Complexation of Cm(III)/Eu(III) with silicates in basic solutions

The complexation of Cm(III) and Eu(III) with dissolved silica was studied by solubility measurement and time resolved laser fluorescence spectroscopy (TRLFS) in basic solutions over a range of total silica concentrations and ionic strengths (NaNO3)- In initial experiments on the solubility of Eu(OH)3 in silicate containing solutions we observed a rapid increase in the soluble Eu(III) concentration under basic conditions. The Eu(III)/Cm(III) silicate complexes that formed caused a significant increase of the hypersensitive D-5(0) -> F-7(2) band around 615 nm relative to the non-hypersensitive D-5(0) -> F-7(1) band at 592 nm for Eu(III). Further studies of Eu(III) and Cm(III) containing solutions showed a shift of the fluorescence spectral maximum from 594 nm to up to 607 nm for Cm(III) along with a significant increase of fluorescence intensities. The fluorescence lifetimes for Eu(III) species increased from 115 mu s to 1.8 ms in 3.0 M and 5.0 M NaNO3, corresponding to full coordination I and from 68 mu s to 202 mu s for Cm(III) in 0. 1 M NaNO3, consistent with the removal of 6-7 water molecules upon silicate complexation. The variations of the fluorescence intensity and the concentrations of the monomeric and polymeric silicates suggested that in basic silicate solutions, Eu(III)/Cm(III) mainly complexes with polysilicates.