Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 75, Issue 2, Pages 416-426Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2010.10.012
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- European Community through the MIR Early Stage Training Network [MEST-CT-2005-021120]
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The dissolution rates of natural, well crystallized variscite (AlPO4 center dot 2H(2)O) were determined from the evolution of aqueous Al and P concentrations in closed and open-system mixed-flow reactors at 25 degrees C and pH from 1.5 to 9.0. Measured dissolution rates decrease with increasing pH, from 6 x 10(-16) mol/cm(2)/s at pH 1.5 to 5 x 10(-17) mol/cm(2)/s at pH 5.89, and then increase with increasing pH to 4 x 10(-16) mol/cm(2)/s at pH 9.0. Geochemical modeling calculations, performed using measured dissolution rates, indicate that it would take no more than a few weeks or months to equilibrate a mildly acidic, Al and P-free solution with variscite. Hence, variscite can buffer aqueous phosphate concentrations in mildly acidic near surface environments. This conclusion is confirmed by consideration of the compositions of natural waters. (C) 2010 Elsevier Ltd. All rights reserved.
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