RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Laboratory experiments have been performed on magnetite according to the batch method. The sorption of three cations of three different oxidation states has been investigated under various pH: Cs (I) and Ba (II) which have long lived isotopes, and Eu (III) which can be considered as a chemical analogue of Am (III). Results showed that magnetite has a high capacity of retention for Ba²⁺ and Eu³⁺, especially under pH conditions expected in a deep geological disposal. Cs⁺ is not sorbed on a pure magnetite but it can be sorbed if magnetite contents some impurities such as silica. In this case the sorption was strongly dependent on the presence of other alkaline metal ions such as sodium. A good fitting of these experimental results has been obtained by using the surface complexation theory (fiteql 3.2 code) with the diffuse layer model (DLM) (leading to the species ≡XOHBa²⁺, ≡XOBaOH, ≡XOHEu³⁺, ≡XOEu(OH)₂ with log K respectively equal to 4.05–11.50 6.43 and −14.87).