Chapter 12.10 Cation and Anion Exchange

This chapter gives a brief survey of cation and anion exchange with particular reference to the definition and determination of the cation exchange capacity (CEC) of clay minerals. Ion exchange is of fundamental and practical importance to soil studies and all fields in which clay materials feature. The ability of colloidal particles (including clay minerals) to retain and exchange positively charged ions is perhaps the most important chemical property of natural porous media. This property has a controlling influence on the mobility of positively charged chemical species in soil, such as potassium (from fertilizers) and heavy metal ions as well as on the geochemical cycling of cations in general. The upsurge of interest in such issues as fertilizer efficiency or contaminant mobility in the environment contributed to the large increase in publications on cation exchange in soils, particularly with respect to the clay fraction of soils.