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Acid dissolution of synthetic aluminous goethite before and after transformation to hematite by heating

Published online by Cambridge University Press:  09 July 2018

H. D. Ruan
Affiliation:
Soil Science and Plant Nutrition, Faculty of Agriculture, The University of Western Australia, Nedlands, WA 6009, Australia
R. J. Gilkes
Affiliation:
Soil Science and Plant Nutrition, Faculty of Agriculture, The University of Western Australia, Nedlands, WA 6009, Australia

Abstract

Measurements of the kinetics of acid dissolution of synthetic aluminous goethites and corresponding hematites produced by heating of parent Al-goethites at various temperatures were carried out in 1 M HC1 at 30, 40 and 50°C. Dissolution-time curves show sigmoidal shapes for the goethites (110°C), whereas deceleratory shapes were obtained for most of the partly and fully dehydroxylated samples. The dissolution rate for all materials decreased with increasing Al substitution and increased with increasing dissolution temperature, specific surface area and heating temperature. On a unit surface area basis, hematite dissolved ∼ 2–8 times faster than goethite. Dissolution kinetics of most heated goethite samples (200–260°C) were quite well described (R2 > 0.96) by the modified first-order Kabai equation. The activation energy and frequency factor for dissolution increased with increasing Al substitution.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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