Cation Migration in Smectite Minerals: Electron Spin Resonance of Exchanged Fe3+ Probes

V. Luca1 and C. M. Cardile2, 3
1 Chemistry Department, Victoria University of Wellington P.O. Box 600, Wellington, New Zealand
2 Chemistry Division, Department of Scientific and Industrial Research Private Bag, Petone, New Zealand
3 Present address: Research and Development Laboratory, Alcoa of Australia Ltd., P.O. Box 161, Kwinana, Western Australia 6167, Australia.

Abstract: The migration of interlayer Fe3+ cations into the structure of heated montmorillonite and Laponite has been studied by electron spin resonance (ESR), Mössbauer spectroscopy, and magnetic susceptibility measurements. The intensity of the ESR signal corresponding to interlayer Fe3+ in air-dried montmorillonite and Laponite increased linearly as the amount of interlayer Fe3+ increased. Changes in the spectra after thermal treatment indicate that Fe3+ cations migrated into the pseudohexagonal cavities of dehydrated montmorillonite and Laponite. The electrostatic interaction between the Fe3+ and the oxygen atoms defining the entrance to these cavities and the proton of the structural OH groups at the bottom of the cavities differ for the two smectites. Ferric cations were apparently bound more strongly within the pseudohexagonal cavities of the dehydrated montmorillonite than within the cavities of Laponite, because the montmorillonite did not rehydrate after heating. The differences in the binding of Fe3+ cations within the pseudohexagonal cavities of montmorillonite and Laponite were probably due to variations in the ability of the protons of the structural OH groups to reorient. An additional electronic interaction occurred in the heated Laponite, in which small cations were able to promote the formation of structural defects, which gave rise to a sharp ESR signal at g = 2.00. No evidence for the penetration of Fe3+ cations into the vacant octahedral sites of montmorillonite was found.

Key Words: Electron spin resonance • Hofmann-Klemen effect • Ion migration • Iron • Laponite • Montmorillonite • Mössbauer spectroscopy

Clays and Clay Minerals; August 1989 v. 37; no. 4; p. 325-332; DOI: 10.1346/CCMN.1989.0370405
© 1989, The Clay Minerals Society
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