57Fe Mössbauer Spectroscopic Study of Structural Changes During Dehydration of Nontronite: Effect of Different Exchangeable Cations

Vittorio Luca1
Chemistry Department, Victoria University of Wellington, P.O. Box 600 Wellington, New Zealand
1Present address: Department of Chemistry, University of Houston, Houston, Texas 77204.

Abstract: Dehydration-induced migration of different exchangeable cations toward the layers of nontronite has been studied by Mössbauer spectroscopy. As interlayer water is removed exchangeable cations migrate toward Fe3+ sites in the tetrahedral sheets of the nontronite (IVFe3+) causing them to distort. The amount of distortion is linearly related to the ionic potential (IP) of the exchangeable cations and is greatest for cations with highest IP. Octahedral Fe3+ sites (VIFe3+) are also affected by migration of cations into the pseudohexagonal cavities. As exchangeable cations move into the pseudohexagonal cavities, interaction with VIFe3+ sites increases. The intensity of the outer VIFe3+ Mössbauer doublet increases with respect to the inner VIFe3+ doublet as the IP of the exchangeable cation increases. It appears that the exchangeable cations play a significant role in determining the thermal stability of nontronite.

Key Words: Mössbauer • Dehydration • Nontronite • Cation migration • Tetrahedral site

Clays and Clay Minerals; October 1991 v. 39; no. 5; p. 478-489; DOI: 10.1346/CCMN.1991.0390503
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)