Combining CMPO and HEH[EHP] for Separating Trivalent Lanthanides from the Transuranic Elements

Abstract

Combining octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) into a single process solvent for separating transuranic elements from liquid high-level waste is explored. The lanthanides and americium can be co-extracted from HNO₃ into 0.2 mol/L CMPO + 1.0 mol/L HEH[EHP] in n-dodecane. The extraction is relatively insensitive to the HNO₃ concentration within 0.1–5 mol/L HNO₃. Americium can be selectively stripped from the CMPO/HEH[EHP] solvent into a citrate-buffered N-(2-hydroxyethyl)ethylenediaminetriacetic acid solution. Separation factors >14 can be achieved in the range pH 2.5–3.7, and the separation factors are relatively insensitive to pH—a major advantage of this solvent formulation.

Keywords:

• Lanthanide separation
• actinide separation
• CMPO
• HEH[EHP]
• PC88A

ACKNOWLEDGMENT

This work was funded by the U.S. Department of Energy, Office of Nuclear Energy, through the Fuel Cycle Research and Development Program. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC05-76RL01830.