Removal of impurities from crude nickel sulfide by selective dry chlorination and leaching
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MECHANISM O F THE M E T A L SULFIDES CHLORINATION PROCESS The n i c k e l sulfide p r o d u c t , g e n e r a t e d b y the Inco m a t t e s e p a r a t i o n p r o c e s s c o n t a i n s NiaS 2 a s the m a j o r p h a s e with s m a l l a m o u n t s of c o p p e r sulfide (CuzS) and m e t a l l i c a l l o y (Cu-Ni) p h a s e s . E l e c t r o n m i c r o p r o b e a n a l y s i s of t h i s i m p u r e n i c k e l sulfide gave the f o l l o w ing r e s u l t s :
Table I
Average Composition, Wt Pct Phase Nickel Sulfide (NiaS2) Copper Sulfide (Cu2S) Metallic Alloy (Cu-Ni)
Cu
Ni
Co
Fe
S
0.14 76 19
72 2.0 78
0.7 0.10 1
0.01 1.2 1.5
27 20 0.1
The c o p p e r sulfide and m e t a l l i c p a r t i c l e s a m o u n t e d to about 1 p c t b y v o l u m e e a c h of the n i c k e l sulfide and w e r e c l o s e l y a s s o c i a t e d with the n i c k e l sulfide p a r t i c l e s . Though no f r e e c o b a l t sulfide p h a s e was d e t e c t e d , r e s e a r c h w o r k on h i g h e r c o b a l t f e e d s and a c i d l e a c h ing t e s t s of the sulfide i n d i c a t e d that a l a r g e p r o p o r tion of the c o b a l t can be p r e s e n t a s Co9S8. The above o b s e r v a t i o n s l e a d to the a s s u m p t i o n that the p r i m a r y p h a s e s p r e s e n t in the i m p u r e n i c k e l s u l fide a r e NiaS2, Cu2S , Co9S s and N i - C u a l l o y . D u r i n g c h l o r i n a t i o n t h e r m o d y n a m i c a l l y the m o s t f a v o r a b l e reactions are:
Table II
AF ~ (600 K) k J - m o l C12 Cu2S + NiaS2 + C12 NiaS2 + Cl2 1/9 Co~Ss + 8/9 NiaS2 + C12 FeS + NiaS2 + Cl2 NiS + Cl2
-> ~ ~ -~ "-~
2CuCl + 3NiS NiC12+ 2NiS CoC12+ 24/9 NiS FeC12 + 3NiS NiC12+ S
-172.55 -187.61 -225.48 -194.93 -75.06
The f r e e e n e r g y c h a n g e s shown above indicate that c o b a l t and i r o n can be p r e f e r e n t i a l l y c h l o r i n a t e d in the p r e s e n c e of n i c k e l sulfide b~ut c u p r o u s sulfide will not c h l o r i n a t e in p r e f e r e n c e to NisS 2. However, m o r e r e c e n t w o r k shows that the c h l o r i n a t i o n of NisS 2 does not p r o c e e d b e l o w about 570~ while FeS and Cu2S can b e c h l o r i n a t e d n e a r r o o m t e m p e r a t u r e f Thus, k i n e t i c s VOLUME 6B,MARCH 1975-167
MINES
TAILINGS
I
I
COPPER CONCENTRATE
NICKEL CONCENTRATE
IRON CONCENTRATE
Fig. 1--Inco (Ontario Division)--general flow sheet.
FiNiSHEO M A i [ E
SO~
SOz
1
METALLICS
Nia S z CONCENTRATE
L
l
Ni 0 SINTER TO IPC Rg'FINERY
Cu z S - CONCENTRATE
75 90 TO MARKET
1
Ni 0 SINTER TOREFINERIES
BLISTER Cu. TO REFINERY
TO LIQUEFACTION
ACID SOLUBLE NfCKEL OXIDE
IRONORE PELLETS
SULPHURIC ACID
TO M A R K E T
m a y be the o v e r r i d i n g f a c t o r in the s e l e c t i v e c h l o r i n a tion of Cu2S. M i c r o s c o p i c e x a m i n a t i o n of the i m p u r e n i c k e l sulfide c h l o r i n a t e d at 550~ showed a coating of c u p r o u s chlor i d e and some e l e m e n t a l sulfur a r o u n d the n i c k e l s u l fide p a
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