The rehydration properties for Ca-, Mg-, Na-and K-saturated montmorillonites after heating at various temperatures were examined and positions of interlayer cations for unheated, dehydrated and rehydrated specimens were investigated by means ofone-dimensional Fourier analysis.
Mg-saturated specimen dehydrated irreversibly after heating at 400°C, while rehydration was recognized after heating at 600°C for Ca-and Na-saturated specimens and at 700°C for K-saturated specimen. After heating at 600°C for the Na-saturated specimen, the interlayer cations (Na⁺) migrated into shallow part of the hexagonal holes, and the heated specimen restored its original hydrated configuration of interlayer region after water saturation. In the case of after heating at 800°C, the interlayer cations (Na⁺) migrated into deep part of the holes, and rehydration did not occur even after water saturation. These results are due to the fixation of interlayer cations (Na⁺) to the hexagonal holes of SiO₄ network after heating at 800°C, and it becomes difficult to extract these fixed cations from the holes. Therefore, the migrated positions of interlayer cations play an important role in its rehydration properties.