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The alkaline sulphide leaching of tetrahedrite concentrate Raudsepp, Rein 1981

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T H E A L K A L I N E S U L P H I D E L E A C H I N G OF T E T R A H E D R I T E C O N C E N T R A T E b y R E I N R A U D S E P P B . S c , ( E n g i n e e r i n g C h e m i s t r y ) , Q u e e n ' s U n i v e r s i t y , K i n g s t o n , O n t a r i o , 1 9 7 5 A T H E S I S I N P A R T I A L F U L F I L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F A P P L I E D S C I E N C E i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S D e p a r t m e n t o f M e t a l l u r g i c a l E n g i n e e r i n g We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A M a r c h 1 9 8 1 ( c ) R e i n R a u d s e p p , 1 9 8 1 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e H e a d o f my d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . R e i n R a u d s e p p D e p a r t m e n t o f M e t a l l u r g i c a l E n g i n e e r i n g T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 2 0 7 5 W e s t b r o o k M a l l V a n c o u v e r , B . C . C a n a d a V 6 T 1W5 D a t e i i Abstract An inv estigation was made into the leaching of tetrahedrite concentrate . by strong sodium sulphide/sodium hydroxide solutions. The experiments were designed to avoid oxidation of the elements present and so,solubilize antimony as antimony (III) - sulphide complexes. Analytical techniques were developed 2 2 2 for the analysis of caustic and sulphur species (S , S , S O and S0„ ) X""" -L £. J J in antimony-containing solutions. The quantity of antimony extracted from the tetrahedrite was found to be a function of both the sulphide and hydroxide concentrations. Sodium thioferrate, a reaction product of pyrite and sodium sulphide, was indicated as a leaching agent. The solid concentrate decomposition product was x-ray amorphous and colloidal. Though a positive identification of this material was not possible i t was found that one iron and one sulphur were added to the product for each antimony extracted from the tetrahedrite. An analysis of literature stibnite solubility data was done and showed that below log [Sb\ (M) = -0.7 . ^2^4 i s probably the predominant antimony (III) - sulphide complex in saturated soltuion at 25°C. Above log [sb] (M) = -0.7 , 2- Sb^S^ is the most lik e l y predominant complex. The results of the leaching study are not directly applicable to commercial 1 tetrahedrite leach processes where the solutions contain oxidized sulphur species, in particular polysulphide. Antimony leached in these processes exists as antimony (V) - sulphide complexes. T a b l e o f C o n t e n t s A b s t r a c t . , i i T a b l e o f C o n t e n t s i i i L i s t o f T a b l e s . . . v i i L i s t o f F i g u r e s i x A c k n o w l e d g e m e n t s x i C h a p t e r 1 . I n t r o d u c t i o n 1 1 . 1 G e n e r a l 1 1 . 2 T e t r a h e d r i t e 3 1 . 3 C h e m i s t r y 5 1 . 3 . 1 A l k a l i n e S u l p h u r C h e m i s t r y 5 1 . 3 . 2 A l k a l i n e A n t i m o n y - S u l p h u r C h e m i s t r y 9 1 . 3 . 3 M i s c e l l a n e o u s A l k a l i n e S u l p h i d e C h e m i s t r y . . 1 3 1 . 4 T h e S u n s h i n e L e a c h P r o c e s s 1 8 C h a p t e r 2 . E x p e r i m e n t a l 2 2 2 . 1 M a t e r i a l s 2 2 2 . 1 . 1 T e t r a h e d r i t e C o n c e n t r a t e 2 2 2 . 1 . 2 R e a g e n t s 2 6 2 . 2 L e a c h i n g A p p a r a t u s 2 6 2 . 3 L e a c h P r o c e d u r e 2 7 2 . 4 S u l p h i d e O x i d a t i o n 3 0 2 . 5 E v a p o r a t i o n 3 0 C h a p t e r 3 . A n a l y t i c a l C h e m i s t r y 31 3 . 1 A u t o m a t i c T i t r a t i o n 3 1 3 . 2 . S o l u b l e S u l p h u r S p e c i e s A n a l y s i s 3 3 3 . 2 . 1 S u l p h i d e , P o l y s u l p h i d e S u l p h u r , T h i o s u l p h a t e A n d S u l p h i t e D e t e r m i n a t i o n 3 3 3 . 2 . 2 T h e E f f e c t O f A n t i m o n y ( 1 1 1 ) On T h e S u l p h i d e D e t e r m i n a t i o n 3 7 3 . 2 . 3 T h e E f f e c t O f A n t i m o n y ( V ) On T h e S u l p h i d e A n d P o l y s u l p h i d e D e t e r m i n a t i o n s 3 9 3 . 3 T h e D e t e r m i n a t i o n O f S u l p h u r l a S o l i d s 4 1 3 . 4 C a u s t i c D e t e r m i n a t i o n 4 1 3 . 4 . 1 C a u s t i c D e t e r m i n a t i o n I n S u l p h i d e S o l u t i o n . 4 1 3 . 4 . 2 T h e E f f e c t O f A n t i m o n y ( 1 1 1 ) O n T h e C a u s t i c D e t e r m i n a t i o n 4 2 3 . 4 . 3 T h e E f f e c t O f A n t i m o n y ( V ) O n T h e C a u s t i c D e t e r m i n a t i o n .44 3 . 5 A t o m i c A b s o r p t i o n A n d F l a m e E m m i s s i o n A n a l y s i s . . 4 4 C h a p t e r 4 . R e s u l t s A n d O b s e r v a t i o n s 4 6 4 . 1 L e a c h i n g E x p e r i m e n t s C o n s i d e r e d 4 6 4 . 2 A n t i m o n y L e a c h i n g - E q u i l i b r i u m R e s u l t s 4 6 4 . 2 . 1 A n t i m o n y L e a c h e d I n A l k a l i n e S u l p h i d e S o l u t i o n s 4 6 4 . 2 . 2 A n t i m o n y L e a c h e d I n C a u s t i c - O n l y S o l u t i o n s . 5 0 4 . 3 L e a c h i n g I n W e a k S o d i u m S u l p h i d e S o l u t i o n s W i t h o u t A d d e d C a u s t i c 5 1 4 . 4 T h e E x c e s s O f C o n c e n t r a t e U s e d 5 2 4 . 5 F i l t e r a b i 1 i t y O f T h e L e a c h e d P r o d u c t S l u r r y ' 5 2 4 . 6 T h e C h a n g e I n S u l p h i d e C o n c e n t r a t i o n 5 3 4 . 7 T h e C h a n g e I n C a u s t i c C o n c e n t r a t i o n 5 5 4 . 8 A r s e n i c D i s s o l u t i o n 5 8 4 . 9 T h e P r e s e n c e O f O x i d i z e d S u l p h u r S p e c i e s A n d A n t i m o n y ( V ) 6 0 4 . 1 0 A n t i m o n y A n d S u l p h i d e C o n c e n t r a t i o n s V e r s u s T i m e 6 0 4 . 1 1 A p p e a r a n c e O f T h e C o n c e n t r a t e A n d P r o d u c t S o l i d s 6 3 4 . 1 2 X - r a y D i f f r a c t o m e t r y O f T h e P r o d u c t S o l i d s 6 3 4 . 1 3 C o m p a r i s o n O f T e t r a h e d r i t e A n d T h e D e c o m p o s i t i o n P r o d u c t B y E l e c t r o n M i c r o a n a l y s i s 6 3 4 . 1 4 L e a c h e s A t L o w P u l p D e n s i t y 6 9 4 . 1 5 I n c o n s i s t e n c y O f S o d i u m I n T h e C o n c e n t r a t e D e c o m p o s i t i o n P r o d u c t 7 1 4 . 1 6 T h e S o d i u m T o A n t i m o n y R a t i o O f T h e L e a c h e d S o l i d s W a s h W a t e r 7 2 4 . 1 7 P y r i t e L e a c h i n g 7 4 4 . 1 8 S i l i c a - I r o n O x i d e P a r t i c l e s 7 4 C h a p t e r 5 . D e p e n d e n c y O f A n t i m o n y S o l u b i l i t y O n S u l p h i d e I o n C o n c e n t r a t i o n 7 7 5 . 1 S t i b n i t e S o l u b i l i t y P l o t s . 7 7 5 . 2 T e t r a h e d r i t e S o l u b i l i t y P l o t s 8 3 C h a p t e r 6 . D i s c u s s i o n 9 1 6 . 1 R e v i e w O f T h e R e s u l t s 9 1 6 . 2 C a u s t i c F o r m a t i o n A n d S u l p h i d e D e p l e t i o n 9 3 6 . 3 S o d i u m T h i o f e r r a t e 94 6 . 4 D i s i n t e g r a t i o n O f T h e S o l i d s 9 5 6 . 5 T h e C h a r a c t e r i s t i c s O f T h e L e a c h 9 6 6 . 6 S u l p h i d e A s T h e L e a c h i n g A g e n t 9 8 6 . 7 T h i o f e r r a t e A s T h e , L e a c h i n g A g e n t 9 9 6 . 8 S o d i u m A s T h e L e a c h i n g A g e n t 1 0 1 6 . 9 T h e L e a c h E q u i l i b r i u m 1 0 1 6 . 1 0 T h e P r o g r e s s O f T h e L e a c h . . 1 0 4 C h a p t e r 7 . C o n c l u s i o n s 1 0 5 C h a p t e r 8 . R e c o m m e n d a t i o n s F o r F u t u r e S t u d y 1 0 8 A p p e n d i x A T h e H S ~ - S 2 " - O H E q u i l i b r i u m C a l c u l a t i o n a t 1 0 0 °C ' 1 0 9 A p p e n d i x B X - R a y D i f f r a c t o m e t r y 1 1 0 A p p e n d i x C C o n c e n t r a t e S t o i c h i o m e t r y . C a l c u l a t i o n s 1 1 2 A p p e n d i x D E x p e r i m e n t a l R e s u l t s 1 1 4 A p p e n d i x E A n t i m o n y a n d S u l p h i d e C o n c e n t r a t i o n s v e r s u s T i m e 1 1 7 A p p e n d i x F A n a l y s i s o f t h e S t i b n i t e D i s s o l u t i o n D a t a . . 1 1 8 A p p e n d i x G C a l c u l a t i o n o f L o g A n t i m o n y a n d L o g S u l p h i d e D a t a f r o m E x p e r i m e n t a l R e s u l t s 1 2 2 R e f e r e n c e s 1 2 8 L i s t o f T a b l e s T a b l e 1 - 1 : P r o p o s e d S t i b n i t e a n d A n t i m o n y ( 1 1 1 ) R e a c t i o n s 1 1 T a b l e 1 - 2 : A n t i m o n y - S u l p h i d e C o m p l e x R e d u c t i o n P o t e n t i a l s 1 4 T a b l e 1 - 3 : R e a c t i o n s F o r m i n g S o l u b l e S u l p h i d e C o m p l e x e s 1 5 T a b l e 1 - 4 : S o l u b i l i t y o f M e t a l S u l p h i d e s a n d O x i d e s i n S o d i u m S u l p h i d e S o l u t i o n 1 6 T a b l e 1 - 5 : S u n s h i n e L e a c h P l a n t B a l a n c e 2 1 T a b l e 2 - 1 : C h e m i c a l A n a l y s i s o f S u n s h i n e C o n c e n t r a t e ( D r y ) 2 3 T a b l e 2 - 2 : W e t S c r e e n i n g R e s u l t s . . . 2 4 T a b l e 3 - 1 : S u l p h i d e D e t e r m i n a t i o n i n A n t i m o n y ( I I I ) S o l u t i o n 38 T a b l e 3 - 2 : S u l p h i d e a n d P o l y s u l p h i d e S u l p h u r D e t e r m i n a t i o n s i n A n t i m o n y ( I I I ) S o l u t i o n . . . . 4 0 T a b l e 3 - 3 : C a u s t i c A n a l y s i s i n A n t i m o n y ( V ) S o l u t i o n 4 3 T a b l e 4 - 1 : M i c r o p r o b e A n a l y s i s R e s u l t s 6 8 T a b l e 4 - 2 : D a t a a n d R e s u l t s f r o m L o w P u l p D e n s i t y L e a c h i n g E x p e r i m e n t s . . . . 7 0 T a b l e 4 - 3 : R e s u l t s f r o m F i l t e r C a k e W a s h i n g 7 3 T a b l e 5 - 1 : M e a n A n t i m o n y t o S u l p h i d e R a t i o s a n d S l o p e s t a k e n f r o m F i g u r e s 5 - 2 a n d 5 - 4 8 8 T a b l e B - l : X - R a y D i f f r a c t o m e t r y R e s u l t s I l l T a b l e D - l : D a t a f o r L e a c h i n g E x p e r i m e n t s C o n s i d e r e d i n t h e S t u d y 1 1 4 T a b l e D - 2 : D a t a f o r L e a c h i n g E x p e r i m e n t s N o t C o n s i d e r e d 1 1 6 T a b l e E - l : S b a n d N a S v e r s u s T i m e R e s u l t s 1 1 7 y i i i T a b l e F - l : R e s u l t s o f L o g { S b } - L o g { F r e e S^"} C a l c u l a t i o n s 1 1 9 T a b l e F - 2 : R e s u l t s o f E q u i l i b r i u m C o n s t a n t C a l c u l a t i o n s 1 2 0 T a b l e F - 3 : R e s u l t s f r o m C a l c u l a t i o n s o n D a t a f r o m D u b e y - a n d G h o s h ( 1 9 6 2 ) : 1 2 1 T a b l e G - l : R e s u l t s o f C a l c u l a t i o n s f o r L o g A n t i m o n y v e r s u s L o g S u l p h i d e P l o t s 1 2 3 T a b l e G - 2 : A n t i m o n y t o S u l p h i d e R a t i o s 1 2 4 i x L i s t o f F i g u r e s F i g u r e 1 - 1 S u l p h u r E - p H D i a g r a m a t 1 0 0 ° C - 6 F i a u r e 1 - 2 S u l p h u r O x i d a t i o n S t a t e D i a g r a m a t 1 0 0 ° C , p H = 1 2 . . .' 7 F i g u r e 1 - 3 F r a c t i o n o f A d d e d S o d i u m S u l p h i d e a s t h e S E " I o n a t 1 0 0 ° C 8 F i g u r e 1 - 4 S t r u c t u r e s f o r t h e P r o p o s e d A n t i m o n y ( 1 1 1 ) - S u l p h i d e C o m p l e x e s ( P l a n V i e w s ) 1 2 F i g u r e 2 - 1 T h e L e a c h i n g A p p a r a t u s 2 8 F i g u r e 3 - 1 T h e P o t e n t i a l a n d F i r s t D e r i v a t i v e C u r v e s f o r t h e T i t r a t i o n o f S o d i u m S u l p h i d e w i t h H y d r o c h l o r i c A c i d 34 F i g u r e 4 - 1 T h e F i n a l A n t i m o n y C o n c e n t r a t i o n s v e r s u s t h e F i n a l T o t a l S o d i u m S u l p h i d e C o n c e n t r a t i o n s - 0 . 5 a n d 2 M I n i t i a l C a u s t i c 47 F i g u r e 4 - 2 T h e F i n a l A n t i m o n y C o n c e n t r a t i o n s v e r s u s t h e F i n a l T o t a l S o d i u m S u l p h i d e C o n c e n t r a t i o n s - 0 a n d 1 M I n i t i a l C a u s t i c 4 8 F i g u r e 4 - 3 T h e F i n a l A n t i m o n y C o n c e n t r a t i o n s v e r s u s t h e F i n a l T o t a l S o d i u m S u l p h i d e C o n c e n t r a t i o n s - 1 M I n i t i a l C a u s t i c a n d L o w S u l p h i d e 4 9 F i g u r e 4 - 4 T h e D i f f e r e n c e s B e t w e e n t h e I n i t i a l a n d F i n a l S o d i u m S u l p h i d e C o n c e n t r a t i o n s - A b s o l u t e ( T o p ) a n d R e l a t i v e ( B o t t o m ) , v e r s u s t h e F i n a l A n t i m o n y C o n c e n t r a t i o n s . . . . 54 F i g u r e 4 - 5 T h e D i f f e r e n c e s B e t w e e n t h e I n i t i a l a n d F i n a l S o d i u m H y d r o x i d e C o n c e n t r a t i o n s v e r s u s t h e F i n a l S o d i u m S u l p h i d e C o n c e n t r a t i o n s . 56 F i g u r e 4 - 6 ' T h e F i n a l A n t i m o n y C o n c e n t r a t i o n s v e r s u s t h e P r o d u c t o f t h e F i n a l S o d i u m S u l p h i d e a n d S o d i u m H y d r o x i d e C o n c e n t r a t i o n s (1 M I n i t i a l C a u s t i c ) 57 F i g u r e 4 - 7 T h e A r s e n i c V e r s u s t h e A n t i m o n y C o n c e n t r a t i o n s 5 9 F i g u r e 4 - 8 T h e S o l u t i o n A n t i m o n y C o n c e n t r a t i o n s a s a F u n c t i o n o f T i m e 6 1 F i g u r e 4 - 9 T h e S o d i u m S u l p h i d e C o n c e n t r a t i o n s a s a F u n c t i o n o f T i m e 6 2 F i g u r e 4 - 1 0 T h e T e t r a h e d r i t e C o n c e n t r a t e ( a ) a n d t h e L e a c h P r o d u c t S o l i d s ( b ) a t 2 , 1 0 0 x 6 4 F i g u r e 4 - 1 1 T h e T e t r a h e d r i t e C o n c e n t r a t e ( a ) a n d t h e L e a c h P r o d u c t S o l i d s ( b ) a t 2 1 , 0 0 0 x . . ." 6 5 F i g u r e 4 - 1 2 S E M X - r a y A n a l y s e r S p e c t r a f o r t h e T e t r a h e d r i t e a n d t h e D e c o m p o s i t i o n P r o d u c t P h a s e s 6 6 F i g u r e 4 - 1 3 S E M M i c r o g r a p h o f a S i l i c a - I r o n O x i d e P a r t i c l e ( a ) a n d t h e C o r r e s p o n d i n g S i l i c o n ( b ) a n d I r o n . ( c ) X - r a y E n e r g y M a p s 7 5 F i g u r e ' 5 - 1 T h e L i t e r a t u r e S t i b n i t e L e a c h i n g D a t a P l o t t e d C o n s i d e r i n g S b ^ S ^ . " a t L o w S u l p h i d e a n d S b i S ^ a t H i g h S u l p h i d e ( S b S £ " S t a b l i l t y A r e a S h o w n ) 7 9 F i g u r e 5 - 2 S o l u b i l i t y P l o t f o r T e t r a h e d r i t e E x p e r i m e n t a l R e s u l t s 8 4 F i g u r e 5 - 3 E x p e r i m e n t a l R e s u l t s P l o t t e d f o r ^ t h e S b e S ^ . ' I o n a t L o w S u l p h i d e ; S b 4 S ^ I o n a t H i g h S u l p h i d e 8 6 F i g u r e 5 - 4 S o l u b i l i t y P l o t f o r T e t r a h e d r i t e E x p e r i m e n t a l R e s u l t s ( H i g h S u l p h i d e ) 8 7 F i g u r e 5 - 5 T h e A n t i m o n y t o S u l p h i d e ( A r s e n i c C o r r e c t e d ) V a l u e s v e r s u s L o g A n t i m o n y 8 9 F i g u r e G - l T h e S t i b n i t e S o l u b i l i t y D a t a o f A r n t s o n e t a l . , ( 1 9 6 6 ) P l o t t e d C o n s i d e r i n g S b p S ^ " a n d S b ^ S a 1 2 7 ACKNOWLEDGEMENTS I would l i k e t o s i n c e r e l y thank my s u p e r v i s o r , Dr. E. P e t e r s , f o r the many, many hours he spent w i t h me i n c o n s u l t a t i o n on t h i s p r o j e c t . I would a l s o l i k e t o thank a l l the members of the M e t a l l u r g y Department f o r t h e i r unending a s s i s t a n c e and s u p p o r t . I am g r a t e f u l t o the Sunshine M i n i n g Co. f o r s u p p l y i n g the t e t r a h e d r i t e c o n c e n t r a t e used i s t h i s s t u d y . The f i n a n c i a l s u p p o r t of the N a t i o n a l S c i e n c e and E n g i n e e r i n g C o u n c i l i s g r e a t l y a p p r e c i a t e d . 1 C h a p t e r 1. I n t r o d u c t i o n 1.1 G e n e r a l T e t r a h e d r i t e i s a c o p p e r a n t i m o n y s u l p h o s a l t o f w i d e s p r e a d o c c u r r e n c e a n d o f v a r i e d e l e m e n t a l s u b s t i t u t i o n . I t s p r i m a r y m e t a l l i c c o n s t i t u e n t i s c o p p e r , b u t e c o n o m i c a l l y s i g n i f i c a n t q u a n t i t i e s o f s i l v e r a r e o f t e n a s s o c i a t e d w i t h t h i s m i n e r a l . A n t i m o n y ( a l o n g w i t h a r s e n i c , t h e m a j o r s u b s t i t u e n t f o r a n t i m o n y i n t e t r a h e d r i t e ) i s d i f f i c u l t t o s e p a r a t e f r o m c o p p e r b y c o n v e n t i o n a l r e v e r b e r a t o r y f u r n a c e - c o n v e r t e r c o p p e r p y r o m e t a l l u r g y . T h a t p o r t i o n w h i c h i s s e p a r a t e d i s l a r g e l y v o l a t i l i z e d d u r i n g c o n v e r t i n g a n d m u s t b e r e m o v e d f r o m a s u l p h u r d i o x i d e - l a d e n g a s s t r e a m t o a v o i d e n v i r o n m e n t a l c o n t a m i n a t i o n . A n t i m o n y a n d a r s e n i c a r e a l s o v o l a t i l i z e d b y m a t t e s m e l t i n g . T h e s m a l l a m o u n t s o f t h e s e t w o e l e m e n t s w h i c h r e p o r t t o t h e b l i s t e r c o p p e r d i s s o l v e d u r i n g e l e c t r o r e f i n i n g a n d r e m a i n i n t h e t a n k h o u s e e l e c t r o l y t e s o l u t i o n f r o m w h i c h t h e y m u s t b e p u r g e d o r s t r i p p e d . F o r t h e s e r e a s o n s s i g n i f i c a n t e c o n o m i c p e n a l t i e s a r e a s s e s s e d a g a i n s t t h e a n t i m o n y a n d a r s e n i c c o n t e n t o f c o n c e n t r a t e s b y c u s t o m c o p p e r s m e l t e r s . A n t i m o n y i s s o l u b l e i n s u l p h i d e s o l u t i o n ( a s i s a r s e n i c ) a n d l e a c h i n g p r o c e s s e s f o r • s t i b n i t e , S b 2 S 3 , a p p l y t h i s 2 c h e m i s t r y . S i m i l a r l i x i v i a n t s c a n e x t r a c t a n t i m o n y f r o m t e t r a h e d r i t e l e a v i n g s o l i d s s u i t a b l e f o r c o p p e r s m e l t i n g . A p l a n t b a s e d o n t h i s l e a c h h a s o p e r a t e d i n S u n s h i n e , I d a h o s i n c e 1 9 4 2 . A n o t h e r p l a n t u n d e r c o n s t r u c t i o n i n H o u s t o n , B r i t i s h C o l u m b i a i s e x p e c t e d t o b e g i n o p e r a t i o n i n 1 9 8 1 . T h e p u r p o s e o f t h i s s t u d y w a s t o i n v e s t i g a t e t h e e q u i l i b r i u m b e t w e e n t e t r a h e d r i t e a n d s o d i u m s u l p h i d e / s o d i u m h y d r o x i d e l e a c h s o l u t i o n s , a n d 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 l e a c h p r o d u c t s . I n d u s t r i a l l e a c h i n g p r o c e s s e s a r e o p e r a t e d t o p r o d u c e t h e h i g h e s t p r a c t i c a l m e t a l c o n c e n t r a t i o n i n s o l u t i o n , a n d s o t h i s w o r k w a s f o c u s e d o n e q u i l i b r i u m e x p e r i m e n t s d o n e i n s t r o n g s o l u t i o n s . A l e a c h t e m p e r a t u r e o f 1 0 0 ° C w a s c h o s e n t o c o n f o r m w i t h i n d u s t r i a l p r a c t i c e , a n d S u n s h i n e c o n c e n t r a t e ( w h i c h c o n t a i n s m i n e r a l s o t h e r t h a n t e t r a h e d r i t e ) w a s l e a c h e d . T h e r e s u l t s o b t a i n e d a r e n o t d i r e c t l y a p p l i c a b l e t o t h e S u n s h i n e p r o c e s s s i n c e t h e S u n s h i n e l e a c h s o l u t i o n c o n t a i n s o x i d i z e d s u l p h u r s p e c i e s n o t c o n s i d e r e d i n t h i s w o r k . T h e s e s p e c i e s , p o l y s u l p h i d e a n d t h i o s u l p h a t e i n p a r t i c u l a r , a r e p o t e n t i a l o x i d a n t s i n t h e l e a c h i n g c h e m i s t r y . 3 1 . 2 T e t r a h e d r i t e S u l p h o s a l t s a r e a c l a s s o f m i n e r a l s w h i c h h a v e t h e g e n e r a l f o r m u l a A T X w h e r e t h e e l e m e n t s d e s i g n a t e d a s A a r e : C u , P b , m n p = A g ; a s T : A s , S b , B i a n d a s X : S ' ( T a k e u c h i a n d S a d a n a g a , 1 9 6 2 ) . W i t h i n t h e i r s t r u c t u r e t h e r e ' i s a t r i v a l e n t T s p e c i e s c o v a l e n t l y b o n d e d t o t h r e e s u l p h u r s t o f o r m a l o w p y r a m i d w i t h T a t t h e v e r t e x . T h e p r e s e n c e o f t h e s e a n i o n i c T S 3 p y r a m i d s , a r r a n g e d e i t h e r s i n g l y o r i n c o m p l e x g r o u p s , d i s t i n g u i s h e s s u l p h o s a l t s f r o m s u l p h i d e s . T e t r a h e d r i t e , a c o p p e r a n t i m o n y s u l p h o s a l t , h a s t h e n o m i n a l f o r m u l a C u 1 2 S b 4 S 1 3 . I t s c r y s t a l s t r u c t u r e w a s o r i g i n a l l y b e l i e v e d t o b e d e r i v e d b y a n o r d e r l y s u b s t i t u t i o n o f s p h a l e r i t e , Z n S , w h i c h h a s t e t r a h e d r a o f z i n c a n d s u l p h u r a b o u t e a c h o t h e r . H o w e v e r , t h e i n a b i l i t y o f a n t i m o n y t o f o r m a f o u r t h b o n d p r o d u c e s d i s t o r t i o n s a n d s u l p h u r v a c a n c i e s r e l a t i v e t o t h e s p h a l e r i t e l a t t i c e . I n t e t r a h e d r i t e h a l f t h e c o p p e r a t o m s a r e t e t r a h e d r a l l y b o n d e d t o f o u r s u l p h u r s , w h i l e t h e o t h e r h a l f a r e t r i g o n a l l y - c o o r d i n a t e d t o t h r e e ( W u e n s c h , 1 9 6 4 ) . A b o v e 9 5 ° C t e t r a h e d r i t e s h o w s a w i d e s o l i d s o l u t i o n r a n g e : C u 1 2 + x S b 4 + v S 1 3 ' w h e r e ° - i : L < x K i - 7 7 / ° - 0 3 < Y < . 