SOLVENT-EXTRACTION OF METAL-IONS AND SEPARATION OF NICKEL(II) FROM OTHER METAL-IONS BY ORGANOPHOSPHORUS ACIDS

Such physicochemical properties of bis(2-ethylhexyl)phosphinic acid, 2 -ethylhexylphosphonic acid mono-2-ethylhexyl ester and bis(2-ethylhexy l)phosphoric acid as the solubilities and the dissociation constants i n water, the dimerization constants in organic solvent and distributio n constants in organic solvent-water were examined by a potentiometric two-phase titration. The solvent extraction of seven kinds of transit ion metal ions and magnesium(II) from aqueous sulfate media was studie d with the three organophosphorus acids. The pH1/2 values obtained wer e discussed in terms of the separation efficiency between nickel(II) a nd the other metal ions. Bis(2-ethylhexyl)phosphinic acid was found to exhibit the best separation efficiency compared with the other two ex tractants. As a practical application, the purification of unrefined n ickel sulfate solution containing the other metal ions as impurities w ith three extractants was studied by the sequential multistage extract ion method with a separatory funnel.