Solvent extraction by dialkyl-substituted diphosphonic acids in a depolymerizing diluent. II. Fe(III) and actinide ions

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 butyle ne- (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 h ave been ascribed to extraction of metal nitrates through a solvation mecha nism made possible by facile transfer of nitrate ions into the 1-decanol ph ase. The use of l-decanol as the diluent gives rise to strong suppression o f metal extraction, which increases along the series Fe(III)< U(VI)< Am(III )< Th(IV) and H2DEH[MDP] < H2DEH[EDP] less than or equal to H2DEH[BuDP]. Th e extractant dependencies of U(VI) and Th(IV) have slopes equal to 2 with a ll extractants. Those for Am(LII) and Fe(LII) exhibit variable slopes with limiting values of 1 at the lowest and 3 at the highest extractant concentr ations. From the combined information provided by the acid and extractant d ependencies, stoichiometries and probable structures for complexes formed i n the organic phase have been proposed. The data obtained in this work sugg est a simple route for actinide stripping from diphosphonic acid extractant s loaded in nonpolar diluents.