Hydrofluorocarbon Diluent for CMPO Without Third Phase Formation: Extraction of Uranium(VI) and Lanthanide(III) Ions

ABSTRACT

The extraction behaviors of trivalent lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and hexavalent uranium with octylphenyl($N$,$N$-diisobutylcarbamoylmethyl)phosphine oxide (CMPO) from a nitric acid medium were studied using hydrofluorocarbon (1,1,1,2,2,3,4,5,5,5- decafluoropentane: HFC-43) as a nonflammable diluent. It was revealed that HFC-43 exhibits high solubility of CMPO even in the absence of tributylphosphate (TBP), which has typically been necessary to prevent third-phase formation in the conventional TRUEX process using $n$-dodecane as a diluent. Distribution ratios have been studied as a function of aqueous HNO${ }_3$ concentrations, CMPO concentrations, and ionic radii of lanthanide(III) ions. The stoichiometry of the extracted coordination complex was examined based on the slope analysis, and it was determined that two to three CMPO molecules are coordinated to one lanthanide or uranium ion. The feasibility of the process is indicated by the distribution ratio, which is comparable to the conventional system using $n$-dodecane as diluent. In addition, the safety benefits of applying the nonflammable solvent HFC to the TRUEX process are also presented.

KEYWORDS:

• Solvent extraction
• nuclear fuel reprocessing
• truex process

Acknowledgements

The authors are grateful to Dr. Suguru Ohta for his involvement in our experiments. This work was supported by JSPS KAKENHI Grant Number 26630478 (Grant-in-Aid for Exploratory Research).

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Funding

This work was supported by the JSPS.