New flowsheet for the recovery of cadmium, cobalt and nickel from spent Ni–Cd batteries by solvent extraction

Abstract

A new solvent extraction flowsheet for recovery of cadmium, cobalt and nickel in pure and marketable forms from sulphate solutions is proposed. The solutions processed were equivalent to those expected from sulphuric acid leaching of Ni–Cd–Co-containing residues and of spent rechargeable batteries, assaying about 80 g/l Ni, 30 g/l Cd and 1–3 g/l Co. In the new process proposed the metals are separated in two solvent extraction circuits: the cadmium separation circuit where the organophosphoric acid DEHPA (1 M) is used as extractant and the cobalt separation circuit where the organophosphinic acid Cyanex 272 (0.5 M) is the extractant. It is demonstrated that these two extractants are more efficient and selective than other competitors, namely the organophosphonic acid Ionquest 801. Under optimised conditions 99.7% of the cadmium can be recovered in the first circuit. After scrubbing of the loaded DEHPA with a pure cadmium solution this metal can be stripped into an aqueous phase assaying 195 g/l Cd, 0.14 g/l Co and 0.04 g/l Ni. The raffinate from cadmium separation is further processed in the cobalt circuit. A recovery of 99.5% of the cobalt can be attained in this second circuit. After scrubbing the loaded Cyanex 272 with a pure cobalt aqueous solution, the cobalt is stripped generating strip liquor with 126 g/l Co, 0.07 g/l Ni and 0.05 g/l Cd. The production of pure and marketable chemicals dictated the solvent extraction strategy and the conditions selected for the separation process proposed.