**1. Introduction**

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> It is well known that natural zeolites consist of aluminia and silica tetrahedra which, bound in a definite way, include crystal structure vacancies, channels and pores [1,2]. About 40 natural zeolites have been identified during the past 200 years; the most widespread are analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, and phillipsite. More than 150 zeolites have been synthesized; the most common are zeolites A, X, Y, and ZMS-5. Clinoptilolite has the structural formula (Na,K)6(Al6Si30O72). 20H2O, characterized by two different rings, which are 8(3,3x4,6 Å) T and 10(3,0x7,6 Å) T on the abplane, and channels with rings of 8(2,6x4,7 Å) T on the bc-plane. As shown in Figure 1, there are exchangeable cations of Na+, K+, Ca2+ and Mg2+ through the channels

> Because clinoptilolite has rings of two different dimensions, it is used in retention and separation of various gases, as an adsorbent, and as a molecular sieve. Because of its exchangeable cations clinoptilolite, which has the property of ion exchange, is used in producing biological and water filters, in retention of various heavy metal ions and radio-isotopes, in production of fillers in animal feeds, and in the horticulture and agriculture as a soil additive.[4, 5, 6]

> Clinoptilolite is a material that is used in both its natural and modified forms. Both forms of clinoptilolite have widespread application but, apart from their general ion-exchange properties and the high quantities of exchangeable cations through their channels, their general properties are different [7, 8].
