Sorption behavior of curium(III) on hydrous silica: a kinetic and thermodynamic study

Sorption of tracer curium, Cm3+, on SiO2 center dot H2O (silica gel) was investigated under different experimental conditions such as time of equilibration, concentration of Sm3+, pcH. and temperature. Sm3+ was used as a carrier for Cm3+ ions in this study. From the sorption kinetics data, the diffusion coefficient Of Cm3+ ion was calculated to be 1.20(+/- 0.05) x 10(-11) m(2)s(-1) under particle diffusion-controlled conditions. The sorption rate was determined to be 3.47( +/- 0.19) x 10(-3) s(-1) at 298 K, pcH 5.25(+/- 0.03) in 0.20 M (NaClO4). The sorption data were fitted in Freundlich, Lanamuir and Dubinin-Radushkevich (D-R) isotherms. A synergistic enhancement in the sorption of Cm3+(Sm3+)-ligand (e.g., CO32-, F-, H2PO4- and C2O42-) complexes on silica gel was observed. The presence of these anions increase the sorption of Cm3+(Sm-3(+)) in the following order: CO32- < F- < C2O42- < H2PO4-. Temperature variation experiments gave enhanced sorption with increased temperature for Cm3+ indicating an endothermic enthalpy.