Anion-exchange separation in hydrochloric acid solutions for the ultrahighpurification of cobalt

Recent applications in advanced electronics have increased the practical im portance of ultrahigh-purity cobalt. Anion exchange in HCl media is conside red an efficient alternative to the combination of the conventional purific ation methods. Anion-exchange distribution functions have been determined f or cobalt and the main impurity elements by the technique of batch equilibr ation. Spectrophotometric and elution studies confirmed the established ani on-exchange behavior patterns. Based on the new and the available distribut ion functions, combined with the assessment of thermodynamic stability, a p rocedure of anion-exchange separation has been devised to eliminate virtual ly all the impurities from the cobalt-chloride solution. The major shortcom ing of previously proposed anion-exchange procedures-failing to separate co pper sufficiently-has been corrected by the introduction of a preliminary s tep under reduced conditions, removing copper from the solution by sorption in the monovalent state. The rest of the impurities are eliminated in a se cond anion-exchange step by applying rinsing and elution stages under oxidi zing conditions. The optimum parameters of the procedure have been determin ed according to performance characteristics (purification ratios, yields, a nd volume efficiencies) derived from the analysis of elution curves obtaine d with laboratory-scale ion-exchange columns. Special computer programs hav e been developed to facilitate thermodynamic simulation, analytical correct ion, and data processing.