Sorption behavior and coordination state of Eu(III) and Cm(III) in hydrochloric acid-methanol mixture/cation exchange resin system studied by time-resolved laser-induced fluorescence spectroscopy

Abstract

A role of methanol on the enhancement of the sorption of M(III) [M=Eu, Cm] in HCl-CH3OH mixture/cation exchange resin system was investigated by comparing the distribution coefficient of M(III) with its coordination states both in the solution and the resin phases. The inner-sphere hydration number (NH2O) of M(III),i.e., the number of water molecules in the first coordination sphere, was determined by the measurement of the luminescence lifetime of M(III) using Time-Resolved Laser-induced Fluorescence Spectroscopy. From the results showing a decrease of NH2Owith an increase of methanol mole fraction (XCH3OH), it was found that the inner-sphere complexations of M(III) both with Cl-in the solution phase and with exchange group, SO3-, in the resin phase were promoted with an increase of XCH3OH. The variation of the coordination environment around Eu(III) estimated from the emission spectra was correlated well with the variation of the NH2O. It was concluded that the increase of the sorption is mainly resulted from the inner-sphere complexation of M(III) with SO3-in the resin phase.