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UBC Theses and Dissertations

Reduction of thio-molybdate in aqueous solutions Okita, Yoshiaki 1969

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THE REDUCTION OF THIO-MOLYBDATE IN AQUEOUS SOLUTIONS by YOSHIAKI OKITA B. E n g . , The U n i v e r s i t y o f T o k y o , 1962 M. E n g . , The U n i v e r s i t y o f T o k y o , 1964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e D e p a r t m e n t o f METALLURGY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF B R I T I S H COLUMBIA December, 1969 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 an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . YOSHIAKI OKITA D e p a r t m e n t o f M e t a l l u r g y The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada i i ABSTRACT The h i g h t e m p e r a t u r e b e h a v i o u r o f the molybdenum (VI) - s u l p h u r (-II) -water s y s t e m i n the p r e s e n c e o f an ammoniacal b u f f e r was s t u d i e d . At 150°C. a l l s p e c i e s o f t h e form MoO. S were 4-x x shown to e x i s t and the s t a b i l i t y c o n s t a n t s o f mono-, d i - , 2 - 1 5 t r i - , and t e t r a - t h i o m o l y b d a t e were 2.3 x 10 M. , 3.5 x 10 M." 2, 2.7 x 1 0 8 M." 3, 7.0 x 1 0 1 0 M.~ 4, r e s p e c t i v e l y . T h e r e were s t r o n g i n d i c a t i o n s o f the f o r m a t i o n of p r o t o n a t e d s p e c i e s , Mo(SH)g, i n s o l u t i o n s c o n t a i n i n g low c o n c e n t r a t i o n of f r e e ammonia. A p p l i c a t i o n of r e d u c i n g g a s e s to t h i s s y s t e m p r o -duced a m i x t u r e of a s u l p h i d e and an o x i d e o f molybdenum , whose c o m p o s i t i o n depended on the i n i t i a l c o m p o s i t i o n of , the s o l u t i o n . Under h y d r o g e n , the r e d u c t i o n r e a c t i o n was a u t o -c a t a l y t i c , r a t e b e i n g f i r s t o r d e r i n p r o d u c t amount and h y d r o g e n p r e s s u r e . A mechanism was p r o p o s e d i n w h i c h the r a t e d e t e r m i n i n g s t e p was h e t e r o g e n e o u s a c t i v a t i o n of h y d r o g e n on the s u r f a c e s o f p r e c i p i t a t e s f o l l o w e d by two p a t h s , one to p r o d u c e the s u l p h i d e and t h e o t h e r to p r o d u c e the o x i d e . The p r o p o r t i o n of the s u l p h i d e to the o x i d e was dependent on t h e s o l u t i o n c o m p o s i t i o n , the h i g h e r the f r a c t i o n a l d i s t r i b u t i o n of t e t r a - t h i o m o l y b d a t e and the h i g h e r the c o n c e n t r a t i o n o f h y d r o g e n i o n , the more the s u l p h i d e b e i n g p r o d u c e d . Under c a r b o n monoxide the r e d u c t i o n r e a c t i o n was f o u n d to have an i n d u c t i o n p e r i o d . The molybdenum i n s o l u t i o n t h e n f o l l o w e d a l i n e a r d e c r e a s e i n c o n c e n t r a t i o n w i t h t i m e . The s l o p e of t h i s p l o t showed Langmuir t y p e of dependence on b o t h molybdenum c o n c e n t r a t i o n and p r e s s u r e . A mechanism was p r o p o s e d i n w h i c h the r a t e d e t e r m i n i n g s t e p was a s l o w d e c o m p o s i t i o n of some complex between t h i o m o l y -b d a t e s and c a r b o n monoxide a d s o r b e d s t r o n g l y on c a t a l y t i c p r e c i p i t a t e w h i c h was p r o d u c e d d u r i n g the i n d u c t i o n p e r i o d . i v ACKNOWLEDGEMENT I am g r a t e f u l to Dr. I.H. Warren f o r h i s d i r e c t i o n , p a t i e n c e and enc o u r a g e m e n t s t h r o u g h o u t the p r e p a r a t i o n of t h i s t h e s i s . I w i s h a l s o to thank a l l members o f the D e p a r t -ment of M e t a l l u r g y f o r t h e i r c o u n t l e s s a s s i s t a n c e s i n v a r i o u s f i e l d s d u r i n g my s t a y . I am t h a n k f u l and i n d e b t e d to the p e o p l e o f Canada f o r g r a n t s i n a i d o f r e s e a r c h t h r o u g h the N a t i o n a l R e s e a r c h C o u n c i l o f Canada and f o r f e l l o w s h i p s t h r o u g h the L e a d - Z i n c F o u n d a t i o n and the Uranium R e s e a r c h F o u n d a t i o n . To my w i f e I say thank y o u . V TABLE OF CONTENTS T a b l e Page INTRODUCTION 1 1 G e n e r a l 1 2 L i t e r a t u r e s u r v e y . 2 2-1 T e c h n o l o g y of molybdenum i n d u s t r y 2 2-2 H y d r o m e t a l l u r g i c a l t r e a t m e n t s o f moly-bdenum o r e s 4 2-3 R e d u c t i o n of aqueous molybdenum s o l u t i o n s 6 2-4 The molybdenum (VI) - s u l p h u r (-II) -water s y s t e m 8 2-4-a S a l t s o f t e t r a - s u b s t i t u t e d s p e c i e s 10 2-4-b S a l t s o f d i - s u b s t i t u t e d s p e c i e s . . 14 2-4-c S a l t s o f mono- and t r i - s u b s t i t u t e d s p e c i e s 15 2-4-d S p e c i e s o t h e r t h a n t h o s e of the form MoO, S  2~ 16 H — X X 2-4-e S t u d i e s of the e q u i l i b r i u m between the complex s p e c i e s 17 2-4-f A c i d d e c o m p o s i t i o n o f the complex s p e c i e s . . 17 2-5 S y n t h e s i s of molybdenum d i - s u l p h i d e . . . . 21 3 Scope o f p r e s e n t work 24 PART 1 - STUDY OF EQUILIBRIUM IN THE MOLYBDENUM (VI) -SULPHUR (-II) -WATER SYSTEM 26 1 P r i n c i p l e o f e x p e r i m e n t 26 2 E x p e r i m e n t a l 30 2-1 A p p a r a t u s and p r o c e d u r e s 30 2-2 Re a g e n t s 32 2- 3 A n a l y t i c a l methods 33 3 R e s u l t s and c a l c u l a t i o n s 36 3- 1 O b s e r v e d s p e c t r o g r a m 36 3-2 C a l c u l a t i o n of f o r m a t i o n f u n c t i o n and f r e e s u l p h i d e c o n c e n t r a t i o n 37 3-3 C o n v e r s i o n o f f r e e s u l p h i d e c o n c e n t r a t i o n to aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n 42 3-4 C a l c u l a t i o n o f s t a b i l i t y c o n s t a n t s f r o m f o r m a t i o n c u r v e 44 v i T a b l e Page 3-4-a B j e r r u m ' s H a l f - n Method 44 3-4-b Two-parameter A p p r o x i m a t i o n . . . . 47 3-4-c C a l c u l a t i o n of 49 3-4-d N u m e r i c a l c a l c u l a t i o n o f s t a b i l i t y c o n s t a n t s (1) 51 3-5 N u m e r i c a l c a l c u l a t i o n of s t a b i l i t y c o n s t a n t s (2) 53 4 D i s c u s s i o n and c o n c l u s i o n s 60 PART 2 - STUDY OF REDUCTION IN THE MOLYBDENUM (VI) -SULPHUR (-II) -WATER SYSTEM . . 72 1 E x p e r i m e n t a l 72 1-1 A p p a r a t u s and p r o c e d u r e s 72 1-2 A n a l y t i c a l p r o c e d u r e s 74 1-2-a A n a l y s i s of s o l u t i o n s 74 1-2-b A n a l y s i s o f p r e c i p i t a t e s 75 2 P r e c i p i t a t i o n i n an i n e r t a t m o sphere . 81 3 P r e c i p i t a t i o n i n h y d r o g e n 87 3-1 R e d u c t i o n p r o d u c t s 87 3-1-a Aqueous phase 87 3-1-b P r e c i p i t a t e s 87 3-2 K i n e t i c s t u d y 105 3-2-a E f f e c t of p r e s s u r e 107 3-2-b E f f e c t o f t e m p e r a t u r e 109 3-2-c E f f e c t o f c a t a l y s t 121 3- 2-d E f f e c t o f s o l u t i o n c o n d i t i o n s . . . . 123 3- 3 D i s c u s s i o n and C o n c l u s i o n 133 4 P r e c i p i t a t i o n i n c a r b o n monoxide 137 4- 1 R e d u c t i o n p r o d u c t s 137 4-2 K i n e t i c s t u d y 1 4 1 4- 2-a I n d u c t i o n p e r i o d 1^5 4-2-b Growth 1 4 8 v i i T a b l e Page 4 - 2 - b - l E f f e c t of s u l p h i d e c o n c e n t r a t i o n 148 4-2-b-2 E f f e c t of p r e s s u r e . . . 148 4-2-b-3 E f f e c t o f t o t a l moly-bdenum c o n c e n t r a t i o n . . . 150 4-3 D i s c u s s i o n and C o n c l u s i o n s 154 GENERAL SUMMARY AND CONCLUSIONS. 161 SUGGESTED FUTURE WORK 163 REFERENCES 165 APPENDICES 170 A E x p e r i m e n t a l d a t a 171 B S p e c t r o g r a m of s o l u t i o n s 184 C Rate of e q u i l i b r a t i o n 191 L I S T OF FIGURES T e c h n o l o g y o f molybdenum i n d u s t r y . . . . . P r e s s u r i z e d s o l u t i o n i n j e c t i o n s y s t e m . . . P l o t o f e q u a t i o n (10) C a l c u l a t i o n o f n n v s . S^ C o n v e r s i o n o f S. t o [H„S] r z aq. F o r m a t i o n c u r v e o f t h i o m o l y b d a t e s y s t e m a t 150°C. . . C a l c u l a t i o n o f k^ , 150°C. . . C a l c u l a t i o n o f k^ , 120°C N u m e r i c a l c a l c u l a t i o n o f s t a b i l i t y c o n s t a n t s (2) P l o t o f n u m e r i c a l c a l c u l a t i o n (2) S c h e m a t i c d i a g r a m o f t h i o m o l y b d a t e s y s t e m . V a r i a t i o n o f c o n c e n t r a t i o n s u n d e r n i t r o g e n F i r s t o r d e r p l o t X - r a y d i f f r a c t i o n p a t t e r n s o f p r e c i p i t a t e s T.G.A. o f p r e c i p i t a t e s f r o m r u n s . . . . D.T.A. o f p r e c i p i t a t e s f r o m r u n s . . . . C o m p o s i t i o n o f p r e c i p i t a t e s , v s . i n i t i a l s o l u t i o n c o m p o s i t i o n r d e p e n d e n c y on a c i d i t y ( r S + r H 2 ~ 3 ) V S ' r S P l 0 t ' ' ' .T.G.A. r e s u l t s , w e i g h t l o s s v s . r MOj v s . S^ and t i m e S V a r i a t i o n o f Mo T v s . t i m e , u n d e r i x F i g u r e Page 24 Log (Mo Q - Mo) v s . t i m e I l l 25 S l o p e and i n t e r c e p t v s . p r e s s u r e 112 26 Two-stage r u n 114 27 P l o t of a~ v s . a, d u r i n g p r e c i p i t a t i o n i n H 2 . . . . . 116 28 V a r i a t i o n o f t o t a l p r e s s u r e 118 29 P l o t of l n ( P / ( a + Po - P ) ) v s . time 120 30 E f f e c t of c a t a l y s t .' 122 31 E f f e c t of s o l u t i o n c o n d i t i o n , Mo^ v a r i a t i o n . . . 124 32 E f f e c t o f s o l u t i o n c o n d i t i o n , (NH^)^ SO^ amount v a r i a t i o n 126 33 P l o t o f s l o p e v s . a and [ N H ^ + ] / [ N H ^ J , 1 5 1 . 6 ° C . . 129 34 S l o p v s . ct 4 [ N H 4 + ] / [NH 3 J , combined 130 35 P l o t of 1 / s l o p e v s . 1/ ( a ^ [NH^"*"] / [NH^ ] ) 130 36 E f f e c t of s o l u t i o n c o n d i t i o n , S T v a r i a t i o n , 158.8°C 132 37 V a r i a t i o n o f Mo^ and S T , under CO 139 38 D.T.A. r e s u l t s o f p r e c i p i t a t e s from CO r u n . . . 140 39 V a r i a t i o n o f Mo^ under CO, h i g h M o T > P v a r i e s . . 142 40 V a r i a t i o n of Mo^ under CO, low Mo^, P v a r i e s . . 143 41 V a r i a t i o n of Mo^, under CO, h i g h Mo^,, S v a r i e s . . 144 42 I n d u c t i o n p e r i o d v s . p r e s s u r e 147 43 I n d u c t i o n r a t e c o n s t a n t v s . S^ 147 44 Growth r a t e v s . i n d u c t i o n p e r i o d 149 45 E f f e c t o f Mo T on r a t e , 158.8°C 149 46 Growth under CO, r a t e v s . p r e s s u r e 151 47 1 / r a t e v s . 1 / P C 0 p l o t 15? 48 I n t e g r a l p l o t , Y = l n Mo + a t . . . . . . . . . . 155 X F i g u r e Page B - l S p e c t r o g r a m o f s o l u t i o n s , E q u i l i b r i u m 186 B-2 S p e c t r o g r a m o f s o l u t i o n s , E q u i l i b r i u m l o w NH 3 187 B-3 S p e c t r o g r a m o f s o l u t i o n s , Run u n d e r ^ . . . . 188 B-4 S p e c t r o g r a m o f s o l u t i o n s , Run u n d e r CO . . . . 188 B-5 S p e c t r o g r a m o f s o l u t i o n s , Run u n d e r B.^ . . . . 189 B-6 S p e c t r o g r a m o f s o l u t i o n s , e q u i l i b r a t i o n . . . . 190 C - l V a r i a t i o n o f c o m p l e x c o n c e n t r a t i o n , room t e m p e r a t u r e 193 C-2 C 3 v s . t i m e , S T v a r i e d 194 C-3 C 3 / M o T S T v s . t i m e 196 C-4 P l o t o f r a t e v s . c o n c e n t r a t i o n ( n o r m a l i z e d ) 197 C-5 T e s t o f i n t e g r a l e q u a t i o n . 200 C-6 P l o t f o r C,, E q u a t i o n (C-5) 200 x i L I S T OF TABLES T a b l e Page 1 Summary o f s t a b i l i t y c o n s t a n t s c a l c u l a t e d by v a r i o u s methods 61 2 E f f e c t o f t e m p e r a t u r e on c o n s e c u t i v e c o n s t a n t s 69 3 P r o p e r t i e s o f v o l a t i l e m a t e r i a l s p r o d u c e d by h e a t i n g t h e p r e c i p i t a t e s 88 4 X - r a y d i f f r a c t i o n d a t a f o r M0S2 and p r e c i p i t a t e s f r o m v a r i o u s c o n d i t i o n s 90 5 C o m p o s i t i o n o f p r e c i p i t a t e s 96, 97 6 A n a l y s i s o f o x y g e n i n t h e p r e c i p i t a t e s 97 7 V a r i a t i o n o f r g and r R by t h e e x t e n t o f r e a c t i o n 2 106 8 E f f e c t o f t e m p e r a t u r e on t h e r a t e 120a A - l The s t u d y o f e q u i l i b r i u m 171 A-2 P r e c i p i t a t i o n u n d e r 175 A-3 P r e c i p i t a t i o n u n d e r H 2 1 7 6 A-4 P r e c i p i t a t i o n u n d e r CO 1 8 1 1 INTRODUCTION 1. G e n e r a l M o l y b d e n i t e , M 0 S 2 , i s w e l l known to be an e x c e l l e n t l u b r i c a n t , p a r t i c u l a r l y f o r h i g h t e m p e r a t u r e a p p l i c a t i o n s ^ . I t i s u s u a l l y m a n u f a c t u r e d by a complex p r o c e s s i n v o l v i n g m i n e r a l d r e s s i n g o f m o l y b d e n i t e c o n c e n t r a t e and l e a c h i n g w i t h 2 h y d r o f l u o r i c a c i d to remove a b r a s i v e m a t e r i a l s s u c h as s i l i c a Owing to i n c r e a s i n g demand, many a t t e m p t s have been made to 3 p r o d u c e m o l y b d e n i t e s y n t h e t i c a l l y . Most o f the a t t e m p t s have i n v o l v e d d i r e c t f u s i o n o f molybdenum compounds and s u l p h u r , w i t h v a r y i n g r e s u l t s , b ut no a t t e m p t s to p r o d u c e i t from an aqueous s y s t e m have been r e p o r t e d e x c e p t i n some e x p e r i m e n t s o f g e o c h e m i c a l i n t e r e s t . N o m i n a l l y m o l y b d e n i t e i s a compound o f t e t r a -v a l e n t molybdenum w i t h s u l p h u r . As the u s u a l and most s t a b l e s t a t e of molybdenum i s + 6 , p r o d u c t i o n o f m o l y b d e n i t e i s l i k e l y to i n v o l v e r e d u c t i o n and s u l p h i d i z a t i o n . The p r e s e n t work was u n d e r t a k e n to s t u d y the r e d u c t i o n o f aqueous s o l u t i o n s c o n t a i n i n g molybdenum i n the h e x a - v a l e n t s t a t e i n the p r e s e n c e o f s u l p h i d e i o n w i t h the o b j e c t o f p r o d u c i n g M 0 S 2 and of d e v e l o p i n g a r e c o v e r y t e c h n i q u e f o r molybdenum from p r o c e s s s o l u t i o n s . In the l i t e r a t u r e s u r v e y below, the f o l l o w i n g s u b j e c t s a r e r e v i e w e d : -2 1. The t e c h n o l o g y o f the molybdenum i n d u s t r y . 2. The h y d r o m e t a l l u r g i c a l t r e a t m e n t o f molybdenum o r e s and i n t e r m e d i a t e s . 3. The r e d u c t i o n o f aqueous s o l u t i o n s o f molybdenum. 4. The Mo(VI) - S ( - I I ) - w a t e r s y s t e m . 5 . The s y n t h e s i s o f M o S 2 -2. L i t e r a t u r e S u r v e y 2-1 T e c h n o l o g y of the molybdenum i n d u s t r y Molybdenum i s known to improve the q u a l i t y o f i r o n 4 and s t e e l a l l o y s . I t i s c l a s s i f i e d as a s t r a t e g i c m a t e r i a l and i t s use i s i n c r e a s i n g i n s p i t e o f i t s r e l a t i v e s c a r c e -n e s s i n n a t u r e (3/10,000 of i r o n ) " * . A l t h o u g h the major use of molybdenum i s i n the i r o n and s t e e l i n d u s t r y , t h e c o r r o s -i o n r e s i s t a n c e o f molybdenum m e t a l , the s p e c i a l l u b r i c a t i n g p r o p e r t i e s of M 0 S 2 and the c h e m i c a l u s e f u l n e s s o f molybdenum compounds as p i g m e n t s , c a t a l y s t s and r e a g e n t s have e s t a b l i s h e d molybdenum as an i n d i s p e n s a b l e e l e m e n t o f modern i n d u s t r y . The t e c h n o l o g y o f molybdenum p r o d u c t i o n i s summarized i n F i g . 1, i n w h i c h m a t e r i a l s u n d e r l i n e d r e p r e -s e n t the p r o d u c t forms t r a d e d w i t h the p e r c e n t a g e s l i s t e d as the l i m i t s o f the s p e c i f i c a t i o n . More t h a n 90% of molybdenum p r o d u c e d comes from m o l y b d e n i t e , of w h i c h about h a l f comes as a b y - p r o d u c t o f c o p p e r c o n c e n t r a t e p r o d u c t i o n . Owing to the f a c t t h a t no more p u r i f i c a t i o n i s done f o r t h e m a j o r i t y molybdenite(MoS 2) o x i d i z e d ores primary ore grade: 0.2 - l.C$MoS 2 copper by-products O.OI-O.O5/0M0S2 CaMo04, FbMo04, Fe 2(Mo0 4) 3, e t c . above 0.1#Mo mineral d r e s s i n g p u r i f i c a t i o n l e a c h i n g w i t h HF s o l u t i o n s molybdenite concentrates above 85%MoS2, below lfoCu r o a s t i n g t e c h n i c a l molybdic oxide(M0O3) above 55</oMo, below lfoCu and 0.25$S H y d r o m e t a l l u r g i c a l : treatments b r i q u e t t i n g w i t h p i t c h pyro- r e a c t i o n s u b l i m a t i o n metallurgy w i t h CaO : pure MoS 2  above99.9$MoS 2 above 52$Mo~ no s i l i c a t e s below 12$C, : below 0.5#Cu f e r r o -M0O3 b r i q u e t t molybdenum pure molybdic oxide above 99.5$>Mo03 r e a c t i o n r e a c t i o n w i t h NaOH w i t h WH3 CaMo04 58-6^Mo hydrogen r e d u c t i o n Na 2MoQ 4 ammonium- molybdenum metal molybdate powder  : above 95%Mo, below : 2.5f0Fe, 1 .5$Si, 0.5#Cu. l u b r i c a n t use: f e r r o - a l l o y s and foundries 85.Cf0 pigment f e r t i l i z e r c a t a l y s t s reagents sheet, rod, w i r e , nonferrous a l l o y s io-v.se i s i n terms of molybdenum content, i n lT.Sr.A. i n I966. r e f . "Mineral Yearbook" F i g . 1. Technology of molybdenum, (underlined are commercial forms w i t h s p e c i f i c a t i c e s below) 4 o f u s e s , m o l y b d e n i t e c o n c e n t r a t e must meet s t r i n g e n t p u r i t y r e q u i r e m e n t s . A l t h o u g h t h e m i n e r a l d r e s s i n g o f m o l y b d e n i t e i s t e r m e d s i m p l e 7 , s e v e r a l c l e a n i n g and r e - c l e a n i n g s t e p s w i t h i n t e r m e d i a t e l o w t e m p e r a t u r e r o a s t i n g o r s t e a m i n g and g r i n d i n g a r e n e c e s s a r y , s o m e t i m e s a t t h e e x p e n s e o f r e c o v e r y , 8 i n o r d e r t o meet t h e s p e c i f i c a t i o n s . I f p u r i t y s p e c i f i - . c a t i o n s a r e n o t met a f t e r t h e s e t r e a t m e n t s , h y d r o m e t a l l u r g i c a l o r o t h e r p r o c e s s i n g t e c h n i q u e s must be u s e d . H y d r o m e t a l l u r -g i c a l p r o c e s s i n g i s e s s e n t i a l i n t h e t r e a t m e n t o f o x i d i z e d o r e s o f molybdenum. L u b r i c a n t g r a d e m o l y d b e n i t e must meet e v e n more s t r i n g e n t p u r i t y r e q u i r e m e n t s s i n c e i t must be f r e e o f a l l a b r a s i v e s , p a r t i c u l a r l y s i l i c a , w h i c h i s n o r m a l l y 2 removed by t r e a t m e n t w i t h h y d r o f l u o r i c a c i d . M a j o r i t y o f m o l y b d e n i t e c o n c e n t r a t e s a r e r o a s t e d t o remove s u l p h u r and t h e r e s u l t i n g t e c h n i c a l m o l y b d i c o x i d e i s u s e d m a i n l y i n f e r r o -a l l o y s and f o u n d r i e s w i t h o u t f u r t h e r p u r i f i c a t i o n . F o r p r o d u c t i o n o f m e t a l and c h e m i c a l s a n o t h e r s t e p o f p u r i f i -c a t i o n i s n e c e s s a r y . S u l p h u r and o t h e r i m p u r i t i e s a r e removed by s u b l i m a t i o n o r h y d r o m e t a l l u r g i c a l t r e a t m e n t s , t h u s p r o d u c -i n g p u r e molybdenum t r i o x i d e , w h i c h i s f u r t h e r p r o c e s s e d t o p r o d u c e t h e d e s i r e d end products"''' ^  ' . 2-2 H y d r o m e t a l l u r g i c a l t r e a t m e n t o f molybdenum o r e s and  i n t e r m e d i a t e s . H y d r o m e t a l l u r g i c a l methods a r e c u r r e n t l y e m p l o y e d i n t h e p u r i f i c a t i o n o f t e c h n i c a l m o l y b d i c o x i d e and t h e p r o c e s s i n g o f o x i d i z e d o r e s . The f o r m e r i n v o l v e s 1) d i s s o -l u t i o n i n d i l u t e ammonia to remove s u l p h i d e s , s i l i c a and o t h e r i n s o l u b l e s 2) p r e c i p i t a t i o n and f i l t r a t i o n o f heavy m e t a l s s u c h as c o p p e r as s u l p h i d e s by a d d i t i o n o f ammonium h y d r o s u l p h i d e 3) p r e c i p i t a t i o n o f ammonium m o l y b d a t e by a c i d i f i c a t i o n 4) r e e r y s t a l l i z a t i o n and 5) c a l c i n a t i o n i n -to m o l y b d i c oxide'''"'". The s e c o n d a p p l i c a t i o n o f h y d r o -m e t a l l u r g y w h i c h i s more r e c e n t i s i n the p r o c e s s i n g of o x i d i z e d o r e s o f molybdenum, f o u n d o v e r l a y i n g s u l p h i d e o r e b o d i e s as f i n e l y d i s p e r s e d f e r r i c - m o l y b d a t e s e t c . , m o s t l y i n i r o n m i n e r a l s . I t i n v o l v e s 1) d i s s o l u t i o n i n a c i d 2) a d s o r p t i o n on c h a r c o a l 3) s t r i p p i n g w i t h an aqueous ammonia 4) c r y s t a l l i z a t i o n o f ammonium m o l y b d a t e and 12 5) c a l c i n a t i o n to p r o d u c e t e c h n i c a l g r a d e m o l y b d i c o x i d e The l e a c h i n g o f m o l y b d e n i t e c o n c e n t r a t e s has come to be a s u b j e c t o f i n t e r e s t b e c a u s e i t o f f e r s the p o t e n t i a l of p r o c e s s i n g l o w e r grade c o n c e n t r a t e s and g i v e s a c h o i c e o f p u r i f i c a t i o n methods. The l e a c h i n g methods p r o p o s e d a r e : -(a) i n a c i d media: HN0 3+H 2 SC> 4 1 3 ' 1 4 , H 2 S 0 4 + N a C 1 0 3 1 4 , H „ S 0 . + M n 0 o 1 5 2 4 2 (b) i n a l k a l i n e media: N a 2 C 0 3 + H C 1 0 1 6 ' 1 7 ' 1 8 , KOH+C>2 19 ( h i g h t e m p e r a t u r e ) (c) b a c t e r i a l l e a c h i n g . A l t h o u g h l e a c h i n g was s u c c e s s f u l , the o x i d a n t s employed were fo u n d c o s t l y . 6 V a r i o u s s t r i p p i n g and c o n c e n t r a t i o n methods f r o m t h e l e a c h e d s o l u t i o n were s u g g e s t e d , e.g. p r e c i p i t a t i o n as 13 14 20 f e r r i c m o l y b d a t e ' , molybdenum t r i - h y d r o x i d e and ammonium 17 21 23 m o l y b d a t e ' ' , i o n e x c h a n g e u s i n g a n i o n e x c h a n g e r e s i n s 18,24,25 , . 26 , ,12 and s o l v e n t e x t r a c t i o n u s i n g TBP , c h a r c o a l and 2 7 o t h e r s 2-3 R e d u c t i o n o f aqueous s o l u t i o n o f molybdenum R e d u c t i o n o f molybdenum c o m p l e x e s i n a c i d s o l u t i o n 2 8 i s known t o be p o s s i b l e , a l t h o u g h i t i s r e p o r t e d t h a t 29 m o l y b d a t e i o n i s r e d u c e d i n f i n i t e l y s l o w l y i n a l k a l i n e m e d i a An i n d u s t r i a l method has been s u g g e s t e d f o r r e c o v e r y o f molybdenum f r o m a c i d s o l u t i o n s as Mo(OH)^ a f t e r r e d u c i n g M 6 + • . ..20 Mo w i t h i r o n m e t a l 30 P a a l and Buetter s t u d i e d t h e a b s o r p t i o n o f g a s e -ous h y d r o g e n a t a t m o s p h e r i c p r e s s u r e and a t room t e m p e r a t u r e i n s o l u t i o n s (-0.05M.) o f ammonium m o l y b d a t e i n t h e p r e s e n c e o f a v e r y a c t i v e p a l l a d i u m h y d r o s o l added as a c a t a l y s t . A b s o r p t i o n was n o t e d t o o c c u r i n i t i a l l y v e r y r a p i d l y ( w i t h i n 30 min.) up t o a b o u t 5 0 ~ 6 0 % o f t h e t h e o r e t i c a l v a l u e o f r e d u c t i o n f r o m +6 t o +4, f o l l o w e d by a v e r y s l o w p r o c e s s , , c o m p l e t e r e d u c t i o n b e i n g a c h i e v e d o n l y a f t e r t h r e e d a y s . They a l s o r e p o r t e d t h a t t h e r e d u c t i o n p r o c e e d e d f u r t h e r , when h e a t (~60°C.) and s l i g h t o v e r p r e s s u r e o f h y d r o g e n was a p p l i e d , u n t i l r e a c h i n g t h e t h e o r e t i c a l v a l u e e q u i v a l e n t t o t h e r e -d u c t i o n o f h e x a - v a l e n t t o t r i - v a l e n t . From t h e p r e c i p i t a t e i n t h e i n i t i a l s t a g e , t h e y c o u l d , a f t e r c a r e f u l d r y i n g , 7 o b t a i n Mo(OH) 4' MoO(OH) and MoO 2 ' s u c c e s s i v e l y . L y a p i n a and Z e l i k m a n 31 s t u d i e d t h e h y d r o g e n r e -d u c t i o n i n a c i d s o l u t i o n . They r e p o r t e d t h a t t h e b a t c h r e d u c t i o n by h y d r o g e n was two t o f o u r t i m e s as f a s t when " p r i m e d " by molybdenum powder ( 7 % o f s t o i c h i o m e t r i c amount) t o f o r m M 0 O 2 s e e d c r y s t a l . The r e c o v e r i e s i n f o u r h o u r s a t 200°C. f r o m s o l u t i o n s c o n t a i n i n g 43.62 g . / l . o f molybdenum w i t h t h e i n i t i a l pH o f 2 were 99, 82, 70 and 34%, r e s p e c t i v e l y , f o r t h e h y d r o g e n p r e s s u r e o f 60, 40, 20 and 10 atm. ( f i n a l pH were 7.0, 6.56, 3.94 and 2.67, r e s p e c t i v e l y ) . A t 200°C, 60 atm. and i n f o u r h o u r s , an i n i t i a l pH o f 3, 5 and 7 gave 8 1 . 1 , 38.3 and 11.7% r e c o v e r y , r e s p e c t i v e l y . A t 100°C. ev e n an i n i t i a l pH o f 2 gave o n l y 4 1 % p r e c i p i t a t i o n u n d e r t h e same c o n d i t i o n . A t 200°C., 60 atm. and i n one h o u r , t h e r e c o v e r y i n c r e a s e d f r o m 78% t o 99% when i n i t i a l c o n c e n t r a -t i o n s o f molybdenum were d e c r e a s e d f r o m 43.6 t o 5.33 g . / l . 32 I n a s u b s e q u e n t p a p e r t h e y r e p o r t e d t h e s e l e c t i v e r e d u c t i o n o f t u n g s t e n f r o m a s o l u t i o n c o n t a i n i n g t u n g s t e n and m o l y -bdenum. When a s o l u t i o n c o n t a i n i n g 41.0 g.Mo/1. and 5 g.W/1. a t i n i t i a l pH o f 2 was r e d u c e d a t 200°C. and P 20 atm. f o r 90 m i n . , t h e s o l u t i o n c o n t a i n e d 38.9 g.Mo/1. and 0.5 g.W/1. and t h e p r e c i p i t a t e was 47% and 40% i n Mo and W r e s p e c t i v e l y . When t h e s o l u t i o n was r e d u c e d s u b s e q u e n t l y a t 200°C. and P = 60 atm. w i t h Mo powder added as an a c c e l e r a t o r , t h e s o l u t i o n c o n t a i n e d 0.3 g . / l . o f Mo and W r e s p e c t i v e l y . As t h e pH v a l u e v a r i e d c o n s i d e r a b l y t h e i r d a t a a r e d i f f i c u l t t o a n a l y s e . 2 2 A somewhat d i f f e r e n t a p p r o a c h t o t h e r e d u c t i o n i n 33 an a c i d s o l u t i o n was a d o p t e d by Dodonova who s t u d i e d t h e p h o t o l y s i s o f a c i d i f i e d s o d i u m m o l y b d a t e s o l u t i o n s (made pH = 2 by H C l a d d i t i o n ) u n d e r v a r i o u s a t m o s p h e r e s s u c h as H 2 , CO, C 0 2 , He, vacuum, H 2 + 0 2 and CO + 0^. He n o t e d t h e 6+ a p p e a r a n c e o f b l u e c o l o r due t o t h e r e d u c t i o n o f Mo t o Mo^ + u n d e r H 2 and CO and no a p p e a r a n c e u n d e r t h e o t h e r s . He a t t r i b u t e d t h e l a t t e r f a c t t o t h e o x i d a t i o n o f Mo"'+ by t h e p h o t o l y s i s p r o d u c t s o f w a t e r , w h i c h w o u l d o t h e r w i s e c o mbine w i t h H 2 and CO t o f o r m H 20 and HCHO t h u s a v o i d i n g t h e r a p i d 5 + r e o x i d a t i o n o f Mo . When 0 2 was i n c r e a s e d i n H 2 + 0 2 m i x t u r e , t h e b l u e c o l o u r d i s a p p e a r e d . R e d u c t i o n o f molybdenum w i t h h y d r o g e n i n a m m o n i a c a l s o l u t i o n was s t u d i e d , w i t h an i n d u s t r i a l a p p l i c a t i o n i n m i n d , g by Kunda and Rudyk . The e f f e c t s o f c a t a l y s t , s o l u t i o n r e c y c l i n g , c o n c e n t r a t i o n s o f ammonium i o n , f r e e ammonium and i n i t i a l molybdenum, h y d r o g e n p a r t i a l p r e s s u r e and temperT a t u r e , on t h e r a t e and e x t e n t o f p r e c i p i t a t i o n were d e t e r -m i n e d . They a g a i n f o u n d p a l l a d i u m v e r y e f f e c t i v e ( a d d e d as 0.5% P d C l 2 s o l u t i o n ) as a c a t a l y s t , as w e l l as m e t a l l i c molybdenum powder, m e t a l l i c n i c k e l and g r a p h i t e , a t 177°C., and 24.5 atm. H 2 f o r a s o l u t i o n c o n t a i n i n g 1 M.Mo, 1~1.5 M . ( N H 4 ) 2 S 0 4 and 1.5~2 M.NH^• They f o u n d an a p p r o x i m a t e l i n e a r i n c r e a s e o f t h e r a t e o f p r e c i p i t a t i o n w i t h t h e c o n -c e n t r a t i o n s o f c a t a l y s t s and ( N H ^ ^ S O ^ and w i t h p a r t i a l p r e s s u r e o f h y d r o g e n ( b e l o w 23 a t m . ) , and a l i n e a r d e c r e a s e o f t h e r a t e o f p r e c i p i t a t i o n w i t h t h e i n i t i a l c o n c e n t r a t i o n o f molybdenum. I n c r e a s e o f f r e e ammonium d e c r e a s e d the r a t e o f r e d u c t i o n . The t e m p e r a t u r e dependence o f the r a t e of p r e c i p i t a t i o n a t c e r t a i n v a l u e s o f v a r i a b l e s was s t u d i e d w i t h P d C l ^ and Mo m e t a l powder as t h e c a t a l y s t . In b o t h c a s e s t h e a p p a r e n t a c t i v a t i o n e n e r g y was f o u n d to be 16.4 K c a l . / m o l e . T h e i r p r e c i p i t a t e s c o n t a i n e d 60-65% Mo and 4-5% NH^, s u g g e s t i n g t h a t the r e d u c t i o n had p r o c e e d e d p a r t l y to t h e t r i v a l e n t s t a t e (67% Mo i n Mo(0H> 3). 2-4 The M o ( V I ) - S ( - I I ) - w a t e r s y s t e m In the M o ( V I ) - w a t e r s y s t e m , under weak a c i d c o n -4- 34 d i t i o n s , l a r g e i s o p o l y i o n s a r e f o r m e d , e.g., Mo^C^^ and a l a r g e f a m i l y o f h e t e r o p o l y i o n s w i t h many m e t a l l i c and n o n - m e t a l l i c i o n s , e.g., r v n + M rt ,m(2x-36-n)- „ ...2+ _ 2+ 2+ 2+ 4+ ro3+ [X Mo,0 ] , X = N l , Co , Mn , Cu , Se ,P , 6 x m 35 e t c . . But under s u f f i c i e n t l y a l k a l i n e c o n d i t i o n s t h e s e 2-complex i o n s decompose i n t o the s i m p l e m o l y b d a t e i o n , MoO^ . 2-When s u l p h i d e i o n , S , i s i n t r o d u c e d i n t o the 2-M o ( V I ) - w a t e r s y s t e m , i n t e r c h a n g e o f o x i d e i o n , 0 , w i t h s u l p h i d e i o n can be e x p e c t e d b e c a u s e o f t h e s i m i l a r i t y o f t h e s e i o n s . Most o f the s t u d i e s o f t h i s s y s t e m up to 1928 3 6 were r e v i e w e d by M e l l e r and up to 1963 by the C h e m i c a l 3 7 S o c i e t y o f London . The more r e c e n t s t u d i e s a r e r e v i e w e d i n t h e f o l l o w i n g o r d e r : 10 2 _ (a) s a l t s o f t e t r a - s u b s t i t u t e d s p e c i e s , MoS^ , 2 -(b) s a l t s o f d i - s u b s t i t u t e d s p e c i e s , M 0 O 2 S 2 , ( c ) s a l t s o f mono- and t r i - s u b s t i t u t e d s p e c i e s , M o 0 3 S 2 ~ , M o O S 3 2~, 9 (d) s p e c i e s o t h e r t h a n o f t h e f o r m MoO, S (x = 1 - 4 ) , (e) s t u d i e s o f t h e e q u i l i b r i a b e t w e e n t h e c o m p l e x s p e c i e s , ( f ) a c i d d e c o m p o s i t i o n o f t h e c o m p l e x s p e c i e s . 