Energy efficient separation of magnetic alloy from the carbothermic reduction of NKANA Cu-Co concentrates

The Nkana Cu-Co mineral sulphide concentrates containing 40 wt.% SiO₂ were carbothermically reduced in the presence of CaO by following the equilibrium: MS + CaO + C = M + CaS + CO(g), where M represents the metallic Cu, Co and Fe, over a temperature range of 1073 K – 1323 K. We investigated the magnetic separation of alloy phases into copper-cobalt rich and iron-cobalt rich fractions. The proposed approach appears more energy efficient than melting a mixture which yields a ternary alloy composed of Cu, Co and Fe, and a non-magnetic fraction (CaS, excess CaO and SiO₂). The extent of magnetic separation was affected by the temperature and mole ratios of MS/CaO and C/CaO, used for the reduction of mineral concentrate. The reduced and magnetically separated samples were characterised by XRD, SEM-EDX and XRF techniques. The alloy phase contained ~92 wt% of metallic constituents, with remaining 8 wt.% as mixture of CaS and SiO₂. The utilisation of this gangue mixture in the process is briefly discussed.