Interlayer water and swelling properties of monoionic montmorillonites

The dehydration of two montmorillonites saturated by 10 different cations is investigated by X-ray spectroscopy, in different conditions of temperature and environmental relative humidity. We consider, in particular, the cation “solvatation” water and propose a model, on the basis of which we show that, in the case of the 15-Å structure the stability of the H20-cation-silicate complex depends essentially on the electrostatic energy of the water molecule dipole in the cation field. In the 12-A case, on the other hand, sometimes the energy change associated with the redistribution of the electrical charges of the cation and of the silicate seems to prevail, depending on the interlayer spacing. We also show a correlation between cationic radius and closest interlayer spacing in the conditions of extreme dehydration.