Lactic Acid Partitioning in TALSPEAK Extraction Systems

Abstract

The TALSPEAK process, developed in the 1960s at the Oak Ridge National Laboratory and demonstrated in various forms up to pilot scale elsewhere, has emerged as a primary method for partitioning of trivalent transplutonium actinides from fission product lanthanides in advanced nuclear fuel cycles. The baseline process relies on the monoacidic dialkyl phosphoric acid extractant bis-(2-ethylhexyl)phosphoric acid (HDEHP), the aqueous complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), and high concentrations of a pH 3.5 buffer, usually 1-2 M lactic acid (HL). Previous reports have established that HL not only buffers the pH, but also increases phase transfer kinetics, improves the radiation stability of DTPA, and has been implicated as a possible participant in the formation of ternary complexes in both the aqueous and organic phases. One feature central to the interpretation of these results is the extent of partitioning of HL between the phases. In this study, ¹⁴C-labeled HL has been used to examine the details of its partitioning between aqueous solutions and organic solutions relevant to the possible deployment of TALSPEAK. It is found that, contrary to previous reports, HL partitions into the organic phase independently of the amount and identity of the metal ions that are present.

Keywords:

• actinide-lanthanide separations
• DTPA
• HDEHP
• lactic acid
• TALSPEAK

ACKNOWLEDGEMENTS

This work was supported by the U.S. Department of Energy Office of Nuclear Energy Science and Technology under the Nuclear Energy Research Initiative-Consortium (NERI-C) program under project number DE-FC07-02ID14896.

Dr. Kazuyoshi Uruga is acknowledged for insightful conversations regarding possible organic phase interactions.