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Fluid supersaturation and crystallization in porous media

Published online by Cambridge University Press:  01 May 2009

Andrew Putnis
Affiliation:
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
Manuel Prieto
Affiliation:
Departamento de Geologia, Universidad de Oviedo, 33005 Oviedo, Spain
Lurdes Fernandez-Diaz
Affiliation:
Departamento de Cristalograf‡a y Mineralog‡a, Universidad Complutense de Madrid, 28040 Madrid, Spain

Abstract

The relationship between the supersaturation at the point of crystallization and the rate at which supersaturation increases has been studied from nucleation experiments on barite BaSO4, strontianite SrCO3, witherite BaCO3 and gypsum CaSO4.2H2O. The crystallization experiments have been carried out by the counter-diifusion of cations and anions through a column of porous silica gel transport medium. Nucleation is suppressed in a finely-porous medium resulting in very high values of supersaturation before crystallization from the solution begins. This threshold supersaturation for nucleation depends on the solubility of the salt, the porosity of the medium and the supersaturation rate. Nucleation inhibitors were used to extend the range of supersaturation attainable. In all cases the experimental data fits the general expression: rate of change of supersaturation ∝ (threshold supersaturation)m. These results are compared to previous work from the field of chemical engineering on the relationship between supersaturation, volume and cooling rate in aqueous salt solutions. These experiments have important implications to supersaturation in natural fluids and subsequent crystallization in relation to geological problems including crystallization in low temperature sedimentary environments and fluid-rock ratios in hydrothermal mineral deposits.

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Copyright
Copyright © Cambridge University Press 1995

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