Modeling and Speciation Study of Uranium(VI) and Technetium(VII) Coextraction with DEHiBA.
The N,N-dialkylamide DEHiBA (N,N-di-2-ethylhexyl-isobutyramide) is a promising alternative extractant to TBP (tri-n-butylphosphate) to selectively extract uranium(VI) from plutonium(IV) and spent nuclear fuel fission products. Extraction of technetium, present as pertechnetic acid (HTcO4) in the spent fuel solution, by DEHiBA was studied for different nitric acid and uranium concentrations. The uranium(VI) and technetium(VII) coextraction mechanism with DEHiBA was investigated to better understand the behavior of technetium in the solvent extraction process. Uranium and technetium distribution ratios were first determined from batch experiments. On the basis of these data, a thermodynamic model was developed. This model takes into account deviations from ideality in the aqueous phase using the simple solution concept. A good representation of uranium and technetium distribution data was obtained when considering the formation of (DEHiBA)i(HNO3)j(HTcO4)k complexes, as well as mixed (DEHiBA)2(UO2)(NO3)(TcO4) and (DEHiBA)3(UO2)(NO3)(TcO4)(HNO3) complexes, where one pertechnetate anion replaces one nitrate in the uranium coordination sphere in the two complexes (DEHiBA)2(UO2)(NO3)2 and (DEHiBA)3(UO2)(NO3)2(HNO3). Combination of complementary spectroscopic techniques (FT-IR and X-ray absorption) supported by theoretical calculations (density functional theory) enabled full characterization of the formation of mixed uranium-technetium species (DEHiBA)2(UO2)(NO3)(TcO4) in the organic phase for the first time. The structural parameters of this complex are reported in the paper and lead to the conclusion that the pertechnetate group coordinates the uranyl cation in a monodentate fashion in the inner coordination sphere. This study shows how combining a macroscopic approach (distribution data acquisition and modeling) with molecular-scale investigations (FT-IR and X-ray absorption analysis supported by theoretical calculations) can provide a new insight into the description of a solvent extraction mechanism.
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Pauline
P
Moeyaert
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Thomas
T
Dumas
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Dominique
D
Guillaumont
European Synchrotron Radiation Facility , 38000 Grenoble, France.|iHelmholtz Zentrum Dresden-Rossendorf , Institute of Resource Ecology, 01314 Dresden, Germany.
Kristina
K
Kvashnina
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Christian
C
Sorel
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Manuel
M
Miguirditchian
French Alternative Energies and Atomic Energy Commission, CEA , Nuclear Energy Division, Radio Chemistry & Processes Department, DRCP, BP 17171, F-30207 Bagnols sur Cèze, France.
Philippe
P
Moisy
Institut de Chimie Séparative de Marcoule, Université de Montpellier 2, UMR 5257 CEA/CNRS/UM2/ENSCM BP 17171 30207 Bagnols sur Cèze Cedex, France.
Jean-François
JF
Dufrêche