Oxidation of zinc sulfide in a fluidized bed
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MANY
e x p e r i m e n t a l s t u d i e s 1-12 have b e e n conducted on the oxidation k i n e t i c s of ZnS. Z i n c sulfide of s t o i c h i o m e t r i c c o m p o s i t i o n i s s t a b l e in the u n r e a c t e d i n n e r core of the p a r t i c l e d u r i n g the oxidation, and the k i n e t i c a n a l y s i s is f a c i l i t a t e d as c o m p a r e d with o t h e r n o n s t o i c h i o m e t r i c sulfide m i n e r a l s . It can be concluded f r o m the p r e v i o u s work 4-9 that the i n t e r f a c i a l r e a c t i o n i s the r a t e - d e t e r m i n i n g step below about 700~ and i n w a r d diffusion of O2 gas t h r o u g h the o u t e r oxide s h e l l d e t e r m i n e s the o v e r a l l r a t e above this temperature. A few e x p e r i m e n t a l s t u d i e s 1~ w e r e conducted on the oxidation of ZnS p a r t i c l e s i n f l u i d i z e d bed r e a c t o r s , in which the u n i f o r m - p h a s e m o d e l for fluidized bed was e m p l o y e d . Along with the d e v e l o p m e n t of the f l u i d i z a t i o n t e c h n i q u e , however, it was r e c o g n i z e d that an a g g r e g a t i v e g a s - s o l i d fluidized bed is c o m p o s e d of gas b u b b l e s and a n e m u l s i o n p h a s e and that the b e h a v i o r of fluidized beds is c l o s e l y r e l a t e d to the r i s i n g gas b u b b l e s . 1~ It is a l s o r e c o g n i z e d that the exc e s s f l u i d i z i n g gas above that r e q u i r e d f o r i n c i p i e n t f l u i d i z a t i o n r i s e s t h r o u g h the bed i n the f o r m of gas b u b b l e s in which the f r a c t i o n of s o l i d p a r t i c l e s is ext r e m e l y low. ~4'24 The s o l i d p a r t i c l e s i n the gas b u b b l e s a r e s u p p o s e d to m o v e at the t e r m i n a l v e l o c i t y . The e m u l s i o n p h a s e is r e g a r d e d to be v e r y s i m i l a r to the s t a t e of i n c i p i e n t f l u i d i z a t i o n and the flow r a t e of gas i n the e m u l s i o n p h a s e is p r e s u m e d to be at the s u p e r f i c i a l velocity in i n c i p i e n t f l u i d i z a t i o n . In the k i n e t i c s of f l u i d i z e d bed r o a s t i n g of sulfide p a r t i c l e s i n which the m a s s t r a n s f e r through the g a s - f i l m on the p a r t i cle s u r f a c e m a y play an i m p o r t a n t r o l e , it i s p r e f e r a b l e to employ the t w o - p h a s e m o d e l and to e v a l u a t e Y. FUKUNAKAis a Post-Doctoral Fellow, the University of Toronto, Toronto, Canada. T. MONTAis now with the Musashino Commtmication Laboratories, Japan Telephone and Telegraph Corporation, Musashino, Tokyo, Japan. Z. ASAKI and Y. KONDO, members of AIME, are Lecturer and Professor, respectively, Department of Metallurgy, Kyoto University, Kyoto, Japan. Y. Fukunaka and T. Monta are both former Graduate Students, Kyoto University, Kyoto, Japan. Manuscript submitted September 23, 1975. METALLURGICALTRANSACTIONSB
s e p a r a t e l y the g a s - f i l m m a s s t r a n s f e r coefficient of p a r t i c l e
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