A mathematical model for multicomponent ion exchange uptake on chabazite zeolite

Binary and muiticomponent models for liquid ion exchange on chabazite zeolite are presented. The kinetic model assumes pore diffusion within the particle. Film mass transfer resistance is assumed to occur external to the particle. Several equilibrium models including the Langmuir, Dubinin-Polyani and a thermodynamic model are presented and utilized to complete the description of mass transport and ion exchange of strontium, cesium, calcium and/or magnesium in solution with sodium on chabazite zeolite.

A Langmuir model of the equilibrium for binary exchange, when used in the pore diffusion model, adequately predicted uptake rates of strontium and cesium. Kinetic uptake of calcium and magnesium from solution was not predicted as well, presumably because of the less accurate predictions of equilibrium by the Langmuir model.

Multicomponent uptake from solution in this system (Sr-Cs-Ca-Mg-Na) was not able to be predicted by the Dubinin-Polyani model due to instabilities encountered in the model. Kinetic multicomponent uptake for this system was predicted quite accurately by the thermodynamic model for two experimental runs taken at different total concentrations. Uptake curve variances for these two runs were found to be in the range of 1.7% to 34.2%.