ABSTRACT
Interest in the ion-exchange processes taking place in inorganic materials has undergone a recent revival. The presence of aluminum isomorphously substituted in silicon tetrahedral positions confers a net negative charge on the zeolite aluminosilicate framework. Zeolite equilibria are illustrative of a general problem when more than one exchange site is available for ion occupancy. It is well known that cation site populations change in zeolites as a function of temperature and are conditioned by cation size and charge and presence of water. R. M. Barrer and J. D. Falconer first considered the use of a statistical thermodynamic approach to exchange in felspathoids. Earlier work concerned with the quantification of cation self-diffusion processes in zeolites has been collated by Barrer. In several cases where self-exchange processes are being followed, the phenomenon observed is that of a two-stage process. R. W. Thompson and M. Tassopoulos have considered this by a semianalytical interpretation and shown good fits between model simulations and experimental data.
