Speciation of Europium(III) Sorbed on a Montmorillonite Surface in the Presence of Polycarboxylic Acid by Laser-Induced Fluorescence Spectroscopy

Laser-induced fluorescence spectroscopy was applied for the characterization of Eu(III) species sorbed on organic−inorganic hybrids such as montmorillonite coated with poly(acrylic acid) or poly(methacrylic acid) in aqueous solution (suspension). The emission lifetime and the emission spectra of Eu(III) sorbed on the organic−inorganic hybrid indicated that Eu(III) can be sorbed as an Eu(III)−polycarboxylate complex on montmorillonite. The stabilities of the Eu(III)−polycarboxylate complex and inorganic Eu(III) species sorbed on montmorillonite control the species of Eu(III), i.e., organic or inorganic, sorbed on the organic−inorganic hybrid. It was suggested that Eu(III) can be sorbed as a humate complex when an Eu(III) ion is contacted with an organic−inorganic hybrid, such as a humic acid−clay mineral hybrid, in a natural aquifer.