Selective extractions of Zn and Cd from ZnCdCoNi sulphate solution using di-2-ethylhexyl phosphoric acid extractant

Abstract

A bench scale solvent extraction study has been carried out on mixed electrolyte solutions containing zinc, cadmium and cobalt as sulphates. Very high separation factors or ΔpH 0.5 were obtained. These values indicate the ease of separation of these metals under appropriate conditions. In batch countercurrent experiments using a plant solution containing 83.2 g/l Zn, 52.8 g/l Cd, 2 g/l Co and 0.10 g/l Ni and 30 v/o di-2-ethylhexyl phosphoric acid (DEHPA) plus 4 v/o TBP in SX-1, stepwise (selective) extractions of zinc and cadmium from the mixed electrolyte solution were achieved, leaving cobalt and nickel in the raffinate. Zinc was extracted at pH 2.0 followed by cadmium extraction at pH 3.7. The Zn-loaded organic was scrubbed with ZnSO 4 solution to remove any co-extracted cadmium and cobalt contaminants at equilibrium pH 2–2.2. Similarly, the Cd-rich organic phase was scrubbed with CdSO 4 solution to remove any co-extracted cobalt and nickel species at pH 3.6–3.7. Under the experimental conditions, overall cobalt and nickel extractions were negligible.