Modeling of ion exchange of Pb²⁺ in fixed beds of clinoptilolite

Ion exchange of Pb²⁺ on natural clinoptilolite in fixed bed and batch operations has been studied and simple models on experimental data have been applied. The operations are conducted at ambient temperature, an initial concentration of 0.01 N and at pH 4. Paterson's model is used to describe batch kinetics, the Langmuir isotherm is used to correlate equilibrium data and a solid diffusion controlled process is used to describe the fixed bed operation. The evaluated operating capacity is in the range of 0.21-1 meq/g and the diffusion coefficient is in the range of (0.07-5.4) × 10 ^-12 m²/s. The experimental results obtained put the basic theory under question. According to these experiments, the capacity and diffusion coefficient in fixed bed systems are flow dependent and different from those measured in the batch-reactor systems. This could be explained if the type of experimental setup influenced both the equilibrium isotherm and the system behavior.