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 (bmimNTf(2)), has been exploited for the extraction of uranium (VI) from nitric acid medium using 1.1 M solution of tri-n-butylphosphate (TBP) in bmimNTf(2), 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/bmimPF(6). 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/bmimNTf(2) on a glassy carbon working electrode was studied using cyclic voltarnmetry. The voltammogram consists of a single reduction wave occurring at a peak potential of -1.3 V (versus I'd 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/bminiNTf(2) 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. (c) 2007 Elsevier B.V. All rights reserved.