154 CARNEGIE INSTITUTION OF WASHINGTON. 



The reaction can not at present be satisfactorily worked out on a quantitative 

 basis owing to the fact that pyrrhotite varies in composition and is attacked 

 by one of the reaction products, namely, sulphuric acid. Chalcopyrite alters to 

 covellite and chalcocite. The reaction between chalcopyrite and cupric 

 sulphate to form chalcocite has been shown to be represented by the equation 



oCuFeS2+llCuS04+8H20 = 8Cu2S+5FeS04+8H2S04 



When chalcopyrite alters to covellite the experiments point strongly to the 

 reaction represented by the following equation: 



CuFeS2+CuS04 = 2CuS+FeS04 

 and also indicate that this reaction is involved in the alteration to chalcocite. 

 Barnite alters to chalcocite as follows: 



5CU5FCS4+IICUSO4+8H2O = 18Cu2S+5FeS04+8H2S04 

 It has also been shown that bornite may alter to covellite and chalcocite thus: 



Cu5FeS4+CuS04 = 2Cu2S+2CuS+FeS04 

 Covellite alters to chalcocite as follows : 



5CuS+3CuS04+4H20 = 4Cu2S+4H2S04 



The experiments also furnish evidence that this reaction proceeds in two 

 stages, thus: 



CuS+7CuS04+4H20 = 4Cu2S04+4H2S04 

 4CuS+4Cu2S04 = 4Cu2S+4CuS04 



It is very probable that the latter reaction is involved when these sulphides 

 alter to chalcocite and when cupric sulphate is the enriching agent. Sphalerite 

 and galena alter first to covellite and subsequently to chalcocite: 



ZnS + CUSO4 = CuS + ZnS04 

 5CuS+3CuS04+4H20 = 4Cu2S+4H2S04 



PbS + CUSO4 = CuS + PbS04 

 5CuS+3CuS04+4H20 = 4CUS+4H2SO4 



(3) The order of stability of the sulphide enrichment products toward cupric- 

 sulphate solutions is: chalcopyrite, covelUte, chalcocite; each of them changing 

 into the succeeding sulphide by the further action of cupric sulphate. Chalco- 

 cite is by far the most stable sulphide of all, under these conditions, but it may 

 finally be converted into metallic copper and sulphuric acid, tliough very 

 slowly indeed even at 200°. The most favorable conditions which have been 

 observed for the formation of the intermediate products, chalcopyrite and 

 coveUite, are the exposure of a large surface of the reacting sulphide to the 

 action of a comparatively dilute solution of copper sulphate. 



(4) All these reactions have been studied at several temperatures ranging 

 from 200° down to 30°. In the main the rate rather than the nature of the 

 reaction is changed by raising the temperature, but there are a number of 

 secondary reactions, slight or negligible at Ioav temperatures, which become 

 pronounced at higher temperatures. Thus ferrous sulphate is partly changed 

 into ferric sulphate by cupric sulphate: 



2CuS04+2FeS04^i^Cu2S04-|-Fe2(S04)3. 



At elevated temperatures, hydrolysis generally conditions the formation of 

 considerable hematite, cuprite, and metallic copper from the two primary 

 products of the above reaction. To what extent the metallic copper and 

 cuprite sometimes found in the natural enrichment zone are derived from 

 the hydrolysis of cuprous sulphate is not clear from these experiments. 



