Recovery of cobalt from spent copper leach solution using continuous ion exchange

Significant amounts of cobalt are present in readily accessible spent copper leach solutions. The Bureau of Mines investigated the feasibility of extracting cobalt from one of these solutions in a multiple-compartment ionexchange (MCIX) column. The effects of aqueous flow rate, resin flow rate, column height, and compartment height on cobalt extraction were determined. Cobalt extractions of 92% or higher were achieved at solution flow rates of up to 5.5 gpm/ft² (13.4 m³/h m²) of column cross-sectional area and an aqueous-to-resin flow ratio of 40:1. Overall cobalt extraction increased as the column height increased, but cobalt extraction per unit of height was more efficient in 2.4 and 3.7 m columns that in a 5.5 m column. Solvent extraction procedures were utilized to purify and concentrate the MCIX column eluates and produce a cobalt sulfate solution containing 70 to 80 g/L Co. Metallic cathodes, containing over 99% Co, were electrowon from this solution. Nickel, zinc, and copper byproducts were also recovered during processing of the ion-exchange eluates.

Estimated total capital cost for a commercial-scale plant processing 10,000 gpm (2,270 m3/h) of a spent leach solution containing 26 mg/L Co was $23.1 million (U.S.). With credits for zinc, nickel, and copper byproducts, the estimated net operating cost was $5.10/lb ($11.24/kg) of cobalt.