e S l T/MCl - S.C1./S„ i n t e r f a c e , hy p h y s i c a l d i s s o l u t i o n N n 2 2 8 * J J T J o f S X T o r a c o m b i n a t i o n o f t h e s e f a c t o r s . N I f s u c h a s u l p h u r f i l m d i d f o r m i t would be e x p e c t e d t o f o r m i n a l l c a s e s but t h e c o m p l e t e r e a c t i o n o f g a l e n a w i t h s u l p h u r c h l o r i d e does not r e q u i r e l a r g e amounts o f s u l -phur d i s s o l v e d i n t h e s u l p h u r c h l o r i d e . A l s o , i f t h e a c t i o n o f t h e c a t a l y s t s CAg, Sb e t c . ) i n the g a l e n a r e a c t i o n i s t o i n h i b i t the f o r m a t i o n o f a v i s c o u s s u l p h u r f i l m t h e n t h i s e f f e c t s h o u l d o c c u r i n t h e r e a c t i o n o f p y r i t e , but no s u c h e f f e c t was o b s e r v e d . On t h i s b a s i s , r a t e c o n t r o l by t h e f o r m a t i o n o f a v i s c o u s l a y e r o f p o l y m e r i c s u l p h u r seems un-l i k e l y so i t i s r e a s o n a b l e t o c o n s i d e r t h e p r o p e r t i e s o f t h e m e t a l c h l o r i d e r e a c t i o n p r o d u c t . Scheme B o f F i g u r e 22 r e p r e s e n t s f o r m a t i o n o f an a d h e r e n t l a y e r o f m e t a l c h l o r i d e p r o d u c t on t h e s u l p h i d e s u r f a c e . Such a f i l m may be p o r o u s or d e n s e . F o r m a t i o n o f a p o r o u s m e t a l c h l o r i d e l a y e r on t h e r e a c t i n g s u r f a c e i s c o n s i s t e n t w i t h t h e p a r a b o l i c k i n e t i c s o f t h e i r o n - s u l p h u r c h l o r i d e r e a c t i o n : as t h e p o r o u s l a y e r t h i c k e n s t h e r e a c -t i o n r a t e d e c r e a s e s due t o t h e i n c r e a s e d d i f f u s i o n p a t h f o r r e a c t a n t s u l p h u r c h l o r i d e and p r o d u c t s u l p h u r . F o r m a t i o n o f a dense m e t a l c h l o r i d e ' l a y e r on the r e a c t i n g i n t e r f a c e i s c o n s i s t e n t w i t h t h e r e a c t i o n s o f s p h a l e r i t e and p y r r -h o t i t e where t h e r a t e s a r e i n i t i a l l y r a p i d - c o r r e s p o n d i n g t o t h e p e r i o d f o r b u i l d - u p o f a p r o t e c t i v e l a y e r . Then the r a t e d e c r e a s e s t o a v e r y s m a l l v a l u e as t h e dense a d h e r e n t - 83 -l a y e r p r e v e n t s , a c c e s s o f t h e s u l p h u r c h l o r i d e t o t h e s u r f a c e . Scheme C r e p r e s e n t s a m e t a l s u l p h i d e — s u l p h u r c h l o r i d e r e a c t i o n i n w h i c h t h e m e t a l c h l o r i d e p r o d u c t e i t h e r does n o t a d h e r e t o the s u l p h i d e s u r f a c e o r i s removed by d i s s o l u t i o n and p r e c i p i t a t e d away from t h e s u r f a c e . In t h i s scheme, r a t e c o n t r o l c o u l d be by l i q u i d phase d i f f u s i o n or s u r f a c e r e a c t i o n k i n e t i c s . In t h e r e a c t i o n s s t u d i e d , t h e h i g h a c t i v a t i o n e n e r g y v a l u e s and i n d e p e n d e n c e o f r a t e on s t i r -r i n g i n d i c a t e r a t e c o n t r o l by s u r f a c e r e a c t i o n k i n e t i c s . Scheme C i s c o n s i s t e n t w i t h t h e r e s u l t s o f e x p e r i m e n t s on g a l e n a Cwith p u r e s u l p h u r c h l o r i d e ) and p y r i t e and c h a l c o -p y r i t e Cwith 40 wt % S . S C l j ) . Thus, on t h e b a s i s o f t h e e x p e r i m e n t a l e v i d e n c e o f t h i s s t u d y , i t seems p r o b a b l e t h a t t h e d i f f e r e n c e s i n r e s -ponse o f m e t a l s u l p h i d e s t o r e a c t i o n w i t h s u l p h u r c h l o r i d e depend on t h e n a t u r e o f t h e m e t a l c h l o r i d e p r o d u c t . I f t h i s m e t a l c h l o r i d e p r o d u c t forms a c o h e r e n t s u r f a c e l a y e r t h e n p a r a b o l i c k i n e t i c s o r v i r t u a l p a s s i v i t y a r e o b s e r v e d Cdepending on t h e p o r o s i t y o f t h e f i l m ) w h i l e i f t h e m e t a l c h l o r i d e p r o d u c t i s non a d h e r e n t , r a t e c o n t r o l i s by s u r f a c e r e a c t i o n and l i n e a r k i n e t i c s a r e o b s e r v e d . 