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EPR Study of Montmorillonites from Several Deposits

R. Lück, R. Stösser, D. Gyepesová, H. Slosiariková, and L. Kolditz

Institute of Physical Chemistry, University of Hamburg, W-2000 Hamburg


Abstract: EPR spectroscopic and magnetochemical investigations of natural montmorillonites originating from different deposits reveal the nature and localization of paramagnetic centres contained in the samples. The EPR spectra show that all montmorillonites investigated especially contain Fe3+ ions. These ions occupy lattice sites of the montmorillonite structure of maximal and, to a larger extent, slight to moderate rhombic deformation in the region g' almost-equal-to 4 (g' = effective g-factor). Effective magnetic interactions (dipole-dipole and exchange interactions) occur between the Fe3+ ions located in Al3+ sites of the montmorillonite structure and those located in the interlayer space or on the surface of the crystallites. Analysis of the EPR spectra and of the dependence of magnetic susceptibility χ values on the strength of the external magnetic field indicates that magnetically ordered phases are only rarely formed.Additionally, the EPR spectra of montmorillonites from Jelsovy Potok, Askangel, Borsa, and Pyzhevskii display hyperfine structures of isolated Mn2+ ions in the g' almost-equal-to 2 range. In the case of the montmorillonite from Jelsovy Potok these Mn2+ ions are localized in moderately deformed octahedral sites of the montmorillonite structure. Mn2+ ions in samples of montmorillonites from Askangel, Borsa, and Pyzhevskii are preferentially located in Ca2+ Sites of calcite impurities. A resonance at g' almost-equal-to 2.009 indicates the existence of paramagnetic oxygen defect centres in the samples. Measurements of the static magnetic susceptibility disclose strong paramagnetism for the samples from Borsa, Branany, and Taganskii. In contrast, those from Askangel, Jelsovy Potok, and Pyzhevskii are only weakly paramagnetic.

Full paper in Portable Document Format: 472a79.pdf


Chemical Papers 47 (2) 79–84 (1993)

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