  The kinetics of water adsorption by a natural zeolite (clinoptilolite) sample
has been investigated by high-frequency AC current intensity measurements.
According to the achieved kinetic results, cations should play a relevant role
in the clinoptilolite hydration, in fact most of adsorbed water stay in the
cationic sites. The water molecules associate with cation one-by-one. In
particular, the forced adsorption of water molecules in a wet atmosphere is a
quite slow process, while water desorption in air or dry atmosphere is a
spontaneous and fast process. The observed increase of cation mobility could be
adequately explained by assuming an arrangement of water molecules between the
cation and the negatively charged oxygens contained in the cationic site. Such
molecular arrangement could increase the strength of both dipole-cation and
hydrogen bond interactions.