2 -2-4-a S a l t s o f t e t r a - s u b s t i t u t e d s p e c i e s , MoS^ S a l t s o f t h e t e t r a - s u b s t i t u t e d s p e c i e s ( o r t e t r a -2-t h i o m o l y b d a t e ) MoS^ , have b e e n c l a i m e d by a number o f * 36 w o r k e r s . The ammonium s a l t ( NH^^MoS^ was p r e p a r e d as a b l o o d - r e d , n e e d l e - l i k e c r y s t a l by Kruess i n 1884 by s a t u r -a t i n g an a m m o n i a c a l ammonium p a r a m o l y b d a t e s o l u t i o n w i t h , 3 9 h y d r o g e n s u l p h i d e g a s . T r i d o t and B e r n a r d a l s o p r e p a r e d i t s i m i l a r l y f o r t h e i r v i s i b l e and U.V. s p e c t r o s c o p i c s t u d y . A l k a l i m e t a l s a l t s have been o b t a i n e d 3 ^ . Spacu and c o - w o r k e r 4 ^ p r e p a r e d t h e s a l t s o f c o m p l e x m e t a l l i c amine o f Cu and C r : [ C r ( N H 3 ) 6 ] [ M O S 4 ] N 0 3 | H 2 0 , [ C r ( N H 3 ) 6 C l ] [ M o S 4 ] , [ C r 4 ( O H ) 6 e n 6 ] I M O S 4 ] 2 S 0 4 , [ C r 4 ( O H ) 6 e n 6 ] [ M o S 4 ] 2 C l 2 and [Cu e n 2 ] [ M o S 4 ] | H 2 0 . and s t a t e d t h a t t h e s e s a l t s were more s t a b l e t h a n t h e s i m p l e a l k a l i m e t a l s a l t s . They a l s o p r e p a r e d t h e s a l t s o f o r g a n i c b a s e s s u c h as t h o s e o f a m i n o p y r i d i n e , e t h y l e n e d i a m i n e , h e x a -m e t h y l e n e t e t r a m i n e and 1 , 1 0 - p h e n a n t h r o l i n e . P e r e l ' m a n and 41 c o - w o r k e r s e m p l o y e d t h e s o l u b i l i t y method t o s t u d y t h e s o d i u m s a l t s s y s t e m . A f t e r d i s s o l v i n g N a ^ o O ^ , N a 2 S and NaOH a t 60-70°C. i n w a t e r t o make up t h e c o m p o s i t i o n r a n g e o f M o 6 + = 3~30%, S 2 " = 6~13% and NaOH = 5~40%, t h e m i x t u r e s were k e p t a t 25°C. f o r 24 h o u r s and s o l i d and l i q u i d p h a s e s were a n a l y s e d . They r e p o r t e d t h a t N a ^ o S ^ d i d n o t e x i s t b e l o w 27% NaOH c o n c e n t r a t i o n p e r h a p s due t o t h e i n s t a b i l i t y 42 o f t h e N a 2 M o S 4 l a t t i c e . Bock and L a n g r o c k p r e p a r e d an u n s t a b l e compound, t e t r a - t h i o m o l y b d i c a c i d , H 2 M o S 4 , by p a s s -i n g a s o l u t i o n o f t h e ammonium s a l t t h r o u g h t h e H + f o r m o f a 43 + c a t i o n e x c h a n g e r e s i n . C l a r k and D o y l e c o n f i r m e d t h e K and NH"!" s a l t s b u t d e n i e d t h e e x i s t e n c e o f t h e s a l t s o f 4 C o ( l l ) , N i ( I I ) , C u ( I I ) and Z n ( I I ) , s t a t i n g them t o be m i x -t u r e s o f s u l p h i d e s o f t h e s e m e t a l s w i t h molybdenum t r i s u l p h i d e 44 L e r o y and c o - w o r k e r s p r e p a r e d q u a r t e r n a r y ammonium s a l t s by t h e r e a c t i o n o f m o l y b d i c a c i d w i t h NX^OH (X = Me o r E t , ) . The s o l u t i o n was s a t u r a t e d w i t h h y d r o g e n s u l p h i d e and a f t e r a few d a y s c r y s t a l s o f (NMe^^MoS^ and ( N E t ^ ^ M o S ^ were f o r m e d a t -5°C. They a l s o p r e p a r e d ( P P h ^ ^ M o S ^ and ( A s P h ^ ^ MoS^ by r e a c t i o n o f t h e ammonium s a l t w i t h t h e c h l o r i d e o f . t h e c o r r e s p o n d i n g t e t r a p h e r i y l c o m p l e x . S a x e n a and c o -45 46 w o r k e r s ' c o n f i r m e d t h e f o r m a t i o n o f PbMoS^ by ampero-m e t r i c t i t r a t i o n o f P b ( N 0 , j ) 2 and t h i o m o l y b d a t e s o l u t i o n . C r y s t a l l o g r a p h i c s t u d y o f t h e s a l t s o f t e t r a -t h i o m o l y b d a t e s and s p e c t r o s c o p i c s t u d y o f t h e t e t r a - t h i o -m o l y b d a t e i o n i n s o l u t i o n h a v e b e e n r e p o r t e d by s e v e r a l 3 8 w o r k e r s . Kruess grew l a r g e c r y s t a l s o f ( N H ^ ^ M o S ^ and K^MoS^ and f r o m t h e m e a s u r e m e n t s o f a n g l e s b e t w e e n h a b i t p l a n e s , H a u s h o f e r r e p o r t e d them as h a v i n g r h o m b i c symmetry op / 7 w i t h ;a:b-:c = 0.7846:1 :0.5692 . G a t t o w made an X - r a y s t u d y of t h e ammonium t e t r a - t h i o m o l y b d a t e c r y s t a l and r e p o r t e d i t t o be o r t h o r h o m b i c w i t h t h e u n i t c e l l l e n g t h as a = 9.599, b = 1 2 . 2 8 8 , c = 7.000 A, and i t s s p a c e g r o u p t o be - Pnam, i s o - m o r p h o u s w i t h K^SO^ t y p e c r y s t a l , i n w h i c h NH^ i o n and MoS^ 2 t e t r a h e d r a l i o n a r e p a c k e d r a t h e r l o o s e l y 4 8 + + G a t t o w and F r a n k e s u m m a r i z e d t h e i r X - r a y d a t a f o r K , Rb , + + 4 9 5 0 Cs and NH^ s a l t s . S c h a e f f e r e t a l . r e p o r t e d t h e same 2-e x p e r i m e n t and s t a t e d t h a t MoS^ t e t r a h e d r a are s l i g h t l y d i s t o r t e d . The Mo-S bond s t r e n g t h has been s t u d i e d by I.R. and Raman s p e c t r o s c o p y . G a t t o w , F r a n k e and M u e l l e r ^ m e a s u r e d t h e I.R. s p e c t r a o f I^MoS^ c r y s t a l s , where M = K + , + + + + 5 2 Rb , Cs NH^ and T l , and r e p o r t e d t h a t t h e band f r e q u e n c i e s o b s e r v e d f o r c o m p l e x a n i o n s a r e p r a c t i c -a l l y u n c h a n g e d by t h e v a r i o u s c a t i o n s . Bands were f o u n d a t 4 6 0 , 4 8 0 , 1 5 5 , 195 and 280 cm." 1, and t h e f i r s t t h r e e o f 2-t h e s e were a s s i g n e d t o v ^ » v 3 a n ^ v i b r a t i o n o f MoS^ t e t r a -43 + h e d r a . C l a r k and D o y l e s t u d i e d t h e c r y s t a l s o f K and + 2-NH^ s a l t s a l o n g w i t h MoO^ s a l t s and r e p o r t e d t h e e x i s t e n c e of d i s c r e t e MoS 2- i o n s and t h e e f f e c t o f s u b s t i t u t i o n o f 4 by S 2- was t o a p p r o x i m a t e l y h a l v e the v i b r a t i o n a l f r e -q u e n c i e s . The t h e o r e t i c a l t r e a t m e n t by M u e l l e r and c o -w o r k e r s 53 r e v e a l e d t h e h i g h e r d o u b l e b o n d i n g c h a r a c t e r of Mo-S bonds. L e r o y , Kaufman and C h a r l i o n e t 44 s t a t e d t h a t t h e y d i d n o t o b s e r v e much s h i f t i n bands nor a p p e a r a n c e o f new bands i n I.R. s p e c t r a of t h e i r q u a r t e r n a r y ammonium s a l t s , by the change of the s i z e o f c a t i o n . The e l e c t r o n i c s t a t e o f t h e t e t r a - t h i o m o l y b d a t e i o n can be s t u d i e d by t h e v i s i b l e and U.V. s p e c t r o s c o p y o f 39 th e aqueous s o l u t i o n . T r i d o t and B e r n a r d s t u d i e d t h e s p e c t r o g r a m between 200 and 500 my o f t h e aqueous s o l u t i o n s , -4 (1.25x10 M.), o b t a i n e d by d i s s o l v i n g c r y s t a l s o f ammonium s a l t w h i c h t h e y p r e p a r e d by K r u s s ' s method. They r e p o r t e d the a b s o r p t i o n peaks a t 210, 240, 325 and 465 my and the m o l a r e x t i n c t i o n c o e f f i c i e n t s a t 392.5 and 465 my as 700 and - 1 - 1 54 10,800 M. cm. , r e s p e c t i v e l y . Y a t s i m i r s k i and Z a k h a r o v a 39 d i d n o t o b s e r v e t h e p e a k s , s t a t e d by T r i d o t and B e r n a r d , i n t h e i r s p e c t r o p h o t o m e t r i c s t u d y of d i l u t e s o l u t i o n s o b t a i n e d by m i x i n g ammonium m o l y b d a t e s o l u t i o n and sodium s u l p h i d e s o l u t i o n . T h i s d i s a g r e e m e n t may be due t o the s l o w n e s s o f the r a t e o f a p p r o a c h to the e q u i l i b r i u m n o t e d by T r i d o t and B e r n a r d . Companion and Mackin"'"' i n t e r p r e t e d t h e a b s o r p t i o n peaks as the c h a r g e t r a n s f e r o f an e l e c t r o n on t h e s u l p h i d e i o n to a m o l e c u l a r o r b i t a l l o c a l i z e d on t h e m e t a l i o n . M u e l l e r , R i t t e r and N a g a r a j a n 56 compared t h e 2- 2-e l e c t r o n a b s o r p t i o n s p e c t r a o f MoO^ and MoS^ and s t a t e d t h a t TT-bonds must a l s o be assumed i n t h e t h i o a n i o n . L a t e r M u e l l e r and E k k e h a r d ^ 7 summarized t h e i r s p e c t r o s c o p i c s t u d y on MX^ a n i o n s where M = V, Mo, W and X = 0, S, Se. They i n t e r p r e t e d t h a t t h e band c o r r e s p o n d e d to t ^ -»- 2e, t r a n s -i t i o n of e l e c t r o n f r o m t h e n o n - b o n d i n g m o l e c u l a r o r b i t a l t ^ to a weak a n t i - b o n d i n g m o l e c u l a r o r b i t a l 2e w h i c h i s e s s e n t i a l l y l o c a l i z e d on the m e t a l atom, and t h a t the s t r o n g l y - b o n d i n g m o l e c u l a r o r b i t a l l e i s s t a b i l i z e d by t h e i n c r e a s e i n a n t i - b o n d i n g c h a r a c t e r o f m o l e c u l a r o r b i t a l 2e. 2 -2-4-b S a l t s of d i - s u b s t i t u t e d s p e c i e s , MoO^S^ The ammonium s a l t o f the d i - s u b s t i t u t e d s p e c i e s , o r 2 — " 3 8 d i - t h i o m o l y b d a t e M 0 O 2 S 2 , was p r e p a r e d by K r i i s s by t h e same p r o c e d u r e as f o r the s a l t of t h e t e t r a - t h i o m o l y b d a t e e x c e p t t h a t a c h i l l e d s o l u t i o n h a v i n g a s l i g h t l y h i g h e r ammonium c o n c e n t r a t i o n was u s e d . He o b t a i n e d y e l l o w c r y s t a l s w h i c h r e d d e n e d on e x p o s u r e to a i r . R e c e n t l y H o f m e i s t e r and G a t t o w ^ p r e p a r e d i t by the same method. P e r e l ' m a n e t a l . 4 " ' ' p o s t u l a t e d the e x i s t e n c e o f Na2Mo02S2 to e x p l a i n t h e i r r e s u l t s of a s o l u b i l i t y i n v e s t i g a t i o n a t low Na 2S and NaOH 39 c o n c e n t r a t i o n . T r i d o t and B e r n a r d p r e p a r e d the ammonium s a l t by K r u s s ' s method, e x c e p t t h a t t h e y added the ammonium c h l o r i d e to f a c i l i t a t e the c r y s t a l l i z a t i o n . From t h e U.V. s p e c t r o g r a m o f the aqueous s o l u t i o n t h e y r e p o r t e d t h e m o l a r 2-e x t i n c t i o n c o e f f i c i e n t of M o 0 2 S 2 i o n a t 290 my o f 6,950, -1 -1 54 M. cm. . Y a t s i m i r s k i i and Zakh'arova p r o v e d t h e e x i s t e n c e 2 -o f M 0 O 2 S 2 I o n f r o m a s p e c t r o g r a p h i c s t u d y o f d i l u t e s o l u -t i o n , when s o d i u m s u l p h i d e t o ammonium m o l y b d a t e r a t i o i s g r e a t e r t h a n 4 t o 1 i n 2 x 10 4 M. Mo s o l u t i o n . M u e l l e r and 59 G a t t o w i n v e s t i g a t e d t h e I.R. s p e c t r o s c o p y o f t h e ammonium s a l t and r e p o r t e d t h e f u n d a m e n t a l f r e q u e n c i e s t o be 8 3 6 , 800, 4 88, 305 and 200 cm." 1. They compared t h e s e w i t h t h e -2 s p e c t r u m o f MoO^ s a l t and s t a t e d t h a t t h e e n t r y o f two . 2-s u l p h u r atoms i n t o MoO^ d e c r e a s e d t h e M-0 bond s t r e n g t h . 6 0 L e r o y and Kaufman o b s e r v e d t h e Raman s p e c t r u m o f t h e ammonium s a l t u s i n g a He-Ne l a s e r as t h e e x c i t a t i o n s o u r c e . The r e c o r d e d l i n e s were i n d e x e d on t h e a s s u m p t i o n t h a t 2-M 0 O 2 S 2 has symmetry. 2-2-4-c S a l t s o f mono- and t r i - s u b s t i t u t e d s p e c i e s , MoO„S 2-and MoOS 3  Few s t u d i e s o f t h e mono- and t r i - s u b s t i t u t e d s a l t s , 2- 2-o r mono- and t r i - t h i o m o l y b d a t e MoO^S and MoOS^ , h a v e 3 8 be e n r e p o r t e d . Kruess c l a i m e d t o have p r e p a r e d t h e s o d i u m 41 s a l t o f m o n o - t h i o m o l y b d a t e , Na2Mo0.jS. P e r e l ' m a n e t a l . p o s t u l a t e d b o t h mono—and t r i - t h i o m o l y b d a t e t o e x p l a i n t h e i r 61 s t a b i l i t y d a t a . H o f m e i s t e r and G l e m s e r s t a t e d t h a t t h e t r i - and m o n o - t h i o m o l y b d a t e were t h e p r o d u c t o f h y d r o l y s i s o f t e t r a - and d i - t h i o m o l y b d a t e , r e s p e c t i v e l y . T r i d o t and 6 2 B e r n a r d s t u d i e d t h e a b s o r p t i o n o f h y d r o g e n s u l p h i d e by a l k a l i n e m o l y b d a t e s o l u t i o n and f r o m t h e s p e c t r o g r a m s o f t h e s o l u t i o n s a t d i f f e r e n t d e g r e e s o f s u l p h i d i z a t i o n , t h e y c o n -c l u d e d t h a t m o n o - t h i o m o l y b d a t e d i d n o t e x i s t b u t t h a t t r i -t h i o m o l y b d a t e e x i s t s and has t h e a b s o r p t i o n peak a t 392.5 my w i t h t h e m o l a r e x t i n c t i o n c o e f f i c i e n t s a t 392.5 and 465 my o f 9,850 and 400 M. cm. ^, r e s p e c t i v e l y . Y a t s i m i r s k i i and 54 Z a k h a r o v a s t u d i e d more d i l u t e s o l u t i o n s by J o b ' s method and c l a i m e d t o h a v e p r o v e d t h e e x i s t e n c e o f m o n o - t h i o m o l y b d a t e 2- -3 i n t h e s o l u t i o n o f (Mo) + (S ) - 1 x 10 M. L e r o y , Kaufman 44 and C h a r l i o n e t s u c c e e d e d i n p r e p a r i n g t r i - t h i o m o l y b d a t e as q u a r t e r n a r y ammonium s a l t s , (NX^^MoOS^ where X = E t and Me. They a l s o p r e p a r e d t h e c e s i u m s a l t C s ^ o O S ^ by t h e r e a c t i o n o f ( N H 4 ) 2 M o 0 2 S 2 w i t h C s C l a t -5°C. T h e i r U.V. and v i s i b l e 2-s p e c t r u m o f MoOS^ r e v e a l e d t h r e e s i g n i f i c a n t b ands a t 3 1 7 , 392.5 and 465 my and I.R. s p e c t r u m o f t h e c r y s t a l s gave t h r e e s t r o n g a b s o r p t i o n bands a t 467 , 477 and 857 cm. . The f i r s t two and t h e l a s t were a t t r i b u t e d t o Mo-S and Mo-0 6 3 2 — v i b r a t i o n , r e s p e c t i v e l y . I t was p r o v e n l a t e r t h a t MoOS^ has symmetry i n t h e c r y s t a l . 2-2-4-d S p e c i e s o t h e r t h a n t h o s e o f t h e f o r m MoO. S — 1 • 4-x x — (x = 1-4) 2-A f o r m o f i o n i c s p e c i e s o t h e r t h a n MoO^ ^ S ^ 3 6 (x = 1~4) has been c l a i m e d by v a r i o u s w o r k e r s . R e c e n t l y 64 S r i v a s t a v a and Ghosh s t a t e d t h a t , a t l o w e r pH v a l u e s , 4- 2-y e l l o w (HgMoSg) and o r a n g e (HgMoSg) were f o r m e d i n s o l u -t i o n s o f [Mo] = 0.025 M. and [ M o ] : [ S ] r a t i o g r e a t e r t h a n 54 1:8. Y a t s i m i r s k i i and Z a k h a r o v a s u g g e s t e d t h e p r e s e n c e ; o f 2-Mo o0,S f r o m t h e f a c t t h a t t h e a b s o r b a n c e o f i s o m o l a r s o l u -te D t i o n (0.1M.) a t 4 6 5 , 500 and 520 my p a s s e d t h r o u g h a maximum a t S:Mo = 1:2, w h i c h i s r a t h e r d u b i o u s b e c a u s e o f t h e h i g h m o l a r i t y and a l s o t h e p o s s i b l e i n a d e q u a c y o f t h e w a v e l e n g t h c h o s e n . S a x e n a , J a i n and M i t t a l ^ ~ \ s t u d i e d t h e a c i d i f i c a t i o n o f s o d i u m t h i o m o l y b d a t e w i t h H C l by pH and c o n d u c t o m e t r i c m e a s u r e m e n t s and s u g g e s t e d t h e f o r m a t i o n o f t h r e e d i f f e r e n t p o l y m e r i z e d s p e c i e s ( M o ^ S ^ ) , ( M o 2 S 7 > ~ and ( M o ^ S ^ ) ~ a t pH o f 8.5-7.5, 5.3-4.2 and 3.3-2.8, r e s p e c t i v e l y . 2-4-e S t u d i e s o f t h e e q u i l i b r i u m b e t w e e n t h e c o m p l e x s p e c i e s A d e t a i l e d s t u d y o f t h e e q u i l i b r i u m b e t w e e n t h e c o m p l e x s p e c i e s o f M o ( V I ) -S £-II)_water s y s t e m has n o t b een 61 p e r f o r m e d . H o f m e i s t e r and G l e m s e r s t u d i e d t h e h y d r o l y s i s r e a c t i o n o f t e t r a - and d i - t h i o m o l y b d a t e a c c o r d i n g t o t h e e q u a t i o n s ( a ) and ( b ) : -M o S 4 2 " + H 20 -*• M o O S 3 2 + H 2S •> e t c . . . . . ( a ) M o 0 2 S 2 2 ~ + H 20 •*• M o 0 3 S 2 + H 2S + e t c . . . . . (b) a t t e m p e r a t u r e s o f 20 t o 60°C. They r e p o r t e d t h a t t h e r a t e was i n d e p e n d e n t o f t h e h y d r o g e n i o n c o n c e n t r a t i o n b e t w e e n pH o f 7 t o 9. They gave t h e a c t i v a t i o n e n e r g y f o r t h e h y d r o l y s i s r e a c t i o n o f t e t r a - and d i - t h i o m o l y b d a t e as 19.7 and 26.5 R e a l . / m o l e , r e s p e c t i v e l y , b u t no f u r t h e r d e t a i l s a r e a v a i l a b l e f r o m t h e i r r e p o r t . 6 2 B e r n a r d and T r i d o t p e r f o r m e d t h e most e x t e n s i v e w ork. They m e a s u r e d t h e a b s o r p t i o n o f h y d r o g e n s u l p h i d e gas a t one a t m o s p h e r i c p r e s s u r e and a t 19°C. d u r i n g c e r t a i n t i m e 18 i n t e r v a l s , by 10 ml. of a s o l u t i o n c o n t a i n i n g 0.06 M. (NH^J^MoO and 0.06 M. o r 0.12 M. ammonia i n a c l o s e d v e s s e l , and s p e c t r o p h o t o m e t r i c a l l y d e t e r m i n e d the c o n c e n t r a t i o n s o f t e t r a - , t r i - , and d i - t h i o m o l y b d a t e u s i n g the v a l u e s o f m o l a r e x t i n c -39 t i o n c o e f f i c i e n t s t h e y had p r e v i o u s l y d e t e r m i n e d . They a l s o c a l c u l a t e d t h e c o n c e n t r a t i o n o f m o l y b d a t e and t o t a l f r e e s u l p h i d e c o n c e n t r a t i o n by the mass b a l a n c e a s s u m i n g t h a t m o n o - t h i o m o l y b d a t e d i d n o t e x i s t . They a l s o used a s o l u t i o n c o n t a i n i n g 0.06 M. ( N H 4 ) 2 M o 0 2 S 2 and 0.06 M. ammonia. They d i d n o t r e p o r t the e q u i l i b r i u m c o n s t a n t s t h a t c o u l d have been c a l c u l a t e d f r o m the d a t a but r e a c h e d the c o n c l u s i o n t h a t : -(a) t h i o m o l y b d a t e s a r e n o t s t a b l e below pH = 7, (b) i n a l k a l i n e s o l u t i o n the s u b s t i t u t i o n o f oxygen by s u l p h u r i s q u a n t i t a t i v e and o c c u r s i n t h r e e s t e p s : i ) i n i t i a l l y d i - t h i o m o l y b d a t e i o n f o r m s , q u a n t i -t a t i v e l y , e s p e c i a l l y a t s u l p h i d e c o n c e n t r a t i o n s up to the l i m i t o f S/Mo = 2 i n 0.001 M.Mo s o l u -t i o n ; i i ) s e c o n d s t e p b e i n g the f o r m a t i o n of t r i - t h i o m o l y -b d a t e i o n , marked by the a p p e a r a n c e o f an a b s o r p -t i o n peak a t 392.5 my w h i c h goes t h r o u g h a maximum as s u l p h i d i z a t i o n p r o c e e d s ; i i i ) t h i r d l y t e t r a - t h i o m o l y b d a t e i o n o c c u r s as the f i n a l end p r o d u c t o f s u l p h i d i z a t i o n . T h e i r d a t a was p r o c e s s e d by the p r e s e n t a u t h o r to o b t a i n t h e c o n s e c u t i v e c o n s t a n t s u s i n g t h e l i t e r a t u r e v a l u e s f o r t h e d i s s o c i a t i o n c o n s t a n t s o f ammonium i o n , a q u e o u s h y d r o g e n s u l p h i d e and h y d r o s u l p h i d e i o n . The r e s u l t s showed t h a t a) t h e r e i s a d o u b t a b o u t t h e i r e q u i l i b r i u m c o n d i t i o n , b) i f e q u i l i b r i u m i s a s s u m e d , m o n o - t h i o m o l y b d a t e must be assumed t o e x i s t and t h e l o g a r i t h m s o f t h e c o n s e c u t i v e c o n -s t a n t s ( i n M . _ 1 ) , k 4 = ( M o S 4 2 ~ ) / ( M o O S 3 2 " ) ( H 2 S ) , k 3 = ( M o O S ^ - ) / ( M o 0 2 S 2 2 ~ ) ( H 2 S ) , k 2 = ( M o 0 2 S 2 2 - ) / ( M o 0 3 S 2 _ ) (H 2S)- and ^ = ( M o 0 3 S 2 - ) / ( M o 0 4 2 ~ ) ( H 2 S ) a r e 2.7, 3.4, 4.4 and 5.5 r e s p e c t i v e l y . 54 Y a t s i m i r s k i i and Z a k h a r o v a u s e d a r a t h e r d i l u t e s o l u t i o n . B u t t h e i r d a t a are n o t p r o c e s s a b l e f o r t h e c o n -s e c u t i v e c o n s t a n t s b e c a u s e J o b ' s method i s n o t r e l i a b l e i n t h e c o m p l e x s y s t e m i n w h i c h many s p e c i e s a r e e x i s t i n g i n e q u i l i b r i u m w i t h e a c h o t h e r . A r o u n d t h e i r c o n c e n t r a t i o n r a n g e and w a v e l e n g t h s e m p l o y e d , mono- and d i - t h i o m o l y b d a t e and a s m a l l amount o f t r i - t h i o m o l y b d a t e c a n be e x p e c t e d t o e x i s t f r o m T r i d o t ' s d a t a . 2 - 4 - f A c i d d e c o m p o s i t i o n o f t h e c o m p l e x s p e c i e s A c i d d e c o m p o s i t i o n o f t h i o m o l y b d a t e s was o b s e r v e d 3 6 t o o c c u r . When a c i d was added t o a t e t r a - t h i o m o l y b d a t e s o l u t i o n , molybdenum t r i s u l p h i d e p r e c i p i t a t e d , l i b e r a t i n g h y d r o g e n s u l p h i d e g a s . However, a d i - t h i o m o l y b d a t e s o l u t i o n 38 y i e l d e d no h y d r o g e n s u l p h i d e . 6 6 Z v o r y k i n , P e r e l ' m a n and T a r a s o v s t u d i e d t h e e q u i l i b r i u m c o m p o s i t i o n o f p r e c i p i t a t e s w i t h a c i d i f i e d s o l u -t i o n s (made pH = 4.5 w i t h HC1) o f t h e N a 2 M o 0 4 - N a ^ - w a t e r s y s t e m by t h e s o l u b i l i t y method. The p r e c i p i t a t e d p h a s e s i n r e l a t i o n t o t h e s t a r t i n g m o l a r r a t i o , r = ( S ) / ( M o ) , were f o u n d t o b e : -MoS 3 r _> 3 2 M o S 3 ' 5 M o 0 3 , 2 > r > 1 and M o S 3 ' 5 M o 0 3 0.67 j> r >^  0.50 The l a s t two c a n be w r i t t e n t e n t a t i v e l y as 3MoS20*4Mo0 3 and 3 M 0 S O 2 * 3 M o 0 3 , r e s p e c t i v e l y , s u g g e s t i n g t h e s i m p l e r e p l a c e -ment o f 0 w i t h S i n m o l y b d i c o x i d e , Mo0 3« 61 H o f m e i s t e r and G l e m s e r s t u d i e d t h e a c i d decom-p o s i t i o n r e a c t i o n s , e q u a t i o n ( c ) and ( d ) , b e t w e e n 2- + 1 - 2 MoS, + H ^ HMoS. + MoS„ + HS . . . . ( c ) 4 - ^ 4 3 2- + 1 2 M o 0 2 S 2 + 2H " H 2 M o 0 2 S 2 + M o O x S y + H 2 S . . . . (d) pH = 1 and 4 and s t a t e d t h a t t h e r a t e d e t e r m i n i n g s t e p s were s t e p 2, t h a t t h e d e c o m p o s i t i o n r e a c t i o n s w e re o f t h e 1 f i r s t o r d e r , and t h a t t h e pH d e p e n d e n c e o f t h e f i r s t o r d e r r a t e c o n s t a n t s s u g g e s t e d p r e - e q u i l i b r i u m s t e p 1. The r e a c t i o n p r o d u c t s s u g g e s t e d i n e q u a t i o n ( c ) as HS and i n 3 8 e q u a t i o n (d) as H 2S a r e c o n t r a r y t o p r e v i o u s k n o w l e d g e S r i v a s t a v a and Ghosh*' 7 s t u d i e d the p r e c i p i t a t i o n of molybdenum s u l p h i d e f r o m a s o l u t i o n c o n t a i n i n g 0.025 M. m o l y b d a t e by the a d d i t i o n o f 2N H C l and f o u n d t h a t p r e c i p -i t a t i o n was c o m p l e t e o n l y when the amount of s u l p h i d e added as 0.05 M. NaHS e x c e e d e d the m o l a r r a t i o of Mo:S = 1:8. He p r o p o s e d the p o s s i b l e form of the p r e c i p i t a t e as 3MoS^ iH^S 'H^O. 6 — He a l s o s t a t e d t h a t o n l y the t h i o s a l t o f the form H,MoS n 4 8 c o u l d be decomposed by a c i d to g i v e molybdenum s u l p h i d e . 6 5 Saxena, J a i n and M i t t a l s t a t e d t h a t t e t r a - t h i o m o l y b d a t e decomposed i n t o MoS 3*H20 a t pH of l e s s t h a n 2.5. 2-5 S y n t h e s i s of m o l y b d e n u m ' d i s u l p h i d e The f i r s t s y n t h e s i s was made by B e r z e l i u s i n 1826; he s t a t e d t h a t when an aqueous s o l u t i o n o f t e t r a - t h i o m o l y -b d a t e was b o i l e d i n a c l o s e d v e s s e l , molybdenum d i s u l p h i d e 3 6 p r e c i p i t a t e d a l o n g w i t h o t h e r complex s u l p h i d e s . S i n c e t h e n many s y n t h e s e s of m o l y b d e n i t e have been made. A r u t y u n y a n 6 8 and K h u r s h u d y a n r e v i e w e d the methods r e p o r t e d up t o 1966 and the f o l l o w i n g i n f o r m a t i o n i s a b s t r a c t e d p a r t l y from < t h e i r work Most of the molybdenum d i s u l p h i d e f o u n d i n n a t u r e i s r e p o r t e d t o be of t h e h e x a g o n a l m o d i f i c a t i o n w i t h e l o n -g a t e d b i - m o l e c u l a r u n i t c e l l s e x c e p t f o r a few r a r e examples h a v i n g a r h o m b o h e d r a l s t r u c t u r e w i t h a t r i - m o l e c u l a r 69 h e x a g o n a l c e l l . The s u l p h u r atoms s u r r o u n d i n g molybdenum i n M 0 S 2 a r e a t the c o r n e r s o f r i g h t e q u i l a t e r a l t r i g o n a l > p r i s m s w h i c h s h a r e v e r t i c a l edges w i t h one a n o t h e r t o b u i l d . up c o m p l e t e M ° S 2 l a y e r s n o r m a l to the C Q a x i s . In the h e x a g o n a l m o d i f i c a t i o n the c r y s t a l i s b u i l t up by r e p e a t -i n g t h e s e c o m p l e t e l a y e r s on- one a n o t h e r a c c o r d i n g to the a l t e r n a t i n g r e q u i r e m e n t s o f h e x a g o n a l c l o s e - p a c k i n g , and i n a r h o m b o h e d r a l m o d i f i c a t i o n , a c c o r d i n g to t h o s e o f the t h r e e l a y e r c u b i c c l o s e - p a c k i n g . By d e n o t i n g s u l p h u r p o s i t i o n s w i t h c a p i t a l l e t t e r s and molybdenum p o s i t i o n s w i t h s m a l l l e t t e r s , the f o r m e r can be d e s c r i b e d as I I ' ' 68 AbA/BaB/A and the l a t t e r as AbA/BcB/CaC/A , where I I I I s l a s h e s i n d i c a t e the p o s i t i o n s o f d o u b l e l a y e r s o f s u l p h u r . The d i s t a n c e between t h e s e s u l p h u r atoms i s l a r g e r than the d i s t a n c e between the s u l p h u r atoms f o r m i n g the t r i g o n a l b i - p y r a m i d s (3.66A a g a i n s t 2.98A i n h e x a g o n a l m o d i f i c a t i o n ) ^ The weak b o n d i n g between the s u l p h u r d o u b l e l a y e r s i s s a i d to be the s o u r c e o f the l u b r i c a t i n g p r o p e r t i e s o f t h i s m a t e r i a l ^ . The l u b r i c a t i n g q u a l i t i e s o f the two modifi-? 7 1 c a t i o n s were r e p o r t e d to be e s s e n t i a l l y the same . T h e r e can be o t h e r m o d i f i c a t i o n s w h i c h may r e s u l t from a l t e r n a t i n g 7 2 c o m b i n a t i o n s o f h e x a g o n a l and r h o m b o h e d r a l p a c k i n g s The methods o f s y n t h e s i z i n g M o $ 2 were c l a s s i f i e d 6 8 by A r u t y u n y a n and K h u r s h u d y a n i n t o f o u r g r o u p s : -1. R e a c t i o n i n a gaseous medium: the i n i t i a l components a r e v o l a t i l e molybdenum c h l o r i d e s and h y d r o g e n s u l p h i d e gas, r e a c t i n g a t a t e m p e r a t u r e o f 700-800°C. 2. R e a c t i o n i n m o l t e n s a l t s : the i n i t i a l components may be Mo0 3 + S, CaMoO^ + N a 2 C 0 3 + S, or Mo0 3 + Na2CC>3 + S. The u s u a l t e m p e r a t u r e o f s y n t h e s i s r a n g e s f r o m 700° t o 900°C. 3. R e a c t i o n b e t w e e n t h e molybdenum compounds i n s o l i d p h a s e w i t h s u l p h u r v a p o u r o r h y d r o g e n s u l p h i d e gas a t a t e m p e r a t u r e o f 700-800°C. 4. D e c o m p o s i t i o n o f molybdenum t r i s u l p h i d e a t a h i g h t e m p e r a t u r e , ( o v e r 500°C. i n an i n e r t a t m o s p h e r e ) . A f u r t h e r method w h i c h s h o u l d be added i s 5. T h e r m a l 7 3 ' ' 7 4 o r h y d r o t h e r m a l ^ 8 d e c o m p o s i t i o n o f molybdenum t h i o - c o m p l e x s a l t s . A l m o s t a l l t h e s y n t h e t i c molybdenum d i s u l p h i d e s s u b j e c t e d t o X - r a y a n a l y s i s a r e r e p o r t e d t o be r h o m b o h e d r a l e x c e p t f o r a few h e x a g o n a l e x a m p l e s p r e p a r e d u n d e r e x t r e m e c o n d i t i o n s o r a f t e r p r o l o n g e d a n n e a l i n g a t h i g h t e m p e r a t u r e s . 6 8 T h i s p o i n t was made c l e a r by A r u t y u n y a n and K h u r s h u d y a n f r o m t h e i r s t u d y o f t h e h y d r o t h e r m a l d e c o m p o s i t i o n o f t h i o -m o l y b d a t e s . T h e i r e x p e r i m e n t s c o n s i s t e d o f s e a l i n g aqueous 2 -s o l u t i o n s , c o n t a i n i n g maximum o f 0.5 M. MoS^ w i t h pH o f 8-12 w i t h NaOH, i n a g l a s s b o t t l e and h e a t i n g a t 300-700° C. f o r 1~100 h o u r s . T h e i r r e s u l t s were s u m m a r i z e d a l o n g w i t h t h o s e o f t h e o t h e r w o r k e r s , as f o l l o w s : -24 C r y s t a l M o d i f i c a t i o n T e m p e r a t u r e C o n d i t i o n s amorphous 20-300°C pH<6~7 c o l l o f o r m i c 200-300° r h o m b o h e d r a l 250-900° s h o r t d u r a t i o n o f h e a t i n g h e x a g o n a l 600°C 22 days h e x a g o n a l 1300°C 2 h o u r s i n s i l i c a t e m e l t They d e m o n s t r a t e d the t r a n s i t i o n to the h i g h e r l e v e l o f c r y s t a l l i z a t i o n by the use o f X - r a y d i f f r a c t i o n . 3• Scope o f P r e s e n t Work From a r e v i e w o f the l i t e r a t u r e , the f o l l o w i n g p o i n t s seem c l e a r : -1. The demand f o r molybdenum i s g r o w i n g , l e a d i n g to a s e a r c h f o r p r o c e s s e s to t r e a t l o w e r grade o r e s . 2. H y d r o m e t a l l u r g i c a l methods can t r e a t low grade s u l p h i d e o x i d e o r e s to p r o d u c e p r e g a n t molybdenum s o l u t i o n . 3. R e d u c t i o n of aqueous s o l u t i o n s of molybdenum w i t h h y d r o g e n gas can p r o c e e d a t e l e v a t e d t e m p e r a t u r e s w i t h the a i d of c a t a l y s t s to p r o d u c e t e t r a - or t r i - v a l e n t molybdenum compounds. 4. A f a i r l y e x t e n s i v e s t u d y has been p e r f o r m e d o f the M o ( V I ) - S ( - I I ) - w a t e r s y s t e m e s p e c i a l l y f o r the p r e p -a r a t i o n and c h a r a c t e r i z a t i o n of t h i o - c o m p l e x s a l t s . 25 The s t u d y o f e q u i l i b r i u m i n the s y s t e m i s i n c o m p l e t e and no s t u d i e s on t h e s y s t e m a t e l e -v a t e d t e m p e r a t u r e s have been r e p o r t e d . 5. S y n t h e s i s o f molybdenum d i s u l p h i d e has been m o s t l y p e r f o r m e d i n non-aqueous media and when t h i o m o l y b d a t e was used as s t a r t i n g m a t e r i a l , t h e p r o c e s s used was s i m p l e t h e r m a l and h y d r o t h e r m a l d e c o m p o s i t i o n . T h e r e f o r e , no p o s i t i v e e f f o r t has been made to r e d u c e the molybdenum i n s o l u t i o n p r i o r t o p r e c i p i t a t i o n of the s u l p h i d e . In v i e w o f the above f a c t s t h e f o l l o w i n g was t a k e n as the s c o p e o f the p r e s e n t work:-1. To s t u d y the e q u i l i b r i u m o f the M o ( V I ) - S ( - I I ) - w a t e r s y s t e m a t e l e v a t e d t e m p e r a t u r e s w i t h t h e o b j e c t o f e s t a b l i s h i n g the e q u i l i b r i u m c o n s t a n t s between com-p l e x s p e c i e s . 2. To i n v e s t i g a t e the r e d u c t i o n o f the M o ( V I ) - S ( - I I ) -w a t e r s y s t e m w i t h h y d r o g e n and c a r b o n monoxide and t o a n a l y s e r e d u c t i o n p r o d u c t s and k i n e t i c s . 26 PART I : STUDY OF EQUILIBRIUM IN THE Mo (VI)-S(-11)-WATER  SYSTEM 1. P r i n c i p l e s o f the e x p e r i m e n t From a r e v i e w o f the p r e v i o u s works on t h i s s y s t e m , th e f o l l o w i n g f a c t s seem t o have been e s t a b l i s h e d : -(a) In c r y s t a l s and i n a l k a l i n e s o l u t i o n s t h i o - c o m p l e x 2-s p e c i e s o f t h e form MoO, S (x = 1-4) e x i s t . t ™" X . 