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

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 (N-H2O) 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 N-H2O with 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 X-CH3OH. The variation of the coordination environment around Eu(III) estimated from the emission spectra was correlated well with the variation of the N-H2O. 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.