Speciation of Uranium in Solvent Extraction Systems Related to the ALSEP Process

Climate changes dictate securing a reliable energy source with net-zero carbon oxide emission. An advanced nuclear fuel cycle would facilitate utilization of the nuclear energy. In order to better understand behavior of the used fuel components in advanced reprocessing schemes, the speciation of uranium relevant to the ALSEP process conditions has been studied. In particular, uranium(VI) in 3 M HNO₃ was extracted by HEH[EHP] and/or T2EHDGA in dodecane and the speciation of U(VI) in the organic phases was analyzed using extended x-ray absorption fine structure (EXAFS) spectroscopy and Fourier-Transformed Infra-Red Spectroscopy. In the U(VI)-HNO₃-HEH[EHP]-dodecane system, the EXAFS data suggested a mixture of UO₂(A₄) (30%) and UO₂(NO₃)₂(H₂A₂) (70%) (A= EH[EHP]) where UO₂(A₄) collectively represents the species UO₂(HA₂)₂, [UO₂•2 H₂A₂][NO₃]₂ and a UO₂(HA₂)₂/[UO₂•2 H₂A₂][NO₃]₂ mixture. In the U(VI)-HNO₃-T2EHDGA-dodecane system, EXAFS results were consistent with presence of UO₂(NO₃)₂(T2EHDGA). in this case, the coordination number of the uranium for the first coordination sphere was found to be eight with one nitrate coordinated in a bidentate mode and another one coordinated in a monodentate mode. In the ALSEP mixed solvent conditions (U(VI)-HNO₃-HEH[EHP]-T2EHDGA-dodecane system) EXAFS results indicated the presence of 60% UO₂(NO₃)₂•H₂A₂ and 40% UO₂(A₄). The obtained results are compared with the literature data for other organophosphorus and diamide ligands.