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 montmorillonite. 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(III) was incorporated into the silica. This fact was confirmed through the dependence on aging time and the desorption behavior after acidification. In the montmorillonite system, the Eu(III) aquo ion was sorbed as an outer-sphere complex on montmorillonite below pH 6. Two species with different fluorescence lifetimes were separately detected in higher pH regions in montmorillonite 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. Similar studies on Eu(III) sorbed on kaolinite was also conducted for comparison with the results on montmorillonite. (orig.)