3.4 E l e m e n t a l S u l p h u r from C h l o r i n a t i o n o f M e t a l S u l p h i d e s E l e m e n t a l s u l p h u r i s a p r o d u c t o f r e a c t i o n s between m e t a l s u l p h i d e s and S CI . The r e a c t i o n s were n o r m a l l y - 84 -done a t t e m p e r a t u r e s s u c h t h a t t h e s u l p h u r d i s s o l v e d i n e x c e s s s u l p h u r c h l o r i d e p r e s e n t . E l e m e n t a l , s u l p h u r Cin r h o m b i c o r m o n o c l l n i c f o r m ! can be c r y s t a l l i z e d f r o m S.S2CI2 s o l u t i o n by c o o l i n g C29). The s i z e o f t h e p r e c i p -i t a t e d s u l p h u r c r y s t a l s can be c o n t r o l l e d by t h e c o o l i n g r a t e a n d / o r by a d d i t i o n o f s e e d c r y s t a l s t o a c t as n u c l e a -t i o n s i t e s . Two s i z e s o f r h o m b i c s u l p h u r c r y s t a l s p r e -c i p i t a t e d f r o m s o l u t i o n a r e shown i n F i g u r e 2 3 . Such c r y s -t a l s a r e e a s y t o f i l t e r and wash, and a r e f r e e - f l o w i n g when d r y . Some c h l o r i d e i s a l w a y s p r e s e n t i n t h e c r y s t a l s u l p h u r , b o t h on t h e s u r f a c e and i n t h e b u l k . The s u r f a c e c h l o r i n e can be removed, and r e c o v e r e d by w a s h i n g the c r y s t a l s w i t h I n o r g a n i c s o l v e n t s s u c h as c a r b o n t e t r a c h l o r i d e , and d i s t i l l a t i o n o f t h e wash l i q u o r f o r s e p a r a t e r e c o v e r y o f s o l v e n t and s u l p h u r c h l o r i d e . C h l o r i d e r e m a i n i n g a f t e r t h i s t r e a t m e n t can be removed down t o v e r y low l e v e l s -w i t h o u t d i s r u p t i n g t h e c r y s t a l s t r u c t u r e - by water w a s h i n g . C h l o r i d e removed by t h i s p r o c e d u r e i s h y d r o l y z e d t o aqueous h y d r o c h l o r i c a c i d , ( 3 0 ) and l o s t f r o m t h e p r o c e s s . A summary o f c h l o r i n e c o n t e n t s o f s u l p h u r c r y s t a l s a f t e r v a r i o u s w a s h i n g p r o c e d u r e s i s p r e s e n t e d i n T a b l e 11. - 85 -3CM S U L P H U R C R Y S T A L L I Z E D F R O M S - S C I S O L U T I O N 2 2 Figure 23: Rhombic Sulphur Crystals P r e c i p i t a t e d from S.S 2C1 2 Solution. - 86 -Tab.le 11: C h l o r i n e C o n t e n t o f P r e c i p i t a t e d S u l p h u r Hash. Sequence ttt. % CI 1) e x c e s s s o l v e n t d r a i n e d 1.54 2) washed i n C C l ^ and 0 . 12 f i l t e r e d 3) w a t e r washed f o r 1 h r . 0.03 and f i l t e r e d -28 + 44 mesh r h o m b i c c r y s t a l s p r e c i p i t a t e d f r o m S s a t u r a t e d S 2 C 1 2 a t 6 Q - 5 0 ° C . 3.5 P o t e n t i a l M e t a l l u r g i c a l Uses f o r S u l p h u r C h l o r i d e 3.51 U s e f u l P r o p e r t i e s o f S u l p h u r C h l o r i d e The r e s u l t s o f t h i s s t u d y i n d i c a t e t h a t s u l p h u r c h l o r i d e has s e v e r a l p r o p e r t i e s w h i c h may be u s e f u l i n t h e m e t a l l u r g i c a l t r e a t m e n t o f s u l p h i d e s . I t was f o u n d t h a t under a p p r o p r i a t e c o n d i t i o n s , s u l p h u r c h l o r i d e can r a p i d l y and c o m p l e t e l y decompose c e r t a i n s u l p h i d e m i n e r a l s ( p y r i t e , c h a l c o p y r i t e , g a l e n a ) t o f o r m m e t a l c h l o r i d e s and ( d i s s o l v e d ) e l e m e n t a l s u l p h u r . These r e a c t i o n s a r e e x o t h e r m i c ( T a b l e 1) and o c c u r a t t e m p e r a t u r e s below the b o i l i n g p o i n t s o f the s o l u t i o n s u s e d , so t h e r e a c t i o n s can be t h e r m a l l y s e l f -s u s t a i n i n g and p r e s s u r e (above a t m o s p h e r i c ) i s n o t r e q u i r e d . The s u l p h u r p r o d u c t o f s u c h r e a c t i o n s can be c o m p l e t e l y r e -c o v e r e d by c o o l i n g t h e s o l v e n t t o c r y s t a l l i z e d i s s o l v e d s u l p h u r . By c r y s t a l l i z i n g s u l p h u r a t t e m p e r a t u r e s below 95°C, s t a b l e r h o m b i c s u l p h u r c r y s t a l s can be p r o d u c e d - 87 -( A p p e n d i x H, (.47)) i n a r a n g e o f s i z e s . S u l p h u r i n t h i s f o r m c o u l d be e a s i l y h a n d l e d and f r e e f r o m d u s t . O t h e r m e t a l s u l p h i d e s ( m o l y b d e n i t e , p u r e s p h a l e r i t e ) were f o u n d t o be e s s e n t i a l l y u n r e a c t i v e t o s u l p h u r c h l o r i d e so s e l e c t i v e d e c o m p o s i t i o n o f v a r i o u s components o f s u l p h i d e c o n c e n t r a t e s can be a c c o m p l i s h e d w i t h s u l p h u r c h l o r i d e . Examples o f s u c h s e l e c t i v e r e a c t i o n s a r e t h e d e c o m p o s i t i o n o f g a l e n a i n t h e p r e s e n c e o f s p h a l e r i t e and the d e c o m p o s i t i o n o f c h a l c o p y r i t e or g a l e n a i n t h e p r e s e n c e o f m o l y b d e n i t e . On t h e b a s i s o f t h e s e r e s u l t s , some p o t e n t i a l p r o c e s -s e s f o r m e t a l l u r g i c a l t r e a t m e n t o f s u l p h i d e s by s u l p h u r c h l o r i d e s a r e s u g g e s t e d . 