Mechanism of trivalent actinide/lanthanide separation using synergistic mixtures of di(chlorophenyl)dithiophosphinic acid and neutral O-bearing co-extractants

Abstract

The mechanism of synergistic selective extraction of Am(III) over Eu(III) from aqueous nitric acid solutions using di(chlorophenyl)dithiophosphinic acid [(ClΦ)2PSSH] and neutral O-bearing organophosphorus co-extractants (B) has been investigated. (ClΦ)2PSSH forms weaker complexes with Am(III) than R2PSSH (where R = alkyl group). However, the Am(III)/(ClΦ)2PSSH complexes are stronger than the corresponding Eu(III)/(ClΦ)2PSSH complexes, although the difference is not as large as in the case of the corresponding complexes formed with R2PSSH. The donor properties of co-extractants are also discussed. Chemical shifts in the 31P NMR spectra of the organophosphorus co-extractants correlate qualitatively with the extractability of Am(III) and Eu(III) in (ClΦ)2PSSH + B synergistic mixtures. The synergistic effect determines the selectivity not only qualitatively but also quantitatively. The high selectivity observed using tri-2-ethylhexyl phosphate (T2EHP) is caused by a synergistic bonding effect for the Am(III) complex and an antagonistic effect for Eu(III).