3 0 ( T a t s u k a a n d M o r i m o t o , 1 9 7 3 ) . B e l o w 9 5 ° C t h e s o l i d s o l u t i o n r e a d i l y d i s s o c i a t e s i n t o t w o i m m i s i b l e t e t r a h e d r i t e p h a s e s : o n e c o p p e r - p o o r , t h e o t h e r c o p p e r - r i c h , w i t h c o m p o s i t i o n s a p p r o a c h i n g C u 1 2 S b 4 S 1 3 a n d C u ^ S b ^ S ^ . . T h e c o p p e r a t o m s o f t e t r a h e d r i t e c a n d i f f u s e r a p i d l y a n d i t 4 i s p o s s i b l e t o c o n v e r t o n e f o r m o f t e t r a h e d r i t e t o t h e . o t h e r b y c o l d p r e s s i n g w i t h c o p p e r p o w d e r o r s u l p h u r ( T a t s u k a a n d M o r i m o t o , 1 9 7 3 ) . C o p p e r - p o o r t e t r a h e d r i t e c a n b e o b t a i n e d b y i m m e r s i n g t h e c o p p e r - r i c h p h a s e i n t o c a r b o n d i s u l p h i d e c o n t a i n i n g 5% s u l p h u r f o r m i n g a c o p p e r s u l p h i d e ( C u S ) f i l m . W i t h t h e p a r t i a l s u b s t i t u t i o n o f c o p p e r a n d a n t i m o n y b y o t h e r e l e m e n t s o n l y t h e c o p p e r - p o o r s t o i c h i o m e t r y i s f o u n d c o n s i s t e n t w i t h t h e c o m p o s i t i o n s o b s e r v e d i n n a t u r a l t e t r a h e d r i t e s : ( C u , A g ) I Q ( F e , Z n , H g , C u * ) 2 ( S b , A s ) 4 S 1 3 ( T a t s u k a a n d M o r i m o t o , 1 9 7 3 ) . C u * i s l i m i t e d t o l e s s t h a n 0 . 2 a t o m i n m o s t n a t u r a l s p e c i m e n s . C u * h a s a n u p p e r l i m i t o f 0 . 8 w h e n t h e r e i s m o r e t h a n o n e F e . T h e a r s e n i c a n a l o g u e o f t e t r a h e d r i t e i s t e n n a n t i t e a n d t h e f o r m u l a g i v e n a b o v e h o l d s f o r b o t h . I r o n i s a l w a y s f o u n d i n t e t r a h e d r i t e ( 1 - 1 3 % ) a n d z i n c u s u a l l y ( 0 - 8 % ) ; l e s s c o m m o n l y s i l v e r , l e a d a n d m e r c u r y s u b s t i t u t e f o r c o p p e r . T h e a r g e n t i f e r o u s v a r i e t y , k n o w n a s f r e i b e r g i t e , c o n t a i n s u p t o 1 8 % s i l v e r ( H u r l b u t a n d K l e i n , 1 9 7 7 ) . T e t r a h e d r i t e i s u s u a l l y f o u n d i n h y d r o t h e r m a l v e i n s o f c o p p e r , s i l v e r , l e a d a n d z i n c . I t i s o f t e n a s s o c i a t e d w i t h c h a l c o p y r i t e , p y r i t e , s p h a l e r i t e , g a l e n a a n d v a r i o u s o t h e r s i l v e r , l e a d a n d c o p p e r m i n e r a l s ( H u r l b u t a n d K l e i n , 1 9 7 7 ) . 5 1.3 C h e m i s t r y 1.3.1 A l k a l i n e S u l p h u r C h e m i s t r y S u l p h a t e s h o u l d be the p r o d u c t of s u l p h i d e o x i d a t i o n a t 100°C i n a l k a l i n e s o l u t i o n on the b a s i s , of thermodynamic r e a s o n i n g . The 100°C s u l p h u r E-pH diagram i s shown i n F i g u r e 1- 1. However, f o r k i n e t i c r e a s o n s SO 2' may form o n l y a t 4 p o t e n t i a l s up t o 0.5 v o l t h i g h e r than those t h e r m o d y n a m i c a l l y r e q u i r e d . The s u l p h u r o x i d a t i o n s t a t e diagram a t pH 12 ( F i g u r e 1-2) i n d i c a t e s t h a t i f the p o t e n t i a l f o r SO^ 2" f o r m a t i o n were t o be r a i s e d , more s i g n i f i c a n t c o n c e n t r a t i o n s of p o l y s u l p h i d e , S O 2 " and SO 2" would e x i s t i n s o l u t i o n . 2 3 3 S u l p h i d e ' o x i d a t i o n t o s u l p h a t e under a l k a l i n e c o n d i t i o n s i s ob s e r v e d w i t h i o d i n e , i o d a t e , h y p o c h l o r i t e and hydrogen p e r o x i d e o x i d a n t s ( B l a s i u s et a l . , 1968). The p o t e n t i a l of a p a r t i a l l y o x i d i z e d s o l u t i o n i s not d e t e r m i n e d by the S 2 " / S 0 ^ 2 " c o u p l e (which i s q u i t e i r r e v e r s i b l e ) , but r a t h e r by the s u l p h i d e / p o l y s u l p h i d e c o u p l e ( F e r r e i r a , 1975). Though the e q u i l i b r i u m c o n c e n t r a t i o n of p o l y s u l p h i d e i s s m a l l i n a l k a l i n e s o l u t i o n , a v e r y r e v e r s i b l e e q u l i b r a t i o n w i t h s u l p h i d e o c c u r s . When sodium s u l p h i d e , Na S-9H 0, i s d i s s o l v e d i n w a t e r , HS" and 2 2 OH" a r e formed by h y d r o l y s i s ( E q u a t i o n 1-1). nNa S + mNaOH + n ( F - l ) H 0. = nF Na S + n(F-l)NaHS + 2 2 2 {m + n(F-l)NaOH) ... (1-1) F i g u r e 1-3 shows the . f r a c t i o n of added Na 2S which e x i s t s as S 2" at 100°C as a f u n c t i o n of the i n i t i a l Na S and NaOH 6 1.6 1.2 0.8 0.4 0 -0.4 -0 .8 -1.2 Sulphur Concentration Decode = 0.073 V-Equiv (VI to o E CO _ J _ CVJ » ™ to CO CO CO CO to 1 _ L to I to -2 0 1 2 . Sulphur Oxidation State ( Equiv ) Figure 1 -2: Sulphur O x i d a t i o n State Diagram at 100°C , pH=12 8 F i g u r e 1 - 3 F r a c t i o n o f A d d e d S o d i u m S u l p h i d e a s t h e S 2 - i o n a t 1 0 0 * C . 9 c o n c e n t r a t i o n s . A p p e n d i x A s h o w s t h e c a l c u l a t i o n s u s e d . U n i t a c t i v i t y c o e f f i c i e n t s w e r e a s s u m e d f o r a l l s p e c i e s a s n o a c t i v i t y d a t a w a s a v a i l a b l e f o r H S " a n d S 2 ~ . 1 . 3 . 2 A l k a l i n e A n t i m o n y - S u l p h u r C h e m i s t r y A n t i m o n y h a s t w o m a j o r o x i d i z e d v a l e n c e s t a t e s , S b ( I I I ) a n d S b ( V ) . B o t h f o r m b i n a r y s u l p h u r c o m p o u n d s a n d s o l u b l e s u l p h i d e c o m p l e x e s . T h e S b ( 1 1 1 ) - s u l p h u r b i n a r y c o m p o u n d i s s t i b n i t e , S b ^ S ^ I n t h e s t i b n i t e s t r u c t u r e ( S c a v n i c a r , 1 9 6 0 ) h a l f t h e a n t i m o n y a t o m s a r e b o n d e d t o t h r e e s u l p h u r s i n a t r i g o n a l S b S 3 p y r a m i d a s i n S b s u l p h o s a l t s . T h e o t h e r h a l f i s b o n d e d t o f i v e s u l p h u r s i n a s q u a r e S ^ p y r a m i d . B y a v a l e n c e e l e c t r o n h y b r i d i z a t i o n a r g u m e n t ( S c a v n i c a r , 1 9 6 0 ) S b ( I I I ) c o m p l e t e s i t s 5 s 2 p 3 v a l e n c y s h e l l t o a n o c t e t o f f o u r t e t r a h e d r a l l y a r r a n g e d e l e c t r o n p a i r s b y f o r m i n g t h r e e c o v a l e n t b o n d s i n t r i g o n a l p y r a m i d c o n f i g u r a t i o n . I f t h e t w o d e l e c t r o n s a r e c o n s i d e r e d i n s p 3 d 2 h y b r i d i z a t i o n , t h e m o s t p r o b a b l e c o n f i g u r a t i o n i s s i x o c t a g o n a l l y a r r a n g e d e l e c t r o n p a i r s : a 5 - c o o r d i n a t e p y r a m i d p l u s a l o n e p a i r . C o m p l e x s u l p h i d e s w i t h a l k a l i m e t a l s h a v e b e e n p r e p a r e d b y h i g h t e m p e r a t u r e s a l t f u s i o n t e c h n i q u e s ( M o s s a n d S m i t h , 1 9 7 5 ) . T h e s e s a l t s a r e N a 3 S b S 3 , N a 6 S b ^ S ^ a n d N a S b S 2 p l u s s o m e o f t h e i r L i , K , R b a n d C s a n a l o g u e s . T h e y d o n o t c r y s t a l l i z e f r o m a q u e o u s s o l u t i o n . A c o m p a r i s o n o f t h e n u c l e a r q u a d r a p o l e 10 r e s o n a n c e s p e c t r a o f N a ^ S b S ^ , N a S b S 2 a n d A g ^ S b S 3 , a s i l v e r s u l p h o s a l t , i n d i c a t e d t h a t t h e s t r u c t u r e s o f t h e s o d i u m s a l t s w e r e b a s e d o n S b S t r i g o n a l p y r a m i d s ( B u s l a e v e t a l . , 1 9 7 1 ) . T h e x - r a y c r y s t a l s t r u c t u r e o f K ^ S ^ S , , s h o w e d S b S a n d S b - c e n t e r e d S g r o u p s ( M o s s a n d S m i t h , 1 9 7 5 ) . V a r i o u s S b ( 1 1 1 ) - s u l p h i d e c o m p l e x e s h a v e b e e n p r o p o s e d : S b S 0 " , S b S , 3 " , S b „ S „ 2 - , S b ^ S r 4 ' a n d S b , S ^ 2 ' . H o w e v e r , t h e i r r e l a t i v e d o m a i n s o f s t a b i l i t y h a v e n o t b e e n m a p p e d o u t a n d i t i s n o t e v e n c e r t a i n t h a t a l l o f t h e m e x i s t . S o m e t h e r m o d y n a m i c d a t a a n d e q u i l i b r i a c o n s t a n t s f r o m s t i b n i t e s o l u b i l i t y s t u d i e s h a v e b e e n p u b l i s h e d ( T a b l e 1 - 1 ) ( S i l l e n a n d M a r t e l l , 1 9 6 4 ; B a r n e r a n d S c h e u e r m a n , 1 9 7 8 ; B u t l e r , 1 9 6 4 ; L a t i m e r , 1 9 5 2 ) , b u t n o t a l l t h i s i n f o r m a t i o n s h o u l d b e t a k e n a t f a c e v a l u e . F o r e x a m p l e , L a t i m e r ' s 1 9 5 2 e s t i m a t e o f t h e A G ° f o r S b S 3 3 " r e m a i n s u n c h a n g e d i n B a r n e r a n d S c h e u e r m a n ' s 1 9 7 8 c o m p i l i a t i o n o f d a t a d e s p i t e a m a j o r c h a n g e t o S b 2 S 3 ' s A G ° w h i c h m u s t h a v e f o r m e d t h e b a s i s f o r t h e o r i g i n a l e s t i m a t e . N o a c t i v i t y c o e f f i c i e n t d a t a a r e a v a i l a b l e f o r a n y o f t h e c o m p l e x e s . F i g u r e 1 - 4 s h o w s p o s s i b l e s t r u c t u r e s f o r t h e S b ( I I l ) - s u l p h i d e s c o m p l e x e s l i s t e d a b o v e . S b S 2 " s e e m s u n l i k e l y b e c a u s e t h e r e a r e n o S b S 3 u n i t s . S b 2 S 5 4 " a l s o s e e m s u n l i k e l y b e c a u s e o f t h e l a r g e n u m b e r o f s i n g l y b o n d e d s u l p h u r s . C o v a l e n t l y b o n d e d s u l p h i d e i s c a p a b l e o f t w o , f o u r o r s i x s i n g l e b o n d s o r f o u r s i n g l e a n d o n e d o u b l e b o n d ( V a u g h a n a n d C r a i g , 1 9 7 8 ) . T h e s t r u c t u r e o f S b ^ S ^ 2 " s h o w n i s b a s e d o n t h e s t i b n i t e u n i t c e l l ( S c a v n i c a r , 1 9 6 0 ) . T a b l e 1 - 1 : P r o p o s e d S t i b n i t e a n d A n t i m o n y ( 1 1 1 ) R e a c t i o n s * 1 / 2 S b 2 S 3 ( s ) + 3 / 2 S " 2 = S b S \ J K ( 2 9 8 ) = 0 . 8 9 l / 2 S b 2 S j ( s ) + 1 / 2 S 2 ' 2 = S b S 2 " 2 K ( 2 9 8 ) = 0 . 4 5 S b S ( s ) + S " 2 = S b S " 2 K ( 3 0 3 ) = 2 . 0 8 2 3 2 4 S b S + H S " = H S b S - ( ? ) K ( 2 9 8 ) = " 2 . 3 3 2 3 2 4 S b S 2 " + S " 2 = S b S 3 " 3 K ( 2 9 8 ) = 0 . 4 4 • R e f e r e n c e s : S i l l e n a n d M a r t e l l ( 1 9 6 4 ) ; B u t l e r ( 1 9 6 4 ) \ 12 F i g u r e 1-4: S t r u c t u r e s f o r the Proposed A n t i m o n y ( I I I ) - Sulphide Complexes (Plan Views) 13 T h e s i m p l e a q u a t e d S b 3 + i o n h a s n e v e r b e e n d e t e c t e d ( M o s s a n d S m i t h , 1 9 7 5 ) w h i l e a n t i m o n y o x y - a n i o n s , S b C > 2 " f o r e x a m p l e , a r e s t a b l e . A n t i m o n y ( V ) s u l p h i d e , S b 2 s 5 ( a s p r e c i p i t a t e d ) , h a s b e e n s h o w n t o c o n t a i n o n l y S b ( I I I ) b y M o s s b a u e r s p e c t r o s c o p y ( M o s s a n d S m i t h , 1 9 7 5 ) . T h e o n l y r e p o r t e d S b ( V ) - s u l p h i d e a q u e o u s c o m p l e x i s S b S ^ 3 ~ . S o d i u m t h i o a n t i m o n a t e , N a ^ S b S ^ 9 ^ 0 , i t s s o l i d a n a l o g u e , c a n b e c r y s t a l l i z e d f r o m s o l u t i o n . T h e o x i d a t i o n o f S b ( I I I ) t o S b ( V ) b y p o l y s u l p h i d e ( E q u a t i o n 1 - 2 ) ( x - l ) S b S 3 3 " + S x 2 " = ( x - l ) S b S 4 3 " + S 2 " . . . ( 1 - 2 ) i s r e p o r t e d t o b e q u a n t i t a t i v e ( S e v r y u k o v a n d M u r t i , 1 9 6 6 ) . T h e e l e c t r o l y t i c r e d u c t i o n o f a n t i m o n y s u l p h i d e c o m p l e x e s i s t h e b a s i s f o r i n d u s t r i a l e l e c t r o w i n n i n g . V a r i o u s r e d u c t i o n p o t e n t i a l s h a v e b e e n m e a s u r e d ( T a b l e 1 - 2 ) . 1 . 3 . 3 M i s c e l l a n e o u s A l k a l i n e S u l p h i d e C h e m i s t r y M a n y m e t a l s u l p h i d e s h a v e e x t r e m e l y l o w s o l u b i l i t y p r o d u c t s a n d a r e c o n s i d e r e d t o b e v i r t u a l l y i n s o l u b l e . H o w e v e r , m e t a l c o n c e n t r a t i o n s i n s o l u t i o n c a n b e r a i s e d b y m a n y o r d e r s o f m a g n i t u d e i f s u l p h i d e c o m p l e x e s a r e f o r m e d . T a b l e 1 - 3 s h o w s r e a c t i o n s w h i c h a r e p o s s i b l e i n a l k a l i n e s u l p h i d e s o l u t i o n . T a b l e 1 - 4 s h o w s t h e m e a s u r e d s o l u b i l i t i e s o f v a r i o u s m e t a l s u l p h i d e s a n d o x i d e s i n s u l p h i d e s o l u t i o n ( p r e s u m a b l y a t 2 5 ° C ) . O n e r e p o r t e d s o l u b i l i t y f o r c o p p e r f r o m C u 2 S i s g i v e n a s 0 . 0 1 4 M i n 1 . 1 M s u l p h i d e ( B a i b o r o d o v e t a l . , 1 9 7 5 ) w h e r e a s i t s T a b l e 1-2: A n t i m o n y - S u l p h i d e Complex R e d u c t i o n P o t e n t i a l SbS 2 " + 3e~ = Sb + 2S" 2 E° = -0.85 V S b S 3 - 3 .+' 3e"= Sb + 3S" 2 E° = -0.9 V 1/2 Sb 2S 5--« + 3e"= Sb + 2.5S" 2 E° = -0.86 V SbS, - 3 + 5e"= Sb + 4S" 2 E° = -0.78 V 4 SbS, - 3 + 2e-= SbS " 3 + S- 2 E° = -0.61 V 4 o *REFERENCES: L a t i m e r ( 1 9 5 2 ) , B a i b o r d o v e t a l . (1975) 15 T a b l e 1-3: R e a c t i o n s F o r m i n g S o l u b l e S u l p h i d e Complexes* Log K(298) Ag + + S - 2 = AgS" 23. 9 HgS( s) + S" 2 = HgS 2 - 2 0. 58 A S 2 S 3 (a) + 1/2 S- 2 = AsS 2 1. 0 SnS 2 ( s ) + S" 2 = SnS 3 " 2 5. 04 2Au + 2HS" + 1/20 (g) = 2AuS" + H 20 29. 7 * R e r e r e n c e s : S i l l e n and M a r t e l l ( 1 9 6 4 ) ; B u t l e r (1964) 16 T a b l e 1 - 4 : S o l u b i l i t y o f M e t a l S u l p h i d e s a n d O x i d e s i n S o d i u m S u l p h i d e S o l u t i o n * M e t a l C o n e . N a S C o n e . 2 ( 1 0 ' * M) (M) P b S 0 . 3 6 8 1 . 1 0 Z n S 0 . 3 8 4 1 . 1 0 C d S 0 . 1 1 . 1 0 F e S 1 . 9 6 1 .4 -0 C u S 1 4 . 0 5 1 . 1 0 2 * C u S 1 . 8 1 . 4 5 2 Mo.S 9 1 . 4 0 2 B i S 1 1 . 4 0 2 P b O 0 . 7 1 . 4 5 Zn O 5 . 5 1 . 5 3 C d O 1 . 9 1 . 4 5 F e 0 0 . 0 5 1 . 4 5 2 3 N i O 2 . 1 1 . 4 5 * R e f e r e n c e : B a i b o r d o v e t a l . ( 1 9 7 5 ) 17 T h e s o l u b i l i t y o f s u l p h i d e m i n e r a l s g e n e r a l l y i n c r e a s e s w i t h t e m p e r a t u r e . H y d r o t h e r m a l s u l p h i d e m i n e r a l d e p o s i t s c a n b e c r e a t e d b y t h e l o c a l i z e d p r e c i p i t a t i o n o f s o l i d s u l p h i d e s f r o m h o t n a t u r a l w a t e r s b y c o o l i n g ( V a u g h a n a n d C r a i g , 1 9 7 8 ) . A r s e n i c ' s s u l p h i d e s o l u t i o n c h e m i s t r y i s s i m i l a r t o t h a t o f a n t i m o n y . A c o m p a r i s o n o f T a b l e s 1 - 1 a n d 1 - 3 s h o w s t h a t A s S 2 " i s 3 . 5 t i m e s m o r e s t a b l e t h a n i t s a n t i m o n y a n a l o g u e . I n s u l p h i d e s o l u t i o n a n t i m o n y i s r e d u c e d f r o m S b ( V ) t o S b ( I I I ) i n f a v o u r o f A s ( I I I ) o x i d a t i o n t o A s ( V ) ( B a i b o r o d o v , 1 9 7 6 ) . T h e e x i s t e n c e o f f e r r i c i r o n i n s u l p h i d e s o l u t i o n a s a l k a l i m e t a l t h i o f e r r a t e , M F e S 2 , h a s r e c e n t l y b e e n i n v e s t i g a t e d ( T a y l o r a n d S h o e s m i t h , 1 9 7 8 ) . T h i o f e r r a t e i s r e p o r t e d t o b e a n e u t r a l c o l l o i d a l s p e c i . e s w i t h a ( F e S 2 ) n c h a i n s t r u c t u r e . T h e d i s p e r s e d f o r m w a s m a d e b y t h e a d d i t i o n o f f e r r i c i o n s t o s u l p h i d e s o l u t i o n a t p H 1 1 - 1 2 . I t h a d a n i n t e n s e g r e e n - b l a c k c o l o u r . T h e f u r t h u r a d d i t i o n o f a n e q u a l v o l u m e o f a c e t o n e , 1 M MOH o r 1 M M C I f l o c c u l a t e d a c o l l o i d a l s o l i d , M F e S 2 ' x H 2 0 w h e r e M i s N a o r K . A t 2 5 ° C b o t h N a F e S 2 a n d K F e S 2 d e c o m p o s e d i n a c i d s o l u t i o n . ( E q u a t i o n 1 - 3 ) . 2 M F e S 2 + 6 H + = 2 M + + 2 F e 2 + + 3 H 2 S + S ° . . . ( 1 - 3 ) A t p H 1 1 a n d g r e a t e r t h e y w e r e s t a b l e , b u t o n l y w i t h H S ' i n s o l u t i o n . A t 8 0 ° C N a F e S 2 d e c o m p o s e d r a p i d l y e v e n i n t h e p r e s e n c e o f H S " ( E q u a t i o n 1 - 4 ) w i t h • t h e f o r m a t i o n o f p o l y s u l p h i d e . 2 N a F e S 2 = 2 N a + + 2 F e 2 + + S 2 2 " + 2 S 2 " . . . ( 1 - 4 ) L i t h i u m a d d e d a s 1 M L i O H d i s p e r s e d d r y s o l i d N a F e S 2 a n d K F e S 2 18 a n d f e r r i c o x i d e / h y d r o x i d e w a s p r o d u c e d . 1 . 4 T h e S u n s h i n e L e a c h P r o c e s s L e a c h i n g a t t h e S u n s h i n e p l a n t ( B a r r , 1 9 7 3 ; H o l m e s , 1 9 4 4 ) i s c a r r i e d o u t o n a b a t c h b a s i s i n f o u r 2 0 t o n , c o v e r e d , p r o p e l l e r a g i t a t e d , s t e e l t a n k s . B a r r e n s o l u t i o n i s p u m p e d i n t o a t a n k a n d h e a t e d b y s t e a m c o i l s t o b e g i n t h e l e a c h i n g c y c l e . W h e n t h e s o l u t i o n r e a c h e s 9 5 ° C e l e m e n t a l s u l p h u r a n d c a u s t i c s o l u t i o n a r e a d d e d t o b r i n g t h e N a ? S s t r e n g t h u p t o 3 0 0 ^ / 1 ( 3 . 8 M) a n d f i v e t o n s o f t e t r a h e d r i t e c o n c e n t r a t e a r e f e d i n . T h e l e a c h g o e s f o r 14 h o u r s a t 1 0 0 - 1 0 3 ° C . A f t e r l e a c h i n g , t h e p r o d u c t s l u r r y i s p u m p e d t o a b a t c h t h i c k n e r a n d a l l o w e d t o s e t t l e . T h e s o l i d s a r e f i l t e r e d t w i c e w i t h w a t e r w a s h i n g a n d s h i p p e d w e t t o a c o p p e r s m e l t e r . T h e f i l t r a t i o n i s d i f f i c u l t a n d t h e f i l t e r c a k e c o n t a i n s . N a 9 S a n d m o r e t h a n 20% m o i s t u r e . T h e c l e a r p r e g n a n t s o l u t i o n i s e l e c t r o w o n o n m i l d s t e e l c a t h o d e s p r o d u c i n g a n o n - a d h e r e n t d e p o s t : 95% S b , 5% A s , p l u s 6 - 1 0 o z / t o n A g . T h e a n o d e s , a l s o m a d e o f m i l d s t e e l , a r e i m m e r s e d i n a n a n o l y t e s o l u t i o n w h i c h i s s e p a r a t e d f r o m t h e c a t h o l y t e b y a c a n v a s d i a p h r a g m . B o t h t h e c a t h o l y t e a n d t h e a n o l y t e a r e c i r c u l a t e d a b o u t s e p a r a t e s t o r a g e t a n k s u n t i l s p e n t . T h e s p e n t c a t h o l y t e i s u s e d f o r l e a c h i n g a n d t o m a k e u p f r e s h a n o l y t e w h i c h i s ' d e - s u l p h i d e d ' b y a n o d i c r e a c t i o n s . T h e s p e n t a n o l y t e i s f u l l y o x i d i z e d i n a n a u t o c l a v e . T h e s o d i u m a n t i m o n a t e 19 w h i c h i s ' d e - s u l p h i d e d ' b y a n o d i c r e a c t i o n s . T h e s p e n t a n o l y t e i s f u l l y o x i d i z e d i n a n a u t o c l a v e . T h e s o d i u m a n t i m o n a t e p r o d u c e d , N a S b ( 0 H ) 6 , i s s e t t l e d o u t a n d r e l e a c h e d w h i l e t h e l i q u i d i s s e n t t o t h e c o n c e n t r a t o r t a i l i n g s p o n d . S i n c e t h e l e a c h s o l u t i o n i s g e n e r a t e d f r o m c a u s t i c a n d e l e m e n t a l s u l p h u r S 2 ~ , s 2 ° 3 2 ~ a n < ^ p o l y s u l p h i d e , S ^ 2 " , a r e f o r m e d d i r e c t l y . ( E q u a t i o n s 1 - 5 a n d 1 - 6 ) 4 S ° +' 6 0 H - = 2 S 2 " + S 2 0 3 2 " + 3 H 2 0 . . . ( 1 - 5 ) ( x - l ) S ° + S 2 " = S 2 " . . . ( 1 - 6 ) x O x i d a t i o n p r o d u c e s s u l p h a t e . T h e l e a c h e d a n t i m o n y e x i s t s i n t h e p e n t a v a l e n t f o r m a s S b S ^ 3 ~ d u e t o t h e o x i d i z i n g p o w e r o f p o l y s u l p h i d e . A t t h e c a t h o d e s o f t h e e l e c t r o w i n n i n g c e l l s t h e t h i o a n t i m o n a t e c o m p l e x i s r e d u c e d t o m e t a l ( E q u a t i o n . 1 - 7 ) . S b S 4 3 " + 5 e " = S b + 4 S 2 ~ . . . ( 1 - 7 ) T h e c u r r e n t e f f i c i e n c y o f t h i s p r o c e s s i s l o w e r e d b y t h e r e d u c t i o n o f o x i d i z e d s u l p h u r s p e c i e s , p r i m a r i l y p o l y s u l p h i d e ( E q u a t i o n 1 - 8 ) . S 2 - + 2 ( x - l ) e " = x S 2 " . . ( 1 - 8 ) x S u l p h u r o x i d a t i o n r e a c t i o n s w h i c h c o n s u m e s u l p h i d e a n d c a u s t i c t a k e p l a c e a t t h e a n o d e ( E q u a t i o n s 1 - 9 a n d 1 - 1 0 , f o r e x a m p l e ) . S 2 " + 3 0 H - = 1 / 2 S 2 0 3 2 - +. 3 / 2 H 2 0 + 4 e " . . . ( 1 - 9 ) 1 / 2 S 2 0 3 2 " + 5 0 H - = S 0 4 2 " + 5 / 2 H O + 4 e " . . . ( 1 - 1 0 ) T h e a n i o n i c a n o d i c p r o d u c t s a r e k e p t a w a y f r o m t h e c a t h o d e b y t h e d i a p h r a g m a n d e l e c t r o s t a t i c f o r c e s . T h e c r e a t i o n o f 20 diaphragm adds t o i t as the OH" i o n has a r e l a t i v e l y h i g h t r a n s p o r t number. Sodium i o n s m i g r a t e from the a n o l y t e to the c a t h o l y t e a g a i n s t the a n i o n s . A p a r t i a l mass b a l a n c e about the Sunshine l e a c h p l a n t i s g i v e n i n T a b l e 1-5. T a b l e 1 - 5 : S u n s h i n e L e a c h P l a n t B a l a n c e * Wt C u S b A g % D i s t r i b u t i o n (%) (%) ( O Z ) C u S b A g I n : S i l v e r C o n e 1 0 0 2 5 . 