- © The Mineralogical Society Of America
The world is faced with increasing demands for high-quality drinking water and for removal of contaminants from municipal, agricultural, and industrial wastewaters. Treatment is required to obtain drinking water from most natural resources as well as from wastewaters with varying amounts of impurities. These impurities may occur in a variety of forms including large particles such as microorganisms or suspended solids or as dissolved or colloidal inorganic and organic substances. This chapter provides an overview of the use of natural zeolites in removal of impurities from water or wastewater (Murphy et al. 1978, Tarasevich 1994, Kalló 1995).
Most technologies using natural zeolites for water purification are based on the unique cation-exchange behavior of zeolites through which dissolved cations can be removed from water by exchanging with cations on a zeolite’s exchange sites (see Pabalan and Bertetti, this volume). The most common cation in waters affecting human and animal health is NH4+. It can be removed by exchanging with biologically acceptable cations such as Na+, K+, Mg2+, Ca2+ or H+ residing on the exchange sites of the zeolite. Fortunately, many natural zeolites (e.g. clinoptilolite, mordenite, phillipsite, chabazite) are selective for NH4+ (vide infra), meaning that they will exchange NH4+ even in the presence of larger amounts of competing cations. Clinoptilolite and mordenite are also selective for transition metals (e.g. Cu2+, Ag+, Zn2+, Cd2+, Hg2+, Pb2+, Cr3+, Mo2+, Mn2+, Co2+, Ni2+), which are often present in industrial waters and can be very toxic even in concentration as low as several mg/L. As emphasized in discussions of radioactive waste treatments, both clinoptilolite and mordenite …