12.4. ION-EXCHANGE PROCESSES
12.4A. Introduction and Ion-Exchange Materials
Ion-exchange processes are basically chemical reactions between ions in solution and ions in an insoluble solid phase. The techniques used in ion exchange so closely resemble those used in adsorption that for the majority of engineering purposes ion exchange can be considered as a special case of adsorption.
In ion exchange, certain ions are removed by the ion-exchange solid. Since electroneutrality must be maintained, the solid releases replacement ions to the solution. The first ion-exchange materials were natural-occurring porous sands called zeolites, which are cation exchangers. Positively charged ions in solution such as Ca2+ diffuse into the pores of the solid ...