Sorption of silicon on magnetite and other corrosion products of iron

The sorption of Si on various iron corrosion products of nuclear waste canisters (magnetite Fe ₃O ₄ , goethite α-FeOOH, and siderite FeCO ₃) and pyrite FeS ₂ was evidenced in the presence of a background electrolyte (NaCl or NaClO ₄ ). 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 log K complexation = 8.6 . Influence of magnetite on glass lifetime was evaluated and it was estimated negligible.