Influence of counterion species on the dehydroxylation of Ca2+-, Mg2+-, Na+- and K+-exchanged Wyoming montmorillonite

The dehydroxylation of Ca-, K-, Mg- and Na-saturated Wyoming montmorillonite has been studied by thermogravimetry (TG), infrared (IR) spectroscopy and X-ray diffraction (XRD). Samples saturated with either Ca2+ or Mg2+ show a predominantly diffusion-controlled reaction step, whereas Wyoming montmorillonite with Na' and K+ in the interlayer exhibit control closer to first order. The activation energy of dehydroxylation is not significantly correlated to the type of interlayer cation present, in turn demonstrating that the role of vacancy location in the octahedral sheet is more significant a control on dehydroxylation.