3C (b) P r e d o m i n a n t a b s o r p t i o n bands i n the v i s i b l e and n e a r U.V. ran g e o f t h e above s p e c i e s a r e : -M o S 4 2 " — 4 6 5 and 315my, MoOS 3 2~—392.5my, M o 0 2 S 2 2 " — 2 9 0 m y . (c) I n a c i d i c s o l u t i o n s , t h e r e can be v a r i o u s complex c o n d e n s e d f o r m s . (d) E s t a b l i s h m e n t o f e q u i l i b r i u m between t h e complex 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 s i s r a t h e r s l o w a t room t e m p e r a t u r e b ut t h e f o r m a t i o n o f t h e t h i o -a n i o n i s h i g h l y f a v o u r e d i n the p r e s e n c e o f a v e r y d i l u t e c o n c e n t r a t i o n o f s u l p h i d e i o n . T h e r e f o r e , when c o n d u c t i n g e x p e r i m e n t s i n an ammoni-a c a l s o l u t i o n a t h i g h e r t e m p e r a t u r e s , the f o l l o w i n g s i m p l e 2-e q u i l i b r i u m between the s p e c i e s o f the form M o 0 4 _ x S x (x = 1-4) can be e x p e c t e d : -2 7 2- 2-MoO. + H„S = MoO.S + H o0 : k, 4 2 3 2 1 M o 0 3 S 2 ~ + H 2S = M o 0 2 S 2 2 ~ + H 20 : fc M o 0 2 S 2 2 ~ + H 2S = M o O S 3 2 " + H 20 : k 3 MoOS 2 ~ + H.S = MoS 2 ~ + H_0 : k, 3 2 4 2 4 where k's a r e t h e c o n s e c u t i v e c o n s t a n t s . I n g e n e r a l , a c o m p l e x s y s t e m w i t h one c e n t r a l m e t a l i o n , M, and a maximum c o - o r d i n a t i o n number o f N i s f u l l y d e s c r i b e d by t h e c o n c e n t r a t i o n s o f t o t a l m e t a l , M T , t o t a l l i g a n d , L T , or f r e e l i g a n d , L , and by a s e t o f s t a b i l i t y c o n s t a n t s , 8^  . i 8 = IT k . , i = 1~N j = l J M T = [ M ] + [ M L ] + [ M L 2 ] + . . + [ M L N ] = [ M ] [ l + B jL + 8 2 L 2 + . . + 8 N L N ] L T = L + [ML] + 2[ML2] + . . . + N[MLN] = L + [M][ BjL + 262L2 +...' + N8NLN] An a l t e r n a t i v e i s t o use t h e f o r m a t i o n f u n c t i o n o f t h e s y s t e m , n, d e f i n e d by B j e r r u m 7 " ' as t h e a v e r a g e number o f l i g a n d s p e r atom when t h e c o n c e n t r a t i o n o f f r e e l i g a n d i s L , and i s u n i q u e f o r a p a r t i c u l a r s y s t e m . Once ri-is o b t a i n e d as a f u n c t i o n o f L , 8n c a n i n t u r n be c a l c u l a t e d by s e v e r a l 28 n = ( L T - L ) / M T N N = (E n3 L n ) / ( 1 + E B L n ) . . . . (1) n-1 n n=l n methods d e s c r i b e d by R o s s o t t i and R o s s o t t i 7 ^ . C o n s i d e r a t i o n o f e q u a t i o n (1) shows t h a t n i s g i v e n f r o m the f r a c t i o n a l d i s t r i b u t i o n o f the s p e c i e s M L c > a^, a g a i n s t the f r e e l i g a n d c o n c e n t r a t i o n , L, by the e q u a t i o n ( 2 ) : -n = c - (d l n a /d l n L) . . . . (2) c N where a = [ML 1/M = B f , L C / ( l + E B L n ) c c i c j } = i n The u s u a l method to use e q u a t i o n (2) i s a t f i r s t by p u t t i n g L = L^, f o l l o w e d by s u c c e s s i v e a p p r o x i m a t i o n s and g r a p h i c a l d i f f e r e n t i a t i o n s to o b t a i n f i n a l s e t s o f n and L. I f , however, the c o n c e n t r a t i o n s o r some p r o p e r t i e s p r o p o r t i o n a l to the c o n c e n t r a t i o n s o f two s u c c e s s i v e s p e c i e s , ML . and r ' m-1 ML , a r e known, e q u a t i o n (2) can be f u r t h e r s i m p l i f i e d by m s u b s t i t u t i n g the e q u i l i b r i u m r e l a t i o n s h i p between t h e s e s p e c i e s , i . e . ML , + L = ML , k = a /a _L m-1 m m m m-1 By d i f f e r e n t i a t i o n 29 d I n L = -d l n (k a - /a ) = -d l n a . + d l n a m m-1 m m-1 m T h e r e f o r e e q u a t i o n (2) w i l l be r e w r i t t e n as e q u a t i o n (3) n = c- (d l n a )/(d l n a - d l n a ,) . . . . (3) c m m-1 F o r t h e p r e s e n t s y s t e m , and c a n be o b t a i n e d by m e a s u r i n g Mo^ and a b s o r p t i o n s a t 395 my and 465 my and u s i n g t h e m o l a r e x t i n c t i o n c o e f f i c i e n t s g i v e n by B e r n a r d 3 9 6 2 and T r i d o t ' . Thus e q u a t i o n (4) a p p l i e s . n = 4 - 1/(1 - d l n a_/d l n a.) . . . . (4) 3 4 T h e r e f o r e n c a n be c a l c u l a t e d f r o m t h e s l o p e s o f t h e p l o t o f l o g a 3 a g a i n s t l o g by g r a p h i c a l d i f f e r e n t i a t i o n . P r e -l i m i n a r y c a l c u l a t i o n s showed t h e b r e a k d o w n o f e q u a t i o n (4) a t l o w and f o r s u c h c a s e s e q u a t i o n (5) was u s e d : -- - 3 1 5 n = 3 - l / ( l - d l n /d l n a^) . . . . (5) "315 where i s a s p e c i f i c a b s o r p t i o n by s p e c i e s ML^ a t 315 my and w i l l be d i s c u s s e d l a t e r . E q u a t i o n (2) w i t h s u c c e s s i v e a p p r o x i m a t i o n was a l s o u s e d when was t o o low t o o b t a i n n. From n v a l u e , t h e c o n c e n t r a t i o n o f f r e e s u l p h i d e , S^, was c a l c u l a t e d u s i n g t o t a l c o n c e n t r a t i o n o f molybdenum, and s u l p h i d e , Mo^, and S^, by e q u a t i o n ( 6 ) : -30 S f = S T - n Mo T . . . . (6) 2. E x p e r i m e n t a l 2-1 A p p a r a t u s and P r o c e d u r e E x p e r i m e n t s were c o n d u c t e d i n a s t a i n l e s s s t e e l a u t o c l a v e , s e r i e s 4 5 0 0 , m a n u f a c t u r e d by P a r r Co. L t d . , e q u i p p e d w i t h a t i t a n i u m l i n e r ( i n s i d e v o l u m e 1990 m l . a t room t e m p e r a t u r e ) and a s t a i n l e s s s t e e l l i d t o w h i c h t h e f o l l o w i n g were a t t a c h e d : a s t i r r e r m e c h a n i s m , two t h e r m o -c o u p l e w e l l s , a s o l u t i o n i n j e c t i o n s y s t e m , a s a m p l i n g s y s t e m , a gas i n l e t and a gas o u t l e t . A l l t h e p a r t s i n c o n t a c t w i t h t h e s o l u t i o n were t i t a n i u m . The s t i r r e r was b e l t - d r i v e n by an e l e c t r i c m o t o r -H e a t i n g was p r o v i d e d by a Bunsen b u r n e r f o r r a p i d h e a t i n g and a r i n g t y p e b u r n e r c o n t r o l l e d by a s o l e n o i d v a l v e a c t i v a t e d by a T h e r m i s t e m p t e m p e r a t u r e c o n t r o l l e r , M o d e l 71 ( Y e l l o w s p r i n g s I n s t r u m e n t Co.) i n c o n j u n c t i o n w i t h a t h e r m i s t o r p r o b e i n one t h e r m o c o u p l e w e l l . T e m p e r a t u r e was m e a s u r e d by t h e e.m.f. o f a A l u m e l - C h r o m e l t h e r m o c o u p l e i n a n o t h e r t h e r m o c o u p l e w e l l w i t h i c e - w a t e r as a c o l d j u n c t i o n and was u s u a l l y w i t h i n ±0.5°C. o f t h e s e t v a l u e . As t h e t e m p e r a t u r e s e l e c t e d f o r e x p e r i m e n t a t i o n , was above t h e b o i l i n g p o i n t o f w a t e r , a p r e s s u r i z e d s o l u t i o n , i n j e c t i o n s y s t e m was c o n s t r u c t e d w i t h Type 316 s t a i n l e s s . 31 s t e e l p a r t s as shown i n F i g u r e 2. The w h o l e s y s t e m was p o s i t i o n e d v e r t i c a l l y . I n j e c t i o n s w e r e c a r r i e d o u t by f i r s t f l u s h i n g t h e s y s t e m w i t h d i s t i l l e d w a t e r t h r o u g h S, , and t r a p w i t h V 2 and c l o s e d . was t h e n c l o s e d and t h e s y s t e m was e v a c u a t e d . A f t e r a t t a i n i n g a s u i t a b l e vacuum s o l u t i o n was s u c k e d i n t o B f r o m S by c l o s i n g and o p e n i n g . Then was c l o s e d and was opened t o a p p l y a n i t r o g e n p r e s s u r e o f h i g h e r v a l u e t h a n t h e i n s i d e p r e s s u r e o f t h e a u t o c l a v e , w h i c h was m e a s u r e d w i t h a 1500 p s i . h e l i c o i d gauge w i t h a s c a l e o f 10 p s i . p e r d i v i s i o n . By o p e n i n g s o l u t i o n was f l u s h e d i n t o t h e a u t o c l a v e t h r o u g h t h e s t a i n l e s s t u b i n g , t h e t i p o f w h i c h was s l i g h t l y above t h e s u r f a c e o f t h e s o l u -t i o n i n s i d e t h e a u t o c l a v e . The c o m p l e t i o n o f i n j e c t i o n was d e t e c t e d by a s h a r p d r o p o f p r e s s u r e m e a s u r e d i n t h e gas s y s t e m . was c l o s e d and one c y c l e o f t h e i n j e c t i o n p r o c e s s was c o m p l e t e d . By t h i s method an a p p r o x i m a t e l y c o n s t a n t amount (-10 ml.) o f s o l u t i o n was i n j e c t e d . A l t h o u g h t h e d e c o m p o s i t i o n r e a c t i o n s o f t e t r a -and d i - t h i o m o l y b d a t e a t room t e m p e r a t u r e w e re r e p o r t e d l y . s l o w , s a m p l e s o l u t i o n s were q u e n c h e d t o f r e e z e t h e e q u i l i b r i u m e x i s t i n g a t t h e e l e v a t e d t e m p e r a t u r e . The s a m p l i n g s y s t e m c o n s i s t e d o f t h e f o l l o w i n g s e q u e n c e : a 1/16 i n . O.D. t i t a n i u m t u b i n g i mmersed i n t h e s o l u t i o n i n s i d e t h e a u t o c l a v e , a s t a i n l e s s s t e e l v a l v e w i t h T e f l o n p a c k i n g a t t a c h e d t o t h e l i d and a c o o l i n g c o i l o f 31a T A V|,V2,\^,V4 « high pressure valves, 3I6SS. A > autoclave. B : high pressure bottle, 316SS. T ' trap. S : container of solutions to be injected, glass. F i g . 2. S O L U T I O N I N J E C T I O N S Y S T E M . 1/16 i n . O.D. s t a i n l e s s s t e e l t u b i n g immersed i n a c o l d w a t e r b a t h ( 7 ~ 1 0 ° C . ) . The i n s i d e volume of the s a m p l i n g l i n e f r o m end to end was a p p r o x i m a t e l y 1.5 ml. The h i g h t e m p e r a t u r e s e c t i o n o f the s y s t e m was about a q u a r t e r o f i t s l e n g t h . S o l u t i o n s o f molybdenum o r s u l p h i d e were i n j e c t e d . O p e r a t i o n s f o r t h e l a t t e r c a s e a r e d e s c r i b e d b elow. O n e . l i t r e of s o d i u m m o l y b d a t e s o l u t i o n i n a NH^ - (NH 4> 2 SO^ b u f f e r and 100 ml. o f sodium s u l p h i d e s o l u t i o n i n the same b u f f e r c o m p o s i t i o n were p r e p a r e d f r e s h from s t o c k s o l u t i o n s . M o l y -bdenum s o l u t i o n was c h a r g e d i n the a u t o c l a v e , the a tmosphere was r e p l a c e d w i t h n i t r o g e n gas and the s y s t e m was s e a l e d , h e a t e d and e q u i l i b r a t e d w h i l e s t i r r i n g . S u l p h i d e s o l u t i o n was t h e n i n j e c t e d t h r o u g h the i n j e c t i o n s y s t e m , the s o l u t i o n -m i x t u r e was a l l o w e d to s t a n d f o r 30 m i n u t e s to a t t a i n e q u i l i b r i u m between the s p e c i e s , and the sample s o l u t i o n was t h e n w i t h d r a w n w h i l e s t i r r i n g . The f i r s t 5 ml. o f the sample s o l u t i o n quenched by the c o o l i n g s y s t e m was d i s c a r d e d and s u b s e q u e n t l y 10 ml. was f i l t e r e d t h r o u g h a d r y g l a s s f i l t e r ( P y r e x " F i n e " g r a d e ) to remove any p r e c i p i t a t e s , i n t o a d r y g l a s s b o t t l e and s t o r e d f o r a n a l y s i s . The i n j e c t i o n and , s a m p l i n g were r e p e a t e d s u c c e s s i v e l y . 2-2 R eagents The e x p e r i m e n t a l s o l u t i o n s were made from s t o c k s o l u t i o n s of 1 M.Na^oO^ ( s t o r e d i n a p o l y e t h l e n e b o t t l e ) , 0.4 M.Na.S ( s t o r e d i n a d a r k g l a s s b o t t l e ) , 10 M.NH and 4 M. (NH^^SO^ u s i n g r e a g e n t grade c h e m i c a l s . A l l t h e r e a g e n t s u s e d i n a n a l y s i s were of r e a g e n t grade and were used as p u r c h a s e d . D e - i o n i z e d w a t e r was used f o r a l l p u r p o s e s . The n i t r o g e n gas was t h e low oxygen grade s u p p l i e d c o m m e r c i a l l y i n a c y l i n d e r and used w i t h o u t f u r t h e r p u r i f -i c a t i o n . 2-3 A n a l y t i c a l methods The c o n c e n t r a t i o n s o f t o t a l molybdenum, t o t a l s u l -p h i d e , t o t a l ammonium and complex s p e c i e s i n the sample s o l u t i o n were d e t e r m i n e d . T o t a l molybdenum was d e t e r m i n e d c o l o r i m e t r i c a l l y u s i n g a Beckman Model B s p e c t r o m e t e r a c c o r d i n g to Buchwald 7 7 and R i c h a r d s o n ' s method , i n w h i c h the molybdenum c o n t e n t o f the s o l u t i o n was c a l c u l a t e d f r o m the a b s o r b a n c e of a s o l u t i o n a t 420 mu by c o m p l e x i n g i n a 0.05 M. a c e t a t e b u f f e r (pH = 5.2) w i t h sodium -2 , 3 - d i h y d r o x y - n a p h t h a l e n e - 6 - s u l f o n a t e ( a f t e r o x i d i z i n g s u l p h i d e i n a sample s o l u t i o n w i t h #2^2 ^ n NaOH a l k a l i n e , a d d i n g Na2S0.j to r e d u c e e x c e s s H2O2, a d d i n g HNO^ t o d r i v e o f f e x c e s s SO2, b o i l i n g t o e x p e l the lower n i t r o g e n o x i d e , and n e u t r a l i z i n g to pH=5.2 w i t h NaOH). The a n a l y s i s o f t o t a l s u l p h i d e i n the t h i o m o l y b d a t e s y s t e m i s known to be d i f f i c u l t . In P a r t 1 the a n a l y s i s ,was done by a m o d i f i e d V o l h a r d method, w h i c h was a l s o employed 41 by P e r e l ' m a n e t a l . . An a l i q u o t of sample s o l u t i o n was added to a known e x c e s s amount o f AgN0„ s t a n d a r d s o l u t i o n i n a m m o n i a c a l s o l u t i o n t o p r e c i p i t a t e s u l p h i d e i o n as Ag^S. The s o l u t i o n was h e a t e d t o a g g l o m e r a t e A g 2 S p r e c i p i t a t e s w h i c h were f i l t e r e d o f f a f t e r c o o l i n g and washed w i t h a d i l u t e ammonium s o l u t i o n . The f i l t r a t e and w a s h i n g s were c o m b i n e d and a c i d i f i e d by a d d i n g 5N HNO^ and t h e A g + r e m a i n i n g i n t h e s o l u t i o n was t i t r a t e d w i t h a s t a n d a r d KCNS s o l u t i o n u s i n g 3+ Fe s o l u t i o n as an i n d i c a t o r , and t h e s u l p h i d e amount was c a l c u l a t e d by t h e d i f f e r e n c e f r o m t h e b l a n k . T o t a l ammonium c o n t e n t was d e t e r m i n e d by a d i s t i l -l a t i o n m ethod. An a l i q u o t o f a s a m p l e s o l u t i o n was f e d * , i n t o t h e K i r k ' s a p p a r a t u s , w h i c h c o n t a i n e d an a queous s o l u t i o n o f KMnO^ i n H^SO^, t h e f o r m e r t o o x i d i z e s u l p h i d e i n t o s u l f a t e and t h e l a t t e r t o f i x t h e f r e e ammonia. A f t e r w a i t i n g a few m i n u t e s t o a l l o w t h e o x i d a t i o n and n e u t r a l i z a t i o n t o be c o m p l e t e d , c o n c e n t r a t e d NaOH was added and ammonia was d i s t i l l e d i n t o a known amount o f t h e s t a n d a r d H 2SO^ s o l u t i o n . The r e m a i n i n g a c i d was t i t r a t e d w i t h a s t a n d a r d NaOH s o l u t i o n t o pH = 5 u s i n g Beckman pH m e t e r and t h e t o t a l ammonium c o n t e n t was c a l c u l a t e d by t h e d i f f e r e n c e f r o m t h e b l a n k . ; The c o n c e n t r a t i o n o f c o m p l e x s p e c i e s was d e t e r m i n e d c o l o r i m e t r i c a l l y . The s p e c t r o g r a m o f t h e s a m p l e s o l u t i o n was t a k e n b e t w e e n 600 and 260 my w i t h a Beckman DK-2 s p e c -t r o m e t e r u s i n g a 0.1 cm. q u a r t z c e l l , w i t h o u t d i l u t i o n , and 39 6 2 w i t h d i s t i l l e d w a t e r as a r e f e r e n c e . B e r n a r d and T r i d o t ' gave m o l a r e x t i n c t i o n c o e f f i c i e n t s o f t h e t e t r a - and t r i -t h i o m o l y b d a t e a t 19°C. as f o l l o w s : -35 e 392.5 Q . 2 ^ 465 . __2 e 3 = 98.5 x 10 e 3 = 4 x 10 392.5 _ . _2 . 465 . , h2 e 4 7 x 10 e 4 = 108 x 10 where i s a m o l a r e x t i n c t i o n c o e f f i c i e n t ( M . ^ c m . - 1 ) o f 2 — 7 8 a s p e c i e s i (MoO^^S ) a t w a v e l e n g t h A(my) . From the a b s o r b a n c e s a t w a v e l e n g t h A , A \ (A = 392.5 and 465 my) of the s o l u t i o n , t h e c o n c e n t r a t i o n s of t e t r a - and t r i -t h i o m o l y b d a t e , and C 3 , r e s p e c t i v e l y , were c a l c u l a t e d by e q u a t i o n s (7) as s u m i n g no i n t e r f e r e n c e by the o t h e r i o n s . C 3 - (1.018 A 3 9 2 , 5 - 0.066 A 4 6 5 ) x 1 0 ~ 3 M, ( 7 ) C 4 = (0.928 A 4 6 5 - 0.038 A 3 9 2 , 5 ) x 1 0 . 3 M. The c o n c e n t r a t i o n of d i - t h i o m o l y b d a t e was n o t c a l c u l a t e d f r o m the a b s o r b a n c e a t 290 my as t h e r e was a doubt about e 6 2 g i v e n by B e r n a r d and T r i d o t . I n s t e a d t h e s p e c i f i c - 3 1 5 a b s o r b a n c y of d i - t h i o m o l y b d a t e a t 315 my, A ^ , w h i c h i s pro-p o r t i o n a l to the f r a c t i o n a l d i s t r i b u t i o n of d i - t h i o m o l y b d a t e , was c a l c u l a t e d by e q u a t i o n ( 8 ) . A 2 3 1 5 = A 3 1 5 - 2.01. x 1 0 4 a 4 . . . . (8) ~315 315 where A = A /Mo^, a 4 = C^/Ko^, ( t h e c o n s t a n t w i l l be d i s c u s s e d l a t e r ) . F o r most c a s e s f i x i n g o f s u l p h i d e and ammonia f o r a n a l y s i s was p e r f o r m e d i m m e d i a t e l y . a f t e r s a m p l e w i t h d r a w a l . The s p e c t r o g r a m was t a k e n w i t h i n 10=20 m i n u t e s . O n l y a s l i g h t c hange was o b s e r v e d when t h e s p e c t r o g r a m o f a s a m p l e was t a k e n r e p e a t e d l y (= 10 m i n u t e s l a t e r ) , ( s e e A p p e n d i x C) 3. R e s u l t s and C a l c u l a t i o n s 3-1 O b s e r v e d S p e c t r o g r a m F i g u r e R l i n A p p e n d i x B shows an e x a m p l e o f a s e r i e s o f s p e c t r o g r a m s where s u l p h i d e s o l u t i o n was i n j e c t e d s u c c e s s -i v e l y . I t i s c l e a r t h a t no a b s o r p t i o n peak e x i s t s o t h e r t h a n t h o s e a t 4 6 5 , 3 9 5 , 315 and 290 my r e p o r t e d by B e r n a r d 3 9 6 2 54 e t c . and T r i d o t ' and o t h e r a u t h o r s ' " . I t a l s o shows t h a t t h e peak a t 290 my i n c r e a s e s , r e a c h e s a maximum and d e c r e a s e s as t h e t o t a l s u l p h i d e c o n c e n t r a t i o n i n c r e a s e s . The same i s t r u e f o r t h e peak a t 395 my. The peak a t 465 my i n c r e a s e s as s u l p h i d e c o n c e n t r a t i o n i n c r e a s e s . , I n a s e r i e s where t h e c o n c e n t r a t i o n o f f r e e ammonium was s m a l l ( S e r i e s D ) , v a r i a t i o n i n p o s i t i o n and m a g n i t u d e o f t h e a b s o r p t i o n peak was o b s e r v e d as shown i n F i g u r e B2 i n A p p e n d i x B. The p eak a t 465 my, c o r r e s p o n d i n g t o t h e t e t r a -t h i o m o l y b d a t e , r e a c h e d maximum a t a s m a l l t o t a l c o n c e n - . .: t r a t i o n o f s u l p h i d e and d e c r e a s e d as more s u l p h i d e was a d d e d . The m a g n i t u d e was a l s o s m a l l e r . The peak a t 395 my d e g e n e r a t e d a f t e r r e a c h i n g a maximum and a new peak a t a r o u n d 380 my was o b s e r v e d a t h i g h e r s u l p h i d e c o n c e n t r a t i o n . A new peak was a l s o o b s e r v e d a t a r o u n d 270 my, a l t h o u g h t h i s was o b s c u r e d by a g e n e r a l i n c r e a s e i n a b s o r p t i o n a r o u n d t h i s w a v e l e n g t h r a n g e . A s c a n t o 210 my showed no o t h e r peak t h a n t h e one a t a r o u n d 230 my, due t o f r e e s u l p h i d e i o n . I n v i e w o f t h e f a c t t h a t when f r e e ammonium was k e p t h i g h , no s u c h peak was o b s e r v e d a t 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 , t h e new p e a k s were c o n s i d e r e d t o be c a u s e d by p r o t o n a t e d s p e c i e s o f t h i o m o l y b d a t e . 3-2 C a l c u l a t i o n o f n and S^ . A t f i r s t and were c a l c u l a t e d and p l o t t e d i n l o g - l o g s c a l e t o o b t a i n n v a l u e s g r a p h i c a l l y . T h i s was f o u n d t o g i v e t o o l a r g e v a l u e s o f n a t l o w v a l u e s o f r e s u l t i n g i n t h e i n c o n s i s t e n c y o f m a t e r i a l b a l a n c e . B e c a u s e had t o o l o w a v a l u e , t h e e q u a t i o n (4) was n o t m e a n i n g f u l . 39 B e r n a r d and T r i d o t s t a t e d t h a t t h e a b s o r p t i o n a t 315 my i s c a u s e d by d i - and t e t r a - t h i o m o l y b d a t e w i t h o u t g i v i n g t h e m o l a r e x t i n c t i o n c o e f f i c i e n t s , i . e . , A 3 1 5 = le 3 1 5 C 0 + le 3 1 5 C. ; I', path l e n g t h , . . . . (9) 2 2 4 4 I f t h e e q u i l i b r i u m i s assumed b e t w e e n d i - , t r i - and t e t r a -t h i o m o l y b d a t e , e q u a t i o n (9) c a n be r e w r i t t e n as e q u a t i o n ( 1 0 ) : A 3 1 5 c 4 / c 3 2 = ( £ e 2 3 1 5 k 4 / k 3 ) + £ e 4 3 1 5 ( c 4 / c 3 ) 2 . . . . ( 1 0 ) 315 2 9 Thus from the p l o t of A C^/C^ a g a i n s t (C^/C^) , 315 can be o b t a i n e d . F i g u r e 3 shows an example o f s u c h a p l o t o f S e r i e s A. Good l i n e a r i t y was f o u n d f o r the o t h e r s g i v i n g t h e r e s u l t s b e l o w : -S e r i e s £4 315 £2 3 1V k3 M . cm. Temper- N o m i n a l MT 1 -1 cm. a t u r e °C. C o n c e n t r a t i o n s M. A 1 .96 x 1 0 4 41.4 x 1 0 2 150 NH„ = 1.0, NH* = 1.0 3 4 B 2 .04 x 1 0 4 40.5 x 1 0 2 150 NH 3 = 0.5, NH* = 1 . 0 C 1 .95 x 1 0 4 44.6 x 1 0 2 120 NH = 1.0, NH + » 1.0 3 4 From t h i s t a b l e the m o l a r e x t i n c t i o n c o e f f i c i e n t o f 2 -1 -1 t e t r a - t h i o m o l y b d a t e a t 315 my was t a k e n as 201 x 10 M. cm... Then a b s o r p t i o n due to d i - t h i o m o l y b d a t e a t 315 my i s g i v e n -by e q u a t i o n ( 1 1 ) : 315 315 2 & 2 = & ~ 201 x 1 0 Z I C 4 . . . . (11) - 315 D i v i d i n g t h i s w i t h Mo^ g i v e s t h e s p e c i f i c a b s o r p t i o n 315 = A^ /Mo T, w h i c h i s p r o p o r t i o n a l to the f r a c t i o n a l d i s -t r i b u t i o n o f d i - t h i o m o l y b d a t e , , needed i n n c a l c u l a t i o n by e q u a t i o n ( 5 ) . F i g u r e 4 shows an example o f t h e p l o t o f a n d : - 315 a g a i n s t a ^ . By g r a p h i c a l d i f f e r e n t i a t i o n o f the s m o o t h l y f i t t i n g c u r v e s and by u s i n g e q u a t i o n s (4) and (5) f o r h i g h and low v a l u e s o f r e s p e c t i v e l y , n was c a l c u l a t e d f o r each e x p e r i m e n t a l p o i n t . The c a l c u l a t e d n and a r e p l o t t e d i n F i g u r e 5 and l i s t e d i n A p p e n d i x A, T a b l e A - l - 1 Fig. 3 PLOT OF EQUATION (10) TO OBTAIN ^ ' T3I5 XIO 4 M:1 cm?1 OQZO 0.050 0.100 0.200 0.500 1.000 Fig. 4 CALCULATION OF n , I50°C., SERIES A 41 42 3-3 Conversion of f r e e s u l p h i d e c o n c e n t r a t i o n to aqueous  hydrogen sul p h i d e c o n c e n t r a t i o n The f r e e s u l p h i d e c o n c e n t r a t i o n must be converted to the aqueous hydrogen s u l p h i d e c o n c e n t r a t i o n i n order to c a l c u l a t e the consecutive constants and the s t a b i l i t y c o n stants. Since the d i s s o c i a t i o n constants of aqueous hydrogen sul p h i d e are not known with great accuracy f o r high temperatures, the f o l l o w i n g method was employed f o r c a l c u l a t i o n . The r e l a t i o n s h i p between aqueous hydrogen s u l p h i d e c o n c e n t r a t i o n and f r e e s u l p h i d e c o n c e n t r a t i o n i s given by the mass balance equation, [ H 2 S ^ a q " V ( 1 + < K s l / [ H + ] ) + ( K s l K s 2 / t H + ] 2 ^ U s u a l l y pK g2 i s estimated to be l a r g e r than pK g^ by 3.5 and consequently the l a s t term i n the denominator i s n e g l i g i b l e 37 i n weak a l k a l i n e s o l u t i o n . Hydrogen ion concentr.ation i s p r o p o r t i o n a l to the r a t i o of ammonium ion c o n c e n t r a t i o n and fr e e ammonia c o n c e n t r a t i o n . Therefore the above equation i s r e d u c e d t o , [ H 2 S ] a q = S f / ( 1 + M I N H . 3 J / [ N H J ] ) . . . . (12) i or [NH+]/[NH 3] = ( 1/IH 2S] ) ( S f[NH*] / [NH 3] ) -m where m i s a constant. Therefore by p l o t t i n g [NH 4 +]/[NH 3] against S f [ N H 4 + ] / [ N H 3 ] f o r t h e c o n s t a n t v a l u e o f [H_S] , m can be o b t a i n e d as z a q the i n t e r c e p t . At f i r s t c o n c e n t r a t i o n s o f f r e e ammonia and ammon-ium i o n were c a l c u l a t e d f r o m the pH and t o t a l ammonium, N T , of the quenched s o l u t i o n s a t room t e m p e r a t u r e , knowing t h a t f o r the s e r i e s o f e x p e r i m e n t s a t 150°C. th e same amount o f ammonium s u l p h a t e was added. From m a t e r i a l b a l a n c e and , e q u i l i b r i u m e q u a t i o n s , + i v \ i o p H N T = [NH 4 ] + [NH 3] = [NH 4 ] + ( [ N H ^ ] K^) where K M i s t h e d i s s o c i a t i o n c o n s t a n t o f ammonium i o n a t room t e m p e r a t u r e . Thus the p l o t o f a g a i n s t 10 p I* would be a s t r a i g h t l i n e and the i n t e r c e p t at 1 0 p H = 0 g i v e s the v a l u e o f ammonium i o n and, c o n s e q u e n t l y , f r e e ammonia. The p r o p o r t i o n o f ammonium i o n and f r e e ammonia t h u s o b t a i n e d was c o n s i d e r e d n o t to change w i t h t e m p e r a t u r e c o n s i d e r i n g t h a t the amount of molybdenum and s u l p h i d e were a m a g n i t u d e s m a l l e r . (Ammonia l o s s due to f l u s h i n g ' a t the o u t l e t o f s a m p l i n g l i n e was f o u n d n e g l i g i b l e ) . S e c o n d l y f r e e s u l p h i d e c o n c e n t r a t i o n s a t the c o n s t a n t n - v a l u e s were r e a d f r o m F i g u r e 5 f o r d i f f e r e n t [ N H 4 + ] / [ N H 3 ] v a l u e s . S i n c e the f o r m a t i o n f u n c t i o n i s a u n i q u e f u n c t i o n of the f r e e l i g a n d c o n c e n t r a t i o n f o r the m o n o - n u c l e a r com-p l e x s y s t e m , c o n s t a n t n i s e q u i v a l e n t to c o n s t a n t [H„S] a t the p r e s e n t c a s e . 2 aq r 44 F i g u r e s 6a and 6b show the p l o t s of v s . 10^^ and [ N H 4 + ] / [ N H 3 ] v s . S [NH 4 + ] / [ N H 3 ] , r e s p e c t i v e l y , and Table A - l - 2 i n Appendix A g i v e s the r e l e v a n t d a t a . F r o m Figure 6b m was obtained to be 5.8 and was c o n v e r t e d to [H„S] by e q u a t i o n ( 1 2 ) . F i g u r e 7 shows the p l o t of n 3. Q v s . [H„S] at 150°C. n v a l u e s of S e r i e s D at h i g h f r e e 2 aq 6 s u l p h i d e c o n c e n t r a t i o n s were not i n c l u d e d i n t h i s f i g u r e s i n c e the i n t e r f e r e n c e by the appearence of new peaks became l a r g e and a c c u r a c y of the d e t e r m i n a t i o n of a 4 became l e s s . 3-4 C a l c u l a t i o n of s t a b i l i t y c o n s t a n t s from the f o r m a t i o n  curve 3-4-a Bjerrum's H a l f - n Method Bjerrum suggested the use of the r e c i p r o c a l l i g a n d c o n c e n t r a t i o n at a l l h a l f - n v a l u e s f o r c o n s e c u t i v e c o n s t a n t s , namely, k = l / L n n where k i s the c o n s e c u t i v e c o n s t a n t f o r the s t e p - n : n r ML n + L = ML n-1 n and L i s the l i g a n d c o n c e n t r a t i o n at n • n = n - 1/2 The p r i n c i p l e i s based on the f a c t t h a t a s o l u t i o n w i t h a n-value of (n - 1/2) must c o n t a i n a p p r o x i m a t e l y e q u a l amount of the ML ,- and ML - c o m p l e x e s ^ . n-1 n ^ T h i s method was a p p l i e d to the p r e s e n t case. The f o l l o w i n g v a l u e s were read from F i g u r e 7:-45 1.4 TOTAL AMMONIA 0.8 (NH^/uNHj) 2 3 antilog(pH- 9 ) -/ ( 6b ) -4 n = 0.85 O 1.42 • 15 _ 2 0 MJCIO 3 , 1 0 S f[NH4)/(NH 3) Fig. 6a, 6b CONVERSION OF S f TO (HgS^ , PLOT FOR m 5 Curve method Fig. 7 THE FORMATION CURVE OF THE THIOMOLYBDATE SYSTEM, 150°C. 47 rt L 1/2 0 . 35 X i o - 3 M. 3/2 1.4 X l O " 3 M. 5/2 2 . 3 X i o " 3 M. 7/2 8.0 X i o " 3 M. The c a l c u l a t e d s t a b i l i t y c o n s t a n t s a r e g i v e n i n T a b l e 1. When n - v a l u e s were c a l c u l a t e d w i t h e q u a t i o n (1) u s i n g the s t a b i l i t y c o n s t a n t s t h u s o b t a i n e d , the r e s u l t d i d n o t a g r e e w i t h t h e o b s e r v e d v a l u e s e x c e p t a t the mid p o i n t as shown i n F i g u r e 7 l i n e - 1 . R o s s o t t i and R o s s o t t i ^ d i s c u s s e d t h e v a l i d i t y o f the B j e r r u m ' s H a l f - n method and c o n c l u d e d t h a t the n e c e s s a r y c o n d i t i o n was k ../k > 10 4. S i n c e none o f the two n-1 n n e i g h b o u r i n g c o n s e c u t i v e c o n s t a n t s were fo u n d t o be d i f f e r -e n t enough to s a t i s f y t h e c o n d i t i o n , t h i s method was n o t a d e q u a t e . 3-4-b Two-parameters a p p r o x i m a t i o n A s y s t e m c o n t a i n i n g many complexes o f d i f f e r e n t d e g r e e o f c o m p l e x i n g may be d e s c r i b e d i n terms of o n l y two p a r a m e t e r s . One p a r a m e t e r g i v e s t h e m a g n i t u d e o f the o v e r -a l l s t a b i l i t y c o n s t a n t of the s y s t e m and t h e o t h e r the r a t i o o f the n e i g h b o u r i n g c o n s e c u t i v e c o n s t a n t s ^ . D y r s s e n and S i l l e n assume t h a t the r a t i o o f t h e ;n e i g h b o u r i n g c o n s e c u t i v e c o n s t a n t s i s c o n s t a n t : R = . k /k ,, = R = c o n s t a n t n n n+1 48 B j e r r u m assumes t h a t depends on n i n a s t a t i s t i c a l way: R n = ( (N - n + l ) ( n + 1 ) / ( N - n ) n ) x 2 where N i s the maximum c o o r d i n a t i o n number and x i s the " s p r e a d i n g f a c t o r " , d e f i n e d by B j e r r u m as a c o n s t a n t and u n i q u e p a r a m e t e r f o r a complex s y s t e m and r e l a t e d to the m i d - p o i n t s l o p e o f the f o r m a t i o n c u r v e . F o r t h e c a s e where t h e maximum c o o r d i n a t i o n number i s f o u r , the above two methods l e a d to t h e f o l l o w i n g e q u a t i o n s : -D y r s s e n and S i l l e n : ii = ( R 3 a + 2 R 4 a 2 + 3 R 3 a 3 + 4 a 4 ) / ( l + R 3 a + R 4 a 2 + R 3 a 3 + a 4 ) . . . . (13) a = VL, v: c o n s t a n t 3 4 2 3 3 4 B x = R v, 3 2 = R v , 3 3 = R J v , 3 A = v B j e r r u m : 3 4 2 3 3 4 n = (4x b + 12x b + 12x b + 4b ) / ( l + 4 x 3 b + 6 x 4 b 2 + 4 x 3 b 3 + b 4 ) . . . (14) b = k L , k: c o n s t a n t 3 4 2 3 3 4 0 X = 4x k, 3 2 = 6x k , 3 3 = 4x k , 3 4 = k F a m i l i e s of n o r m a l i z e d d i a g r a m s of n-a and n-b were c o n s t r u c t e d f o r v a r i o u s v a l u e s o f R and x, r e s p e c t i v e l y , 49 and t h e b e s t f i t v a l u e s were s o u g h t by p l a c i n g F i g u r e 7 abjove them. The f o l l o w i n g v a l u e s gave t h e most s a t i s f a c t o r y r e s u l t s and t h e c a l c u l a t e d v a l u e s o f s t a b i l i t y c o n s t a n t s by e q u a t i o n (13) and (14) a r e g i v e n i n T a b l e 1. \ v 3 - 1 Dyr'ssen and S i l l e n : R = 1.05, v = 0.57 x 10 M, B j e r r u m : . x = 0.65, k = 0.57 x 1 0 3 M . _ 1 B o t h t h e D y r s s e n and S i l l e n method and t h e B j e r r u m method gave a p p r o x i m a t e l y t h e same v a l u e s o f s t a b i l i t y c o n -s t a n t s . The l i n e 2 i n F i g u r e 7 r e p r e s e n t s t h e v a l u e s o f n i i c a l c u l a t e d by t h e D y r s s e n and S i l l e n method u s i n g t h e v a l u e s g i v e n a b o v e . C l e a r l y t h i s method gave a b e t t e r f i t t h a n t h e H a l f - n M ethod a l t h o u g h t h e f i t s a t t h e h i g h e s t a n d , t h e i l o w e s t v a l u e s o f f r e e l i g a n d c o n c e n t r a t i o n s were p o o r . 3-4-c C a l c u l a t i o n o f k, 4 From t h e e q u i l i b r i u m r e l a t i o n s h i p b e t w e e n t e t r a -i -and t r i - t h i o m o l y b d a t e , t h e r a t i o o f t h e c o n c e n t r a t i o n o f I t h e t e t r a - t h i o m o l y b d a t e t o t h a t o f t h e t r i - t h i o m o l y b d a t e i s p r o p o r t i o n a l t o t h e c o n c e n t r a t i o n o f t h e aqueous h y d r o g e n s u l p h i d e : L . r i f ) C 4 / C 3 = k 4 [ H 2 S ] a q F i g u r e 8 shows t h e p l o t o f t h e d a t a a t 150°C. The l i n e a r i t y was c o n s i d e r e d good. The s l o p e g i v e s t h e v a l u e 2 - 1 f o r k, as 2,6. x 10 M. 4 2 F i g u r e 9 shows t h e s i m i l a r p l o t f o r t h e d a t a a t 1 2 0 ° C , where C^/C^ were p l o t t e d a g a i n s t t h e f r e e s u l p h i d e c o n c e n t r a t i o n i n s t e a d o f t h e c o n c e n t r a t i o n o f t h e aqueous h y d r o g e n s u l p h i d e s i n c e t h e c o n v e r s i o n f a c t o r was n o t ob-t a i n e d e x p e r i m e n t a l l y a t t h i s t e m p e r a t u r e . The l i n e a r i t y 2 -1 was a l s o good ( s l o p e : 0.43^ x 10 M. ) . F a i r l y r e l i a b l e d a t a o f K„, t h e a c i d d i s s o c i a t i o n c o n s t a n t o f t h e ammonium N i o n , are a v a i l a b l e i n t h e l i t e r a t u r e s and a t 120° and 150°C. 37 pK^ a r e 7.0g and 6.6^, r e s p e c t i v e l y . S i n c e m i n t h e c o n v e r s i o n e q u a t i o n i s t h e r a t i o o f t h e f i r s t a c i d d i s s o c i a t i o n c o n s t a n t o f t h e aqueous h y d r o g e n s u l p h i d e , K g^, t o , pK a t 150°C. was c a l c u l a t e d t o be 5.8^. By i n t e r p o l a t i o n w i t h t h e v a l u e a t 25°C. ( 7 . 0 Q ) i n t h e l i t e r a t u r e 3 7 , p K g l a t 120°C. was e s t i m a t e d t o be 6.0,.. T h i s y i e l d e d t h e v a l u e f o r m a t 120°C. as 10.^ and c o m b i n e d w i t h t h e s l o p e f r o m F i g u r e 9, 2 - 1 k. a t 120°C. was o b t a i n e d as 5 . 3 r x 10 M. 4 5 3-4-d N u m e r i c a l c a l c u l a t i o n o f s t a b i l i t y c o n s t a n t s (1) When k^ i s known, t h e e q u a t i o n (1) c a n be h a n d l e d w i t h t h e l e a s t s q u a r e s method by t r a n s f o r m i n g i t as f o l l o w s Y -= e 3 + 3 2x 2 + e 1x 1 where Y = n/Z, X 2 - ( 2 - i i ) L 2 / Z , X± = ( l - i i ) L/Z and Z = ( 3 - i i ) L 3 + ( 4 - n ) L 4 By m a k i n g use o f t h e " m u l t i p l e l i n e a r r e g r e s s i o n p r o g r a m " o f t h e HP9100A c a l c u l a t o r , t h e b e s t f i t v a l u e s o f the c o n s e c u t i v e c o n s t a n t s were s o u g h t u s i n g k^ v a l u e s ob-t a i n e d i n s e c t i o n 3-4-c. When the p o i n t s a t the l o w e s t t h r e e v a l u e s o f the c o n c e n t r a t i o n o f the aqueous h y d r o g e n s u l p h i d e i n F i g u r e 7 were t a k e n i n t o c o n s i d e r a t i o n , 3-^  became n e g a t i v e and t h e c a l c u l a t e d n - v a l u e s d e v i a t e d g r e a t l y a t the h i g h e r v a l u e s o f the l i g a n d c o n c e n t r a t i o n s . Thus t h e s e p o i n t s were n e g l e c t e d f o r t h e c a l c u l a t i o n and the l i n e 3 i n F i g u r e 7 shows the f o r m a t i o n c u r v e t h u s c a l c u l a t e d . 3 - v a l u e s a r e l i s t e d i n T a b l e 1. S i m i l a r c a l c u l a t i o n s were p e r f o r m e d to n and f r e e s u l p h i d e c o n c e n t r a t i o n s f o r the S e r i e s C, 120°C. The d o t t e d l i n e i n F i g u r e 5, S e r i e s C, 120°C. shows the c a l c u l a t e d f o r m a t i o n c u r v e and 3 - v a l u e s a r e l i s t e d i n T a b l e 1. 