A study on the oxidative ammonia/ammonium sulphate leaching of a complex (Cu–Ni–Co–Fe) matte

The oxidative ammonia/ammonium sulphate leaching of an artificial matte was carried out to investigate the extraction behavior of copper, nickel, and cobalt. The composition of the synthetically prepared Cu–Ni–Co–Fe matte was: 24.9% Cu, 35.1% Ni, 4.05% Co, 11.5% Fe, and 24.5% S. The major mineral phases associated with the matte were: CuFeS2, CuS2, (FeNi)9S8, (FeNi)S2, Ni9S8, Ni3S2, (CoFeNi)9S8 and Co metal. To optimize the leaching conditions, parameters like oxygen partial pressure, temperature, concentration of leaching reagents and time were studied. Under optimum leaching conditions (2 M NH4OH + 2 M (NH4)2SO4, 213 psi pressure, 200 °C and 1 h), 93.8% Cu, 85.3% Ni and 76.5% Co were effectively recovered. From the X-ray diffraction analysis, the partially undissolved Cu, Ni and Co phases were assumed to be CuFeS2, (FeNi)9S8 and (CoFeNi)9S8, respectively. The iron present in the CuFeS2 phase was mostly converted to goethite [α-FeO(OH)], as the CuFeS2 phase dissociated and subsequently remained in the residue.