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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
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.

Type
Research Article
Copyright
Copyright © 1992, The Clay Minerals Society

References

Douglas, B., McDaniel, D. H. and Alexander, J. J., 1983 Concepts and Models of Inorganic Chemistry New York John Wiley and Sons.Google Scholar
Dunitz, J. D., 1956 The structure of sodium dithionite and the nature of the dithionite ion Acta Cryst. 9 579586 10.1107/S0365110X56001601.CrossRefGoogle Scholar
Griffen, D. T., 1992 Silicate Crystal Chemistry Oxford Oxford University Press.Google Scholar
Hodgson, W. G., Neaves, A. and Parker, C. A., 1956 Detection of free radicals in sodium dithionite by paramagnetic resonance Nature 489.CrossRefGoogle Scholar
Khaled, E. M. and Stucki, J. W., 1991 Effects of iron oxidation state on cation fixation in smectites Soil Sci. Soc. Am. J. 55 550554 10.2136/sssaj1991.03615995005500020045x.CrossRefGoogle Scholar
Komadel, P. and Stucki, J. W., 1988 The quantitative assay of Fe2+ and Fe3+ using 1, 10-phenanthroline: III. A rapid photochemical method Clays & Clay Minerals 36 379381 10.1346/CCMN.1988.0360415.CrossRefGoogle Scholar
Komadel, P., Lear, P. R. and Stucki, J. W., 1990 Reduction and reoxidation of nontronite: Reaction rates and extent of reduction Clays & Clay Minerals 37 203208 10.1346/CCMN.1990.0380212.CrossRefGoogle Scholar
Lear, P. R. and Stucki, J. W., 1985 The role of structural hydrogen in the reduction and reoxidation of iron in nontronite Clays & Clay Minerals 37 539545 10.1346/CCMN.1985.0330609.CrossRefGoogle Scholar
Lear, P. R. and Stucki, J. W., 1987 Intervalence electron transfer and magnetic exchange interactions in reduced nontronite Clays & Clay Minerals 35 373378 10.1346/CCMN.1987.0350507.CrossRefGoogle Scholar
Lear, P. R. and Stucki, J. W., 1989 Effects of iron oxidation state on the specific surface area of nontronite Clays & Clay Minerals 37 547552 10.1346/CCMN.1989.0370607.CrossRefGoogle Scholar
Lide, D. R., 1992 1992 Boca Raton CRC Press.Google Scholar
Lynn, S., Rinker, R. G. and Corcoran, W. H., 1964 The monomerization rate of dithionite ion in aqueous solution J. Phys. Chem. 68 2363 10.1021/j100790a505.CrossRefGoogle Scholar
McBride, M. B., Pinnavaia, T. J. and Mortland, M. M., 1975 Perturbation of structural Fe3+ in smectites by exchange ions Clays & Clay Minerals 23 103107 10.1346/CCMN.1975.0230204.CrossRefGoogle Scholar
Neta, P., Huie, R. E. and Rose, A. B., 1988 Rate constants for reactions of inorganic radicals and aqueous solution J. Phys. Chem. Ref. Data 17 10311032 10.1063/1.555808.CrossRefGoogle Scholar
Nickless, G., 1968 Inorganic Sulfur Chemistry Amsterdam Elsevier Publishing Co. 519522.Google Scholar
Rinker, R. G., Gordon, T. P., Mason, D. M. and Corcoran, W. H., 1959 The presence of the SO2− radical ion in aqueous solutions of sodium dithionite J. Phys. Chem. 63 302 10.1021/j150572a042.CrossRefGoogle Scholar
Roth, C. B., Tullock, R. J. and Serratosa, J. M., 1973 Deprotonation of nontronite resulting from chemical reduction of structural ferric iron Proc. Int. Clay Conf., Madrid, 1972 107114.Google Scholar
Rozenson, I. and Heller-Kallai, L., 1976 Reduction and oxidation of Fe3 in dioctahedral smectite-I: Reduction with hydrazine and dithionite Clays & Clay Minerals 24 271282 10.1346/CCMN.1976.0240601.CrossRefGoogle Scholar
Rozenson, I. and Heller-Kallai, L., 1976 Reduction and oxidation of Fe3+ in dioctahedral smectite-II: Reduction with sodium sulphide solution Clays & Clay Minerals 24 283288 10.1346/CCMN.1976.0240602.CrossRefGoogle Scholar
Stucki, J. W., Stucki, J. W., Goodman, B. A. and Schwertmann, U., 1988 Structural iron in smectites Iron in Soils and Clay Minerals Dordrecht D. Reidel 625675 10.1007/978-94-009-4007-9_17.CrossRefGoogle Scholar
Stucki, J. W., Lear, P. R., Coyne, L. M., Blake, D. and McKeever, S., 1989 Variable oxidation states of iron in the crystal structure of smectite clay minerals Structures and Active Sites of Minerals Washington, D.C. American Chemical Society 330358.Google Scholar
Stucki, J. W. and Roth, C. B., 1976 Interpretation of infrared spectra of oxidized and reduced nontronite Clays & Clay Minerals 24 293296 10.1346/CCMN.1976.0240604.CrossRefGoogle Scholar
Stucki, J. W. and Roth, C. B., 1977 Oxidation-reduction mechanism for structural iron in nontronite Soil Sci. Soc. Am. J. 41 808814 10.2136/sssaj1977.03615995004100040041x.CrossRefGoogle Scholar
Stucki, J. W. and Tessier, D., 1991 Effects of iron oxidation state on the texture and structural order of Na-nontronite Clays & Clay Minerals 39 137143 10.1346/CCMN.1991.0390204.CrossRefGoogle Scholar
Stucki, J. W., Roth, C. B. and Baitinger, W. E., 1976 Analysis of iron-bearing clay minerals by electron spectroscopy for chemical analysis (ESCA) Clays & Clay Minerals 32 186190.Google Scholar
Stucki, J. W., Golden, D. C. and Roth, C. B., 1984 Preparation and handling of dithionite reduced smectite suspension Clays & Clay Minerals 32 191197 10.1346/CCMN.1984.0320306.CrossRefGoogle Scholar
Stucki, J. W., Golden, D. C. and Roth, C. B., 1984 The effect of reduction and reoxidation on the surface charge and dissolution of dioctahedral smectites Clays & Clay Minerals 32 350356 10.1346/CCMN.1984.0320502.CrossRefGoogle Scholar
van der Heijde, H. B., 1953 Tracer studies on the exchange reaction of some oxygen acids of sulfur Rev. Trans. Chim. Pays-Bes. 72 9596 10.1002/recl.19530720204.CrossRefGoogle Scholar
Vedrine, J. C., Stucki, J. W. and Banwart, W. L., 1980 General theory and experimental aspects of electron spin resonance Advanced Chemical Methods for Soil and Clay Minerals Research Dordrecht D. Reidel 331389 10.1007/978-94-009-9094-4_7.CrossRefGoogle Scholar