Symmetrical dialkylsulphoxides in ionic liquid as extractants for uranyl ion. Extraction efficacy and aggregation behavior

The behavior of three symmetrical sulphoxides, R₂SO, where R = Di-(2-ethylhexyl) (DEHSO), R = dihexyl (DHSO) or R = diisoamyl (DIASO) in ionic liquid diluent, 1-methyl-3-octylimidazolium hexafluorophosphate (C₈mimPF₆) were examined for the extraction of uranyl ion from nitric acid medium. The extraction efficiency is found to be higher for sulphoxides with branched-chain alkyl substituents (DEHSO and DIASO) as compared to the one with linear chain (DHSO). Between branched chain analogues, the one with longer alkyl chain showed better extraction. The stoichiometry of the uranyl species extracted and its redox characteristics were probed by slope analysis, and cyclic voltammetry respectively. The aggregation behavior of the extractant, DEHSO in ionic liquid was examined by small-angle X-ray scattering and is compared with that of DEHSO in dodecane. The extractant remains as aggregates in ionic liquid while in non-polar diluent like dodecane, no aggregates were formed. (author)