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 ion-exchange (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 pct 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 than 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 carbon monoxide Metallic cathodes, containing over 99 pct 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.
Nuclear & Chem. Waste Management, V. 8, June 1988, PP. 37-44