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An Infrared Reflectance Study of Si–O Vibrations in Thermally Treated Alkali- Saturated Montmorillonites

Abstract Infrared reflectance spectra of Li-, Na-, K-, Rb- and Cs-saturated samples of montmorillonite Zenith-N (Milos, Greece) have been measured in the 400-1300 cm-1 region in an attempt to elucidate the behaviour and migration properties of alkali cations after heating the montmorillonites at 300°C for 24 h. Deconvolution of the complex Si-O stretching band reveals that the component band that arises from the asymmetric stretching vibrations of the silicon-apical oxygen units exhibits the biggest change upon heating the montmorillonites. The normalized absorption area of this band has been correlated with the decrease in the layer charge due to the cation migration. Analysis of the IR data for each alkali-saturated montmorillonite has shown that only Li+ migrates near, or to, vacant octahedral sites.