Role of acetic acid on U(VI) sorption on silica
Résumé
The influence of acetate on U(VI) sorption on silica from aqueous solutions was studied at pH 2–7 by complementary experimental methods of macroscopic measurement, spectroscopic investigation and thermodynamic calculation. Sorption percentage of U(VI) in the absence and in the presence of different acetate concentrations was determined by batch sorption procedures. Attenuated total reflection Fourier transform infra-red spec-troscopy (ATR-FTIR) was used to elucidate the mechanisms of uranyl sorption on silica in the presence of acetate, by investigating, in-situ, the changes in the U(VI) sorption on silica surface in presence of ligand: the absorption bands of carboxylate ν(COO) in the range 1300–1700 cm −1 and those around 850–950 cm −1 of uranyl species νas(UO 2) are followed. The decrease of U(VI) sorption with increasing acetate concentration was observed. Sorption of U(VI)-acetate (U-Ac) species on silica surface was demonstrated for the first time. ATR-FTIR investigations clearly evidenced the absorption bands characteristic of sorbed U-Ac complexes both from the acetate and uranyl spectral regions those the wavenumbers correspond to sorbed species. No sequence effect of acetate and uranyl on the sorption on silica in ternary systems U(VI)-acetate-silica was observed from the sorption data. From the ATR-FTIR investigations, we can induce that the sorption of U-Ac leads to chemical equilibria and makes possible the modeling of sorption isotherms by surface complexation models. The related thermodynamic constants were modeled using CCM surface complexation modeling.