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 alpha-FeOOH, and siderite FCO3) 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 x 10(-6) mol(Si) g(magnetite)(-1)), goethite (79 x 10(-6) mol(Si) g(goethite)(-1)) and siderite (20 x 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 (equivalent to XO)(2)Si(OH)(2) and logK(complexation) = 8.6. Influence of magnetite on glass lifetime was evaluated and it was estimated negligible. (c) 2005 Elsevier B.V. All rights reserved.