Detection of Tetrahedral Fe3+ Sites in Nontronite and Vermiculite by Mössbauer Spectroscopy

Vittorio Luca1
Chemistry Department, Victoria University, P.O. Box 600 Wellington, New Zealand
1Present address: Department of Chemistry, University of Houston, Houston, Texas 77204-5641, U.S.A.

Abstract: Mössbauer spectra were obtained for five Ca-exchanged nontronites and one Ca-exchanged vermiculite as the 2-layer hydrates following dehydration at 200°C. Exchange of the samples with Ca2+ and subsequent dehydration resulted in the appearance of a shoulder at about -0.50 mm/s in the Mössbauer spectra of some of the samples. The appearance of these shoulders necessitated the inclusion of doublets with Mössbauer parameters corresponding to tetrahedrally-coordinated Fe3+ (IVFe3+) in the model used to fit the Mössbauer spectra. That the IVFe3+ sites detected in these samples were those in the nontronite structure was confirmed using samples whose IVFe3+ contents have been previously determined from chemical analysis. It appears that this sample preparation method allowed IVFe3+ contents to be determined to within 40%. On this basis, the IVFe3+ content appeared to be unrelated to the total Fe content for the samples studied.

Key Words: Dehydration • Isomorphic substitution • Mössbauer spectroscopy • Nontronite • Tetrahedral iron • Vermiculite

Clays and Clay Minerals; October 1991 v. 39; no. 5; p. 467-477; DOI: 10.1346/CCMN.1991.0390502
© 1991, The Clay Minerals Society
Clay Minerals Society (www.clays.org)