Improving Americium/Curium Separation Factors in the AmSel Process through Symmetry Lowering of the Diglycolamide Extractant

Partitioning and transmutation are important strategies for closing the nuclear fuel cycle. The diglycolamide extractant TODGA has played a major role in the development of solvent extraction processes for nuclear fuel reprocessing due to its good extraction performance, its hydrolytic and radiolytic stability, and its compliance with the CHON principle. However, due to drawbacks such as the tendency to form a third phase during extraction if no phase modifiers are used, continued research on diglycolamide-type extractants has led to the development of diglycolamides with decreased symmetry. In this study, it is shown that the recently developed diglycolamide, <i>N</i>,<i>N</i>-diisopropyl-<i>N</i>',<i>N</i>'-didodecyldiglycolamide (iPDdDGA), is a potential alternative to TODGA with improved separation between Am and Cm or the Ln. Using the AmSel system as a reference, the extraction kinetics, influence of the acid concentration, influence of the iPDdDGA concentration, and influence of temperature were evaluated. Slope analysis indicates similar average stoichiometries for iPDdDGA and TODGA complexes, but the extraction efficiency of iPDdDGA is orders of magnitude higher. The feasibility of selective americium stripping in combination with the hydrophilic sulfonated bis-triazinyl bipyridine SO₃-Ph-BTBP complexant was demonstrated. Selective stripping of americium was found to be possible, and the use of iPDdDGA gave an unexpected improvement in Am/Cm separation, with SF_Cm/Am values of up to 3.0. This represents a small but significant improvement compared to the 2.5 value typically found for TODGA, and it demonstrates the potential of this solvent extraction system to improve existing processes based on diglycolamide-type extractants.