Toward a better understanding of the role of lactic acid in the TALSPEAK process

Among the methods currently considered to be ready for technological deployment for the separation of trivalent actinides from lanthanides is the TALSPEAK Process. This solvent extraction method is based on the partitioning of lanthanides and actinides between an acidic organophosphorus extractant (HDEHP) solution and an aqueous phase containing a high concentration of a carboxylic acid buffer (usually lactic acid) and a polyaminopolycarboxylate complexant (DTPA). The possible presence of ternary metal-lactate-DTPA complexes in the aqueous phase or of mixed metal-lactate-DEHP complexes in the organic phase has been suggested but never confirmed using techniques for molecular characterization. Some observations suggest the presence of reverse micelles in the extractant phase. In this report the results of NMR experiments and ESI-MS analysis of solutions possibly containing such species are described. These studies are designed to improve understanding of the complicated effect of lactic acid on extraction mechanisms in the TALSPEAK process.