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Reduction of Structural Iron in Ferruginous Smectite by Free Radicals

Published online by Cambridge University Press:  28 February 2024

Huamin Gan ,
Joseph W. Stucki  and
George W. Bailey
Huamin Gan
Affiliation:
Department of Agronomy, University of Illinois, 1102 South Goodwin Avenue, Urbana, Illinois 61801
Joseph W. Stucki*
Affiliation:
Department of Agronomy, University of Illinois, 1102 South Goodwin Avenue, Urbana, Illinois 61801
George W. Bailey*
Affiliation:
U. S. Environmental Protection Agency, 960 College Station Road, Athens, Georgia 30613
*
1Post-Doctoral Research Associate and Professor of Soil Physical Chemistry, respectively, Department of Agronomy, University ofIllinois, 1102 South Goodwin Avenue, Urbana, Illinois 61801 USA.
2Research Soil Physical Chemist, Chemistry Branch, Environmental Research Laboratory, U. S. Environmental Protection Agency, 960 College Station Road, Athens, Georgia 30613.
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Abstract

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The oxidation state of structural iron greatly influences the physical-chemical properties of clay minerals, a phenomenon that may have significant implications for pollutant fate in the environment, for agricultural productivity, and for industrial uses of clays. Knowledge of redox mechanisms is fundamental to understanding the underlying basis for iron's effects on clays. Past studies revealed that the extent of Fe reduction varied depending on the reducing agent used, but this variation may not have been a simple function of the reduction potential of the reducing agent. The objective of this study was to identify the relationship between the Fe reduction mechanism and free radical activity in the reducing agent. Several reducing agents and their mixtures with the Na-saturated, 0.5 to 2 μm size fraction of ferruginous smectite (SWa-1) were analyzed by electron spin resonance (ESR) spectroscopy to determine the presence of unpaired electrons or free radicals. Only Na2S2O4 exhibited paramagnetic free-radical behavior with a signal at about g = 2.011, which was attributed to the sulphoxylate (S02− ·) free radical. The free radical was labile in aqueous solution, and the ability of Na2S2O4 solution to reduce structural Fe in the smectite decreased with age of the solution and paralleled the disappearance of the free radical signal in the ESR spectrum. The paramagnetic species was preserved and enhanced if Na2S2O4 was added to the clay suspension, indicating that either the clay surface stabilized the SO2− · radical or the additional unpaired electrons were produced in the clay structure.

Keywords

ClayDithioniteElectron spin resonance spectroscopyESRHydrazineIronReductionSmectiteSulfideThiosulfate
Type
Research Article
Information
Clays and Clay Minerals , Volume 40 , Issue 6 , December 1992 , pp. 659 - 665
Copyright
Copyright © 1992, The Clay Minerals Society

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