0 1 7 . 0 % 1 3 0 0 1 0 0 1 0 0 1 0 0 O u t : A g - C u R e s i d u e 91 2 7 . 5 1 . 5 % 1 4 2 9 1 0 0 8 . 0 3 1 0 0 S b S o l u t i o n 8 . 1 7 0 g / 1 8 1 . 9 7 D i s c a r d A n o l y t e 0 . 9 1 0 g / 1 1 0 . 0 0 * R e f e r e n c e : B a r r ( 1 9 7 3 ) C h a p t e r 2. E x p e r i m e n t a l 22 2.1 M a t e r i a l s 2.1.1 T e t r a h e d r i t e C o n c e n t r a t e T e t r a h e d r i t e c o n c e n t r a t e w a s r e c e i v e d f r o m t h e S u n s h i n e M i n i n g C o . , S u n s h i n e , I d a h o . T h e m a t e r i a l w a s p a s s e d t h r o u g h a n 8 - m e s h s c r e e n t o b r e a k u p t h e l u m p s , m i x e d a n d b a g g e d . T h e c o n c e n t r a t e c o n t a i n e d a p p r o x i m a t e l y 7.5% m o i s t u r e a n d w a s u s e d w e t . X - r a y d i f f r a c t o m e t e r r e s u l t s ( s h o w n i n A p p e n d i x B ) i n d i c a t e d t h e p r e s e n c e o f t e t r a h e d r i t e , a r g e n t i a n t e t r a h e d r i t e , c h a l c o p y r i t e , p y r i t e , m a r c a s i t e a n d g a l e n a i n t h e c o n c e n t r a t e . A d d i t i o n a l p h a s e s w e r e u n d o u b t e d l y p r e s e n t a s r e p r e s e n t e d b y t h e u n a s s i g n e d l i n e s , b u t t h e l a r g e t o t a l n u m b e r o f l i n e s m a d e t h e i r d e s i g n a t i o n d i f f i c u l t . X - r a y f l u o r o m e t r y i n d i c a t e d t h e p r e s e n c e o f a n t i m o n y , c o p p e r , s i l v e r , a r s e n i c , z i n c a n d l e a d ( o n l y e l e m e n t s w i t h a n a t o m i c n u m b e r g r e a t e r t h a n 22 w e r e d e t e c t e d b y t h e i n s t r u m e n t u s e d ) . A p a r t i a l c h e m i c a l a n a l y s i s o f t h e c o n c e n t r a t e i s s h o w n i n T a b l e 2-1. T a b l e 2-2 s h o w s w e t s c r e e n i n g r e s u l t s w i t h a p a r t i a l c h e m i c a l a n a l y s i s o f e a c h f r a c t i o n . A n t i m o n y w a s T a b l e 2-1: C h e m i c a l A n a l y s i s of Sunshine C o n c e n t r a t e (Dry) % Cu 26.0 Fe 14 .6 Sb 13.1 S 29.1 As 1. 58 Zn 1. 67 Mn 0.19 Na 0.00 Ag 3.6* * A n a l y s i s done by t h i r d y e a r M e t a l l u r g y l a b s t u d e n t s . T a b l e 2 - 2 : W e t S c r e e n i n g R e s u l t s 24 F r a c t i o n % R e t a i n e d ( M e s h s i z e ) + 1 0 0 2 . 0 - 1 0 0 + 1 4 0 5 . 7 - 1 4 0 + 2 0 0 1 1 . 3 - 2 0 0 + 2 7 0 1 3 . 6 - 2 7 0 + 4 0 0 1 1 . 5 - 4 0 0 5 2 . 7 S c r e e n L o s s 3 . 2 W e i g h t e d M e a n ( 9 6 . 8 % ) A n a l y s i s S b C u (%) F e 1 1 . 5 2 0 . 6 1 7 . 1 1 1 . 1 2 0 . 8 1 9 . 1 1 0 . 6 22 . 5 1 8 . 8 1 0 . 2 2 4 . 2 1 7 . 3 1 4 . 0 2 5 . 2 2 0 . 4 1 3 . 6 2 7 . 8 1 3 . 4 1 2 . 6 2 5 . 8 1 5 . 8 25 s l i g h t l y m o r e c o n c e n t r a t e d i n t h e f i n e f r a c t i o n s . A m o u n t e d a n d p o l i s h e d s a m p l e o f c o n c e n t r a t e w a s s t u d i e d u s i n g t h e x - r a y e n e r g y a n a l y s e r o f a s c a n n i n g e l e c t r o n m i c r o s c o p e ( S E M ) . T h e t e t r a h e d r i t e p h a s e w a s f o u n d t o c o n t a i n i r o n , s i l v e r , z i n c a n d a r s e n i c a s w e l l a s c o p p e r , a n t i m o n y a n d s u l p h u r . T h e c o m m o n l y u s e d s u l p h u r a n d l e a d e n e r g y d i s p e r s e d p e a k s v i r t u a l l y o v e r l a p , s o s m a l l q u a n t i t i e s o f l e a d i n t e t r a h e d r i t e w o u l d b e u n d e t e c t a b l e b e c a u s e o f t h e l a r g e s u l p h u r c o n t e n t . H o w e v e r , p a r t i c l e s c o n t a i n i n g o n l y l e a d a n d s u l p h u r ( g a l e n a ) w e r e f o u n d , a s w e l l a s p a r t i c l e s c o n f o r m i n g w i t h t h e p h a s e s d e t e r m i n e d i n t h e d i f f T a c t o m e t e r s t u d y . P a r t i c l e s c o n t a i n i n g s i l i c a , a n d i r o n , c o p p e r a n d m a n g a n e s e o x i d e s w e r e a l s o f o u n d . T h e S E M x - r a y a n a l y s e r c a n d e t e c t e l e m e n t s w i t h a n a t o m i c n u m b e r g r e a t e r t h a n 9 . B a s e d o n t h e c h e m i c a l a n d m i n e r a l o g i c a l a n a l y s e s d o n e , t h e c o n c e n t r a t e c a n b e s t b e d e s c r i b e d a s ( C u 9 - 7 , F e 0 < 5 , Z n 0 i 8 , A g 1 0 ) ( S b 3 > 4 A s 0 6 ) S 1 3 + 3 . 0 C u F e S + 4 . 6 F e S . T h e t e t r a h e d r i t e c o m p o s i t i o n i n d i c a t e d , ( C u g Q A g ^ ) ( F e 0 5 f Z n 0 g , C u * 0 7 ) c o n f o r m s w i t h t h e o b s e r v e d c o m p o s i t i o n s o f n a t u r a l t e t r a h e d r i t e s ( S e c t i o n 1 . 2 ) . T h e c o n c e n t r a t e c o m p o s i t i o n c a l c u l a t i o n i s s h o w n i n A p p e n d i x C . A s a m p l e o f t h e ' c o n c e n t r a t e w a s l e a c h e d w i t h 1% H C 1 o v e r n i g h t i n a s e a l e d a g i t a t e d f l a s k a t r o o m t e m p e r a t u r e . A s o l u t i o n a n a l y s i s b y a t o m i c a b s o r p t i o n i n d i c a t e d t h a t 10% o f t h e c o n c e n t r a t e ' s i r o n a n d 1% o f i t s c o p p e r h a d b e e n e x t r a c t e d . I r o n a n d c o p p e r d i s s o l v e d u n d e r t h e s e c o n d i t i o n s w i l l h a v e b e e n 26 p r e s e n t as o x i d e s or s a l t s , but not as s u l p h i d e s . 2.1.2 Reagents Reagent grade sodium h y d r o x i d e and sodium s u l p h i d e were used i n the l e a c h i n g s t u d i e s . D e i o n i z e d water was used t h r o u g h o u t . A 100 ml s o l u t i o n w i t h 24.07 g of Na 2S'9H 20 (1.002 M) was made up under a n a e r o b i c c o n d i t i o n s . A n a l y s i s of the s u l p h u r s p e c i e s gave 0.945 M S 2", 0.041 M SO 2 " , 0.024 M p o l y s u l p h i d e s u l p h u r (S° , ) and no S O 2 ': 1.010 M t o t a l s u l D h u r . ( A ^ x-1 2 3 s u l p h a t e a n a l y s i s was not d o n e . ) j s i m i l a r s o l u t i o n s were a s s a y e d f o r t h e i r c a u s t i c c o n t e n t - t h e s e cave 0.019, 0.026, and 0.030 moles of c a u s t i c per mole s u l p h i d e . 2.2 L e a c h i n g A p p a r a t u s The l e a c h v e s s e l was a round 150 ml pyrex f l a s k w i t h a f l a t b ottom. The f l a s k was s e a l e d w i t h a rubber bung t h r o u g h which a s t i r r e r s h a f t p a s s e d e n c a s e d i n a 5 cm s e c t i o n of g l a s s t u b i n g . The s t i r r e r was a t r i a n g u l a r s e c t i o n of T e f l o n , a p p r o x i m a t e l y 1 cm per s i d e , 2 cm l o n g . T h i s s t i r r e r was easy t o i n s e r t i n t o the n a r r o w - n e c k e d f l a s k s and gave good m i x i n g a t 1400 rpm, t h e f u l l speed of the Eberb a c h L a b - S t i r motors used. These motors were u n r e l i a b l e when t h r o t t l e d t o lower speeds and c o n v e n t i o n a l s t i r r e r s were too v i o l e n t a t 1400 rpm. 27 T h e . l e a c h t e m p e r a t u r e was m a i n t a i n e d by a v i o l e n t l y b o i l i n g steam b a t h e q u i p p e d w i t h an a u t o m a t i c water l e v e l c o n t r o l s e t on a l a r g e L i n d b e r g h o t p l a t e . Four l e a c h i n g e x p e r i m e n t s c o u l d be accomodated s i m u l t a n e o u s l y as shown i n F i g u r e 2-1. Each f l a s k was clamped immersed t o the neck w i t h the c o n c e n t r i c steam b a t h r i n g s p l a c e d t o keep the exposed b o i l i n g water s u r f a c e a r e a t o a mi n imum. The t e m p e r a t u r e of the l e a c h m i x t u r e was measured t o be 99.6°C. T h i s s t e a d y s t a t e v a l u e was a c h i e v e d f i v e m i n u t e s a f t e r i mmersion of the f l a s k i n t o the b a t h . 2.3 L e a c h P r o c e d u r e . Four, l e a c h i n g e x p e r i m e n t s were done s i m u l t a n e o u s l y . The i n i t i a l s o l u t i o n s were made up by d i s s o l v i n g s o l i d r e a g e n t s or by d i l u t i n g s t r o n g e r s o l u t i o n s . Care was • t a k e n t o a v o i d s u l p h i d e o x i d a t i o n . The sodium s u l p h i d e was d i s s o l v e d i n d e a e r a t e d water i n s e a l e d f l a s k s under n i t r o g e n and o n l y s m a l l w e l l - s e a l e d b o t t l e s of s o l i d r e a g e n t were used t o m i n i m i z e o x i d a t i o n d u r i n g s t o r a g e . Wet c o n c e n t r a t e was weighed i n t o the l e a c h i n g f l a s k s and p r e - m i x e d s o l u t i o n s were added by p i p e t t e w i t h a sample of each r e t a i n e d f o r a n a l y s i s . The bungs and s t i r r e r s were i n s e r t e d , the f l a s k s clamped i n t o t h e b o i l i n g water b a t h , and the a g i t a t i o n begun. The l e a c h i n g t i m e was 24 h o u r s (± 15 m i n u t e s ) . 28 F i g u r e 2 - 1 T h e L e a c h i n g A p p a r a t u s 29 The l e a c h t e m p e r a t u r e of 100°C conformed w i t h the i n d u s t r i a l p r a c t i c e of the Sunshine M i n i n g Co. l e a c h p l a n t , and was easy t o m a i n t a i n w i t h a b o i l i n g water b a t h . E x c e s s c o n c e n t r a t e was used t o a c h i e v e c h e m i c a l e q u i l i b r i u m . An antimony e x t r a c t i o n of l e s s than 50% a t e q u i l i b r i u m was the t a r g e t . T w e n t y - f o u r h o u r s was c o n s i d e r e d t o be an adequate time f o r the l e a c h t o e q u i l i b r a t e . A f t e r l e a c h i n g , the f l a s k s were removed from the b a t h and a 15 ml s l u r r y sample of each was t a k e n and p r e s s u r e f i l t e r e d under t h r o u g h a f i n e g l a s s f r i t . The b u l k of each p r o d u c t s l u r r y was d e w a t e r e d and water washed on a Buchner f u n n e l u s i n g p r e - w e i g h e d f i n e f i l t e r paper (Whatman No. 4 2 ) . The Buchner f i l t r a t e s were made up t o 500 ml and r e t a i n e d f o r a n a l y s i s a l o n g w i t h t h e p r e s s u r e f i l t r a t e s . The s o l u t i o n a n a l y s e s were done i m m e d i a t e l y . The l e a c h s o l i d s were d r i e d , weighed and r e t a i n e d . B e f o r e p r e s s u r e f i l t r a t i o n , the f r i t s were p r e - f l u s h e d w i t h N^. I f t h i s was not done, the f i r s t s o l u t i o n t h r o u g h would show the c h a r a c t e r i s t i c y e l l o w c o l o u r of p o l y s u l p h i d e . The i n i t i a l l e a c h s o l u t i o n s were a n a l y s e d f o r S 2*, s2°3 2 and S 0 3 2 " . The f i n a l l e a c h s o l u t i o n s were a n a l y s e d f o r S 2", S ° s o 2", SO 2", OH', Sb and As. The Buchner f i l t r a t e s x~* 1 ' 2 3 3 were a n a l y s e d f o r Sb. 30 2 . 4 S u l p h i d e O x i d a t i o n T o i n v e s t i g a t e s u l p h i d e o x i d a t i o n , 8 5 m l p e r m i n u t e o f a i r w e r e b u b b l i n g t h r o u g h 5 0 0 m l o f 0 . 8 5 5 M N a 2 S a f t e r p r e t r e a t m e n t w i t h a 2 M N a O H s o l u t i o n . B o t h s o l u t i o n f l a s k s w e r e i m m e r s e d i n a b o i l i n g w a t e r b a t h . O v e r t w o h o u r s o f a e r a t i o n n o s u l p h i d e o x i d a t i o n w a s o b s e r v e d i n s a m p l e s t a k e n a n d a n a l y s e d f o r S 2 " , S 2 0 3 2 " a n d S ° . ( T h i s r e s u l t w a s s u r p r i s i n g a s s u l p h i d e w a s e x p e c t e d t o b e m o r e r e a c t i v e . ) 2 . 5 E v a p o r a t i o n "~ E v a p o r a t i o n w a s c o n s i d e r e d t o b e a p r o b l e m b e c a u s e o f t h e h i g h v a p o u r p r e s s u r e o f t h e w a t e r i n t h e l e a c h s o l u t i o n s a t 1 0 0 ° C . A l t h o u g h t h e f l a s k s w e r e w e l l s e a l e d , t h e l e a c h t i m e w a s l o n g . E v a p o r a t i o n w a s m e a s u r e d b y w e i g h i n g t h e l e a c h f l a s k s c o m p l e t e w i t h t h e i r b u n g s a n d s t i r r e r s i m m e d i a t e l y b e f o r e a n d a f t e r l e a c h i n g e x p e r i m e n t s . O f 1 2 m e a s u r e m e n t s t a k e n , t h e a v e r a g e w e i g h t c h a n g e o f 1 1 w a s - 0 . 3 2 g . ( 0 . 2 % e v a p o r a t i o n b a s e d o n 1 3 0 m l o f l e a c h s o l u t i o n w i t h 1 g o f w a t e r p e r m l o f s o l u t i o n . ) t h e 1 2 t h . w a s - 4 . 9 6 g ( 3 . 8 % e v a p o r a t i o n ) . E v a p o r a t i o n a p p e a r e d t o b e a p r o b l e m o n l y i n s p e c i f i c e x p e r i m e n t s r a t h e r t h a n a g e n e r a l p h e n o m e n o n . 31 C h a p t e r 3 . A n a l y t i c a l C h e m i s t r y 3 . 1 A u t o m a t i c T i t r a t i o n T h e d e t e r m i n a t i o n o f c a u s t i c a n d s u l p h u r s p e c i e s ( S 2 ~ , S 0 , , S ~ 0 2 ~ a n d S O - 2 " ) i n t h e l e a c h s o l u t i o n s a m p l e s w a s d o n e x - 1 z j j b y a u t o m a t i c t i t r a t i o n u s i n g a R a d i o m e t e r R T S 8 2 2 t i t r a t i o n s y s t e m e q u i p p e d w i t h i n d i c a t o r a n d r e f e r e n c e e l e c t r o d e s . T h e f i r s t d e r i v a t i v e o f t h e i n d i c a t o r - r e f e r e n c e p o t e n t i a l d i f f e r e n c e w i t ' h r e s p e c t t o t i m e w a s a u t o m a t i c a l l y p l o t t e d a s a f u n c t i o n o f t h e t i t r a t i o n v o l u m e . T h i s d e r i v a t i v e i s e f f e c t i v e l y p o t e n t i a l w i t h r e s p e c t t o v o l u m e , A E / 4 V , s i n c e t h e t i t r a t i o n s w e r e d o n e a t a c o n s t a n t t i t r a n t a d d i t i o n r a t e . T h e e n d p o i n t o f a t i t r a t i o n a s d e f i n e d b y t h e m a x i m u m v a l u e o f A E / A V i s i d e n t i c a l w i t h t h e t r u e s t o i c h i o m e t r i c e q u i v a l e n c e p o i n t o n l y i f t h e t i t r a t i o n c u r v e ( p o t e n t i a l a s a f u n c t i o n o f v o l u m e ) i s s y m m e t r i c a l a b o u t t h e e q u i v a l e n c e p o i n t ( B a s s e t t e t a l . , 1 9 7 8 ) . A s y m m e t r i c t i t r a t i o n c u r v e i s p r o d u c e d w h e n t h e i n d i c a t o r e l e c t r o d e i s r e v e r s i b l e a n d w h e n t h e r e a r e a n e q u a l n u m b e r o f t i t r a n t r e a g e n t a n d r e a c t a n t s p e c i e s i n t h e e q u i v a l e n c e e q u a t i o n . T h e p H t i t r a t i o n c u r v e f o r e q u a t i o n 3 - 1 w o u l d b e s y m m e t r i c ; t h e p o t e n t i a l t i t r a t i o n c u r v e f o r E q u a t i o n 3 - 2 w o u l d n o t . 32 H* + OH" = H 20 ... (3-1) 5 F e 2 * + MhO4- + 8H* = 5 F e 3 * + Mn 2 * + 4H 20 . . . ( 3 - 2 ) ' The t i t r a t i o n e r r o r , the d i f f e r e n c e between the end p o i n t and the e q u i v a l e n c e p o i n t , i s s m a l l when the p o t e n t i a l change at the e q u i v a l e n c e p o i n t i s l a r g e ( B a s s e t t e f a l . , 1978). Most s t a n d a r d a n a l y t i c a l t i t r a t i o n s have a l a r g e e q u i v a l e n c e p o i n t p o t e n t i a l .changes. A t i t r a t i o n e r r o r can a l s o be g e n e r a t e d i f the s o l u t i o n c o n t a i n s a s p e c i e s w h i c h c h e m i c a l l y i n t e r f e r e s w i t h the t i t r a n t or r e a c t a n t and i n d o i n g so, d i s t o r t s the t i t r a t i o n c u r v e symmetry.. T h i s e r r o r i s g r e a t e s t when the e q u i l i b r i u m c o n s t a n t f o r the r e a c t i o n between the r e a c t a n t (or the t i t r a n t ) and an i n t e r f e r i n g s p e c i e s a p p r o a c h e s the c o n s t a n t f o r the r e a c t i o n between the t i t r a n t and the r e a c t a n t . I f t h e i n t e r f e r e n c e r e a c t i o n i s w i t h the t i t r a n t , a second end p o i n t may be seen. In a c i d - b a s e pH t i t r a t i o n s an a c i d s t r e n g t h d i f f e r e n c e of s i x o r d e r s of magnitude ( A pKa = 6) i s r e q u i r e d f o r the c l e a n s e p a r a t i o n of two end p o i n t s ( B a s s e t t et a1. , 1978). The co- t i t r a t i o n of OH" (pKa =.14.0) and S 2 ' (pKa = 12.9) w i t h a c i d shows o n l y one end p o i n t . In a l l c a s e s the magnitude of t h i s t y p e of t i t r a t i o n e r r o r depends h e a v i l y on the r e l a t i v e q u a n t i t i e s of the s p e c i e s i n v o l v e d . As w e l l as d e p e n d i n g on s o l u t i o n c h e m i s t r y f a c t o r s , the a c c u r a c y of an a u t o m a t i c a l l y t i t r a t e d end p o i n t a l s o depends on the i n d i c a t o r e l e c t r o d e g i v i n g the c o r r e c t p o t e n t i a l f o r the t i t r a n t volume d i s p e n s e d . The c o n t e n t s of the t i t r a t i o n v e s s e l have t o be w e l l mixed and the e l e c t r o d e must be i n e q u i l i b r i u m 33 w i t h t h e s o l u t i o n . F o r t h e a n a l y t i c a l t i t r a t i o n s p e r f o r m e d t h e m o s t p o w e r f u l s t i r r e r a v a i l a b l e w a s u s e d . . I n a t e s t o f t h e s y s t e m a d r o p o f d y e w a s a d d e d t o t h e t i t r a t i o n v e s s e l a n d w a s i n s t a n t l y d i s p e r s e d . A t t h e e n d p o i n t o f e a c h t i t r a t i o n a s l o w r a t e w a s u s e d , 0 . 0 5 - 0 . 2 0 m l p e r m i n u t e , t o g i v e t h e e l e c t r o d e t i m e t o a c h i e v e e q u i l i b r i u m . H o w e v e r , i t i s u n l i k e l y t h a t e q u i l i b r i u m w a s e v e r c o m p l e t e l y a c h i e v e d d u e t o t h e r a p i d c h a n g e s i n p o t e n t i a l a t e n d p o i n t s . B e c a u s e o f t h e s l o w r a t e s u s e d , t h e v o l u m e e r r o r s w e r e n o t e x p e c t e d t o b e l a r g e . . T h e t i t r a t i o n a n d f i r s t d e r i v a t i v e c u r v e s f o r t h e t i t r a t i o n o f s o d i u m s u l p h i d e w i t h H C 1 a r e s h o w n i n F i g u r e 3 - 1 . 3 . 2 S o l u b l e S u l p h u r S p e c i e s A n a l y s i s 3 . 2 . 1 S u l p h i d e , P o l y s u l p h i d e S u l p h u r , T h i o s u l p h a t e A n d S u l p h i t e D e t e r m i n a t i o n . T h e d e t e r m i n a t i o n o f S 2 ' , S ° , , S„ 0 2 " a n d S O , 2 ' w a s d o n e x - 1 2 3 3 b y t i t r a t i o n w i t h H g C l 2 s o l u t i o n u s i n g a R a d i o m e t e r R T S 8 2 2 t i t r a t i o n s y s t e m a n d O r i o n A g / S s p e c i f i c i o n a n d A g C l / C l d o u b l e j u n c t i o n r e f e r e n c e e l e c t r o d e s . T h e m e t h o d u s e d w a s d e v e l o p e d f o r t h e a n a l y s i s o f s u l p h u r s p e c i e s i n s u l p h i d e p u l p i n g l i q u o r s ( P a p p , 1 9 7 1 ) . T h e a c t i v e e l e m e n t o f a A g / S s p e c i f i c i o n " e l e c t r o d e i s a 34 F i g u r e 3-1 The P o t e n t i a l and F i r s t D e r i v a t i v e Curves f o r the T i t r a t i o n of Sodium Sulph i d e w i t h H y d r o c h l o r i c A c i d 35 s o l i d Ag^S membrane which shows a N e r s t i a n response t o the a c t i v i t i e s of Ag* and S 2~ over the a c t i v i t y range of of 10° t o 10" 7 M i n each. W i t h m e r c u r i c i o n i n s o l u t i o n a HgS f i l m forms on the membrane which must be o c c a s i o n a l l y removed. In s u l p h i d e s o l u t i o n the s o l u t i o n j u n c t i o n o f a normal A g C l / C l r e f e r e n c e e l e c t r o d e would p l u g w i t h p r e c i p i t a t e d Ag 2S. To a v o i d t h i s , a doubl e j u n c t i o n e l e c t r o d e i s used w i t h an o u t e r f i l l i n g s o l u t i o n of 10% KNC"v> made up t o pH 12 w i t h KOH. When a m i x t u r e of s u l p h u r a n i o n s : S 2"; S 2";S„0 2"; and x ' 2 3 SO^ 2", i s t i t r a t e d w i t h H g C l 2 , S 2" r e a c t s f i r s t ( E q u a t i o n 3-3), and the s u l p h i d e of S 2" next ( E q u a t i o n 3-4). S 2" + Hg 2 + = HgS ... (3-3) S 2" + Hg !* = HgS + (x-l)S° ...(3-4) Though i t i s p o s s i b l e t o d e t e c t end p o i n t s f o r f r e e s u l p h i d e and f o r each p o l y s u l p h i d e ' s p e c i e s (x = 2,3,...) the t o t a l s u l p h i d e i s b e s t d e t e r m i n e d on t h e . b a s i s of . the f i n a l end p o i n t of the s e r i e s which i s unambiguous. W i t h o u t e x t r a c a u s t i c i n s o l u t i o n the S 2" i o n ( t h e o n l y s u l p h u r i o n t h a t the Ag/S e l e c t r o d e responds t o ) i s not s t a b l e enough t o be d e t e r m i n e d i n d e p e n d e n t l y of S 2 0 3 2 " and SO^ 2". The s o l u t i o n must be made up t o 0.1-1.0 M NaOH. A f t e r the s u l p h i d e end p o i n t the t i t r a t i o n i s stopped and the e x c e s s c a u s t i c i s n e u t r a l i z e d (pH 7.0-7.5) w i t h 40% a c e t i c a c i d . The t i t r a t i o n i s r e s t a r t e d and S 20 2 ~ and SO^ 2" are d e t e r m i n e d t o g e t h e r a t the next end p o i n t ( E q u a t i o n s 3-5 and 3- 6) . S2'°3 2" + H g 2 * = H (3 S?°3 ...(3-5) 36 S 0 3 7 ' + H g 2 * = H g S 0 3 ...(3-6) A l t h o u g h S 2 ~ d o e s n o t a p p e a r t n t h e s e r e a c t i o n s , t h e e l e c t r o d e d e t e c t s t h e e x c e s s H g 2 * p r e s e n t a f t e r t h e e n d p o i n t b y t h e c o u p l i n g o f H g 2 + a n d S 2 ~ i n E q u a t i o n 3 - 1 . S 2 ° 3 2 ~ * s d e t e r m i n e d b y m a s k i n g ' t h e S O ^ 2 " w i t h f o r m a l d e h y d e ( E q u a t i o n 3 - 7 ) . HCHO + S 0 3 2 " + I T = C H 2 O H SO " ...