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The formation of green rust and its transformation to lepidocrocite

U. Schwertmann and H. Fechter
The formation of green rust and its transformation to lepidocrocite
Clay Minerals (March 1994) 29 (1): 87-92


The formation of Fe (super II,III) hydoxy salts (green rusts) from Fe (super II) sulphate and chloride solutions and their transformation to lepidocrocite, gamma -FeOOH, was studied at ambient temperature, constant pH of approximately 7.0 and under controlled air flow. The formation of green rust and its subsequent transformation to lepidocrocite could be distinguished by the reaction rate and solution chemistry. The SO (sub 4) (super 2-) and Cl (super -) concentrations in solution attain a minimum at the break between the two reaction steps and are completely restored to their initial values after complete transformation to lepidocrocite. While the green rust is being formed, its Fe (super II) /Fe (super III) ratio shows a minor decrease and its Fe (super III) /anion ratio a minor increase. These ratios, however, deviate from the ideal pyroaurite-type structure (M (super 2+) /M (super 3+) = 3; M (super 3+) /A (super -) = 1; M: metal; A (super -) : anion) and possibilities to accommodate this deviation are discussed. A period during which no protons were produced (i.e. no base consumed) was found to separate the two reactions in the chloride, but not in the sulphate system. During this period a partial solid state oxidation of the green rust took place, leading to its destabilization and eventual decomposition.

ISSN: 0009-8558
Serial Title: Clay Minerals
Serial Volume: 29
Serial Issue: 1
Title: The formation of green rust and its transformation to lepidocrocite
Affiliation: Technische Universitaet Muenchen, Lehrstuhl fuer Bodenkunde, Freising-Weihenstephan, Federal Republic of Germany
Pages: 87-92
Published: 199403
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 24
Accession Number: 1995-002819
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
Update Code: 199502
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