Kinetics and mechanism of the reduction of molten nickel sulfide by hydrogen
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G. L. REMPEL,
AND
N. TAKEBE
The k i n e t i c s and m e c h a n i s m of the r e d u c t i o n of NiaS2 by h y d r o g e n h a v e been i n v e s t i g a t e d b e t w e e n 1133 ~ and 1300~ When high flow r a t e s of h y d r o g e n and a r g o n o r h e l i u m bubbling t h r o u g h the m e l t a r e m a i n t a i n e d the r a t e - d e t e r m i n i n g s t e p i s a c h e m i c a l p r o c e s s which can be e x p r e s s e d b y a r a t e law of the f o r m rH2 S = kexpt ( N s -- Ot )'2 pH 2-1/2
PH2 ~ 0.88 a t m w h e r e kexpt = 85.1 a i m -1/2 rain -1, a = 0.17 at 1250~ The e x p e r i m e n t a l a c t i v a t i o n e n e r g y for t h i s p r o c e s s i s 20.1 • 3.0 k c a l p e r m o l e . T h e s e r e s u l t s a r e d i s c u s s e d in t e r m s of p o s s i b l e c a t a l y s i s by n i c k e l .
R E A C T I O N S b e t w e e n m o l t e n m e t a l s u l f i d e s and r e ducing g a s e s have r e c e i v e d l i t t l e a t t e n t i o n e s p e c i a l l y f r o m the k i n e t i c and m e c h a n i s t i c standpoint. Although r e a c t i o n s of t h i s type a r e not often e n c o u n t e r e d in metaIlurgical chemistry, since the conventional route f r o m s u l f i d e to m e t a l c o n s i s t s of a r o a s t i n g r e a c t i o n and the s u b s e q u e n t r e d u c t i o n of the oxide to m e t a l , it a p p e a r s that d i r e c t r e a c t i o n of the s u l f i d e with h y d r o gen m a y be p r o m i s i n g . A n u m b e r of r e p o r t s on the t h e r m o d y n a m i c p r o p e r t i e s of the b i n a r y s y s t e m s N i - S , F e - S , C u - S 1-s a s w e l l a s the t e r n a r y s y s t e m s N i - F e - S , N i - C u - S , and F e - C u S a r e a v a i l a b l e . 4 - 8 In m a n y of t h e s e i n v e s t i g a t i o n s the t h e r m o d y n a m i c d a t a w e r e o b t a i n e d by e q u i l i b r a t i n g an HaS-He g a s m i x t u r e with the m o l t e n m e t a l s u l f i d e . In t h i s p r e s e n t i n v e s t i g a t i o n the k i n e t i c s and p o s s i b l e m e c h a n i s m of the r e a c t i o n of m o l t e n n i c k e l s u l f i d e with h y d r o g e n a r e r e p o r t e d . The r e a c t i o n i s r e p r e s e n t e d by the following s t o i c h i o m e t r y NiaSa(I ) + 2 H2{g) ~ 3 Ni(s ) + 2 HaS(g)
given in Eq. [1] the following r e l a t i o n s h i p m a y be written
Modifying open s y s t e m t h e o r y for the c a s e of c o m p l e t e m i x i n g in a s t i r r e d flow r e a c t i o n a s d i s c u s s e d by Denbigh et al., s rH2 S and ~'H2 m a y be e x p r e s s e d a s follows ~'H2S =
dCH a
dt
CH2S
U
+ V~
(CH2 -- CHa)
M(S)
M(t)
[3] [4] [5]
v(t) = D - - ~ - D(S) where
CH2 S = h y d r o g e n s u l f i d e c o n c e n t r a t i o n in outlet g a s
mixture CHa. = h y d r o g e n c o n c e n t r a t i o n in outlet g a s m i x t u r e C H2 ~ = h y d r o g e n c o n c e n t r a t i o n in inlet g a s m i x t u r e U = i n l e t g a s flow r a t e v(f)
EXPERIMENTAL
dCHas + U dt V~
"--YH2=
[1]
Data r e q
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