DEHYDRATION OF NATURAL CLINOPTILOLITE UNDER THE EFFECT OF ELECTROMAGNETIC RADIATION IN THE MICROWAVE RANGE

Natural zeolites, in particular, clinoptilolite, are characterized by a high adsorption capacity for many pollutants, as well as a significant cation exchange capacity. Therefore, it is widely used in natural and wastewater treatment processes, medicine, etc. Modification of natural zeolites, for example, with silver ions, makes it possible to ensure, in addition to sorption, their antibacterial properties. Previous studies have established that modification of pre–dehydrated clinoptilolite makes it possible to increase its sorption capacity with respect to modifier ions, for example, silver. Studies on the dehydration of natural clinoptilolite were carried out after saturating it with water vapor until reaching equilibrium at a temperature of 30 ºС. It was established that the sorption capacity of clinoptilolite, previously thermally activated at a temperature of 100 ºС, with respect to water vapor increases with an increase in the size of zeolite particles from 0.25 to 2.5 mm. This may be due to the influence of the state of the surface of the particles. As the particle size increases further, the sorption capacity naturally decreases. The method of thermogravimetric analysis confirmed that thermal dehydration of clinoptilolite occurs in three temperature ranges. The first of them in the range of 20—175 ºС corresponds to the desorption of physically sorbed water. Using the DTA method, it was established that after treatment of clinoptilolite saturated with water vapor in the microwave field (frequency 2.45 GHz, power 500 W), only about 70 % of the physically sorbed water desorbs before reaching a constant mass (its total content was determined by the DTA method of the initial sample). Moreover, several temperature intervals are clearly distinguished on the DTG and DTA curves, where the endo effect and mass loss are observed. At the same time, on the DTG and DTA curves for the initial (untreated in the microwave field) samples, the allocation of physically sorbed water is manifested by one clear minimum. The obtained data give grounds for asserting that under the action of the microwave field, after desorption of part of the water whose molecules are dipoles, the rest is retained in the 3D structure of clinoptilolite due to the cation-dipole interaction.