Selective recovery of nickel and cobalt from cobalt-enriched Ni–Cu matte by two-stage counter-current leaching

This work presents investigations on the selective recovery of Ni and Co from Ni–Cu matte by two-stage counter-current leaching. The investigations indicated that the sulphuric acid used during leaching can be fully replaced by sulphur. The leaching behavior of nickel and cobalt were determined and the influences of temperature, the amount of sulphur and oxygen pressure on leaching process were also investigated. A pilot plant experiment was carried out to confirm the developed process. It is found that, under two leaching conditions: (1) Ambient pressure leaching: sulphur coefficient = 1.15, T = 85 ± 5 °C and time = 2.5 h with a liquid to solid ratio of 5:1 (i.e., L/S = 5:1), and (2) Elevated pressure leaching: L/S = 5:1, T = 150 ± 5 °C, pressure = 1.45 MPa, air flowrate = 1500 ± 50 N m3/h and time = 6 h; the achieved recoveries of Ni and Co were >96.02%. The ratio of Cu/Ni is higher than 45 in the resulting residue, which is favorable for effective recovery Cu by simple H2SO4 leaching followed by electrowinning step to obtain copper metal. Therefore, the leaching liquor can be used to recover Ni and Co after removal of iron and Cu can be extracted from the residue.