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/ft 2 (13.4 m 3/h m 2) 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.