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 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 (19×10-6molSigmagnetite-1), goethite (79×10-6molSiggoethite-1) and siderite (20×10-6molSigsiderite-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 logKcomplexation=8.6logKcomplexation=8.6. Influence of magnetite on glass lifetime was evaluated and it was estimated negligible.