Kinetic investigation of water-cation interaction in clinoptilolite at room temperature

TL;DR

This study investigates the water adsorption kinetics in clinoptilolite, revealing that cations significantly influence hydration, with water molecules associating individually and adsorption/desorption rates depending on environmental conditions.

Contribution

It provides new insights into the role of cations in water adsorption kinetics in clinoptilolite using high-frequency AC measurements.

Findings

Cations play a key role in hydration by hosting most adsorbed water.

Water molecules associate with cations one-by-one.

Water desorption is rapid in dry conditions.

Abstract

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.