The origin of enriched mantle beneath São Miguel, Azores

T. Elliot, J. Blichert-Toft, A. Heumann, G.W. Koetsier, V.H. Forjaz

    Research output: Contribution to JournalArticleAcademicpeer-review

    Abstract

    Sulfate and selenate adsorption on iron oxides are important reactions in natural systems under a very wide range of pH values, ionic strengths, and electrolyte compositions. Under such conditions, spectroscopic and theoretical calculations have demonstrated the potential importance of a variety of surface species. Understanding the variations in the surface speciation of these oxyanions is fundamental to prediction of their partitioning between minerals and aqueous solutions. In the present study, published experimental spectroscopic and theoretical molecular evidence of the identity of sulfate/selenate surface species are integrated with a surface complexation model consistent with a wide variety of experimental adsorption, surface titration, and proton coadsorption data to define the surface speciation of sulfate and selenate on iron oxides under a wide range of conditions. The analysis was carried out with the extended triple layer model (ETLM) taking into account the electrostatics of water dipole desorption during ligand exchange reactions. On seven out of eight goethites studied, sulfate and selenate surface reactions can be represented by the formation of a monodentate-mononuclear inner-sphere and a bidentate-binuclear outer-sphere (or H-bonded) species according to> FeOH + H
    Original languageEnglish
    Pages (from-to)1-270
    JournalGeochimica et Cosmochimica Acta
    Volume71
    DOIs
    Publication statusPublished - 2007

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