3-5 N u m e r i c a l c a l c u l a t i o n o f s t a b i l i t y c o n s t a n t s (2) The c a l c u l a t i o n methods so f a r d e s c r i b e d made use of the f o r m a t i o n f u n c t i o n o b t a i n e d by t h e g r a p h i c a l d i f f e r -e n t i a t i o n o f the p l o t s o f t h e f r a c t i o n a l d i s t r i b u t i o n s of the t e t r a - and t r i - t h i o m o l y b d a t e . The f o l l o w i n g semi-numer-i c a l method was d e r i v e d to e l i m i n a t e the g r a p h i c a l d i f f e r -e n t i a t i o n p r o c e s s . From t h e d e f i n i t i o n of the f r a c t i o n a l d i s t r i b u t i o n o f the m o n o - n u c l e a r complex s y s t e m , i N a. = 3.L 1/U, U = 1 + Z 3.L 1 i i . , x and a./a. , - k. L i D e f i n i n g a f u n c t i o n as i - 1 i i - 1 i F Q = a / a = (B / B ) U i i - 1 i i - 1 S u b s t i t u t i o n o f the above r e l a t i o n s h i p s y i e l d s N k F 0 " E a k 8 • k=0 k where g = * ±/<* ±_ 1 a n d a f c = ( 6 k / 8 i - i ) k i ^ F o r the c a s e where i = 4, a 0 = k 4 / k l k 2 k 3 B 0 = 1 a l = k 4 / k 2 k 3 6 1 = ( a i / a 0 ) k a 2 = k 4 / k 3 6 2 = ( a 2 / a Q ) k a 3 - 1 6 3 = ( l / a Q ) k 3 a 4 = 1 3 4 = ( l / a Q ) k 4 a 5 = k 5 / k 4 B 5 = ( a 5 / a Q ) k a 6 = k 6 k 5 / k 4 3 6 = ( a 6 / a 0 ) k e t c . e t c F Q and g can be o b t a i n e d from the e x p e r i m e n t a l v a l u e s o f the f r a c t i o n a l d i s t r i b u t i o n s o f the n e i g h b o u r i n g s p e c i e s . By f i n d i n g a s e t o f c o e f f i c i e n t s o f the p o l y n o m i n a l of g, and a v a l u e o f , s t a b i l i t y c o n s t a n t s can be c a l c u -l a t e d w i t h o u t t h e g r a p h i c a l d i f f e r e n t i a t i o n . N o t i n g t h a t a^ and a^ i n the f u n c t i o n F ^ a r e u n i t y by d e f i n i t i o n , w o r k i n g f u n c t i o n s F ^ and H, d e f i n e d as f o l l o w i n g , were used F l H where h S i n c e t h e summation i n t h e f u n c t i o n H c o n t a i n s a l l the p o l y -n o m i n a l forms o f t h e i n v e r s e o f h, the p l o t o f H a g a i n s t h w i l l d i v e r g e i n t o i n f i n i t y as h approaches z e r o i f t h e r e were any a p p r e c i a b l e amount o f complexes o f h i g h e r c o o r d i n -a t i o n t h a n the t e t r a - s u b s t i t u t e d s p e c i e s . T h e r e f o r e the p l o t of H v s . h can be used as the d e t e c t o r o f h i g h e r complex f o r m a t i o n . F i g u r e 1 0 shows t h e p l o t s o f F^ v s . g and H v s . h f o r the d a t a o f s e r i e s B where the n o m i n a l r a t i o o f f r e e F 0 " 8 - g N a Q + a 1 g + a 2 g + Z a f cg ( C 4 / C 3 ) J (Mo T - C 3 - C 4 ) / C 3 = V g ' a 0 + a-h + a„h + E a, h 2 1 0 . c k k=5 = 1/g. ammonia t o ammonium i o n was 0.5 and the t e m p e r a t u r e was 1 5 0 °C. As t h e f u n c t i o n H c o n c a v e s - u p a t low h v a l u e s , the need o f a h i g h e r complex term i s i n d i c a t e d . J u d g i n g f r o m the o b s e r v a t i o n i n s e c t i o n 3-2 t h a t new a b s o r p t i o n bands a p p e a r e d i n t h e s p e c t r u m when the f r e e ammonia c o n c e n t r a t i o n was low and t h a t the peaks c o r r e s p o n d i n g to the t e t r a -s u b s t i t u t e d s p e c i e s s t o p p e d i n c r e a s i n g a l t h o u g h t h e t o t a l s u l p h i d e c o n c e n t r a t i o n was i n c r e a s e d and t h a t the new peaks i n c r e a s e d as t h e s u l p h i d e c o n c e n t r a t i o n was i n c r e a s e d , a p r o t o n a t e d s p e c i e s Mo(SH)g was p o s t u l a t e d : MoO 2" + 6H.S + 2 H + = M o ( S H ) c + 4H.0 4 2 6 2 2 6 Then F± = a Q + a ^ + a 2 g + a & g . . . . (16) The b e s t f i t t i n g v a l u e s of a's were o b t a i n e d g r a p h i c -a l l y u s i n g the e x t r a p o l a t i o n method s i m i l a r i n p r i n c i p l e to the method of F r o n a e u s f o r the t r e a t m e n t of n as a f u n c t i o n of the f r e e l i g a n d c o n c e n t r a t i o n ^ . At low v a l u e s o f g, F^ t e n d s t o a s t r a i g h t l i n e o f i n t e r c e p t a^ and o f s l o p e a^. A f t e r a^ was known ( o r e s t i -mated) the f u n c t i o n F 2 = CF Q - a Q ) / g = a x + a 2 g + a 6 g 5 was c a l c u l a t e d and p l o t t e d a g a i n s t g, to g i v e a^ as an i n t e r c e p t and a 2 as t h e l i m i t i n g s l o p e . S i m i l a r l y the f u n c t i o n 58 F 3 = ( F 2 - a i ) / g = a 2 + a 6 g 4 4 was c a l c u l a t e d and p l o t t e d a g a i n s t g t o g i v e a 2 as an i n t e r c e p t and a^ as t h e s l o p e . S i n c e t h e e r r o r a c c u m u l a t e s i n t h e v a l u e o f a , , 6 c a l c u l a t i o n p r o c e d u r e was r e v e r s e d by c a l c u l a t i n g and p l o t -t i n g a f u n c t i o n G l = F 1 7 S 6 = F l h 6 = a 6 + a 2 h 4 + a l h 5 + a 0 h 6 4 a g a i n s t h t o o b t a i n a^ as t h e i n t e r c e p t . S u b s e q u e n t l y f u n c t i o n s G 2 = ( G 1 - a 6 ) / h 4 = a 2 + a^h + a Q h 2 G 3 = ( G 2 ~ a 2 ) / h " a l + a 0 h were c a l c u l a t e d and p l o t t e d a g a i n s t h t o o b t a i n a 2 , a^ and ag. Then t h e s u c c e s s i v e a p p r o x i m a t i o n was u s e d t o match two s e t s o f a ' s . A f t e r a_ , a . , a„ and 2, were o b t a i n e d 0 1 2 6 and r e f i n e d , s t a b i l i t y c o n s t a n t s were c a l c u l a t e d u s i n g t h e v a l u e o f k. o b t a i n e d i n s e c t i o n 3-4-c. 4 F i g u r e s 11a and l i b show t h e e x a m p l e o f s u c h p l o t s f o r t h e d a t a o f S e r i e s B. The b e s t f i t v a l u e s o f a ^ , a ^ , a 2 and a g were 0.072, 0.037, 0.68 and 0.27 r e s p e c t i v e l y . : E q u a l l y good f i t was o b t a i n e d by p u t t i n g a^ as z e r o , o r 59 a s s u m i n g t h a t m o n o - s u b s t i t u t e d s p e c i e s d i d n o t e x i s t and the v a l u e s o b t a i n e d f o r a n . a„ and a, were 0.080, 0.70„ 0 2 6 8 and 0.27^ r e s p e c t i v e l y . The c a l c u l a t e d s t a b i l i t y c o n s t a n t s a r e g i v e n i n T a b l e 1. The c a l c u l a t e d v a l u e s of n f r o m t h e s e s t a b i l i t y c o n s t a n t s a r e p l o t t e d i n F i g u r e 7 as l i n e " 4. Good f i t was o b s e r v e d between n o f 1 and 3 but f i t was poor a t h i g h and low v a l u e s of l i g a n d c o n c e n t r a t i o n . S i m i l a r c a l c u l a t i o n f o r the S e r i e s A, o r 150°C. and n o m i n a l r a t i o of f r e e ammonia to ammonium i o n b e i n g 1:1, i n d i c a t e d a s m a l l amount o f h i g h e r complex f o r m a t i o n . S e r i e s C, 120°C. and 1:1, i n d i c a t e d no f o r m a t i o n of h i g h e r complex. The b e s t f i t v a l u e s o f a^, a^, a^ and a^ f o r S e r i e s A and S e r i e s C were 0.105, 0.045, 0.58 and 0.30, and 0.085, 0.025, 0.87 and 0.00 r e s p e c t i v e l y . The c a l c u l a t e d v a l u e s o f s t a b i l i t y c o n s t a n t s u s i n g the v a l u e s of k^ i n s e c t i o n 3-4-c a r e g i v e n i n T a b l e 1. n v a l u e s were c a l c u l a t e d f o r S e r i e s C u s i n g the s t a b i l i t y c o n s t a n t s t h u s o b t a i n e d and compared w i t h the v a l u e s o b a t i n e d by g r a p h i c a l d i f f e r e n t i a t i o n method. The agreement was n o t so good compared w i t h t h e one o b t a i n e d by the n u m e r i c a l method ( 1 ) . ( S o l i d l i n e i n F i g u r e 5, C) 4 . D i s c u s s i o n and C o n c l u s i o n s T a b l e 1 shows the summary of the c a l c u l a t e d s t a b i l i t y c o n s t a n t s o b t a i n e d by t h e v a r i o u s methods a l r e a d y d e s c r i b e d . S i n c e a good l i n e a r i t y was o b s e r v e d f o r the p l o t o f C./C a g a i n s t aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n i n 61 TABLE 1 Summary o f S t a b i l i t y C o n s t a n t s C a l c u l a t e d By V a r i o u s Methods 150°C . Method MT 1 B2 MT 2 h M : 3 h M : 4 h M: 6 k 4 M : 1 L i n e i n F i g u r e 7 x l 0 ~ 3 x l O - 6 x l 0 ~ 9 x l O " 1 2 x l O " 1 8 x l O - 3 H a l f - i i 2.9 2 ' ° 6 0 .89 0 . 11 - 0 .13 1 Two-parameter D y r s s e n 0 .66 0.40 0 .22 0.11 - 0.49 2 Two-parameter Bj errum 0.63 0 . 35 0 .21 0.11 - 0 .52 -k. c a l c n . 4 - - - - - 0.262 -N u m e r i c a l (1) N u m e r i c a l (2) 0.23 0. 35 0.27 0.070 — 0.262 ( s e t ) 3 S e r i e s B S e r i e s B S e r i e s A 0.13 0.00 ( s e t ) 0. 11 0 .65 0.61 0. 38 0 . 25 0.22 0.-17 0.065 0.059 0. 045 0 . 0012 0.0011 0.0009 4 0.262 ( s e t ) 0 . 262 ( s e t ) 0.262 ( s e t ) 4 120°C. N u m e r i c a l (1) 4 ' 2 6 9 ' 8 o 3 - S 1.8 ? - 0 .53 ( s e t ) d o t N u m e r i c a l (2) 0. 16 2 . 9 1. 8 0.96 0. 0 ( s e t ) 0 .53 ( s e t ) s o l i d ' k^ C a l c u l a - - - - - - 0. 53 5 t i o n L i n e i n F i g u r e 5. k^ was o b t a i n e d by u s i n g the e s t i m a t e d v a l u e of d i s s o c i a t i o n c o n s t a n t of aqueous h y d r o g e n s u l p h i d e a t 120°C. the c a l c u l a t i o n of i n s e c t i o n 3-4-c (Figure 8 ) , the general method of c a l c u l a t i o n of n, and the estimates of molar e x t i n c t i o n c o e f f i c i e n t s of t e t r a - and t r i -39 thiomolybdates given by T r i d o t and Bernard were considered to be c o r r e c t . Therefore F i g u r e 7 was used f o r the compar-s i o n of methods employed. No simple method of c a l c u l a t i o n y i e l d e d a r e s u l t f i t t i n g the t o t a l range of the l i g a n d c o n c e n t r a t i o n . C a l c u l a t e d values of n were g e n e r a l l y too high at the hi g h -est values of aqueous hydrogen s u l p h i d e c o n c e n t r a t i o n and too low at the lowest values of the aqueous hydrogen su l p h i d e c o n c e n t r a t i o n . However at lower values of l i g a n d c o n c e n t r a t i o n , a l l the methods gave approximately the same values of n. Therefore i t was concluded that n values obtained by the g r a p h i c a l d i f f e r e n t i a t i o n method were ra t h e r i n e r r o r and too l a r g e i n the lowest r e g i o n of aqueous hydrogen s u l p h i d e c o n c e n t r a t i o n . This i s p l a u s i b l e s i n c e the slope at the lowest values of i n Figure 4 was ex-t r a p o l a t e d from the higher values and may be too l a r g e . The v a l i d i t y of the H a l f - n Method has been d i s c u s s e d a l r e a d y , and i t s inadequacy f o r the present system o u t l i n e d . Although the Two-parameter Approximation gave a ; "good f i t " , the c a l c u l a t e d k^ values were twice the values obtained i n s e c t i o n 3-4-c as shown i n the column 7 i n Table 1 Therefore the Two-parameter Approximation method was con-r s i d e r e d not to be adequate to d e s c r i b e t h i s system. I n t h e n u m e r i c a l c a l c u l a t i o n ( 1 ) , v a l u e o b t a i n e d i n t h e s e c t i o n 3-4-c was u s e d . The n v a l u e s c a l c u l a t e d by u s i n g t h e s t a b i l i t y c o n s t a n t s o b t a i n e d by t h i s method a g r e e d f a i r l y w e l l w i t h t h e v a l u e s o b t a i n e d by the g r a p h i c a l d i f f e r -e n t i a t i o n i n t h e s e c t i o n 3-2, as can be se e n by a d o t t e d l i n e i n F i g u r e 5 c u r v e C and by t h e l i n e 3 i n F i g u r e 7. ; When the f r a c t i o n a l d i s t r i b u t i o n s o f v a r i o u s s p e c i e s were c a l c u -l a t e d , i t was o b s e r v e d t h a t (a) s i m p l e m o l y b d a t e and t e t r a - t h i o m o l y b d a t e were t h e dominant s p e c i e s , (b) mono-t h i o m o l y b d a t e was l e s s s i g n i f i c a n t i n a l l range o f the l i g a n d c o n c e n t r a t i o n , and (c) t r i - and d i - t h i o m o l y b d a t e were f a i r l y s i g n i f i c a n t ( a r o u n d 20%) a r o u n d the l i g a n d c o n c e n t r a t i o n r a n g e where s i m p l e m o l y b d a t e and t e t r a - t h i o m o l y b d a t e were o f the same amount. From the c a l c u l a t e d v a l u e s o f f r a c t i o n a l -d i s t r i b u t i o n of d i - t h i o m o l y b d a t e and t h e measured v a l u e s o f the s p e c i f i c a b s o r p t i o n o f the d i - t h i o m o l y b d a t e a t 315 my, - 315 , the m o l a r e x t i n c t i o n c o e f f i c i e n t o f the d i - t h i o m o l y -4 -1 -1 b d a t e a t 315 my was c a l c u l a t e d to be 0.9,. x 10 M. cm. ( T a b l e A - l - 1 i n A p p e n d i x A ) . In t h e n u m e r i c a l c a l c u l a t i o n (2) i t was n e c e s s a r y to p o s t u l a t e a p r o t o n a t e d s p e c i e s of h i g h e r c o o r d i n a t i o n , w h i c h was n o t n e c e s s a r y i n t h e o t h e r methods. The a c c u r a c y of e x p e r i m e n t was n o t h i g h enough to c o n f i r m t h e v a l i d i t y o f t h i s a s s u m p t i o n . However t h i s p r o t o n a t e d s p e c i e s o f f e r s an e x p l a n a t i o n f o r the o b s e r v a t i o n i n S e r i e s D, i n w h i c h t h e c o n c e n t r a t i o n of t e t r a - s u b s t i t u t e d s p e c i e s s t o p p e d f a r s h o r t o f the v a l u e s e x p e c t e d f r o m the o t h e r s e r i e s and a l s o new peaks a p p e a r e d and i n c r e a s e d i n i n t e n s i t y as the amount-of t o t a l s u l p h i d e was i n c r e a s e d . S i n c e the s t a b i l i t y c o n s t a n t f o r t h e p r o t o n a t e d s p e c i e s Mo(SH)^ c o n t a i n s the s q u a r e o f t h e h y d r o g e n i o n c o n c e n t r a t i o n , $, would o i n c r e a s e i n p r o p o r t i o n to t h e s q u a r e o f t h e h y d r o g e n i o n c o n c e n t r a t i o n , o r t o the s q u a r e o f the r a t i o of ammonium i o n c o n c e n t r a t i o n to f r e e ammonia c o n c e n t r a t i o n , and a t a v e r y h i g h v a l u e o f t h i s r a t i o , t h e term c o n t a i n i n g B,. would 6 d o m i n a t e the whole complex s y s t e m d e c r e a s i n g the f r a c t i o n a l d i s t r i b u t i o n of a l l the o t h e r s p e c i e s , w h i c h a g r e e s w i t h t h e o b s e r v a t i o n . The p r o t o n a t e d s p e c i e s o f the forms HMoS. and H.MoS. 4 2 4 were r e j e c t e d on t h e ground t h a t by t h e e q u i l i b r i u m e q u a t i o n s MoO 2" + 4H.S + H + = HMoS. + 4H.0 4 2 4 2 MoO 2 + 4H„S + 2 H + = H.MoS. + 4H.0 4 2 2 4 2 the c o n c e n t r a t i o n s of t h e s e s p e c i e s would be p r o p o r t i o n a l to t h e f o u r t h power of t h e l i g a n d c o n c e n t r a t i o n . T h e r e f o r e the p l o t o f f u n c t i o n H a g a i n s t h i n the n u m e r i c a l c a l c u l a t i o n (2) would n o t c o n c a v e up as h a p p r o a c h e s to z e r o , w h i c h i s c o n t r a r y to the o b s e r v a t i o n . 6 4 The p r o t o n a t e d s p e c i e s p r o p o s e d by Ghosh e t a l . , 65 4- 2-HgMoSg and HgMoSg , were a l s o r e j e c t e d s i n c e by the e q u i l i b r i u m e q u a t i o n s Mo0 2~ + 8H„S = H,MoS 4" + 2 H + + 4H„0 4 2 6 8 2 = HgMoSg + 4H 20 the c o n c e n t r a t i o n o f t h e s e s p e c i e s would n o t be a f f e c t e d o r would be a d v e r s e l y a f f e c t e d by the i n c r e a s e o f h y d r o g e n i o n c o n c e n t r a t i o n . T h e r e might be a f o r m a t i o n o f p o l y n u c l e i s p e c i e s p r o p o s e d by Saxena e t a l . to e x p l a i n the r e s u l t s o f t h e i r e x p e r i m e n t s where t h i o m o l y b d a t e s o l u t i o n s were t i t r a t e d w i t h HC1^"\ However, i n t h e i r work t h e pH was on the a c i d s i d e . The p r e s e n t e x p e r i m e n t a l d a t a i n ammoniacal s o l u t i o n a p p e a r to be a d e q u a t e l y e x p l a i n e d w i t h o u t t h e n e c e s s i t y o f p o s t u l a t i n g p o l y n u c l e i s p e c i e s . C o n s e q u e n t l y t h e molybdenum ( V I ) - s u l p h u r (-II) -water s y s t e m may be d e s c r i b e d as a r e s u l t a n t o f the i n t e r -a c t i o n o f t h e f o l l o w i n g two f o r m a t i o n c u r v e s : (a) A c u r v e r e p r e s e n t i n g the e q u i l i b r i a between 2-th e s p e c i e s o f t h e f o r m MoO, S , w h i c h does n o t v a r y *\ X X w i t h the h y d r o g e n i o n c o n c e n t r a t i o n . ( C u r v e 1) (b) A c u r v e r e p r e s e n t i n g the e q u i l i b r i u m between m o l y b d a t e i o n and t h e p r o t o n a t e d s p e c i e s , Mo(SH)^,which v a r i e s w i t h t h e h y d r o g e n i o n c o n c e n t r a t i o n . ( C u r v e 2) F i g u r e 12 shows the s c h e m a t i c d e s c r i p t i o n o f t h e above s t a t e m e n t . T h e r e f o r e at a v e r y low v a l u e o f h y d r o g e n i o n c o n -c e n t r a t i o n , o r i n a f a i r l y h i g h a l k a l i n e s o l u t i o n , c u r v e 2 w i l l be c o m p l e t e l y s u p p r e s s e d and h i g h f r a c t i o n a l d i s t r i b u -2-t i o n o f the s p e c i e s o f t h e f o r m MoO. S would be 4-x x e x p e c t e d . T h i s was c o n f i r m e d by an e x p e r i m e n t i n P a r t 2 s e c t i o n 3, where t h e f o l l o w i n g c o n c e n t r a t i o n s were r e a l i z e d when a r e a c t i o n m i x t u r e i n a s h a k i n g a u t o c l a v e a t 150°C. was quenched to room t e m p e r a t u r e w i t h i n 20 m i n u t e s . NH 3 0.86 M. C 3 0.00012 2 M. (NH.).SO. 0.49 M. C. 0.0005 6 _•M. 4 2 4 4 5 Na 2S 0.33 1 M. Mo^ 0.00067 M. T h e r e was no a p p e a r e n c e o f the "new p e a k s " o b s e r v e d i n S e r i e s D. The c a l c u l a t e d v a l u e s o f n and aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n w i t h the method d e s c r i b e d i n s e c t i o n _3 3-3 were 3.82 and 27 x 10 M., r e s p e c t i v e l y , a s s u m i n g t h a t the h i g h t e m p e r a t u r e e q u i l i b r i u m was f r o z e n . T h i s p o i n t i s shown i n F i g u r e 7 w i t h a d o u b l e c i r c l e . The agreement was c o n s i d e r e d good. The a c t u a l s t r u c t u r e o f the p r o t o n a t e d s p e c i e s may be a c o l l o i d a l molybdenum t r i s u l p h i d e , MoS 3*3H 2S, i n s t e a d of a m o l e c u l e i n w h i c h s i x h y d r o - s u l p h i d e i o n s a r e c o o r d i n a t e d to molybdenum atom, s i n c e (a) t h e e x p e r i m e n t a l m i x t u r e s n higher CH +) Curve I Curve 2 Log (H2S) Fig. 12 SCHEMATIC DIAGRAM OF THIOMOLYBDATE SYSTEM Curve I 1MoQ^sf + HgS = MoO^sf", + H20 (i»0,l,2,3) Curve 2 s Moo|" + 2H + + S^S = Mo(SH)6 + 4 h ^ 0 i n S e r i e s D p a s s e d t h r o u g h t h e f i n e s t grade g l a s s f i l t e r ( P y r e x ) to g i v e the same amount of molybdenum c o n c e n t r a t i o n o r i g i n a l l y c h a r g e d , but (b) t h e a b s o r p t i o n o f the new peaks d i d not seem to f o l l o w the B e e r ' s Law. In T a b l e 2 the l o g a r i t h m o f the c o n s e c u t i v e c o n -s t a n t s a r e l i s t e d f o r v a r i o u s t e m p e r a t u r e s . The v a l u e s a t 120° and 1 5 0°C. a r e from the r e s u l t s o f the n u m e r i c a l c a l c u -l a t i o n method ( 1 ) . The v a l u e s a t 19°C. a r e c a l c u l a t e d from 3 9 6 2 the e x p e r i m e n t a l d a t a by T r i d o t and B e r n a r d ' . The r o u g h e s t i m a t e s o f e n t h a l p y and e n t r o p y changes f o r the exchange o f o x i d e i o n w i t h s u l p h i d e i o n i n the t h i o m o l y b d a t e s p e c i e s were p e r f o r m e d u s i n g t h e s e d a t a and l i s t e d i n t h e column -5 and 6. The e n t h a l p i e s o f t h e exchange were n e g a t i v e and d e c r e a s e d i n m a g n i t u d e as the c o o r d i n a t i o n of s u l p h i d e i o n i n c r e a s e d . I t i s r e p o r t e d t h a t " s t e p - w i s e l i g a n t i o n a l e n t h a l p i e s f o r a s s o c i a t i o n w i t h i o n i c l i g a n d s i n aqueous . s o l u t i o n a r e u s u a l l y between 0 and ±5 kcal./mole, but may be as l a r g e as -10 kcal./mole, f o r r e a c t i o n s o f e.g. s i l v e r ( I ) or m e r c u r y ( I I ) w i t h c y a n i d e o r i o d i d e i o n s . The v a l u e s a r e u s u a l l y between 0 and -5 k c a l . / m o l e f o r n e u t r a l u n i -d e n d a t e l i g a n d s , but may be as l a r g e as -20 k c a l . / m o l e w i t h 7 9 n e u t r a l m u l t i - d e n d a t e l i g a n d s " . The p r e s e n t v a l u e s were w i t h i n the v a l u e s f o r t h e n e u t r a l l i g a n d s . The l a r g e n e g a t i v e v a l u e f o r the exchange o f one oxygen i o n w i t h s u l -p h i d e i o n and s u b s e q u e n t d e c r e a s e i n m a g n i t u d e as more 69 TABLE 2 E f f e c t of T e m p e r a t u r e on the C o n s e c u t i v e C o n s t a n t s T e m p e r a t u r e (°C.) AH K c a l . / mole AS 19 120 150 e.u. l o g k ± 5 . 20 5 . 81 3 . 63 2.36 - 1 1 . 9 10 . l o g k 2 4 . 08 4 . 74 3 . 36 3.18 " 5 ' 5 " 3'4 l o g k 3 3.30 3 . 51 2 .55 2 . 89 " 3'4 " 5 ' 5 l o g k 4 2.68 2 . 76 2 .73 2.41 - 0.8 Q " 9 - 9 k v a l u e s a t 19°C. were c a l c u l a t e d from t h e e x p e r i m e n t a l d a t a by T r i d o t and B e r n a r d , r e f . 39. k v a l u e s a t 120° and 150°C. were from the r e s u l t s of n u m e r i c a l method ( 1 ) . The e f f e c t i v e f i g u r e s of l o g k and AH,and AS would be two and one. oxygen i o n s were exchanged i n d i c a t e s c l e a r l y t h e f o r m a t i o n o f s t r o n g e r c o v a l e n t bonds by t h e exchange and s u b s e q u e n t d e c r e a s e i n e f f e c t as t h e exchange becomes s a t u r a t e d . T h i s t r e n d i s i n good agreement w i t h t h e o b s e r v a t i o n t h a t the f i r s t a b s o r p t i o n peaks moved to l o n g e r w a v e l e n g t h as the exchange a d v a n c e d . The f o r m a t i o n of c o v a l e n t bonds i s a t t r i b u -t e d to be the c a u s e o f t h e a p p e a r a n c e o f a b s o r p t i o n peaks 2-i n the v i s i b l e r a n g e when i o n s ClO^, CrO^ and MnO^ ,80 were compared The e n t r o p i e s o f exchange d e c r e a s e d as t h e exchange a d v a n c e d . I f t h e r e i s no c o n t r i b u t i o n f r o m the t h i o m o l y b d a t e s p e c i e s , t h e e n t r o p y o f exchange f o r each s t e p would be the d i f f e r e n c e of e n t r o p y between water and aqueous h y d r o g e n 80 s u l p h i d e , namely -12.5 e.u. . The e n t r o p y of exchange f o r the s t e p between t r i - and t e t r a - m o l y b d a t e a p p r o a c h e d • c l o s e to t h i s v a l u e and the d i f f e r e n c e i n c r e a s e d as the s t e p d e c r e a s e d . S i n c e the e n t r o p i e s o f t h i o m o l y b d a t e i o n s would be s i m i l a r , the d i f f e r e n c e was i n t e r p r e t e d as the d i f f e r e n c e i n t h e e n t r o p i e s o f h y d r a t i o n . In o t h e r words the amount of w a t e r m o l e c u l e bound to the t h i o m o l y b d a t e i o n s d e c r e a s e d as t h e s u b s t i t u t i o n o f s u l p h i d e i o n a d v a n c e d . 8 2 T h i s i s u n d e r s t a n d a b l e s i n c e t h e " i c e b e r g " a r ound the i o n s would become s m a l l e r as the c o v a l e n t n a t u r e of t h e moly- . b d e n u m - l i g a n d bonds i n c r e a s e s , r e l e a s i n g more w a t e r m o l e c u l e s . 71 In c o n c l u s i o n 1. The e x p e r i m e n t s a t 150°C. showed the e x i s t e n c e 2-of the s p e c i e s of t h e f o r m MoO._ S and the s t a b i l i t y f ™ X X c o n s t a n t s o f mono-, d i - , t r i - , and t e t r a - t h i o m o l y b d a t e were 0.23 x 1 0 3 M." 1, 0.35.x 1 0 6 M.~ 2, 0.27 x 1 0 9 M." 3, and 12 -4 0.070 x 10 M. , r e s p e c t i v e l y . 2. T h e r e were s t r o n g i n d i c a t i o n s o f t h e f o r m a t i o n of p r o t o n a t e d s p e c i e s , M o ( S H ) 6 > as the pH o f the s o l u t i o n d e c r e a s e d . T h i s s p e c i e s may be the c o l l o i d a l f o r m o f moly-bdenum t r i s u l p h i d e . 3. M o l a r e x t i n c t i o n c o e f f i c i e n t s a t 315 my o f t e t r a - and d i - t h i o m o l y b d a t e were e s t i m a t e d to be 2.01 and 0.95 x 10 4 MT1 cmT1 > r e s p e c t i v e l y . 4. A c a l c u l a t i o n o f thermodynamic p a r a m e t e r s i n d i c a t e d the c o m p e n s a t i n g e f f e c t o f e n t h a l p y and e n t r o p y f o r the s t e p - w i s e s u b s t i t u t i o n o f o x i d e i o n by s u l p h i d e i o n . PART 2: STUDY OF REDUCTION IN THE Mo-S-H^O SYSTEM Hydrogen and c a r b o n monoxide were c h o s e n as r e d u c -i n g gases b e c a u s e o f t h e i r r e a d y a v a i l a b i l i t y f o r any i n d u s t r i a l p r o c e s s t h a t m ight be d e v e l o p e d . Some s t u d i e s were made o f s t a b i l i t y i n the s y s t e m a t h i g h t e m p e r a t u r e s under an i n e r t a t m o s p h e r e ( N 2 ) b e c a u s e some d e c r e a s e o f molybdenum i n s o l u t i o n was n o t e d under t h i s l a t t e r c o n d i t i o n . S i n c e r e d u c t i o n p r o c e s s e s w i t h h y d r o g e n and c a r b o n monoxide a p p e a r to d i f f e r , the r e a c t i o n s under the t h r e e g a s e s , N 2 , H 2 and CO w i l l be d i s c u s s e d s e p a r a t e l y . P r o d u c t s o f any r e a c t i o n and the k i n e t i c s of the r e a c t i o n s were s t u d i e d i n each c a s e . 1. E x p e r i m e n t a l 1-1 A p p a r a t u s and p r o c e d u r e s A s e r i e s of e x p e r i m e n t s was p e r f o r m e d w i t h t h e same a p p a r a t u s and p r o c e d u r e s d e s c r i b e d i n P a r t 1. A f t e r the t e m p e r a t u r e was e q u i l i b r a t e d , a sample was w i t h d r a w n f r o m the a u t o c l a v e . A g i t a t i o n was s t o p p e d and r e d u c i n g gas was i n t r o d u c e d to the d e s i r e d p a r t i a l p r e s s u r e . A g i t a t i o n was resumed and time was measured f r o m t h e n on. The r e a c t i o n was f o l l o w e d by w i t h d r a w i n g samples at c e r t a i n time inter-?-v a l s . The t o t a l p r e s s u r e i n the a u t o c l a v e was m a i n t a i n e d , c o n s t a n t by a d m i t t i n g more gases m a n u a l l y . In the c a s e o f two s t a g e r u n s , t h e end o f t h e f i r s t s t a g e was n o t e d by t h e d i s a p p e a r e n c e of an o r a n g e - ., 73 y e l l o w c o l o r f r o m the s o l u t i o n . A g i t a t i o n was s t o p p e d and molybdenum s o l u t i o n was i n j e c t e d w i t h the i n j e c t i o n s y s t e m . A sample was w i t h d r a w n i m m e d i a t e l y and a g i t a t i o n was resumed to c o n t i n u e the r e a c t i o n . At t h e end o f the r u n the a u t o -c l a v e was quenched i n c o l d w a t e r . A s e r i e s o f b a t c h e x p e r i m e n t s u s i n g h y d r o g e n as the r e d u c i n g gas was p e r f o r m e d i n a s t a i n l e s s s t e e l s h a k i n g 84 a u t o c l a v e d e s c r i b e d by McAndrew . E x p e r i m e n t a l s o l u t i o n s were p r e p a r e d a t room t e m p e r a t u r e f r o m s t o c k s o l u t i o n s . In some c a s e s sodium s u l p h i d e a nd/or ammonium s u l p h a t e was added i n c r y s t a l l i n e f o r m . A c o n s t a n t volume o f t h e e x p e r -i m e n t a l s o l u t i o n was c h a r g e d , t h e n the s y s t e m was s e a l e d , f l u s h e d w i t h n i t r o g e n g as, h e a t e d and e q u i l i b r a t e d to the d e s i r e d t e m p e r a t u r e w h i l e s h a k i n g . A g i t a t i o n was t h e n s t o p p e d t e m p o r a r i l y and h y d r o g e n gas was i n t r o d u c e d . The r e a c t i o n was i n i t i a t e d by r e s u m i n g the s h a k i n g and the p r e s s u r e change o f t h e whole s y s t e m was f o l l o w e d by the r e a d i n g of a h e l i c o i d gauge (0 - 1500 p s i . , 10 p s i . / d i v . , f i l l e d w i t h s i l i c o n e o i l to m i n i m i z e the dead v o l u m e ) . At the end o f each r u n when t h e p r e s s u r e drop c e a s e d , c a l i -b r a t i o n was p e r f o r m e d by i n t r o d u c i n g more h y d r o g e n from a b o t t l e o f a known volume and m e a s u r i n g t h e p r e s s u r e v a r i a t i o n s o f the s y s t e m and t h e b o t t l e . A f t e r c a l i b r a t i o n the a u t o c l a v e was quenched by a p p l y i n g a w a t e r c o o l i n g c o i l a r o u n d i t s head. Q u e n c h i n g the r e a c t i o n i n t h e m i d d l e o f t h e r u n was p e r f o r m e d by the same c o o l i n g method. The t e m p e r a t u r e d r o p p e d from 160°C. to 120°C. i n l e s s t h a n 5 m i n u t e s . A f t e r t h e s y s t e m was c o o l e d to room t e m p e r a t u r e , the s l u r r y was f i l t e r e d and the p r e c i p i t a t e was washed t h o r o u g h l y w i t h w a t e r , d r i e d o v e r n i g h t a t room t e m p e r a t u r e i n a vacuum d r y e r , and s t o r e d i n a b o t t l e i n a d e s i c c a t o r f o r a n a l y s i s . As the p r e c i p i t a t e s were f o u n d to c a t a l y z e the r e d u c t i o n r e a c t i o n , the s u r f a c e s o f t h e a u t o c l a v e s were c l e a n e d each time by b o i l i n g w i t h a d i l u t e n i t r i c a c i d s o l u -t i o n or a d i l u t e sodium h y d r o x i d e - h y d r o g e n p e r o x i d e s o l u t i o n . By t h e p r o c e d u r e employed the t h e r m a l h i s t o r y o f the s o l u t i o n s b e f o r e s t a r t i n g t h e r e d u c t i o n r e a c t i o n was a p p r o x i m a t e l y the same. 1-2 A n a l y t i c a l p r o c e d u r e 1-2-a A n a l y s i s o f the s o l u t i o n The a n a l y s i s o f sample s o l u t i o n s t a k e n d u r i n g the r u n was p e r f o r m e d by the same p r o c e d u r e d e s c r i b e d i n P a r t 1, e x c e p t f o r s u l p h i d e , where i n some c a s e s the f o l l o w i n g method was employed:-A s u i t a b l e a l i q u o t o f t h e sample s o l u t i o n was t a k e n i n t o a b e a k e r c o n t a i n i n g 10 ml. o f 1 N.NaOH. Then 25 ml. o f 0.05 N.NaCIO s o l u t i o n , and 100 ml. o f d i s t i l l e d w a t e r was added, f o l l o w e d by 10 ml. o f 2 N.I^SO^ to make the pH of the s o l u t i o n a p p r o x i m a t e l y 2. The s o l u t i o n was s w i r l e d a r o u n d and l g . o f K l c r y s t a l s was added. The r e s u l t i n g I„ -, was t i t r a t e d by 0.05 N.Na2S20 3 s o l u t i o n , s t a n d a r d i z e d i m m e d i a t e l y b e f o r e use a g a i n s t KIO^ s t a n d a r d s o l u t i o n . The s u l p h u r c o n t e n t was c a l c u l a t e d f r o m t h e d i f f e r e n c e from t h e r e a g e n t b l a n k a s s u m i n g t h a t s u l p h u r was o x i d i z e d f r o m -2 to +6 v a l e n c e s t a t e . In some c a s e s t h e s p e c t r o g r a m was t a k e n w i t h a q u a r t z c e l l o f 1cm. l i g h t p a t h and samples were d i l u t e d so t h a t t h e y c o u l d be accommodated on the s c a l e . A l t h o u g h t h e s p e c t r o g r a m o f the Mo-S-R^O m i x t u r e made up a t room t e m p e r a t u r e changed r a p i d l y w i t h time and d i l u t i o n , the s p e c t r o g r a m o f the s o l u t i o n s f r o m the r e d u c t i o n e x p e r i m e n t d i d not show a p p r e c i a b l e change w i t h t i m e and d i l u t i o n . 