Influence of the nature of the non-framework cations on the sorption properties of natural stilbite

A natural zeolite of stilbite type, collected from the Deccan traps (Aurangabad, M.S., India), has been investigated for its selectivity sequence in exchanging extra-framework cations for the first time, using Ca2+: Sr2+, Ba2+, Mg2+ Na+ and Ag+ cations as the probe cations. The different cation-exchanged forms were characterised by X-ray powder diffraction, IR spectroscopy, TG/DTA, chemi cal analysis and water sorption capacity. Water sorption isotherms in the temperature range 303-393 K were obtained as a function of different non-framework cations up to a pressure of 22 Torr. The sorption data were analysed in terms of different sorption models. The characteristics and population of the non-framework cations were found to influence the chemical affinity for water sorbate almost in a similar trend.