Back extraction of platinum metals from liquid membranes in an electric field

A new method for back extraction of platinum metals from the salts of tertiary amines and quaternary onium bases in the organic phase is proposed. This method allows the back extraction of platinum metals into diluted solutions of mineral acids over one stage. The method involves the passing of direct current through a system in which the extract containing a platinum metal is a liquid membrane. This method allows a practically complete back extraction of the anions PtCl₆ ^2-, RuNOCl₅ ^2- and Ru₂OCl₁₀ ^4- (the latter passes into the aqueous phase without breaking the dimer anion). It was found that when PtCl₆ ^2-, PdCl₄ ^2- and Ru₂OCl₁₀ ^4- are in a liquid membrane based on Oct₃NHCl in 1.2-dichloroethane, under the action of an electric field all these anions are transferred into aqueous 1 M HCl (E > 85%). To provide maximum back extraction of platinum metal anions, it is necessary to use small concentrations of extractants in 1.2-dichloroethane (0.1 M for Oct₃NHCl and 0.03–0.04 M both for Oct₄NCl and Ph₄PCl) over the period of the back extraction. Cyclic voltametry has demonstrated the determining role of chloroions in current transport through the interface of phases I and II.