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    The effect of pH, grain size, and organic ligands on biotite weathering rates

    232230_232230.pdf (2.219Mb)
    Access Status
    Open access
    Authors
    Bray, A.
    Oelkers, E.
    Bonneville, S.
    Wolff-Boenisch, Domenik
    Potts, N.
    Fones, G.
    Benning, L.
    Date
    2015
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Bray, A. and Oelkers, E. and Bonneville, S. and Wolff-Boenisch, D. and Potts, N. and Fones, G. and Benning, L. 2015. The effect of pH, grain size, and organic ligands on biotite weathering rates. Geochimica et Cosmochimica Acta. 164: pp. 127-145.
    Source Title
    Geochimica et Cosmochimica Acta
    DOI
    10.1016/j.gca.2015.04.048
    ISSN
    0016-7037
    School
    Department of Applied Geology
    Remarks

    This open access article is distributed under the Creative Commons license http://creativecommons.org/licenses/by/4.0/

    URI
    http://hdl.handle.net/20.500.11937/44349
    Collection
    • Curtin Research Publications
    Abstract

    Biotite dissolution rates were determined at 25 °C, at pH 2–6, and as a function of mineral composition, grain size, and aqueous organic ligand concentration. Rates were measured using both open- and closed-system reactors in fluids of constant ionic strength. Element release was non-stoichiometric and followed the general trend of Fe, Mg > Al > Si. Biotite surface area normalised dissolution rates (ri) in the acidic range, generated from Si release, are consistent with the empirical rate law: ri=kHiaH+xi where kH,i refers to an apparent rate constant, aH+aH+ designates the activity of protons, and xi stands for a reaction order with respect to protons. Rate constants range from 2.15 × 10−10 to 30.6 × 10−10 (molesbiotite m−2 s−1) with reaction orders ranging from 0.31 to 0.58. At near-neutral pH in the closed-system experiments, the release of Al was stoichiometric compared to Si, but Fe was preferentially retained in the solid phase, possibly as a secondary phase. Biotite dissolution was highly spatially anisotropic with its edges being ~120 times more reactive than its basal planes. Low organic ligand concentrations slightly enhanced biotite dissolution rates. These measured rates illuminate mineral–fluid–organism chemical interactions, which occur in the natural environment, and how organic exudates enhance nutrient mobilisation for microorganism acquisition.

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