3.52 S p e c i f i c P o t e n t i a l Uses f o r S u l p h u r C h l o r i d e 3.521 P y r i t e I t has been shown t h a t p y r i t e can be c o m p l e t e l y and u n i f o r m l y decomposed by s u l p h u r c h l o r i d e c o n t a i n i n g 25-40 wt % d i s s o l v e d s u l p h u r . On t h e b a s i s o f t h e s e r e s u l t s , a p r o c e s s (61) i s p r o p o s e d f o r t h e m e t a l l u r g i c a l t r e a t m e n t o f p y r i t e t o r e c o v e r e l e m e n t a l s u l p h u r , p u r e i r o n o x i d e , and a c o n c e n t r a t e o f t h e n o n - f e r r o u s m e t a l s . In t h i s p r o p o s e d p r o c e s s , p y r i t e w i l l be decomposed by r e a c t i o n w i t h 25-40 wt % S . S 2 C 1 2 . The s o l i d p r o d u c t s ( m e t a l c h l o r i d e s ) o f t h i s r e -a c t i o n w i l l be t r e a t e d w i t h oxygen to c o n v e r t i r o n c h l o r i d e s t o o x i d e s and g e n e r a t e c h l o r i n e f o r r e u s e i n t h e s u l p h i d e d e c o m p o s i t i o n r e a c t i o n . Any n o n - f e r r o u s m e t a l c h l o r i d e s - 88 -on t h e s o l i d r e s i d u e w i l l not he c o n v e r t e d to o x i d e s and w i l l be r e c o v e r e d by aqueous l e a c h i n g o f th_e i r o n o x i d e p r o d u c t . The l i q u i d phase from the d e c o m p o s i t i o n r e a c t i o n w i l l be c o o l e d t o c r y s t a l l i z e an amount of s u l p h u r e q u i v a l e n t to the s u l p h i d e c o n t e n t of the p y r i t e , p r o d u c t s u l p h u r s e p a r a t e d , and the r e m a i n i n g s o l u t i o n r e c y c l e d t o the de-c o m p o s i t i o n s t e p . A s c h e m a t i c f l o w s h e e t f o r t h i s p r o c e s s i s shown i n A p p e n d i x E. O f the u n i t o p e r a t i o n s i n the proposed p r o c e s s , the d e c o m p o s i t i o n of p y r i t e and c r y s t a l l i z a t i o n of p r o d u c t s u l -phur have been demonstrated i n t h i s s t u d y , and the o x i d a t i o n of f e r r i c c h l o r i d e has been a c c o m p l i s h e d ( 9 ) i n a bench s c a l e e x p e r i m e n t . Some advantages of the proposed p r o c e s s are the p r o d u c t i o n o f e l e m e n t a l s u l p h u r i n a c o n v e n i e n t form, f a s t r e a c t i o n s , and the ( e x p e c t e d ) p u r i t y o f the i r o n o x i de and n o n - f e r r o u s metals produced. 3.522 G a l e n a R e s u l t s of experiments on g a l e n a c o n c e n t r a t e s have shown t h a t g a l e n a can be c o m p l e t e l y decomposed by s u l p h u r -s u l p h u r c h l o r i d e s o l u t i o n s under r e l a t i v e l y m i l d c o n d i t i o n s and t h a t s p h a l e r i t e i s u n r e a c t i v e under these c o n d i t i o n s . From these r e s u l t s , a p r o c e s s f o r t r e a t m e n t of l e a d concen-t r a t e i s proposed. In t h i s Cproposed) p r o c e s s , l e a d con-c e n t r a t e w i l l be decomposed by s u l p h u r - s u l p h u r c h l o r i d e - 8 9 -s o l u t i o n s c o n t a i n i n g a c e r t a i n amount o f s i l v e r and a n t i m o n y or b i s m u t h as c a t a l y t i c a g e n t s . The s o l i d p r o d u c t s o f t h i s r e a c t i o n w i l l be l e a c h e d i n h o t b r i n e t o d i s s o l v e l e a d c h l o r i d e l e a v i n g u n r e a c t e d s p h a l e r i t e as a r e s i d u e . Lead c h l o r i d e w i l l be r e c r y s t a l l i z e d by c o o l i n g the s o l u t i o n , f i l t e r e d o f f , and e l e c t r o l y z e d i n a c h l o r i d e m e l t f o r p r o -d u c t i o n o f l e a d m e t a l and c h l o r i n e f o r r e c y c l e . S u l p h u r w i l l be r e c o v e r e d by c r y s t a l l i z a t i o n f r o m the s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n u s e d 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 . A. s c h e m a t i c f l o w s h e e t f o r t h i s p r o p o s e d p r o c e s s i s shown i n A p p e n d i x F. The p r o p o s e d p r o c e s s i n c o r p o r a t e s a m e t a l l u r g i c a l s e p a r a t i o n o f l e a d f r o m mixed l e a d - z i n c c o n c e n t r a t e s and p r o d u c e s e l e m e n t a l s u l p h u r . C o n s u m p t i o n o f c h l o r i n e by m i n e r a l s o t h e r t h a n g a l e n a w i l l be s m a l l s i n c e i n the p r e s -ence o f s i l v e r and a n t i m o n y or s i l v e r and b i s m u t h (as c a t a -l y s t s ) g a l e n a has been shown t o r e a c t w i t h s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s under c o n d i t i o n s i n w h i c h o t h e r m i n e r a l s ( e . g . p y r i t e ) r e a c t v e r y s l o w l y . 