RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The sorption of Th on amorphous colloidal particles of SiO₂ (Aerosil OX 200) has been studied in perchlorate media in order to obtain quantitative information on the sorption of The on silica. In order to quantify the pH dependence of the charge of the silica surface, potentiometric surface titrations of the silica particles have also been made. The results from the studies were modelled using a surface complexation model with a diffuse layer correction for electrostatic terms. The sorption and surface charge data can be explained by the following surface complexation reactions: ≡SiOH ⇌≡SiO⁻ + H⁺ log Q_a^int=−6.9±0.1 2≡SiOH + Th⁴⁺ ⇌ (≡SiO)₂Th²⁺ + 2H⁺ log Q₁^int = −1.9±0.4

The errors are given as three standard deviations in the fitted constants. According to model predictions, which are confirmed by literature data, the sorption of Th on silica will only be important in the pH range 3–6.