TY - JOUR
T1 - The effect of pH, grain size, and organic ligands on biotite weathering rates
AU - Bray, Andrew W.
AU - Oelkers, Eric H.
AU - Bonneville, Steeve
AU - Wolff-Boenisch, Domenik
AU - Potts, Nicola J.
AU - Fones, Gary
AU - Benning, Liane G.
N1 - This study was enabled by funding from the UK Natural Environment Research Council Weathering Science Consortium (NE/C004566/1) and The Geological Society of London William George Fearnsides Fund, both of which the authors are extremely grateful for.
PY - 2015/9/1
Y1 - 2015/9/1
N2 - 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.
AB - 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.
KW - NE/C004566/1
KW - RCUK
KW - NERC
UR - http://linkinghub.elsevier.com/retrieve/pii/S0016703715002628
U2 - 10.1016/j.gca.2015.04.048
DO - 10.1016/j.gca.2015.04.048
M3 - Article
SN - 0016-7037
VL - 164
SP - 127
EP - 145
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -