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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: [email protected]
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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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References

Brunauer, S., Emmett, P. and Teller, E. (1938) Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 60, 309–319.CrossRefGoogle Scholar
Chairat, C. Schott, J., Oelkers, E.H., Lartigue, J.E. and Harouiya, N. (2007) Kinetics and mechanism of natural fluorapatite dissolution at 25°C and pH 3 to 12. Geochimica et Cosmochimica Ada, 71, 5901–5912.CrossRefGoogle Scholar
Dougan, W.K. and Wilson, A.L. (1974) The absorptio-metric determination of aluminium in Water. A comparison of some chromogenic reagents and the development of an improved method. Analyst, 99, 413–430.CrossRefGoogle Scholar
Georgantas, D.A. and Grigoropoulou, H.P. (2007) Orthophosphate and metaphosphate ion removal from aqueous solution using alum and aluminum hydroxide. Journal of Colloid and Interface Science, 315, 70–79.CrossRefGoogle ScholarPubMed
Harouiya, N., Chairat, C. Kohler, S.J., Gout, R. and Oelkers, E.H. (2007) The dissolution kinetics and apparent solubility of natural apatite in closed system reactors at temperatures from 5 to 50°C and pH from 1 to 6. Chemical Geology, 244, 554–568.CrossRefGoogle Scholar
Murphy, J. and Riley, J.P. (1962) A modified single solution method for the determination of phosphate in natural waters. Analytica Chimica Ada, 27, 31–36.Google Scholar
Oelkers, E.H. and Valsami-Jones, E. (2008) Phosphate mineral reactivity and global sustainability. Elements, 4, 83–88.CrossRefGoogle Scholar
Parkhurst, D. (1998) PHREEQC (Version 2) - a computer program for speciation, batch-reaction, one dimensional transport, and inverse geochemical calculations. Available from: http://www.brr.cr.usgs.gov/projects/GWCcoupled/phreeqc/ Google Scholar
Stumm, W. and Morgan, J.J. (1996) Aquatic Chemistry, Chemical Equilibria and Rates in Natural Waters. 3r edition. John Wiley and Sons Inc., New York.Google Scholar