(3-7) P o l y s u l p h i d e c a n b e o x i d i z e d t o ^ 0 2 ~ ^ m i l d h e a t i n g w i t h N 3 2 ^ 3 m ^ n u t e s ( E q u a t i o n 3 - 8 ) . S 2 " + ( x - l ) S O 2 - = S 2 - + ( x - l ) S 0 2 " . . . ( 3 - 8 ) x 3 2 3 T h e e x c e s s S O ^ 2 " i s m a s k e d w i t h f o r m a l d e h y d e a n d t h e i n c r e m e n t a l S 0 2 ~ i s r e p o r t e d a s p o l y s u l p h i d e s u l p h u r , S ° . A t o t a l 2 3 x - 1 s u l p h u r s p e c i e s a n a l y s i s r e q u i r e s t h r e e s e t s o f d e t e r m i n a t i o n s : S 2 ' a n d S 2 0 3 2 - + SC>3 2 ' ; S 2 * a n d S 2 0 3 2 " ( S 0 3 2 ' b y d i f f e r e n c e ) ; a n d S 2 " a n d S O a f t e r N a S O , t r e a t m e n t ( S ° b y d i f f e r e n c e ) . T h e a n a l y t i c a l p r o c e d u r e f o r a 1 M N a S s o l u t i o n c o n t a i n i n g s m a l l c o n c e n t r a t i o n s o f t h e o t h e r s u l p h u r s p e c i e s i s a s f o l l o w s : A 5 m l s a m p l e i s t a k e n a n d m a d e u p t o 1 0 0 m l . 5 m l a l i q u o t s o f t h e d i l u t e d s o l u t i o n a r e p i p e t t e d i n t o t i t r a t i o n b e a k e r s w i t h 2 m l o f 1 0 M N a O H , a n d m a d e u p t o 6 0 m l w i t h d e a e r a t e d w a t e r . T h e t i t r a t i o n s a r e d o n e i m m e d i a t e l y . T w o m i c r o s p a t u l a s o f r e a g e n t g r a d e N a 2 S 0 3 a r e a d d e d t o t h e b e a k e r s a n d t h e b e a k e r s a r e w a r m e d o n a h o t p l a t e o v e r t w o a s b e s t o s p a d s f o r 1 5 m i n u t e s t o o x i d i z e t h e p o l y s u l p h i d e . T h e H g C l 2 s o l u t i o n u s e d i n t h e a n a l y s e s w a s 0 . 0 5 M w h i c h w o u l d g i v e a S 2 " t i t r a t i o n o f 5 m l f o r t h e s a m p l e d e s c r i b e d . I n p r a c t i c e t h e S 2 " e n d p o i n t p e a k s o f t h e d e r i v a t i v e p l o t s w e r e l a r g e , s h a r p a n d e a s y t o i n t e r p r e t . T h e 3*' a n < ^ ^ 2 ^ 3 2 " 37 + S 0 ^ 2 ~ p e a k s w e r e s m a l l e r a n d b r o a d e r b u t s t i l l e a s y t o i n t e r p r e t i f t h e v o l u m e s e p a r a t i n g t h e m f r o m t h e S 2 " p e a k w a s g r e a t e r t h a n 0 . 2 m l . W i t h s m a l l e r d i f f e r e n c e s t h e p e a k s t r u c t u r e s w e r e o f t e n c o m p l e x s u g g e s t i n g i n t e r f e r e n c e e f f e c t s . S m a l l q u a n t i t i e s o f s u l p h i d e w e r e a l w a y s o x i d i z e d i n t h e N a SO t r e a t m e n t . A r e p r o d u c i b l e e n d p o i n t , r e p r e s e n t i n g a v e r y s m a l l t i t r a n t v o l u m e , w a s o b s e r v e d i n s o m e s o l u t i o n s i m m e d i a t e l y a f t e r t h e p H s h i f t . K n o w n a d d i t i o n s s h o w e d t h a t t h i s p e a k w a s u n a f f e c t e d b y S ^ ^ 2 " o r S O ^ 2 ~ . T h e p r i m e s u s p e c t i s c o n s i d e r e d t o b e p o l y t h i o n a t e , S XC k , 2 ~ w h i c h h a s c h e m i s t r y s i m i l a r t o S 2 " a n d S 2 0 3 2 " ( B l a u s i u s e t a l . , 1 9 6 8 ) , b u t t h i s w a s n o t c o n f i r m e d . T h e t i t r a n t v o l u m e c o n s u m e d b y t h i s s p e c i e s w a s s u b t r a c t e d w h e r e r e l e v a n t . 3 . 2 . 2 T h e E f f e c t O f A n t i m o n y ( 1 1 1 ) On T h e S u l p h i d e D e t e r m i n a t i o n T o t h e a u t h o r ' s k n o w l e d g e , a H g C l 2 t i t r a t i o n m e t h o d f o r t h e d e t e r m i n a t i o n o f t h e s u l p h u r s p e c i e s i n a n t i m o n y - c o n t a i n i n g s o l u t i o n s h a s n o t b e e n r e p o r t e d . V a r i o u s q u a n t i t i e s o f t e c h n i c a l g r a d e s t i b n i t e w e r e d i s s o l v e d i n N a 2 S s o l u t i o n . S u l p h i d e w a s d e t e r m i n e d b y t i t r a t i o n : a n t i m o n y b y a t o m i c a b s o r p t i o n a n a l y s i s . T h e m e a s u r e d r a t i o o f i n c r e m e n t a l S 2 " t o S b w a s 1 . 6 0 ± 0 . 1 3 v e r s u s t h e s t o i c h i o m e t r i c r a t i o o f 1 . 5 0 ( T a b l e 3 - 1 ) . T h e d e t e r m i n a t i o n o f S b ( 1 1 1 ) - c o m p l e x e d s u l p h i d e w a s c o n s i d e r e d t o b e q u a n t i t a t i v e . T a b l e 3 - 1 : S u l p h i d e D e t e r m i n a t i o n i n A n t i m o n y ( 1 1 1 ) S o l u t i o n S b S A d d e d 2 3 ( g / l O O m l ) S b C a l c . ( g / D S b D e t e r . ( g / D s 2 - (M) A S 2 - / A S b ( m o l e / m o l e ) 0 0 1.0*1 1.08J . 0 9 0 . 57 4 . 0 9 4 . 1 6 1 . 1 5 1 . 7 8 1 . 0 6 7 . 6 0 7 . 4 4 1 . 18 1 . 52 1 . 5 3 1 1 . 0 1 0 . 8 1 . 2 1 1 . 4 3 2 . 0 0 1 4 . 3 1 4 . 2 1.26 1 . 5 3 2 . 6 2 1 8 . 8 1 8 . 6 1 . 34 1 . 64 3 . 1 2 2 2 . 4 22 . 1 1 . 4 0 M e a n 1 . 7 2 = 1.60+0.13 ( 9 5 % C . L . 39 3.2.3 The E f f e c t Of Antimony(V) On The S u l p h i d e And P o l y s u l p h i d e D e t e r m i n a t i o n s Sodium t h i o a n t i m o n a t e , Na 3 SbS^. 9H ^0, was made by a p r o c e d u r e , o u t l i n e d by Sevryukov and M u r t i (1966). V a r i o u s q u a n t i t i e s of t h i s s a l t were d i s s o l v e d i n d e a e r a t e d water and S 2~ and s° x_i were d e t e r m i n e d by HgCl t i t r a t i o n w h i l e Sb was d e t e r m i n e d by a t o m i c a b s o r p t i o n a n a l y s i s . The r e s u l t s a r e shown i n T a b l e 3-2. • A p p r o x i m a t e l y f o u r s u l p h i d e s per antimony were d e t e r m i n e d i n the s u l p h i d e a n a l y s i s i n d i c a t i n g a q u a n t i t a t i v e a n a l y s i s f o r Sb(V)-complexed s u l p h i d e . Sevryukov and M u r t i (1966) r e p o r t e d t h a t the h e a t i n g of S b ( V ) - S 2 " s o l u t i o n s w i t h added N a 2 S 0 3 a f f e c t e d a r e d u c t i o n of the antimony ( E q u a t i o n 3-8). S b S 4 3 " + S 0 3 2 - = S b S 3 3 ' . + S 2 0 3 2 ' ...(3-8) T h i s would produce an a p p a r e n t S° , a n a l y s i s and a drop i n the S 2" a n a l y s i s e q u i v a l e n t t o the amount of Sb(V) p r e s e n t . The r e s u l t s show t h a t the Sb t o S 2~ r a t i o dropped a f t e r the Na 2SO^ tr e a t m e n t but d i d not r e a c h t h r e e . The r e d u c t i o n r e a c t i o n c o n d i t i o n s were a p p a r e n t l y i n a d e q u a t e t o complete E q u a t i o n 3-8. The i n c r e m e n t a l S „0_ 2" (S° . ) a c c o u n t e d f o r o n l y about o n e - h a l f 2 3 x - 1 of the drop i n s u l p h i d e . A drop i n S 2" a s s a y a f t e r Na 2SO^ t r e a t m e n t c o u p l e d w i t h a p o s i t i v e S° x - 1 d e t e r m i n a t i o n i s the o n l y i n d i c a t o r of Sb(V) i n s u l p h i d e s o l u t i o n t h a t the a u t h o r has found. However, the Table 3-2: Sulphide and Polysulphide Sulphur Determinations In Antimony (V) Solution Sulphide Analysis Polysulphide Sulphur Analysis_ N a . S b S , - 9 J L 0 L H I Sb c a l c Sb d e t e r . S ' s 2 7 s b s 2 7 s b A S 2 / S b * S ° . / S b x - 1 2.19 4 .08 8.48 16. 50 ( g / 1 ) ( g / D (M) (mole/mole) (mole/mole) (mole /mo le ) ( m o l e / n 5.54 5.20 0.173 4.05 3.35 0.70 0.35 10.3 9.58 0.328 4.17 3. 51 0.66 0.36 21.5 19.9 0.676 4.15 3.56 0.59 ^ 0.34 41.8 38.9 1.33 4.17 3.13 1.04 0.54 * k S 2~ i s the difference between the sulphide analysis and the sulphide analysis after treatment with fta^i®?. 41 r e d u c t i o n p r o c e d u r e used appears o n l y to be an i n d i c a t o r of S b ( V ) . A p r o p e r a n a l y s i s would have t o i n v o l v e a b o i l i n g t r e a t m e n t w i t h Na,, SO 3 under an i n e r t gas cov e r t o p r e v e n t S 2" o x i d a t i o n . 3.3 The D e t e r m i n a t i o n Of S u l p h u r In S o l i d s The s u l p h u r c o n t e n t of the c o n c e n t r a t e and the l e a c h p r o d u c t s was d e t e r m i n e d g r a v i m e t r i c a l l y by the c o n v e r s i o n of s u l p h u r t o barium s u l p h a t e , BaSO^ (Young, 1971). 3.4 C a u s t i c D e t e r m i n a t i o n ; 1 — 1 —-• 3.4,1 C a u s t i c D e t e r m i n a t i o n In S u l p h i d e S o l u t i o n C a u s t i c was d e t e r m i n e d by t i t r a t i o n w i t h HC1 s o l u t i o n u s i n g a Radiometer RTS 822 t i t r a t i o n system and a C a n l a b c o m b i n a t i o n p H / r e f e r e n c e e l e c t r o d e . The t i t r a t i o n beaker was put under s u c t i o n t o ta k e away the H 2S found d u r i n g the d e t e r m i n a t i o n . W i t h c a u s t i c and s u l p h i d e i n s o l u t i o n , two end p o i n t s a re o b s e r v e d . OH" and S 2" t i t r a t e s i m u l t a n e o u s l y ( S e c t i o n 3.1) w i t h an end p o i n t a t pH 7.5 w h i l e HS" t i t r a t e s w i t h an end p o i n t at pH 4.5. P o l y s u l p h i d e t i t r a t e s as S 2" and i s observed t o decompose, but i t i s not c e r t a i n whether E q u a t i o n 3-9 or 3-10 d e s c r i b e s the t i t r a t i o n c h e m i s t r y . 42 S 2 " + H * = HS " = H S " + S ° . . . . ( 3 - 9 ) x x x - 1 • S * - + H * = S 2 " + S ° . + H * = H S " + S ° . . . ( 3 - 1 0 ) x x - 1 x - 1 S i n c e w e a k b a s e s , s u c h a s S 0 3 2 ~ , t e n d t o t i t r a t e w i t h H S " , t h e t i t r a n t v o l u m e d i f f e r e n c e b e t w e e n t h e t w o s u l p h i d e e n d p o i n t s ( S 2 " a n d H S " ) m a y n o t b e m e a n i n g f u l . C a u s t i c i s b e s t , d e t e r m i n e d b y t h e r e s u l t o f t h e f i r s t e n d p o i n t m i n u s t h e S 2 " d e t e r m i n a t i o n . T h e t i t r a t i o n s w e r e p e r f o r m e d b y p i p e t t i n g 1 o r 2 m l o f s a m p l e i n t o a t i t r a t i o n b e a k e r , d i l u t i n g t o 6 0 m l a n d . t i t r a t i n g w i t h 1 M - H C 1 . 3 . 4 . 2 T h e E f f e c t O f A n t i m o n y ( 1 1 1 ) On T h e C a u s t i c D e t e r m i n a t i o n T h e s o l u t i o n s c o n s i d e r e d i n S e c t i o n 3 . 3 . 2 w e r e t i t r a t e d w i t h H C 1 a s d e s c r i b e d i n t h e p r e v i o u s s e c t i o n . T h e r e s u l t s a r e g i v e n i n T a b l e 3 - 3 . A 2 : 1 S b ( I I l ) : S 2 " c o m p l e x a p p e a r e d t o b e p r e s e n t a t t h e f i r s t e n d p o i n t c o n s i s t e n t w i t h S b S 2 " o r S f c ^ S ^ 2 " . W i t h S b ( I I I ) i n s o l u t i o n , c a u s t i c i s d e t e r m i n e d b y t h e r e s u l t o f t h e f i r s t e n d p o i n t m i n u s t h e S 2 " d e t e r m i n a t i o n p l u s t w i c e t h e S b a s s a y . A f t e r t h e f i r s t e n d p o i n t t h e s o l u t i o n s d e v e l o p e d c o l o u r s v a r y i n g f r o m o r a n g e t o b l a c k - a n d S b ^ S ^ p r e c i p i t a t e d a f t e r t h e s e c o n d e n d p o i n t . T a b l e 3 - 3 : C a u s t i c A n a l y s i s i n A n t i m o n y ( I I I ) S o l u t i o n 43 S b 2 % ( g / 1 0 0 m l ) S b d e t e r . ( g / D I A S 2 " / S b * ( m o l e / m o l e ) • 1 s t . E . p . e ' q u i v . (M) I I A S 2 - / S b * * ( m o l e / m o l e ) I - I I ( m o l e / m o l e ) 0 0 1 . 1 4 1 1 . 1 0 • 1 . 1 2 j 0 . 57 4 . 1 6 1 . 7 8 1 . 1 2 - - 1 . 0 6 7 . 44 1 . 5 2 1 . 0 9 - 0 . 4 3 1 . 9 5 1 . 5 3 1 0 . 8 1 . 4 3 1 . 08 - 0 . 4 2 1 . 8 5 2 . 0 0 14 . 2 1 . 5 3 1 . 07 - 0 . 4 5 1 . 9 8 2 . 62 1 8 . 6 1 . 64 1 . 04 - 0 . 51 2 . 1 5 3 . 1 2 2 2 .1 1 . 7 8 1 . 03 - 0 . 50 2 . 2 2 m e a n .= 1 . 9 9 x 0 . 1 5 * t a k e n f r o m T a b l e 3 - 1 * * i \ S 2 - i s t h e e q u i v a l e n t d i f f e r e n c e b e t w e e n t h e f i r s t e n d p o i n t t i t r a t i o n o f t h e b l a n k s a n d t h e s a m p l e 44 3.4.3 The E f f e c t Of Antimony(V) On The C a u s t i c D e t e r m i n a t i o n The s o l u t i o n s of S e c t i o n 3.3 were t i t r a t e d w i t h HC1. The pH dropped i n s t a n t l y as the t i t r a t i o n was begun. No f r e e S 2~ i o n s appeared t o be p r e s e n t c o n s i s t e n t w i t h the Sb(V) complex, SbS^-3, i n s o l u t i o n . The s o l u t i o n s i m m e d i a t e l y t u r n e d orange and and S b 2 S 5 p r e c i p i t a t e d a f t e r the 'second' end p o i n t . 3.5 Atomic A b s o r p t i o n And Flame Emmission A n a l y s i s Copper, i r o n , antimony, z i n c , a r s e n i c and manganese were d e t e r m i n e d by atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y on a P e r k i n - Elmer 306 i n s t r u m e n t . Sodium was d e t e r m i n e d by flame emmission on the same s p e c t r o p h o t o m e t e r . For a l l the a n a l y s e s , s t a n d a r d s were made up t o app r o x i m a t e the c o m p o s i t i o n of the unknowns. For the c o n c e n t r a t e and l e a c h p r o d u c t a n a l y s e s two s e t s were used: one c o n t a i n i n g c o p p e r , i r o n and antimony, and the o t h e r c o n t a i n i n g z i n c , a r s e n i c , sodium and manganese i n a s t r o n g s o l u t i o n of the f i r s t t h r e e e l e m e n t s . T h i s p r o c e d u r e g r e a t l y reduced the time r e q u i r e d t o make up s t a n d a r d s w h i l e compensating f o r the flame m a t r i x e f f e c t s of the unknowns. The unknown and s t a n d a r d s o l u t i o n s were a l l made up i n 20% HC1 t o p r e v e n t antimony h y d r o l y s i s . Samples of the l e a c h s o l u t i o n s and the a n t i m o n y - a r s e n i c s t a n d a r d s were made up i n 0.2 M Na 2 S and 0.2 M NaOH. Care was ta k e n t o a v o i d m i x i n g t h i s Na~S w i t h the a c i d s u s u a l l y p r e s e n t 45 i n the b u r n e r head d r a i n r e s e r v o i r . F l e x i b i l i t y i n sample d i l u t i o n i s a v a i l a b l e i f the atomic a b s o r p t i o n burner head i s r o t a t e d t o change the flame p a t h l e n g t h . The l i n e a r p o r t i o n of each element's a b s o r p t i o n v e r s u s c o n c e n t r a t i o n c u r v e can be i n c r e a s e d by a p p r o x i m a t e l y 20 times by h a v i n g the burner normal t o the lamp beam l i n e r a t h e r than c o - l i n e a r w i t h i t . Fewer sample d i l u t i o n s are so r e q u i r e d . Chapter 4. 46 R e s u l t s and O b s e r v a t i o n s 4.1 L e a c h i n g E x p e r i m e n t s C o n s i d e r e d F o r t y - s e v e n e q u i l i b r i u m l e a c h i n g e x p e r i m e n t s were done i n t o t a l , but of t h e s e , o n l y the r e s u l t s of 28 a r e c o n s i d e r e d i n the f o l l o w i n g s e c t i o n s . A p r e l i m i n a r y group of 16 c o n t a i n e d too many i n c o n s i s t e n c i e s and the r e s u l t s of t h r e e subsequent e x p e r i m e n t s were c o n s i d e r e d t o be anomalous. Data from a l l 47 runs are shown i n Appendix D. 4.2 Antimony L e a c h i n g - E q u i l i b r i u m R e s u l t s 4.2.1 Antimony Leached In A l k a l i n e S u l p h i d e S o l u t i o n s F i g u r e s 4-1 t o 4-3 show the c o n c e n t r a t i o n of antimony l e a c h e d a f t e r 24 hours a t 100°C as a f u n c t i o n of the f i n a l Na 2S c o n c e n t r a t i o n . Four l e v e l s of i n i t i a l c a u s t i c c o n c e n t r a t i o n were i n v e s t i g a t e d : 0, 0.5, 1.0, and 2.0 M . Curves were not i n t e r p o l a t e d t h r o u g h the d a t a p o i n t s as the f i n a l NaOH c o n c e n t r a t i o n s v a r i e d . 4 0 36 h Initial NaOH v 05 M • 2 M 0.4 0.8 1.2 1.6 Final Na 2 S (M) 2.0 F i g u r e 4-1 The F i n a l Antimony C o n c e n t r a t i o n s versus the F i n a l T o t a l Sodium Sulphide C o n c e n t r a t i o n s - 0.5 and 2 M I n i t i a l C a u s t i c 48 0.4 0 8 1.2 1.6 Final Na 2S ( M ) F i g u r e 4-2 The F i n a l Antimony C o n c e n t r a t i o n s versus the F i n a l T o t a l Sodium Sulphide C o n c e n t r a t i o n s - 0 and 1 M I n i t i a l C a u s t i c 49 0.02 0.04 0.06 0.08 Final Na 2 S ( M ) o i F i g u r e 4 - 3 The F i n a l Antimony C o n c e n t r a t i o n s versus the F i n a l T o t a l Sodium Sulphide C o n c e n t r a t i o n s - 1 M I n i t i a l C a u s t i c and Low Sulphide 50 4.2.2 Antimony Leached In C a u s t i c - O n l y S o l u t i o n s L e a c h i n g e x p e r i m e n t s were done i n 0.5, 1.0 and 2.0 M NaOH s o l u t i o n s . Sodium s u l p h i d e was not added and no s u l p h i d e was found i n any of the f i n a l s o l u t i o n s . The c a u s t i c t i t r a t i o n s ' of the f i n a l s o l u t i o n s w i t h HC1 showed two end p o i n t s : one f o r OH" and a n o t h e r which appeared t o be f o r the n e u t r a l i z a t i o n of the Sb0 2" i o n ( E q u a t i o n 4-1). SbO " + 4HC1 = SbCl " + 2H 0 ...(4-1) 2 4 2 The t i t r a n t volume d i f f e r e n c e between the two end p o i n t s c o r r e s p o n d e d t o a Sb:H* r a t i o of a p p r o x i m a t e l y 4 and was the same f o r a l l t h r e e s o l u t i o n s s u g g e s t i n g 0.3 g/1 of Sb i n s o l u t i o n . The t o t a l t i t r a n t volume at the second end p o i n t was a p p r o x i m a t e l y e q u i v a l e n t t o the i n i t i a l c a u s t i c c o n c e n t r a t i o n . S i n c e the q u a n t i t i e s of c o n c e n t r a t e and s o l u t i o n c h a r g e d t o each of t h e s e e x p e r i m e n t s were i d e n t i c a l , the r e s u l t s suggest t h a t an antimony o x i d e was l e a c h e d from the c o n c e n t r a t e . However, the l e a c h i n g of an o x i d e would i n c r e a s e the net c a u s t i c c o n c e n t r a t i o n , and t h i s was not o b s e r v e d . 51 4.3 L e a c h i n g In Weak Sodium S u l p h i d e S o l u t i o n s Without Added Caust i c Four e x p e r i m e n t s were done a t 0.03, 0.06, 0.09 and 0.12 M Na 2S w i t h o u t added c a u s t i c . The r e s u l t a n t s l u r r i e s were u n f i l t e r a b l e by the p r e s s u r e and vacuum t e c h n i q u e s d e s c r i b e d i n S e c t i o n 2.3. A f t e r the e x c e s s c o n c e n t r a t e was a l l o w e d t o s e t t l e the s o l u t i o n s were the deep g r e e n - b l a c k c o l o u r c h a r a c t e r i s t i c of t h i o f e r r a t e . Added ac e t o n e appeared t o f l o c c u l a t e a m a t e r i a l , presumably N a F e ^ • xH 20 . A l t h o u g h t h e s e s o l u t i o n s were not q u a n t i t a t i v e l y a s s a y e d , a q u a l i t a t i v e r e s u l t was o b t a i n e d by SEM x- r a y a n a l y s i s on a drop of 0.12 M Na^ S p r o d u c t s o l u t i o n e v a p o r a t e d onto a carbon > s t u b . A r s e n i c , s i l i c o n , antimony, i r o n and copper as w e l l as sodium and s u l p h u r were p r e s e n t . The i r o n peak was much l a r g e r than the copper peak a g a i n s u g g e s t i n g the pr e s e n c e of NaFeS 2. The 0.12 M Na 2S p r o d u c t s o l u t i o n e v e n t u a l l y f l o c c u l a t e d as d i d the b l a c k f i l t r a t e from a 0.45 M Na S / 0 M NaOH l e a c h i n g 2 e x p e r i m e n t . The s u p e r n a t e n t s were c o l o u r l e s s i n d i c a t i n g t h a t the t h i o f e r r a t e p r e s e n t was s t a b l e . The d e c o m p o s i t i o n of t h i o f e r r a t e would have produced a y e l l o w s u p e r n a t e n t s o l u t i o n i n d i c a t i v e of p o l y s u l p h i d e ( S e c t i o n 1.3.3). ( T h i s may be a d e c e p t i v e r e s u l t s i n c e p o l y s u l p h i d e i s not a s t a b l e s p e c i e s i n a l k a l i n e s o l u t i o n . ) 52 4.4 The Ex c e s s Of C o n c e n t r a t e Used E x c e s s c o n c e n t r a t e was c h a r g e d t o each l e a c h i n g experiment i n an e f f o r t t o e q u i l i b r a t e the s o l i d s w i t h the s o l u t i o n s . Antimony e x t r a c t i o n s of l e s s than 50% were sought. In a c t u a l i t y the antimony e x t r a c t i o n s v a r i e d between 8 and 62% w i t h a mean of 35%. Only one e x t r a c t i o n was above 50%. The e x t r a c t i o n s a r e t a b u l a t e d w i t h the l e a c h d a t a i n Appendix D. 4.5 F i l t e r a b i 1 i t y Of The Leached P r o d u c t S l u r r y D u r i n g the l e a c h the c o n c e n t r a t e d i s i n t e g r a t e d i n t o f i n e r m a t e r i a l which p r o v e d t o be d i f f i c u l t t o f i l t e r . These f i n e s , t o g e t h e r w i t h the e x c e s s c o n c e n t r a t e used produced a v e r y t h i c k I p r o d u c t s l u r r y , p a r t i c u l a r l y i n those runs which had h i g h Na 2S c o n c e n t r a t i o n s . A p r a c t i c a l e x p e r i m e n t a l l i m i t of 2 M N a 2 S had to be imposed t o a c h i e v e a s o l i d / l i q u i d s e p a r a t i o n a t the end of l e a c h i n g . The p r e s s u r e f i l t r a t i o n r e q u i r e d 25 p s i g of n i t r o g e n t o produce 10 ml of f i l t r a t e i n 5-10 m i n u t e s . Large Buchner f u n n e l s were used t o a c h e i v e r e a s o n a b l e vacuum f i l t r a t i o n r a t e s f o r the b u l k of the s o l u t i o n s . D u r i n g water washing of the l e a c h e d s o l i d s the f i l t r a t i o n r a t e s dropped and what appeared t o be f i n e s o l i d s broke t h r o u g h the f i l t e r p a p e r . The SEM x- r a y a n a l y s e s of t h e s e s o l i d s when they e v e n t u a l l y s e t t l e d ( f l o c c u l a t e d ) i n d i c a t e d t h a t i r o n , sodium and s u l p h u r were 53 p r e s e n t . When the l e a c h e d s o l i d s were washed w i t h a weak c a u s t i c s o l u t i o n i n s t e a d of w a t e r , the f i l t r a t i o n r a t e d i d not dr o p , nor d i d m a t e r i a l break t h r o u g h . T h i s f i l t r a t i o n b e h a v i o r and the SEM a n a l y s e s seem i n d i c a t i v e of the p r e s e n c e of sodium t h i o f e r r a t e . As w e l l as f i l t e r i n g p o o r l y , the l e a c h e d s o l i d s d i d not s e t t l e w e l l . I f a l l o w e d t o s i t w h i l e h o t , o n l y 5 mm of c l e a r l i q u i d were produced over 10 cm of s l u r r y i n 10 m i n u t e s . 