STUDIES ON U-Th SEPARATION USING TRI-sec-BUTYL PHOSPHATE

In this work, the extraction of Am(III), U(VI), Th(IV) and Fe(III) by P,P′-di(2-ethylhexyl) methylene- (H₂DEH[MDP]), ethylene- (H₂DEH[EDP]), and butylene- (H₂DEH[BuDP]) diphosphonic acids dissolved in the monomerizing diluent 1-decanol has been investigated. A comparison of the acid dependencies with those observed in o-xylene has revealed a number of novel features which have been ascribed to extraction of metal nitrates through a solvation mechanism made possible by facile transfer of nitrate ions into the 1-decanol phase. The use of 1-decanol as the diluent gives rise to strong suppression of metal extraction, which increases along the series Fe(III)2DEH[MDP]2DEH[EDP]≤H₂DEH[BuDP]. The extractant dependencies of U(VI) and Th(IV) have slopes equal to 2 with all extractants. Those for Am(III) and Fe(III) exhibit variable slopes with limiting values of 1 at the lowest and 3 at the highest extractant concentrations. From the combined information provided by the acid and extractant dependencies, stoichiometries and probable structures for complexes formed in the organic phase have been proposed. The data obtained in this work suggest a simple route for actinide stripping from diphosphonic acid extractants loaded in nonpolar diluents.