3.523 M o l y b d e n i t e M o l y b d e n i t e was f o u n d t o be u n a t t a c k e d by s u l p h u r -s u l p h u r c h l o r i d e s o l u t i o n s under c o n d i t i o n s i n w h i c h p y r i t e , c h a l c o p y r i t e and g a l e n a a r e c o m p l e t e l y decomposed. On t h e b a s i s o f t h e s e r e s u l t s , i t i s p r o p o s e d t h a t m o l y b d e n i t e c o n -c e n t r a t e s c o n t a i n i n g d e l e t e r i o u s amounts o f t h e s e m i n e r a l s can be p u r i f i e d by t r e a t m e n t w i t h s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s t o s e l e c t i v e l y decompose the i m p u r i t i e s . The - 90 -s o l i d r e s i d u e f r o m t h i s r e a c t i o n would be a c i d l e a c h e d t o remove s o l u b l e m e t a l c h l o r i d e s f r o m the u n a t t a c k e d m o l y b d e n i t e . C l e a n i n g ( r e m o v a l o f s m a l l amounts o f i m p u r i t i e 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 s by f l o t a t i o n f r e q u e n t l y r e s u l t s i n a l o w e r f i n a l m o l y b d e n i t e r e c o v e r y , so s e l e c t i v e l e a c h i n g 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 by s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s would have t h e a d v a n t a g e o f making a h i g h g r ade p r o d u c t w i t h h i g h r e c o v e r y s i n c e no m o l y b d e n i t e w i l l be de-composed by s u l p h u r c h l o r i d e l e a c h i n g . 3.53 P r o b l e m s i n t h e Use o f S u l p h u r C h l o r i d e I t has been shown t h a t s u l p h u r c h l o r i d e may be u s e f u l i n t h e p r o c e s s i n g o f s u l p h i d e m i n e r a l s - p a r t i c u l a r l y p y r i t e , g a l e n a , and m o l y b d e n i t e . However, t h e use o f s u l p h u r c h l o r i d e as a m e t a l l u r g i c a l r e a g e n t p o s e s a number o f p r o b -lems . S u l p h u r c h l o r i d e i s h i g h l y c o r r o s i v e t o a number o f m e t a l s ( i r o n , t i t a n i u m , c o p p e r , l e a d — see A p p e n d i x G.) so a s u i t a b l e m a t e r i a l must be f o u n d f o r p r o c e s s e q u i p m e n t . P r e l i m i n a r y t e s t s ( A p p e n d i x G) i n d i c a t e d t h a t monel a l l o y has s i g n i f i c a n t r e s i s t a n c e t o a t t a c k by s u l p h u r c h l o r i d e . S u l p h u r c h l o r i d e h y d r o l y z e s r e a d i l y , so w a t e r must be e x c l u d e d f r o m any s y s t e m u s i n g s u l p h u r c h l o r i d e t o a v o i d p r o d u c t i o n o f t h e u n d e s i r a b l e h y d r o l y s i s p r o d u c t s ( h y d r o g e n c h l o r i d e and s u l p h u r d i o x i d e ) . A l s o , s u l p h u r c h l o r i d e i s t o x i c (51) and has an o f f e n -s i v e o d o u r , so i t must be c o m p l e t e l y e n c l o s e d i n any l a r g e s c a l e a p p l i c a t i o n . - 91 -4. CONCLUSIONS From t h e f o r e g o i n g , i t has been e s t a b l i s h e d t h a t t h e s u l p h i d e m i n e r a l s p y r i t e , g a l e n a , and c h a l c o p y r i t e can be t r e a t e d w i t h s u l p h u r c h l o r i d e ( c o n t a i n i n g d i s s o l v e d s u l -p h u r ) t o c o n v e r t m e t a l s t o t h e i r c h l o r i d e s and e x t r a c t s u l -p h u r . On t h i s b a s i s , p r o c e s s e s have been f o r m u l a t e d f o r p o t e n t i a l c o m m e r c i a l a p p l i c a t i o n i n t h e t r e a t m e n t o f f l o t a -t i o n c o n c e n t r a t e s o f p y r i t e , g a l e n a , and m o l y b d e n i t e . C o n d i t i o n s have a l s o been d e t e r m i n e d f o r t h e c o m p l e t e d e c o m p o s i t i o n o f p y r i t e , c h a l c o p y r i t e , and g a l e n a by s u l p h u r c h l o r i d e . Under c o n d i t i o n s i n w h i c h c o m p l e t e r e a c t i o n i s o b s e r v e d , t h e r e a c t i o n p r o d u c t s a r e i r o n ( I I I ) c h l o r i d e , c o p p e r ( I I ) c h l o r i d e , l e a d ( I I ) c h l o r i d e and e l e m e n t a l s u l -p h u r . P y r i t e was f o u n d t o r e a c t u n i f o r m l y and c o m p l e t e l y i n s u l p h u r c h l o r i d e c o n t a i n i n g 25-40% d i s s o l v e d s u l p h u r , but r e a c t e d o n l y p a r t i a l l y i n s u l p h u r , c h l o r i d e c o n t a i n i n g 0-10 wt % d i s s o l v e d s u l p h u r . C h a l c o p y r i t e was c o m p l e t e l y decom-po s e d by s u l p h u r c h l o r i d e c o n t a i n i n g 40 wt % d i s s o l v e d s u l -p h u r . G a l e n a was decomposed by s u l p h u r c h l o r i d e c o n t a i n i n g 0-10 wt % d i s s o l v e d s u l p h u r when s m a l l q u a n t i t i e s o f s i l v e r and a n t i m o n y .or s i l v e r and b i s m u t h were p r e s e n t as c a t a l y s t s - 92 -i n t h e r e a c t i o n m i x t u r e . C a l c u l a t e d v a l u e s o f s p e c i f i c r e a c t i o n r a t e s and a c t i v a t i o n e n e r g i e s f o r t h e s e r e a c t i o n s a r e p r e s e n t e d i n T a b l e 12. Under c o n d i t i o n s where u n i f o r m r e a c t i o n was o b s e r v e d , t h e r a t e s o f t h e s e r e a c t i o n s were f o u n d t o be c h e m i c a l l y c o n t r o l l e d i n t h e t e m p e r a t u r e r a n g e ( 4 0 - 1 5 0 ° C ) o f t h i s s t u d y and t o be p r o p o r t i o n a l t o t h e s u r f a c e a r e a o f t h e s o l i d s u b s t r a t e . T a b l e 12: Summary o f R a t e s and A c t i v a t i o n E n e r g i e s S u b s t r a t e S o l v e n t Rate o f A E^ P e n e t r a t i o n a t T°C -70 + 100 m 40 wt % S . S - C l 1.96 x 10 4 cm/min 21.3 S u l l i v a n F e S 0 a t 147°C + _. „ . .