In the high pressure-high temperature oxidation-leaching of chalcopyrite ore concentrates the oxidation of the sulfides results in the formation of sulfuric acid, the dissolution of the water-soluble and acid-soluble metals, and the generation of heat due to the exothermic nature of the oxidation reactions. The oxidation reactions proceed according to the following equations: EQU 1. CuFeS.sub.2 + 4O.sub.2 .sup.H.sbsp.2.sup.SO.sbsp.4 CuSO.sub.4 + FeSO.sub.4 + Heat EQU 2. 2FeSO.sub.4 + H.sub.2 SO.sub.4 + 1/20.sub.2 .fwdarw. Fe.sub.2 (SO.sub.4).sub.3 + H.sub.2 O EQU 3. fe.sub.2 (SO.sub.4).sub.3 + 3H.sub.2 O .revreaction. Fe.sub.2 O.sub.3 .dwnarw. + 3H.sub.2 SO.sub.4
Frequently, lime (CaO) or limestone (CaCO.sub.3) is fed to the leaching autoclave to neutralize a portion of the acidity in order to precipitate arsenic or iron, or simply to reduce the acidity and adjust the pH as desired for subsequent steps of the process. Where lime is used, neutralization proceeds according to the equation: EQU 4. CaO + H.sub.2 SO.sub.4 .fwdarw. CaSO.sub.4 + H.sub.2 O
where limestone is used as the neutralizer, the reaction proceeds as follows: EQU 5. CaCO.sub.3 + H.sub.2 SO.sub.4 .fwdarw. CaSO.sub.4 + H.sub.2 O + CO.sub.2
in accomplishing neutralization the extremely important economic consideration of operation at optimal metal extraction rates may well be overlooked or defeated by maintenance of acidity levels which are not commensurate with high extraction rates. In similar vein various means are resorted to for removal of the heat generated in order to avoid buildup of excessive internal pressures, etc. Here again the extent to which heat is removed in order to minimize pressure buildup will very likely not necessarily result in optimal temperatures for maximum copper extraction.
It is an object of this invention to provide a method of oxidation-leaching of chalcopyrite and other similar copper sulfide concentrates employing oxygen-containing gases which results in a maximum rate of copper extraction from the concentrate while extracting a maximum percentage of copper from the concentrate and at the same time retaining a minimum amount of dissolved iron in the resulting solution.
It is another object of this invention to provide a method of oxidation-leaching which simultaneously allows the maximum rate and percentage of copper extraction with minimum iron in solution and optimal composition of the precipitates produced for efficient liquid-solids separation at a later stage in the copper recovery process.