黄銅鉱, 斑銅鉱を主とする銅精鉱のアンモニア浸出

抄録

The oxidation of several sulphide minerals, particularly copper sulphide minerals in anueous ammoniaral cnhitinn has been discussed thermodynamically. Ammonia leaching experiments have been performedby usine two copper sulphide concentrates, the one which contains chalcopyrite and is associated with pyrite and the other which contains bornite and is associated with chalcopyrite.
The results are as follows:
(1) The Cu (NH₃)₄²⁺stable regions at various temperatures were estimated in termsofpH and [NH₃] + [NH₄⁺] concentration. The region became narrower in its pH range and shifted to lower pH with increasing temperature.
(2) The equilibrium potentials for anodic reactions of typical sulphide minerals in ammoniacal solution were estimated under the assumption that copper in sulphide would be dissolved at first as cuprous ammine ions which would then be oxidized to cupric ammine ions. The series of the potentials suggested that sulphide minerals were readily oxidized in the order: Cu₂S, CuS, Cu₅FeS₄, CuFeS₂, ZnS, NiS and Ag₂S. This order corresponded well to the order obtained from the experimental results reported previously.
(3) Leaching rate was enhanced significantly by increasing the agitation velocity.
(4) Increased oxygen partial pressure accelerated leaching reactions, but its effect became very small when it exceeded 5kg/cm²
(5) Variation of NH₃/Cu molar ratio influenced the copper extraction only slightlyduring the early stage of leaching. A good copper extraction from the chalcopyrite-containine concentrate was obtainedat NHS/Cu molar ratio of more than The copper extraction was about 80% when the bornite-containing concentrate wasleached at a NH₃/Cu molar ratio of 9. At lower NH₃/Cu molar ratios of 5 or 6, copper extraction was limited to ratherlow value even with a long leach time because of an insufficient amount of NH3 to keep copper ammine ions stable.
(6) An increase in the leach temperature promoted the leaching reactions. However, the change of the leaching rate with temperature was relatively small.
(7)(NH₄)₂SO₄addition enhanced leaching rate for bornite-containing concentrate but gave a little effect to the leaching of the chalcopyrite-containing concentrate. Na₂SO₄addition gave no distinguishable effect to the leaching of both the concentrates. The effect of (NH₄) ₂SO₄was to be attributed to buffer action of NH₄⁺.
(8) The presence of (NH₄) ₂SO₄provided a good copper extraction from bornite and chalcocite, for which the oxidation reactions might be OH^--generating ones. The transport of oxygen sufficient to oxidize the minerals was the most important in leaching chalcopyrite and enargite, for which the oxidation reactions might be H⁺-generating ones.