• . 2 - 2 K c a l / m o l e -150 + 200 m 10 wt % S.S 2C1 a. c a t a l y z e d a. 15.4 P i n e P o i n t PbS , c c i n - 4 . . + . v . , • 1.55 x 10 cm/mm - 2 K c a l / m o l e a t 60°C b. u n c a t a l y z e d b. 17.6 -5 + 0.43 x 10 cm/min - 2 K c a l / m o l e a t 60°C -140 + 200 m 40 wt % S.S_C1 1.06 x 1 0 ~ 4 cm/min 16.4 C u F e S 2 a t 80°C - 2 K c a l / m o l e N a t u r a l and s y n t h e t i c p y r r h o t i t e were f o u n d t o r e a c t p a r t i a l l y with, s u l p h u r c h l o r i d e and s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s t o form f e r r i c c h l o r i d e and e l e m e n t a l s u l p h u r . T h i s r e a c t i o n i s i n h i b i t e d by t h e p r e s e n c e o f f e r r i c c h l o r -i d e i n t h e r e a c t i o n m i x t u r e . R e a c t i o n o f r e l a t i v e l y p ure ( P i n e P o i n t ) s p h a l e r i t e w i t h s u l p h u r c h l o r i d e and s u l p h u r - s u l p h u r c h l o r i d e s o l u t i o n s - 9 3 -was f o u n d t o be n e g l i g i b l e a t t e m p e r a t u r e s up t o 150°C. Some i r o n and z i n c s u l p h i d e s were decomposed ( t o z i n c c h l o r -i d e , i r o n ( I I I ) c h l o r i d e and s u l p h u r ) when a m a r m a t i t i c ( S u l l i v a n ) z i n c c o n c e n t r a t e was t r e a t e d w i t h s u l p h u r c h l o r i d e . M o l y b d e n i t e was f o u n d t o be i n e r t t o s u l p h u r c h l o r i d e as p r e d i c t e d by thermodynamic c a l c u l a t i o n s . The s u l p h u r p r o d u c e d by d e c o m p o s i t i o n o f m e t a l s u l -p h i d e s w i t h s u l p h u r c h l o r i d e can be q u a n t i t a t i v e l y r e c o v e r e d by c r y s t a l l i z a t i o n o f r h o m b i c s u l p h u r c r y s t a l s . The c r y s -t a l l i z e d s u l p h u r c o n t a i n s c h l o r i d e w h i c h can be p a r t i a l l y removed by w a s h i n g w i t h c a r b o n t e t r a c h l o r i d e , and n e a r l y c o m p l e t e l y removed - w i t h o u t d i s r u p t i o n o f t h e c r y s t a l s t r u c t u r e - by w a t e r w a s h i n g . The r e s u l t s o f t h i s s t u d y i n d i c a t e t h a t s u l p h u r c h l o r i d e may be u s e f u l i n t h e m e t a l l u r g i c a l t r e a t m e n t o f p y r i t e , g a l e n a , and m o l y b d e n i t e c o n c e n t r a t e s . - 94 -5. SUGGESTIONS FOR FURTHER WORK 1. A s t u d y o f the r e a c t i o n s o f p y r r h o t i t e and i r o n i n S . S ^ C l ^ s o l u t i o n s c o n t a i n i n g >40 wt % S and i n C l ^ / C C l ^ s o l u t i o n s may d e t e r m i n e w i t h more c e r t a i n t y t h e r e a s o n s f o r t h e i n c o m p l e t e r e a c t i o n o f p y r r h o t i t e w i t h S . S 2 C I 2 s o l u t i o n s u nder 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 . 2. A s t u d y o f t h e p a r a m e t e r s a f f e c t i n g c r y s t a l l i z a -t i o n o f s u l p h u r from S . S 2 C I 2 s o l u t i o n s s h o u l d l e a d t o minim-i z a t i o n o f t h e c h l o r i d e c o n t e n t o f p r o d u c t s u l p h u r . 3. A s t u d y o f t h e c o r r o s i o n b e h a v i o u r o f h i g h n i c k e l a l l o y s ( . i n c l u d i n g monel) may i n d i c a t e a . m a t e r i a l w h i c h can r e l i a b l y r e s i s t c o r r o s i o n i n S . S 2 C I 2 s o l u t i o n s . 4. The p r o d u c t i o n o f l e a d by m o l t e n s a l t e l e c t r o l y s i s o f P b C l 2 s h o u l d be s t u d i e d f u r t h e r t o d e t e r m i n e t h e e n e r g y e f f i c i e n c y and maximum a t t a i n a b l e c u r r e n t d e n s i t i e s . - 95 -REFERENCES 1. F o g a r t y , C.F., and R.D. M o l l i s o n i n I n d u s t r i a l M i n e r a l s and Rocks ( t h i r d e d i t i o n ) , J . L . G i l l s o n , Ed. AIME, New Y o r k , 1960, p. 824. 2. L i n d g r e n , W. M i n e r a l D e p o s i t s ( f o u r t h e d i t i o n ) . M c G r a w - H i l l , New Y o r k , 1933, p. 386. 3. L o w e l l , J.D., and J.M. G u i l b e r t , Economic G e o l o g y , 6 5, 4, J u n e - J u l y , 1970, p. 373. 4. L i p p e r t , K.K., H.B. P i e t s c h , A. Roeder and H.W. Walden, T r a n s . I n s t n . M i n i n g and Met. Sec. C, 7_8 , 1969 , p. C98-107. 5. T a y l o r , J.H., and P.F. Whelan, T r a n s . I n s t n . M i n i n g and Met., 5J2 , 1942-43 , p. 35-71. 6. 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N i c k l e s s , E l s e v i e r P u b l i s h i n g Co., 1968, p. 241-258. 