4.6 The Change In S u l p h i d e C o n c e n t r a t i o n F i g u r e 4-4 shows the d i f f e r e n c e s i n the t o t a l Na 2 S c o n c e n t r a t i o n s between the i n i t i a l and f i n a l s o l u t i o n s p l o t t e d - a g a i n s t the f i n a l antimony c o n c e n t r a t i o n s . The d i f f e r e n c e s a r e shown on an a b s o l u t e and on a r e l a t i v e b a s i s . A s m a l l net d r o p i n s u l p h i d e c o n c e n t r a t i o n was o b s e r v e d i n a l l the e q u i l i b r i u m e x p e r i m e n t s e x c e p t one. The a b s o l u t e drop was u n r e l a t e d t o the antimony c o n c e n t r a t i o n . At low antimony (low s u l p h i d e ) the r e l a t i v e l o s s r o s e s h a r p l y . The one run which showed a net i n c r e a s e i n Na^S c o n c e n t r a t i o n was the o n l y e xperiment i n which the antimony e x t r a c t i o n exceeded 50%. In t h i s case the e x t r a c t i o n was 62%. 54 " A ?° V A V ° o ° * ° o Q ° ° A " • -© - i 1 1 I °. < 5 10 15 2 0 Sb (g /1 ) 25 30 35 -o A O • Initial NaOH A 0 M v 0 5 M o 1 M o 2 M - V A * O o o ° A * • - — 1 > — i 1 1 o , i 0 5 10 15 20 25 30 35 Sb (g/1) F i g u r e 4-4 The D i f f e r e n c e s Between the I n i t i a l and F i n a l Sodium Sulphide C o n c e n t r a t i o n s - A b s o l u t e (Top) and R e l a t i v e (Bottom), versus the F i n a l Antimony C o n c e n t r a t i o n s 55 4.7 The Change In C a u s t i c C o n c e n t r a t i o n Fi'gure 4-5 shows the d i f f e r e n c e s i n the NaOH c o n c e n t r a t i o n s between the f i n a l s o l u t i o n s and th o s e c a l c u l a t e d f o r the i n i t i a l s o l u t i o n s as a f u n c t i o n of the f i n a l Na 2S c o n c e n t r a t i o n s . An a s c e n d i n g s o l i d l i n e was f i t t e d t h r o u g h the p o i n t s f o r 0.5, 1.0 and 2.0 M i n i t i a l c a u s t i c , w h i l e the broken l i n e f i t t e d t h r o u g h the p o i n t s f o r no added c a u s t i c had a n e g a t i v e s l o p e . I f the 1 M i n i t i a l NaOH p o i n t s of F i g u r e 4-2 a r e compared a g a i n s t the c o r r e s p o n d i n g d a t a (Appendix D), the 'low p o i n t s ' appear t o be a s s o c i a t e d w i t h s m a l l e r ^OH's than the 'hig h p o i n t s ' . F i g u r e 4-6 shows a p l o t of the l e a c h antimony c o n c e n t r a t i o n s p l o t t e d a g a i n s t the p r o d u c t of the f i n a l Na 2S c o n c e n t r a t i o n s and the f i n a l NaOH c o n c e n t r a t i o n s . The p o i n t s of F i g u r e 4-2 a r e s e l e c t i v e l y s h i f t e d p r o d u c i n g F i g u r e 4-6, a p l o t w i t h much l e s s s c a t t e r . j The i n i t i a l NaOH c o n c e n t r a t i o n s were not measured but r a t h e r c a l c u l a t e d from the added c a u s t i c . The c a u s t i c c o n t e n t of the Na 2S was d e t e r m i n e d t o be 0.02 - 0.03 mole per mole ( S e c t i o n 2.1.2). A c o r r e c t i o n was not a p p l i e d t o the i n i t i a l l e a c h s o l u t i o n c a u s t i c a s s a y s . 56 0.4 0.3 ^ 0.2 1 0.1 0 -0.1 O O V . n o _ x u V. • V O Initio! NoOH (o) A 0 M V 0.5 M \ O 1 M \ " A O 2 M ! 1 0 0.5 1.0 1.5 Na 2 S ( M ) 2.0 F i q u r e 4-5 The D i f f e r e n c e s Between the I n i t i a l and F i n a l Sodium Hydroxide C o n c e n t r a t i o n s versus the F i n a l Sodium Sulp h i d e C o n c e n t r a t i o n s Final Na 2 S x Na OH ( M 2 ) F i g u r e 4 - 6 The F i n a l Antimony C o n c e n t r a t i o n s versus the Product of the F i n a l Sodium S u l p h i d e and Sodium Hydroxide C o n c e n t r a t i o n s ( 1 M I n i t i a l C a u s t i c ) 58 4.8 A r s e n i c D i s s o l u t i o n F i g u r e 4-7 shows the a r s e n i c c o n c e n t r a t i o n s of .12 l e a c h s o l u t i o n s p l o t t e d a g a i n s t the antimony c o n c e n t r a t i o n s . E q u a t i o n 4-2 was f i t t e d t h r o u g h the p o i n t s . As(g/1) = 0.21 + 0.068 Sb(g/1) ...(4-2) The a r s e n i c t o antimony r a t i o of the c o n c e n t r a t e i s r e p r e s e n t e d by the broken l i n e ( S e c t i o n 2.1.1). The s l o p e of the e x p e r i m e n t a l l i n e i s l e s s than the s l o p e of the c o n c e n t r a t e l i n e due to the p r e s e n c e of an i n s o l u b l e a r s e n i c - c o n t a i n i n g phase - most l i k e l y a r s e n o p y r i t e , AsFeS , At low s u l p h i d e t h e s e l i n e s c r o s s because a r s e n i c - s u l p h i d e complexes a r e more s t a b l e than t h e i r antimony c o u n t e r p a r t s and because t h e r e were adequate q u a n t i t i e s of a r s e n i c a v a i l a b l e a t the exposed m i n e r a l p a r t i c l e s u r f a c e s . At h i g h e r s u l p h i d e l e v e l s the a r s e n i c was . o n l y made a v a i l a b l e t h r o u g h the d e c o m p o s i t i o n of t e t r a h e d r i t e . <? The z e r o - i n t e r c e p t of the f i t t e d l i n e (0.21 g/1 As) i s an a r t i f a c t c r e a t e d by the l i n e a r l e a s t squares f i t which was done. The t r u e v a l u e i s p r o b a b l y s m a l l e r . 0 4 8 12 16 20 2 4 28 32 Sb (g/1) F i g u r e 4-7 The A r s e n i c Versus the Antimony Co n c e n t r a t i o n s 60 4.9 The P r e s e n c e Of O x i d i z e d S u l p h u r S p e c i e s And Antimony(V) The r e s u l t s of the a n a l y s e s f o r o x i d i z e d s u l p h u r s p e c i e s and so f o r Sb(V) ( S e c t i o n 3.2.3) d i d not show any s y s t e m a t i c p a t t e r n . C o n s i d e r i n g the o x i d a t i o n problems i d e n t i f i e d i n the s o l i d / l i q u i d s e p a r a t i o n ( S e c t i o n 2.3) and i n the S°x_i d e t e r m i n a t i o n ( S e c t i o n 3.2..1), i t i s u n l i k e l y t h a t s i g n i f i c a n t q u a n t i t i e s of t h e s e s p e c i e s were p r e s e n t a t the end of the l e a c h e s . 4.10 Antimony And S u l p h i d e C o n c e n t r a t i o n s V e r s u s Time F i g u r e s .4-8 and 4-9 show the antimony and s u l p h i d e c o n c e n t r a t i o n s of f o u r l e a c h i n g e x p e r i m e n t s p l o t t e d , a g a i n s t t i m e . The antimony c u r v e s show a r e g u l a r r i s e , w h i l e the s u l p h i d e c u r v e s a r e more complex. The d a t a f o r the s e runs i s g i v e n i n Appendix E. 32 / 0 I 1 1 . 1 1 1 0 3 0 0 6 0 0 9 0 0 1200 1500 Time (min.) ' F i g u r e 4 - 8 T h e S o l u t i o n A n t i m o n y C o n c e n t r a t i o n s a s a F u n c t i o n o f T i m e ^ I.55T- 10 CM O 0.85$- co (M o 0.75 0.65 0.55 2 0 0 4 0 0 6 0 0 8 0 0 1000 Time ( M in ) 1200 1400 F i g u r e 4 - 9 The Sodium Sulphide C o n c e n t r a t i o n s as a Function o.f Time t-o 63 4.11 Appearance Of The C o n c e n t r a t e And P r o d u c t S o l i d s F i g u r e s 4-10 and 4-11 show SEM m i c r o g r a p h s of the c o n c e n t r a t e and the l e a c h e d p r o d u c t s o l i d s a t 2,100 and 21,000 t i m e s . (The p r o d u c t i o n of the p r o d u c t s o l i d s i s d e s c r i b e d i n T a b l e 4-2,' l e a c h 2.) The c o n c e n t r a t e i s o b v i o u s l y c r y s t a l l i n e w h i l e the p r o d u c t s o l i d s a r e n o t . The l e a c h e d p a r t i c l e s a r e much l e s s than 1 um i n s i z e . 4.12 X-ray P i f f r a c t o m e t r y Of The P r o d u c t S o l i d s The x - r a y d i f f r a c t i o n l i n e p a t t e r n . f o r the p r o d u c t s o l i d s was i d e n t i c a l t o the p a t t e r n f o r the c o n c e n t r a t e . The c o n c e n t r a t e d e c o m p o s i t i o n p r o d u c t was x - r a y . amorphous, c o n s i s t e n t w i t h i t s ' f u z z y ' appearance. 4.13 Comparison Of T e t r a h e d r i t e And The D e c o m p o s i t i o n P r o d u c t By E l e c t r o n M i c r o a n a l y s i s F i g u r e 4-12 shows SEM x - r a y a n a l y s e r s p e c t r a t a k e n from t e t r a h e d r i t e and d e c o m p o s i t i o n p r o d u c t a r e a s on a mounted and p o l i s h e d sample of l e a c h e d m a t e r i a l ( l e a c h 2, T a b l e 4-2). The s p e c t r a , c o n t a i n i n g 500,000 c o u n t s each, a r e shown s e p a r a t e l y and superimposed t o a c c e n t u a t e t h e i r d i f f e r e n c e s . The g r e a t e s t d i f f e r e n c e s a r e the d i s a p p e a r a n c e of the antimony from t e t r a h e d r i t e and the l a r g e i n c r e a s e of i r o n i n t h e p r o d u c t . The  (a) (b) F i g u r e 4-11 The T e t r a h e d r i t e Concentrate (a) and the Leach Product S o l i d s (b) at 21,000 x U1 66 A: Tetrohedrite * • x • . • B : Decomposition Product * * * * * * A *v-v . A. A and B Superimposed A i i Cu As Na Si I Ag ^ Mn Fe Fe CU t Cu Zn F i g u r e 4-12 SEM X-ray. A n a l y s e r Spectra f o r the T e t r a h e d r i t e and the Decomposition Product Phases 67 p r o d u c t a l s o g a i n e d s o d i u m , s i l i c o n a n d m a n g a n e s e w h i l e t h e t e t r a h e d r i t e l o s t a r s e n i c . T h e p r o d u c t s s h o w b o t h t h e s i l v e r a n d z i n c f o u n d i n t h e t e t r a h e d r i t e . ( T h e s e s p e c t r a a r e o n l y q u a l i t a t i v e . ) T a b l e 4 - 1 s h o w s t h e r e s u l t s o f a n e l e c t r o n m i c r o p r o b e a n a l y s i s o n t h e t e t r a h e d r i t e a n d d e c o m p o s i t i o n p r o d u c t a r e a s . W i t h c o p p e r a s a t i e , t h e s e r e s u l t s i n d i c a t e t h a t w i t h i n t h e e r r o r l i m i t s s t a t e d , o n e i r o n a n d o n e s u l p h u r a r e a d d e d f o r e a c h a n t i m o n y e x t r a c t e d . T h e m i c r o p r o b e a n a l y s i s c o m p u t e r p r o g r a m , M a g i c I V , w a r n e d t h a t t h e s u l p h u r a n a l y s e s w e r e i n c o r r e c t d u e t o a h i g h a b s o r p t i o n c o r r e c t i o n , m o r e t h a n 1 0 0 % . T h i s o c c u r s w h e n a l i g h t e l e m e n t i s a n a l y s e d i n a h e a v y e l e m e n t m a t r i x . T h e d e c o m p o s i t i o n p r o d u c t w a s f i n e a n d o f v a r y i n g d e n s i t y s o i t w a s n o t p o s s i b l e t o k n o w e x a c t l y w h a t t h e b e a m . w a s f o c u s e d o n . D e s p i t e p o l i s h i n g t h e p r o d u c t a r e a s w e r e r o u g h s i n c e t h e p r o d u c t w a s s o f t . T h e s e f a c t o r s l e a d t o t h e p o o r p r e c i s i o n i n t h e d e c o m p o s i t i o n p r o d u c t a n a l y s e s . T e t r a h e d r i t e w a s n o t s t a b l e u n d e r t h e m i c r o p r o b e b e a m a n d t h e s a m p l e h a d t o b e m o v e d a t 50jj.m p e r m i n u t e t o g i v e a v a l i d a n a l y s i s . T a b l e 4-1: M i c r o p r o b e A n a l y s i s R e s u l t s 68 T e t r a h e d r i t e (atom %) v T e t r a h e d r i t e * Decomp. C u - t i e P r o d u c t (atom %) (atom %) (atom %) No. of P o i n t s 8 A n a l y s e d S Cu Fe Sb 4 6.4+0.4 3 5.0±0.5 5.3±0.3 13.3+0.4 39.8 30 . 0 4 . 5 11 . 4 50+6 30+6 20 + 3 0 + 0 + 10 0 + 15 -11 *The t e t r a h e d r i t e a n a l y s e s were a d j u s t e d t o use a copper t i e . ) 69 4.14 Leaches At Low P u l p D e n s i t y T a b l e 4-2 shows the l e a c h i n g c o n d i t i o n s and r e s u l t s from t h r e e low p u l p d e n s i t y l e a c h i n g e x p e r i m e n t s . Leaches 1 and 2 were d u p l i c a t e s done a t 100°C. Leach 3 was done a t 200°C under 200 p s i g of n i t r o g e n i n a s m a l l s h a k i n g a u t o c l a v e . In these e x p e r i m e n t s the t e t r a h e d r i t e s h o u l d have decomposed c o m p l e t e l y b e f o r e e q u i l i b r i u m w i t h the s o l u t i o n was a t t a i n e d . Leaches 1 and 2 produced s i g n i f i c a n t l y d i f f e r e n t antimony d i s s o l u t i o n r e s u l t s , 2.27 v e r s u s 2.73 g/1 Sb. The antimony c o n c e n t r a t i o n s were w e l l below those o b s e r v e d i n the c o r r e s p o n d i n g e x c e s s c o n c e n t r a t e e x p e r i m e n t , 12 g/1 Sb. However, the e q u i l i b r i u m e x p e r i m e n t was done w i t h 50 g of wet c o n c e n t r a t e f o r 130 ml of l e a c h s o l u t i o n a g a i n s t 5 g i n 125 ml i n the low p u l p d e n s i t y r u n s . The antimony e x t r a c t i o n s of l e a c h e s 1 and 2 were o n l y 42 and 46%, f i g u r e s which a re u n r e a l i s t i c a l l y low i n view of t h e i r a p p arent d e p a r t u r e from e q u i l i b r i u m . A l l t he l e a c h p r o d u c t s o l i d s c o n t a i n e d q u a n t i t i e s of sodium too h i g h t o be j u s t i f i e d on the b a s i s of e n t r a i n e d l e a c h s o l u t i o n . These s o l i d s appeared t o have c o n t a i n e d 25 - 60 wt. % l e a c h s o l u t i o n w h i l e wet though they a l l had been t h o r o u g h l y f i l t e r e d and washed. The 200°C p r o d u c t was e a s i e s t t o f i l t e r but c o n t a i n e d the most sodium. The Cu:Fe and S:Fe r a t i o s of the l e a c h e d s o l i d s both dropped compared t o the c o n c e n t r a t e - s l i g h t l y f o r the.100°C and T a b l e 4-2: Data and R e s u l t s f Exper intents L each 1 Temp ( C) 100 Time ( h r ) 24 Cone (g-wet) 5.00 Cone ' ( g-dry )• 4 . 6 3 - Leach v o l (ml) 125 Na 2S (M) 0/964 P r o d u c t ( g - d r y ) 4.38 Sb(%) 6.7 Cu(%) 26.7 Fe (%) 15.4 S (%) 30.1 Na(%) 1.09 S o l u t i o n Sb(g/1) 2.27 F i n a l Na S (M) 1.031 2 Sb ( o u t ) / S b ( i n ) 0.95 Sb ( s o l i d s ) / S b ( i n ) 0.48 Na ( s o l i d s ) / S b ( s o l ' n ) 0.89 (mole/mole) Le a c h S o l n e q u i v 1.1 t o Na (ml) S o l i d s Cu/Fe (g/g) 1.73 S o l i d s S/Fe (g/g) 1.94 70 Low P u l p D e n s i t y "Leaching 2 3 C o n c e n t r a t e 100 200 24 4 5.0 0 5.0 0 4.63 4.63 125 50 0.967 0.972 4.40 ( 3 . 8 4 ) * 6.1 3.9 13.1 26.7 28.8 26.0 15.6 17.6 14.6 30.2 32.2 29.1 1.33 2.84 0.0 2.73 9.32 0.996 0.975 1.01 1.02 0.44 0.25 0.91 ' 1.24 1.3 2.5 1.71 1.64 1.78 1.96 1.83 1.99 *weigh t c a l c u l a t e d from Fe b a l a n c e ; p o r t i o n of sample l o s t . 71 s i g n i f i c a n t l y f o r the 200°C l e a c h . The copper may have_ l e a c h e d w h i l e the s u l p h u r may have o x i d i z e d t o s u l p h a t e . 4.15 I n c o n s i s t e n c y Of Sodium In The C o n c e n t r a t e D e c o m p o s i t i o n P r o d u c t Sodium m i c r o a n a l y s e s were a t t e m p t e d , but the sodium was not u n i f o r m l y d i s p e r s e d and was o b s e r v e d o n l y i n some of the d e c o m p o s i t i o n p r o d u c t a r e a s . A l s o the apparent number of the sodium a r e a s changed each time the sample was r e p o l i s h e d . (The p o l i s h i n g was done down t o 5^m g r i t w i t h o u t the use of water.) These o b s e r v a t i o n s were made by t a k i n g SEM x - r a y a n a l y s e r s p e c t r a such as F i g u r e 4-11. When a m i c r o p r o b e a n a l y s i s was a t t e m p t e d no a r e a c o u l d be found where the sodium x _ r a y count was more than t w i c e the background. Twice the background i s c o n s i d e r e d t o be the minimum f o r a v a l i d a n a l y s i s . The d e c o m p o s i t i o n p r o d u c t was so f i n e and s o f t t h a t t h e s e a r e a s were d i f f i c u l t t o p o l i s h f l a t . Sodium x - r a y s a r e r e l a t i v e l y weak and r e a d i l y a b s o r b e d by h e a v i e r e l e m e n t s , so a f l a t sample s u r f a c e i s e s s e n t i a l t o t h e i r d e t e c t i o n . 4 .16 Water 72 The Sodium To Antimony R a t i o Of The Leached S o l i d s Wash To i n v e s t i g a t e the d i s p o s i t i o n of sodium d u r i n g the washing of the l e a c h e d s o l i d s , a l e a c h s l u r r y was f i l t e r e d on a Buchner f u n n e l and water washes of 100 ml were sucked t h r o u g h the c a k e . As a c o n t r o l a s l u r r y of c e l l u l o s e f i l t e r i n g p u l p was made up w i t h the l e a c h f i l t r a t e and .then f i l t e r e d and washed i n a s i m i l a r manner. Each s o l u t i o n was a s s a y e d f o r Na and Sb. T a b l e 4-3 shows the r e s u l t s of the washing e x p e r i m e n t s . The Na:Sb r a t i o of the l e a c h s o l i d wash s o l u t i o n s c l e a r l y i n c r e a s e d r e l a t i v e t o the c o n t r o l s . Sodium must have been l i b e r a t e d from a s o l i d phase i n the l e a c h e d m a t e r i a l t o account f o r t h i s r e s u l t . E x p e r i m e n t s were a t t e m p t e d i n which the. f i l t e r e d s o l i d s were r e p u l p e d a f t e r each wash. The s o l i d s p r o v e d t o be d i f f i c u l t t o d i s p e r s e and the r e s u l t a n t s l u r r i e s were v i r t u a l l y i m p o s s i b l e t o f i l t e r . S o l i d s broke t h r o u g h even two f i n e f i l t e r p a p e r s . S o l i d b r e a k t h r o u g h s were o b s e r v e d i n the d i s p l a c e m e n t washes r e p o r t e d above and i n the e q u i l i b r i u m l e a c h i n g e x p e r i m e n t s ( S e c t i o n 4.5). T a b l e 4 - 3 : R e s u l t s f r o m F i l t e r C a k e W a s h i n g 73 S b ( p p m ) N a ( p p m ) N a / S b L e a c h e d S o l i d s L e a c h S o l u t i o n W a s h 1 W a s h 2 W a s h 3 1 4 5 0 0 7 6 0 2 . 8 1 . 0 2 9 3 0 0 0 1 6 0 0 0 5 4 6 2 8 0 2 0 . 2 2 1 . 1 1 9 5 2 8 0 C e l l u l o s e F i l t e r P u l p ( c o n t r o l ) : L e a c h S o l u t i o n 1 0 4 0 0 2 0 0 0 0 0 1 9 . 2 W a s h 1 1 3 9 0 2 5 7 0 0 1 8 . 5 W a s h 2 2 2 . 5 5 9 0 . 2 6 . 2 W a s h 3 0 . 8 20 2 5 . 0 7 4 4.17 P y r i t e L e a c h i n g A sample of c o a r s e c r u s h e d p y r i t e was l e a c h e d i n 0.03 M Na S f o r s i x hours a t 100°C. The r e s u l t a n t s o l u t i o n was a deep g r e e n - b l a c k c o l o u r s u g g e s t i v e of sodium t h o i f e r r a t e . A s i m i l a r sample of p y r i t e was t r e a t e d w i t h c o l d 1% HC1 t o remove o x i d e s , and r i n s e d t h o r o u g h l y with, water. A 1 M Na S s o l u t i o n was added and i m m e d i a t e l y t u r n e d b l a c k . A f t e r 12 hours of l e a c h i n g a t 100°C the s o l u t i o n had darkened s i g n i f i c a n t l y . Acetone added t o a hot s o l u t i o n sample f l o c c u l a t e d the t h i o f e r r a t e and no p o l y s u l p h i d e y e l l o w was o b s e r v e d . A SEM x- r a y a n a l y s i s on a drop of f l o c c u l a t e d s o l u t i o n i n d i c a t e d the pr e s e n c e of sodium, s u l p h u r , s i l i c o n and i r o n . The b u l k of the s o l u t i o n f l o c c u l a t e d t h i o f e r r a t e upon c o o l i n g but appeared t o r e d i s p e r s e when he a t e d t o b o i l i n g . 4.18 S i l i c a - I r o n Oxide P a r t i c l e s F i g u r e 4-13 shows a SEM m i c r o g r a p h of a s i l i c a - i r o n o x i d e p a r t i c l e i n the c o n c e n t r a t e and i t s S i and Fe x - r a y energy maps. The b r i g h t a r e a s on each map i n d i c a t e t h e ' s o u r c e s of the x - r a y s f o r the element under c o n s i d e r a t i o n . The x - r a y spectrum, from a dark grey a r e a showed s i l i c o n w i t h much s m a l l e r i r o n and copper peaks w h i l e the l i g h t g rey a r e a showed i r o n , copper and manganese (but no s u l p h u r ) . T h i s phase i s the o n l y source of manganese i n the c o n c e n t r a t e and i s presumably the source of manganese i n the d e c o m p o s i t i o n p r o d u c t . P a r t i c l e s such as the s e (b) (c) F i g u r e 4 - 1 3 S E M M i c r o g r a p h o f a S i l i c a - I r o n O x i d e P a r t i c l e ( a ) a n d t h e C o r r e s p o n d i n g S i l i c o n ( b ) a n d I r o n ( c ) X - r a y E n e r g y M a p s 76 were not found i n the l e a c h e d m a t e r i a l . 77 Chapter 5. Dependency of Antimony S o l u b i l i t y on S u l p h i d e Ion C o n c e n t r a t i o n 5.1 S t i b n i t e S o l u b i l i t y P l o t s A l t h o u g h ' t h e r e i s a l a c k of agreement as t o which ant irnony (111 ) - s u l p h i d e c o m p l e x ( e s ) i s formed from Sb S 2 3 d i s s o l u t i o n i n s u l p h i d e s o l u t i o n s , the l i t e r a t u r e g i v e s e x p e r i m e n t a l r e s u l t s which m e r i t f u r t h e r a n a l y s i s . No o r i g i n a l Sb2S3 d i s s o l u t i o n d a t a was produced i n t h i s s t u d y . I f SbS 2~ i s c o n s i d e r e d t o be the s t a b l e S b ( l I I ) complex i n s o l u t i o n , then a p l o t of the l o g of the a c t i v i t y of the SbS 2 ~ i o n v e r s u s the l o g of the a c t i v i t y of the s u l p h i d e i o n ( l o g a ( S b S 2 " ) v e r s u s l o g a ( S 2 ~ ) s h o u l d be a s t r a i g h t l i n e w i t h a s l o p e of 0.5 ( E q u a t i o n s 5-1 t o 5-3). However, c o n c e n t r a t i o n s r a t h e r than a c t i v i t i e s a r e e x p e r i m e n t a l l y d e t e r m i n e d and a c t i v i t y c o e f f i c i e n t d a t a has not been p u b l i s h e d f o r HS~, S 2~ or any S b ( 1 1 1 ) - s u l p h i d e complex. 