Oxidation–precipitation of Co from Zn–Cd–Co–Ni sulphate solution using Caro's acid

Abstract

A process utilizing Caro's acid to precipitate cobalt from a Zn–Cd–Co–Ni sulphate solution has been investigated. Caro's acid oxidizes Co(II) to Co(III) species. About 98–99% of the cobalt contained in the feed solution was precipitated as Co(OH) 3 at pH 3.5–4.0. However, at pH≤2.5, less than 8% of the cobalt present in the feed was precipitated. At such low pH's, a dark green colloidal suspension was generated and this was difficult to filter. Results obtained from both batch and continuous experiments were similar. The cobalt content of the Co(OH) 3 precipitate was 47–49% which is fairly close to the theoretical value of 53.6%. The impurities consisted of 3–4% Zn, about 1% Cd and less than 0.005% Ni.