Kinetics of the thermal dissociation of Co 4 S 3 under reduced pressure
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o n e - t h i r d of all m e t a l s o c c u r in n a t u r e as sul f i d e m i n e r a l s . C o n v e n t i o n a l p r o c e s s e s for m e t a l winning f r o m s u l f i d e s include r o a s t i n g followed by r e duction with a g a s e o u s or m e t a l l i c r e d u c t a n t , m a t t e s m e l t i n g and c o n v e r t i n g , l e a c h i n g with or without p r e t r e a t m e n t followed by c e m e n t a t i o n or e l e c t r o l y s i s , d i r e c t m e t a l l o t h e r m i c r e d u c t i o n and m a t t e e l e c t r o l y s i s . H o w e v e r , the d i r e c t t h e r m a l d i s s o c i a t i o n of s u l t i d e s as an a l t e r n a t e p r o c e s s of winning m e t a l s , is w o r t h y of s e r i o u s a t t e n t i o n . F r o m a t h e r m o d y n a m i c v i e w p o i n t , the d i s s o c i a t i o n of Sb, I r , and Sn s u l f i d e s to t h e i r c o n c e r n e d e l e m e n t s is f e a s i b l e u n d e r s t a n d a r d c o n d i t i o n s . A few o t h e r s u l f i d e s s u c h as those of Mo, Cu, C o , and so f o r t h , a l s o show a tendency to d i s s o c i a t e u n d e r high v a c u u m . T h e r m a l d i s s o c i a t i o n as a m e a n s of e x t r a c t i n g m e t a l s c o m p r i s e s a l e s s e r n u m b e r of m e t a l l u r g i c a l s t e p s , e n a b l e s r e c o v e r y of s u l f u r as a v a l u a b l e b y - p r o d u c t , and should y i e l d m e t a l s with low oxygen content. The f o r m a t i o n of m o l y b d e n u m m e t a l on heating MoS2 in an e l e c t r i c a r c f u r n a c e has b e e n r e p o r t e d by G u i c h a r d 1-3 as e a r l y as 1896. A f t e r a l a p s e of about t h r e e d e c a d e s , G r u b e r and c o w o r k e r s 4 o b s e r v e d (in 1928) the f o r m a t i o n of m o l y b d e n u m m e t a l by t r e a t i n g MoS2 at 1400~ u n d e r r e d u c e d p r e s s u r e of 2 to 4 m m Hg. In the s a m e y e a r , P a r r a v a n o and M a l q u a r r i 5 a l s o m a d e s i m i l a r s t u d i e s on the d i s s o c i a t i o n of MoS2 und er r e d u c e d p r e s s u r e in the t e m p e r a t u r e r a n g e 1400 ~ to 1500~ H o w e v e r , P i c o n 6 who s u b s e q u e n t l y w o r k e d on this p r o c e s s , w a s the f i r s t to p r e p a r e the m e t a l f r e e f r o m s u l f u r . S i m i l a r s t u d i e s on the d i s s o c i ation of MoS2 have a l s o been c a r r i e d out at C l i m a x L a b o r a t o r i e s ~ and the c o n d i t i o n s f o r p r o d u c i n g m o l y b de n u m m e t a l by d i s s o c i a t i o n of m o l y b d e n i t e u n d e r r e duced p r e s s u r e at 1600 ~ to 1700~ have been s t a n d ardized. In addition to m o l y b d e n u m , d i s s o c i a t i o n s t u d i e s on o t h e r s u l f i d e s have a l s o been c a r r i e d out. F o u r S. K. JAIN, P. M. PRASAD, and P. K. JENA are Senior Research Fellow, Reader in Process Metallurgy, and Professor of Metallurgy, respectively, Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu
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