Extraction of uranium (VI) by 1.1 M tri-n-butylphosphate/ionic liquid and the feasibility of recovery by direct electrodeposition from organic phase

The diluent characteristics and the wide electrochemical window of the room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide (bmimNTf2), has been exploited for the extraction of uranium (VI) from nitric acid medium using 1.1 M solution of tri-n-butylphosphate (TBP) in bmimNTf2, followed by direct electrodeposition as uranium oxide from organic phase. The extraction of uranium (VI) with 1.1 M TBP/bmimNTf2 has been studied as a function of nitric acid concentration and the distribution ratios were compared with those obtained with 1.1 M TBP/n-dodecane and 1.1 M TBP/bmimPF6. The amount of water and nitric acid co-extracted into the organic phase was measured. The electrochemical behavior of a solution of uranyl nitrate in 1.1 M TBP/bmimNTf2 on a glassy carbon working electrode was studied using cyclic voltammetry. The voltammogram consists of a single reduction wave occurring at a peak potential of −1.3 V (versus Pd quasi-reference electrode) due to the reduction of U(VI) and a broad oxidation wave occuring at 0.56 V. Controlled potential electrolysis of uranium (VI) extracted 1.1 M TBP/bmimNTf2 phase gave a black deposit of uranium (IV) oxide, which on heating or exposure in air leads to a mixture of uranium (IV) and uranium (VI) oxides. The lean organic phase can be recycled after electrodeposition.