Identification of F− and SO42− as the radiolytic products of the ionic liquid C4mimNTf2 and their effect on the extraction of UO22+

A precipitate was found at the interface between the aqueous phase and the ionic liquid (IL) phase during the separation of UO22+UO22+/Eu3+ using irradiated IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (C4mimNTf2), and was analyzed by SEM, EDS, XPS and PXRD. The anions F− and SO42−SO42− were identified as the radiolytic products of C4mimNTf2. The radiation effect on the extraction of UO22+UO22+ from aqueous solution by tri-n-butyl phosphate (TBP) in C4mimNTf2 was studied. For the presence of F− and SO42−SO42−, the utilization of irradiated C4mimNTf2 as diluent reduced the extraction efficiency of UO22+UO22+. The EXAFS measurement showed that the degradation of C4mimNTf2 insignificantly influenced the coordination environment of UO22+UO22+ in the IL phase. Furthermore, it was suggested that the complex of uranyl ion with four TBP molecules is predominant during the extraction of UO22+UO22+ by TBP in C4mimNTf2 from aqueous solution in the absence of nitric acid. This work gives a further assessment for the application of ILs in the processing of spent nuclear fuel.

► The anions F− and SO42−SO42− were identified as the radiolytic products of C4mimNTf2.
► Utilization of irradiated C4mimNTf2 reduced the extraction efficiency of UO22+UO22+.
► Uranyl ion with four TBP molecules is predominant during the extraction.