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Oxidation of Structural Ferrous Iron in Vermiculites: I. Oxidation by Fe3+

Published online by Cambridge University Press:  09 July 2018

H. Graf ,
V. Reichenbach  and
B. Beyme
H. Graf
Affiliation:
Institut für Bodenkunde und Sonderforschungsbereich, 173, Universität Hannover, Herrenhäuser Straβe 2, D-3000 Hannover 21, Federal Republic of Germany
V. Reichenbach
Affiliation:
Institut für Bodenkunde und Sonderforschungsbereich, 173, Universität Hannover, Herrenhäuser Straβe 2, D-3000 Hannover 21, Federal Republic of Germany
B. Beyme
Affiliation:
Institut für Bodenkunde und Sonderforschungsbereich, 173, Universität Hannover, Herrenhäuser Straβe 2, D-3000 Hannover 21, Federal Republic of Germany
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Abstract

Vermiculite prepared from biotite by interlayer cation exchange was reacted with solutions exhibiting redox potentials between 625 and 765 mV. The redox potential was controlled by the Fe2+/Fe3+ activity ratio, measured with a Pt electrode, and kept constant by addition of hydrogen peroxide to balance electron transfer from structural Fe2+ to Fe3+ in solution. Oxidation of structural Fe2+ was followed by Eh-stat titration and the rate of oxidation was shown to depend on the amount of Fe3+ penetrating into interlayer positions. Consequently, it was affected not only by the redox potential, but also by the activity between Fe3+ and all other cations present in solution or in an exchangeable state. Oxidation and cation exchange are coupled reactions. In contrast to the redox potential in solution, the effective redox potential controlling the oxidation of structural Fe2+ was increased by preferential sorption of the Fe3+ ion.

Type
Research Article
Information
Clay Minerals , Volume 23 , Issue 3 , September 1988 , pp. 261 - 270
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1988

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