Applicability of simplified models for the estimation of ion exchange diffusion coefficients in zeolites

The applicability of simplified models for the determination of ion exchange diffusion coefficients in zeolites is examined. The simplified models examined are Vermeulen's, Paterson's, and Nernst-Plank's approximations for isotopic and ion exchange processes, used in ion exchange systems analysis. Parameter analysis indicates the limits for fractional attainment of equilibrium U(t), the ratio of exchangeable ions in liquid to solid phase (w), and the ratio of surface diffusion coefficients of exchangeable ions (a), all clearly inter-related, within which the above-mentioned simplified models can be successfully used. Studies of the applicability of the isotopic exchange simplified models to experimental data for batch-type Na+-Pb2+ exchange on clinoptilolite confirm the parameter analysis conducted. (C) 2001 Academic Press.