EFFECT OF THE TIME OF ACID-THERMAL MODIFICATION OF CLINOPTILOLITE ON ITS STRUCTURE-ADSORPTION CHARACTERISTICS
Literary data concerning the influence of different factors of acid treatment on values of specific surface area (Ssp) of clinoptilolite mined from various deposits are presented and analyzed. These data are compared with our results showing how the time of interaction of natural Ukrainian clinoptilolite with boiling nitric acid affects its structure-adsorption properties. Following IUPAC classification, water vapor ad/desorption isotherms for natural clinoptilolite from Sokirnitskoe deposit and its acid-modified forms belong to IVa type. Values of the specific surface area (Ssp) for the clinoptilolite samples were estimated using the BET equation and by measuring the thermal desorption of argon by the gas chromatographic method. Ssp values estimated by the use of BET equation from water vapor adsorption isotherms and those determined by chromatographic method from thermal desorption of argon are higher for all H-CLI samples than for N-CLI. Values of the monolayer capacity for the clinoptilolite samples have been found to increase in the order N-CLI < H-CLI-0.5 < H-CLI-1 < H-CLI-3 ≈ H-CLI-6 ≈ H-CLI-9 and whereas their C(Q1) parameter have been found to change in the reverse order. Both natural and acid-modified clinoptilolite samples have nonuniform porous structures with prevalence of meso- and macropores. The minimum Ssp value was revealed for natural clinoptilolite and its acid-thermal modification resulted in an increase in the specific surface area.