Zeolites (Greek, zein, "to boil"; lithos, "a
stone") are minerals that have a micro-porous structure. "stone that
boils," They are basically hydrated alumino-silicate minerals with an
"open" structure that can accommodate a wide variety of cations, such
as Na⁺, K⁺, Ca²⁺, Mg²⁺ and
others. Natural zeolites form where volcanic rocks and ash layers react
with alkaline groundwater. Zeolites are the aluminosilicate members of
the family of microporous solids known as "molecular sieves". The term
molecular sieve refers to a particular property of these materials,
i.e. the ability to selectively sort molecules based primarily on a
size exclusion process. This is due to a very regular pore structure of
molecular dimensions. The maximum size of the molecular or ionic
species that can enter the pores of a zeolite is controlled by the
diameters of the tunnels. These are conventionally defined by the ring
size of the aperture, where, for example, the term "8ring" refers to a
closed loop that is built from 8 tetrahedrally coordinated silicon (or
aluminium) atoms and 8 oxygen atoms. These rings are not always
perfectly flat and symmetrical due to a variety of effects, including
strain induced by the bonding between units that are needed to produce
the overall structure, or coordination of some of the oxygen atoms of
the rings to cations within the structure. Therefore, the pore openings
for all rings of one size are not identical.

 

 

Commercial and Domestic

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, as traps for
molecules so they can be analyzed.

Zeolites have the potential of providing precise and specific separation of gases including the removal of H₂O, CO₂ and SO₂ from low-grade natural gas streams. Other separations include: noble gases, N₂, freon and formaldehyde.

 

Synthetic zeolites are widely used as catalysts in the
petrochemical industry, for instance in fluid catalytic cracking and
hydro-cracking. Zeolites confine molecules in small spaces, which
causes changes in their structure and reactivity.

 

Zeolites have uses in advanced reprocessing methods, where their
micro-porous ability to capture some ions while allowing others to pass
freely allow many fission products to be efficiently removed from
nuclear waste and permanently trapped. Equally important are the
mineral properties of zeolites. Their alumino-silicate construction is
extremely durable and resistant to radiation even in porous form.
Additionally, once they are loaded with trapped fission products, the
zeolite-waste combination can be hot pressed into an extremely durable
ceramic form, closing the pores and trapping the waste in a solid stone
block. This is a waste form factor that greatly reduces its hazard
compared to conventional reprocessing systems.

 

In agriculture, clinoptilolite (a naturally occurring zeolite) is
used as a soil treatment. It provides a source of slowly released
potassium. If previously loaded with ammonium, the zeolite can serve a
similar function in the slow release of nitrogen. Cuban studies in the
emerging field of "zeoponics" suggest that some crops may be grown in
100% zeolite or zeolite mixtures in which the zeolite is previously
loaded or coated with fertilizer and micronutrients. Zeolites can also
act as water moderators, in which they will absorb up to 55% of their
weight in water and slowly release it under plant demand. This property
can prevent root rot and moderate drought cycles.

   SiO2 70.19-75.90
   Al2O3 9.90-11.81
   Fe2O3 1.55-4.90
   CaO 2.35-3.30
   K2O 0.10-3.10
   Na2O 2.00-2.26
   C.E.C 150-160
   PH(H2O) 7.5-7.6