51. F a s s e t , D.W., and D.D. I r i s h , Ed. I n d u s t r i a l H y g i e n e and T o x i c o l o g y , Volume 11, I n t e r s c i e n c e , New Y o r k , 1962, p . 905 . 52. L a t i m e r , W.M., The O x i d a t i o n S t a t e s o f t h e E l e m e n t s and t h e i r P o t e n t i a l s i n Aqueous S o l u t i o n s , P r e n t i c e - H a l l , N.J. ( 1 9 5 2 ) . 53. G l a s s n e r , A., The t h e r m o c h e m i c a l p r o p e r t i e s o f the o x i d e s , f l u o r i d e s , and c h l o r i d e s t o 2500°K, Argonne N a t i o n a l L a b o r a t o r y , C h i c a g o , ANL-5750. 54. R e f e r e n c e 44, p. 714. 55. T a g g a r t , A.F., Handbook o f M i n e r a l D r e s s i n g , John W i l e y and Sons, New Y o r k , 1945, 19 p. 142-144. 56. B u r k i n , A.R., The C h e m i s t r y o f H y d r © m e t a l l u r g i c a l P r o -c e s s e s , E. & F.N. Spon L t d . , London, 1966, p. 41. 57. I l l i s , A., G.C. Knowlan and H.J. K o e h l e r , CIM B u l l e t i n , 63, 695 (March 1 9 6 0 ) , p. 352-361. 58. R e f e r e n c e 44, p. 379. 59. R e f e r e n c e 44, p. 865. 60. R e f e r e n c e 44, p. 88. 61. P e t e r s , E . , and R. M c E l r o y , U.S. P a t e n t A p p l i c a t i o n .854 , 444 . - 99 -A p p e n d i x A: S o u r c e s and A n a l y s e s o f N a t u r a l M i n e r a l s Used i n t h i s Study M i n e r a l S o u r c e A n a l y s i s P y r i t e P y r i t e P y r r h o t i t e G a l e n a S u l l i v a n Mine CCominco L t d . ) Noranda Mines L t d , S u l l i v a n Mine CCominco L t d . ) P i n e P o i n t Mine CCominco L t d . ) S p h a l e r i t e S p h a l e r i t e C h a l c o p y r i t e M o l y b d e n i t e P i n e P o i n t Mine CCominco L t d . ) S u l l i v a n Mine CCominco L t d . ) P h o e n i x Mine (Granby M i n i n g L t d . ) A l i c e Arm, B.C. CB.C. Molybdenum Corp 45.2% Fe, 52.4% S, 0.7% Pb , 0.15% Zn, Q.5% S i 0 2 47.1% Fe, 52% S, 0.5% S i 0 2 5 7.0% Fe, 38.8% S, 1.0% Pb, 1.8% Zn, 0.8% Cu 82.0% Pb, 15.1% S, 1.1% Zn, 0.03% As, 0.05% Sb, 0.03% B i , 0.02% Ag, Ca,Cu,Mg, Mn,Si < 0.1% 63.8% Zn, 31.5% S, 0.4% Pb, 1.6% Fe 52.4% Zn, 29.4% S, 6.4% Pb, 9.2% Fe 27 . 6% Cu, 29.6% Fe, 32.0% S a c i d i n s o l u b l e 8% 52.1% Mo, 36.5% S, ) 0.4% Cu, major i m p u r i t y SiO„ A p p e n d i x B: Grades o f M a t e r i a l s and C h e m i c a l s Used i n t h i s S t udy Reagent g r a d e T e c h n i c a l C e ( S 0 4 ) 2 1,10 - o - p h e n a n t h r o l i n e Na a c e t a t e F e C l 2 . 4 H 2 0 Pb , Sn S C f l o w e r s ) , CI a c e t o n e , C C l ^ CS, A s 2 S 3 , S b 2 S 3 , B i 2 S 3 , A g 2 S U n s p e c i f i e d : monel a l l o y , Fe - 100 -A p p e n d i x C: S t o i c h i o m e t r y D e t e r m i n a t i o n s C - l R e a c t i o n o f P y r i t e with. S u l p h u r C h l o r i d e R e a c t i o n c o n d i t i o n s : T = 133°C, t i m e = 5 m i n u t e s R e a c t a n t s : S 2 C 1 2 , S u l l i v a n F e S 2 I n i t i a l sample w e i g h t 1.000 g F i n a l sample w e i g h t C a f t e r wash, p . 24) 0 . 759 L o s s i n w e i g h t 0.241 * '4. A. J l o s s xn w e i g h t 0.241 „, „„ •b p y r i t e r e a c t e d = -—7—.—r . • , - = - — r - r — n = 24.9% * J i n i t i a l w e i g h t - 1.00-0.03 gangue c o r r e c t i o n A n a l y s i s o f w a t e r s o l u b l e p r o d u c t s : Fe ( t o t a l ) 114 mg ( a f t e r C C 1 4 / C S 2 wash, p. 24) Fe ( f e r r o u s ) t r a c e CI ( t o t a l ) 227 rag F e * F e O b s e r v e d = 0.502 ( v s . f o r s t o i c h i o m e t r i c F e C l g = 0.523) C-2 R e a c t i o n o f P y r i t e w i t h 40 wt % S . S 2 C 1 2 R e a c t i o n c o n d i t i o n s : T = 129°C, t i m e = 5 m i n u t e s R e a c t a n t s : 40 wt % S . S 2 C 1 2 , S u l l i v a n F e S 2 I n i t i a l sample w e i g h t 1.QQ0 g F i n a l sample w e i g h t .808 L o s s i n w e i g h t .192 % p y r i t e r e a c t e d = YTb^T'o 3 X 1 0 ° = 1 9 , 8 % A n a l y s i s o f w a t e r s o l u b l e p r o d u c t s : Fe ( t o t a l ) 89 mg Fe ( f e r r o u s ) t r a c e CI ( t o t a l ) 170 mg O b s e r v e d — = .524 ( v s . f o r F e C l g = 0.523) Weight r a t i o - 101 -C-3 A n a l y s i s o f R e s i d u e f r o m L a r g e S c a l e P y r i t e E x p e r i m e n t I n i t i a l sample w e i g h t 40.0 g I n s o l u b l e r e s i d u e * w e i g h t 1.317 g R e s i d u e D i g e s t i o n : HC1/HN0 3 A n a l y s i s F e : 23.2% C306 mg) Zn: 3.9% (51.4 mg) • S : 3.1% (40.8 mg) A l a r g e p a r t o f t h e i n s o l u b l e r e s i d u e a d h e r e d s t r o n g l y t o t h e m a g n e t i c s t i r r i n g b a r . C-4 R e a c t i o n o f P y r r h o t i t e w i t h S u l p h u r C h l o r i d e R e a c t i o n C o n d i t i o n s : T = 113°C, t i m e = 40 m i n u t e s R e a c t a n t s : S 2 C 1 2 , S u l l i v a n FeS I n i t i a l sample w e i g h t 2.000 g F i n a l sample w e i g h t 1.296 Lo s s i n w e