Zeolites are nano-porous crystalline aluminosilicates. Natural zeolites are non-toxic and safe for humans which expand their application in different fields. Clinoptilolite is the most abundant natural zeolite with high purity that occurs in many parts of the world. It has a frame structure in which the tetrahedra of silicon [SiO4/2] and aluminium [AlO4/2]- are interconnected with oxygen bridge. Cations like K+, Na+ and Ca2+ and water are located in its pores and large cavities. Zeolites have

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... gh ion exchange capacity, selective adsorption capacity and thermal and mechanical stability.In this paper, the characterization of the natural zeolite - clinoptilolite from Bulgaria is performed. The investigated clinoptilolite was characterized in terms of its chemical composition, particle size distribution, structural morphology (SEM, XRD, FTIR) and thermal analysis. The chemical analysis show that clinoptilolite contains 69.7% of SiO2 and 11.4% of Al2O3. As specific surface area is the most important characteristic of the materials when used as adsorbents (the most common application of the zeolite) the specific surface area of clinoptilolite was obtained from data of equilibrium adsorption of water vapor at 25oC and using the BET method with nitrogen. To enhance its adsorptive properties clinoptilolite was modified (mechanically activated) and its specific surface area was also determined.