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Comprehensive studies on third phase behavior during solvent extraction of U(vi)/Th(iv) mixtures

Abstract : The third phase formation during liquid/liquid extraction has been studied for decades by several authors[1-3] starting in the 50’s. Those studies were focused on the determination of the maximum organic loading that can be reached for a metal in order to avoid phase splitting during the industrial applications like the PUREX process. More recent studies were driven using a physical approach[4-5] to propose models accounting for phase segregation phenomenon. A new interest on third phase studies appeared in the early 2000’s with the investigations released for the Th-cycle [6-8]. Most of the models and results rely on SANS/SAXS or FTIR data acquired on metal-free or singlemetal systems, and concentrations were often determined through analysis. Despite the huge amount of data concerning LOC (Limiting Organic Concentration) of actinides (IV) for different phosphate based solvent, a lack of data remains in the literature for U(VI) alone and in the presence of Th(IV) or Pu(IV) for TBP/dodecane solvent. Besides, there are few values concerning the composition of both heavy and light organic phases after splitting, and when available, the data covers only a thin range of the 3rd phase existence. Therefore, we have determined LOC value for U(VI)/HNO3/TBP/dodecane system at different HNO3 and TBP concentrations which have not been yet reported in the literature. In addition to these, the behavior of U(VI) and Th(IV) after phase segregation and the composition of each phase was characterized using X ray fluorescence spectroscopy (XFS), allowing metal and TBP direct titration in organic medium for the first time ever according to our knowledge. Nitric acid and water contents were also estimated using acid/base and Karl Fischer titration respectively. Trends were established for U(VI) and Th(IV) independently in the third phase, thus a better understanding of demixing behavior of bimetallic U(VI)/Th(IV) systems was achieved. A parallel has also been drawn by studying transition metals behavior in HCl/TBP/dodecane systems (analyzed by XFS and ICP-OES) in order to determine contributions of metal and acid to phase segregation phenomena. Moreover, we showed that LOC values can vary considerably from a metal to another even when working in the same conditions of extraction; we are currently investigating molecular species that may be involved in phase splitting.
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https://hal-cea.archives-ouvertes.fr/cea-02339289
Contributor : Bibliothèque Cadarache <>
Submitted on : Wednesday, October 30, 2019 - 1:29:07 PM
Last modification on : Wednesday, September 2, 2020 - 1:34:02 PM

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  • HAL Id : cea-02339289, version 1

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J. Durain, D. Bourgeois, D. Meyer, M. Bertrand. Comprehensive studies on third phase behavior during solvent extraction of U(vi)/Th(iv) mixtures. Radchem 2018, May 2018, Marianske Lanze, Czech Republic. ⟨cea-02339289⟩

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