Decomposition of jarosite
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H. V E L T M A N
P r e c i p i t a t i o n of i r o n as a j a r o s i t e is used in v a r i o u s 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 e s . T h e r e a r e s e v e r a l a d v a n t a g e s to this r o u t e , for e x a m p l e e x c e l l e n t l i q u i d - s o l i d s e p a r a t i o n c h a r a c t e r i s t i c s , s e l e c t i v e p r e c i p i t a t i o n of i r o n in e n v i r o n m e n t a l l y m o r e s t a b l e f o r m , r e c o v e r y of s u l f u r as s u l f u r i c acid and higher zinc e x t r a c t i o n . However, j a r o s i t e p r e c i p i t a tion a l s o has d i s a d v a n t a g e s , the m a j o r b e i n g the high cost of r e a g e n t s . A l a b o r a t o r y study was t h e r e f o r e c a r r i e d out on the c o n v e r s i o n of a m m o n i u m j a r o s i t e to i r o n oxide with r e covery of r e a g e n t s as b y p r o d u c t s . The i n v e s t i g a t i o n r e s u l t e d in the d e v e l o p m e n t of t h r e e p r o c e s s p o s s i b i l i t i e s : 1) t h e r m a l d e c o m p o s i t i o n with s e p a r a t e r e c o v e r y of h e m a t i t e , a m m o n i a and s u l f u r dioxide, 2) d e c o m p o s i t i o n of j a r o s i t e in an aqueous s l u r r y to h e m a t i t e and a m m o n i u m sulfate, or 3) d e c o m p o s i t i o n in a n aqueous s l u r r y to m a g n e t i t e and a m m o n i u m s u l f a t e . The conditions affecting the d e c o m p o s i t i o n of j a r o s i t e by a l l t h r e e methods have b e e n defined and the c h e m i c a l , m i n e r a l o g i c a l and p h y s i c a l c h a r a c t e r i s t i c s of the i r o n p r o d ucts a r e identified.
INTRODUCTION W HE 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 of sulfidic o r e s in acid m e d i a p r o d u c e s leach s o l u t i o n c o n t a i n i n g v a r i able q u a n t i t i e s of i r o n . The i r o n c o n c e n t r a t i o n and oxidation s t a t e depends on the c o m p o s i t i o n of the feed m a t e r i a l s , and on the leach c o n d i t i o n s . The c o n c e n t r a t i o n of i r o n in zinc p r o c e s s s o l u t i o n s ~ and in copper p r o c e s s s o l u t i o n s 2'~ has b e e n r e p o r t e d to be as high as 30 and 60 to 90 g/~ r e s p e c t i v e l y . T h e s e leach s o l u t i o n s have to be p u r i f i e d p r i o r the w i n n i n g of p u r e m e t a l and v a r i o u s methods have been s u g g e s t e d to r e m o v e i r o n by p r e c i p i t a t i o n a s : 1) b a s i c i r o n sulfate, 4'~ 2) goethite, ~'~ 3) h e m a t i t e , %*~ 4) m a g n e t i t e , n or 5) j a r o s i t e . 12-~4 Many j a r o s i t e compounds a r e known. D u t r i z a c and K a i m a n listed n i n e compounds .5 of the g e n e r a l f o r m u l a MFe3(SO4)e(OH)6, in which M r e p r e s e n t s H~O§ Na § K § § R b+, A g , N H 4 + , T 1§, l / 2 P b § or 1/2Hg + 2 . W h e n p r e c i p itated f r o m an aqueous s u l f u r i c acid s y s t e m , t h e r e is s o m e s u b s t i t u t i o n of HaO+ for the p r i m a r y cation
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