The chemistry involved
Zeolites are alluminosilicate minerals that contain alkali and alkaline-earth metals, such as sodium, potassium and calcium as well as water molecules within their structural framework. The lattice structure is relatively porous, enclosing interconnected cavities in which the metal cations (positively charged atoms) and water molecules reside. The cations and water molecules have a considerable freedom of movement within the framework of aluminium, oxygen and silicon atoms. This gives the zeolite its free cation exchange and reversible dehydration properties which are crucial for its application as a water softener in detergents.
The porous framework of the zeolites enables them to act as molecular sieves, which can be used to separate molecular mixtures based on their size and shape or for the selective absorption of gases. These unique properties make zeolites a popular choice in diverse industrial applications other than the detergent industry, such as purification of water as well as other liquids and gases, chemical separation, catalysis and the decontamination of radioactive wastes. Zeolites have also found wide application as carriers for certain catalysts that were previously redundant because of their high volatility.
Synthetic zeolites are preferred over natural zeolites for most industrial applications because of their uniform chemical composition and crystallinity. The commercial manufacture of zeolites involves the preparation of highly reactive aluminosilicate gels from aqueous solutions of sodium aluminate, sodium silicate and sodium hydroxide. Zeolites are then recrystalised from these gels at temperatures ranging from room temperatures to about 150
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