Extraction of f Elements by Binary Extractants Based on 1,5-Bis[о-(dioxyphosphoryl)phenoxy]-3-Oxapentane Derivatives and Trioctylamine

This is the first study of uranium(VI), thorium(IV), and lanthanum(III) extraction from nitric acid solutions in 1,2-dichloroethane (DCE) by binary extractants prepared from stoichiometric mixtures of diphosphonic acids, namely, 1,5-bis[o-(dioxyphosphoryl)phenoxy]-3-oxapentane or 1,5-bis[о-(dioxyphosphoryl)- n-ethylphenoxy]-3-oxapentane, and trioctylamine. The binary extractant comprised of 1,5-bis[о-(dioxyphosphoryl)-n-ethylphenoxy]-3-oxapentane and trioctylamine is found to selectively recover Th(IV) from solutions that contain both U(VI) and La(III), with separation factors exceeding 100. A method is developed for an efficient stripping of thorium(IV), uranium(VI), and lanthanum(III) from the saturated organic phase. Conditions are found for recovering the studied binary extractants after stripping to make them reusable.