Combined extractant systems have been shown to offer some advantage in lanthanide actinide separations in TALSPEAK-like systems. To provide additional options for conducting these separations, a series of novel aqueous holdback reagents have been synthesized using the dipicolinic acid (2,6-pyridinedicarboxylic acid) backbone. The functionalization of dipicolinic acid focused on minimizing changes in the coordination environment while adjusting the acidic media solubility of the holdback reagent. Functionalizing at the 4-position of the pyridine ring minimizes changes in the coordination environment. By varying the functional groups the acid solubility can be tuned. The ligands synthesized  focus on the incorporation of oxygen and nitrogen bearing substituents. The functionalized dipicolinic acid derivatives simplify the complex chemistry of TALSPEAK-like systems by removing the need for buffering that is essential for the traditionally-used polyaminopolycarboxylate holdback reagents.  The separation potential of these holdback reagents were characterized by application in conjunction with the promising HEH(EHP)/Cyanex-923 combined extractant system in a reverse-TALSPEAK stripping regime to separate the actinides from the co-extracted lanthanides.Financial support for this research was provided by the U.S. Department of Energy, Fuel Cycle Research and Development program, Sigma Team for Minor Actinide Separations program.

Dipicolinate-based separation of trivalent actinides from lanthanides using mixed extractant solvent extraction

248th National Meeting (2014)

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