1-2-b • A n a l y s i s of the p r e c i p i t a t e s S e v e r a l methods were employed f o r the a n a l y s i s o f p r e c i p i t a t e s , namely, a) C h e m i c a l a n a l y s i s f o r Mo, S, NH^, and Na. b) T h e r m o g r a v i m e t r i c a n a l y s i s i n b o t h Ar and a i r . c) D i f f e r e n t i a l t h e r m a l a n a l y s i s i n b o t h Ar and a i r . d) X - r a y d i f f r a c t i o n . e) O p t i c a l and e l e c t r o n m i c r o s c o p y . f ) I n f r a r e d s p e c t r o s c o p y . g) M a g n e t i c s u s c e p t i b i l i t y measurements. h) O t h e r s . a) C h e m i c a l a n a l y s i s Molybdenum: A weighed amount o f sample was o x i d i z e d w i t h KBr - B r 0 s o l u t i o n and HN0„ and t h e n h e a t e d to d r y n e s a f t e r c o n c e n t r a t e d H C l a d d i t i o n . The r e s i d u e was d i s s o l v e d i n w a t e r and t h e r e s u l t i n g s o l u t i o n was n e u t r a l i z e d t o p h e n o l p h t h a l e i n w i t h NaOH and t h e n a c i d i f i e d w i t h H C l t o 5% by v o l u m e . The s o l u t i o n was c o o l e d t o 5~10°C., a s u i t -a b l e amount o f 2% a - b e n z o i n o x i m e s o l u t i o n was a d d e d , and t h e r e s u l t i n g Mo- a - b e n z o i n o x i m e p r e c i p i t a t e was f i l t e r e d , w ashed ( f i l t r a t e and w a s h i n g s were k e p t f o r S a n a l y s i s ) d r i e d , and i g n i t e d a t 525°C. i n a w e i g h e d p o r c e l a i n c r u c i b l e . The i n c r e a s e i n w e i g h t o f t h e p o r c e l a i n c r u c i b l e was t a k e n as MoO^ and t h e amount o f Mo i n t h e s a m p l e was c a l c u l a t e d . S u l p h u r : The f i l t r a t e and w a s h i n g s f r o m t h e Mo a n a l y s i s were n e u t r a l i z e d w i t h NaOH t o make 0.1 N.HC1, h e a t e d t o n e a r b o i l i n g , 10% B a C ^ s o l u t i o n a d d e d , a n d . t h e BaSO^ p r e c i p i t a t e s f i l t e r e d h o t a f t e r a g i n g o v e r n i g h t . The p r e c i p i t a t e was w a s h e d , d r i e d , and i g n i t e d i n a m u f f l e f u r n a c e a t 800°C., c o o l e d and w e i g h e d ; and t h e s u l p h u r amount was c a l c u l a t e d a f t e r s u b t r a c t i n g t h e b l a n k . N i t r o g e n : A m e a s u r e d amount (=:20mg.) o f s a m p l e was p l a c e d i n a m i c r o - K j e l d a h l f l a s k and d i g e s t e d w i t h h o t c o n c e n t r a t e d H 2 S 0 4 > A f t e r c o m p l e t e d i s s o l u t i o n , t h e s o l u * -t i o n was c o o l e d , d i l u t e d w i t h w a t e r , and c h a r g e d i n t o a K i r k ' s m i c r o - d i s t i l l a t i o n a p p a r a t u s and t h e ammonia d i s t i l l e d i n t o 0.01 N.HC1 s o l u t i o n a f t e r a d d i n g c o n c e n t r a t e d NaOH. The H C l r e m a i n i n g was t i t r a t e d w i t h s t a n d a r d 0.01 N.NaOH... t o pH = 5.2 u s i n g Beckman z e r o m a t i c p H - m e t e r . The d i f f e r -e nce i n H C l c o n s u m p t i o n f r o m t h e r e a g e n t b l a n k gave t h e NH^ 77 amount, hence the N% o f t h e sample. Sodium; Sodium was d e t e r m i n e d f l a m e - p h o t o -m e t r i c a l l y a f t e r d i s s o l v i n g the sample w i t h h o t HNO^. i Oxygen: Oxygen a n a l y s i s was p e r f o r m e d by G u l f G e n e r a l A t o m i c I n c . (San D i e g o , C a l i f o r n i a , U.S.A.). A c c o r d -i n g to t h e i r d e s c r i p t i o n of t h e p r o c e d u r e , a sample i n a p o l y e t h y l e n e b o t t l e , p r e p a r e d and s e a l e d by t h e c u s t o m e r , was i r r a d i a t e d w i t h n e u t r o n s and the i n t e n s i t y o f the 6.13 Mev. gamma-ray p h o t o p e a k o f N"^ , w h i c h was formed by the 16 16 i n t e r a c t i o n w i t h n e u t r o n s v i a t h e 0 (n,p) N r e a c t i o n , was compared a g a i n s t t h e s t a n d a r d . F o r a s e r i e s o f e x p e r i m e n t s under h y d r o g e n atmos-p h e r e u s i n g the s h a k i n g a u t o c l a v e , where the t o t a l amount of p r e c i p i t a t e was s m a l l and s t a y e d m o s t l y on t h e a u t o c l a v e w a l l s , NaOH-H202 s o l u t i o n was added a f t e r t h o r o u g h w a s h i n g w i t h w a t e r to remove f r e e s u l p h a t e , to d i s s o l v e the p r e -c i p i t a t e s . A n a l y s i s o f molybdenum and s u l p h u r was p e r f o r m e d on the l e a c h e d s o l u t i o n s . F o r the c h e m i c a l a n a l y s i s o f the p r e c i p i t a t e s d u r i n g the r u n , sample w e i g h t was d e t e r m i n e d i n d i r e c t l y as f o l l o w s : The p r e c i p i t a t e on the f r i t t e d g l a s s f u n n e l was washed w i t h d i s t i l l e d w a t e r (~50ml.). The p r e c i p i t a t e and t h e f u n n e l were l e f t i n the a t m o sphere u n t i l d r y and the o v e r a l l w e i g h t was measured. The p r e c i p i t a t e on t h e f u n n e l was y d i s s o l v e d w i t h K B r - B ^ s o l u t i o n and HNO^, and washed, f i l t r a t e and w a s h i n g s b e i n g s e t a s i d e f o r Mo and S a n a l y s i s . The f u n n e l was d r i e d as b e f o r e and w e i g h t was measured. The d i f f e r e n c e f r o m t h e v a l u e b e f o r e t r e a t m e n t was t a k e n as sample w e i g h t . I n some i n s t a n c e s a n o r m a l f i l t e r p a p e r was used to c o l l e c t t h e p r e c i p i t a t e . S u b s e q u e n t t r e a t m e n t was the same but a c c u r a c y was much l o w e r i n t h e s e c a s e s . Molybdenum was d e t e r m i n e d s p e c t r o p h o t o m e t r i c a l l y as d e s -c r i b e d i n t h e a n a l y s i s of the sample s o l u t i o n , and s u l p h u r 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 as BaSO^. b) T h e r m o g r a v i m e t r y A sample was mounted i n a q u a r t z v e s s e l , hung f r o m one arm o f a c h e m i c a l b a l a n c e w i t h a t h i n q u a r t z f i b r e i n a V y c o r (30 mm. I.D.) f u r n a c e tube a t t h e c e n t r e of a v e r t i c a l e l e c t r i c f u r n a c e . The w e i g h t change o f the sample was r e c o r d e d on a c h a r t a g a i n s t t i m e t h r o u g h a p h o t o m e t r i c z e r o - b a l a n c i n g mechanism. C o n s t a n t a r g o n gas f l o w , d r i e d and d e o x y g e n a t e d by p a s s i n g t h r o u g h a h e a t e d (. (500°C.) tube c o n t a i n i n g c o p p e r t u r n i n g s , was p a s s e d f o r a t l e a s t one hour b e f o r e the h e a t i n g s t a r t e d . The t e m p e r a t u r e o f the f u r n a c e was r a i s e d l i n e a r l y (~6°C./min.) and the t e m p e r a t u r e of the sample was c a l c u l a t e d f r o m the e.m.f. r e a d i n g of a C h r o m e l - A l u m e l t h e r m o c o u p l e i n a q u a r t z thermo-c o u p l e t u b e , the t i p of w h i c h was e x a c t l y c e n t e r e d i n the: V y c o r tube and 2~4 mm. from t h e b o t t o m o f the q u a r t z v e s s e l . The w e i g h t change r e c o r d i n g was on -80 mg. f u l l s c a l e , w i t h ±2~3 mg. v i b r a t i o n due to a z e r o - b a l a n c i n g t i m e l a g . The b a l a n c e was c a l i b r a t e d e ach t i m e by p l a c i n g known w e i g h t s on the o t h e r s i d e o f the arm o f the c h e m i c a l b a l a n c e . A f t e r t h e r u n the sample was c o o l e d to room temper-a t u r e i n Ar f l o w . The s u b s e q u e n t r u n i n a i r was p e r f o r m e d w i t h the same p r o c e d u r e e x c e p t by p a s s i n g a c o n s t a n t f l o w of d r y a i r . c) D.T.A. D i f f e r e n t i a l t h e r m a l a n a l y s i s o f the p r e c i p i t a t e s was p e r f o r m e d w i t h a p p a r a t u s made i n t h i s d e p a r t m e n t . The sample was d i l u t e d w i t h A ^ O ^ powder and compared a g a i n s t Al^O^ i n a r e f e r e n c e c e l l . In the c a s e o f the r u n under a r g o n a t m o s p h e r e a P t - P t 10% Rh t h e r m o c o u p l e was used i n p l a c e o f t h e A l u m e l - C h r o m e l t h e r m o c o u p l e w h i c h was f o u n d c o r r o d e d by the gas e v o l v e d . (The f u r n a c e t e m p e r a t u r e was r a i s e d a p p r o x i m a t e l y l i n e a r l y a t 11.6 0C./min.) A r g o n gas, d e o x y g e n a t e d by p a s s i n g t h r o u g h h e a t e d c o p p e r t u r n i n g s , was p a s s e d t h r o u g h the s y s t e m a t l e a s t one hour b e f o r e h e a t -i n g was s t a r t e d . A f t e r t h e r u n t h e f u r n a c e was c o o l e d t o room t e m p e r a t u r e i n t h e a r g o n atmosphere and a s u b s e q u e n t t e s t i n a i r was p e r f o r m e d by a l l o w i n g f r e e a c c e s s of a i r . d) X - r a y a n a l y s i s X - r a y d i f f r a c t i o n p a t t e r n was t a k e n w i t h a c o n v e n -t i o n a l X - r a y d i f f r a c t o m e t e r u s i n g a c o p p e r Ka r a d i a t i o n w i t h a n i c k e l f i l t e r . The samples were mounted on s i l i c o n e 80 g r e a s e p a c k e d i n a window o f an a l u m i n u m s h e e t s a m p l e h o l d e r . 0 T h r e e s h a r p p e a k s a t 2.14, 1.85 and 1.56 A. were o b s e r v e d b u t t h e b l a n k r u n o f t h e s i l i c o n e g r e a s e showed t h e same p e a k s and t h u s t h e y were d i s c a r d e d f r o m c o n s i d e r a t i o n . e) M i c r o g r a p h s Q A Z e i s s m e t a l l u r g i c a l m i c r o s c o p e and a H i t a c h i e l e c t r o n m i c r o s c o p e were u s e d t o t a k e m i c r o g r a p h s o f p r e -c i p i t a t e s . S a m ples were f i r s t d i s p e r s e d i n w a t e r t a k i n g c a r e n o t t o g r i n d t o c a u s e a change i n p a r t i c l e s i z e and s h a p e . Then a p o r t i o n o f t h e s u s p e n s i o n was d r o p p e d on a m i c r o s c o p e g l a s s o r on a c a r b o n f i l m and d r i e d f o r i n s p e c t i o n w i t h an o p t i c a l o r e l e c t r o n m i c r o s c o p e , r e s p e c t i v e l y . f ) I n f r a r e d s p e c t r o s c o p y I n f r a r e d s p e c t r o g r a m s were made u s i n g t h e KBr d i s c method w i t h a P e r k i n - E l m e r g r a t i n g I.R. s p e c t r o m e t e r 621. Samples were g r o u n d and m i x e d w i t h KBr c r y s t a l s i n a m o r t a r u n d e r a t m o s p h e r i c c o n d i t i o n s . g) M a g n e t i c s u s c e p t i b i l i t y M a g n e t i c s u s c e p t i b i l i t y was m e a s u r e d w i t h a Gouy b a l a n c e i n t h e C h e m i s t r y D e p a r t m e n t . S a mples were p l a c e d i n a s m a l l P y r e x g l a s s t u b e h a n g i n g on t h e arm o f t h e a u t o -m a t i c b a l a n c e . The w e i g h t change b e f o r e and a f t e r a p p l i -c a t i o n o f t h e m a g n e t i c f i e l d was m e a s u r e d and m a g n e t i c s u s c e p t i b i l i t y was c a l c u l a t e d a f t e r s u b t r a c t i o n o f the b l a n k r e a d i n g . C a l i b r a t i o n was made w i t h m e r c u r y ( I I ) t e t r a -t h i o c y a n a t e c o b a l t a t e ( I I ) , Hg(Co(NCS)^) , w h i c h was s u p p l i e d by Mr. B. C a l i f o r d o f t h e C h e m i s t r y D e p a r t m e n t . h) O t h e r me t h o d s O t h e r methods employed were d i g e s t i o n o f the samples i n v a r i o u s media and w i l l be d i s c u s s e d e l s e w h e r e i n t h e t e x t . 2. P r e c i p i t a t i o n i n an I n e r t Atmosphere D u r i n g t h e e x p e r i m e n t s i n P a r t 1, a s m a l l b u t s i g n i f -i c a n t d e c r e a s e o f the t o t a l molybdenum c o n c e n t r a t i o n i n t h e s o l u t i o n was n o t e d i n the s e r i e s where the t o t a l c o n -c e n t r a t i o n o f s u l p h i d e i o n was i n c r e a s e d . [See A p p e n d i x A - l - 1 , S e r i e s A, No. 8.] The d e c r e a s e s l o w e d down a t t h e h i g h c o n c e n t r a t i o n s o f s u l p h i d e i n d i c a t i n g some e q u i l i b r i a be-tween the s o l u t i o n and the p r e c i p i t a t e . The e q u i l i b r a t i o n i s c l e a r l y d e m o n s t r a t e d i n F i g u r e 13 w h i c h was t h e r e s u l t o f a b a t c h r u n under a n i t r o g e n a t m o s p h e r e . F i g u r e B-3 i n A p p e n d i x B shows the change i n t h e s p e c t r o g r a m c o r r e s p o n d i n g t o t h i s r u n . A r e g u l a r d e c r e a s e i n t r a n s m i s s i o n w i t h time i s c l e a r l y s e e n . The b r o k e n l i n e shows the s p e c t r o g r a m o f the i n i t i a l s o l u t i o n m i x t u r e a t room t e m p e r a t u r e , i n d i c a t i n g t h e d i f f e r e n c e i n the e x t e n t of c o m p l e x i n g from the s o l u t i o n s a t h i g h t e m p e r a t u r e . I 1 —I 1 1 —I I I I 0 2 0 r 4 0 6 0 8 0 100 120 140 160 TIME min. Fig.13 VARIATION OF CONCENTRATION UNDER N 2 158 8°C A p p a r e n t l y a good l i n e a r i t y i s o b t a i n e d when l o g [X-Xe] i s ' p'l'o'tted a g a i n s t time as shown i n F i g u r e 14, where X and Xe a r e i n s t a n t a n e o u s and e q u i l i b r i u m c o n c e n t r a t i o n s , Xe's were assumed. T a b l e A-2 i n A p p e n d i x A l i s t s the b e s t f i t v a l u e s " o f k and Xe c a l c u l a t e d by u s i n g the i n t e g r a t e d f o r m : X = Xe + a x e k x t . . . . (17) ,' \' ) When the c a l c u l a t e d k was d i v i d e d by Xe, a number \ A • • ) x was f o u n d w h i c h was r o u g h l y c o n s t a n t , e x c e p t f o r [Mo]^, w h i c h showed c o n s t a n c y when k^.Q / [ M o ] [ S ] was c a l c u l a t e d , as shown i n T a b l e A-2 l i n e 13-16 i n t h e A p p e n d i x A. Thus the e m p i r i c a l r a t e e q u a t i o n was assumed t o be d [ M o ] T / d t => - k M j M o ] e [ S ] e ( [ M o ] - [ M o ] e ) . . . . (18) and d [ X ] / d t = - k y [ X ] ( [ X ] - [X] ) X ." S T ' C 4 ' °3 From the e m p i r i c a l e q u a t i o n (17) f o r s u l p h u r and molybdenum, t h e m o l a r r a t i o o f s u l p h u r and molybdenum i n t h e p r e c i p i t a t e was c a l c u l a t e d by e q u a t i o n (19) r s c a l c = ^ t S ] T / A [ M o ] T = ( [ S ] Q - [ S ] ) / ( [ M o ] Q - [Mo]) ( X - X e ) M*I03 0 4 0 80 120 160 T J M E min. Fig.14 FIRST ORDER PLOT = ( a s / a M o ) ( l - e _ k s t ) / ( l - e ^ o 1 ) . . . . (19) s u b s t i t u t i n g the v a l u e s o f t i m e , t , a t the end o f the e x p e r i m e n t s . The l a s t l i n e of T a b l e A-2 i n A p p e n d i x A shows t h e r e s u l t s . The agreement w i t h t h e o b s e r v e d v a l u e s was c o n s i d e r e d good. The e m p i r i c a l r a t e c o n s t a n t s f o r molybdenum and s u l p h u r were fo u n d to be a l m o s t the same. T h i s i m p l i e s t h a t t h e r e was a s t o i c h i o m e t r i c p r e c i p i t a t i o n , i . e . d [ S ] / d [ M o ] = ( d [ S ] / d t ) / ( d [ M o ] / d t ) = k s ( [ S ] - [ S ] e ) / k M o ( [ M o ] - [ M o ] e ) = ( [ S ] - [ S I )/([Mo] - [Mol ) e e I n t e g r a t i o n g i v e s f o r t h e i n s t a n t a n e o u s v a l u e s o f [S] and [Mo]; l o g ( [ S J - [ S J e ) = l o g ([Mo] - [ M o ] g ) + c o n s t a n t T h e r e f o r e [ S ] q - [S] = u ( [ M o ] o - [ M o ] ) , where u i s a c o n s t a n t . C h e m i c a l a n a l y s i s of the p r e c i p i t a t e s r e v e a l e d t h a t f a i r l y l a r g e amounts o f s u b s t a n c e s o t h e r t h a n moly-bdenum and s u l p h u r were p r e s e n t . The X - r a y a n a l y s i s showed b r o a d d i f f r a c t i o n between 26=30° and 6 0 ° , w h i c h was a l s o o b s e r v e d f o r t h e p r e c i p i t a t e s o f b o t h h y d r o g e n and c a r b o n a t m o s p h e r e s . T h e r m o g r a v i m e t r i c a n a l y s i s showed a r a p i d w e i g h t l o s s [-10%] a t a r o u n d 280° C. i n a r g o n and a n o t h e r 12% i n s u b s e q u e n t t e s t s i n t h e a i r at about 330° C. No molybdenum t h i o - o x y compound i s r e p o r t e d to have t h i s p r o p e r t y and t h u s the p r e c i p i t a t e i s most l i k e l y a m i x t u r e 89 of a s u l p h i d e and an oxy- or h y d r o x y - compound From the c o n c e n t r a t i o n s o f t e t r a - and t r i - t h i o m o l y -b d a t e i o n s c o u p l e d w i t h t h e o t h e r a n a l y t i c a l d a t a , the c o n -3 -1 s e c u t i v e c o n s t a n t k, was e s t i m a t e d to be 0.29,. x 10 M. 4 5 The c o n v e r s i o n f a c t o r m a t 158.8° C. i n t h e e q u a t i o n (12) was e s t i m a t e d as 4.9 w i t h the same method d e s c r i b e d i n P a r t 1, s e c t i o n 3-4-c. The agreement i n m a g n i t u d e w i t h the v a l u e a t 150° C. ( 0 . 2 6 2 x 1 0 3 M. - 1) was f a i r . The mechanism o f t h e p r e c i p i t a t i o n i n the i n e r t a t m o s phere may be the same as the a c i d d e c o m p o s i t i o n of t h i o m o l y b d a t e o b s e r v e d by v a r i o u s a u t h o r s (See I n t r o d u c t i o n L i t e r a t u r e s u r v e y - s e c t i o n 2 - 4 - f ) . However s i n c e t h e r e was a c o n c e n t r a t i o n o f aqueous s u l p h i d e i n t h e e q u a t i o n ( 1 8 ) , a s l o w r e d u c t i o n r e a c t i o n m ight be t a k i n g p l a c e consuming a p a r t o f d i v a l e n t s u l p h i d e . The c a l c u l a t i o n o f the v a l e n c y o f molybdenum i n the p r e c i p i t a t e s a s s u m i n g t h a t s u l p h u r was i n the h y d r o s u l p h i d e form and t h e l a r g e u n a c c o u n t e d r e s i d u a l s were h y d r o x i d e , i n d i c a t e d t h a t molybdenum was r e d u c e d s l i g h t l y . 87 3. P r e c i p i t a t i o n w i t h Hydrogen 3-1 R e d u c t i o n p r o d u c t s 3-1-a Aqueous phase The a b s o r p t i o n s p e c t r o g r a m s o f t h e s o l u t i o n s d u r i n g r e d u c t i o n were o b s e r v e d to be the same as t h o s e d e s c r i b e d i n P a r t 1 ( S t u d y of the e q u i l i b r i u m ) . No new a b s o r p t i o n peaks were e v i d e n t between 700 and 260 my as shown i n A p p e n d i x B, F i g u r e B5. The r e g i o n s 210-260 my and above 700 my were found a l s o the same as t h o s e o b s e r v e d i n t h e e q u i l i b r i u m s t u d y . T h e r e f o r e i t was c o n c l u d e d t h a t s o l u b l e complexes of molybdenum i n l o w e r o x i d a t i o n s t a t e t h a n 6 was n o t p r o -duced i n s u f f i c i e n t c o n c e n t r a t i o n to be d e t e c t e d and t h a t i f a r e d u c t i o n i n t e r m e d i a t e e x i s t e d i t must be s h o r t l i v e d . 3-1-b P r e c i p i t a t e s P r e c i p i t a t e s were f i n e b l a c k powders s i m i l a r i n a p p e a r e n c e to c a r b o n b l a c k . When t h e y were h e a t e d i n Ar a t m o s p h e r e , a w h i t e v o l a t i l e m a t e r i a l e v o l v e d . A t o t a l i d e n t i f i c a t i o n of t h i s v o l a t i l e m a t e r i a l , was n o t a t t e m p t e d but the q u a l i t a t i v e o b s e r v a t i o n s l i s t e d i n T a b l e 3 s u g g e s t t h a t i t was some compound o f s u l p h i d e and n i t r o g e n . O p t i c a l and e l e c t r o n m i c r o g r a p h s of p r e c i p i t a t e s showed t h a t : (a) P a r t i c l e shapes were v e r y i r r e g u l a r and a g g l o m e r -a t i o n seemed e x t e n s i v e . 83 T a b l e 3 P r o p e r t i e s o f the v o l a t i l e m a t e r i a l p r o d u c e d by h e a t i n g (a) P r o d u c e d i n Ar a t m o s p h e r e a t a r o u n d 150°C. S o l i d i f i e s a t room t e m p e r a t u r e and t r a p p e d c o m p l e t e l y i n a c o l d t r a p ( a r o u n d -10° C . ) . E v a p o r a t e s s l o w l y i n the a i r a t room t e m p e r a t u r e . (b) D i s s o l v e d e a s i l y i n 0.1 N HCl s o l u t i o n and the r e s u l t i n g s o l u t i o n r e d u c e d an ^ - s t a r c h s o l u t i o n , 2+ o x i d i z e d a Fe s o l u t i o n and r e a c t e d w i t h the N e s l e r r e a g e n t t o g i v e a s i m i l a r b u t s l i g h t l y d i f f e r e n t a b s o r p t i o n s p e c t r u m from t h a t g i v e n by ammonium. (c) C o r r o d e d an A l u m e l - C h r o m e l t h e r m o c o u p l e w i r e i n Ar atmosphere a t a r o u n d 300° C. The c o r r o s i o n d i d n o t o c c u r i n the a i r i n d i c a t i n g t h a t t h i s m a t e r i a l was n o t p r o d u c e d i n o x i d i z i n g a t m o s p h e r e . (b) T h e r e was no a p p a r e n t s i z e change o f p a r t i c l e s w i t h v a r i a t i o n of h y d r o g e n p r e s s u r e . ( c ) T h e r e was no a p p a r e n t change i n s i z e and shape of p a r t i c l e s , when t h e i n i t i a l c o n d i t i o n s were ( [ S ] / [ M o ] ) i > 2 and l a r g e ([NH^~ ] ) . (d) When ( [ S ] / [ M o ] ) ± < 2, and/or low [NH*], an i n c r e a s e i n the s i z e o f t h e f i n a l p r o d u c t s was o b s e r v e d as t h e ( [ S ] / [ M o ] ) ^ d e c r e a s e d . The s i z e o f p a r t i c l e s f r o m r u n s i n t e r r u p t e d h a l f w a y was f o u n d to be s m a l l e r t h a n the s i z e o f p a r t i c l e s f r o m the d u p l i c a t e r u n s w h i c h was a l l o w e d to go to c o m p l e t i o n , i n d i c a t i n g p a r t i c l e growth d u r i n g the r u n . X - r a y d i f f r a c t i o n p a t t e r n s o f the p r e c i p i t a t e s d i d not g i v e any s h a r p l y d e f i n e d p e a k s . T h e r e was a g e n e r a l i n c r e a s e o f r e f l e c t i o n between 26 = 30 and 60 d e g r e e s and, when the p r e c i p i t a t e s were h e a t e d i n A r , two d i s t i n c t peaks were n o t e d i n t h i s a r e a (d = 2.68 and 1.56 A ) . A l s o a b r o a d peak a t d = 6.4A was d e v e l o p e d ( F i g u r e 1 5 ) . These peaks r o u g h l y c o r r e s p o n d to t h o s e o f the r h o m b o h e d r a l m o d i f i c a t i o n of M0S2 r e p o r t e d by s e v e r a l a u t h o r s (See T a b l e 8 3 4 ) . ^ ° ^3 s y n t h e s i z e d by C h i y a ' s method d i d not g i v e any r e f l e c t i o n . The d i f f r a c t i o n p a t t e r n s o f (NH^^MoS^ were c o m p l e t e l y d i f f e r e n t . Some e l e c t r o n d i f f r a c t i o n p i c t u r e s of the p r e c i p i t a t e s showed a h e x a g o n a l symmetry, w h i c h i s 90 TABLE 4 X - r a y D i f f r a c t i o n D a t a f o r MoS„ and P r e c i p i t a t e s Rhombohedral P r e c i p i t a t e s by H y d r o t h e r m a l De- p p t s MoS 2 c o m p o s i t i o n o f T h i o m o l y b d a t e by H 2 (1) (2) (3) d A I h k i l d A I d A I d A I d A I 6 . 2 100 0003 6 . 1 10 6 . 0 10 6.0 5 6.4 w 3.05 3 0006 3 . 02 1 - — - - -2.72 19 1010 2 .77 9b 2 .72 9b 2 .71 10b 2 .68 b 2 . 64 14 - - - - - - - - -2 . 359 18 1014 2 . 345 4 - - - - , - -- - - - - 2 .254 5b - - - -2 . 205 20 1015 2 . 198 5 - - - - - -2 .051 11 0009 2 . 053 6 2 . 050 2 - - - -1.857 9 1017 1.874 4 - - - - - -- - - - - 1.824 4b - - - -1.766 5 1018 1.754 3 - - - - • - -1. 704 1 1019 - - - - - - - -1.586 15 1120 1.578 8 1.578 10 1.568 10b 1.56 b 1.524 18 000 ,12 1.528 8 1.529 8 - - - -1.429 1 O i l , 1 1 - - - - - - - -1. 360 2 2022 1. 353 1 1. 361 2 1.362 3 - -1.314 2 2022 - - 1.297 2 - - - -1. 253 5 1129 1. 246 5 1. 248 5 - - - . -1.228 3 000,15 - - - - - - - -1. 217 2 2027 - - - - - - - -- - 112,12 1. 094 7 1.097 8 - - -000,18 1.029 1 1.034 4 1.033 2 Rhombohedral MoS 2; A f t er B e l l and H e r f e r t , r e f . 71. H y d r o t h e r m a l d e c o m p o s i t i o n ; A f t e r A r u t y u n y a n and K h u r s h u d y a n , r e f . 68. C o n d i t i o n s : (1) 6 4 0 ° C , 20 h o u r s . (2) 550°C . , 3 h o u r s . (3) 380°C . , 4 h o u r s . P r e c i p i t a t e s by h y d r o g e n : 1 5 8 . 8 ° C , 500 p s i . , [Mo] = 0.01 M. , [S] = 0.05 M., [NH 3] = 1.0 M., [NH+] = 1.0 M., t i t a n i u m a u t o c l a v e . P r e c i p i t a t i o n c o m p l e t e d w i t h i n one h o u r . 1 . S I L I C O N E 2 . C O 3 . C O , H E A T E D 5 . H 2 , H E A T E D 6. No 40 30 2 © F i g . 1 5 X - R A Y D I F F R A C T I O N P A T T E R N S O F P R E C I P I T A T E S • 92 r e p o r t e d t o be the c h a r a c t e r i s t i c of the Mo-S n e t w o r k s e e n i n b o t h m o d i f i c a t i o n o f M 0 S 2 . T h e r e f o r e i t was s u g g e s t e d t h a t the s u l p h i d e form i n the p r e c i p i t a t e d p r o d u c t s i s a v e r y f i n e p a r t i c l e of t h e molybdenum d i s u l p h i d e . A p r e c i p i t a t e p r o d u c e d by h y d r o g e n r e d u c t i o n showed an a p p a r e n t weak p a r a m a g n e t i s m a m o u n t i n g to a p p r o x i m a t e l y 0.32 u n p a i r e d e l e c t r o n p e r mole o f molybdenum. The n a t u r a l d i s u l p h i d e i s r e p o r t e d t o have a v e r y weak d i a m a g n e t i s m , and MoO^ and MoO^ a weak p a r a m a g n e t i s m . The o b s e r v e d p a r a -magnetism d i s a p p e a r e d c o m p l e t e l y when the p r e c i p i t a t e s were h e a t e d i n Ar atmosphere a t 300°C. I n f r a r e d s p e c t r u m o f p r e c i p i t a t e s were compared w i t h M 0 S 2 and MoS^- The n a t u r a l M 0 S 2 d i d not show any s p e c i f i c a b s o r p t i o n band. I t s a b s o r p t i o n d e c r e a s e d g r a d -u a l l y as the f r e q u e n c y d e c r e a s e d u n t i l i t was a l m o s t t r a n s -p a r e n t a t around 650 cm. 1 . MoS^ s y n t h e s i z e d by decompo-8 3 s i t i o n o f (NH^^MoS^ s o l u t i o n w i t h a c i d gave weak a b s o r p t i o n a r o u n d 1650, 1425, 1125, 950, and 900 cm." 1. The p r e c i p i t a t e s under h y d r o g e n atmosphere gave t h e f o l l o w i n g a b s o r p t i o n s : 6 2 0 ( s h ) , 8 8 0 - 9 3 5 ( s ) , 1 0 2 0 ( s h ) , 1 1 1 5 - 1 1 9 0 ( b ) , 1 3 9 5 ( s , s h ) , 1 6 0 0 ( b ) , and 3 4 5 0 ( b ) , where s, s h , b means s t r o n g , s h a r p , and b r o a d r e s p e c t i v e l y . They d i s a p p e a r e d c o m p l e t e l y when the sample was h e a t e d i n Ar a t m o s p h e r e . T h e r e f o r e the peaks o b s e r v e d were c o n s i d e r e d to be due to the v o l a t i l e m a t e r i a l . F i g u r e 16 shows t h e r e s u l t s of the t h e r m o g r a v i m e t r i c a n a l y s i s o f p r e c i p i t a t e s from a s e r i e s o f e x p e r i m e n t s where I I I I I I 0 100 200 300 4 0 0 5 0 0 Temperature °C. Fig. 16 TGA OF PRECIPITATES, WEIGHT LOSS vs. TEMPERATURE. CONDITIONS OF PRECIPITATION ; I58.8°C, 600psi., NH3=0.8M., NH4 = I.OM., Mo =0.1 M., S = varies (( S/Mo * I) 0.66,2) 0.97 3) 1.30 , 4) 2.01 , 5) 2.84 , 6) 5.77, Initially )) the i n i t i a l c o n c e n t r a t i o n o f s u l p h i d e i o n was v a r i e d . The w e i g h t l o s s i n Ar atmosphere v a r i e d i n p o s i t i o n and m a g n i t u d e s t a r t i n g a t a r o u n d 150°C. and e n d i n g a t ar o u n d 350°C. The samples w h i c h had been h e a t e d i n Ar atmosphere showed a w e i g h t g a i n at 350°C. ( f o r low ( [ S j / l M o ] ^ c a s e s ) and a w e i g h t l o s s a t around 4 50°C. when t h e y were r e - h e a t e d i n a i r . F i g u r e 17 shows t h e r e s u l t s of the d i f f e r e n t i a l t h e r m a l a n a l y s i s of p r e c i p i t a t e s . The n a t u r a l M 0 S 2 gave peaks a t h i g h e r t e m p e r a t u r e t h a n s y n t h e t i c MoS^ and the p r e -c i p i t a t e s p r o d u c e d i n t h e s e e x p e r i m e n t s . The peaks o b s e r v e d f o r MoS^ and t h e p r e c i p i t a t e s were s i m i l a r , but the d i f f e r -ence i n t h e r a t i o of peaks a t around 350°C. and 5 0 0 ° C . i n -d i c a t e s some d i f f e r e n c e i n n a t u r e i s i n v o l v e d . When the D.T.A. was p e r f o r m e d i n Ar atmosphere t h e r e was no peak o b s e r v e d , and when the e x p e r i m e n t was r e p e a t e d i n a i r s u c c e s s i v e l y t h e peak at 350°C. d i s a p p e a r e d . T h e r e f o r e the d e c o m p o s i t i o n r e a c t i o n i n Ar to p r o d u c e v o l a t i l e m a t e r i a l a p p a r e n t l y t o o k p l a c e a t a c o m p a r a t i v e l y low t e m p e r a t u r e . C h e m i c a l a n a l y s i s o f p r e c i p i t a t e s r e v e a l e d t h a t t h e c o m p o s i t i o n v a r i e d d e p e n d i n g on the c o m p o s i t i o n o f the j e x p e r i m e n t a l s o l u t i o n s f r o m w h i c h t h o s e p r e c i p i t a t e s were o b t a i n e d . T a b l e s 5a, 5b show some of the r e s u l t s o f a n a l y s i s , i n w h i c h r e s u l t s o f a n a l y s i s o f the p r e c i p i t a t e s f r o m n i t r o g e n and c a r b o n monoxide atmosphere were i n c l u d e d . In a l l c a s e s t h e r e was a l a r g e r e s i d u a l when the molybdenum and s u l p h u r amount was s u b t r a c t e d . A n a l y s i s f o r n i t r o g e n and sodium i n d i c a t e d t h a t t h e s e were o n l y m i n o r . c o n s t i t u e n t s . J I I _J I 100 200 3 0 0 400 500 600 Temperature °C. 1.17 DTA OF PRECIPITATES FRQM H 2 RUNS Curve I. natural molybdenite, in air 2. synthetic molybdenum tri sulphide, in air 3. precipitate under hydrogen, in air 4. H , in Ar 5. II , in air after Ar 96 TABLE 5a C o m p o s i t i o n s o f P r e c i p i t a t e s No . Gas C o m p o s i t i o n s M a i n O t h e r Mo% S% X% ; V a r i a b l e s C o n d i t i o n s 46 N 2 44.9 39 .8 15 .3 - (Mo T = 0.020M., S T = 0.056M., NH„ = NH. + = 3 _ 4 l.OM., 1 5 8 . 8 ° C . ) 40 H 2 48 . 0 32 . 7 19 . 3 P = 5 0 0 p s i . (Mo T = 0.020M., S„ = 42 44 H H 2 47 . 7 47 . 2 34.4 36.8 17 16 . 9 . 0 300 100 T T 0.056M., NH = NH. = 3 4 l.OM., 1 5 8 . 8 ° C . , ) 86 H 2 47.4 33 . 3 19 . 3 S T = 0.195M. (Mo _ = 0.1M. , NH„ = 85 83 H H 2 50.2 53.9 20 . 8 14.4 29 31 . 0 . 7 1 0 . 096 0 . 065 T 3 0.9M., NH 4 = 1.OM., 158. 8 ° C . , P u = ' 6 0 0 p s i . H 2 106 H 49.8 32.5 17 . 7 = 0.98M. (Mo T = 0.1M. , S T ' = 108 H 2 53 . 4 29 . 4 17 . 2 0 . 39 l 1 0.2M., no NH 3, 1 5 1 . 6 ° C . P u = 8 8 0 p s i . ) H 2 61 CO 33 . 4 22 . 2 44 . 4 Mo T = 0.001M. ( S T = 0 . 023M. , 15 1 . 6 ° C . , P c o = 7 0 0 p s i . , N H 3 = N H 4 + = l.OM.);. 23 CO 49 . 0 30 . 7 20 . 3 S T = 0.011M. (Mo T = 0.020M., P C Q = 5 0 0 p s i . , NH 3 = N H 4 + = l.OM.) 25 26 CO CO 48.6 44.7 33.6 33 . 7 17 21 .8 .5 1 0 .033 0.089 X% = 100 - Mo% - S%. 97 TABLE 5b D e t a i l e d A n a l y s i s of a P r e c i p i t a t e C o n d i t i o n s of p r e c i p i t a t i o n s : Run 64. Mo T = 0.010M., S T = 0.049M., NH 3 = NHt = 1. OM. , P H = 500 p s i . , t w o - s t a g e r u n i n t i t a n i u m a u t o c l a v e , no c a t a l y s t a d d i t i o n as p r e c i p i t a t e d 3 a f t e r h e a t i n g * 3 Mo 47.1% 59.0% S 32.7 32.8 N 2.5 0.3 Na 0.0 0.0 d i f f e r e n c e 17.7 7.9 100.0 100.0 e q u i v a l e n t / m o l e Mo 15.0 15.6 %Mo d i s s o l v e d ^ by 0.2M NH C l 18.5 n.d, by (1 + 1) H C l 33.7 n.d, by w a t e r 19.3 n.d, by 2 N NaOH 83. n.d, a - washed w i t h w a t e r and vacuum d r i e d , b - 3 0 0 ° C , 2 h o u r s i n A r . c - r e d u c i n g e q u i v a l e n t w i t h NaClO. d - 60°C., 1 hour i n A r . TABLE 6 A n a l y s i s of Oxygen i n the P r e c i p i t a t e s Sample No. Mo S X 0 64 47.1 32 . 7 20 . 2 28.1 64d 59 . 0 32.8 8 . 2 12 . 6 102 50.1 32 . 3 17 . 6 20.0 105 5 8.3 17 .6 24.1 23.2 106 49.8 32.5 17 . 7 22 . 8 108 53.4 29.4 17 . 2 24.9 C o n t e n t i n %, X = 100 - Mo - S , Mo and S a r e by the a u t h o r and 0 by G.G.A. The r e s u l t s o f t h e oxygen a n a l y s i s w i t h t h e n e u t r o n a c t i v a t i o n method p e r f o r m e d by G u l f G e n e r a l A t o m i c , C a l i f -o r n i a , U.S.A., were compared w i t h t h e r e s i d u a l s t a t e d above i n T a b l e 6. A l t h o u g h a c t i v a t i o n a n a l y s i s r e s u l t s and c h e m i c a l a n a l y s i s r e s u l t s (by t h e d i f f e r e n c e f r o m 100%) d i d ; not a g r e e e x a c t l y and the f o r m e r gave h i g h e r v a l u e s i n g e n e r a l , the t r e n d a g r e e d . T h e r e f o r e i t was c o n c l u d e d t h a t t h e r e s i d u a l s were p r e d o m i n a n t l y oxygen. The r a t i o of molybdenum to s u l p h u r i n t h e p r e c i p i -t a t e s depended p r i m a r i l y on t h e r a t i o of molybdenum and s u l p h i d e c o n c e n t r a t i o n i n the i n i t i a l s o l u t i o n s . F i g u r e 18 shows the p l o t of the r a t i o o f molybdenum to s u l p h u r i n the p r e c i p i t a t e , r c = (S/Mo) , a g a i n s t t h e r a t i o o f the c o n -b pp t c e n t r a t i o n s of molybdenum and s u l p h i d e i n the i n i t i a l s o l u t i o n , ( [ S ] / [ M o ] ) _ ^ , when the s o l u t i o n was w e l l b u f f e r e d . C l e a r l y r c = ( [ S ] / [ M o ] ) . ( d o t t e d l i n e ) when ( [ S ] / [ M o ] ) . i s b x x s m a l l e r t h a n 2 and when l a r g e r t h a n 2, rg a p p r o a c h e s some l i m i t i n g v a l u e . V a r i a t i o n of the pH o f the s o l u t i o n by v a r y i n g t h e amount o f (NH.)-SO. a d d i t i o n to t h e m i x t u r e of Na„MoO. and 4 2 4 2 4 Na 2S s o l u t i o n y i e l d e d a v a r i a t i o n of r g . At low l e v e l p f (NH^^SO^ a d d i t i o n the p r e c i p i t a t i o n was n o t c o m p l e t e b ut above the e q u i v a l e n t amount o f (NH^^SO^ t o n e u t r a l i z e s u l p h i d e , the p r e c i p i t a t i o n was c o m p l e t e and rg a p p r o a c h e d t h a t f o r the h i g h l y b u f f e r e d s o l u t i o n ( F i g u r e 1 9 ) . The c o n s u m p t i o n of h y d r o g e n v a r i e d a l s o p r i m a r i l y w i t h the r a t i o o f the c o n c e n t r a t i o n o f s u l p h i d e and molybdenum 99 2.5 2.0 1.5 1.0 0.5 h 0.0 -/ o • -i ; • / y i « / 1 / I s f f • Mo S NH3 T p — • 0.1 M. varies 0.80 M. LOOM. 158.8 .