The technical and economic aspects of producing high-purity cobalt and nickel from superalloy scrap utilizing a double-membrane electrolytic cell

Abstract

US Bureau of Mines researchers have developed a process to recover high-purity cobalt and nickel from superalloy scrap (SAS). The process utilizes novel, Bureau-developed double-membrane electrolytic cells to electrorefine SAS into high-purity cobalt cathodes and high-purity nickel cathodes. The cells anodically dissolve carburized SAS producing a chloride anolyte. This anolyte is treated by a series of hydrometallurgical provedures which yield chromium chemicals and purified cobalt chloride s and nickel chloride solutions. The purified solutions are utilized as catholytes in the double membrane electrolytic cells to recover high-purity cobalt and nickel cathodes. Energy consumption in the double membrane electrolytic cells was determined to be comparable to that of conventional electrowinning cells, and laboratory tests have produced cobalt cathodes meeting National Defense Stockpile Specifications and high-grade nickel cathodes. A preliminary economic evaluation for the process is presented. The evaluation indicates a 25.8% interest rate of return. The fixed capital cost for a plant processing 16,800 kg of SAS per day is estimated to be $22.6 million, based upon second quarter 1991 costs.