A Mineralogical Study of the Phases Formed During the CuSO₄–H₂SO₄–O₂ Leaching of Nickel-Copper Matte

Abstract

A mineralogical study has been carried out to identify the changes occurring in the sulphide phases during the leaching of Ni–Cu matte in CuSO₄-H₂SO₄-O₂ solutions. The unleached matte consists predominantly of Ni₃S₂, Cu₂S and a Ni alloy. During attack by CuSO₄-H₂SO₄-O₂ media, the Ni₃S₂ reacts with CuSO₄ and O₂ to form soluble nickel, polydymite (Ni₃S₄) and covellite (CuS). The Cu₂S present in the original matte is converted sequentially to digenite (Cu_1.8S) and then to covellite; finally the covellite and Ni₃S₄ are oxidized to copper sulphate and nickel sulphate by O₂-H₂SO₄. Iron present in the sulphides or in the Ni alloy also is dissolved but re-precipitates, at least in part, as ammonium jarosite. The ammonium jarosite itself seems to dissolve to a limited extent in various parts of the circuit. Oxides present in the feed pass through the processing cycle largely unaffected although extensive silicate dissolution does occur.