^ 600psi varies 0.21 M. 0.86 0.98 151.6 860 - j O total 0.016 M. II II 1677 530 i l i i i i i D 1 2 3 4 5 6 7 (CS)/[Mo)) | n r t j a | Fig.18 COMPOSITION OF PRECIPITATES BY REDUCTION r8 DEPENDENCE ON THE INITIAL SOLUTION COMPOSITION 100 i n the i n i t i a l s o l u t i o n . T h i s i s shown more c l e a r l y when ( r + r - 3) i s p l o t t e d a g a i n s t r„ as shown i n F i g u r e 20, n o b where r u i s the r a t i o of h y d r o g e n c o n s u m p t i o n to molybdenum n c o n s u m p t i o n . I t i s c l e a r t h a t when r a p p r o a c h e s z e r o , i . e . no s u l p h i d e f o r m a t i o n h y p o t h e t i c a l l y , r ^ a p p r o a c h e s 1. In o t h e r words molybdenum i n o x i d e and/or h y d r o x i d e was i n t e t r a - v a l e n t s t a t e . The e m p i r i c a l e q u a t i o n was g i v e n by: r u = 1 + 0 . 1 8 r c . . . . (20) n b Assuming t h a t the o x i d e ( o r h y d r o x i d e ) and the s u l p h i d e ( o r h y d r o s u l p h i d e ) i n the p r e c i p i t a t e a r e e x p r e s s e d by MoO H and MoS H , r e s p e c t i v e l y , r„ and r„ have the x z y u y ' H S f o l l o w i n g r e l a t i o n s h i p s : r n = y[MoS H ]/([MoS H ] + [MoO H ]) S y u y u x z r R = ( ( 3 - x + 1/2 z)[MoO H ] + (3 - y + 1/2 u) [MoS H ])/([MoO H ] + [MoS H ]) y u x z y u Then [ r R + r g - 3] = -[x - 1/2 z] + [ ( x - 1/2 z + 1/2 u ) / y ] r g or r H = [3 - x + 1/2 z] + [ ( [ x - 1/2 z] - [y - 1/2 u ] ) / y ] r s By c o m p a r i n g w i t h the e m p i r i c a l r e l a t i o n s h i p s were d e r i v e d ; e q u a t i o n (20) the f o l l o w i n g 2.0 1.8 ~ 1.6 0.0 (Value from Nr^ =.9aNHj=l)- & ° -O O 0.2 0.4 (NH^SQi Fig. 19 rs DEPENDENCE ON ACIDITY M. 0.6 I ro h O A -I -2 Mo+S constant S varies Mo varies (NhL^C^ varies P varies 0 Fig.20 0.5 1.0 1.5 2.0 (r H + r s - 3 ) vs. r§ 2.5 x - 1/2 z = 2 y - 1/2 u = 2 - 0.18 y = 1.6.'- 0.07, u y o T h i s i n d i c a t e s t h a t molybdenum i n the s u l p h i d e ( o r h y d r o -s u l p h i d e ) has the v a l e n c y o f l e s s t h an 3.4 on the a v e r a g e , and t h a t the s u l p h i d e may be composed of a m i x t u r e o f t e t r a -and t r i v a l e n t molybdenum d e p e n d i n g on the v a l u e o f u. I f u = 3, y = 2.92, c l o s e to the v a l u e o f molybdenum t r i - h y d r o s u l p h i d e , Mo(SH) . The c o m p o s i t i o n of the p r e c i p i t a t e was f u r t h e r s t u d i e d by c o m p a r i n g the r e s u l t s o f T.G.A. w i t h t h o s e from c h e m i c a l a n a l y s i s . F i g u r e 21 shows t h e p l o t of v a r i o u s w e i g h t l o s s i n gram p e r mole o f molybdenum i n the p r e c i p i -t a t e s measured by T.G.A., a g a i n s t r g . T h r e e w e i g h t l o s s e s were c o n s i d e r e d : AW.^  : w e i g h t l o s s i n Ar a t 200°C. AW^: w e i g h t l o s s i n Ar a t 650°C. AW^: w e i g h t l o s s i n a i r at 550°C. a f t e r p e r f o r m -i n g T.G.A. i n A r . AW^ and AW2 a r e e x p e c t e d t o show the e f f e c t o f d e c o m p o s i t i o n r e a c t i o n s i n t h e i n e r t a t m o s p h e r e . AW^ i s e x p e c t e d to show the o x i d a t i o n c h a r a c t e r i s t i c s o f the sample a f t e r d e c o m p o s i -t i o n was c o m p l e t e i n i n e r t a t m o s p h e r e . 103 40 Fig.2l T6A RESULTS, WEIGHT LOSS vs. r8 WEIGHT LOSS IN g./mote Mo in precipitates 104 A l t h o u g h AW2 showed a c o n s i d e r a b l e s c a t t e r when r g was g r e a t e r t h a n 1.7, a l l t h r e e v a l u e s showed l i n e a r d e p e n d e nces on r . The i n t e r c e p t s a t r = 0 g i v e the h y p o t h e t i c a l b e h a v i o u r s o f the o x i d e ( o r h y d r o x i d e ) and a g r e e f a i r l y w e l l w i t h t h o s e o f h y d r a t e d molybdenum d i o x i d e as shown below. Weight L o s s Found g./mole Mo D e c o m p o s i t i o n R e a c t i o n Weight L o s s g./mole Mo AWX 16 M o ( 0 H ) 4 -> Mo(OH) 20+ H 20 18 AW2 36 M o ( 0 H ) 4 -* Mo0 2 + 2 H 20 36 AW3 -19 Mo0 2 Mo0 3 - | o 2 -16 AW3 i n c r e a s e d by 18g. f o r each a d d i t i o n o f a mole of s u l p h u r to a mole of molybdenum i n the p r e c i p i t a t e . The r e p l a c e m e n t o f oxygen w i t h s u l p h u r i n the p r e c i p i t a t e s a t c o n s t a n t amount o f molybdenum s h o u l d y i e l d the d i f f e r -ence i n m o l e c u l a r w e i g h t between s u l p h u r and oxygen, namely 16g., s l i g h t l y s m a l l e r t h a n the v a l u e o b s e r v e d . T h e r e f o r e the s u l p h u r a d d i t i o n must be a s s o c i a t e d w i t h the p a r t i a l r e d u c t i o n of t e t r a v a l e n t molybdenum to t r i v a l e n t , i n a g r e e -ment w i t h the o b s e r v a t i o n o f h y d r o g e n c o n s u m p t i o n . But the g r o s s v a l u e a g r e e d f a i r l y w e l l w i t h the s i m p l e r e p l a c e m e n t of molybdenum d i o x i d e w i t h molybdenum d i s u l p h i d e i n a g r e e -ment w i t h the o b s e r v a t i o n o f X - r a y p a t t e r n . AW_ , below r = 1.7, and AW., d e c r e a s e d by 12 and 4g., r e s p e c t i v e l y , f o r each a d d i t i o n o f a mole of s u l p h u r to a mole of molybdenum i n t h e p r e c i p i t a t e . T h i s s u g g e s t s the s i m p l e r e p l a c e m e n t o f oxygen w i t h s u l p h u r below r g = 1.7, and p r o d u c t i o n o f v o l a t i l e m a t e r i a l above r s = 1.7. As r and r v a r i e d w i t h the change o f the i n i t i a l o ri c o n d i t i o n s , v a r i a t i o n of r and r u d u r i n g t h e r u n was s u s -b rl p e c t e d . S e v e r a l d u p l i c a t e r u n s were c o n d u c t e d i n w h i c h one e x p e r i m e n t was s t o p p e d a t h a l f w a y and compared w i t h the o t h e r w h i c h was a l l o w e d to go to c o m p l e t i o n . T a b l e 7 shows the. r e s u l t s . When ( [ S ] / [ M o ] ) . > 2 and [NH*] was h i g h , r . and r„ ' i H b H o f the r u n s s t o p p e d h a l f w a y a g r e e d w i t h t h o s e of the r u n s a l l o w e d to go to c o m p l e t i o n . But when ( [ S ] / [ M o ] ) ^ < 2 an d / o r [NH^] was low, r of the r u n s s t o p p e d h a l f w a y was l a r g e r t h a n t h o s e of the r u n s a l l o w e d to go to completion., These f a c t s i n d i c a t e t h a t t h e r e a r e two ( o r more) p a t h s o f molybdenum p r e c i p i t a t i o n : one to form s u l p h i d e and the o t h e r t o form o x i d e , and t h a t under c o n d i t i o n s ( [ S ] / [ M o ] ) ^ > 2 and h i g h [NH^] b o t h p a t h s were f o l l o w e d i n a c e r t a i n p r o p o r t i o n u n t i l molybdenum p r e c i p i t a t i o n was c o m p l e t e , whereas under the c o n d i t i o n ( [ S ] / [ M o ] ) . < 2 a n d / o r low [NH^] t h e s u l p h i d e p a t h p r o c e e d e d f a s t e r t h a n the o x i d e p a t h c o m p l e t i n g the d e p l e t i o n o f s u l p h i d e i o n f r o m the s o l u t i o n . 3-2 K i n e t i c s t u d y The i n v e s t i g a t i o n o f t h e f i n a l p r o d u c t s d e s c r i b e d i n s e c t i o n 3-1 i n d i c a t e d t h a t , a p p a r e n t l y , t h e r e a c t i o n s 106 TABLE 7 • V a r i a t i o n of rS and rH by the E x t e n t of R e a c t i o n No . % r s R H T °C. I n i t i a l C o n d i t i o n [Mo] M. [ s ] T M. [ N H 3 ] M. [ N H { ] M. P«i p s i . 102 100 1.93 1.22 151. 6 0 .099 0 .211 0 .86 0 . 98 858 111 57 1.98 1.37a 151. 6 0.097 0.195 0 . 86 0 .98 865 113 100 2 . 03 1.45 160 . 0 0.100 0 .195 0.86 0.98 821 112 81 1.98 1.52a 160.0 0 . 100 0 . 195 0 .86 0 . 98 826 85 97.5 1.23 1.39 158 . 8 0 .098 0.096 0.85 0.97 600 114 71 1.42 1. 46a 160.0 0 . 100 0.097 0 . 86 0.98 824 110 85 1.66 1. 35 151. 6 0.097 0 . 211 0 . 00 0 . 98 884 115 51 1.83 1.70a 160 . 0 0.098 0 . 195 0 . 00 0 . 98 840 % - Per cent of molybdenum d i s a p p e a r e d from s o l u t i o n . | a - H f o r the runs i n t e r r u p t e d i n h a l f w a y were o b t a i n e d by e x t r a p o l a t i n g the p r e s s u r e drop curves u n t i l the times when the temperatures of the system dropped 2 0 ° C . b - [ N H + ] was added as ammonium s u l p h a t e . c o u l d be c l a s s i f i e d i n t o two t y p e s , d e p e n d i n g on the i n i t i a l c o n c e n t r a t i o n r a t i o o f s u l p h i d e to molybdenum and the amount of ammonium s u l p h a t e p r e s e n t i n s o l u t i o n : t y p e (1) - r a t i o of s u l p h i d e to molybdenum l a r g e r t h a n 2 and h i g h NH^ c o n c e n -t r a t i o n , g i v i n g no v a r i a t i o n i n the p r o d u c t d u r i n g the r e -d u c t i o n r e a c t i o n and the f i n a l p r o d u c t s h a v i n g a l i m i t i n g , v a l u e of s u l p h u r to molybdenum r a t i o ; t y p e (2) - r a t i o of s u l p h i d e to molybdenum l e s s t h a n 2 a n d / o r low NH^ c o n c e n t r a -t i o n , p r e c i p i t a t i n g t h e s u l p h i d e f i r s t f o l l o w e d by t h e o x i d e a n d / o r the h y d r o x i d e . A n a l y s i s o f the s o l u t i o n p r o d u c e d d u r i n g t h e ru n s c o n f o r m i n g to the t y p e (1) showed t h a t t h e r e was i n f a c t no v a r i a t i o n i n the r a t i o of the c o n s u m p t i o n of molybdenum and s u l p h u r from t h e s o l u t i o n d u r i n g the whole p r o c e s s o f p r e -c i p i t a t i o n . F i g u r e 22 shows the p l o t o f t o t a l molybdenum, c o n c e n t r a t i o n a g a i n s t t o t a l s u l p h i d e c o n c e n t r a t i o n i n the s o l u t i o n . The l i n e a r i t y was c o n s i d e r e d good i n view of the r a p i d l y a c c e l e r a t i n g molybdenum d e p l e t i o n as shown by the s o l i d t r i a n g l e s w h i c h c o r r e s p o n d to the open t r i a n g l e . 3-2-a E f f e c t of p r e s s u r e The e f f e c t o f the p a r t i a l p r e s s u r e o f h y d r o g e n f o r the t y p e (1) was f i r s t i n v e s t i g a t e d s i n c e no change o f mechanism was e x p e c t e d d u r i n g the r u n c o n s i d e r i n g the c o n -s t a n c y of t h e r a t i o of comsumption of molybdenum and s u l p h i d e d i s c u s s e d above. o 00 109 F i g u r e 23 shows t h e v a r i a t i o n o f the t o t a l c o n c e n -t r a t i o n o f molybdenum under c o n s t a n t p r e s s u r e a t 1 5 8 . 8 ° C . P r e s s u r e was v a r i e d . The r a t e o f d i s a p p e a r e n c e o f molybdenum from the s o l u t i o n i n c r e a s e d as t h e r e a c t i o n p r o c e e d e d . No s i m p l e o r d e r o f r e a c t i o n on molybdenum c o n c e n t r a t i o n d e s c r i b e s t h i s phenomenon. But when th e l o g a r i t h m o f the amount o f molybdenum removed from s o l u t i o n was p l o t t e d a g a i n s t t i m e , a good l i n e a r i t y was o b s e r v e d e x c e p t f o r the i n i t i a l p a r t s as shown i n F i g u r e 24. The i n t e g r a t e d e q u a t i o n d e s c r i b i n g t h i s r e m o v a l i s : -l o g ( [ M o J 0 - [Mo]) = s t + l o g i . . . . (21) where s and l o g i a r e s l o p e and i n t e r c e p t o f the p l o t d i s -c u s s e d above. The p r e s s u r e dependence of s and i a r e shown i n F i g u r e 25. L i n e a r i t y o f s v s . p r e s s u r e and i v s . V 1 / ( p r e s s u r e ) were o b s e r v e d . T h e r e f o r e the e m p i r i c a l f o r m u l a f o r the molybdenum c o n c e n t r a t i o n was g i v e n by l o g ( [ M o ] Q - [Mo]) = c±Vt + l o g ( c 0 + c 3 / P ) . . . . (22) D i f f e r e n t i a t i o n o f t h i s e q u a t i o n w i t h r e s p e c t to time a t c o n -s t a n t p r e s s u r e y i e l d s : - d [ M o ] / d t = c 1 P ( [ M o ] 0 - [Mo]) . . . . (23) I l l Fig. 24 Log(Moo-Mo) vs. Time 112 xlO Intercept M. xlO 3 200 400 Pressure psi. H 2 psi Fig.25 SLOPE S INTERCEPT vs. PRESSURE xlO? 113 The e q u a t i o n (23) i m p l i e s t h a t t h e r e a c t i o n i s a u t o c a t a l y t i c and t h a t molybdenum and s u l p h i d e c o n c e n -t r a t i o n s do n o t come d i r e c t l y i n t o the r a t e p r o c e s s o f a s p e c t , t w o - s t a g e e x p e r i m e n t s were c o n d u c t e d , i n w h i c h the f i r s t s t a g e was a l l o w e d to go to c o m p l e t i o n , the end p o i n t b e i n g d e t e c t e d by the d i s a p p e a r e n c e of the c o l o u r o f t h i o -m o l y b d a t e c o m p l e x e s . Then a f r e s h molybdenum s o l u t i o n was i n j e c t e d and the r a t e of molybdenum d e p l e t i o n was f o l l o w e d as b e f o r e . the s e c o n d s t a g e was d e c r e a s e d to 200 p s i . from 500 p s i . o f the f i r s t s t a g e . The d e p l e t i o n o f molybdenum i n the s e c o n d s t a g e was a l m o s t l i n e a r a g a i n s t t i m e u n t i l c o m p l e t i o n w h i l e the r a t i o of s u l p h u r to molybdenum of the p r e c i p i t a t e s r e m a i n e d p r a c t i c a l l y c o n s t a n t . T h i s i n d i c a t e s t h a t i n the s e c o n d s t a g e molybdenum was a c t i n g s i m p l y as a s u b s t r a t e w h i c h was e a s i l y r e d u c e d . The r a t e s o f d e p l e t i o n of molybdenum at the end of the f i r s t s t a g e and a t t h e b e g i n n i n g of the s e c o n d s t a g e were fo u n d to be 2.6 and 6.2 x 10 M. min. , r e s p e c t i v e l y . In the o t h e r r u n where the p r e s s u r e of b o t h s t a g e s were k e p t c o n s t a n t a t 500 p s i . , the r a t e o f molybdenum d e p l e t i o n a t the i n i t i a l p a r t o f the s e c o n d s t a g e was found to i n c r e a s e by 5 . 3 - f o l d compared w i t h t h a t a t the end of the f i r s t s t a g e . T h i s i n c r e a s e was i n t e r p r e t e d to be c a u s e d by t h e a c t i v a t i o n of the p r e c i p i t a t e f r o m the f i r s t molybdenum d e p l e t i o n . In o r d e r to c l a r i f y more o f t h i s F i g u r e 26 shows the r e s u l t s , where the p r e s s u r e o f Tig. 26 TWO STAGE RUN, H 2 , 500psi., I58.8°C. s t a g e by d i s s o l v e d h y d r o g e n d u r i n g the t i m e i n t e r v a l be-tween the two s t a g e s . Assuming t h a t the r a t e c o n s t a n t i n the e q u a t i o n (23) was p r o p o r t i o n a l to p r e s s u r e , the r a t e o f d e p l e t i o n of molybdenum a t the i n i t i a l p a r t o f the s e c o n d s t a g e was c a l c u l a t e d from the r a t e of d e p l e t i o n a t t h e end o f the f i r s t s t a g e c o r r e c t i n g the a c t i v i t y change m e n t i o n e d above. The c a l c u l a t e d v a l u e was 5.5 x 10 M. min. ^ i n c l o s e agreement w i t h the o b s e r v e d v a l u e . F i g u r e 26 a l s o i n c l u d e s the c o n c e n t r a t i o n changes of o t h e r s p e c i e s . The v a r i a t i o n w i t h time was s i m i l a r to t h e t o t a l molybdenum c o n c e n t r a t i o n v a r i a t i o n . The d i s t r i b u t i o n o f complex s p e c i e s d u r i n g the r e d u c t i o n r e a c t i o n was i n v e s t i g a t e d by p l o t t i n g the f r a c -t i o n a l d i s t r i b u t i o n o f t r i - t h i o m o l y b d a t e (ot^) a g a i n s t t h a t of t e t r a - t h i o m o l y b d a t e (oi^) i n l o g - l o g s c a l e w i t h t h e same r e a s o n i n g g i v e n i n P a r t 1 ( S t u d y o f e q u i l i b r i u m ) . F i g u r e 27 shows the r e s u l t s where d a t a f r o m the same run are i n d i c a t e d by the same symbol. A l s o the l i n e s r e p r e s e n t i n g the e q u i l i b r i u m o b t a i n e d i n P a r t 1 a t 150° and 120°C. a r e r e - , p r o d u c e d . A l t h o u g h t h e r e i s s c a t t e r , the p o i n t s r e p r e s e n t -i n g the samples d u r i n g t h e r e d u c t i o n r e a c t i o n s a t 1 5 8 . 8 ° C . l i e i n c l o s e agreement and t e n d e n c y w i t h the e q u i l i b r i u m r e l a t i o n s h i p . T h e r e f o r e i t was c o n c l u d e d t h a t the complex s p e c i e s were i n e q u i l i b r i u m w i t h each o t h e r d u r i n g the ; r e d u c t i o n r e a c t i o n and exchange r e a c t i o n s between the com-p l e x s p e c i e s were not r a t e c o n t r o l l i n g . 0.40 0.30 h 0.20 h log scale 0.15 0.10 line l : Equilbrium at I20°C. line 2= .. I50°C. 0.05 0.07 I58.8°C. NH3 = I M. NH* = I M. ± ± JL Fig. 27 PLOT OF rf3 0.10 0.15 0.20 0.30 0.50 o< 4 log scale vs. c<4 , DURING PRECIPITATION IN HYDROGEN ATMOSPHERE S i n c e the r e d u c t i o n r e a c t i o n a c c e l e r a t e d r a p i d l y towards the end of the r e a c t i o n , i t was d i f f i c u l t to o b t a i n a c o n v e n i e n t s a m p l i n g method to f o l l o w the r e a c t i o n . T h e r e -f o r e a n o t h e r e x p e r i m e n t a l method was employed i n w h i c h the e x p e r i m e n t was c o n d u c t e d i n a c o n s t a n t volume a u t o c l a v e d e s c r i b e d i n the e x p e r i m e n t a l s e c t i o n and the r e a c t i o n was f o l l o w e d by r e a d i n g the t o t a l p r e s s u r e d r o p o f the s y s t e m . P r e s s u r e d e c r e a s e s w i t h time were s i m i l a r to the d e c r e a s e s o f the t o t a l molybdenum c o n c e n t r a t i o n w i t h time d i s c u s s e d above as shown i n F i g u r e 28, namely the r a t e o f h y d r o g e n c o n s u m p t i o n i n c r e a s e d as the r e a c t i o n proceeded., I f the same r a t e e q u a t i o n as e q u a t i o n (23) a p p l i e s , the r a t e e q u a t i o n i n terms o f h y d r o g e n p r e s s u r e would be o f the form - dP/dt = k P ( Y ( P Q - P) + 6) . . . . (24) where y and 6 a r e c o n s t a n t s r e p r e s e n t i n g the s t o i c h i o m e t r i c r e l a t i o n s h i p between molybdenum and h y d r o g e n , and t h e i n i t i a l c o n d i t i o n o f the s y s t e m , r e s p e c t i v e l y . Upon i n t e g r a t i o n , l n [ P / ( a + P Q - P ) ] = - k y ( P Q + a) t + l n ( P Q / a ) . . . . (25) where a_ = 6 /y. Q I 1 1 1 1 1 u 50 100 150 200 250 Time min. Fig.28 VARIATION OF TOTAL PRESSURE, H2 dbns. 119 F i g u r e 29 shows the p l o t o f the l e f t hand s i d e o f e q u a t i o n (25) a g a i n s t t i m e where a. was t a k e n as 10 p s i . F l u c t u a t i o n o f p o i n t s was c a u s e d by t h e t e m p e r a t u r e f l u c -t u a t i o n o f a p p r o x i m a t e l y 0.3°C. Good l i n e a r i t y was o b s e r v e d and the s l o p e s were fo u n d to be p r o p o r t i o n a l to (Po + a) as p r e d i c t e d by the e q u a t i o n (25) as shown i n the i n s e r t e d F i g u r e i n F i g u r e 29. T h e r e f o r e the e q u a t i o n (24) was c o n -s i d e r e d to h o l d and f u r t h e r a n a l y s i s o f e x p e r i m e n t a l d a t a was p e r f o r m e d by p l o t t i n g t h e r e d u c e d r a t e ( 1 / P ) ( - d P / d t ) a g a i n s t h y d r o g e n c o n s u m p t i o n , ( P Q - P ) . The i n s t a n t a n e o u s r a t e s o f h y d r o g e n c o n s u m p t i o n , - d P / d t , were o b t a i n e d by g r a p h i c a l d i f f e r e n t i a t i o n of s m o o t h l y f i t t i n g c u r v e s o f the p r e s s u r e r e a d i n g s a g a i n s t t i m e . 3-2-b E f f e c t o f t e m p e r a t u r e The e f f e c t of t e m p e r a t u r e on the r e a c t i o n was com-p a r e d f o r the two e x p e r i m e n t a l methods employed, namely (A) 2 1 . - t i t a n i u m a u t o c l a v e , p r e s s u r e m a i n t a i n e d c o n s t a n t and (B) 120ml. s t a i n l e s s - s t e e l a u t o c l a v e , p r e s s u r e v a r i e d as the r e a c t i o n p r o c e e d e d . T a b l e 8 shows the r e s u l t s i n w h i c h the r a t e c o n s t a n t s f o r (A) a r e the s l o p e o f the p l o t of the e q u a t i o n (23) and > f o r (B) t h e s l o p e of the r e d u c e d r a t e a g a i n s t the amount o f h y d r o g e n consumed. In s p i t e of the d i f f e r e n c e i n the e x p e r -i m e n t a l methods and the c o n c e n t r a t i o n r a n g e employed, the a c t i v a t i o n e n e r g i e s were f o u n d a l m o s t the same, i n d i c a t i n g t h a t the same r a t e c o n t r o l l i n g s t e p was o p e r a t i n g and the 120 Time min. Fig. 29 PLOT OF ln( P/ (a + Po- P ) ) vs. TIME 120a TABLE 8 E f f e c t of T e m p e r a t u r e on the Rate A. t N H 3 J = 1 - ° M - » I ( N H 4 ) 2 S 0 4 ] = 0.5 M., P H 2 = 27.2 atm. I n i t i a l c o n c e n t r a t i o n s : [ M o J T = 0.020 M., [ S ] T = 0.056 M. No. T e m p e r a t u r e k 41 1 5 8 . 8 ° C . 3.03 x 1 0 " 2 m i n . _ 1 45 1 5 1 . 6 ° C . 2.03 x 1 0 ~ 2 m i n . _ 1 E = 20 k c a l /mole B. I N H 3 J = ° - 9 M>> I ( N H 4 ) 2 S 0 4 ] = 0.45 M., I n i t i a l c o n d i t i o n s : [Mo]_ = 0.10 M., [S]„ = 0.20 M., P u v= 57 atm. T 2 No. T e m p e r a t u r e k 111 1 5 1 . 6 ° C . 1.12 x 1 0 ~ 3 a t m . " 1 m i n . " 1 112 16-0.0°C. 1.74 x I O - 3 a t m . ~ 1 m i n . ~ 1 E = 21 k c a l . A /mole 121 s t e p d i d n o t depend on the c o n c e n t r a t i o n s o f molybdenum and s u l p h i d e i n s o l u t i o n . 3-2-c E f f e c t of c a t a l y s t By d i v i d i n g e q u a t i o n (24) w i t h p r e s s u r e , e q u a t i o n (26) was d e r i v e d . - d i n P/dt = k ( y ( P o - P) + 5) . . . . (26) The v a l u e i n s i d e t h e b r a c k e t i n t h e r i g h t hand s i d e c o r r e -sponds to the amount o f c a t a l y s t e x i s t i n g , u nder t h e same c o n d i t i o n s o f s o l u t i o n c o m p o s i t i o n . A d d i t i o n o f c a t a l y s t a t t h e b e g i n n i n g o f the ru n s would be e x p e c t e d to c a u s e a change i n o n l y 6 . When p r e c i p i t a t e s f r o m the o t h e r r u n were added, t h e r e was an i n c r e a s e i n t o t a l c o n s u m p t i o n of h y d r o g e n as the amount was i n c r e a s e d . However the p l o t of r e d u c e d r a t e s a g a i n s t h y d r o g e n c o n s u m p t i o n s showed a good p a r a l l e l i s m when the end p o i n t s were matched as shown i n F i g u r e 30. The s l o p e t h a t f i t t e d w e l l to the r u n 118 (no a d d i t i o n ) was t a k e n to draw b e s t f i t l i n e s to the r u n 117 (200 mg.) and the r u n 116 (400 mg.). The i n t e r c e p t s a t z e r o h y d r o g e n c o n s u m p t i o n f o r the r u n 118 were p l o t t e d a g a i n s t amount o f p r e c i p i t a t e s added i n the i n s e r t o f F i g u r e 30. A good l i n e a r i t y was o b s e r v e d . T h e r e f o r e 6 i n the e q u a t i o n (26) d i d i n f a c t c o r r e s p o n d to the i n i t i a l c o n d i t i o n o f c a t a l y s t and y was i d e n t i c a l f o r s o l u t i o n s o f the same c o m p o s i t i o n s . 122 123 The i n i t i a l h i g h v a l u e s i n F i g u r e 30 were co n -s i d e r e d to be c a u s e d by the d i s s o l u t i o n o f p r e c i p i t a t e s and exchange o f o x i d e w i t h s u l p h i d e i n t h e p r e c i p i t a t e s . T h i s i s i n agreement w i t h the e m p i r i c a l e q u a t i o n ( 2 0 ) . 3-2-d E f f e c t o f s o l u t i o n c o n d i t i o n s From t h e a n a l y s i s o f the f i n a l p r o d u c t s , d e s c r i b e d i n s e c t i o n 3-1, i t was f o u n d t h a t the c o m p o s i t i o n o f p r e -c i p i t a t e s v a r i e d w i t h the i n i t i a l s o l u t i o n c o n d i t i o n s . S i n c e i t was shown t h a t t h e r a t e o f molybdenum d e p l e t i o n f r o m s o l u t i o n was p r i m a r i l y c o n t r o l l e d by the h y d r o g e n p r e s s u r e and t h e amount o f p r e c i p i t a t e , t h e r e a p p e a r to be s t e p s ( o r a s t e p ) f o l l o w i n g the r a t e c o n t r o l l i n g s t e p w h i c h d e t e r m i n e the c o m p o s i t i o n and the n a t u r e o f the p r e c i p i t a t e s . S e v e r a l s e r i e s o f e x p e r i m e n t s were p e r f o r m e d to c l a r i f y t h i s a s p e c t . F i g u r e 31 shows the e f f e c t s o f t h e v a r i a t i o n of the c o n c e n t r a t i o n of molybdenum a t c o n s t a n t amount o f s u l p h i d e and a t h i g h c o n c e n t r a t i o n s o f f r e e ammonia and ammonium s u l p h a t e . C l e a r l y when the i n i t i a l m o l a r r a t i o o f s u l p h i d e t o molybdenum, S/Mo, were above 2, the r e d u c e d r a t e d r o p p e d s h a r p l y to z e r o a f t e r r e a c h i n g the maximum, whereas when S/Mo were l e s s t h a n 2, t a i l s were o b s e r v e d a f t e r r e a c h i n g the maximum a t a p p r o x i m a t e l y the same amount of h y d r o g e n c o n s u m p t i o n . From the e x p e r i m e n t s d e s c r i b e d i n s e c t i o n 3-1 where the r u n was i n t e r r u p t e d i n h a l f w a y and the r e s u l t i n g s o l u t i o n was a n a l y z e d , i t was f o u n d t h a t Reduced rate M.mia' atm" xlO 10 . 1 5 _ . Hydrogen consumed M. xlO Fig. 31 EFFECT OF SOLUTION CONDITION, MoTI VARIATION , IN H, NJ s u l p h i d e d e p l e t e d f i r s t when S/Mo was l e s s t h a n 2. T h e r e -f o r e t h e p o r t i o n s b e f o r e t h e maximum were c o n s i d e r e d to c o r r e s p o n d to t h e s u l p h i d e p r e c i p i t a t i o n . F i g u r e 32 shows t h e e f f e c t s o f the v a r i a t i o n of ammonium s u l p h a t e c o n c e n t r a t i o n where the i n i t i a l m o l a r r a t i o o f s u l p h i d e to molybdenum was s l i g h t l y above 2. Molybdenum and s u l p h i d e were added as sodium s a l t s . T h e r e was a v a r i -a t i o n i n the r a t e c u r v e s w i t h the amount o f the ammonium s u l p h a t e , namely when the amount was l e s s t h a n the eq u i v - . a l e n t to n e u t r a l i z e t h e sodium s u l p h i d e l o n g i n d u c t i o n p e r i o d s were o b s e r v e d , whereas a t above t h e e q u i v a l e n t v a l u e , h i g h i n i t i a l r a t e o f h y d r o g e n c o n s u m p t i o n was o b s e r v e d . From the above two s e r i e s o f r e s u l t s , i t was i n d i c a t e d t h a t t h e d i s t r i b u t i o n o f v a r i o u s complex s p e c i e s and the pH of t h e s o l u t i o n seemed to p l a y i m p o r t a n t r o l e s i n d e t e r m i n i n g the c o m p o s i t i o n s o f the p r e c i p i t a t e s . From the e q u a t i o n ( 2 5 ) , i t i s s u g g e s t e d t h a t the s l o p e o f the p l o t of - d i n P/dt v s . (Po - P) would r e p r e s e n t the e f f e c t o f s o l u t i o n c o n d i t i o n s on the c o m p o s i t i o n of p r e c i p i t a t e s . I n i t i a l c o m p o s i t i o n s o f the s o l u t i o n were c a l c u l a t e d by u s i n g t h e r e s u l t s o b t a i n e d i n P a r t 1, as f o l l o w s : -F o r m a t i o n f u n c t i o n was assumed a s : n = n (L) , L = [H S] . . . . (27) Z aq 126 Fig. 32 EFFECT OF SOLUTION CONDITION, IN H2 (NH4)2S04 AMOUNT VARIATION The m a t e r i a l b a l a n c e f o r s u l p h i d e y i e l d e d 127 = nM T + S f = nM T + [ H 2 S ] + [ S 2 ~ ] The c h a r g e b a l a n c e e q u a t i o n y i e l d e d , n o t i n g the same c h a r g e f o r a l l molybdenum s p e c i e s , [ N a + ] + [ H + ] + [NH+] = 2M T + 2 [ S 0 2 _ ] + [OH -] + [HS ] + 2 [ S 2 ~ ] + - 2-By n e g l e c t i n g H , OH and S , as b e i n g s m a l l i n c o m p a r i s o n w i t h t h e o t h e r i o n i c s p e c i e s and s u b s t i t u t i n g the r e l a t i o n -s h i p s : [ H 2 S ] = S f / ( 1 + m[NH 3]/[NH+]) [HS~] = [ H 2 S ] m ( N T - [NH+])/[NH+] the f o l l o w i n g e q u a t i o n s were d e r i v e d f o r n and L as f u n c t i o n s of the c o n c e n t r a t i o n of ammonium i o n , ; n = S T/M T - (1 - m + mN T/N 1) L/M^ . . . . (28) L = ( N 1 - 2M T - 2 [ S 0 2 " ] + [ N a + ] ) N^m (N^ - . . (29) A s s u m p t i o n was made t h a t t h e f o r m a t i o n f u n c t i o n a t 150°C. a p p l i e s a l s o a t 1 5 1 . 6 ° C . Then n and L were c a l c u -l a t e d f r o m e q u a t i o n (28) and (29) s e l e c t i n g a s u i t a b l e v a l u e o f to s a t i s f y t h e e q u a t i o n (27) by t h e method o f s u c c e s -s i v e a p p r o x i m a t i o n s f o r a s e t o f v a l u e s o f , S^, , 128 + 2-[Na ] , and [SO^ ] . The v a l u e o f m was t a k e n as 5.8 as o b t a i n e d i n P a r t 1. A f t e r o b t a i n i n g the v a l u e o f the aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n , L, t h e f r a c t i o n a l d i s t r i b u t i o n s o f v a r i o u s t h i o m o l y b d a t e s p e c i e s were c a l c u l a t e d by u s i n g the s t a b i l i t y c o n s t a n t s o b t a i n e d i n P a r t 1. F i g u r e s 33a and 33b show the p l o t s of t h e s l o p e s of F i g u r e s 31 and 32 a g a i n s t f r a c t i o n a l d i s t r i b u t i o n s and the r a t i o o f ammonium i o n to f r e e ammonia, r e s p e c t i v e l y . S i n c e the e x p e r i m e n t s o f F i g u r e s 31 and 32 were c o n d u c t e d at t h e same t e m p e r a t u r e , t h e s l o p e s f r o m t h e s e two s e r i e s c o u l d be combined and e x p r e s s e d by an a p p r o p r i a t e f u n c t i o n of the f r a c t i o n a l d i s t r i b u t i o n s and t h e r a t i o o f the ammonium i o n to f r e e ammonia. A f t e r t r i a l and e r r o r , i t was f o u n d t h a t F i g u r e s 33a and 33b c o u l d be combined o n l y when th e s l o p e s were • p l o t t e d a g a i n s t t h e p r o d u c t s o f the f r a c t i o n a l d i s t r i b u t i o n o f t e t r a - t h i o m o l y b d a t e , , w i t h the h y d r o g e n i o n c o n c e n -t r a t i o n , or the r a t i o o f ammonium i o n t o f r e e ammonia, as shown i n F i g u r e 34. The low v a l u e s o f t h e s l o p e s i n the pH s e r i e s were c o n s i d e r e d due to the same e f f e c t by t h e i n i t i a l p r e c i p i t a t e s as were o b s e r v e d i n the c a s e where p r e c i p i t a t e s f r o m a p r e v i o u s r u n were added to the i n i t i a l s o l u t i o n , ( s e c t i o n B-2-3) The i n c r e a s e i n the s l o p e s a t l a r g e amounts o f c o n s u m p t i o n o f h y d r o g e n seen i n F i g u r e 32 seem to s u p p o r t the a s s u m p t i o n . 129 Slope psr'mirn1 x IO% ) 0.2 0.4 0.6 Q AND (NH+)/(NH3) (a) Mo VARIED. 0.8 o • a 0 , + 8 a, 7 a a, 2 i U • (NH+)/(NH3) a psir1 min.1 xlO | 0 (NHj)/(NH3) T (b). (NH4)2S04 VARIED. Fig.33 PLOT OF SLOPE vs. (2 AND (NH+)/(NH3). Slope nnir xlO5 psir1 min"1 o Mo varied I5I.6°C. - A (NH^SC^ « — — o — A 1 0 0.05 Fig. 34 SLOPE vs. 0.10 0.15 0.20 a4(NHj)ANr%) CX4(NHj)/(NH3) , COMBINED 0.25 1/Slope 2 -psi. mm. xlO r 4 I -O o Mo varied i 1 Fig. 35 0 4 0 80 120 160 1/lQ (NHj)/(NH3)) PLOT OF I/Slope vs. 1/( a4(NH4)/(NH3) F i g u r e 34 i n d i c a t e s a s a t u r a t i o n e f f e c t a t the l a r g e v a l u e o f the p r o d u c t s t a t e d above. When the i n v e r s e of t h e s l o p e was p l o t t e d a g a i n s t the i n v e r s e of the p r o d u c t , a good l i n e a r i t y was o b s e r v e d as shown i n F i g u r e 35, namely, 1 / s l o p e = A± + A 2 / ( a 4 [ N H 4 ] / [ N H 3 ] ) where and c o n s t a n t s . T h e r e f o r e s l o p e = ( a 4 [ N H 4 J / [ N H 3 ] ) / [ A 2 + A±(a^ [NH+]/[NH 3])] N o t i n g t h a t [ N H 4 ] / [ N H 3 ] i s p r o p o r t i o n a l to h y d r o g e n i o n c o n c e n t r a t i o n , [ H + ] , t h e above r e l a t i o n s h i p can be w r i t t e n as s l o p e = k ' [ a 4 [ H + ] / ( k ' ' + a 4 [ H + ] ) ] T h i s t r e a t m e n t o f t h e d a t a was a l s o s u c c e s s f u l when i t was a p p l i e d t o the r e s u l t s o f a s e r i e s where amount o f sodium s u l p h i d e was v a r i e d w h i l e k e e p i n g the c o n c e n t r a t i o n s of molybdenum, ammonium s u l p h a t e and ammonia c o n s t a n t . F i g u r e 35a shows t h e p l o t of s l o p e a g a i n s t and [ N H 4 ] / [ N H 3 ] where s t a b i l i t y c o n s t a n t s a t 150°C. were used f o r the c a l c u -l a t i o n . F i g u r e 36b shows the p l o t o f s l o p e a g a i n s t the p r o d u c t of the two v a r i a b l e s . T h e r e f o r e the e m p i r i c a l r a t e e q u a t i o n was assumed t o b e : 0.02 0.04 0.06 0.08 a4(NHj)/(NH3) Fig.36 EFFECT OF SOLUTION CONDITION , S VARIED. 0.10 133 -d l n P/dt = k [ a 4 [ H + ] / ( k 1 1 + a 4 [ H + ] ) ] ( P o - P) + k''' . . . . (30) 3-3 D i s c u s s i o n and c o n c l u s i o n s The e x p e r i m e n t a l r e s u l t s a r e summarized as f o l l o w s : 1. The p r e c i p i t a t e s o b t a i n e d were m i x t u r e s of moly-bdenum t e t r a - h y d r o x i d e and p o s s i b l y molybdenum t r i -h y d r o s u l p h i d e . 