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

Andrew W. Bray, Eric H. Oelkers, Steeve Bonneville, Domenik Wolff-Boenisch, Nicola J. Potts, Gary Fones, Liane G. Benning

    Research output: Contribution to journalArticlepeer-review

    81 Downloads (Pure)

    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: Turn MathJaxon where kH,i refers to an apparent rate constant, 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.
    Original languageEnglish
    Pages (from-to)127-145
    Number of pages19
    JournalGeochimica et Cosmochimica Acta
    Volume164
    Early online date7 May 2015
    DOIs
    Publication statusPublished - 1 Sep 2015

    Keywords

    • NE/C004566/1
    • RCUK
    • NERC

    Fingerprint

    Dive into the research topics of 'The effect of pH, grain size, and organic ligands on biotite weathering rates'. Together they form a unique fingerprint.

    Cite this