Solvent extraction process for the separation of cobalt from nickel in aqueous sulphate-containing solutions

Abstract

An improved process for separating cobalt values from nickel values in an aqueous nickel and cobalt sulphate-containing solution in which the solution is contacted with a water-immiscible organic solution containing an organophosphorous acid in a cobalt extraction circuit. The process is particularly useful for aqueous solutions containing high total metals content and elevated cobalt concentrations, while avoiding the formation and precipitation of ammonium sulphate containing double salts during the solvent extraction of the cobalt. The improvement includes contacting a portion or all of the water-immiscible organic solution required for cobalt extraction with a nickel-containing ammoniacal solution to produce a nickel-loaded organic phase and a partially nickel-depleted raffinate. The nickel-loaded organic phase is then passed to the cobalt extraction circuit for selective cobalt extraction in which nickel is displaced from the organic phase by cobalt, to produce a cobalt-depleted, nickel-enriched, raffinate and a cobalt-loaded organic phase. Advantageously, the nickel-containing ammoniacal solution is generated by adjustment of the nickel-containing raffinate from the cobalt extraction circuit, by additions of ammonia, preferably as ammonium hydroxide, and ammonium sulphate.