Zeolites
Zeolite
is a mineral with porous structure, which allows some molecules to
pass through and causes others to be either excluded, or broken down.
The term has been derived from Greek words "zein" and "boil,"
which mean "to boil" and "a stone." This term was
originally coined by Axel Fredrick Cronstedt, a Swedish mineralogis in
the 18th century. He observed that upon heating a natural mineral
rapidly, the stones began to dance about as the water evaporated.
More than 150 types of zeolite have been synthesized. There are 48
known naturally occurring zeolites. They are basically a hydrated
alumino-silicate minerals with an "open" structure which can
accommodate a wide variety of positive ions, like Na+, K+,
Ca2+, Mg2+ and others.
These ions are held loosely and can be exchanged readily for others
in a contact solution. Some more common mineral zeolites are as
follows:
- Analcime
- Chabazite
- Heulandite
- Natrolite
- Phillipsite
- Stilbite
An example mineral formula is as follows:
Na2Al2Si3O10-2H2O
- The formula for natrolite.
Uses of Zeolites
Commercial and Domestic - It is widely been used as ion-exchange beds
in both domestic and commercial water purification, softening, and
other applications. In chemistry, it separates molecules, only of
certain sizes and shapes can pass through, as traps for molecules so
that they can be analyzed, or as catalysts by confining molecules in
small spaces that causes changes in their structure and reactivity.
Zeolites even carries the potentiality of providing precise and
specific separation of gases including the removal of H2O, CO2 and SO2
from the lower grade natural gas streams. Some other separations
includes HCHO, Noble gases, N2, Freon and Formaldehyde. However, the
true potential for improving the handling of such gases in this manner
remains unknown.
Agriculture - Clinoptilolite, a naturally occurring zeolite, is used
as a soil treatment in agriculture. It provides a source of slowly
released potassium. If the zeolite is previously loaded with ammonium,
it can serve a similar function in the slow release of nitrogen. Cuban
studies even suggests that some crops may be grown in 100% zeolite or
zeolite mixtures, where the zeolite is previously loaded or has been
coated with fertilizer and micronutrients.
Medical - Zeolite-based oxygen generation systems are used in
producing medical grade oxygen. It is used as a molecular sieve for
extracting oxygen from air, in a process which involves adsorption of
atmospheric nitrogen. The usage of zeolite is also being explored for
a quick clotting of severe bleeding.
Heating and Refrigeration - Zeolites can also be used as solar
thermal collectors and for adsorption refrigeration. Their high heat
of adsorption and ability to hydrate and dehydrate is exploited while
maintaining the structural stability. This hygroscopic property along
with an inherent exothermic reaction, while transitioning from
dehydrated to a hydrated form, make the natural zeolites effective in
the storage of solar and the waste heat energy.
Detergents - Synthetic zeolite is widely used as the global laundry
detergent.
Gemstones - Thomsonites is collected as gemstones from a series of
lava flows along the Lake Superior (Minnesota) and in a lesser degree
in Michigan (USA).
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