Scrubbing of Cadmium and Nickel from Cyanex 272 Loaded with Cobalt

Abstract

A process for the scrubbing of cadmium and nickel from Cyanex 272 loaded with cobalt was studied and is presented in this paper, as a part of a global solvent extraction process proposed for the recycling of spent Ni‐Cd batteries. After cadmium recovery in a first extraction circuit, the resulting solution containing about 80 g/L Ni, 1 g/L Co, and a residual Cd concentration of 0.10 g/L is processed in the second circuit where cobalt is extracted by 0.5 M Cyanex 272. The resulting organic phase containing about 7 g/L Co is contaminated with about 2 g/L Ni and 0.5 g/L Cd. The removal of nickel was successfully attained by scrubbing with cobalt sulphate solutions containing more than 8.7 g/L Co, at organic/aqueous (O/A) = 4 (95–98% efficiency in a single stage), while cadmium removal by this process was inefficient. The scrubbing of cadmium was achieved with high efficiency using aqueous complexing agents, namely 1 M sodium thiosulphate or 3 M ammonium chloride (scrubbing efficiencies of 97% and 80%, respectively, in a single stage at O/A = 4). The selectivity Cd/Co observed when using these two inorganic ligands was very promising since only about 0.01% or 0.14% of cobalt was scrubbed. An overall countercurrent multistage system was proposed consisting on two scrubbing operations: (1) scrubbing with a cobalt sulphate solution (8.7 g/L Co) for Ni removal and (2) scrubbing with 1 M sodium thiosulphate or 3 M ammonium chloride for Cd removal. The overall scrubbing efficiencies were respectively, 98.6% for Ni and 99.1% or 97.9% for Cd. The final organic phase contained 9.1 g/L Co, 0.03 g/L Ni and 0.005 or 0.012 g/L Cd, anticipating the recovery of a cobalt product with good purity.