2. The m o l a r r a t i o s o f h y d r o g e n consumed, and s u l p h u r i n the p r e c i p i t a t e s , to the molybdenum were r e l a t e d w i t h t h e f o l l o w i n g e q u a t i o n : -r„ = 1 + 0.18 r . . . . (20) 3. The e m p i r i c a l r a t e e q u a t i o n s were f o r the molybdenum consump t i o n : --d [Mo]/dt = k P ([Mo] 0 - [Mo]) . . . . (23) and f o r h y d r o g e n c o n s u m p t i o n :.--d In P/dt = k ( a 4 [ H + ] / ( k 1 1 + a 4 [ H + ] ) ( P o - P) + k ' 1 1 . . . . (30) 4. The v a r i o u s complex s p e c i e s of molybdenum i n the s o l u t i o n a r e i n r a p i d e q u i l i b r i u m w i t h each o t h e r . 5. The a c t i v a t i o n e n e r g y o f the r a t e o f molybdenum d e p l e t i o n f r o m s o l u t i o n was a r o u n d 20 k c a l . / m o l e . The above o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e f o l l o w i n g mechanism: (1) P r e c i p i t a t i o n o f c a t a l y t i c m a t e r i a l t h r o u g h t h e same r e a c t i o n p a t h as the one o b s e r v e d i n the i n e r t a t m o s p h e r e . ... i n i t i a t i o n . (2) R a p i d and s t r o n g a d s o r p t i o n on the c a t a l y s t o f v a r i o u s t h i o m o l y b d a t e s p e c i e s w h i c h were i n e q u i l i b r i u m e ach o t h e r i n the s o l u t i o n as w e l l as on the s u r f a c e s o f the c a t a l y s t . (3) Weak a d s o r p t i o n o f h y d r o g e n on t h e c a t a l y s t s u r f a c e s . (4) A c t i v a t i o n of the a d s o r b e d h y d r o g e n . ... r a t e d e t e r -m i n i n g s t e p . (5) C o n s u m p t i o n of t h e a c t i v a t e d h y d r o g e n t h r o u g h two p a t h s ; (a) R e a c t i o n w i t h t h e p r o t o n a t e d t e t r a - t h i o m o l y b d a t e to p r o d u c e the s u l p h i d e , consuming 1.5 mole o f h y d r o g e n per mole of molybdenum. c a t a l y s t g e n e r a t i o n . (b) R e a c t i o n w i t h s i m p l e m o l y b d a t e a d s o r b e d to p r o d u c e the o x i d e or h y d r o x i d e consuming one mole o f h y d r o -gen p e r mole of molybdenum. The i n i t i a t i o n s t e p was n e c e s s a r y to e x p l a i n the s l o w r e d u c t i o n a t the b e g i n n i n g of r e a c t i o n . S i n c e t h i s slow p a r t d i s a p p e a r e d when p r e c i p i t a t e s were added o r when the s u r f a c e s o f the a u t o c l a v e were not c l e a n e d , the d e l a y was c o n s i d e r e d to be due to an i n h e r e n t s l o w n e s s of any homogeneous r e a c t i o n s . The s t e p (2) assumes t h a t the f r a c t i o n a l d i s t r i -b u t i o n of v a r i o u s t h i o m o l y b d a t e i s t h e same b o t h i n t h e . s o l u t i o n and on the s u r f a c e s o f the c a t a l y s t . The e q u i l i b -r i u m between t e t r a - t h i o m o l y b d a t e and i t s p r o t o n a t e d form g i v e s :-MoS 2~ + H + = HMoST , 4 4 or [HMoS~] = K [ M o S 2 ~ ] [ H + ] , (Where K i s t h e e q u i l i b -r i u m c o n s t a n t ) . T h e r e f o r e the f r a c t i o n o f a d s o r b e d p r o t o n a t e d t e t r a - t h i o -m o l y b d a t e on the c a t a l y s t s u r f a c e s i s g i v e n by y ' = a 4 [ H + ] / ( k 1 + a 4 [ H + ] ) where c o n t a i n s c o n c e n t r a t i o n s o f a l l t h e o t h e r s p e c i e s . The s t e p ( 3 ) assumes t h a t the amount o f h y d r o g e n on the s u r f a c e s o f the c a t a l y s t i s p r o p o r t i o n a l to the p a r t i a l p r e s s u r e of h y d r o g e n . [ H 2 ] a d s = k 2 C s P • • • ' ( 3 1 ) where C i s the number of a c t i v e s i t e s , s 136 The s t e p (4) assumes t h a t t h e r a t e e q u a t i o n i s e x p r e s s e d by - d P / d t = ' • ' • <32) S u b s t i t u t i o n o f e q u a t i o n (31) i n t o e q u a t i o n (32) y i e l d s •dP/dt = k 2 k 3 C g P . . . . (33) The s t e p (5) assumes t h a t t h e amount o f c a t a l y s t p r o d u c e d i s p r o p o r t i o n a l t o t h e p r o d u c t o f t h e amount o f h y d r o g e n consumed w i t h t h e f r a c t i o n o f p r o t o n a t e d t e t r a -t h i o m o l y b d a t e on t h e c a t a l y s t s u r f a c e e x i s t i n g . Namely dC / d t = eyl (-dP/dt) . . . . (34) s where £ i s t h e c o n v e r s i o n f a c t o r t o r e l a t e t h e p r e s s u r e d r o p i n t o mole/1, when t h e a c t i v e s i t e number i s e x p r e s s e d by mole molybdenum i n t h e p r e c i p i t a t e p e r l i t e r o f s u s p e n -s i o n . I f Y'does n o t v a r y much d u r i n g t h e r e d u c t i o n r e a c t i o n , t h e e q u a t i o n (34) can be i n t e g r a t e d t o g i v e t h e amount o f c a t a l y s t as c s = E Y ' ( P 0 - P ) + C S 0 and s u b s t i t u t i o n i n t o t h e e q u a t i o n (33) y i e l d s t h e e q u a t i o n (26) . When y 1 v a r i e s as t h e r e a c t i o n p r o c e e d s t h e i n t e g r a -t i o n o f e q u a t i o n (34) and (33) becomes d i f f i c u l t b u t q u a l -i t a t i v e l y the v a r i a t i o n o f F i g u r e 34 can be e x p l a i n e d w i t h t h i s mechanism. As the d e p l e t i o n o f molybdenum p r o c e e d s two mole o f ammonium i o n would be consumed to keep the c h a r g e b a l a n c e , making th e pH o f the s o l u t i o n l a r g e r . T h i s c a u s e s a l s o the d e c r e a s e of and y ' w o u l d become i n c r e a s i n g l y s m a l l e r . The s t e p (5) a l s o i n d i c a t e t h a t r u and r a r e H S r e l a t e d to y 1 by r R = 1.5 y ' + (1 - Y') = 1 + 0.5 y ' r s = 3 y < hence r = 1 + 0.16-. r H / S The c o e f f i c i e n t i s i n c l o s e agreement w i t h the one i n equat i o n ( 2 0 ) . The a c t i v a t i o n e n e r g y of 20 k c a l . / m o l e i s r e a s o n -a b l e f o r t h e h e t e r o g e n e o u s a c t i v a t i o n of h y d r o g e n on v a r i o u s c a t a l y s t s u r f a c e s 4. P r e c i p i t a t i o n i n Carbon Monoxide Atmosphere 4-1 R e d u c t i o n p r o d u c t s The a b s o r p t i o n s p e c t r a o f t h e s o l u t i o n s d u r i n g the e x p e r i m e n t s were the same as t h o s e o b s e r v e d i n the e x p e r i m e n t s w i t h h y d r o g e n as shown i n F i g u r e B-4 i n A p p e n d i x B. No new a b s o r p t i o n peak was o b s e r v e d i n the v i s i b l e r a n g e . T h e r e f o r e the s o l u b l e c a r b o n y l complexes of molybdenum, i f t h e y e x i s t e d , were c o n s i d e r e d t o be of v e r y s m a l l q u a n t i t y and s h o r t - l i v e d . As the D.T.A. c u r v e s of t h e p r e c i p i t a t e s ( d i s c u s s e d below) were f o u n d to be s i m i l a r to t h o s e o f the p r e c i p i t a t e from th e h y d r o g e n r e d u c t i o n , no i n s o l u b l e c a r b o n y l complex was c o n s i d e r e d t o form. The s i m p l e c a r b o n y l of molybdenum, Mo(CO)g, was n o t e x p e c t e d t o f o r m s i n c e i t s s y n t h e s i s i s 1 87 p o s s i b l e o n l y under a n h y d r o u s c o n d i t i o n s : . No p r e c i p i t a t e corresponding to t h i s carbonyl was observed. The t o t a l c o n c e n t r a t i o n s o f b o t h molybdenum [Mo]^ and s u l p h i d e , [ S ] ^ , i n the s o l u t i o n d e c r e a s e d as the r e a c t i o n p r o c e e d e d when the i n i t i a l r a t i o , [ S ] T / [ M o ] ^ , was s m a l l . But as can be s e e n i n F i g u r e 37, where [S]^, was p l o t t e d a g a i n s t [Mo] a good l i n e a r i t y was o b s e r v e d t h r o u g h -out the r e a c t i o n , i n d i c a t i n g the e x i s t e n c e of s t o i c h i o m e t r y between molybdenum and s u l p h i d e d u r i n g the p r e c i p i t a t i o n p r o c e s s . F o r t h e d i f f e r e n t i n i t i a l c o n d i t i o n s , t h e s l o p e o f the c u r v e v a r i e d , but l i n e a r i t y was o b s e r v e d . V a r i a t i o n i n the c o m p o s i t i o n of t h e p r e c i p i t a t e s i s a l s o shown by t h e D.T.A. r e s u l t s shown i n F i g u r e 38, where t o t a l s u l p h i d e c o n c e n t r a t i o n was v a r i e d . The peak a r o u n d 550° C. c o r r e s p o n d s to the o x i d a t i o n o f the molybdenum 89 compound to form MoO^ i n agreement w i t h l i t e r a t u r e v a l u e s . The peak a t a round 390° C. i n c r e a s e d as the s u l p h i d e c o n c e n -Fig. 37 VARIATION OF (Mo)T AND (S3 T UNDER CO All curves are in the exothermic scale. Precipitation Conditions S/Mo of precipitates ro 500 psi., 160° C, (Mo)Tj= 0.0 2 M. (S) T i = 0.033 M. />\ /1 \ /» I / ' \ / * \ 2.23 CO n 1 J i \ 500 psi., I60°C. fMo)TI = 0.020 M. CSJT, » 0.01 1 M. i i / i \ /. / \ h \ V 1.67 CO 500 psi, 160° C. (Mo)Ti = 0.020 M. [ S ) T | = 0.023 M. /—i V / / \ / /' V 1.87 CO 500 psi., I 60°C . (Mo)T| = 0.020M. CSJJ, ' 0 . 0 3 3 M ^ ^ _ / ' \ / * \ / ' I I-is \ — / \ I I i i i 200 400 TEMPERATURE ° c . 600 Fig. 38 ai : A. RESULTS t r a t i o n i n c r e a s e d , w h i c h i s i n a g r e e m e n t w i t h t h e i n c r e a s e o f S/Mo r a t i o o f p r e c i p i t a t e s and s u g g e s t s t h e m i x t u r e o f s u l p h i d e and h y d r o x i d e s t a t e d i n s e c t i o n 3-1. 4-2 K i n e t i c s t u d y The mode o f d e c r e a s e o f t h e t o t a l c o n c e n t r a t i o n o f molybdenum a g a i n s t t i m e v a r i e d a c c o r d i n g t o t h e i n i t i a l c o n d i t i o n o f t h e s o l u t i o n . F i g u r e 39 shows t h e r e s u l t s o f a s e r i e s a t h i g h v a l u e s o f i n i t i a l c o n c e n t r a t i o n s o f molybdenum and s u l p h i d e , [ M o ] ^ ^ and [ S ] ^ , where t h e p a r t i a l p r e s s u r e o f c a r b o n m o n o x i d e was v a r i e d . The c u r v e s show a p p r o x i m a t e l y t h e same i n i t i a l i n d u c t i o n p e r i o d f o l l o w e d by l i n e a r d e c r e a s e u n t i l t h e d e p l e t i o n was c o m p l e t e . ,p! F i g u r e 40 shows t h e r e s u l t s o f a s e r i e s a t low [Mo]^_^ and h i g h [ S ] ^ where t h e p a r t i a l p r e s s u r e o f c a r b o n m o n o x i d e was v a r i e d . The c u r v e s show r a t h e r s h o r t i n d u e - ; t i o n p e r i o d s f o l l o w e d by t h e d e p l e t i o n o f t o t a l molybdenum c o n c e n t r a t i o n w i t h a s t e a d y d e c r e a s e o f t h e s l o p e . F i g u r e 41 shows t h e r e s u l t s o f a s e r i e s a t h i g h ,,, [Mo]^,_^ and c o n s t a n t p a r t i a l p r e s s u r e o f c a r b o n m o n o x i d e , where [ S ] T ^ was v a r i e d . The c u r v e s showed l a r g e v a r i a t i o n o f t h e i n d u c t i o n p e r i o d f o l l o w e d by l i n e a r d e c r e a s e o f t o t a l molybdenum c o n c e n t r a t i o n . A t l o w e s t c o n c e n t r a t i o n o f s u l p h i d e s t u d i e d , t h e l i n e a r d e c r e a s e p a r t was n o t e v e n c l e a r w i t h i n t h e e x p e r i m e n t a l p e r i o d . Fig. 40 VARIATION OF CONCENTRATION UNDER CO , LOW (MoU, P VARIES M Lo • CS)T= O.OIIM. • (S) T=0.033M. A « 0.023" A « 0.0 56 " 0 40 80 TIME min. 120 160 Fig.4l VARIATION OF CONCENTRATION UNDER CO, HIGH (Mo)T , ( S ] T VARIES 145 The k i n e t i c s were a n a l y z e d i n two s e c t i o n s , the i n d u c t i o n p e r i o d and the l i n e a r p o r t i o n . The i n d u c t i o n t i m e -was o b t a i n e d by e x t r a p o l a t i n g t h e l i n e a r p o r t i o n back to the i n i t i a l molybdenum c o n c e n t r a t i o n . When the l i n e a r p a r t was not c l e a r , the i n d u c t i o n r e a c t i o n r a t e c o n s t a n t was c a l c u l a t e d by the method d i s c u s s e d below. 4-2-a I n d u c t i o n p e r i o d When [Mo]^ v a l u e s i n the i n i t i a l p a r t were p l o t t e d a g a i n s t t h e s q u a r e o f t i m e , a good l i n e a r i t y was o b s e r v e d , i . e . [ M o ] 0 - [Mo] = ( k t ) 2 . . . . (35) and the i n v e r s e of the r a t e c o n s t a n t , k, was fo u n d to be p r o p o r t i o n a l to t h e i n d u c t i o n t i m e , x, o b t a i n e d by the e x t r a p o l a t i o n method. x « l / k T h e r e f o r e f o r the c a s e s where the l i n e a r p o r t i o n was not c l e a r enough to use the e x t r a p o l a t i o n method, t h e s e r a t e c o n s t a n t s were used f o r t h e a n a l y s i s of the i n d u c t i o n r e a c t i o n . The p r e s s u r e dependence o f the i n d u c t i o n time i s shown i n F i g u r e 42. T h e r e was no a p p a r e n t dependence on t h e p r e s s u r e i n the ran g e i n v e s t i g a t e d . T h e r e f o r e the i n d u c -t i o n p e r i o d i s c o n c l u d e d n o t to depend on the r e d u c t i o n r e a c t i o n by c a r b o n monoxide. 146 The s u l p h i d e c o n c e n t r a t i o n v a r i e d the i n d u c t i o n p e r i o d g r e a t l y as i s shown i n F i g u r e 43. T h i s showed r o u g h l y t h a t k ex [ S ] T , or T oc l/[s] T . . . . (36) The p r e c i p i t a t i o n u nder n i t r o g e n a t m o sphere f o l l o w s e q u a t i o n ( 1 8 ) . Thus the i n i t i a l r a t e o f p r e c i p i t a t i o n u n der n i t r o g e n i s g i v e n by s u b s t i t u t i n g t h e i n i t i a l c o n -c e n t r a t i o n of molybdenum, namely, ( - d [ M o ] T / d t ) 0 = k M [ M o ] e [ S ] e ( [ M o ] Q - [ M o ] e ) The t i m e At r e q u i r e d to y i e l d a c o n s t a n t amount A[Mo] o f p r e c i p i t a t e a t t h i s r a t e i s g i v e n by At = A [ M o ] T / ( - d [ M o ] T / d t ) 0 = { A [ M o ] _ / k M [ M o ] o ( [ M o ] n - [Mol ) } / [ S l - 1 / [ S ] _ I M e U e e Te w h i c h i s o f the same form as e q u a t i o n ( 3 6 ) . T h e r e f o r e the i n d u c t i o n p e r i o d i s c o n c l u d e d to be c a u s e d by the slow p r e c i p i t a t i o n of c a t a l y s t w i t h the same r e a c t i o n s t a t e d i n P a r t 2, s e c t i o n 2. 0 1 0 induction time 5f-mm. 1 4 7 0 I 1 1 1 i o 2 0 pco a t m ' 4 0 Fig.42 INDUCTION PERIOD, VS. PRESSURE 0 10 20 30 40 ( S l T ml. ot the stock solution added Fig.43 INDUCTION PERIOD, k vs. (S)T 148 4-2-b Growth ( l i n e a r p o r t i o n ) 4 - 2 - b - l E f f e c t o f s u l p h i d e c o n c e n t r a t i o n The i n i t i a l s u l p h i d e c o n c e n t r a t i o n a l s o v a r i e d t h e s l o p e of the l i n e a r p o r t i o n , r a t e , o f the r a t e c u r v e . But when the r a t e was p l o t t e d a g a i n s t the i n d u c t i o n r e a c t i o n r a t e c o n s t a n t , k, f o r t h e s e r i e s where o n l y t h e s u l p h i d e c o n -c e n t r a t i o n was v a r i e d , a good l i n e a r i t y was o b s e r v e d , as shown i n F i g u r e 44.. T h e r e f o r e i t was c o n c l u d e d t h a t the s u l p h i d e c o n c e n t r a t i o n v a r i e s o n l y the amount and q u a l i t y of c a t a l y s t p r o d u c e d d u r i n g the i n d u c t i o n p e r i o d and has no d i r e c t e f f e c t on the l i n e a r p o r t i o n , i . e . , the growth p a r t . I n o t h e r words, s u l p h i d e i o n does n o t come i n t o t h e r a t e d e t e r m i n i n g s t e p . 4-2-b-2 E f f e c t o f p a r t i a l p r e s s u r e o f c a r b o n monoxide The e f f e c t o f p a r t i a l p r e s s u r e o f c a r b o n monoxide on the r a t e was s t u d i e d under v a r i o u s c o n d i t i o n s . When the s l o p e s o f the l i n e a r p o r t i o n o f the s e r i e s w i t h h i g h i n i t i a l c o n c e n t r a t i o n o f molybdenum and s u l p h i d e and the i n i t i a l s l o p e s o f the s e r i e s o f the low i n i t i a l c o n c e n -t r a t i o n o f molybdenum were p l o t t e d a g a i n s t the p a r t i a l p r e s -s u r e o f c a r b o n monoxide, a n o n - l i n e a r dependence was o b s e r v e d a p p r o a c h i n g some l i m i t i n g v a l u e a t h i g h p r e s s u r e r e g i o n as shown i n F i g u r e 46. T h i s t y p e o f c u r v e s may be e x p e c t e d to f o l l o w t h e r e l a t i o n s h i p , r a t e = B ^ / C l + B 2 P ) (37) RATE 149 0 10 20 30 k minT Fig. 44 R A T E vs. I N D U C T I O N P E R I O D I M O I T RATE mm. x 10 r l o £ 0 = 200 psi. o Q 400 A 700 • A — " " A " " ~ A 1 I 0 0.2 0.4 0.6 (McOj M . x | 0 3 Fig.45 EFFECT OF [Molj ON RATE , I60°C. 0.8 1.0 150 t h u s 1 / r a t e = ( B 2 / B ] L ) ( i / P ) + ( l / B ^ F i g u r e 47 shows t h e p l o t o f 1 / r a t e a g a i n s t 1/P. A good l i n e a r i t y i s o b s e r v e d i n t h i s p l o t , i n d i c a t i n g a dependence of the r a t e on p a r t i a l p r e s s u r e o f c a r b o n monoxide as g i v e n i n e q u a t i o n ( 3 7 ) . The c a l c u l a t e d v a l u e s o f B^ and B 2 a r e a l s o l i s t e d i n T a b l e A-4 i n A p p e n d i x A. 4-2-b-3 E f f e c t of t o t a l molybdenum c o n c e n t r a t i o n When [ S ] ^  i s v e r y l a r g e compared to [Mo]^, a s l i g h t v a r i a t i o n i n [Mo]^ does n o t change a p p r e c i a b l y the c o n c e n t r a -t i o n o f f r e e s u l p h i d e . C o n s e q u e n t l y the d e g r e e o f complex-i n g does n o t change a p p r e c i a b l y i n such a c a s e . T h e r e f o r e the e f f e c t o f the t o t a l molybdenum c o n c e n t r a t i o n was i n v e s t i -g a t e d under such c o n d i t i o n s . In S e r i e s C i n T a b l e A-4-1 i n A p p e n d i x A, where the p a r t i a l p r e s s u r e o f c a r b o n monoxide was v a r i e d , [S]^, = 0.022 M. , and.[Mo] = 0.0010 ~ 0.0008 M. Hence, the con-,, d i t i o n s t a t e d above was f u l f i l l e d . The i n i t i a l r a t e d e t e r m i n e d a t P c o = 20.4 atm. was the r e s u l t from [Mo] = 0.0008 M. The i n t e r p o l a t e d v a l u e o f the i n i t i a l r a t e a t P ^ = 20.4 atm. f r o m th e r e s u l t s of a s e r i e s o f e x p e r i m e n t s w i t h [Mo]^ = 0.0010 M., i s compared i n the t a b l e below. Fig.46 GROWTH UNDER CO, RATE vs. PRESSURE 152 0 5 1/ P C Q 10 atrrc' x IO2 15 Fig.47 I/RATE vs. I / P r n PLOT 153 [ M o ] T I n i t i a l Rate k' M. x 1 0 3 M. • - 1 i n 5 min. x 10 min. ^ x 10^ 0.8 1 . 44 ( f o u n d ) 1. 80 1.0 1 . 81 ( i n t e r p o l a t e d ) 1.81 where k' = ( I n i t i a l R a t e ) / [ M o ] T F a i r agreement i s n o t e d f o r the f i r s t o r d e r r a t e c o n s t a n t c a l c u l a t e d , i n d i c a t i n g the pseudo f i r s t o r d e r dependence o f the r a t e on the t o t a l molybdenum c o n c e n -t r a t i o n when the s u l p h i d e c o n c e n t r a t i o n was i n l a r g e e x c e s s . The dependence o f the r a t e on the m olybdenum c o n -c e n t r a t i o n was f u r t h e r s t u d i e d by a n a l y z i n g the r a t e c u r v e s o f the s e r i e s o f h i g h s u l p h i d e to molybdenum r a t i o . When ([ M o J ^ / R a t e ) was p l o t t e d a g a i n s t [Mo]^ f o r the P s e r i e s , where [Mo]^ and R ate = (-d [Mo ] ^ ,/dt) a r e the i n s t a n t a n e o u s v a l u e s , good l i n e a r i t y was o b s e r v e d w i t h a l l the l i n e s a t -v a r i o u s p r e s s u r e s h a v i n g a c o n s t a n t i n t e r c e p t as shown i n F i g u r e 45. T h e r e f o r e the r a t e e q u a t i o n f o r t h i s s e r i e s was assumed to be [ M o ] T / ( - d [ M o ] T / d t ) = a + b [ M o ] T or - d [ M o ] / d t = C [ M o ] T / ( a + b [ M o ] T ) 154 The I n t e g r a t i o n g i v e s Y = l n [Mo] + a t = -b [ M o ] T + c o n s t a n t The l e f t - h a n d s i d e was c a l c u l a t e d by p u t t i n g a = 0.11 min. o b t a i n e d from F i g u r e 45, and p l o t t e d a g a i n s t [Mo]^ to o b t a i n the s l o p e b. The v a l u e s of the s l o p e b were f o u n d to be p r o p o r t i o n a l to the i n v e r s e of p r e s s u r e . The p l o t t i n g s a r e shown i n F i g u r e 48 . T h e r e f o r e the r a t e e q u a t i o n i s g i v e n by, -d [ M o ] T / d t = [ M o ] T / [ a + ( b ' / P ) [ M o ] T ] . . . . (38) where b 1 i s a c o n s t a n t . F o r the i n i t i a l r a t e e q u a t i o n (38) i s r e d u c e d to e q u a t i o n (39). ( - d [ M o ] T / d t ) i = [ M o ] T i P / ( a P + b ' [ M o ] T ± ) . . . . (39) 4-3 D i s c u s s i o n The e x p e r i m e n t a l o b s e r v a t i o n s a r e shown by e q u a t i o n (35) to (38). A mechanism c o n s i s t e n t w i t h the above o b s e r v a t i o n s f o r growth i s p r o p o s e d as f o l l o w s : ( i ) F a s t e q u i l i b r i u m between v a r i o u s molybdenum com-p l e x e s MoO S 2~ + H„S t MoO ,S2~ f , v + H_0 n 4-n 2 n-1 4 - ( n - l ) 2 155 156 ( i i ) F a s t and s t r o n g a d s o r p t i o n e q u i l i b r i u m o f a molybdenum complex and c a r b o n monoxide on c a t a l y s t surfaces, C g, 2- 2-C c + MoO S. [MoO S. ] b n 4-n n 4-n J , ad s C_ + CO CO , s aq ads ( i i i ) F a s t e q u i l i b r i u m between a d s o r b e d s p e c i e s to form an a d d u c t 2- 2-[MoO S. ] , + CO , [MoO S. ••• CO] . n 4-n ads ads n 4-n ads ( i v ) Slow d e c o m p o s i t i o n of the a d d u c t [MoO S2~ ••• CO] i C 2 ~ + C 0 o n 4-n s 2 ads (v) R a p i d n e u t r a l i z a t i o n to c a u s e t h e growth of the p r e c i p i t a t e s . The r a t e of molybdenum p r e c i p i t a t i o n g i v e n from the above a s s u m p t i o n i s -d [Mo] / d t = k [MoO S? ••• CO] . . . . (40) T n 4-n ads 2-The s t r o n g a d s o r p t i o n e q u i l i b r i u m between ^ a d s ' ^ ° ^ n ^ 4 - n ^ a d s and [MoO S?~ . . . CO] , y i e l d s n 4-n ads 1 5 7 [MoOnS^- •••C0] a d s = C se M C O[MoO N S 4?n — C O ] / ( W C O + n M[MoO n S^?n 1 +niC0 [ M o 0n sU-n •••C°]) ...» (hi) a s s u m i n g the Langmuir t y p e o f a d s o r p t i o n , where n's a r e a d s o r p t i o n c o e f f i c i e n t s . The e q u i l i b r i u m a t the s t e p ( i i ) and ( i i i ) g i v e s [MoO S. ••• CO] = K 1 [MoO S. ] P . . . . (42) n 4-n n 4-n co where K 1 i s an e q u i l i b r i u m c o n s t a n t . U s i n g the f r a c t i o n a l d i s t r i b u t i o n o f s p e c i e s , [MoO S, ] i s n 4-n r e l a t e d to the t o t a l c o n c e n t r a t i o n o f molybdenum by . [MoO S ] = a [Mo] . . . . (43) n 4-n n 1 S u b s t i t u t i o n of e q u a t i o n s ( 4 1 ) , (42) and (43) i n t o (40) y i e l d s : -d [Mo] T/dt = kC s M C 0 K a n [ M o ] T P C 0 Aacopco + n' M°nf M o^ + nM^a n[Mo] TP C 0) ..(kk) 158 For l a r g e v a l u e s o f [Mo]^ the f i r s t term i n the denomin-a t o r i s n e g l i g i b l e v e r s u s o t h e r s and e q u a t i o n (44) r e d u c e s t o -a [Mo] T/dt = ( k c se I C 0K)P C 0/(ri M + n McoKP C O) w h i c h i s e q u i v a l e n t to the e q u a t i o n ( 3 7 ) . F o r low v a l u e s of [Mo]^, the l a s t term i n the d e n o m i n a t o r i s n e g l i g i b l e v e r s u s o t h e r s and e q u a t i o n (44) r e d u c e s to -d [ M o ] T / d t = ( k C s £ M C 0 ^ n ) P C 0 [ M o ] T / ( n C 0 p C 0 + N MV M O ]T) w h i c h i s e q u i v a l e n t to the e q u a t i o n ( 3 8 ) , ( 3 9 ) . The a c t u a l [MoJ^-time c u r v e i s the r e s u l t o f the c o m b i n a t i o n of the molybdenum d e p l e t i o n by a) the c a t a l y s t p r o d u c t i o n p r o c e s s , w h i c h w i l l be d e n o t e d , and by b) the c a t a l y t i c r e d u c t i o n p r o c e s s w h i c h w i l l be d e n o t e d M 2. i . e . , i n i t i a l t o t a l molybdenum = f M ] T i = I M ] + [M-^] + t M 2 The r a t e e q u a t i o n s o b t a i n e d f o r (a) and (b) a r e i n s i m p l i f i e d forms , dM 1 = k (M - M ) . . . . ( 4 5 ) d t i u i dM 2 C [M] P = k_ . . . . ( 4 6 ) dt P + k 3 [M] + k^ [M] P I f we assume Cs = y " w h e r e y"= shape f a c t o r the e q u a t i o n s ( 4 5 ) and ( 4 6 ) can be combined to g i v e the r a t e e q u a t i o n f o r the molybdenum c o n c e n t r a t i o n i n aqueous p h a s e : -d[M] dM dM = - + -dt dt d t Y'M1 [M] P k (M - M ) + k 1 V 1 0 1J 2 k l M 1 0 e _ k l t + k 2 Y " M 1 0 ( 1 - e'^) . . . . ( 4 7 ) P + k 3 [M] + k 4 [M] P [M] P P + k 3 [M] + k 4 [M] P F o r l a r g e v a l u e s of [M] and s m a l l v a l u e s of t , e q u a t i o n ( 4 7 ) i s r e d u c e d , on e x p a n s i o n , to 160 d [M] P - k l M 1 0 + k l M 1 0 ( k 2 Y"- k l } t d t X 1 i U Z k + k P 1 T h i s i s the same form as e q u a t i o n ( 3 5 ) , i f the f i r s t term, - k i t i . e . , k^, i s s m a l l . F o r l a r g e v a l u e s o f t , e 1 - 0, thus , d [M] [M] P = k„ y-'M. d t 2 P + k 3 [M] + k 4 [M] P 1 0 i n agreement w i t h the o b s e r v e d r a t e e q u a t i o n . The a s s u m p t i o n o f a d s o r b e d a d d u c t o f t h i o m o l y b d a t e s and c a r b o n monoxide i n the s t e p ( i i i ) i s r e a s o n a b l e i n view of the e x i s t e n c e of v a r i o u s organq-molybdenum complexes 8 7 c o n t a i n i n g c a r b o n monoxide as a l i g a n d . H a l v e r s o n a l s o p o s t u l a t e d the a d s o r b e d a d d u c t o f c o b a l t i c ammine w i t h c a r b o n monoxide i n h i s s t u d y o f the r e d u c t i o n o f c o b a l t i c 8 8 s u l p h a t e s o l u t i o n w i t h c a r b o n monoxide 161 GENERAL SUMMARY AND CONCLUSION 1. E q u i l i b r i u m s t u d y of molybdenum (VI) - s u l p h u r (-II) -water s y s t e m was made a t 120° and 150°C. S p e c i e s o f 2-the form MoO. S e x i s t e d f o r a l l v a l u e s o f x between 1 4-x x and 4, a l t h o u g h m o n o - t h i o m o l y b d a t e was l e s s s i g n i f i c a n t a t a l l r a n g e s of aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n . Rough e s t i m a t i o n of thermodynamic p a r a m e t e r s i n d i c a t e d t h a t exchange o f o x i d e i o n i n the m o l y b d a t e i o n w i t h s u l p h i d e i o n c a u s e s a s t r o n g c o v a l e n t bond f o r m a t i o n y i e l d i n g n e g a t i v e e n t h a l p y o f exchange and p o s i t i v e e n t r o p y p r o d u c t i o n w h i c h may n o t be compensated by the n e g a t i v e d i f f e r e n c e i n e n t r o p y between aqueous h y d r o g e n s u l p h i d e and w a t e r . 2. In t h e . i n e r t a tmosphere a t e l e v a t e d t e m p e r a t u r e the t h i o m o l y b d a t e s y s t e m was not s t a b l e and decomposed to a p p r o a c h e q u i l i b r i u m . T h e r e was an i n d i c a t i o n o f r e d u c t i o n of molybdenum by s u l p h i d e i o n i n the ammoniacal a l k a l i n e s o l u t i o n . 3. Under h y d r o g e n atmosphere the r e d u c t i o n r e a c t i o n was f o u n d to be a u t o c a t a l y t i c , r a t e b e i n g f i r s t o r d e r i n the amount of molybdenum w h i c h has l e f t s o l u t i o n and h y d r o g e n p r e s s u r e . A mechanism was s u g g e s t e d i n w h i c h the r a t e determining s t e p was the a c t i v a t i o n o f the a d s o r b e d h y d r o g e n on the s u l p h i d e p r e c i p i t a t e s , f o l l o w e d by two a l t e r n a t i v e p a t h s , one to p r o d u c e s u l p h i d e i n w h i c h molybdenum was t r i - v a l e n t and the o t h e r to p r o d u c e o x i d e 162 i n w h i c h molybdenum was t e t r a - v a l e n t . The s u l p h i d e p r o d u c e d by the f o r m e r p a t h was c o n s i d e r e d c a t a l y t i c a l l y a c t i v e and the p r o p o r t i o n o f s u l p h i d e to o x i d e i n the p r o d u c t was de-t e r m i n e d by t h e s o l u t i o n c o n d i t i o n s . 4. Under t h e c a r b o n monoxide atmosphere the r e d u c t i o n r e a c t i o n was f o u n d to have an i n d u c t i o n p e r i o d f o l l o w e d by a l i n e a r d e c r e a s e i n c o n c e n t r a t i o n . A mechanism i s s u g g e s t e d i n w h i c h the i n d u c t i o n p e r i o d p r o d u c e s a c a t a l y s t . T h i s c a t a l y s t i s t h e n a c t i v e f o r a main r e a c t i o n where slow d e c o m p o s i t i o n of a d d u c t s between s t r o n g l y a d s o r b e d t h i o m o l y -b d a t e s and c a r b o n monoxide was r a t e d e t e r m i n i n g . The c a t a -l y s t amount was c o n s i d e r e d n o t to change s i g n i f i c a n t l y d u r i n g the main r e a c t i o n . 163 SUGGESTED FUTURE WORK 1. Use o f the t r i - and t e t r a - t h i o m o l y b d a t e c o u p l e as an i n d i c a t o r of aqueous h y d r o g e n s u l p h i d e c o n c e n t r a t i o n (a) D e t e r m i n a t i o n o f thermodynamic p r o p e r t i e s o f aqueous h y d r o g e n s u l p h i d e at e l e v a t e d t e m p e r a t u r e s i s p o s s i b l e by the e x p e r i m e n t a l method d e s c r i b e d i n P a r t 1, a f t e r d e t e r m i n i n g more a c c u r a t e l y the c o n s e c u t i v e c o n s t a n t k^ a t v a r i o u s t e m p e r a t u r e s . (b) S o l u b i l i t y p r o d u c t s of heavy m e t a l s u l p h i d e s a t e l e v a t e d t e m p e r a t u r e s can be d e t e r m i n e d by measur-i n g the a c t i v i t y of aqueous h y d r o g e n s u l p h i d e by a d d i n g s m a l l amount of molybdenum to the s o l u t i o n s . In t h i s c a s e the i n v e s t i g a t i o n of c o - p r e c i p i t a t i o n of molybdenum w i t h heavy m e t a l may be r e q u i r e d . 2. C a t a l y t i c m a t e r i a l p r o d u c e d d u r i n g the h y d r o -gen and c a r b o n monoxide r e d u c t i o n may be w o r t h i n v e s t i g a t i o n f o r t h e i r n a t u r e s as a g e n e r a l h y d r o g e n a t i o n c a t a l y s t . 3. S t r i p p i n g o f molybdenum from the s o l u t i o n by the method was f o u n d c o m p l e t e . Thus the s t u d y o f the p o t e n t i a l of t h i s s y s t e m f o r the p r o c e s s i n g i n molybdenum i n d u s t r y can be w o r t h w h i l e . 4. 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Chem., 5_4 (516) (1967) 229 ; CA 6_7 48779w. 57. M u e l l e r , A. and E k k e h a r d , D., Z. Chem., 8 (5) (1968) 197; CA 6>9 30182c. 58. H o f m e i s t e r , H.K. and Gattow, G., N a t u r w i s s . , 4_7 (1960) 466 ; CA 55. 5076f. 59. M u e l l e r , A. and Gattow, G., Z. A n o r g . A l l e g . Chem. 348 (1-2) (1966) 71; CA 66 41982c. 60. L e r o y , M.J.F. and Kaufman, G., CR, Ac a d . S c i . , P a r i s , S e r . C, 26_5 (1967) 1322 ; CA 68 34488J . 61. H o f m e i s t e r , H.K. and G l e m s e r , 0., Angew. Chem., 7JL (1960) 584. 62. B e r n a r d , J.C. and T r i d o t , G., B u l l . S c i . Chim. F r a n c e , 1961 818. 63. L e r o y , M.J.F., Kaufman, G. and Rohmer, R., B u l l . S c i . Chim. F r a n c e , 1967 (10) 3640 ; CA 68_ 34418m. 64. S r i v a s t a v a , M.H.N, and Ghosh, S., P r o c . N a t l . A c a d . S c i . I n d i a , S e c t . A 29^  p t . 2 , (1960) 181; CA 55. 101721. 65. Saxena, R.S., J a i n , M.C. and M i t t a l , M.L., A u s t . J . Chem., 21 (1) (1968) 91; CA 68 72831y. 66. Z v o r y k i n , A. Ya., P e r e l ' m a n , F.M. and T a r a s o v , V.V., R u s s i a n J . I n o r g . Chem., j6 (9) (1961) 1021. 67. S r i v a s t a v a , M.H.N, and Ghosh, S., P r o c . N a t l . A c a d . S c i . I n d i a , Sec. A 29 p t . 2 , (1960) 178 ; CA 55. 101721. 68. A r u t y u n y a n , L.A. and K h u r s h u d y a n , E.Kh., Geochem. I n t e r n a t i o n a l , 1966, 479. 169 69. T r a i l l , R . J . , Canad. M i n e r , 7_ (3) (1963) 524. 70. W y c k o f f , R.W.G., I b i d . , v. 1, p. 280. 71. B e l l , R.E. and H e r f e r t , R.E., J . Amer. Chem. S o c , _79 (13) (1957) 3351. 72. Z e l i k m a n , A.N., C h i s t y a k o v , Yu.D.', Indenbaum, G.V. and K r e i n , 0.E., K r i s t a l l o g r a f i y a , 6 (3) (1961) 389 ; CA 57 5391e. 73. S p e n g l e r , G. and Weber, A., Chem. B e r . , 9\2 (1959) 2163 ; CA 5_4 873e. 74. ° R o m a n o v s k i , W., R o c z n i k i Chem., 3_7 (9) (1963) 1077 ; CA 60 6 4 6 7 f . 75. B j e r r u m , J . , " M e t a l Ammine f o r m a t i o n i n Aqueous S o l u -t i o n , " P. H a s s e and Son, C o p e n h a g e n , (1957) p. 14. 76. R o s s o t t i , F . J . C . and R o s s o t t i , H., "The D e t e r m i n a t i o n o f S t a b i l i t y C o n s t a n t s , " M c G r a w - H i l l , New Y o r k , ( 1 9 6 1 ) , Chap. 5. 77. B u c h w a l d , H. and R i c h a r d s o n , E., T a l a n t a , 9_ ( 1 9 6 2 ) 613. 78. M u e l l e r , A., R i t t e r , W., and N a g a r a j a n , G., Z. P h y s . Chem. N.F., 5_4 (1967) 229. T h i s work g i v e s a d i f f e r e n t v a l u e o f m o l a r e x t i n c t i o n c o e f f i c i e n t o f t e t r a -t h i o m o l y b d a t e a t 467 my. i 79. R o s s o t t i , F . J . C . , "Modern C o o r d i n a t i o n C h e m i s t r y " Ed. by L e w i s , J . and W i l k i n s , R.G., I n t e r s c i e n c e , New Y o r k , ( 1 9 6 0) C h a p t e r 1. 80. W o l f b e r g , M. and H e l m h o l z , L. , J . Chem. P h y s . , 20_ (1952) 837 . 