Fe microenvironments in heat treated rare-earth exchanged montmorillonites

Abstract

The rare-earth bentonites were prepared from Ca-bentonite by suspending Ca-bentonite in rare-earth (Ce, La, Y) perchlorate solution. 57Fe Mössbauer spectra of rare earth montmorillonites before heat treatments showed a doublet envelop at room temperature, reflecting dominantly Fe3+ assigned to (cis) octahedral site in the montmorillonite. At the same time, the 80 K spectra of these rare-earth exchanged montmorillonites revealed an additional magnetically split component, too, associated with iron atoms intercalated in the interlayer space. In the case of heat treated samples (250 °C, 360 °C and 500 °C for 4 h), a new doublet component associated with Fe3+ at trans octahedral site, appeared in both the 295 K and 80 K Mössbauer spectra. Powder X-ray diffractometry (XRD) measurements of the heat treated rare earth montmorillonites revealed that a gradual mineral phase transformation of montmorillonite to muscovite occurred upon the applied heat treatments, being consistent with the completing electron magnetic resonance (EMR) and Mössbauer spectroscopy (MS) results.

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Acknowledgements

Open access funding provided by Eötvös Loránd University (ELTE). The financial supports from NKFIH OTKA (No. K115913, K115784, K131963, and K120265) and Hungarian-Croatian S&T (No TÉT_16-1-2016-0002) as well as by the EU and co-financed by the European Regional Development Fund under the project GINOP-2.3.2-15-2016-00008 grants are acknowledged. Z.K. expresses thanks to Prof. Ferenc Simon (Institute of Physics, Budapest University of Technology and Economics, Budapest, Hungary) for making available the applied spectrometer for recording the EMR spectra.

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Correspondence to Erno Kuzmann.

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This article is part of the Topical Collection on Proceedings of the 5th Mediterranean Conference on the Applications of the Mössbauer Effect (MECAME 2019) and 41st Workshop of the French-speaking Group of Mössbauer Spectroscopy (GFSM 2019), Montpellier, France, 19-23 May 2019

Edited by Pierre-Emmanuel Lippens, Yann Garcia, Moulay-Tahar Sougrati and Mira Ristic (†)

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Kuzmann, E., Kovács, E.M., Homonnay, Z. et al. Fe microenvironments in heat treated rare-earth exchanged montmorillonites. Hyperfine Interact 240, 87 (2019). https://doi.org/10.1007/s10751-019-1622-7

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Keywords

  • Rare earth-montmorillonite
  • 57Fe Mössbauer spectroscopy
  • Interlayer Fe
  • Phase transition
  • Electron magnetic resonance