Low temperature sulphidization of Cu-Co slag in the presence of calcium sulphide

The investigation focuses on sulphidization of Cu, Co and Fe from a 7wt%CuO-7wt%CoO-10wt%CaO-40wt% SiO₂-(30 wt%Fe,6 wt%Al)₂O₃ slag in the presence of calcium sulphide (CaS), over a temperature range of 1173 K – 1323 K. The metal oxides phases (CuO, CoO, FeO and Fe₃O₄) in the slag were converted into metal sulphide phases (Cu₂S, CuFeS₂, FeS, Cu₅FeS₄, Co₈S₉) via MO + CaS + SiO₂ = MS + CaSiO₃ reaction, where M represents metallic Cu, Co or Fe. Cu₂S and CoS formed preferentially at low molar ratio of MO/CaS and below 1173 K. The sulphidized slag was reduced in the presence of lime (CaO) and carbon at 1323 K by following the equilibrium: MS + CaO + C = M + CaS + CO(g). The reaction products were characterised by X-ray diffraction and scanning electron microscopy techniques. The proposed method of recovering metallic phases (Cu, Co and Fe) from a Cu-Co slag via sulphidization and reduction at lower reduction temperature than 1373 K offers an energy efficient process.