Ion exchange in chabazite. Part 2.—Comparison of experimental and theoretical rates of Na+/K+ exchange

Abstract

The kinetics of the ion exchange reaction K-chabazite + Na⁺_soln→ Na-chabazite + K⁺_soln and the corresponding reverse exchange have been measured at 28°C. These experimental rates have been compared with rates predicted from a finite difference solution of the diffusion equation in which the interdiffusion coefficient contains (a) constant self-diffusion coefficients equal to their values measured using the respective pure homoionic forms of chabazite, and (b) self-diffusion coefficients which vary with concentration as described in Part 1. Reasonable agreement between theory and experiment is obtained in this second case whereas with constant self-diffusion coefficients the predicted rates are the reverse of the experimental rates.

Non-ideality thermodynamic correction functions, derived from an accurately determined exchange isotherm, were also introduced into the interdiffusion coefficients but these had little effect on the predicted rates.