Clays and Clay Minerals, Vol. 57, No. 1, 40–45, 2009.
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Authors
Seiffarth, Torsten
Kaps, Christian
Issue Date
2009
Type
Article
Language
Keywords
Periodicals , Geology , Acid Activation , Cu Fixation , De-ammonization , DRIFT , FTIR , Hofmann-Klemen Effect , Montmorillonite , NH4 Clay
Alternative Title
Structural Characterization Of (cu2+,na+)- And (cu2+,nh4 +)-exchanged Bentonites Upon Thermal Treatment
Abstract
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 Cu2+, th e exact location of cation fixation withre spect to the clay layers is difficult to determine. Namontmorillonite was prepared from the <2 mm fraction of the bentonite Calcigel (from Bavaria, Germany) and exchanged by Cu2+ and Na+ or by Cu2+ and NH4 + cations. The resulting materials (bi-ionic Cu-Na and Cu-NH4 samples, respectively, as well as homo-ionic forms with Cu2+, Na+ and NH4 +) were heated for 24 h at temperatures of 300 and 450ºC 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 12.5A ˚ . Upon heating at 300 and 450ºC, the layers collapsed to 9.5 A ˚ . In contrast, the d001 value in th e NH4 sample and Cu-NH4 sample decreased to 10.0 A ˚ and 10.2 A ˚ , respectively, during the heat treatment. The Cu2+ ions migrated irreversibly into the montmorillonite structure. For the NH4 and the Cu-NH4 samples, DSC analyses show that NH3 evolved at between 300 and 400ºC 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 Cu2+ was trapped in the octahedral sheet. In the case of the Cu-NH4 form, bothCu 2+ fixation and de-ammonization occurred during the heat treatment. Other than maintaining the basal spacing, no effect of the presence of NH4 + on the Cu2+ fixation could be found for the montmorillonite studied.
Description
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Citation
Clays and Clay Minerals, Vol. 57, No. 1, 40–45, 2009.
Publisher
The Clay Minerals Society
License
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