1/2 S b 2 S 3 + 1/2 S 2" = SbS " ...(5-1) K ( S b S 2 " ) = a ( S b S 2 2 - ) a 0 5 ( S 2 - ) ...(5-2) 78 l o g a(SbS ") = 1/2 l o g a ( S 2 ' ) + l o g K f S b S ^ ) ...(5-3) On a c o n c e n t r a t i o n b a s i s E q u a t i o n 5-4 i s a n a l o g o u s t o E q u a t i o n 5-3. l o g { S b S 9 " } = 1/2 l o g { S 2 " } + l o g v 0 5 ( S 2 - ) + logK(SbS ") ...(5-4) Y ( S b S 2 " ) S i n c e each a c t i v i t y c o e f f i c i e n t , Y , i s a f u n c t i o n of the t o t a l i o n i c s t r e n g t h (among o t h e r f a c t o r s ) i t i s a common e x p e r i m e n t a l d e v i c e t o add a l a r g e c o n c e n t r a t i o n of i n e r t i o n s t o keep the reagent a c t i v i t y c o e f f i c i e n t s v i r t u a l l y c o n s t a n t . The s t i b n i t e s o l u b i l i t y d a t a g i v e n by A r n t s o n et a l . (1966) was c o n v e r t e d i n t o a c o n c e n t r a t i o n - b a s e d l o g p l o t format f o r the s p e c i e s : SbS 2 _ , Sb„S. 2~, Sb S /" and Sb S 2". SbS " 3 2 4 2 5 4 7 2 has the same antimony t o s u l p h i d e r a t i o as Sb 2S 2 '. No one has proven t h a t b o t h i o n s e x i s t and Sb^S 2 ' seems more l i k e l y by a bonding argument ( S e c t i o n 1.3.2). A summary of the c a l c u l a t i o n scheme and the r e s u l t s are shown i n Appendix F. The f r e e S 2" i o n c o n c e n t r a t i o n was o b t a i n e d by s u b t r a c t i n g the a p p r o p r i a t e number of moles of s u l p h i d e per mole of antimony f o r the complex c o n s i d e r e d and then c a l c u l a t i n g the HS"-S 2"-OH" e q u i l i b r i u m a t 25°C. T h i s c a l c u l a t i o n p a r a l l e l s the one t h a t was used f o r F i g u r e 1-3, S e c t i o n 1.3.1 The r e s u l t s i n d i c a t e t h a t SbS 3~ cannot e x i s t i n h i g h f r e e 3 S 2" s o l u t i o n - the t o t a l S 2":Sb. r a t i o f e l l below t h r e e . In an e l e c t r o c h e m i c a l s t u d y S h e s t i k o and Demina (1971) s u g g e s t e d t h a t SbS 3" was s t a b l e i n the r e g i o n shown i n the lower r i g h t hand 3 c o r n e r of F i g u r e 5-1. The dashed l i n e o n l y c o n n e c t s t h e i r 0 -0.2 h -0.4 _ - 0 . 6 - - 0 . 8 - 0 -I O int IXJ cn 5-1.2 -1.4 -1.6 -1.8 O Arnstonet.al.(l966) • Dubey and Ghosh (1962) V Shsstiko and Demina (1971) cP O Sb4Sf cP sb 2 s| - / sbs; / 2.4 0.4 0 20 1.6 1.2 0.8 Log [ F r e e S 2"] ( M ) Figure 5-1: The L i t e r a t u r e S t i b n i t e Leaching Data P l o t t e d C o n sidering S b 2 S 4 2 " at Low Sulphide and S b 2 S 7 2 " at High Sulphide ( S b S 3 3 _ S t a b l i l i t y Area Shown) 80 e x p e r i m e n t a l l y d e r i v e d p o i n t s and does not mean t o i n f e r a r e l a t i o n s h i p between SbS^ 3" and o t h e r complexes. s k 2 s 5 4 ~ a n < ^ Sb S 2" were i n d i c a t e d t o be s t a b l e t o the l e f t of t h i s r e g i o n . 4 7 - T h i s work i n d i c a t e s t h a t SbS^ 3" c o u l d not have been p r e s e n t i n the s o l u t i o n s s t u d i e d by A r n t s o n et a l . (1966). S h e s t i k o and Denina(1971) s t u d i e d the r e s t p o t e n t i a l of a m e t a l l i c antimony e l e c t r o d e i n s o l u t i o n s c o n t a i n i n g v a r i o u s c o n c e n t r a t i o n s of s u l p h i d e and d i s s o l v e d antimony. The s l o p e s of the l i n e s on a p o t e n t i a l v e r s u s t o t a l s u l p h i d e p l o t showed 'knees' at the u l p h i d e l e v e l where the dominant S b ( 1 1 1 ) - s u l p h i d e c o m p l e x ( e s ) changed from Sb S 4 * and Sb S 2" t o SbS 3". These 2 5 4 7 3 'knee' p o i n t s a r e shown on F i g u r e 5-1. The r e s u l t s of the f r e e S 2" c a l c u l a t i o n f o r Sb S *' became 2 5 e r r a t i c a t h i g h S 2" though the S 2":Sb r a t i o d i d not f a l l below 2.5. The e x i s t e n c e of t h i s complex i s a l s o c o n s i d e r e d t o be d u b i o u s i n the s o l u t i o n s s t u d i e d by Arnson et a l . (1966). The s o l u b i l i t y l o g p l o t s f o r the complexes Sb^S^ 2" and S b 2 S 2 " ( A p p e n d i x F) b o t h show d i s c o n t i n u i t i e s a t l o g {Sb} = - 0.7. However, t h i s d i s c o n t i n u i t y d i s a p p e a r s i f the d a t a f o r Sb S 2" a t low s u l p h i d e i s p l o t t e d w i t h the d a t a f o r Sb S 2" at 2 4 r r 4 ? h i g h s u l p h i d e ( F i g u r e 5-1). The predominant S b ( 1 1 1 ) - s u l p h i d e complex ap p e a r s t o change from Sb^S^ 2" t o Sb^S 2~; a l o g i c a l t r a n s i t i o n , as the more complex i o n forms i n s t r o n g e r s o l u t i o n s . A 1:2 S b ( I I I ) t o s u l p h i d e complex at low f r e e S 2" was s u g g ested i n the c a u s t i c t i t r a t i o n s s t u d i e s ( S e c t i o n 3.4.2). For b o t h s p e c i e s the i d e a l i z e d s l o p e s of the c o r r e s p o n d i n g 81 l o g p l o t s s h o u l d be one ( E q u a t i o n s 5-5 t o 5-9). Sb s + S 2" = S b 0 s / ' ...(5-5) {Sb} = {Sb S 2"} x 2 ...(5-6) 2 3 l o g ( { S b S }x2) = l o g { S 2 ' } + l o g K ( S b S 2") + l o g 2 + 2 4 4 7 ' l o g Y ( S 2 - ) Y (Sb.S, 2") ... (5-7) 2 4 2 Sb S + S 2 " = S b S 2 " ...(5-8) 2 3 4 7 l o g ( { S b 4 S 2 ? } x 4) = l o g { S 2 - } + l o g K(Sb S J") + l o g 4 l o g Y ( S 2 - ) Y (Sb S 2") . . .(5-9) 4 7 The Sb S 2' r e g i o n has a s l o p e of 0.81; the Sb S 2 -; 0.97. The 2 4 " 4 7 d i f f e r e n c e s between the s e s l o p e s and u n i t y can be a t t r i b u t e d to a c t i v i t y e f f e c t s . Even the weakest s o l u t i o n i n t h i s s e r i e s had a t o t a l i o n i c s t r e n g t h of 0.12 m o l a l - a s t r e n g t h h i g h enough t o r e q u i r e c o r r e c t i o n s beyond the Debye H u c k e l term f i r s t range. On a c o n c e n t r a t i o n b a s i s K(Sb S , 2") was c a l c u l a t e d t o be 2 4 0.95 ± 0.15 (95% c o n f i d e n c e l e v e l ) i n the low s u l p h i d e range and K(Sb,S 2") was 0.34 ± 0.01. The K v a l u e s may a l s o be a f f e c t e d 4 7 by a c t i v i t y c o e f f i c i e n t changes. A r n t s o n et a l . (1966) b e l i e v e d t h a t Sb S 2" e x i s t e d i n 4 7 s o l u t i o n . However, the K(Sb S 2") v a l u e g i v e n i n t h e i r paper i s 4 7 not comparable t o the r e s u l t above as t h e i r v a l u e was c a l c u l a t e d f o r E q u a t i o n 5-10 assuming the t o t a l h y d r o l y s i s of S 2". 2 Sb ?S 3 + HS" + OH" = Sb S 2" + H _0 . . . ( 5 - 1 0 ) . T h e i r q u o t e d K ( S b y S 7 2 " ) v a l u e of 5 t r a n s l a t e d t o 0.42 u s i n g the thermodynamics of Appendix F a p p l i e d t o E q u a t i o n 5-8. 82 The r e s u l t s of Dubey and Ghosh (1962) a r e a l s o shown on F i g u r e 5-1 a f t e r c a l c u l a t i o n s g i v e n i n Appendix F. T h e i r work, done a t 30°C (and c a l c u l a t e d as i f a t 25°C), was i n t e r p r e t e d i n terms of the Sb 2S 2" i o n - the s p e c i e s they b e l i e v e d t o be i n s o l u t i o n . The s l o p e of the l i n e from t h e i r r e s u l t s was 1.22 w i t h a K(Sb S, 2") v a l u e of 2.01 ± 0.13. T h e i r r e p o r t e d 2 4 K(Sb S 2") v a l u e was 120 based on an e r r o n e o u s s u l p h i d e 2 4 - ^ h y d r o l y s i s c o n s t a n t . The same d a t a i n terms of the c u r r e n t l y a c c e p t e d h y d r o l y s i s c o n s t a n t y i e l d s a FUSb^S^ 2") v a l u e of 1.2. KC1 was added t o f i x the a c t i v i t y c o e f f i c i e n t s of the s p e c i e s i n t h e i r s t u d y , and was u n d o u b t e d l y r e s p o n s i b l e f o r the poor match between t h e i r r e s u l t s and th o s e of A r n t s o n e t a l . (1966). Dubey and Ghosh (1962) used two l e v e l s of added KC1: 0.5 and 1.0, however, the l a c k of d i f f e r e n c e between t h e s e two s e t s seems anomalous i n view of the d i f f e r e n c e between the two s t u d i e s . 83 5.2 T e t r a h e d r i t e S o l u b i l i t y P l o t s A t r e a t m e n t a n a l o g o u s t o the one used f o r the p u b l i s h e d s t i b n i t e d a t a i n the p r e c e e d i n g s e c t i o n was used t o a n a l y s e the t e t r a h e d r i t e r e s u l t s generated." i n t h i s work. The S b ( I I I ) - s u l p h i d e complexes p r e s e n t i n s o l u t i o n were not e x p e c t e d to be the same as tho s e found i n the s t i b n i t e r e s u l t s s i n c e the S 2':Sb r a t i o s a r e much h i g h e r (Sb S a t 25°C i s more s o l u b l e than t e t r a h e d r i t e a t 100°C). The r e s u l t s of the t e t r a h e d r i t e e q u i l i b r i u m s t u d i e s were c o n v e r t e d i n t o a s o l u b i l i t y l o g p l o t format w i t h l o g {Sb} v e r s u s l o g { t o t a l N a 2S}, l o g { f r e e S 2"} and l o g { r e s i d u a l f r e e S 2'} c o n s i d e r i n g the complexes: Sb,S_ 2", Sb S 2', Sb S 2" and S b S 3 " . ^ ^ 4 / ' 2 4 2 5 3 In a l l c a s e s a c o r r e c t i o n f o r a r s e n i c ' i n s o l u t i o n was made assuming AsS ' was p r e s e n t ( S e c t i o n 4.8). The HS - - S 2~ - OH' e q u i l i b r i u m a t 100°C was c a l c u l a t e d t o d e t e r m i n e the f r e e S 2" c o n c e n t r a t i o n a f t e r the a p p r o p r i a t e number of moles of S 2" per mole of Sb were deducted f o r the complex under c o n s i d e r a t i o n . The c a l c u l a t i o n s and t h e i r r e s u l t s a r e shown i n Appendix G. A n a l y s i s of the l o g p l o t s produced was not v e r y u s e f u l . No complexes were e x c l u d e d by v i r t u e of the S 2":Sb r a t i o s of the s o l u t i o n s and the s c a t t e r of the p o i n t s on each p l o t was comparable. For 1 M i n i t i a l c a u s t i c t h e r e i s a f u l l range of l o g - l o g d a t a ( F i g u r e 5-2) and a d i s c o n t i n u i t y appears t o be p r e s e n t a t log{Sb} = -1.05 or log{Sb} =• -1.35 depending on the 0.4 h Line Fitted for I M initiol NoOH, Discontinuity ot Log ISbJ — 1.05 — 1.35 Initiol NoOH A 0 M V 0 5 M O I M D 2 M -2.4 -2.0 -1.6 -1.2 -08 -0.4 0 Log [Total No2S ] ( M ) F i g u r e 5 - 2 S o l u b i l i t y P l o t f o r T e t r a h e d r i t e E x p e r i m e n t a l R e s u l t s 0.4 85 i n t e r p r e t a t i o n chosen. In the f i r s t case the d i s c o n t i n u i t y appears as a gap between p a r a l l e l l i n e s , but a gap so wide t h a t a s s i g n i n g d i f f e r e n t complexes t o the s i d e s cannot c l o s e i t . In the second c a s e , the d a t a forms two i n t e r s e c t i n g l i n e s , but l i n e s t h a t i n t e r s e c t r e g a r d l e s s of the c h o i c e of complexes making up the p a i r . F i g u r e 5-3 i s a p l o t w i t h Sb S 2~ assumed 2 4 a t low S 2-; Sb S 2" a t h i g h S 2'. 4 7 * F i g u r e s 5-2 and 5-4 show log{Sb} v e r s u s l o g { t o t a l Na^S} c o r r e c t e d f o r AsS^". These p l o t s a r e i n t e n d e d t o show the r e s u l t s r a t h e r than t o e x p r e s s an e q u i l i b r i u m r e l a t i o n s h i p . T a b l e 5-1 g i v e s the s l o p e s and mean Sb/Na S v a l u e s f o r v a r i o u s 2 ' p o r t i o n s of t h e two f i g u r e s . The s l o p e s above log{Sb} = -1.05 d e c r e a s e w i t h i n c r e a s i n g i n i t i a l c a u s t i c and the mean Sb/Na^S v a l u e s i n c r e a s e . These e f f e c t s may be r e a l , due t o the s c a t t e r of the d a t a or due t o a c t i v i t y e f f e c t s . A l l the s l o p e s measured a p p r o x i m a t e d u n i t y . F i g u r e 5-5 i s a p l o t of Sb/Na 2S v e r s u s l o g { S b } . At low antimony c o n c e n t r a t i o n s the a r s e n i c c o r r e c t i o n s were r e l a t i v e l y l a r g e and the u n a d j u s t e d v a l u e s a r e a l s o shown. At h i g h antimony c o n c e n t r a t i o n s the d a t a are s u f f i c i e n t l y s c a t t e r e d so t h a t the p o i n t s f o r d i f f e r e n t i n i t i a l c a u s t i c s a r e i n t e r m i x e d . The 1 M i n i t i a l c a u s t i c p o i n t s show an upward 'jump' at log{Sb} -1.0. (The d i s c o n t i n u i t y i n F i g u r e 5-2 g i v e s the same i n f o r m a t i o n . ) A change such as t h i s would o c c u r i f a change i n the dominant S b ( 1 1 1 ) - s u l p h i d e complex o c c u r e d a t t h i s c o n c e n t r a t i o n . -0.4 •0.8 -1.2 -1.6 CO I I O -J -2.0 -2.4 -2.8 -1.6 -1.2 -0.8 - 0 .4 Log [ F r e e S 2"] ( M ) 0.4 Figure 5 -3 Experimental R e s u l t s P l o t t e d f o r the S b a s l " Ion at Low S u l p h i d e ; Sb 4S^~ Ion at High Sulphide 00 -0.4 Log [Total Na 2 S ] ( M ) F i g u r e 5 - 4 S o l u b i l i t y P l o t f o r T e t r a h e d r i t e E x p e r i m e n t a l R e s u l t s ( H i g h S u l p h i d e ) oo 88 T a b l e 5 - 1 : Mean Antomony t o S u l p h i d e R a t i o s and Sl o p e s t a k e n from F i g u r e s 5 - 2 and 5 - 4 I n i t i a l NaOH (M) 0 0 . 5 1 . 0 2 . 0 1 . 0 1 . 0 log{Sb} ( l o g M) > - l . 0 5 > - l . 0 5 > - l . 0 5 >-l . 0 5 <-l . 0 5 > - l . 3 Mean Sb/Na 2S* Slope (As C o r r e c t e d ) (mole/mole) 0 . 1 1 1 1 . 1 9 0 . 1 1 5 1 . 3 7 0 . 1 2 0 0 . 0 1 9 1 . 0 0 0 . 1 9 0 0 . 8 9 0 . 1 4 5 0 . 0 1 4 0 . 8 9 0 . 1 3 4 0 . 0 2 0 1 . 2 6 * 95% c o n f i d e n c e l i m i t s g i v e n 0.25 0.20 0.1 5 P CO CVJ o ^ 0.10 p CO 0.05 Initiol NoOH A 0 M v 0.5 M O I M • 2 M — - q l § — £ y — As Corrected Not As Corrected °2.8 -2.4 -2.0 -1.6 -1.2 -0 .8 -0 .4 Log [Sb] ( M ) Figure 5 - 5 The Antimony to Sulphide (Arsenic Corrected) Values versus Log Antimony 00 90 I f F i g u r e s 5-1 and 5-3 a r e compared (though they a r e a t d i f f e r e n t t e m p e r a t u r e s ) the d i s c o n t i n u i t y i n F i g u r e 5-3 f a l l s on the 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 o r d e r of the SbS^ 3~ r e g i o n i n F i g u r e 5-1. T h i s a c t s as a weak p i e c e of e v i d e n c e f o r SbS^ 3 ~ as the l e a c h e d antimony s p e c i e s . 91 C h a p t e r 6. D i s c u s s i o n 6.1 Review Of The R e s u l t s The f o l l o w i n g r e s u l t s a r e of s i g n i f i c a n c e i n u n d e r s t a n d i n g the p r o c e s s e s o c c u r r i n g d u r i n g the l e a c h . i ) Antimony was e x t r a c t e d from the c o n c e n t r a t e and h e l d i n s o l u t i o n . The q u a n t i t y l e a c h e d depended on the sodium s u l p h i d e and, t o a l e s s e r e x t e n t , on the sodium h y d r o x i d e c o n c e n t r a t i o n ( S e c t i o n 4.2.1). i i ) The antomony d i s s o l u t i o n r e s u l t s f o r 1 M i n i t i a l c a u s t i c p l o t t e d a g a i n s t the sodium s u l p h i d e c o n c e n t r a t i o n s were smoothed by a d d i t i o n of a sodium h y d r o x i d e f a c t o r ( S e c t i o n 4.7). i i i ) The net sodium s u l p h i d e c o n c e n t r a t i o n changes over the 24 hour e q u i l i b r i u m l e a c h i n g e x p e r i m e n t s were s m a l l . Most of the changes were n e g a t i v e ( S e c t i o n 4.6). However, w i t h i n the d u r a t i o n of e x p e r i m e n t s the sodium s u l p h i d e l e v e l s were observed to b o th f a l l and r i s e . i v ) The net c a u s t i c c o n c e n t r a t i o n rose i n a l l e x p e r i m e n t s e x c e p t i n t h e s e w i t h s u l p h i d e c o n c e n t r a t i o n s of g r e a t e r than 1 M 92 w i t h o u t added c a u s t i c ( S e c t i o n 4.7). v) An i n c r e a s e d c o n c e n t r a t i o n of Lron was found i n the c o n c e n t r a t e d e c o m p o s i t i o n p r o d u c t r e l a t i v e t o the t e t r a h e d r i t e phase. The p r o d u c t c o n t a i n e d z i n c and s i l v e r from the t e t r a h e d r i t e , and manganese, s i l i c o n and sodium from s o l u t i o n and from the o t h e r phases p r e s e n t i n the ' c o n c e n t r a t e ( S e c t i o n 4.13) . v i ) Sodium t h i o f e r r a t e appeared t o be p r e s e n t i n the l e a c h e d s o l i d s ( S e c t i o n 4.3). Sodium, presumably from t h i o f e r r a t e , was e x t r a c t e d by water washing ( S e c t i o n 4.16). v i i ) P y r i t e was d i s s o l v e d by sodium s u l p h i d e s o l u t i o n and sodium t h i o f e r r a t e was o b s e r v e d t o form ( S e c t i o n 4.17). v i i i ) The c o n c e n t r a t e d e c o m p o s i t i o n p r o d u c t was v e r y f i n e and x - r a y amorphous. For t h e s e r e a s o n s a p o s i t i v e i d e n t i f i c a t i o n of t h i s p r o d u c t was not p o s s i b l e by x - r a y d i f f r a c t i o n or by m i c r o p r o b e a n a l y s i s . j 93 6.2 C a u s t i c F o r m a t i o n And S u l p h i d e D e p l e t i o n The p r e s e n c e of o x i d e (and p o s s i b l y o x i d i z e d phases) was c o n f i r m e d by d i r e c t o b s e r v a t i o n and a c i d l e a c h i n g ( S e c t i o n 4 . 1 8 and 2.1.1). I f t h e s e o x i d e s were t o d i s s o l v e i n c a u s t i c and i f c o r r e s p o n d i n g s u l p h i d e s were more s t a b l e , then an i n c r e a s e i n c a u s t i c c o n c e n t r a t i o n would o c c u r c o u p l e d t o a d e c r e a s e i n s u l p h i d e ( E q u a t i o n s 6-1 and 6-2). MO + 20H- = MO 2 " + H 0 ...(6-1) 2 2 MO 2" + S 2" + 2H 0 = MS + 40H" ...(6-2) i 2 2 These changes were o b s e r v e d i n the m a j o r i t y of the e q u i l i b r i u m l e a c h i n g e x p e r i m e n t s . Fe, Cu, Mn and S i have c a u s t i c - s o l u b l e s p e c i e s ; Fe, Cu and Mn have s t a b l e s u l p h i d e s . S i n c e S i S ^ i s u n s t a b l e i n c o n t a c t w i t h aqueous s o l u t i o n , the p o s s i b i l i t y of s i l i c o n f o r m i n g a mixed s u l p h i d e seems remote. In the c a u s t i c - o n l y l e a c h i n g e x p e r i m e n t s no NaOH c o n c e n t r a t i o n i n c r e a s e was o b s e r v e d c o n s i s t e n t w i t h the proposed mechanism ( S e c t i o n 4.2.2) as no s u l p h i d e was p r e s e n t . In the s u l p h i d e - o n l y e x p e r i m e n t s ( S e c t i o n 4.7) a c a u s t i c i n c r e a s e was o b s e r v e d o n l y a t low -{Na^S} where h y d r o l y s i s p r o v i d e d t h e n e c e s s a r y c a u s t i c ( S e c t i o n 1.3.1). The c a u s t i c d e p l e t i o n a t h i g h {Na^S} was most l i k e l y due t o the r e t e n t i o n of c a u s t i c as sodium s i l i c a t e i n the s o l i d s . 94 6.3 Sodium T h i o f e r r a t e The i n f e r r e d p r e s e n c e of sodium t h i o f e r r a t e was u b i q u i t o u s t o t h i s l e a c h i n g s t u d y . The d i s p e r s e d c o l l o i d was o b s e r v e d i n weak s u l p h i d e c a u s t i c - f r e e s o l u t i o n s ( S e c t i o n 4.3). The l e a c h p r o d u c t c o n t a i n e d more sodium than e x p l i c a b l e on the b a s i s of e n t r a i n e d l e a c h s o l u t i o n ( S e c t i o n 4.14) and sodium was e x t r a c t a b l e from t h e s e s o l i d s by water washing ( S e c t i o n 4.16). 'Also d u r i n g washing the f i l t e r i n g r a t e s dropped and t h e r e were s m a l l b r e a k t h r o u g h s of i r o n - c o n t a i n i n g m a t e r i a l ( S e c t i o n 4.5). T h i s b e h a v i o u r can be i n t e r p r e t e d as the d e f l o c c u l a t i o n of t h i o f e r r a t e m o b i l i z i n g the sodium and c l o g g i n g the c h a n n e l s of the f i l t e r c a k e . Sodium t h i o f e r r a t e , a f e r r i c i r o n compound, c o u l d c o n c e i v a b l y be d e r i v e d from two s o u r c e s i n the c o n c e n t r a t e : f e r r i c o x i d e s and p y r i t e . 10% of the t o t a l i r o n was a c i d e x t r a c t a b l e ( S e c t i o n 2.1.1) and the a l k a l i n e s u l p h i d e d i s s o l u t i o n of t h i s i r o n c o u l d produce t h i o f e r r a t e . T h i o f e r r a t e was shown t o be produced by a Na 2S l e a c h on c r u s h e d p y r i t e ( S e c t i o n 4.17) . An i n t e r n a l redox r e a c t i o n ( E q u a t i o n 6-3)may o c c u r . 2FeS + Na 2S + S 2 " = 2NaFeS + S 2 2" ... (6-3) T h i s r e a c t i o n i s s p e c u l a t i v e and has never been p r e v i o u s l y r e p o r t e d . The l i t e r a t u r e i n d i c a t e s t h a t t h i o f e r r a t e s h o u l d not be 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 at 100°C ( E q u a t i o n 6-4) ( S e c t i o n 1.3.3). 95 2NaFeS 2 = 2Na* + 2 F e 2 * + S 9 2 " + 2 S 2 ' . . . ( 6 - 4 ) However, sodium (presumably t h i o f e r r a t e sodium) was found i n the s o l i d s of the 100 and 200°C l e a c h i n g e x p e r i m e n t s of S e c t i o n 4.14 and t h i o f e r r a t e was produced from p y r i t e a t 100°C. E q u a t i o n 6-3 p r o v i d e s a n o t h e r mechanism f o r s u l p h i d e d e p l e t i o n . The p o l y s u l p h i d e formed c o u l d d i s p r o p o r t i o n a t e s i n c e the s p e c i e s i s u n s t a b l e i n a l k a l i n e s o l u t i o n ( E q u a t i o n 6-7) o r , more l i k e l y , r e a c t w i t h a s o l i d p h a s e ( s ) p r e s e n t . 