In the present work. ion exchange of lead and cadmium on the sodium form of Western Anatolia clinoptilolite is examined at 25 degreesC and 0.1 total normality. Its total theoretical cation exchange capacity was 2.3 meq/g. But only the sodium was exchanged during the equilibrium experiments. On this basis, the theoretical exchange capacity is 1.74 meq/g. According to the equilibrium studies, the selectivity sequence can be given as Pb2+ > Na+ > Cd2+. The maximum exchange levels expressed as the percentage of the theoretical exchange capacity were 100% for lead and 54% for cadmium. Using the equilibrium data, the thermodynamic analysis of the system was carried out. The solution non-ideality Correction factor has almost no effect on the Kielland plot and so on the numerical values of the thermodynamic equilibrium constant. The thermodynamic equilibrium constant (K,) and the standard free energy of exchange (DeltaGdegrees) were calculated as 16.6 and -3.48 kJ/eq. for lead-sodium system; and 0.16 and +2.27 kJ/eq. for cadmium-sodium system, respectively. Comparing the results of the present work with the data in literature, it can be concluded that the ion exchange capacities and cation selectivities of clinoptilolites with different cationic compositions are different. So, one should carry out cation exchange experiments on representative samples from the deposit before using it as cation exchanger for any practical application. (C) 2003 Elsevier B.V. All rights reserved.