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Evolution of Hematite Surface Microtopography Upon Dissolution by Simple Organic Acids

Published online by Cambridge University Press:  28 February 2024

Patricia A. Maurice
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305
Michael F. Hochella Jr.
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305
George A. Parks
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305
Garrison Sposito
Affiliation:
Department of Environmental Science, Policy, and Management, University of California at Berkeley, Berkeley, California 94720
Udo Schwertmann
Affiliation:
Institute of Soil Science, Technical University of Munich, Germany
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Abstract

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The surface microtopography of hematite over the course of dissolution in oxalic and citric acids was examined by in-situ and ex-situ atomic-force microscopy. In-situ imaging of the basal-plane surface of a centimeter-scale natural hematite sample immersed in 2 mM citric acid demonstrated that the basal-plane surface was relatively unreactive; rather, dissolution occurred along step edges and via etch-pit formation. Ex-situ imaging of synthetic hematite particles following batch dissolution in 1 mM oxalic acid showed similar dissolution features on basal-plane surfaces; in addition, etching along particle edges was apparent. The presence of etch features is consistent with a surface-controlled dissolution reaction. The results are in agreement with previous investigations suggesting that the basal-plane surface is relatively unreactive with respect to ligand exchange. Both in-situ and ex-situ imaging of particle surfaces can provide valuable information on the roles of surface structures and microtopographic features in mineral dissolution.

Information

Type
Research Article
Copyright
Copyright © 1995, The Clay Minerals Society