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

The applicability of simplified models for the determination of ion exchang e diffusion coefficients in zeolites is examined. The simplified models exa mined are Vermeulen's, Paterson's, and Nernst-Plank's approximations for is otopic and ion exchange processes, used in ion exchange systems analysis. P arameter analysis indicates the limits for fractional attainment of equilib rium 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 c an be successfully used. Studies of the applicability of the isotopic excha nge simplified models to experimental data for batch-type Na+-Pb2+ exchange on clinoptilolite confirm the parameter analysis conducted. (C) 2001 Acade mic Press.