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Variscite dissolution rates in aqueous solution: does variscite control the availability of phosphate in acidic natural waters?

Published online by Cambridge University Press:  05 July 2018

T. Roncal-Herrero  and
E. H. Oelkers
T. Roncal-Herrero*
Affiliation:
Biogéochimie et Geochimie Expérimentale, LMTG-Université Paul Sabatier-CNRS-IRD-OMP, 14 av. Edouard Belin 31400 Toulouse. France
E. H. Oelkers
Affiliation:
Biogéochimie et Geochimie Expérimentale, LMTG-Université Paul Sabatier-CNRS-IRD-OMP, 14 av. Edouard Belin 31400 Toulouse. France
*
*E-mail: roncal@lmtg.ob-mip.fr
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Abstract

The dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 pH. Measured dissolution rates decrease with increasing pH from 5.05x10-16 mol/cm2/s at pH = 1.51 to 4.92x10-17 mol/cm2/s at pH = 5.89 and then increase with increasing pH to 1.64x10-17 mol/cm2/s at pH = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous phosphate concentrations in a significant number of near surface environments.

Keywords

variscitedissolution ratesphosphate availabilitynatural waters
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 1 , February 2008 , pp. 349 - 351
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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