RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The sorption of Si on various iron corrosion products of nuclear waste canisters (magnetite Fe₃O₄, goethite α-FeOOH, and siderite FeCO₃) and pyrite FeS₂ was evidenced in the presence of a background electrolyte (NaCl or NaClO₄). For magnetite, goethite and siderite, Si sorption increased with pH in the 3–7 pH range. It reached a plateau, and finally it decreased at pH more than 9. Sorption capacities were determined for magnetite (19 × 10⁻⁶ mol_Si g_magnetite⁻¹), goethite (79 × 10⁻⁶ mol_Si g_goethite⁻¹) and siderite (20 × 10⁻⁶ mol_Si g_siderite⁻¹), while it could be neglected for pyrite since it is almost zero. Sorption data on magnetite was modelled using a surface complexation model with the bidentate surface complex (≡ XO)₂Si(OH)₂ and logK_complexation = 8.6. Influence of magnetite on glass lifetime was evaluated and it was estimated negligible.