i g h t .704 7 0 4 U n c o r r e c t e d % r e a c t i o n = —00~0~ x 1 0 0 = 3 5 « 2 % A n a l y s i s o f w a t e r s o l u b l e p r o d u c t s : Fe ( t o t a l ) 438 mg Fe ( f e r r o u s ) 5 mg CI ( t o t a l ) 860 mg O b s e r v e d = -509 ( v s . ^ y f o r F e C l g = 0.523) - 102 -C-5 R e a c t i o n o f M e t a l l i c I r o n w i t h 40 wt % S . S 2 C 1 2 R e a c t i o n C o n d i t i o n s : T = 13 3 ° C , t i m e = 20 m i n u t e s R e a c t a n t s : 40 wt % S . S g C l , i r o n s t r i p L o s s i n sample w e i g h t = 371 mg A n a l y s i s o f w a t e r s o l u b l e s u r f a c e f i l m 5 ' 1 ( s e e s e c t i o n 3.15) Fe ( t o t a l ) 33 mg Fe ( f e r r o u s ) 32 mg CI ( t o t a l ) 43 O b s e r v e d = .767 ( v s . | y f o r F e C l 2 = .787) Only a f r a c t i o n o f t h e p r o d u c t r e m a i n e d on t h e m e t a l s u r f a c e C-6 R e a c t i o n o f G a l e n a w i t h S u l p h u r C h l o r i d e R e a c t i o n C o n d i t i o n s : T = 70°C, time = 20 m i n u t e s R e a c t a n t s : 10 wt % S . S 2 C 1 2 , P i n e P o i n t PbS I n i t i a l sample w e i g h t 1.000 g R e s i d u e w e i g h t b e f o r e s a l t or w a ter wash ( s e e s e c t i o n 1.018 g 2 • 22 ) Resxdue w e i g h t a f t e r f i n a l wash .891 g A n a l y s i s o f h o t s a l t wash s o l u t i o n : Pb 94 mg ( s u l p h a t e p r e c i p i t a t i o n ) CI 33 mg (by d i f f e r e n c e ) O b s e r v e d — = 2.85 ( v s . | y f o r P b C l 2 = 2.92) - 103 -C-7 R e a c t i o n o f C h a l c o p y r i t e w i t h 40 wt % S . S 2 C 1 2 R e a c t i o n C o n d i t i o n s : T = 70°C, ti m e = 90 m i n u t e s R e a c t a n t s : 40 wt % S . S 2 C 1 2 , -10Q + 140 m P h o e n i x C h a l c o p y r i t e c o n c e n t r a t e I n i t i a l sample w e i g h t 1.00Q g F i n a l sample w e i g h t 0.208 A n a l y s i s o f w a t e r s o l u b l e p r o d u c t s Cu: 272 mg Fe: 245 mg CI : 775 mg C a l c u l a t e d C h l o r i n e r e q u i r e d f o r C u C l £ F e C l : 771 mg R e s i d u e A n a l y s i s Cu: 5 mg Fe:' 47 mg S : 42 mg " P a r t l y p r e s e n t as m a g n e t i t e A p p e n d i x D: S e l e c t e d E x p e r i m e n t a l R e s u l t s D - l R e a c t i o n o f P y r i t e w i t h 40 wt % S.S CI S u b s t r a t e Time T ( ° C ) P e r c e n t o f [ l - ( l - R ) 1 ] r [ l - ( l - R ) 1 ] Rate Mean r a t e ( m i n u t e s ) P y r i t e ° cm m i n - 1 cm m i n - 1 R e a c t e d (cm x 10 ) x 1 0 4 x 1 0 4 -200 + 270m S u l l i v a n i t e 5 139.7 43 . 5 0 . 173 5 . 41 1 .08 1.02 ti 10 tt 67.0 0 .309 9.56 0 . 9 67_ I I 5 129 . 0 ' 19.8 0 . 071 2.22 0 . 444~~ 0 . 449 it 10 it 37.5 0 .145 4.54 0 . 454 I I 30 ti 81.7 0 . 432 13.5 0 . 45 0_ tt 45 ti 96'. 4 0 . 670 21. 0 I I 60 it 98.5 0 . 753 23.6 ti 10 119 . 7 16 . 6 0 .059 1.85 0 . 18 5~~ 0 . 186 it 20 tt 30.9 0 . 116 3.63 0 .182 ti 30 ti 44. 3 0 .177 5.54 0 .185 I I 60 tt 75 . 0 0 .378 11. 6 0 . 193_ tt 5 113 . 0 7.4 0 .025 0.78 0 . 15 6~ it 20 tt 22.6 0 .082 2.57 0 . 129 0.129 I I 40 tt 40 . 3 0 .158 4.95 0 .124 it 60 it 58.5 0 .254 7.95 0 .133 -70 + 100m S u l l i v a n P y r i t e 20 40 60 113 . 0 13 . 2 24. 9 35.3 0 . 046 0.091 0.135 4.07 8.04 11. 9 204 201 198 201 D - l ( c o n t i n u e d ) S u b s t r a t e Time T ( ° C ) P e r c e n t o f [ 1 - ( 1 - R ) 1 / 3 ] r [ l - ( l - R ) 1 / 3 ] Rate Mean r a t e ( m i n u t e s ) P y r i t e ° cm min -" 1" cm m i n ~ l R e a c t e d (cm x 10 ) x 1 0 4 x 1 0 4 -70 + 100m S u l l i v a n P y r i t e 20 40 60 10 20 40 10 20 15 15 10 10 120 . 0 it 126 . 2 ti 133 . 0 it 139 . 7 it 146 . 9 20 . 0 36.9 50 . 7 17 . 4 32 . 8 54.9 28 . 0 46 .1 51 51, 51 52 0.072 0 .142 0.210' 0.062 0.124 0.233 0 .104 0 . 186 Avg.=.215 Avg.=.217 6 12 18 36 6 6 5 . 48 11. 0 20 . 6 9 .19 16 . 4 19.0 19 . 2 . 318 . 315 . 310 0.548" 0.550 0 . 515_ 0. 91? 0 . 820_ 1. 26 1.92 . 314 0.538 .870 1.26 1.92 -70 + 100m Noranda P y r i t e -70 + 100m S u l l i v a n P y r i t e 10 30 45 10 20 40 119 . 9 119 . 9 5 . 3 14. 0 21. 9 10 . 4 20 . 3 37 . 7 0 . 018 0 . 049 0.079 0 .036 0.073 0 .146 1.59 4 .33 6.98 3 . 18 6 . 45 12 . 9 0 . 159 0 . 144 0.155 318 323 323 0 .153 .321 D - l ( c o n t i n u e d ) S u b s t r a t e Time T ( ° C ) P e r c e n t o f [ l - ( l - R ) 1 ] r [ l - ( l - R ) 1 ] Rate Mean r a t e ( m i n u t e d ) P y r i t e ° . cm m i n - 1 cm m i n - 1 R e a c t e d (cm x 10 ) x . 1 0 4 . x 1 0 4 -270 + 325m S u l l i v a n P y r i t e it I I 5 10 20 30 119 11.9 24 . 9 44 . 5 63.0 0 .041 0 .091 0.178 0.282 0.988 2 . 19 4 . 29 6 . 80 0 .198 0 . 219 0 . 215 0 .227 . 215 D-2 R e a c t i o n o f G a l e n a w i t h 10 wt % S.S 2C1 D-2.1 E x p e r i m e n t s W i t h o u t Added C a t a l y s t S u b s t r a t e Time T(°C) P e r c e n t o f [ l - ( l - R ) ' ] r [ l - ( l - R ) ' ] Rate Mean r a t e ( m i n u t e s ) G a l e n a ° cm min-"*" R e a c t e d (cm x 10 ) x 1 0 5 -150 + 200m P i n e P o i n t G a l e n a 10 60 3 . 