The texture of montmorillonites as influenced by the exchangeable inorganic cation and the drying method II: A comparative porosity study

Abstract

Comparative porosity studies based on nitrogen sorption isotherms were carried out on Moosburg montmorillonites saturated with different monovalent and divalent cations which were air dried after sedimentation or freeze dried and various freeze-dried sodium-montmorillonites from various localities. The analysis of mesopores was carried out using the “parallel-plate model”. For supermicropores the “MP” method and for micropores the Dubinin-Radushkevich treatment were used. Most of the surface area is located in the supermicropores (width, 0.70–1.5 nm). From sodium-saturated to caesium-saturated Moosburg clay there is a marked increase in the surface area in this pore type according to the interleaving of the clay plates in the crystal units and increased with an intercrystalline sorption for the rubidium- and caesium-saturated clays. By contrast, there is a higher supermicroporous surface area for the lyophilized clay in comparison with the air-dried clay, while the mesopore surface remains constant. A Moosburg clay with bivalent cations has a lower supermicroporous surface area when lyophilized than when air dried whereas the mesopore surface area is slightly less when the clay is air dried than when it is lyophilized. Micropores seem to be of minor importance. For the group of sodium-lyophilized montmorillonites an increase in the surface area results from an increase in both the supermicroporous and the mesoporous parts and there is also a trend for the number of layers per stacking unit to diminish.