Pressure leaching of copper minerals in perchloric acid solutions
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The leaching of covellite (CuS), chalcocite (Cu2S), bornite (CusFeS4), and chalcopyrite (CuFeS2) was carried out in a small, shaking autoclave in perchloric acid solutions using moderate pressures of oxygen. The temperature range of investigation was 105~ to 140~ It was found that covellite, chalcocite, and bornite leach at approximately similar rates, with chalcopyrite being an order of magnitude slower. It was found that chalcocite leaching can be divided into two stages; first, the rapid transformation to covellite with an activation energy of 1.8 kcal//mole, followed by a slower oxidation stage identified as covelite dissolution with an activation energy of 11.4 kcal/mole. These two stages of leaching were also observed in bornite with chalcocite (or digenite) and covellite appearing as an intermediate step. No such transformations were observed in eovellite or chalcopyrite. Two separate reactions were recognized as occurring simultaneously for all four minerals during the oxidation process; an electrochemical reaction yielding elemental sulfur and probably accounting for pits produced on the mineral surface, and a chemical reaction producing sulfate. The first reaction dominates in strongly acidic conditions, being responsible for about 85 pct of the sulfur released from the mineral, but the ratio of sulfate to elemental sulfur formed increases with decreasing acidity. Above 120~ the general oxidation process appears to be inhibited by molten sulfur coating the mineral particles; the sulfate producing reaction, however, is not noticeably affected above this temperature. For chalcopyrite, activation energies were determined separately for the oxygen consumption reaction and for the production of sulfate, with values of 11.3 and 16.0 kcal//mole respectively. W H E N s u l f i d e s a r e s u b j e c t e d to oxidation leaching in a c i d m e d i a , sulfur is f r e q u e n t l y obtained in good yield. 1 F o r e x a m p l e , a l m o s t 100 pct of the m i n e r a l s u l fur is obtained in the e l e m e n t a l state d u r i n g the oxidation of p y r r h o t i t e , 2 galena,3,4 and s p h a l e r i t e . 5 F o r p y r i t e , the y i e l d i s poor (less than 50 pct). 6'7 Copper sulfide m i n e r a l s p r o d u c e e l e m e n t a l s u l f u r in v a r i a b l e yield, depending on the identity of the m i n e r a l , the n a t u r e of the oxidant, and other v a r i a b l e s . Sullivan8 f i r s t studied the l e a c h i n g of copper m i n e r a l s by f e r r i c sulfate s o l u t i o n s . In a far m o r e s o p h i s t i c a t e d s e r i e s of s t u d i e s , I n g r a h a m and c o w o r k e r s 9-13 studied the l e a c h i n g of h i g h - p u r i t y s y n t h e t i c m i n e r a l s p e c i m e n s a s s p i n n i n g d i s c s in f e r r i c sulfate s o l u t i o n s . In a l l of t h e s e s t u d i e s a wide r a n g e of r a t e s was obt a i n e d but the e l e m e n t a l sulfur yield was e s s e n t i a l l y 100 pct when it was d e t e r m i n e d . J a c k s o n and S t r i c k land studie
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