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Acid Dissolution of Akaganiéite and Lepidocrocite: The Effect on Crystal Morphology

Published online by Cambridge University Press:  02 April 2024

R. M. Cornell  and
R. Giovanoli
R. M. Cornell
Affiliation:
ETH Zentrum Zürich, Laboratory of Inorganic Chemistry, CH-8092 Zürich, Switzerland
R. Giovanoli
Affiliation:
Laboratory for Electron Microscopy, University of Berne, Freiestrasse 3, CH-3000 Berne 9, Switzerland
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Abstract

The rate of dissolution of akaganéite in HCl increased with time over the bulk of the reaction leading to a sigmoid dissolution vs. time curve. The bulk of the dissolution of lepidocrocite could be described by the cube root law. Transmission electron microscopy examination of partly dissolved crystals of akaganéite showed that acid attack proceeded mainly along the [001] direction. Initially, the tapered ends of the crystals became squared, and as dissolution continued the lengths of the crystals decreased steadily. At the same time, the crystals were gradually hollowed out. Acid attack was most pronounced at the edges of the crystals of lepidocrocite and appeared to involve a disruption of the hydrogen bonds that link the sheets of octahedra making up the structure. Defects also acted as sites for preferential acid attack. Dissolution of multi-domainic crystals involved preferential attack along the domain boundaries, as well as at the edges of the crystals. Single-domain crystals were well developed, but appeared to contain internal imperfections, which promoted the formation of holes on the otherwise unreactive (010) faces.

Keywords

AkaganéiteDissolutionIronLepidocrociteMorphologyTransmission electron microscopy
Type
Research Article
Information
Clays and Clay Minerals , Volume 36 , Issue 5 , October 1988 , pp. 385 - 390
Copyright
Copyright © 1988, The Clay Minerals Society

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