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Photochemical Dissolution of Goethite in Acid/Oxalate Solution

Published online by Cambridge University Press:  02 April 2024

R. M. Cornell  and
P. W. Schindler
R. M. Cornell
Affiliation:
University of Berne, Institute of Inorganic Chemistry, Freiestrasse 3, CH-3000 Berne 9, Switzerland
P. W. Schindler
Affiliation:
University of Berne, Institute of Inorganic Chemistry, Freiestrasse 3, CH-3000 Berne 9, Switzerland
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Abstract

During photochemical dissolution of goethite in acid/oxalate solution, Fe3+, Fe2+, and CO2 were released and towards the end of the reaction ferrous oxalate precipitated. The dissolution process involved an initial slow stage followed by a much faster reaction. The slow stage was eliminated by addition of 20 ppm Fe2+ to the system at the start of the reaction. The presence of this Fe2+ did not accelerate the secondary dissolution process. Both protons and oxalate ions appear to have been involved in the dissolution process. Dissolution was accelerated by an increase in oxalate concentration (from 0.0025 to 0.025 M) in the system and also depended on pH, reaching a maximum rate at pH 2.6. Highly substituted (15.9 mole % Al) goethite dissolved more slowly per unit area than unsubstituted goethite. Lepidocrocite (γ-FeOOH) dissolved faster than goethite. The first stage of the dissolution process probably proceeded by slow release of Fe3+ through complexation with oxalate adsorbed on the goethite surface. The faster, secondary step appears to have been a reductive dissolution reaction involving adsorbed ferrous oxalate.

Keywords

GoethiteIronLepidocrocitePhotochemical dissolutionOxalate
Type
Research Article
Information
Clays and Clay Minerals , Volume 35 , Issue 5 , October 1987 , pp. 347 - 352
Copyright
Copyright © 1987, The Clay Minerals Society

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