Separation and recovery of cadmium(II), cobalt(II) and nickel(II) from sulphate leach liquors of spent Ni–Cd batteries using phosphorus based extractants

Solvent extraction separation and recovery of cadmium(II), cobalt(II) and nickel(II) from sulphate leach liquor of spent Ni–Cd batteries was investigated using phosphorus based extractants such as TOPS 99, Cyanex 923, Cyanex 272, Cyanex 302 and Cyanex 301 diluted in kerosene. The composition of the leach liquor used for the present study contains (g/L): Cd, 2.40; Ni, 5.94; Co, 0.05. Among the phosphorus based extractants screened at 0.1 M concentration as a function of aqueous phase equilibrium pH, Cyanex 301 showed selective separation of Cd(II) from Co(II) and Ni(II). On the other hand, stripping of metal from Cd–Cyanex 301 loaded organic (LO) phase needs high acid solution. Two-stage counter-current extraction with 0.06 M Cyanex 301 at unit phase ratio and three-stage stripping of the metal from LO with 6 M HCl at an aqueous to organic (A:O) phase ratio of 2 yielded >99.9% Cd(II) extraction and stripping efficiency. However, Cd(II) concentration in strip solution was reduced to half. Cobalt(II) extraction efficiency of ∼99% was achieved from cadmium raffinate at an equilibrium pH of 6.25 with 0.03 M Cyanex 272 in two counter-current stages at an A:O ratio of 2:1. Complete stripping of metal from LO containing 0.15 g/L Co(II) was carried out using a strip solution pH of 1.0 in two stages at an O:A ratio of 1.75. The enrichment of cobalt during extraction and stripping operations was ∼5.2 times. Complete process flowsheet for the separation and recovery of Cd(II), Co(II) and Ni(II) was proposed.