Desorption – sorption – desorption profile of clinoptilolite in different air media: a DSC-TG study

Abstract

Desorption–sorption processes of clinoptilolite sample from Beli Plast deposit, Bulgaria, were studied in a simultaneous DSC-TG experiment, applying a temperature profile including successive stages of heating up to 300 °C, holding, cooling to 40 °C, holding, and reheating up to 600 °C. Two experiments were provided: in humid static air and dynamic dry air. Thus, in a single experiment, quantitative information was obtained about the behavior of the sample in a complicated temperature profile and specific gas media. The first heating processes took place with almost the same dehydrated amount regardless of air media. In the humid air media, a possible sorbate is H2O molecules, while in the dry air are N2 molecules. In both air media, rapid sorption was observed already with the first steps of cooling, while a corresponding exothermic effect is manifested specifically for both experiments. Different sorption amount of H2O and N2 molecules was explained by their role as dipole or quadrupole and their different way of internal filling into the dehydrated zeolite structure. The desorption of newly sorbed molecules proceeds during the second heating, and after 300 °C the dehydration completes. The presented complicated approach gives information about the behavior of the clinoptilolite at each thermal stage that is of importance for various practical applications.