Zeolites (Greek, zein,”to boil”;lithos,”a stone”) are minerals that have a porous structure. There are about four dozen recognized naturally occurring zeolite minerals and as many or more synthetic varieties. They are basically hydrated alumino-silicate minerals with an “open” structure that can accommodate a wide variety of positive ions, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Some of the more common mineral zeolites are: analcime, chabazite, heulandite, natrolite, phillipsite, and stilbite. An example mineral formula is: Na2Al2Si3O10-2H2O, the formula for natrolite. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. There are several types of synthetic zeolites that form by a process of slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates.
Zeolites are widely used as ion-exchange beds in domestic and commercial water purification, softening, and other applications. In chemistry, zeolites are used to separate molecules (only molecules of certain sizes and shapes can pass through), as traps for molecules so they can be analyzed, or as catalysts by confining molecules in small spaces, which causes changes in their structure and reactivity.
Their use is also being explored for quickly clotting severe bleeding under the brand name “QuikClot” or “Hemosorb”.
Zeolites can be used as solar thermal collectors and for absorption refrigeration.