4S 2- + 80H" = 7 S 2 " + SO 2" ...(6-5) 2 4 6.4 D i s i n t e g r a t i o n Of The S o l i d s The c o n c e n t r a t e was q u i t e f i n e , more than 50% -400 mesh and c r y s t a l l i n e . . The l e a c h p r o d u c t , on the o t h e r hand, d i d not appear c r y s t a l l i n e a t 21,000x and was even f i n e r . The l a c k of d e c o m p o s i t i o n p r o d u c t d i f f r a c t i o n l i n e b r o a d e n i n g (as no p r o d u c t d i f f r a c t i o n l i n e s were produced) i n d i c a t e d a low c r y s t a l o r d e r ( l e s s than 0.01 um). P a r t i c l e s of t h i s s i z e a r e c o l l o i d a l . SEM x - r a y a n a l y s e s were done on a number of p r o d u c t a r e a s of a mounted, p o l i s h e d sample of l e a c h e d s o l i d s a t 80,000x u s i n g a reduced f i e l d of o b s e r v a t i o n . Each a r e a showed a spectrum s i m i l a r t o F i g u r e 4-11. The c o n s i s t e n t r e s u l t s over many a r e a s a t h i g h m a g n i f i c a t i o n suggest t h a t the d e c o m p o s i t i o n p r o d u c t i s f i n e and w e l l mixed. Manganese and s i l i c o n were found everywhere though t h e i r s o u r c e s a r e not i n the t e t r a h e d r i t e ( S e c t i o n 4.18). Sodium was not found everywhere, but t h i s may 96 be an e r r o r ( S e c t i o n 4.13). Because of the i n d i c a t e d f i n e p a r t i c l e s i z e of the d e c o m p o s i t i o n p r o d u c t and i t s x - r a y amorphous n a t u r e , i d e n t i f i c a t i o n of the m a t e r i a l by x-ray d i f f r a c t i o n or e l e c t r o n m i c r o p r o b e a n a l y s i s was not p o s s i b l e . For the same reasons i t i s not c e r t a i n whether the d e c o m p o s i t i o n p r o d u c t has.a d e f i n i t e c o m p o s t i o n a t a l l . The p r o d u c t may be a m i x t u r e of b i n a r y s u l p h i d e s ' or a c o l l e c t i o n of more complex compounds. There i s a p o s s i b i l i t y t h a t the d e c o m p o s i t i o n p r o d u c t i n c l u d e s compounds c o n t a i n i n g Na 2S ( s i m i l a r t o c o l l o i d a l NaFeS 2 ). T h i s would e x p l a i n the l a c k of s u l p h i d e i n s o l u t i o n i n the c a u s t i c - o n l y e x p e r i m e n t s ( S e c t i o n 4.2.3). 6.5 The C h a r a c t e r i s t i c s Of The Leach At low sodium s u l p h i d e c o n c e n t r a t i o n ( F i g u r e 5-2) t h e r e a ppears t o be a c l e a r c o r r e l a t i o n between the antimony and s u l p h i d e c o n c e n t r a t i o n s as would be e x p e c t e d f o r an e q u i l i b r i u m between the two. However, at h i g h s u l p h i d e c o n c e n t r a t i o n where most of the d a t a were c o l l e c t e d , t h e r e was a g r e a t d e a l of s c a t t e r and d e f i n i t i v e s t a t e m e n t s are d i f f i c u l t t o make. In g e n e r a l a t h i g h {Na^S} the antimony i n s o l u t i o n i n c r e a s e d w i t h both s u l p h i d e and c a u s t i c c o n c e n t r a t i o n s . The e f f e c t of c a u s t i c may be t o i n c r e a s e the a c t i v i t y of s u l p h i d e r e l a t i v e t o the antimony complex, but t h i s does not e x p l a i n the l a c k of d i f f e r e n c e between the 0.5 M and c a u s t i c f r e e r e s u l t s 97 o v e r t h e s a m e s o d i u m s u l p h i d e c o n c e n t r a t i o n r a n g e ( S e c t i o n 4.2.1). M o r e r e a s o n a b l y , t h e c a u s t i c m a k e s a c h e m i c a l c o n t r i b u t i o n t o t h e l e a c h i n g c h e m i s t r y , a r e s u l t w h i c h s e e m s t o b e v e r i f i e d b y t h e d e p e n d e n c e o f t h e a n t i m o n y l e a c h e d o n b o t h c a u s t i c a n d s u l p h i d e i n t h e 1 M i n i t i a l c a u s t i c e x p e r i m e n t s ( S e c t i o n 4.7). I f t h e c o n v e r s i o n o f o x i d e s t o s u l p h i d e s i s a s o u r c e o f c a u s t i c t h e n t h e d i s s o l u t i o n o f a n t i m o n y may a l s o b e a s s o c i a t e d w i t h t h i s c o n v e r s i o n . L e a c h i n g a p p e a r s t o b e s e n s i t i v e t o t h e p a t h t h a t t h e r e a c t i o n s f o l l o w . T h e t w o d u p l i c a t e s o f S e c t i o n 4.14 w e r e c a r e f u l l y m a t c h e d , y e t o n e p r o d u c t s o l u t i o n w a s 20% h i g h e r i n a n t i m o n y t h a n t h e o t h e r . S m a l l d i f f e r e n c e s i n m i x i n g o r d u r i n g t h e s h o r t h e a t - u p a n d i n i t i a t i o n p e r i o d o f t h e l e a c h i n g t e s t s m a y h a v e b e e n r e s p o n s i b l e . F i g u r e 4-8 i n d i c a t e s t h a t t h e i n i t i a l a n t i m o n y d i s s o l u t i o n r a t e c a n b e h i g h - l e a c h 3 w a s m o r e t h a n o n e - h a l f c o m p l e t e a f t e r 30 m i n u t e s w h e n t h e f i r s t s a m p l e w a s t a k e n . 98 6.6 S u l p h i d e As The L e a c h i n g Agent I f t e t r a h e d r i t e l e a c h e d i n a manner a n a l o g o u s t o t h a t of s t i b n i t e ( E q u a t i o n 6-6) t h e r e would be an e q u i l i b r i u m e s t a b l i s h e d between the m i n e r a l , s u l p h i d e and the antimony complex. Cu Sb S + S 2 ' = Sb S 2" + 5Cu S + CuS ...(6-6) 12 4 13 4 7 2 ( I n a l l the l e a c h i n g r e a c t i o n s w r i t t e n , the antimony complex and l e a c h p r o d u c t s w r i t t e n s e r v e o n l y t o i l l u s t r a t e the e q u a t i o n r a t h e r than d e s c r i b e the a c t u a l s p e c i e s . The. s p e c i f i c complex formed i s unknown and the s o l i d l e a c h p r o d u c t i s not l i k e l y t o be a d i s c r e e t compound(s) ( S e c t i o n 6 . 4 ) ) . D e s p i t e the o t h e r r e a c t i o n s o c c u r r i n g i n the l e a c h f l a s k , o x i d e - t o - s u l p h i d e c o n v e r s i o n s and t h i o f e r r a t e p r o d u c t i o n , E q u a t i o n 6-11 would e q u i l i b r a t e r e l i a b l y g i v e n the l o n g e x p e r i m e n t a l d u r a t i o n r e l a t i v e t o the a p p a r e n t l y f a s t l e a c h i n g r a t e s ( S e c t i o n 4.10). The r e s u l t s 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 uggest t h a t t h e r e i s a more complex p r o c e s s which l e a d s t o antimony d i s s o l u t i o n . ) 99 6.7 T h i o f e r r a t e As The L e a c h i n g Agent The major p i e c e s of e v i d e n c e t h a t suggest t h a t t h i o f e r r a t e i s the l e a c h i n g agent a r e i t s p r e s e n c e i n the l e a c h and the i n c r e a s e d i r o n c o n t e n t of the c o n c e n t r a t e d e c o m p o s i t i o n p r o d u c t r e l a t i v e t o the t e t r a h e d r i t e . A t h i o f e r r a t e - t e t r a h e d r i t e l e a c h can be seen as o p e r a t i n g by one of two mechanisms. In the f i r s t the (FeS ) c h a i n s of ^ n t h i o f e r r a t e would come i n t o c o n t a c t w i t h the t e t r a h e d r i t e and the i r o n would r e a c t d i s p l a c i n g an antimony, or a s e c t i o n of (FeS ) ° c h a i n would d i s p l a c e an e n t i r e SbS, group ( E q u a t i o n 6- 2 n J 7) . Cu Sb S + 4NaFeS = 4Na + + 2Sb S 2" + Cu Fe S ...(6-7) 12 4 13 2 2 4 12 4 13 The p r o c e s s i s a s o l i d - c o l l o i d a l r e a c t i o n which seems d i f f i c u l t . I t would be f a v o u r e d by t h e r m a l and shear f o r c e s which would s h o r t e n the t h i o f e r r a t e c h a i n s . I r o n replacement f o r antimony seems more r e a s o n b l e than e x t r a c t i o n of an SbS group as a l l the SbS s u l p h u r s a r e bound t o n o n - l e a c h i n g e l e m e n t s . By the second mechanism f e r r o u s i r o n i n e q u i l i b r i u m w i t h the t h i o f e r r a t e would be t h e a c t i v e agent ( E q u a t i o n s 6-8 and 6- 9 ) . 2NaFeS = 2Na + + 2 F e 2 + + S 2" + 2 S 2 ' ...(6-8) 2 2 Cu Sb S + 6 F e 2 + + 8 S 2 " = 2Sb S 2 - + Cu Fe S 12 4 13 2 4 12 4 13 ...(6-9) The p r o c e s s i s a s o l i d - s o l u t e r e a c t i o n which would be f a v o u r e d 100 by c o n d i t i o n s t h a t decompose t h i o f e r r a t e . One of these was g i v e n t o be t e m p e r a t u r e s above 80°C ( S e c t i o n 1.3.3). Both mechanisms p r e s e n t e d l e a c h s u l p h u r t o m a i n t a i n the s o l u t i o n charge b a l a n c e . The s u l p h u r c o u l d o r i g i n a t e i n the p y r i t e (Mechanism 1, O p t i o n 1 and Mechanism 2) or i n the t e t r a h e d r i t e (Mechanism 1, O p t i o n 2 ) . The m i c r o p r o b e a n a l y s i s i n d i c a t e d t h a t one i r o n and one s u l p h u r were added t o the l e a c h p r o d u c t f o r each antimony e x t r a c t e d ( S e c t i o n 4.13). L e a c h i n g Mechanism 1 has t h i s Fe~Sb s t o i c h i o m e t r y w h i l e Mechanism 2 would add 1.5 i r o n atoms per antimony atom e x t r a c t e d . N e i t h e r of the two mechanisms p o s t u l a t e d adds s u l p h u r t o the p r o d u c t . The most l i k e l y source of t h i s s u l p h u r i s p o l y s u l p h i d e formed d u r i n g t h i o f e r r a t e p r o u d u c t i o n . The pure m i x i n g of t h i o f e r r a t e i n t o the d e c o m p o s i t i o n p r o d u c t would te n d t o r a i s e the r a t i o of added i r o n t o added s u l p h u r t o 1:2. However, the e r r o r i n h e r e n t i n the m i c r o p r o b e a n a l y s i s of the p r o d u c t ( S e c t i o n 4.13) t a k e s s i g n i f i c a n c e away from the m i c r o p r o b e r e s u l t s i n g e n e r a l . 101 6.8 Sodium As The L e a c h i n g Agent S i n c e the changes i n s u l p h i d e c o n c e n t r a t i o n d u r i n g the l e a c h were r e l a t i v e l y s m a l l , sodium can be h y p o t h e s i s e d as a p o s s i b l e l e a c h i n g agent ( E q u a t i o n 6-10). Cu Sb S + 12Na + + 8 S 2 " = S Cu S + 2Sb S 2" ...(6-10) 12 4 13 .12 12 13 2 4 However, the p r o d u c t was found t o c o n t a i n too l i t t l e sodium; o n l y one sodium per antimony was added v e r s u s the e x p e c t e d t h r e e ( S e c t i o n 4.14) . 6.9 The Leach E q u i l i b r i u m Of the t h r e e a l t e r n a t i v e s p o s s i b l e f o r the l e a c h i n g agent, t h i o f e r r a t e seems t o be the most l i k e l y , though the e v i d e n c e from the e x p e r i m e n t a l r e s u l t s i s not overwhelming. Of the two t h i o f e r r a t e mechanisms p r e s e n t e d , the f i r s t which h y p o t h e s i s e s t h a t the i r o n from the t h i o f e r r a t e c h a i n s d i s p l a c e s antimony from t e t r a h e d r i t e seems more p l a u s i b l e , but a g a i n t h e r e i s no c o m p e l l i n g e v i d e n c e t o s u p p o r t t h i s v i e w . In any c a s e the n a t u r e of the l e a c h e q u i l i b r i u m has t o be q u e s t i o n e d t o examine the v a l i d i t y of the e q u i l i b r i u m e x p e r i m e n t s done. In c o n s i d e r i n g l e a c h i n g t h e r e a r e t h r e e t y p e s of s o l i d - s o l u t i o n r e a c t i o n m o r p h o l o g i e s . The s i m p l e s t i s s i m p l e d i s s o l u t i o n , i . e . the s o l i d phase t o t a l l y e n t e r s s o l u t i o n . E q u i l i b r i u m i s a c h i e v e d by the a p p r o a c h - t o - e q u i l i b r i u m k i n e t i c s of t h i s d i s s o l u t i o n . In l e a c h p r e c i p i t a t i o n a d i s s o l v e d 102 component p r e c i p i t a t e s and the approach t o e q u i l i b r i u m i s c o n t r o l l e d by the p r e c i p i t a t i o n , as - w e l l as the d i s s o l u t i o n k i n e t i c s . In s e l e c t i v e d i s s o l u t i o n o n l y a p o r t i o n of the i n i t i a l s o l i d d i s s o l v e s l e a v i n g a s u r f a c e r e s i d u e which may adhere t o the s u b s t r a t e i f the m o l a l volume change i s l e s s than ± 40%. The k i n e t i c s of d i s s o l u t i o n i n t h i s case a r e g r o s s l y a f f e c t e d by the c h a r a c t e r i s t i c s of the r e s i d u e and t h i s a f f e c t s the a pproach t o e q u i l i b r i u m . L e a c h - p r e c i p i t a t i o n may resemble s e l e c t i v e d i s s o l u t i o n i f p r e c i p i t a t i o n i s r a p i d . The p r o p o s e d t h i o f e r r a t e - t e t r a h e d r i t e l e a c h i n g mechanism i s a c o m b i n a t i o n of two of the m o r p h o l o g i e s . W i t h r e s p e c t t o t e t r a h e d r i t e s e l e c t i v e l e a c h i n g o c c u r s l e a v i n g a non-adherent c o l l o i d a l r e s i d u e . However, the c o l l o i d i s most l i k e l y f l o c c u l a t e d (as d e m o n s t r a t e d by i t s s e t t l i n g c h a r a c t e r i s t i c ( S e c t i o n 4.5)) which may cause i t t o form a c o a t i n g over the s u b s t r a t e t e t r a h e d r i t e . W i t h r e s p e c t t o the t h i o f e r r a t e l e a c h - p r e c i p a t i o n o c c u r s where the i r o n i s e x t r a c t e d and e n t e r s the l e a c h p r o d u c t . Of c o u r s e t h i o f e r r a t e i t s e l f i s the p r o d u c t of a l e a c h - p r e c i p i t a t i o n p r o c e s s and a c o l l o i d which mixes i n w i t h the d e c o m p o s i t i o n p r o d u c t . The s i t u a t i o n p r e s e n t e d i s complex and i n view of t h i s c o m p l e x i t y i t i s not c e r t a i n whether the e x p e r i m e n t a l l e a c h t e s t s r e ached e q u i l i b r i u m or whether the r e a c t i o n s j u s t s t i f l e d as the a v a i l a b l e t e t r a h e d r i t e s u r f a c e a r e a became b l i n d e d . A l t e r n a t i v e l y t h i o f e r r a t e may have become u n a v a i l a b l e as a r e a g e n t due t o d i l u t i o n by the p r o d u c t . 103 The term ' e q u i l i b r i u m ' evokes the concept of a b a l a n c e between a f o r w a r d and a backward r e a c t i o n . In t h i s case i t seems u n l i k e l y t h a t i f d i s s o l v e d antimony were t o be added t o the f i n a l ' e q u i l i b r i u m ' m i x t u r e s t h a t i n c r e m e n t a l t e t r a h e d r i t e and t h i o f e r r a t e would be t h e ' p r o d u c t . E x c e s s t h i o f e r r a t e a ppears t o be p r e s e n t i n the l e a c h e d s o l i d s (by the sodium a s s a y ) i n d i c a t i n g t h a t the p r o d u c t i o n of t h i o f e r r a t e does not c o n t r o l the l e a c h i n g of the t e t r a h e d r i t e . The e x t e n t of r e a c t i o n i s c o n t r o l l e d by the t h i o f e r r a t e - t e t r a h e d r i t e r e a c t i o n . Though the p o s s i b i l i t y t h a t the l e a c h a c h i e v e s a t r u e c h e m i c a l e q u i l i b r i u m i s i n q u e s t i o n the r e s u l t s s u p p o r t such a p o s s i b i l i t y . With t h i o f e r r a t e as the l e a c h i n g agent the S b ( I I I ) : S 2 _ r a t i o s o l u b i l i z e d i s 1:2. To show a s l o p e of u n i t y on a l o g { S b } - l o g { S 2 • } d i s s o l u t i o n p l o t ( S e c t i o n 5.2), the antimony complex i n s o l u t i o n would have t o be S b S ^ 3 - ( E q u a t i o n 6-11). Cu Sb S + 4NaFeS + 4 S 2 ' = 4Na + + 4SbS 3 " + Cu Fe Sb 12 4 12 2 3 12 4 13 ...(6-11) As d i s c u s s e d p r e v i o u s l y ( S e c t i o n 5.2) the d i s c o n t i n u i t y i n the t e t r a h e d r i t e d a t a f a l l s c l o s e t o the b o r d e r of SbS 3~ s t a b i l i t y 3 as d e t e r m i n e d by S h e s t i k o and Demina (1971) ( F i g u r e s 5-1 and 5- 3) though the t e m p e r a t u r e s c o n s i d e r e d a r e d i f f e r e n t . Most of the t e t r a h e d r i t e d a t a c o l l e c t e d o c c u r s i n the SbS 3 _ s t a b i l i t y 3 f i e l d . 104 6.10 The P r o g r e s s Of The Leach E x a m i n a t i o n of the Sb and, i n p a r t i c u l a r , the N a 2 ^ A v e r s u s time c u r v e s of S e c t i o n 4.10 i n d i c a t e s the l e a c h has two phases. In each phase the c o n v e r s i o n of o x i d e s t o s u l p h i d e and t h i o f e r r a t e p r o d u c t i o n d e p l e t e the s u l p h i d e c o n c e n t r a t i o n and then the t e t r a h e d r i t e l e a c h i n g ' c a t c h e s up' r a i s i n g the s u l p h i d e c o n c e n t r a t i o n . The antimony c o n c e n t r a t i o n always r i s e s . The c o n c e n t r a t e has a l a r g e f r a c t i o n of f i n e s which have a r e l a t i v e l y h i g h s u r f a c e a r e a (and r e a c t i v i t y ) . The f i n e s r e a c t i m m e d i a t e l y g i v i n g the f i r s t phase. C o a r s e r m a t e r i a l r e a c t s s l o w e r t o g i v e the second. The c a u s t i c c o n c e n t r a t i o n s were not measured. I f they had been they would have showed a s t e a d y r i s e much l i k e the Sb c o n c e n t r a t i o n s . The o b s e r v a t i o n t h a t most of the net s u l p h i d e changes were s l i g h t l y n e g a t i v e i s a r e s u l t of the e x t e n t of t h e r e a c t i o n s g i v e n the e x c e s s of c o n c e n t r a t e used. Below 50% Sb e x t r a c t i o n s u l p h i d e consuming r e a c t i o n s d o minated. Above 50% net i n c r e a s e s were o b s e r v e d . 105 Chapter 7. . C o n c l u s i o n s An e x p e r i m e n t a l t e c h n i q u e was d e v e l o p e d t o i n v e s t i g a t e the l e a c h i n g ' of t e t r a h e d r i t e . c o n c e n t r a t e i n sodium s u l p h i d e - s o d i u m h y d r o x i d e s o l u t i o n s . A n a l y t i c a l c h e m i s t r y p r o c e d u r e s were ad a p t e d f o r the d e t e r m i n a t i o n , of -sulphur s p e c i e s , c a u s t i c , a ntimony, and a r s e n i c i n . t h e s o l u t i o n s under c o n s i d e r a t i o n . X- ray d i f f r a c t i o n and e l e c t r o n m i c r o s c o p y were used t o study the c o n c e n t r a t e and the s o l i d l e a c h e d p r o d u c t . From the r e s u l t s the f o l l o w i n g c o n c l u s i o n s can be made : of antimony does not proceed by the s i m p l e antimony from t e t r a h e d r i t e l e a v i n g s o l i d c o p p e r - i ) The l e a c h i n g e x t r a c t i o n of s u l p h i d e s . i i ), The l e a c h s o l u t i o n s r e a c t , not o n l y w i t h t e t r a h e d r i t e , but w i t h . o t h e r phases i n the c o n c e n t r a t e p r o d u c i n g a f i n e , c o l l o i d a l , x - ray amorphous r e s i d u e . I d e n t i f i c a t i o n of the e x a c t n a t u r e of the p r o d u c t s i n the r e s i d u e was not p o s s i b l e . i i i ) I t i s u n l i k e l y t h a t the s o l u t i o n s produced a f t e r 24 h o u r s of l e a c h i n g r e p r e s e n t a t r u e c h e m i c a l e q u i l i b r i u m . The l e a c h i n g r e a c t i o n ( s ) appears t o be h i n d e r e d by the c o l l o i d a l c h a r a c t e r of t h i o f e r r a t e and the d e c o m p o s i t i o n p r e s e n t . 106 i v ) S u l p h u r i s s o l u b i l i z e d a l o n g w i t h the t e t r a h e d r i t e antimony. In the range of p u l p d e n s i t i e s i n v e s t i g a t e d , s u l p h i d e d e p l e t i n g r e a c t i o n s kept the net s u l p h i d e c o n c e n t r a t i o n changes s m a l l . v) C a u s t i c i s d i r e c t l y i n v o l v e d i n the c h e m i c a l r e a c t i o n s which l e a d t o antimony d i s s o l u t i o n . v i ) The t r e a t m e n t of p y r i t e w i t h a weak sodium s u l p h i d e s o l u t i o n p r o d u c e s sodium t h i o f e r r a t e . v i i ) In the l e a c h i n g of t e t r a h e d r i t e c o n c e n t r a t e the p r o d u c t i o n of t h i o f e r r a t e makes a c o n t r i b u t i o n t o the o v e r a l l c a u s t i c - s u l p h i d e c h e m i s t r y . The d e s i g n a t i o n of t h i o f e r r a t e as the t e t r a h e d r i t e l e a c h i n g agent c o u l d not be made c o n c l u s i v e l y . Though many i n t e r e s t i n g and unexpected r e s u l t s were o b t a i n e d i n t h i s s t u d y the work f a i l e d t o meet i t s o b j e c t i v e s . The l e a c h i n g e x p e r i m e n t s d i d not a c h e i v e an unambiguous e q u i l i b r i u m c o n d i t i o n and both the s o l i d d e c o m p o s i t i o n p r o d u c t and the antimony complex formed were not i d e n t i f i e d . The c o n c e n t r a t e c o n t a i n e d s e v e r a l r e a c t i v e phases engaging i n i n t e r l o c k i n g r e a c t i o n s . The f i r m c o n c l u s i o n s produced are s p a r s e , though much s p e c u l a t i o n i s p o s s i b l e . The r e s u l t s produced have a l i m i t e d a p p l i c a t i o n t o the Sun s h i n e l e a c h i n g p r o c e s s . As s t a t e d i n the i n t r o d u c t i o n the l e a c h i n g s o l u t i o n s a t the Su n s h i n e p l a n t c o n t a i n o x i d i z e d s u l p h u r s p e c i e s which were not added t o the e x p e r i m e n t a l l e a c h i n g m i x t u r e s . The sodium s u l p h i d e c o n c e n t r a t i o n s of the 107 Sunshine l e a c h s o l u t i o n a r e h i g h e r than those s t u d i e d i n t h i s work and the e x t r a c t i o n s a r e h i g h e r . The c h e m i c a l f e a t u r e s e x p e r i m e n t a l l y o b s e r v e d s h o u l d be i n d u s t r i a l l y a p p l i c a b l e , but they were not w e l l q u a n t i f i e d . The a n a l y s i s of the l i t e r a t u r e s t i b n i t e s o l u b i l i t y d a t a showed t h a t below log{Sb} = -0.7 , Sb S 2" i s p r o b a b l y the 4 7 predominant a n t i m o n y ( 1 1 1 ) - s u l p h i d e complex i n s a t u r a t e d s o l u t i o n a t 25°C. Above l o g { S b ] = -0.7 , Sb S 2 - i s the most l i k e l y 4 7 predominant comolex. The complexes SbS " SbS 3" and Sb S 2 3 2 5 are minor s p e c i e s i n s t i b n i t e - s a t u r a t e d s o l u t i o n s . 