Hydrolysis of fused calcium chloride at high temperature
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N I C K E L s e g r e g a t i o n p r o c e s s is p r o m i s i n g for r e c o v e r i n g n i c k e l f r o m low grade oxide o r e s . When the oxide o r e is r o a s t e d in a weak r e d u c i n g a t m o s p h e r e in the p r e s e n c e of c a l c i u m c h l o r i d e and s o l i d c a r b o n aceous m a t e r i a l b e t w e e n 1170 and 1270 K, n i c k e l and a p a r t of i r o n s e g r e g a t e f r o m the m a t r i x of the ore to the c a r b o n s u r f a c e and n i c k e l - i r o n a l l o y is p r e c i p i tated. The e n r i c h e d alloy can e a s i l y be r e c o v e r e d by m a g n e t i c s e p a r a t i o n or flotation. 1 Although the d e t a i l e d m e c h a n i s m of n i c k e l s e g r e g a t i o n is not yet d i s c l o s e d , it is p r e s u m e d that the o v e r a l l r e a c t i o n is c o m p o s e d of the following s e q u e n t i a l s t e p s :2 evolution of h y d r o gen c h l o r i d e gas (Eqs. [1] and [2]), f o r m a t i o n of n i c k e l and i r o n c h l o r i d e v a p o r s (Eqs. [3] and [4]), evolution of h y d r o g e n gas on the c a r b o n s u r f a c e (Eq. [5]) and p r e c i p i t a t i o n of n i c k e l - i r o n alloy (Eqs. [6] and [7]). CaC12(/) + H20(g) = CaO(l) + 2 HCl(g)
[1]
CaC12(/) + 2 H20(g) = Ca(OH)2(/) + 2 HCI(g)
[2]
NiO(s) + 2 HCI(g) = NiCl2(g) + H20(g)
[3]
FeO(s) + 2 HCI(g) = FeC12(g) + H20(g)
[4]
C(s) + H20(g) = CO(g) + H2(g)
[5]
NiCl2(g) + H2(g) = N__!(s) + 2 HCl(g)
[6]
FeC12(g) + n2(g) = Fe(s) + 2 HCl(g).
[7]
A m o n g only a few p a p e r s r e c e n t l y p u b l i s h e d on the e q u i l i b r i u m and k i n e t i c s of this p r o c e s s , I w a s a k i 1 p r o p o s e d the o p t i m a l t e m p e r a t u r e and w a t e r v a p o r p r e s s u r e for n i c k e l s e g r e g a t i o n b a s e d on a s i m p l i f i e d t h e r m o d y n a m i c c a l c u l a t i o n . K i m u r a and Kondo 2 also c a r r i e d out a t h e r m o d y n a m i c c a l c u l a t i o n and e s t i H. KONDO, formerly a Graduate Student with the Department of Metallurgy, Kyoto University, is now with Hasaki Research Center, Sumitomo Metal Industries, Ltd., Hasaki, Ibaraki Pref., Japan. Z. ASAKI and Y. KONDO, Members of AIME, are Associate Professor and Professor, respectively, Department of Metallurgy, Kyoto University, Kyoto, Japan. Manuscript submitted September 27, 1977. METALLURGICAL TRANSACTIONS B
mated the nickel content in the precipitated alloy. UedaS studied, on the other hand, the kinetics of hydrolysis of calcium chloride at high temperature using a mixed pellet of calcium chloride and silica. It was reported that the rate of hydrolysis is controlled by the gas diffusion in the outer layer of the pellet where calcium silicate is formed. However, no further discussion was made on the rate of gas diffusion in this layer. As mentioned above, the hydrolysis of fused calcium chloride occurs at the initial step of nickel segregation. In order to clarify the detailed mechanism of this process, it is important to examine the feasibili
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