Characterization of Eu(III) species sorbed on silica and montmorillonite by laser-induced fluorescence spectroscopy

Laser-induced fluorescence spectroscopy and batch experiments were combined to study the sorbed species of Eu(III) on amorphous silica and montmorillo nite. In the silica system, more than six water molecules were removed from the first coordination sphere of Eu(III) above pH 7, suggesting that Eu(II I) was incorporated into the silica. This fact was confirmed through the de pendence on aging time and the desorption behavior after acidification. In the montmorillonite system, the Eu(III) aquo ion was sorbed as an outer-sph ere complex on montmorillonite below pH 6. Two species with different fluor escence lifetimes were separately detected in higher pH regions in montmori llonite system. The faster component may be Eu(III)-hydroxide precipitates or Eu(III) surface precipitates, while for the slower component, the number of water molecules in the first coordination sphere of Eu(III) was 2-3. Si milar studies on Eu(III) sorbed on kaolinite was also conducted for compari son with the results on montmorillonite.