108 C h a pter 8. Recommendations f o r F u t u r e Study Much f u r t h e r work i s w a r r a n t e d i n the study of the a l k a l i n e s u l p h i d e l e a c h i n g of t e t r a h e d r i t e . The f o l l o w i n g i s a summary of recommendations. i ) p r e p a r e "pure" t e t r a h e d r i t e and i n v e s t i g a t e the e f f e c t of s u l p h i d e and t h i o f e r r a t e on t h i s m a t e r i a l i i ) i n v e s t i g a t e the p r o d u c t i o n of t h i o f e r r a t e from p y r i t e by s u l p h i d e , b o t h c h e m i c a l l y and e l e c t r o c h e m i c a l l y i i i ) i n v e s t i g a t e the e f f e c t of o x i d i z e d s u l p h u r s p e c i e s on antimony e x t r a c t i o n and the o t h e r phases p r e s e n t i n the t e t r a h e d r i t e c o n c e n t r a t e 109 Appendix A: The HS -S 2~-OH _ E q u i l i b r i u m C a l c u l a t i o n a t 100°C The d a t a was ta k e n from F e r r e i r a (1975). No a c t i v i t y c o e f f i c i e n t d a t a was a v a i l a b l e f o r HS and S^" t o make c o r r e c t i ons. . . . ( A - l ) K, = {H + HOH-} = 10-^2.21 H+ + S 2~ .= . . . (A-2) N K 2 { H S - } { H T T T S ^ - } = 10 10.98 K K = {OH-}{HS") = 10 1 2 {S 2~} - 1 . 2 3 = 0.0589 zOH + y S 2 ~ + xH 20 = xHS" + ( y - x ) S 2 - + (z+x)OH" ( z + x ) ( x ) = 0.0589 y-x x =-(z + 0.058 ) + V ( z + 0.058 ) + 0.2355y 2 F r a c t i o n added Na2S = y-x as S 2~ 110 Appendix B: X-ray D i f f r a c t o m e t r y T a b l e B - l : X-Ray D i f f r a c t o m e t r y R e s u l t s * Measured 2 e(deg) c*> RI (%) Assignment ** h k l L i t d. (A) 11.99 7 .38 . 5 AT '• ' O i l 7.3 16.90 5.24 5 T 002 5.2 24 .08 3.69 15 T 022 3.69 25. 95 3.43 5 M/G 110/111 3.44/3. 43 29. 62 3.01 100 AT/T//C 222//112 3.00//3 .03 31. 99 2.79 15 AT 123 2.80 33.02 2 . 71 20 M/P 020/200 2.71/2. 71 34 . 26 2.61 15 T 004 2.61 36. 50 2.56 10 36. 95 2 .43 5 T/P 003210 2.46/2. 42 38.48 2.34 5 4 0.73 2.21 5 P . 211 . 2.212 43'.10 2.10 5 G ;220 2.099 44.25 2 . 05 5 T 015,134 2.04 44.72 2.03 5 44.70 1.91 5 T a b l e B - l : X-ray D i f f r a c t o m e t r y R e s u l t s * ( c o n t ) Measured d 2 e ( d e g ) (A) RI Assignment** h k l (%) 4905 49.49 51. 06 54.03 56.25 57 .75 58 . 65 65.05 1.91 1.86 1.79 1.70 1.63 1. 60 1.57 1.43 15 25 5 5 5 5 10 5 C AT M T. T/P C AT 024 044 211 116,234 026/311 132 226 L i t . d (A) 1.8 54 1.855 1.76 1.687 •1.65/1 1. 59 1.58 * spectrum t a k e n a t 40 KV and 20 mA, Cu Ka r a d i a t i o n **Assignment Legend AT C G M P A r g e n t i a n T e t r a h e d r i t e C h a l c o p y r i t e G a l e n a M a r c a s i t e P y r i t e T e t r a h e d r i t e ASTM F i l e # 11-101 9-423 5- 0592 3-0799 6- 0710 1 1 - 1 0 7 112 Appendix C: C o n c e n t r a t e S t o i c h i o m e t r y C a l c u l a t i o n s C a l c u l a t i o n was based on 100 g of dry c o n c e n t r a t e w i t h the c o m p o s i t i o n g i v e n i n the t a b l e below. Mn was not c o n s i d e r e d . Element % MW (g/mol) Moles Cu 26.0 63.55 0.409 Fe 14-. 6 55.85 0.261 Sb 13.1 ' 121.75 0.108 S 29.1 32.06 0.908 As 1. 58 74 . 92 0.021 Zn 1. 67 65.38 0.026 Ag 3. 6 107 .87 0.033 Assuming a l l the a r s e n i c and antimony a r e c o n t a i n e d i n the t e t r a h e d r i t e . The Sb + As:S r a t i o i s 4:13 so S must be 0.419 moles. A l s o Sb+As:Ag+Zn+Cu+Fe i s 4:12 so Cu+Fe i s 0.328 moles. Assuming t h a t the o n l y o t h e r Fe, Cu and S c o n t a i n i n g phases a r e CuFeS and FeS ' the d i s t r i b u t i o n of t h e s e e lements was 2 2 c a l c u l a t e d . L e t : x = Cu i n ^ t e t r a h e d r i t e y = Fe i n t e t r a h e d r i t e a = r e l a t i v e moles of CuFeS 2 b = r e l a t i v e moles of FeS 2 113 E q u a t i o n s : x + y = 0.328 a = 0.409 - x b = 0.261 - a - y 2a + 2b = (0.908 - 0.419) S o l v i n g : x = 0.3115 y = 0.0165 a = 0.0975 b = 0.147 R e s u l t : (Cu , Fe Ag Zn ) ( Sb As ) S + 9.7 0.5 1.0 0.8 3.4 0.6 13 3.0 CuFeS +4.6 FeS 2 2 Lead was the o n l y s u l p h i d e m i n e r a l element not d e t e r m i n e d . S i n c e i t would t i e up e x t r a s u l p h u r as g a l e n a , 2a + 2b would be s m a l l e r and the Fe:Cu r a t i o of the t e t r a h e d r i t e would r i s e . For example, i f t h e c o n c e n t r a t e were 3% l e a d the a n a l y s i s would y i e l d : (Cu Fe Zn Ag ) (Sb As ) S + 0.4 PbS + 9.4 0.7 0.8 1.0 3.4 0.6 13 3.2 CuFeS + 4.1 FeS 2 2 A l e a d c o n t e n t as h i g h as 3% i s u n l i k e l y . A p p e n d i x D : E x p e r i m e n t a l R e s u l t s T a b l e D - l : Data f o r L e a c h i n g E x p e r i m e n t s C o n s i d e r e d i n the Study lutlon Analysis . A ' Inlt lal^ Cond It lone Sb Oil" s 2- s° *s 2- Aa Extraction cm" Uach Vol Cone Cone HjO (g/1 (M) («) (H) (H) (H) (g/D (I) (H) (M) (ml) (g-vet) (X) 0.202 (1.03) 0 0168 1 0.0278 ( l 03) 1 )0 25 I 7. 24 0.556 (1.03) 0 .0398 2 0.0593 1.07 (1.03) 0 .0659 5 0.0943 1.08 (1.03) 0 .0834 5 0.124 2.63 1.06 0 .230 - 0.01 - 0.01 0.38 11 0.265 (0 99) 7. 50 5.75 1.11 0 .48 - 0.07 - 0.01 22 0.48 9.58 1.23 0 .77 4 * ft 0.03 41 0.79 10.2 1.12 0 .93 ft • * 0.02 44 0.96 11.9 1.22 0 .780 - - - '0.04 1.13 26 0.793 5 0 16.1 1.24 0 .901 0.05 0.01 0.01 0.03 1.36 35 0.947 21.2 1.27 1 .18 0.03 * 0.07 0.07 46 1.26 22.2 1.21 1 .44 0.12 ft 0.02 48 1.46 2B.0 1.30 1 .42 * A * 0.06 2.18 42 1.48 75 28.9 1.04 1 .06 ft ft * 0.06 62 1.73 50 \ Table D-l: Data for Leaching Experiments Considered i n the Study (cont) 2-Sb OU- S (g/1) CH) (H) 11.5 2.19 0.470 18.5 2.12 1.01 34.0 2.17 1.46 5.75 0.62 0.510 12.2 0.64 0.987 18.6 0.69 1.54 31.2 0.82 1.92 1.90. 0.15 0.446 12.3 0.05 0.979 18 .4 -0.02 1.49 28.4 -0.09 1.96 Final Solution Analysis / , 0.33 0.54 0.35 Legend i 10.45) 10.96] [2.08] S 2 ° 3 2 " S ° 3 2 " S ° (n) (H? (") 0.02 0.03 0.02 0.06 0.04 0.05 0.02 0.04 0.01 0.01 0.04 0.03 0.04 *S (") 0.03 0.03 An (8/1.) Extrnctlon from solids (X) 25 40 49 I n i t i a l OndUlnns ( ) Indicates value calculated [ ] value equivalent to 2nd end point (Section 4.2.2) • - value of zero determined * result Impossible to Interpret 2- 2-*S difference between normal [S ] determination and 2- IS ] determination after Na^SO^ treatment; potential measure of Sb (V) s 1 - (H) 0.505 1.02 1.54 Oil (H) (•"!) (1.98) 130 I.each vol Cone- Cone.11̂ 0 0.01 0.53 12 0. 55 (0 50) 0.02 1.08 26 1. 06 0.03 1.25 40 1. 50 0.02 2.25 45 1 99 0.29 8 0 587 ( -) 0.09 1.13 24 1 08 A 1.48 40 1.52 0.04 2.13 41 2 .10 1 ( -) 0 .52 2 1.03 1 > 2 .08 130 130 (g-»et) (X) 50 7.50 50 75 25 50 50 75 25 50 50 75 25 25 25 7.50 7.50 7.42 Table D-2: Data for Leaching Experiments Not Consider Flnnl Solution Analysis • Sb Oil" s 2- S2°32" (g/D (11) (H) (M) 6.75 1.07 0.42 0.04 13.9 1.09 0.85 0.06 14.1 1.14 0.84 0.10 23.3 1.17 1.33 0.14 31.3 1.60 - 31.6 1.35 2.32 0.16 37.3 1.42 1.83 - 46.1 1.20 2.59 - 49.7 1 .25 2.83 - 17.8 1.17 0.87 0.12 22.9 2.24 0.94 0.10 27.3 2.75 1.30 0.16 38.6 2.22 1.86 - 41.7 2.90 1.87 0.22 44.1 2.64 1.94 0.24 54.8 5.96 1.57 - (H) 0.10 0.01 0.06 0.09 Initial Conditions s° s— - - • • Oil" Leach Vol . Cone (11) (M) (H) (ml) (g-wet) 0.03 0.48 (1. 02) 180 50 - 0.96 (1. 01) . 200 75 0.01 0.96 (1. .00) 180 75 ' - 1.45 (1. 00) 200 100 0.03 1.95 (1. ,00) 200 125 0.11 2.4 5 1. ,15 140 75 - 1.78 1. .14 120 60 0.09 2.51 1. .17 120 75 0.08 2.83 1 .04 120 85 0.02 0.99 (2.00) 200 75 0.02 0.97 2 .00 120 60 0.19 1.35 2 .25 140 60 0 05 1.92 2 .08 120 60 0.02 1.88 2 .92 120 75 0.02 1.98 2 .14 120 75 0.92 3.89 120 60 10.6 40.7 36.2 1.68 1.59 2.79 0.43 2.53 2.05 0.34 0.05 0.10 0.32 0.99 1.94 0.97 2.07 1.98 117 Appendix E: Antimony and S u l p h i d e C o n c e n t r a t i o n s v e r sus.Time A l l t he l e a c h e s were s t a r t e d w i t h 170 ml of s o l u t i o n and 75 g of wet c o n c e n t r a t e . Leaches 1 and 3 were 1 M i n i t i a l NaOH; 2 and.4 : 2 M NaOH ( c a l c u l a t e d , not measured). The l e a c h t e m p e r a t u r e was 100 C. Each sample was 10 ml. Ta b l e E - l : Sb and Na S v e r s u s Time R e s u l t s 2 Time (min) 0 30 . 60 120 240 480 1440 Leach 1 Sb (g/1) Na S 2 (M) 0 3.60 5.20 7.18 10.1 14.7 16.3 Leach 3 0.848 0.627 0. 595 0.660 0.663 0.701 0.726 Leach 2 Sb (g/1) 0 6.50 9.33 13.6 15.8 19.5 20.9 Leach 4 Na S 2 0.862 0.667 0.698 0.750 0.736 0.776 0.781 (M) Time Sb ( g / D Na S (M) Sb ( g / D Na S (min) 2 2 0 0 1.56 0 1.45 30 15. 8 1.46 18. 6 1.42 60 18. 6 1. 52 20. 3 1.53 120 20. 3 1.48 22. 3 1.48 240 21. 5 1.51 - - 480 25. 0 1.54 27. 3 1.52 1440 28. 2 1.57 - (M) Appendi x F: A n a l y s i s of the S t i b n i t e D i s s o l u t i o n Data 118 The d a t a of A r n t s o n et a l . (1966) was c o n v e r t e d from weight p e r c e n t Na S, Sb S and H 0 t o c o n c e n t r a t i o n s of S and 2 2 3 2 Sb by c o n s i d e r i n g the m o l a r i t y of t h e s e s o l u t i o n s t o be e q u a l t o t h e i r m o l a l i t y . The a p p r o p r i a t e number of moles of S~ 2 per mole of Sb were s u b t r a c t e d from the t o t a l f o r the complex c o n s i d e r e d and the HS"-S~ 2-OH~ e q u i l i b r i u m was c a l c u l a t e d t o de t e r m i n e the c o n c e n t r a t i o n of f r e e S" 2. A c a l c u l a t i o n p a r a l l e l t o t h a t shown i n Appendix A was used w i t h the f o l l o w i n g c o n s t a n t s (25°C): K = {H + }{OH~} = l C f 1 3 - " 7 1 K = {HS-}/{H +} { S 2 - } = i d 2 " 9 2 2 K K = 0.0838 1 2 Table F - l : Results of Log (Sb) - Log (Free S?" ) Calculations D a t a f r o m A r n t s o n e t a l . C o m p l e x C o n s i d e r e d l o g 2 [ F r e e S ~ 1 N a , S s b 2 s 3 ( m o l / k g "2° e o l n ) (Z/100) l o g [ S b ] ( M ) A 2 ( m o l / k g s o l n ) (H) S b 4 S 7 2 " S b 2 S 4 2 " sb 2 s 5 * - SbS33~ 0.058 0.0138 0.9908 -1.559 -1.809 -1.907 -2.167 -2.612 0.09A 0.0250 0.9842 -1.294 -1.502 -1.608 -1,905 -2.505 0.155 0.0426 0.9734 -1.058 -1.193 -1.297 -1.594 -2.234 0.241 0.0683 0.9580 -0.046 -0.932 -1.035 -1.332 -2.023 0.250 . 0.0712 0.9563 -0.827 -0.911 -1.014 -1.313 -2.016 0.315 0.1080 0.9307 -0.630 -0.791 -0.920 -1.352 -2.837 0.464 0.1667 0.9072 -0.434 -0.570 -0.720 -1.166 - 0.496 0.1766 0.9013 -0.407 -0.530 -0.660 -1.107 - 0.629 0.2325 0.8719 -0.273 -0.393 -0.527 -1.010 - 0.672 0.2576 0.8600 -0.223 -0.357 -0.4 97 -1.028 - 0.728 0.2602 0.8521 -0.201 -0.307 -0.438 -1.909 - 0.830 0.3205 0.8236 -0.098 t-0.232 -0.376 -0.948 - 0.917 0.3694 0.8029 -0.036 -0.171 -0.318 -0.917 - T a b l e F-2: R e s u l t s of E q u i l i b r i u m C o n s t a n t C a l c u l a t i o n s Na 0 S Sb S, K(Sb S 2') K(Sb. S 2~) 2 2 3 . 4 7 1 4 (mol/kg s o l n ) (mol/kg s o l n ) f r e e S 2" b a s i s f r e e S 0.058 0.0138 0.444 1 .114 0.094 0.0250 0.404 1.030 0.155 .0.0426 0.341 0.867 0.241 0.0683 0.305 0.773 0.250 0.0712 0.303 0.946 0 . 315 0.1080 0. 356 0 . 957 0.464 0.1667 0. 341 0 . 965 0 .496 0.1776 0.332 0.895 0 . 629 '0.2325 0.330 0.897 0.672 0.2576 0.340 0.940 0 .728 0.2682 0.319 0 .863 0.830 0.3285 0.340 . 0.948 0.917 0.3694 0.341 0.957 Mean K(Sb S 2') l a s t 8 = 0.337±0.008 (95% c o n f i d e n c e l e v e l ) 4 7 Mean K(Sb S 2") f i r s t 5 = 0.95±0.15 121 T a b l e F-3: R e s u l t s from C a l c u l a t i o n s on Data from Dubey and Ghosh (1962) L i t e r a t u r e Data Sb 2S 42- formed (M) Res Na 9S ( M ) Z l o g Sb (M) log „ { f r e e ^ (M) 0.5 M KC1: 0.00985 0.02563 •-1.706 -2.296 1.949 0.01081 0.02974 -1.665 -2.189 1.672 0.01503 0.03059 -1.522 -2.169 2. 219 0.01793 0.03276 -1.445 -2.121 2.367 0.01965 0.03611 -1.406 -2.053 2.217 1 M KC1: 0.01009 0.02722 -1.695 -2.253 1.806 0.01264 0.03000 -1.597 -2.183 1.927 0.01413 0.03170 -1.549 -2 .144 1.968 0.01518 0.03279 -1.518 -2.120 2.001 0.01690 0.03640 -1.471 -2.047 1.882 0.02054 0.03808 -1.386 -2.015 2.130 A l l R e s u l t s Mean K = 2.01±0.13 (95% c o n f i d e n c e l e v e l ) 0.5 M KC1: Mean K = 2 .08±0.31 1.0 M KC1 Mean K = 1. 9 5 ± 0 . 1 1 • *the complex Sb S 2 2 4 was c o n s i d e r e d 2 - 122 Appendix G: C a l c u l a t i o n of Log Antimony and Log S u l p h i d e Data from E x p e r i m e n t a l R e s u l t s The e x p e r i m e n t a l r e s u l t s were c o n v e r t e d i n t o l o g antimony and l o g s u l p h i d e form. S i x d i f f e r e n t forms of l o g s u l p h i d e data were c a l c u l a t e d : l o g { t o t a l S 2 }, l o g { f r e e S2 } and l o g 2 - 7 -{ r e s i d u a l f r e e S } c o n s i d e r i n g the complexes - Sb S~ , A 7 Sb S , Sb S ~ and SbS ~ . In a l l c a s e s a c o r r e c t i o n was made 2 4 2 5 _ 3 f o r a r s e n i c as AsS u s i n g the r e l a t i o n s h i p d e t e r m i n e d i n S e c t i o n 2 4.8 ( E q u a t i o n G - l ) . As(M) = 0.110 Sb(M) + 0.000278 . . . ( G - l ) The HS-S~ _-OH e q u i l i b r i u m at 100°C (Appendix A) was c a l c u l a t e d t o d e t e r m i n e the, f r e e S~ 2 c o n c e n t r a t i o n a f t e r the a p p r o p r i a t e number of . moles of S" 2 per mole of Sb were de d u c t e d f o r the complex under c o n s i d e r a t i o n . T a b l e G - l : R e s u l t s of C a l c u l a t i o n s f o r Log Antimony v e r s u s Log S u l p h i d e P l o t s 2 - l o g [ F r e e S ] * ( H ) S b O i l " s 2 " l o g [ S b ] l o g [ T o t a l S 2 ~ ] A S b . S , 2 ~ S b s 2 " 4 - S b . S , . S b S , 3 " ( M ) ( M ) ( H ) ( M ) ( M ) • 4 7 L j 0 . 0 0 1 6 6 ( 1 . 0 3 ) 0 . 0 1 6 8 - 2 . 7 8 0 - 1 . 9 6 4 - 1 . 9 8 8 - 2 . 1 2 3 - 2 . 1 4 6 - 2 . 1 9 6 - 2 . 2 5 4 0 . 0 0 4 5 7 ( 1 . 0 3 ) 0 . 0 3 9 8 - 2 . 3 4 0 - 1 . 4 7 8 - 1 . 5 0 3 - 1 . 6 2 2 - 1 . 6 4 2 - 1 . 6 6 1 - 1 . 7 3 4 0 . 0 0 8 7 9 ( 1 . 0 3 ) 0 . 0 6 5 9 - 2 . 0 5 6 - 1 . 2 3 4 - 1 . 2 5 6 - 1 . 3 9 0 - 1 . 4 1 3 - 1 . 4 6 1 - 1 . 5 1 8 0 . 0 0 8 8 7 ( 1 . 0 3 ) 0 . 0 8 3 4 - 2 . 0 5 2 - 1 . 1 2 0 - 1 . 1 4 3 - 1 . 2 4 3 - 1 . 2 5 0 - 1 . 2 9 3 - 1 . 3 3 1 0 . 0 2 1 6 1 . 0 6 0 . 2 3 - 1 . 6 6 6 - 0 . 6 5 8 - 0 . 6 8 1 - 0 . 7 6 3 - 0 . 7 7 7 - 0 . 0 0 4 - 0 . 8 3 3 0 . 0 4 7 2 1 . 1 1 0 . 4 8 - 1 . 3 2 6 - 0 . 3 3 3 - 0 . 3 5 5 - 0 . 4 4 1 - 0 . 4 5 4 - 0 . 4 8 3 - 0 . 5 1 4 0 . 0 7 8 7 1 . 2 3 0 . 7 7 - 1 . 1 0 4 - 0 . 1 2 7 - 0 . 1 4 6 - 0 . 2 3 5 - 0 . 2 4 9 - 0 . 2 7 9 - 0 . 3 1 2 0 . 0 8 3 8 1 . 1 2 0 . 9 3 - 1 . 0 7 7 - 0 . 0 4 3 - 0 . 0 6 4 - 0 . 1 4 1 - 0 . 1 5 3 - 0 . 1 7 9 - 0 . 2 0 6 0 . 0 9 7 7 1 . 2 2 0 . 7 8 0 - 1 . 0 1 0 - 0 . 1 2 3 - 0 . 1 4 3 - 0 . 2 5 5 - 0 . 2 7 4 - 0 . 3 1 4 - 0 . 3 5 8 0 . 1 3 3 1 . 2 4 0 . 9 0 1 - 0 . 8 7 8 - 0 . 0 6 3 - 0 . 0 0 2 - 0 . 2 1 9 - 0 . 2 4 2 - 0 . 2 9 3 - 0 . 3 5 1 0 . 1 7 4 1 . 2 7 1 . 1 8 - 0 . 7 5 9 0 . 0 5 5 0 . 0 3 6 - 0 . 0 9 9 - 0 . 1 2 3 - 0 . 1 7 3 - 0 . 2 3 1 0 . 1 8 2 1 . 2 1 1 . 4 1 - 0 . 7 3 9 0 . 1 3 5 0 . 1 1 5 0 . 0 0 0 - 0 . 0 2 0 - 0 . 0 6 1 - 0 . 1 0 7 0 . 2 3 0 1 . 3 0 1 . 4 2 - 0 . 6 3 8 0 . 1 3 5 0 . 1 1 6 - 0 . 0 3 6 - 0 . 0 6 3 - 0 . 1 2 2 - 0 . 1 9 0 0 . 2 3 7 1 . 0 4 1 . 8 6 - 0 . 6 2 5 0 . 2 5 6 0 . 2 3 4 0 . 1 2 0 0 . 1 0 1 0 . 0 6 0 0 . 0 1 5 s u l p h l d o v a l u e s c o r r e c t e d f o r a r s e n i c ( A s S ^ ) Table G-l: Results of Calculations for Log Antimony versus Log Sulphide Plots (con Sb Oil s 2 - l o g Sb l o g , [ T o t a l S 1 * ( H J l o g [ F r e e S 2 ) * ( M ) ( M ) ( H ) ( H ) ( M ) Sb, 4 4 - S b 2 S 5 Sbs 3 3" 0 . 0 9 ' . 5 2 . 1 9 0 . 1 7 0 - 1 . 0 2 5 - 0 . 3 5 3 - 0 . 3 6 4 - 0 . 5 6 7 - 0 . 6 0 6 - 0 . 6 9 5 - 0 . 8 0 7 0 . 1 5 2 2 . 1 2 1 . 0 1 - 0 . 8 1 8 - 0 . 0 1 3 0 . 0 2 5 - 0 . 1 6 4 - 0 . 1 8 8 - 0 . 2 4 0 - 0 . 3 0 0 0 . 2 7 9 2 . 1 7 1 . 4 6 - 0 . 5 5 4 - 0 . 1 4 4 0 . 1 3 3 - 0 . 0 5 5 - 0 . 0 9 0 - 0 . 1 6 9 - 0 . 2 6 6 0 . 0 1 7 2 0 . 6 2 0 . 5 1 0 - 1 . 3 2 6 - 0 . 3 0 6 - 0 . 3 4 3 - 0 . 4 2 3 - 0 . 4 3 6 - 0 . 4 6 2 - 0 . 4 9 1 0 . 0 9 9 0 0 . 6 4 0 . 9 9 - 1 . 0 0 1 - 0 . 0 1 7 - 0 . 0 4 9 - 0 . 1 3 9 - 0 . 1 5 3 - 0 . 1 8 2 - 0 . 2 1 4 0 . 1 5 4 0 . 6 9 1 . 5 4 - 0 . 8 1 1 0 . 1 7 6 0 . 1 4 5 - 0 . 0 5 9 0 . 0 4 5 0 . 0 1 5 - 0 . 0 1 6 0 . 2 5 6 0 . 8 2 1 . 9 2 - 0 . 5 9 1 0 . 2 6 9 0 . 2 4 4 0 . 1 2 2 0 . 1 0 2 0 . 0 5 8 - 0 . 0 1 0 0 . 0 1 5 6 0 . 1 5 0 . 4 4 6 - 1 . 8 0 7 - 0 . 3 5 6 - 0 . 4 5 2 - 0 . . 4 0 1 - 0 . 4 0 5 - 0 . 4 9 4 - 0 . 5 0 3 0 . 1 0 1 0 . 0 5 0 . 9 7 9 - 0 . 9 9 5 - 0 . 0 2 1 - 0 . 1 1 7 - 0 . . 2 1 5 - 0 . 2 3 1 - 0 . 2 6 4 - 0 . 3 0 0 0 . 1 5 1 - 0 . 0 2 1 . 4 9 - 0 . 8 2 2 0 . 1 6 2 0 . 0 6 1 - 0 . . 0 3 9 - 0 . 0 5 5 - 0 . 0 8 9 - 0 . 1 2 6 0 . 2 3 3 - 0 . 0 9 1 . 9 6 - 0 . 6 3 2 0 . 2 7 9 0 . 1 5 6 0 . . 0 2 7 0 . 0 0 6 - 0 . 0 4 1 - 0 . 0 9 4 * e u l p l i l d c v a l u e s c o r r e c t e d f o r n r n e n l c ( A s S ~ ) T a b l e G - 2 : Antimony t o S u l p h i Sb OH S 2 - (M) (M) (M) 0 . 0 0 1 6 6 ( 1 . 0 3 ) o r 0 1 6 8 0 . 0 0 4 5 7 ( 1 . 0 3 ) 0 . 0 3 9 8 0 . 0 0 8 7 9 ( 1 . 0 3 ) 0 . 0 6 5 9 0 . 0 0 8 8 7 ( 1 . 0 3 ) 0 . 0 8 3 4 0 . 0 2 1 6 1 . 0 6 0 . 2 3 0 . 0 4 7 2 1 . 1 1 0 . 4 8 0 . 0 7 8 7 1 . 2 3 0 . 7 7 0 . 0 8 3 8 1 . 1 2 0 . 9 3 0 . 0 9 7 7 1 . 2 2 0 . 7 8 0 . 1 3 3 1 . 24 0 . 9 0 0 . 1 7 4 1 . 2 7 1 . 1 8 0 . 1 8 2 1 . 2 1 1 . 4 1 0 . 2,3 0 1 . 3 0 1 . 4 2 0 . 2 3 7 1 . 0 4 1 . 8 6 125 de R a t i o s ? Sb/S 2 S (M) {As Co r r } {As C o r r } (mole/mole) 0 . 0 1 0 9 0 . 1 5 3 0 . 0 3 3 3 0 . 1 3 8 0 . 0 5 8 3 0 . 1 5 1 0 . 0 7 5 9 0 . 1 1 7 0 . 2 2 0 . 0 9 8 0 . 4 6 0 . 1 0 2 0 . 7 5 0 . 1 0 5 0 . 9 1 0 . 0 9 3 0 . 7 5 0 . 1 3 0 0 . 8 7 0 . 1 5 4 1 . 1 4 0 . 1 5 3 1 . 3 6 0 . 1 3 3 1 . 36 0 . 1 6 9 1 . 8 0 0 . 1 3 1 T a b l e G-2: Antimony t o S u l p h i d e R a t i o s ( c o n t . ) Sb OH (M) (M) 0.0945 2.19 0.152 2.12 0.279 2..17 0.0472 0.62 0.0998 0.64 0.154 0.69 0.256 0.82 0.0156 0.15 0.101 0.05 0.151 -0.02 0.233 -0.09 2- 2-S S (M) (M) {As C o r r } 0.470 0.44 1.01 0.97 1.46 1.39 0.510 0.49 0.99 0.96 1.54 1.50 1.92 1.86 0.446 0.44 0.979 0.95 1.49 1.45 1.96 1.90 , 2-Sb/S {As Corr} (mole/mole 0. 213 0.157 0.200 0.0.95 0.104 0.103 0.138 0. 035 0.106 0.104 0.123 Log [Free S2"] (M) F i g u r e G - l T h e S t i b n i t e S o l u b i l i t y D a t a o f A r n t s o n e t a l . ( 1 9 6 6 ) P l o t t e d C o n s i d e r i n g S b ^ S ^ a n d S b 4 S 7 " 128 REFERENCES A r n t s o n , R.H., F.W. D i c k s o n and G. T u n e l l . S c i e n c e (1966) 153 , p. 1673. B a i b o r o v , P.P., A.P. Ezhkov and S. Ishankhodzhaev. Khim. Redk. T s v e t n . Met. ( 1 9 7 5 ) . pp. 71-109. B a i b o r o v , P.P. T s v e t n . Met. (1975). pp.25-27. B a r n e r , H.E. And R.V. Scheuerman. Handbook of Thermochemical Data f o r Compound and Aqueous S p e c i e s (New York, 1978). John W i l e y & Sons. B a r r , L.N. Sunshine M i n i n g C o . - M e t a l l u r g y Summary ( S u n s h i n e , Idaho, 1973) , Sunshine M i n i n g Co. B a s s e t t , J . , R.C. Denney, G.H. J e f f e r y and J . Mendham. V o g e l ' s Textbook of Q u a n t i t a t i v e I n o r g a n i c A n a l y s i s , (London, 1978 ) ,• Longman . ' B l a s i u s , ^ E . , G. H o r n / A. K n o c h e l , J . Munch and H. Wagner. I n o r g a n i c S u l p h u r C h e m i s t r y , G. N i c k l e s s ( e d . ) , (Amsterdam, 1968), E l s e v e i r P u b l i s h i n g Co., pp. 199-239. B u s l a e v , Y.A., E.A. Krauchenko, I.A. Kuz'min, V.B. L a z a r e v , and A.B. S a l o v . R u s s i a n J . I n o r g . Chem. (1971) 6 , pp. 1782-1784. B u t l e r , J.N. I o n i c E q u i l i b r i u m : A M a t h e m a t i c a l Approach . ( R e a d i n g , M a s s a c h u s e t t s , 1964) , A d d i s o n Wesley P u b l i s h i n g Co. Dubey, K.P., and S. Ghosh. Z. Anorg. A l l g Chem. (1962) 31 , pp. 204-207. F e r r e i r a , R..C.H. L e a c h i n g and R e d u c t i o n i n H y d r o m e t a l l u r g y , A.R. B u r k i n ( e d . ) , ( London, 1975), IMM, pp. 67-83. Homes, W.C. EMJ ( 1 9 4 4 ) , 145 , pp. 54-58. L a t i m e r , W.E. The O x i d a t i o n S t a t e s of the Elements 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 (2nd. Ed. ) , ( Englewood C l i f f s , New J e r s e y , 1952) , P r e n t i c e H a l l I n c . Moss, K.C. And'M.A.R. Smith.. I n o r g a n i c C h e m i s t r y : S e r i e s Two. V o l . 2: Main Group Element-Groups IV and V , D.B. Sowerby ( e d . ) , ( London, 1975), B u t t e r w o r t h s pp. 221-267. Papp, J . C e l l . Chem. Tech. (1971) _5 , pp. 147-159. - S c a v n i c a r , S. Z. K r i s t a l l o g r . (I960) , 114 ,pp. 85-97. Seuryukov, M.N. and R. M u r t i . Zavod. Lab., 32 , pp. 144-146. S h e s t i k o , V.S. and O.P. Demina. Zh. Neorg. Khim. (1971), 1_6 p. 3167. S i l l e n , L.G. and A.E. M a r t e l l . S t a b i l i t y C o n s t a n t s of M e t a l - Ion Complexes ,( London, 1964), The C h e m i c a l S o c i e t y . T a k e u c h i , Y. And R. Sadang'a. Z. R r i s t a l l o g r . (1969) 130 , pp. 346-368. T a t s u k a , K. and N. Morimoto. Am. M i n e r a l . (1973), 58, pp. 425-434. T a y l o r , P. And D.W. Shoesmith. Can. J . Chem. (1978 ), 22. pp. 2798-2802. Vaugharn, D.J. And J.R. C r a i g . M i n e r a l C h e m i s t r y of M e t a l S u l p h i d e s , ( London,- 1978), Cambridge U n i v e r s i t y P r e s s . Wuensch, B.J. Z. K r i s t a 1 l o g r . , 1964, 11 ,pp. 437-453.

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