Chapter 10 - Kinetics of Ion Exchange

Abstract

Ion exchange rates can be controlled by the rates of actual chemical reactions; however, control by diffusion processes is a more common case. Moreover, many ion exchange interactions do not involve any direct chemical reactions and therefore, the overall process is controlled solely by the diffusion which, in turn, is defined by the material structure. Besides the microstructure, macroshape of the material (size of the beads, layers, membranes, etc.) also influences the apparent rates of ion exchange. This is because larger pieces can require more time for the process to be completed if the rate is limited by diffusion through the bulk of the material. More specificity to ion exchange kinetics is added by the quasi-homogeneity of the exchanger phase, the electroneutrality requirement, and other peculiar features of ion exchangers. Therefore, kinetic approaches are very specific for ion exchange materials. This chapter introduces the primary ideas of corresponding kinetic models and representations.