Water sorption and desorption isotherms of some naturally occurring zeolites

Water sorption/desorption isotherms of some naturally occurring zeolites (more appropriately, zeolitic tuffs), such as chabazite, clinoptilolite, erionite, mordenite, and phillipsite, as measured by a volumetric method are reported. As expected, all the zeolites showed the Brunauer Type I isotherms with upward deviation at higher pressures, the latter as a result of multilayer sorption and liquid condensation in mesopores. The desorption branch of the isotherms exhibited small hystereses in all the samples. The micropore-filling capacities of the different zeolites were calculated from the Dubinin equation in order to delineate the effects of mesopores, impurities, crystallinity, and particle size. The Dubinin micropore-filling capacities were more or less found to be coincident to the Langmuir monolayer capacity.