81 . L a t i m e r , W.M., " O x i d a t i o n P o t e n t i a l " , 2nd ed. P r e n t i c e -H a l l , N.Y. ( 1 9 5 2 ) . 82. F r a n k , H.S. and Wen, W.Y., D i s c . F a r a d a y S o c , 2j4, (1957) 133 . 83. C h i y a , T., " M u k i k a g a k u " v . 2, S a n g y o t o s h o . T o k y o , ( 1 9 5 9 ) p. 862. 84. McAndrew, R.T., PhD. T h e s i s , The U n i v e r s i t y o f B r i t i s h C o l u m b i a , ( 1 9 6 2 ) . 169a 85. H a l p e r n , J . , Q u a r t . Rev. Chem. S o c . , ( L o n d o n ) 1_0 (1956) 463. 86. B e e c k , 0., D i s c u s s . F a r a d a y S o c , 8> ( 1 9 50) 118. 87. C o a t e s , G.E., " O r g a n o m e t a l l i c Compounds' 2nd e d . J o h n W i l e y and S o n s , New Y o r k ( 1 9 60) p. 268. Z e i s s , H. ed . ' O r g a n o m e t a l l i c C h e m i s t r y ' R e i n h o l d Pub. Co., New Y o r k ( 1 9 6 0 ) . 88. H a l v o r s o n , H., PhD. T h e s i s . The U n i v e r s i t y o f B r i t i s h C o l u m b i a , ( 1 9 6 6 ) . 89. D u v a l , C , " I n o r g a n i c T h e f o m o g r a v i m e t r i c A n a l y s i s , " E l s e v i e r P r e s s , I n c . , H o u s t o n , T e x a s , ( 1 9 5 3 ) . 170 A P P E N D I X APPENDIX A E x p e r i m e n t a l D a t a T a b l e A - l The Study o f Eq u i l i b r i u m T a b l e A - l - 1 A n a l y t i c a l D a t a S e r i e s A. 1 5 0 ° C , [NH ] = 1 M., [NH. ] = 1 M. , ( n o m i n a l C o n c e n t r a t i o n ) No . Mo M. x l O 3 S T M. x l O 3 a 3 a 4 A 3 1 5 2 M - l " I M. ,cm. xlO -4 n S f M. x l O [H S] M? 3 q x l O 3 a 2 c a l c d . 22 0 . 49 12. 73 0 . 233 0.105 0 .221 1.54 11 .98 1.89 3 0 . 231 3 .97 12 . 26 . 216 .091 . 208 1.47 10 .83 1. 711 .234 4 1.47 12 . 23 . 201 .076 .208 1.41 10 .16 1. 605 .234 5 2 .13 12 .13 . 181 . 060 .188 1.32 9 . 32 1.473 . 231 32 0 .50 5 . 36 0 . 098 0.020 0 .148 0 . 84 4.94 0.781 0 .138 3 1.05 5 . 87 . 088 .014 .138 . 78 5 .05 .798 . 142 4 1.61 5 . 90 .073 .012 .125 .69 4 .79 . 757 . 132 6 2 . 69 6 . 03 . 060 .008 .113 .59 4.44 . 702 .119 4 2 0.50 23.81 0.329 0.327 0 .110 3 ,16 22.23 3 .512 0. 152 3 1.01 24 . 38 . 334 . 311 .123 3.10 21 . 25 3 . 358 . 159 4 1.54 24 . 28 .323 . 291 .132 3.03 19 .61 3.098 . 172 5 2 .07 24 .14 .314 . 256 . 151 2.93 18 .07 2 .855 . 185 72 2 . 008 2 .82 0.017 0.001 0.054 0.4 7 1. 88 0.297 0. 028 3 1.973 5 . 84 . 063 .010 .115 .60 4 .66 .736 . 127 82 0 . 998 2 .49 0 .017 0.001 0.052 0 .47 2 .02 0 .319 0 .032 3 .930 5 . 39 . 065 .011 . 121 .61 4.82 . 762 . 134 4 .880 7 . 38 . 125 . 031 . 171 1.06 6 .45 1.019 .186 5 .871 • 10.47 . 207 . 079 .212 1.42 9.23 1.458 .230 6 .854 14 . 37 . 282 .145 . 229 2.07 12 .60 1.991 . 228 • 7 .828 16 .93 .319 .199 .224 2.52 14.84 -2.345 . 212 8 .821 19.84 .334 . 250 . 195 2.82 17 .52 2 .768 . 189 9 .817 22.44 . 340 . 286 . 172 2.99 20 . 00 3 . 160 . 169 172 SERIES B 150°C, [NH 3] = 0.5 M. , [NH*] = 1 M. (Nominal C o n c e n t r a t i o n s ) No . [Mo] M. 1 xlO [ s ] T M ' 3 xlO a 3 a 4 7 3 1 5 _ A2 _ 2 M.x cm. x l 0 - 4 n [ S ] f M xlO x l O 3 <*2 c a l c d . 92 0. 995 2.41 0.043 0 . 003 0.098 0.57 1.84 0 . 440 0.057 3 . 916 5.40 .163 .044 . 194 1.13 4.37 1.044 . 196 4 .946 8.44 .253 . 104 . 237 1.79 6.75 1.613 .234 5 .956 11 .38 . 301 .172 .226 2 . 58 8 .91 2 .129 . 22 3 6 . 944 14.26 . 327 .235 . 203 2.80 11.62 2 .777 . 189 7 . 912 17 . 23 . 337 . 295 . 172 3 .10 14 .40 3.442 .155 8 .910 19 . 80 . 322 .326 .146 3.21 16 .88 4 .034 . 130 9 .882 22 . 16 .316 .355 .124 3 . 29 19 . 26 4 .603 . 110 SERIES C 120°C, [NH 3] = 1 M., [NH*] = 1 M. (Nominal C o n c e n t r a t i o n s ) No . [Mo] M. xlO [s] T M. xlO a 3 a 4 -315 M. cm. x x l 0 - 4 n [S] M ' 3 xlO 52 0.465 8.16 0 . 215 0 .060 0.192 1.83 7 .31 3 . 865 6 . 30 . 116 .029 . 170 1 .28 5 .19 4 1.407 4.68 - .053 . 008 . 108 .89 3 .43 5 2 .000 4 . 38 .038 .004 .089 . 84 2 . 70 62 0.498 _ 0.319 0 . 285 0 .136 2.61 _ 3 1. 019 - .322 .279 . 151 2 .61 -4 1.494 - .324 . 262 .172 2 . 51 -5 2 . 000 - .320 . 242 . 200 2.43 -122 1.036 3.44 0 . 018 0.004 0.065 0. 81 2 .60 3 1.068 6.64 .095 . 027 . 139 1.15 5.41 4 1.028 10 . 39 . 178 .073 .186 1.62 8.73 5 . 967 14 .10 .246 .130 . 201 1.97 12 .20 6 . 852 17 . 21 . 295 . 193 .191 2 .33 15 .22 7 . 742 20 .78 .328 .257 .175 2 .50 18 .93 8 .671 24 . 28 . 351 . 331 . 133 2.66 22.50 173 TABLE A - l - 1 Study of E q u i l i b r i u m ( c o n t i n u e d ) SERIES D 150°C. N o m i n a l R a t i o (NH 3)/(NH+) = 0.1/1 No . Mo M. xl O S T M. x l 0 J a 3 a 4 x 3 1 5 A 2 n ' 3 x l O M 2 3 q ' 3 xlO" 3 102 1.054 2 . 34 0.095 0 . 013 0.177 0.82 1.48 0 . 75 3 1.051 4.75 0.201 0.076 0.255 1.42 3 .26 1.66 4 1.044 7.17 0 .195 0 .114 0 . 266 3.06 3.97 -5a 1.031 9 .32 - 0.138 - 3.93 5 . 27 -6a 1. 021 13.48 - 0.136 - 4 .18 9 . 21 7a 1.010 11.59? - 0 .133 - 4.26 10.40 -112 1 .024 2 . 58 0.100 0 . 018 0. 186 0 . 88 1.68 0.85 3 1. 015 3 .76 0 . 206 0.080 0.258 1.42 2 . 32 1.18 4 1 .009 7 .61 0 . 198 0. 114 0 . 242 2 . 98 4.60 -5 a 0.990 9 .76 - 0. 138 - 3 .99 5.81 -6a 0 . 988 12.06 - 0 .133 - 4 . 10 8 .10 -7a 0 .985 14 .80 - 0. 130 - 4 .14 10 .73 -8 a 0.985 16.00 - 0 . 127 - 4.15 11.92 -9.a 0 .985 18.76 0 . 124 4 .17 14.66 a - Too much i n t e r f e r e n c e was o b s e r v e d p r o b a b l y due t o the a p p e a r a n c e of p r o t o n a t e d s p e c i e s , and 0:3 and A 2 3 ^ ^ c o u l d n o t be o b t a i n e d . T h e r e f o r e n was c a l c u l a t e d by u s i n g 014 and Srn w i t h s u c c e s s i v e a p p r o x i m a t i o n . But the v a l u e s o b t a i n e d f o r n were r a t h e r d o u b t f u l s i n c e a4 might a l s o c o n t a i n t h e i n t e r f e r e n c e s t a t e d above. 174 TABLE A - l - 2 C a l c u l a t i o n of the C o n v e r s i o n F a c t o r 1. N T v s . l C r p l o t , F i g u r e 6a T e m p e r a t u r e °C. [ N H 3 ] / [ N H + ; M./M. No . pH N T M. 1 0 P H o x l O " 9 [NH ] MT [NH +] M. 150 1/1 8-h 9 . 61 1.557 4.07 0 . 746 0 .811 8-c 9.62 1. 581 4.17 0.770 0.811 0.5/1 9-h 9 . 38 1. 256 2.40 0 . 445 0 . 811 9-c 9 . 39 1.270 2.46 0.459 0. 811 0.1/1 10-h 8 . 82 0. 946 0 .66 0 .135 0 . 811 11-h 8.89 0 .938 0.78 0 .125 0.811 120 1/1 5-h 9.46 1.363 _ 0.542 0 . 821 5-c 9 .43 1.375 - 0.524 0.851 6-h 9 .62 1. 525 - 0 .745 0 .780 6-c 9 .66 1. 640 - 0 . 840 0 . 800 12-h 9 . 70 1.65 — 0 .88 0 .77 pH was measured a t room t e m p e r a t u r e . 'h' and ' c ' i n column 3 mean the sample t a k e n from e x p e r i m e n t a l t e m p e r a t u r e s and t h e sample t a k e n a f t e r s y s tems were c o o l e d to room t e m p e r a t u r e , r e s p e c t i v e l y . 2 - [ N H 4 ] / [ N H 3 ] v s . [S] £[NH,, ]/[NH 3] p l o t , F i g u r e 6b. n [ N H 3 J / [ N H 4 ] ( n o m i n a l ) M./M. ! S ] f M. x l O [NH 3] M. [NH+] M. [ N H 4 ] / [ N H 3 ] 'Sf [ N H 4 ] / [ N H 3 ] M. x l O 3 1.42 1/1 9.2 0 .746 0 .811 1.09 10.0 0.5/1 5 . 3 0.445 0 .811 1. 82 9.6 0 . 1/1 2 . 8 0 .135 0 . 811 6 . 0 16 . 3 0.85 1/1 5.5 0 . 746 0 .811 1.09 6.0 0.5/1 3.3 0.445 0.811 1. 82 6 . 0 0 .1/1 1.6 0 .135 0.811 6 . 0 9.4 1 7 4 a 3. C o n v e r s i o n E q u a t i o n [ H 2 S ] a q = [ S ] f / ( 1 + m I N H t ] ) ' From the p l o t s (1) and ( 2 ) , m = 5.8, and c o n s e q u e n t l y : A: N o m i n a l B: N o m i n a l D: N o m i n a l [ N H 3 J / [ N H j ] = 1/1 ; [ N H 3 ] / [ N H 4 ] = 0.5/1; [NH 3J/[NH^] = 0.1/1; [ H 2 S ] a q = ° - 1 5 8 [ S ] f [ H 2 S ] a q = 0 . 2 3 9 [ S ] F [ H 2 S ] = 0 . 5 0 8 I S ] f 175 TABLE A-2 P r e c i p i t a t i o n Under N i t r o g e n Atmosphere T e m p e r a t u r e 158.8°C [NH ] = 1.0 M, ( N H 4 ) 2 S 0 4 = 0.5 M , S u l p h i d e was added as a (NH 4> 2S s o l u t i o n Run 49 Run 47 Run 46 [Mo [S], X . X X M . x l O 3 M . x l O 3 6 k mm. x l O X . l X e k M . x l O 3 M . x l O 3 • - 1 i n 3 mm. x l O X . l X M . x l O 3 M . x l O 3 k • - 1 i n 3 mm. x l O X. l X M . x l O 3 M . x l O 3 k • - 1 i n 3 mxn. x l O 11. 2 8 . 6 3 . 2 27 . 5 20 . 4 5.8 1.11 0. 68 15.4 2 .93 1. 63 10 . 0 19 .1 16 . 0 11. 3 51. 5 42 . 6 10 . 7 2.97 1. 28 18 .0 4.55 2 . 34 12 . 9 19 . 4 14.5 8.9 53.5 38.5 8 . 8 3 1 22 . 3 3 , 19. 27 27 2 78 35 9 k/X f o r e k M /[Mo] Mo e [S], C 4 C 3 [S] M. -1 . mm . -1 M. -1 . mxn. -1 M. -1 . mm. -1 (M. -2 . mxn . -1 x l O 5 ) 0 .28 22 . 6 .1 1.8 0 .25 14. 5 . 5 1 . 7 0 .23 18. 5.9 1.6 C o m p o s i t i o n o f p r e c i p i t a t e s (%) Mo S d i f f e r e n c e M o l a r r a t i o S/Mo = r. O b s e r v e d C a l c u l a t e d 40 .1 41.4 18 . 5 100 . 0 3 .10 4 . 20 45.0 39.9 15 .1 100.0 2 .65 3 .08 44.9 39 . 8 15 . 3 100 . 0 2.65 2.83 176 TABLE A-3 A-3-1 A n a l y s i s o f P r e c i p i t a t e s , r and r„ b H2 S e r i e s A Mo v a r i a t i o n 1 5 1 . 6 ° C , NH = 0.86 M., NH," = 0.98 M., I n i t i a l c o n d i t i o n s : S = 0.211 M., P = 860 p s i . No . Mo M. S/Mo r s ' - a 101 0 . 049 4 . 28 2 .14 1.29 102 0 . 099 2 . 14 1.93 1 .22 10 3 0.148 1.4 2 1.45 1. 20 104 0 . 198 1.07 1.11 1.16 105 0. 247 0 .85 0.91 1. 15 S e r i e s B S v a r i a t i o n 1 5 8 . 8 ° C , NH = 0.84 M., N H 4 = 0.97 M., I n i t i a l c o n d i t i o n s : Mo = 0.097 M., P = 600 p s i . No . S T M. S/Mo r s 79 0 . 646 7 .0 2 . 30 1. 35 72 0 . 616 6.6 n.d. 1. 24 80 0.327 3.41 2 . 08 1.23 86 0 . 235 2 .42 2 .10 1.41 81 0. 154 1.59 1.53 1.29 85 0 . 116 1. 18 1.23 1.3-9 83 0 .079 0 .81 0 .80 1. 23 S e r i e s C C o n s t a n t (Mo + S ) , 167 . 7 ° C , NH = 0.86 M., NHT = 0.98 M. P = 530 p s i 4 No . Mo M. S T M: S/Mo r s r" 2 94 0 . 0 0 2 0 . 014 7 . 0 2.45 2.5? 95 0 . 004 0 . 0 1 2 3 . 0 2 .16 1.6 96 . 0 . 006 0 . 0 1 0 1.67 1.62 1.6 97 0 . 008 0 . 008 1 . 0 0 1 . 0 2 1. 2 98 0 . 0 1 0 0 . 006 0 .60 0.61 1.2 99 0 . 0 1 2 0 .004 0 . 33 0 .32 1 . 3 1 0 0 0 . 014 0 . 0 0 2 0.17 0 .15 1.1 177 S e r i e s D P v a r i a t i o n . 1 5 8 . 8 ° C , NH 3 = 0.84 M., NH* = 0.96 M. , I n i t i a l c o n c e n t r a t i o n s : Mo = 0.097 M., S = 0.194 M. No . P i n i t i a l 2 p s i . P R f i n a l 2 p s i . r s 8 6 602 420 2 . 10 1.41 87 441 220 1.83 1.51 88 310 95 1.96 1.47 89 228 16 1.96 1.45 1 5 8 . 8 ° C , N H = 1 . 0 0 M., N H * = 0 . 9 9 M., I n i t i a l c o n c e n t r a t i o n s : Mo T = 0 . 0 2 0 M., S T = 0 . 0 5 4 M. t i t a n i u m a u t o c l a v e , p r e s s u r e m a i n t a i n e d c o n s t a n t . No . p s i . r s 44 100 2 . 33 n . d . 43 200 2 .09 n. d . 42 300 2 .16 n. d . 41 400 2 . 06 n . d . 40 500 2 . 04 n. d . S e r i e s E pH v a r i a t i o n 1 5 1 . 6 ° C . , no NH 3, I n i t i a l c o n c e n t r a t i o n s : Na ?MoO, = 0.097 M., Na 2S = 0.211 M., I n i t i a l p r e s s u r e 880 p s i . No . ( N H 4 ) 2 S 0 4 M. r s ^2 Mo T i n f i n a l so u t i o n s , M. 106 0.490 1.96 1.28 n i l . 109 0 .392 1.93 1.26 n i l . 107 0.294 1.85 1.26 n i l . 110 0.245 1.66 1. 35 0 .014 108 0 . 191 1.65 1.48 0.039 178 TABLE A-3-2 A n a l y s i s of P r e c i p i t a t e s T.G.A. R e s u l t s No . r s We i g h t L o s s i n g./mole Mo AW2 AW3 83 0 .80 13 . 4 25 . 6 -5 . 2 85 1. 23 11. 7 23 . 3 3.4 81 1.53 9.8 17 . 6 9.3 86 2 .10 7 .1 25 . 9 17 . 2 80 2 . 08 7 . 4 26 . 8 18 . 5 79 2 . 30 9 . 2 29 . 3 31. 3 87 1. 83 5 . 3 21.6 13 .1 88 1. 96 .7 . 8 21.9 16 . 2 89 1.96 7 . 3 14.3 17 . 3 90 1. 64 11. 1 16.9 12 . 4 91 1. 98 7 . 9 18.3 17 . 7 92 1.99 11.6 28.0 18 . 5 r ^ : m o l a r r a t i o o f s u l p h u r to molybdenum i n p r e c i p i t a t e s AW^ : w e i g h t l o s s i n Ar a t 200°C. AW2: w e i g h t l o s s i n Ar a t 650°C. AW : w e i g h t l o s s i n a i r a t 550°C. a f t e r T.G.A. i n A r . 179 TABLE A-3-3 K i n e t i c Study 3-1 P Dependence — S e r i e s D 1. C o n s t a n t P r e s s u r e 1 5 8 . 8 ° C , NH = 1.00 M., NH = 0.99 M., I n i t i a l C o n c e n t r a t i o n s : Mo T = 0.020 M., S T = 0.054 M. T i t a n i u m A u t o c l a v e , No . PH2 p s i . s l o p e ^ min . i n t e r c e p t M . x l O 3 44 43 42 41 40 100 200 300 400 500 -0 . 0057 -0 . 0140 -0.0214 -0.0301 -0 . 0321 2.57 1.34 1. 25 0.90 0 . 32 S l o p e and i n t e r c e p t were o b t a i n e d by p l o t t i n g the e q u a t i o n : l o g (Mo Q - Mo) = - S t + l o g I 2. C o n s t a n t Volume 1 5 8 . 8 ° C , NH = 0.84 M., NH, = 0.96 M., I n i t i a l C o n c e n t r a t i o n s : Mo T = 0.097 M., S T = 0.194 M. No . P u i n i t i a l n o z p S 1 . s l o p e • -1 mxn. x 86 87 88 89 602 441 310 228 0 . 086 0.061 0.053 0 . 029 S l o p e was o b t a i n e d by p l o t t i n g the e q u a t i o n : l n ( P / ( a + P 0 - P ) ) = - St + l n P 0 / a where a. was t a k e n as 10 p s i . 180 3-2 E f f e c t o f S o l u t i o n C o n d i t i o n s 151. 6°C . No . S l o p e p s i . - I m i n . 1 x l O 5 F r a c t i o n a l D i s t r i b u t i o n ( N H J ) / ( N H 3 ) a o a l a 2 a 3 a 4 101 8 . 3 0 . 020 0.019 0 . 123 0.400 0 .439 0.515 102 7 . 3 0 . 246 0.093 0 .235 0 .298 0 .128 0 .460 103 5 . 7 0 .438 0 . 117 0 . 206 0 .184 0 .055 0 .455. 104 4.8 0 .532 0.120 0 .179 0 .135 0 .034 0 . 450 105 3.5 0 . 606 0 .118 0 . 153 0 . 100 0 .022 0.448 106 3.9? 0 . 208 0 . 086 0 . 233 0 . 323 0 . 150 1.444 109 4 .6? 0 .220 0 .088 0 . 234 0 . 315 0 .142 0.975 107 7 . 0 0 . 243 0 . 093 0 . 234 0 . 300 0 . 129 0.466 110 6.2 0 .277 0.099 0 .233 0.279 0 .112 0 .266 108 3 . 2 0 .389 0 . 113 0 . 217 0 . 211 0 . 069 0 .110 158 . 8°C. No . S l o p e atm. x m i n . x x l 0 3 F r a c t i o n a l D i s t r i b u t i o n (NHJ) / ( N H 3 ) a o a l a 2 a 3 a 4 79 1.5 6 0 . 134 0 . 067 0 . 221 0 . 370 0 . 208 0 .030 72 l - 7 0 0 .106 0 . 058 0 . 211 0 .387 0 .239 0 .037 80 2.4 8 0 . 085 0 . 051 0 . 199 0 .398, 0 . 267 0.250 86 2 . 0 7 0 . 183 0.080 0 . 231 0.339 0 . 167 0 . 4 0.8 81 I . 7 4 0 . 364 0 .111 0 . 222 0 . 22.6 0 .077 0.590 85 1 . 7 4 0 .478 0 . 119 0 . 195 0 . 163 0 .046 0 .696 83 l - 7 3 0 .694 0 . 112 0. 119 0.064 0 .012 0 .815 S l o p e s were o b t a i n e d by p l o t t i n g r e d u c e d r a t e , (-d I n P / d t ) , a g a i n s t h y d r o g e n c o n s u m p t i o n , ( P G - P ) . • a's were c a l c u l a t e d by u s i n g s t a b i l i t y c o n s t a n t s a t 150°C. o b t a i n e d i n P a r t 1. 181 TABLE A-4 P r e c i p i t a t i o n Under Carbon Monoxide Atmosphere T a b l e A -4-1 E f f e c t of P r e s s u r e S e r i e s A 1 5 8 . 8 ° C , [ N H 3 J = 1.0 M., [ (NH ,) S 0 4 ] = 0.5 M., I n i t i a l C o n c e n t r a t i o n s : [ M o ] m = 0 . 0 2 0 M., [ S ] T = 0.056 M. i No . P r e s s u r e I n d u c t i o n Growth r a t e (atm.) p e r i o d ( m i n . ) ( M . m i n . _ 1 ) x l 0 4 39 6 . 8 6 . 1 2.33 38 13 . 6 4.2 4 .13 37 20.4 4 . 3 5 . 85 35 27.2 5.5 7.46 30 34 . 0 5 . 3 8.65 S e r i e s B 1 5 8 . 8 ° C , [NH ] = 1.0 M. , [ (NH. ) SO. ] = 0.5 M., I n i t i a l C o n c e n t r a t i o n s : [Mo] = 0.001 M., [S] = 0.022 M. No . P r e s s u r e (atm.) I n d u c t i o n p e r i o d ( m i n . ) Growth r a t e ( i n i t i a l s l o p e (M.min. -!) x l O 5 56 6 . 8 ( s h o r t ) 0 .98 54 13.6 ( s h o r t ) 1.63 53 20.4 ( s h o r t ) 2.54 52 27 . 2 ( s h o r t ) 3 .12 51 34.0 ( s h o r t ) 3.21 57 40.8 ( s h o r t ) 3 .63 S e r i e s C 1 5 1 . 6 ° C , [NH^] = 1.0 M. , [ ( N H 4 ) S 0 4 ] = 0.5 M., I n i t i a l C o n c e n t r a t i o n s : [Mo] = 0.001 M., [ S ] T = 0.022 M. No . P r e s s u r e (atm.) I n d u c t i o n p e r i o d ( m i n . ) Growth r a t e ( i n i t i a l s l o p e ) (M.min. -1) x l 0 5 63 13 . 6 ( s h o r t ) 1.34 6 2 a 20.4 ( s h o r t ) 1.44 60 27 . 2 ( s h o r t ) 2.26 59 34.0 ( s h o r t ) 2 . 36 58 40.8 ( s h o r t ) 2.85 61 47.6 ( s h o r t ) 5 .06 a: .[Mo] = 0.0008 M. 182 TABLE A-4-1 E f f e c t of P r e s s u r e ( c o n t i n u e d ) S e r i e s D 1 3 9 . 1 ° C , [NH^] = 1.0 M., [NH C l ] = 1.0 M., I n i t i a l C o n c e n t r a t i o n s : [Mo] = 0.010 M. , [ S J T = 1.0 M. T No . P r e s s u r e (atm.) I n d u c t i o n p e r i o d ( m i n . ) Growth r a t e ( M . m i n . _ 1 ) x l 0 4 " 12 13 11 14 6 . 3 10 . 9 17.5 23 . 3 20? 16? 7 10 0.73 1.24 1.37 2 . 45 TABLE A-4-2 E f f e c t o f S u l p h i d e C o n c e n t r a t i o n S e r i e s E 15 8 . 8 ° C . , [ N H 3 J = 1.0 M. , [(NH ) SO ] = 0.5 M., P = 3 4 CO .0 atm. I n i t i a l C o n c e n t r a t i o n s : [Mo] = 0.020 M. No . [ s ] T Growth r a t e I n d u c t i o n I n d u c t i o n r a t e (M.) ( M . m i n ._ 1 ) x l 0 4 p e r i o d ( m i n . ) c o n s t a n t ( m i n T ^ ) 34 0.011 1.3 10. 9 7.1 33 0.023 3 . 2 9.0 11. 7 31 0. 033 4 . 3 8 . 2 14. 7 32a 0.033 5 . 5 8.7 13 . 2 30 0.056 8 . 3 5 . 3 24.4 29 0.089 14 . 4 3 . 2 40.6 < a: The s u r f a c e s o f a u t o c l a v e were n o t t r e a t e d w i t h n i t r i c a c i d . S e r i e s F 1 3 9 . l ' C , [NH ] = 1.0 M.,[(NH ) SO ] = 0.5 M., P C Q = 34.0 atm. 1 4 I n i t i a l C o n c e n t r a t i o n s : [Mo]_ = 0.020 M. No . [ s ] T Growth r a t e ( M . m i n . - 1 ) x l 0 A I n d u c t i o n p e r i o d ( m i n . ) I n d u c t i o n r a t e ^ cons t a n t ( m i n . ) 23 0.011 0. 30 n.d. 0 . 9 24 0 . 023 0.52 n.d. 2.6 25 0.033 1. 26 40 3.3 22 0.056 2 . 87 13. 2 8.9 26 0.08 9 5 .39 7.5 15 .9 183 TABLE A-4-2 E f f e c t o f S u l p h i d e C o n c e n t r a t i o n ( c o n t i n u e d ) S e r i e s G 1 2 0 ° C , [NH ] = 1.0 M. , [(NH ) SO.] = 0.5 M. , I n i t i a l C o n c e n t r a t i o n s : [Mo] = 0.020 M. No . [ s ] T Growth r a t e I n d u c t i o n I n d u c t i o n r a t e l ( M . m i n . ~ 1 ) x l 0 4 p e r i o d ( m i n . ) c o n s t a n t (min.--'-) 27 0.056 0.22? n.d. 1.3 28 0.089 1. 28 42. 3.3 184 A p p e n d i x B S p e c t r o g r a m of the S o l u t i o n S p e c t r o g r a m s of the s o l u t i o n were t a k e n u s i n g the t r a n s m i s s i o n s c a l e and some of them a r e r e p r o d u c e d h e r e w i t h o u t a l t e r a t i o n . In F i g u r e 1, 2, 5 and 6, t h e 0 and 100% t r a n s m i s s i o n of the s o l u t i o n s were a d j u s t e d to the s c a l e a t 600 my ( u s i n g a t u n g s t e n lamp) and the s p e c t r u m was t a k e n to 315 my. Then the l i g h t s o u r c e was changed to the h y d r o g e n lamp and the 0% and 100% r e a d i n g s were a d j u s t e d i n s u c h a way t h a t the t r a n s m i s s i o n v a l u e s a g r e e d w i t h t h e ones o b t a i n e d w i t h the t u n g s t e n lamp a t a r o u n d 350 my. F i n a l l y a f u r t h e r s p e c t r u m was t a k e n to 260 my. i In F i g u r e s 3 and 4, the 0% and 100% t r a n s m i s s i o n s were a d j u s t e d a t 700 my w i t h t h e t u n g s t e n lamp l i g h t s o u r c e and the s c a n was p e r f o r m e d to 300 my. A l i n e a r d r i f t of the 100% l i n e was o b s e r v e d and the n e c e s s a r y c o r r e c t i o n was made f o r the c a l c u l a t i o n of the c o n c e n t r a t i o n s o f complex.; s p e c i e s . • • The use o f the w a v e l e n g t h a t 600 my and 700 my f o r c a l i b r a t i o n was j u s t i f i e d by the f a c t t h a t the t r a n s -m i s s i o n was maximum a t around 700 my and a l s o c l o s e to the v a l u e o b s e r v e d f o r d i s t i l l e d w a t e r . The f o l l o w i n g t a b l e shows the c o n d i t i o n s o f the s o l u t i o n s whose s p e c t r u m were t a k e n . 185 F i g u r e 1 P a r t 1, The s t u d y o f the e q u i l i b r i u m 1 5 0 . 0 ° C , [ M o ] T = 1 x 1 0 ~ 3 M., [S] = 2 - 20 x 1 0 ~ 3 M. n o m i n a l c o m p o s i t i o n s {NH^j = 1 M., [NH^] = 1 M. (See A p p e n d i x A, T a b l e A - l - 1 , S e r i e s A, No. 8, 2 - 9 ) . F i g u r e 2 P a r t 1, The s t u d y o f t h e e q u i l i b r i u m 1 5 0 . 0 ° C , [Mo] = 1 x 1 0 ~ 3 M., [S] = 2 - 20 x 1 0 ~ 3 M. n o m i n a l c o m p o s i t i o n s [NH^] = 0.1 M., [NH*] = 1 M. (See A p p e n d i x A, T a b l e A - l - 1 , S e r i e s D, No. 11, 2 - 9 ) . F i g u r e 3 P a r t 2, P r e c i p i t a t i o n under a n i t r o g e n a t m osphere 158.8° C , [Mo] = 19 x 1 0 " 3 M., [S] = 52 x 1 0 ~ 3 M. , [NH 3] = 1 M., [NH +] = 1 M. (See F i g u r e 1 3 ) . F i g u r e 4 P a r t 2, P r e c i p i t a t i o n under c a r b o n monoxide 158.8° C , [ M o ] n = 20 x 1 0 _ 3 M., [S] = 54 x 1 0 ~ 3 M., [NH ] . = 1 M., [ N H + ] . = 1 M., P_„ = 6.4 atm. 3 l 4 I ' C O F i g u r e 5 P a r t 2, P r e c i p i t a t i o n under h y d r o g e n 150.0° C , [Mo] ± = 1 x 10 3 M., [S] ± = 14 x 1 0 ~ 3 M, [NH_] = 0.7 M., [NH +] = 1.0 M., P„ = 8.3 atm. 3 4 H 2 F i g u r e 6 A p p e n d i x B, The s t u d y o f the e q u i l i b r a t i o n r e a c t i o n , r o o m t e m p e r a t u r e , [Mo] = 1 x 1 0 ~ 4 M., [S] = 19 x 1 0 ~ 3 M., [NH 3] = 1 M., [NH*] » 1 M. 191 A p p e n d i x C Rate o f E q u i l i b r a t i o n The r a t e o f e q u i l i b r a t i o n between v a r i o u s s p e c i e s i n the Mo-S-H^O s y s t e m was s t u d i e d f o r two r e a s o n s : 1) f o r c o m p a r i s o n w i t h t h e r a t e o f molybdenum r e d u c t i o n to che c k t h e r a t e c o n t r o l l i n g s t e p 2) t o chec k the v a l i d i t y o f the q u e n c h i n g method used f o r the s t u d y o f e q u i l i b r i u m between thi o - m o l y b d e n u m c o m p l e x e s . An e x p e r i m e n t a t h i g h t e m p e r a t u r e was a t t e m p t e d u s i n g the h i g h t e m p e r a t u r e s p e c t r o c e l l d e v e l o p e d i n t h i s d e p a r t m e n t , b u t d i f f i c u l t y i n the i n j e c t i o n o f the s o l u t i o n made the o p e r a t i o n i m p o s s i b l e . Thus the r e s u l t s o f room t e m p e r a t u r e e x p e r i m e n t s a r e p r e s e n t e d h e r e . E x p e r i m e n t a l S o l u t i o n s of Mo and S were made f r e s h i n b u f f e r s o l u t i o n s . S u i t a b l e p o r t i o n s were t a k e n i n a b e a k e r and b u f f e r s o l u t i o n was added to make a c o n s t a n t volume [10 m l . ] . The mixed s o l u t i o n was p o u r e d i n t o a s p e c t r o c e l l , a l i d was p l a c e d on top to a v o i d e v a p o r a t i o n and o x i d a t i o n , and the c e l l was p l a c e d i n the l i g h t - p a t h . D i s t i l l e d w a t e r was used as the r e f e r e n c e . In a r u n ( F i g u r e B6 i n A p p e n d i x B ) , wave l e n g t h s c a n was made r e p e a t e d l y w i t h a Beckman DK-2 S p e c t r o m e t e r a t a p p r o x i m a t e l y 10 mi n u t e i n t e r v a l s . The peaks a t 465, 395, 315 and 290 my were r e a d and p l o t t e d a g a i n s t t h e time when t h e y were r e c o r d e d . The i n s t a n t a n e o u s v a l u e s o f the a b s o r b a n c y a t each w a v e l e n g t h were r e a d from the smooth f i t t i n g c u r v e s a t the time d e s i r e d and t h e c o n -c e n t r a t i o n s were c a l c u l a t e d . In t h e o t h e r r u n s r e a d i n g s were made w i t h a Beckman Model B S p e c t r o m e t e r a t t h e wave-l e n g t h s o f 395 and 465 my. Time was measured from the moment when s u l p h i d e and molybdenum s o l u t i o n s were mixed. The m i x i n g was e x p e c t e d to be p e r f e c t w i t h i n h a l f a m i n u t e . T e m p e r a t u r e o f the c e l l was n o t c o n t r o l l e d , b u t i t s t a y e d between 26° and 32° C. d u r i n g the whole e x p e r i m e n t i n most c a s e s . When the DK-2 was u s e d , the t e m p e r a t u r e went up as h i g h as 36° C. towar d s t h e end of the e x p e r i m e n t . R e s u l t s F i g u r e B-6 i n A p p e n d i x B shows t h e time v a r i a t i o n of the s p e c t r o g r a m of a m i x t u r e . S t e a d y i n c r e a s e o f the peaks a t 465 and 395 my and d e c r e a s e of the peak a t 290 my c l e a r l y p o i n t s to the s t e p w i s e s h i f t of c o m p o s i t i o n from 2- 2-MoO^ to MoS^ . The e x i s t e n c e o f e q u i l i b r i u m i s more c l e a r l y 2-s een i n F i g u r e C - l , where c a l c u l a t e d c o n c e n t r a t i o n s o f MoS^ 2 b2 2- 2-MoOS_ and M o O „ S 9 a r e p l o t t e d a g a i n s t t i m e . [See P a r t 2-1 f o r c a l c u l a t i o n methods.] The r a p i d r e a c t i o n to M 0 O 2 S 2 2- 2-and s u b s e q u e n t r e l a t i v e l y s l o w e r s h i f t t o MoOS^ and MoS^. i s o b s e r v e d . F i g u r e C-2 shows, v a r i a t i o n o f t h e c o n c e n t r a t i o n o f 2-s p e c i e s MoOS^ , C^, a g a i n s t time where [Mo]^ was k e p t c o n -s t a n t and [ S ] ^ was v a r i e d . These s e r i e s were measured w i t h 315 the Beckman Model B, thu s k^ was n o t measured. I t was 2-f o u n d t h a t the c o n c e n t r a t i o n o f s p e c i e s MoS^ was l e s s t h a n 2-5% of the c o n c e n t r a t i o n of MoOS^ . In a d d i t i o n , t h i s r a n g e 193 Fig. C l . VARIATION OF COMPLEX CONCENTRATIONS 195 o f time c o r r e s p o n d s to the i n i t i a l r a p i d i n c r e a s e seen i n 2-F i g u r e C - l . T h e r e f o r e the e f f e c t o f MoS^ was c o n s i d e r e d i n s i g n i f i c a n t . When the i n i t i a l maximum s l o p e [ c o r r e s p o n d s to a p p r o x i m a t e l y 3 to 7 m i n u t e r a n g e ] , and the a v e r a g e s l o p e between 20 and 30 m i n u t e s were p l o t t e d a g a i n s t the t o t a l s u l p h i d e c o n c e n t r a t i o n [S] , a good l i n e a r i t y was o b s e r v e d i n b o t h c a s e s and t h e i r s l o p e s , i n t u r n showed a good l i n e a r i t y a g a i n s t the t o t a l molybdenum c o n c e n t r a t i o n [Mo]^,. Thus the same mechanism was s u s p e c t e d f o r b o t h the i n i t i a l r a p i d p a r t and s u b s e q u e n t s l o w e r p a r t o f the c u r v e s . When v a l u e s of were n o r m a l i z e d by the p r o d u c t s of [ M o ] T and [ S ] T , i . e . , C 3/[Mo] [S ] T , and p l o t t e d a g a i n s t t i m e , the d a t a f e l l i n t o two g r o u p s . In t h e r u n s w h i c h had a r a t i o of [ S ] ^  to [Mo]^, g r e a t e r t h a n 26, the p l o t s were a l m o s t i d e n t i c a l [ w i t h i n ±0.1 M. ^ i n the s c a l e ] f o r the whole e x p e r i m e n t a l time r a n g e . F o r the c a s e s where the r a t i o was s m a l l e r t h a n 26, the p l o t s were of the same shape but t h e i r m a g n i t u d e s d e c r e a s e d as the r a t i o d e c r e a s e d . F i g u r e C-3 shows the r e s u l t s , i n w h i c h t h e f i r s t group a r e r e p r e s e n t e d by a v e r a g e d v a l u e s . F i g u r e C-4 shows the p l o t o f the i n s t a n t a n e o u s r a t e s , d ( C 3 / [ M o ] T [ S ] T ) / d t , a g a i n s t C 3 / [ M o ] T [ S ] T . The r a t e was c a l c u l a t e d by a p p r o x i m a t i n g the p l o t s to q u a d r a t i c e q u a t i o n s around the p o i n t i n q u e s t i o n . Y(=C3/MoTST) M: 1 Fig.C4 PLOT OF RATE v s . CONCENTRATION 198 Good l i n e a r i t y was fo u n d w i t h a p p r o x i m a t e l y the same s l o p e as shown i n T a b l e C - l i n column 3, e x c e p t f o r the r e g i o n where C 3 / [ M o ] T [ S ] T was s m a l l c o r r e s p o n d i n g to the i n i t i a l r e g i o n s . TABLE C - l No . I n t e r c e p t M. mm . S l o p e -1 mm. S/Mo S T M.X 1 0 3 k - 3 . -1 mm . k 3 a y S f . -1 mxn . 7,8,9,10 0.67 2 -0 .075, 4 26 13 . 0 0.066, 0 0.0087 11 0.56. 4 - 0 . 0 7 2 0 17 . 3 8 . 7 0 . 067^^ 0.0049 12 0.43 3 - 0 . 0 7 8 1 8,7 4.3 0.076 2 0.0019 13 0 . 3 8 ? - 0 . 0 7 9 3 4.3 4 . 3 0.077, 6 0.0017 14 0.32, 4 -0.081 2 . 2 4.3 0.079^ 6 0.0014 Thus the e m p i r i c a l r a t e e q u a t i o n can be w r i t t e n as e q u a t i o n Cc-i). -dX/dt = I - SX . . . . ( C - l ) where I and S a r e the i n t e r c e p t and n e g a t i v e of the s l o p e of the above p l o t r e s p e c t i v e l y and X = C 3 / [Mo ] ^, [ S ] ^  . I n t e g r a t i o n of e q u a t i o n ( C - l ) g i v e s e q u a t i o n ( C - 2 ) . X = [ I / S ] - B e x p [ - S t ] (C-2) Where B i s t h e i n t e g r a t i o n c o n s t a n t . B was c a l c u l a t e d f o r the a v e r a g e d d a t a o f the c a s e where ( [ S ] .j,/[Mo ] ) > 26 and t h e d i f f e r e n c e s o f c a l c u l a t e d X from the o b s e r v e d v a l u e s a r e shown i n F i g u r e C-5. A g r e e -ment was v e r y good [ l e s s t h a n 1% d i f f e r e n c e ] e x c e p t a t the 2-i n i t i a l and f i n a l p a r t s , where the e f f e c t o f s p e c i e s MoS^ i s e x p e c t e d to r a i s e the o b s e r v e d v a l u e l a r g e r t h a n the c a l c u l a t e d . D i s c u s s i o n The r e s u l t s o b t a i n e d above a r e c o n s i s t e n t w i t h a model i n w h i c h a r a p i d e q u i l i b r i u m i s e s t a b l i s h e d to form 2- 2-s p e c i e s MoO S. w h i c h f u r t h e r r e a c t s t o form MoOS„ 2- 2-+ H 0 S 2-+ H 2S,k 3 2-MoO 4 MoCKS MoOS 3 r a p i d e q u i l i b r i u m t h e n d C 3 / d t = k 3 C 2 [ H 2 S ] - k _ 3 C (C-3) = a ( [ M o ] T - C 3 ) , a = 3 2 [ H 2 S ] 1 + e 1 I H 2 S J + B 2 [ H 2 S ] 2 where 3 ^ a r e s t a b i l i t y c o n s t a n t s , of aqueous h y d r o g e n s u l p h i d e and, [ H 2 S ] i s the c o n c e n t r a t i o n at c o n s t a n t t e m p e r a t u r e 200 7 Y o b s 8 * " e.5 -i r A Y -O. lh Time mm. Fig.C5 TEST OF INTEGRAL EQUATION, AY = Ycjjg ~ X;alc Y = C 3 /Mo T S T Fig.C6 PL0T FOR C 4 t EQUATION C-5 MoT = I x ICT4 M. S T =196 ii NH 3 =NH+ = 1.0 M. C4/C3 201 and pH, i t i s r e l a t e d to the t o t a l c o n c e n t r a t i o n o f f r e e s u l p h i d e s p e c i e s , S^, by the e q u a t i o n : [ H 2 S ] = Y S f , Y = 1/[(1 + ( K s l / [ H + ] ) +' ( K S 1 K S 2 / [ H + ] 2 ) ] where K ^ , K g 2 a r e t h e f i r s t and s e c o n d d i s s o c i a t i o n c o n s t a n t of aqueous h y d r o g e n s u l p h i d e . The e q u a t i o n (C-3) becomes e q u a t i o n (C-4) by s u b s t i t u t i o n . dC = [ k 3 a Y [ M o ] T S f ] - [ k 3 a Y S f + k _ 3 ] C . . . . (C-4) dt D i v i d i n g by [ M o ] T [ S ] T y i e l d s d ( C 3 / [ M o ] T [ S ] T ) / d t = [ k 3 a y S f / [ S ] T ] - [ k 3 a Y S f + k _ 3 ] ( C 3 / [ M o ] T [ S ] T ) 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 s S f « [ S ] T and a - 1 Thus t h e f i r s t t erm w i l l be i n d e p e n d e n t o f the s u l p h i d e c o n c e n t r a t i o n w h i c h a g r e e s w i t h t h e o b s e r v a t i o n . The c o e -f f i c i e n t w i l l a l s o be i n d e p e n d e n t o f the s u l p h i d e c o n c e n -t r a t i o n i f k„ay[S] i s i n s i g n i f i c a n t compared w i t h k „. 202 k _ 3 and k ^ a y t S j ^ w e r e c a l c u l a t e d f r o m the o b s e r v e d v a l u e s o f the i n t e r . c e p t I, s l o p e S and [ S ] ^ , by the f o l l o w i n g e q u a t i o n and t h e r e s u l t s a r e s e e n i n columns '6 land 7 of T a b l e C - l . . ' • [ k 3 a Y S f ] = I • [ S ] T k _ 3 = S - I • [ S ] T The m a g n i t u d e f o u n d j u s t i f i e s the above argument. The s e c o n d o r d e r r a t e c o n s t a n t , k , was e s t i m a t e d i f o r the f i r s t group by p u t t i n g a = 1, [ S ] ^ = [ S ] T and by the l i t e r a t u r e v a l u e s o f d i s s o c i a t i o n c o n s t a n t s f o r NH^ and 2 -1 -1! H^S. The v a l u e f o u n d was 2.3 x 10 M. min. (Note) S i m i l a r c a l c u l a t i o n was p e r f o r m e d f o r t h e v a r i a t i o n 2-o f the c o n c e n t r a t i o n of s p e c i e s MoS^ and the e q u i l i b r a -t i o n r e a c t i o n mechanism a l s o seemed to a p p l y : MoOS 2 + H 0S - MoS. 2 3 2 , 4 ., k-4 d C 4 / d t = k 4 [ H 2 S ] C 3 - k _ 4 C 4 (Note) - The f o l l o w i n g v a l u e s were used f o r c a l c u l a t i o n NH. + 4 = H+ + NH 3 P KN = 9 .50 H 0S 2 aq - H+ + HS~ P R S 1 = 6 .97 HS~ = H + + s 2 - P K S 2 = r e f . 12 37 .89 203 D i v i s i o n by g i v e s ( d C A / d t ) / C 3 = k 4 [ H 2 S ] - k _ 4 ( C 4 / C 3 ) . . . . (C-5) The p l o t o f ( d . C 4 / d t ) / C 3 a g a i n s t [ C 4 / C 3 ] i s shown i n F i g u r e C-6 The l i n e a r i t y seems to h o l d and the r a t e c o n s t a n t s were c a l c u l a t e d a l t h o u g h the a c c u r a c y was r e l a t i v e l y p o o r . k _ . = 0.03 min. ^, k. = 70 M. min. -4 4 F o r most o f the s t u d y o f the e q u i l i b r i u m i n P a r t 1, [ N H 4 + ] = [ NH_3 ] = 1 M. [ S ] T = 2 ~ 20 x 1 0 ~ 3 M. , c i i / c 3 = 0.1 ~ 1, C 2 / C 3 = 1 ~ 1 0 -The e r r o r by the s h i f t of e q u i l i b r i u m was e s t i m a t e d by u s i n g the r a t e e q u a t i o n o b t a i n e d above, i . e . , A C 3 / C 3 = [ k 3 [ H 2 S ] C 2 / C 3 ~ k - 3 " k A C H 2 S 3 + k _ 4 C 4 / C 3 ] At = 0.05At A C 4 / C 4 = [ k 4 [ H 2 S ] C 3 / C 4 - k _ 4 ] At * 0.02At The e s t i m a t e d e r r o r i n 10 min. amounts to maximum 50%. The r a t e o f the d i s a p p e a r a n c e o f molybdenum a t h i g h t e m p e r a t u r e -2 -1 was i n g e n e r a l o f the o r d e r o f 10 min. . In v i e w o f the f a c t t h a t the r a t e o f e q u i l i b r a t i o n was o f the same o r d e r a t room t e m p e r a t u r e , t h e e q u i l i b r a t i o n r e a c t i o n a t 150°C. would n o t i n t e r f e r e i n the r e d u c t i o n r e a c t i o n . 

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