Physical and Chemical Properties of Zeolites
Two major processes have been identified as kinetics of ion-exchange process in zeolites, namely, particle diffusion and film diffusion. Zeolites are one of the greatest cationic interchangers and their cationic interchange capacity is two to three times greater than other types of minerals found in soils. Zeolites are potential adsorbents due to the ability of their microporous structures to adsorb molecules at relatively low pressure. There is a wide variation in the cation-exchange capacity of zeolites because of the differing nature of various zeolite cage structures, natural structural defects, adsorbed ions and their associated minerals. Thus in short, zeolites are natural materials with the ability to exchange ions, absorb gases and vapors, act as molecular-scale sieves and catalyze reactions owing to fixed pore sizes and active sites in the crystal lattice. The size of clinoptilolite channels controls the size of the molecules or ions that can pass through them and therefore a zeolite like clinoptilolite can act as a chemical sieve allowing some ions to pass through while blocking others. Their internal areas mostly fall in the range of 400-850 m2/g. Zeolites vary widely in their chemical composition, particularly with respect to contents of SiO2, CaO, K2O, Al2O3, Na2O, and Fe2O3. The techniques for the separation of clinoptilolites from soil are based on the low specific gravity and fine particle-size characteristics of clinoptilolite.