Unusual extraction of plutonium(IV) from uranium(VI) and americium(III) using phosphonate based task specific ionic liquid

A task specific ionic liquid (TSIL), diethyl-2-(3-methylimidazolium)ethylphosphonatebis(trifluoromethanesulfonyl)imide, ImPNTf2, was synthesized and characterized by H. C-13 NMR, mass and IR spectroscopy. Extraction of Pu(IV), U(VI) and Am(111) from nitric acid medium by a solution of ImPNTf2 in room temperature ionic liquids (RTILs), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (alkyl = butyl or octyl), was studied as a function of concentrations of nitric acid, ImPNTf(2) and temperature. The distribution ratio of Pu(IV) in ImPNTf(2)/bmimNTf(2) decreased with increase in the concentration of nitric acid reached a minimum around 4-5 M in nitric acid followed by increase. The stoichiometry of Pu(IV)ImPNTf2 was determined by the slope analysis of extraction data. In contrast to Pu(TV) extraction, the distribution ratios of Am(111) and U(VI) in ImPNTf(2)/amimNTf(2) and amimNTf(2) were significantly low at all nitric acid concentrations that led to unusually high separation factors for plutonium(TV) from other actinides. Viscosity of ionic liquid phase at various temperatures, and enthalpy change accompanied by the extraction of plutonium(IV) were determined and the results are reported in this paper.