Structural characterization of (Cu2+,Na+)-and Cu2+,NH+4)-Exchanged bentonites upon thermal treatment
Seiffarth, Torsten (Bauhaus University Weimar)
Kaps, Christian (Bauhaus University Weimar)

Date:	2009
Abstract:	Bentonites are excellent materials for sequestering various metal cations because of the cation fixation ability of the constituent montmorillonite layers, but sometimes, such as in the case of Cu, the exact location of cation fixation with respect to the clay layers is difficult to determine. Namontmorillonite was prepared from the <2 μm fraction of the bentonite Calcigel (from Bavaria, Germany) and exchanged by Cu and Na or by Cu and NH cations. The resulting materials (bi-ionic Cu-Na and Cu-NH samples, respectively, as well as homo-ionic forms with Cu, Na and NH ) were heated for 24 h at temperatures of 300 and 450°C and the structural evolution characterized using X-ray diffraction (XRD) analysis, Fourier Transform Infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) analysis. The XRD patterns showed that the Cu sample and the Cu-Na sample have basal spacings of 12. 5 Å. Upon heating at 300 and 450°C, the layers collapsed to 9. 5 Å. In contrast, the d value in th e NH sample and Cu-NH sample decreased to 10. 0 Å and 10. 2 Å, respectively, during the heat treatment. The Cu ions migrated irreversibly into the montmorillonite structure. For the NH and the Cu-NH samples, DSC analyses show that NH evolved at between 300 and 400°C though the octahedral sheet was not altered substantially by the H generated. Infrared spectra show that the bands of the Si-O and OH vibrations of all samples were changed upon heating due to the movement of the dehydrated cations into the hexagonal holes of the tetrahedral sheet. Apparently no Cu was trapped in the octahedral sheet. In the case of the Cu-NH form, both Cu fixation and de-ammonization occurred during the heat treatment. Other than maintaining the basal spacing, no effect of the presence of NH on the Cu fixation could be found for the montmorillonite studied.
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Acid Activation ; Cu Fixation ; De-ammonization ; DRIFT ; FTIR ; Hofmann-Klemen Effect ; Montmorillonite ; NH4 Clay
Published in:	Clays and Clay Minerals, Vol. 57, Núm. 1 (2009) , p. 40-45, ISSN 1552-8367

DOI: 10.1346/CCMN.2009.0570104

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