COMBINING NEUTRAL AND ACIDIC EXTRACTANTS FOR RECOVERING TRANSURANIC ELEMENTS FROM NUCLEAR FUEL
We have been investigating a solvent extraction system that combines a neutral extractant--octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO)--with an acidic extractant--bis(2-ethylhexyl)phosphoric acid (HDEHP)--to form a single process solvent for separating Am and Cm from the other components of irradiated nuclear fuel. It was originally hypothesized that the extraction chemistry of CMPO would dominate under conditions of high acidity (> 1 M HNO3), resulting in co-extraction of the transuranic and lanthanide elements into the organic phase. Contacting the loaded solvent with a solution of diethylenetriaminepentaacetate (DTPA) buffered with lactic or citric acid at pH {approx}3 to 4 would result in a condition in which the HDEHP chemistry dominates. Although the data somewhat support this hypothesis, it is clear that there are interactions between the two extractants such that they do not act independently in the extraction and stripping regimes. We report here studies directed at determining the nature and extent of interaction between CMPO and HDEHP, the synergistic behavior of CMPO and HDEHP in the extraction of americium and neodymium, and progress towards determining the thermodynamics of this extraction system. Neodymium and americium behave similarly in the combined solvent system, with a significant synergy between CMPO and HDEHP in the extraction of both of these trivalent elements from lactate-buffered DTPA solutions. In contrast, a much weaker synergistic behaviour is observed for europium. Thus, investigations into the fundamental chemistry involved in this system have focused on the neodymium extraction. The extraction of neodymium has been systematically investigated, individually varying the HDEHP concentration, the CMPO concentration, or the aqueous phase composition. Thermodynamic modeling of the neodymium extraction system has been initiated. Interactions between CMPO and HDEHP in the organic phase must be taken into account in the thermodynamic modeling; such interactions have been quantified by nuclear magnetic resonance measurements.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1032692
- Report Number(s):
- PNNL-SA-75623; AF5805000; TRN: US1200530
- Resource Relation:
- Conference: Proceedings of the 19th International Solvent Extraction Conference (ISEC 2011), October 3-7, 2011, Santiago, Chile, 68
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMERICIUM
CHEMISTRY
CITRIC ACID
EUROPIUM
HYPOTHESIS
NEODYMIUM
NUCLEAR FUELS
NUCLEAR MAGNETIC RESONANCE
OXIDES
PH VALUE
RARE EARTHS
SIMULATION
SOLVENT EXTRACTION
SOLVENTS
THERMODYNAMICS
TRUSPEAK
lanthanide separation
actinide separation
lanthanide/actinide separation
CMPO
HDEHP