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.