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The kinetics and reaction mechanism of the goethite to hematite transformation

Published online by Cambridge University Press:  05 July 2018

C. J. Goss
C. J. Goss*
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing St., Cambridge CB2 3EQ
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Abstract

A complete mechanism for the transformation goethite to hematite based upon the results of thermogravimetric, transmission electron microscope and X-ray diffraction investigations is presented. A porous microstructure and hematite crystallites in twin orientation are found to develop during transformation. For the main part of the transformation, and at higher temperatures, the reaction is controlled by a two-dimensional phase boundary. Activation energies of 169 ± 8 kJ/mole (for an ore mineral) and 154 ± 15 kJ/mole (for a recent sedimentary goethite) were obtained for this part of the transformation. At early stages and lower temperatures, the mechanism is one of proton/iron transfer across the reaction interface. Important goethite characteristics are grain size, shape, crystallinity and excess water content. The activation energy is found to depend upon temperature and degree of dehydration.

Keywords

goethitehematitereaction mechanismelectron microscopyX-ray diffraction
Type
Mineralogy
Information
Mineralogical Magazine , Volume 51 , Issue 361 , September 1987 , pp. 437 - 451
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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