0 0.010 4.38 0.438 0 . 433 20 I I 5 . 7 0.020 8 . 76 0.438 30 I I 8 . 5 0.029 12 . 7 0.423. 5 70 2 . 8 0.009 3 . 94 0.788 825 10 I I 5 . 6 0 . 019 8 . 32 0.832 20 I I 11.2 0.039 17 .1 0 . 855_ 5 80 5 .4 Avg . 0.019 8 .32 1.66 1. 77 5 ti 6 .5, 10 I I 10 .? Avg .0.043 18.8 1. 88 10 I I 14.0. 5 90 11. 0 0.038 16 . 6 3.32 3. 32 D-2.2 E x p e r i m e n t s With Added C a t a l y s t 1/3 1/3 S u b s t r a t e Time T ( ° C ) P e r c e n t o f [ l - ( l - R ) ' ] r _ [ l - ( l - R ) ' ] Rate Mean r a t e ( m i n u t e s ) G a l e n a ° ,, cm min 1 cm min R e a c t e d (cm x 1 0 4 ) x 1 0 4 x 1 0 4 -150 + 200m P i n e P o i n t G a l e n a 10 30 12 . 3 0.043 1. 88 0.188 0 .189 20 ir 24 . 4 0.089 3 . 90 0.195 30 it 33.0 0.125 5 . 48 0 .183_ 5 40 12 . 2 0.042 1. 84 0 . 368 _ 0.356 10 tl 21. 6 0.078 3 . 42 0.342 15 II 30 . 2 0 .113 4.95 0.330 20 It 44.0 0 .176 7 . 71 0.385 5 50 25 . 6 0.094 4.12 0 . 824" 0.893 10 it 50.5 0 . 209 9 . 15 0 . 915 15 tt 69.0 0.323 14.1 0 . 940_ 5 60 47 . 0 0 .191 8 . 37 1. 67 ~ 1.55 10 ti 69.4 0 . 326 14 . 3 1.43 D-3 R e a c t i o n o f C h a l c o p y r i t e w i t h 40 wt % S.S CI S u b s t r a t e Time T ( ° C ) P e r c e n t o f ( m i n u t e s ) C h a l c o p y r i t e R e a c t e d C l - ( l - R ) 1 7 3 ] r [ 1 - ( 1 - R ) 1 / 3 - . o J (cm x 10 ) -100 + 140m P h o e n i x C h a l c o p y r i t e 5 50 7 . 2 0.025 1.56 10 ii 11.4 0 . 040 2 . 50 20 it 19 . 7 0.071 4 . 44 30 ii 28.4 0 . 105 6 . 5 6 45 I I 34 . 7 0 .132 8.25 60 I I 43 . 9 0 . 175 10 . 9 80 I I 52.7 0 . 221 • 13 . 8 5 60 12 . 4 0.043 2.69 10 it 20 . 7 0.074 4.63 20 it 34 . 4 0 .131. 8 .19 30 ii 44 . 3 0.177 11.1 45 ii 57 . 4 0.248 15 . 5 60 I I 66.9 0.308 19 . 3 5 70 19 . 9 0.071 4 . 44 10 ti 34.9 0.133 8 . 31 15 ii 43.2 0 . 172 10 . 8 20 I I 5 3 . 8 0.227 14 . 2 30 I I 66.5 0.305 19 . 1 5 80 33.2 0 .126 7 . 88 10 I I 53.5 0.225 14.1 15 it 64 . 5 0.292 18 . 3 D-4 C a l c u l a t e d V a l u e s o f r o S c r e e n S i z e G e o m e t r i c Mean r (cm) F r a c t i o n D i a m e t e r (cm) o - 70 + 100 mesh 1.77 x 1 0 ~ 2 8.85 x 1 0 ~ 3 -100 + 140 " 1.25 x 1 0 ~ 2 6.25 x 1 0 ~ 3 -150 + 200 " 8.77 x 1 0 ~ 3 4.38 x 1 0 _ 3 -200 + 270 " 6.26 x 1 0 _ 3 3.13 x 1 0 ~ 3 -270 + 325 " 4.83 x 1 0 ~ 3 2.41 x 1 0 _ 3 - I l l -Appendix E: Schematic Flowsheet for Treatment of P y r i t e with Sulphur Chlo FeS2 concentrate S-S2CI2 /1 sulphur product O2 or air metal chloride <-solution sulphur crystallizer leaching > f liquid-solid separation oxidation of FeCl3 Fe203 & non-ferrous metal chlorides _ i aqueous leach ^ e2^3 P r o cluct ^ - 1 1 2 -Appendix F: Schematic Flowsheet f o r Production of Lead and Sulphur from Galena Concentrate. S S 2 C I 2 t su lphur crystallizer ~ ~ r ~ sulphur product H/NaCI PbS concentrate l e a c h i n g P b C I 2 , F e S 2 , Z n S 4 hot H/NaCI l e a c h -> unreacted Z n S , F e S 2 , e t c . PbC12 c r y s t a l l i z e r J PbCI 2 eTe'cfrofy^ s C l* P b product - 113 -Appendix G: Corrosion of Metals i n Sulphur Chloride In the course of t h i s study, various metals were tested f o r r e a c t i v i t y towards S 2 C I 2 . Monel a l l o y (67% Ni, 30% Cu, 1.5% Fe) i s known to be r e s i s t a n t to c h l o r i n a t i n g environments so a sample disc ( 1 . 2 cm diameter x 0.4 cm thick) was cut and polished. This specimen was held i n the standard experimental apparatus i n contact with 40 wt. % S . S 2 C I 2 for 18 hours at 120°C. The weight of the dis c a f t e r t h i s treatment (and the standard wash sequence) was within ±0 . 1 mg of the o r i g i n a l weight. While t h i s was not a d e f i n i t i v e corrosion t e s t , i t ind i c a t e s that monel i s r e l a t i v e l y immune to corrosion i n a S . S 2 C I 2 environment. Titanium metal turnings were contacted with S 2 C I 2 i n a beaker at room temperature. No immediate reaction occurred so the mixture was warmed s l i g h t l y . A f t e r a short time (^  30 seconds), a v i o l e n t reaction occurred and the metal was completely consumed i n a few seconds leaving only a small s o l i d residue. T i n shot reacted i n a s i m i l a r (but less v i o l e n t ) way. The absence of s o l i d products i n these reactions indicates formation of T i C l ^ and SnCl^ - l i q u i d s which would be expected to be miscible with S „ C 1 „ . - 114 -A p p e n d i x K: C a l c u l a t e d Ca) and E x p e r i m e n t a l l y D e t e r m i n e d (b) S o l u b i l i t y o f S u l p h u r C S g ) i n S u l p h u r C h l o r i d e . -Ca) C a l c u l a t e d (.Ideal) s o l u b i l i t y o f S„ i n 8 S 2 C 1 2 u s i n g t h e method o f G l a s s t o n e (49) and t h e d a t a o f Meyer ( 5 0 ) . (b) E x p e r i m e n t a l s o l u b i l i t y o f S D i n S.C1 8 2 2 a f t e r A t e n ( 4 7 ) . See s e c t i o n 1.322. zrys " i 8 s p(%3iow) A in iamos 

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