Selective Extraction of Minor Actinides from Acidic Media Using Symmetric and Asymmetric Dithiophosphinic Acids

The minor actinides (Am and Cm) and other transplutonium elements represent significant, long-term hazards found in spent nuclear fuel. The selective extraction of the minor actinides from the lanthanides is an important part of advanced reprocessing of spent nuclear fuel. This separation would allow the minor actinides to be fabricated into a target and recycled to a reactor and the lanthanides to be disposed. Due to the similarities in the chemical properties of the trivalent actinides and lanthanides, this separation is difficult to accomplish. The introduction of soft donor groups, such as N or S, into similarly structured ligands increases the differentiation between An(III) and Ln(III) cation coordination. Partly because of limitations imposed by synthetic methodologies, previous studies of dithiophosphinic acid (DPAH) extractants has been restricted to a comparatively small number of symmetrical dialkyl and diaryl derivatives. Research efforts at the Idaho National Laboratory have resulted in the recent development of an innovative synthetic pathway yielding new regiospecific DPAH extractants. The synthesis improves DPAH designs that can address the issues concerning minor actinide separation efficiency and extractant stability. Several new symmetric and asymmetric DPAH extractants have been prepared. The use of these extractants for the separation of minor actinides from lanthanides will be discussed. In addition, the variation in the extent of Am(III) extraction by a related series of DPAH isomers will be presented.