Zeolite is a family of minerals chemically known as hydrated sodium calcium aluminum silicates (HSCAS) of alkali and alkaline earth cations having three dimensional framework composed of bonded aluminosilicate tetrahedral lattices ( Figure 1 ).
- Figure 1 - Bonded aluminosilicate tetrahedral lattices
Aluminosilicates tetrahedral lattice is composed of aluminum dioxide and silicon dioxide atom symmetrically arranged to resemble a triangular pyramid ( Figure 2 ). The triangular pyramid forms a space, which at its normal state contains loosely, bonded water molecules. These water molecules are removed to create an empty space, which makes it available for the adsorption of other molecules.
- Figure 2 - Aluminosilicate tetrahedral lattices resembling a triangular pyramid
Natural zeolites are a collection of these aluminosilicate tetrahedral lattices creating an overall framework of open channels between empty spaces. Within the framework, there are cation molecules present such as calcium, sodium and potassium attached to the aluminosilicate tetrahedral lattice ( Figure 4 ).
Natural zeolites vary in their crystalline pore sizes that may range from 2A to 12A. Most natural zeolite pore sizes range form 3.5 A to 8.0 A ( Figure 3 ).
- Figure 3 - Typical zeolite pore sizes
