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57Fe Mössbauer Spectroscopy of Montmorillonites: A New Interpretation

Published online by Cambridge University Press:  02 April 2024

C. M. Cardile  and
J. H. Johnston
C. M. Cardile
Affiliation:
Chemistry Department, Victoria University of Wellington, Private Bag, Wellington, New Zealand
J. H. Johnston*
Affiliation:
Chemistry Department, Victoria University of Wellington, Private Bag, Wellington, New Zealand
*
1To whom all correspondence should be addressed.
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Abstract

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The 57Fe Mössbauer spectra of several montmorillonites, measured at room temperature and 453 K, showed a considerably broadened Fe3+ resonance which can be computer-fitted with a similarly broadened Fe3+ doublet. In some spectra, particularly if all linewidths were constrained to be equal, this broadened Fe3+ resonance was further resolved into overlapping inner and outer Fe3+ doublets, also having broad linewidths. In accordance with recent electron diffraction evidence, the assignment by previous workers of the inner doublet to Fe3+ in the octahedral sites having the cis-arrangement of OH groups and the outer doublet to the octahedral site having the trans-arrangement of OH groups is incorrect. Instead, the Fe3+ was found to be located largely in the trans-octahedral sites. Because of the relatively low iron content of the montmorillonite examined, the next and more distant neighboring-cation environment varied considerably about the octahedral Fe3+ ions. This variation produced a broadened experimental resonance, and the resulting two-doublet computer fits probably represent the mean extremes of a continuum of slightly different Fe3+ resonances arising from the variable nature of the environment surrounding these such trans-sites, rather than distinct cis- and trans-sites. In addition, a small resonance indicating the substitution of Fe3+ into the tetrahedral sites was observed. The interlayer species probably influenced the Mössbauer resonance of Fe3+ in the tetrahedral and octahedral sites.

Keywords

IronMontmorilloniteMössbauer spectroscopyOctahedral sitesTetrahedral sites
Type
Research Article
Information
Clays and Clay Minerals , Volume 34 , Issue 3 , June 1986 , pp. 307 - 313
Copyright
Copyright © 1986, The Clay Minerals Society

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