Cs+ Ion Exchange Kinetics in Complex Electrolyte Solutions Using Hydrous Crystalline Silicotitanates

TAM-5 is a hydrous crystalline sodium silicotitanate inorganic ion exchanger with a high selectivity for Cs+. The kinetics of Cs+−Na+ ion exchange using TAM-5 in multicomponent electrolyte solutions were determined using batch experiments. For the powder, which is composed of crystals, a single-phase, homogeneous model fit the data best. For the granules, which were prepared from the powder, a two-phase, heterogeneous model resulted in an excellent fit of the data. Macropore and crystal diffusivities were determined by fitting the model to experimental data collected on the powder and the granules. Intracrystalline diffusivities were concentration dependent and were on the order of 10-19 m2/s. Macropore diffusivities were on the order of 10-10 m2/s. Resistance to diffusion in the macropores was not significant for granules with diameters less than 15 μm. A two-phase, homogeneous model, where liquid within the pores is in equilibrium with the solid, was also evaluated for the granules. Surprisingly, for the granules, an excellent fit of the data was obtained; however, the effective macropore diffusivity was 1.1 × 10-11 m2/s, an order of magnitude smaller than the macropore diffusivity found using the two-phase, heterogeneous model.