The introduction of solvent-extraction steps during upgrading of a cobalt refinery

At a South African cobalt refinery, cobalt-bearing feed material is leached in sulphuric acid and the resultant liquor is subjected to classical precipitation methods to produce an upgraded cobalt carbonate. This process flow sheet does not allow the flexibility to accept diverse feed materials containing varying quantities of impurity elements such as nickel, manganese, magnesium and zinc, and at the same time satisfy the market requirement for high-purity cobalt products. The development of two solvent-extraction (SX) circuits that were successfully implemented at the operating refinery to overcome these problems is described. rst SX circuit employs di(2-ethylhexyl)phosphoric acid as the extractant in a pH-controlled circuit to remove contained zinc and manganese. Hydrochloric acid is used as the stripping solution because of the co-extraction of iron and calcium onto the loaded organic phase. A scrub stage is required to minimise the loss of co-extracted cobalt. second circuit, CYANEX®272 is used in pH-controlled extraction and scrub circuits to successfully reject magnesium and nickel in favour of cobalt. Stripping of the loaded organic phase using a sulphuric acid solution is employed to produce a substantially upgraded cobalt sulphate solution from which pure cobalt carbonate is precipitated. ll-scale installation, designed to produce 1 ton of cobalt per day, is described and results obtained during commissioning are discussed.