| Abstract: |
U(VI) sorption on a purified Na-bentonite was investigated from 298±2 to 353±2 K by using a batch experimental method as a function of pH, U(VI) concentration, carbonate concentration and solid-to-liquid ratio (m/V). The data at 298±2 K could be well described by a surface complexation model (SCM) with a complex located on layer sites (X2UO2) and three complexes located on edge sites (≡SOUO2+, ≡SO(UO2)3(OH)5, and ≡SO(UO2)3(OH)72−). The intrinsic equilibrium constants (Kint) of the surface reactions at 333 ± 2 and 353±2 K were obtained by fitting U(VI) sorption curves vs. pH on the Na-bentonite. The model enables U(VI) sorption in the presence of carbonate (pCO2=10−3.58 atm) to be described without considering any ternary surface complexes involving carbonate, except for underestimation around pH 7 (6r Hmθ) of the surface reactions were evaluated from the Kint values obtained at three temperatures (298±2, 333±2 and 353±2 K) via the van´t Hoff equation. The proposed SCM and Δr Hmθ of the surface reactions enable U(VI) sorption on the Na-bentonite at other temperatures to be predicted. |
