Cobalt and zinc recovery from copper sulphate solution by solvent extraction

It has been demonstrated in earlier works that zinc as an impurity can be effectively removed from cobalt sulphate solutions (Zn/Co < 1) by solvent extraction with D2EHPA. Some process residues from copper plants contain both cobalt and zinc as valuable metals, which have to be separately extracted for their recovery. Leaching of such residues leads to solutions with higher Zn/Co ratios (Zn/Co > 10). Again, solvent extraction with D2EHPA has been successfully used to separate cobalt and zinc into their respective solutions, which could further be treated by appropriate techniques for the production of these metals. The method mainly consists of selective copper extraction with LIX 984, iron removal by precipitation with CaCO3, simultaneous cobalt and zinc extraction with D2EHPA followed by their separation by selective stripping with sulphuric acid of different concentrations. The use of a specific cobalt extractant is not necessary. More than 95% copper has been recovered from the pregnant solution typically containing 1.0 g/l Co2+, 2.0 g/l Cu2+, 12.60 g/l Zn2+ and 8.4 g/l Fe3+. The cobalt and zinc recoveries were on an average of 90% each in their respective individual solutions.