Properties & Uses
Zeolites are crystalline, hydrated aluminosilicates that contain alkali and alkaline-earth metals. Their crystal framework is based on a three-dimensional network of SiO4 tetrahedra with all four oxygens shared by adjacent tetrahedra. The alkali and alkaline earth cations are loosely bound within this structure and can be exchanged by other cations or molecular water. Most zeolites can be dehydrated and rehydrated without any change in volume. More than 48 natural zeolite minerals have been identified (Tschernich 1992), and more than 100 zeolites have been synthesized.
Important physical and chemical properties of zeolites:
- High degree of hydration
- Low density and large void volume when dehydrated
- Stability of the crystal structure of many zeolites when dehydrated
- Cation exchange properties
- Uniform molecular-sized channels in the dehydrated crystals
- Ability to adsorb gases and vapors
- Catalytic properties
Molecular sieves are materials that can selectively adsorb molecules on the basis of their size, shape, or electrical charge.
Commercial applications of zeolites are based on the following properties:
Molecular sieving, ion exchange, adsorption, and catalysis. Most zeolites are molecular sieves, but not all molecular sieves are zeolites. Activated carbon, activated clays, aluminum oxide, and silica gels are also molecular sieves. Activated synthetic and natural zeolite molecular sieve products, however, have displaced many of these substances because of their selectivity.
Application of Zeolite
- Ammonium-ion removal from sewage and industrial effluents,aquariums, and commercial fish farms
- Odor control in animal absorbents, floor and carpet cleaning products, and industrial floor absorbents
- Removal of heavy metal ions from nuclear, mine, and industrial effluents
- Agricultural applications as soil conditioners and animal feed supplements
- Desiccants used to adsorb water vapor in sealed containers and packaging
- Carriers for bacteria and enzymes
- Gas separation
Natural zeolites were produced and consumed worldwide. Construction and agricultural applications consumed most of the production, especially in developing countries like India.