Diluent effect on the extraction of uranium(VI) from hydrochloric acid solutions by trioctylamine

The extraction of uranium(VI) and divalent metals (copper, zinc and cadmium) from hydrochloric acid solutions by trioctylamine (TOA) has been examined using various toluene, m-xylene, nitrobenzene, carbon tetrachloride, chloroform and 1,2-dichloroethane. It is found that a parabolic dependence of the distribution coefficient on the solubility parameter of diluent is not observed in these extraction systems. The results obtained are investigated in comparison with the extraction of uranium(VI) and divalent metals by trioctylmethylammonium chloride (TOMAC) in organic solvents in which the distribution coefficient and the enthalpy change associated with the metal extraction can be expressed in terms of the solubility parameter of extractant, diluent and the complex formed in the organic phase and their molar volume by assuming a regular solution. Consequently, since the solutions of TOA x HCl in organic solvents are not regarded as regular solutions, it is expected that the extraction of uranium(VI) from hydrochloric acid solutions by TOA is not always explained in the view point of a regular solution therapy. 16 references, 7 figures, 9 tables