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Natural zeolite is a new and very good natural filter medium available for
the filtration of water. It offers superior performance to sand and carbon
filters, giving purer water and higher throughput rates with less
maintenance required. It has many advantages over sand and can be used to
directly replace sand in a normal sand filter.
There are three main uses of zeolites in
industry: catalysis, gas separation and ion exchange.
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Catalysis:
Zeolites are extremely useful as catalysts for several important
reactions involving organic molecules. The most important are cracking,
isomerisation and hydrocarbon synthesis. Zeolites can promote a diverse
range of catalytic reactions including acid-base and metal induced
reactions. Zeolites can also be acid catalysts and can be used as
supports for active metals or reagents.
Zeolites can be shape-selective catalysts either by transition state
selectivity or by exclusion of competing reactants on the basis of
molecular diameter. They have also been used as oxidation catalysts. The
reactions can take place within the pores of the zeolite, which allows a
greater degree of product control.
The main industrial application areas are: petroleum refining, synfuels
production, and petrochemical production. Synthetic zeolites are the
most important catalysts in petrochemical refineries.
- Adsorption:
Zeolites are used to adsorb a
variety of materials. This includes applications in drying,
purification, and separation. They can remove water to very low partial
pressures and are very effective desiccants, with a capacity of up to
more than 25% of their weight in water. They can remove volatile organic
chemicals from air streams, separate isomers and mixtures of gases. A
widely used property of zeolites is that of gas separation. The porous
structure of zeolites can be used to "sieve" molecules having certain
dimensions and allow them to enter the pores. This property can be fine
tuned by variating the structure by changing the size and number of
cations around the pores. Other applications that can take place within
the pore include polymerisation of semi conducting materials and
conducting polymers to produce materials having unusual physical and
electrical attributes.
- Ion
exchange: Hydrated cations within the zeolite pores are bound
loosely to the zeolite framework, and can readily exchange with other
cations when in aqueous media. Applications of this can be seen in water
softening devices, and the use of zeolites in detergents and soaps. The
largest volume use for zeolites is in detergent formulations where they
have replaced phosphates as water-softening agents. They do this by
exchanging the sodium in the zeolite for the calcium and magnesium
present in the water. It is even possible to remove radioactive ions
from contaminated water.
For more information about the removal
of substances by zeolites click here.
From a practical point of view, zeolite
can be adapted for a variety of uses:
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Agriculture:
- Odour control
- Confined animal environmental
control
- Livestock feed additives
In Eastern Europe, Japan and Cuba
zeolites have been traditionally used in agriculture. About a 5% addition
to livestock rations reduces ammonia and odour emissions, improves feed
utilisation, assists with mycotoxin absorption and may contribute trace
elements. Several years ago NASA used nutrient loaded zeolites as slow
release fertilisers.
Horticulture:
- Nurseries, Greenhouses
- Floriculture
- Vegetables/herbs
- Foliage
- Tree and shrub transplanting
- Turf grass soil amendment
- Reclamation, revegetation,
landscaping
- Silviculture (forestry, tree
plantations)
- Medium for hydroponics growing
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Aquaculture:
- Ammonia filtration in fish
hatcheries
- Biofilter media
In a fish farm the load of the water
with fish can be very high. This results in quick pollution of the water
and as a result the concentrations of toxic substances can increase
rapidly. Therefore extensive water purification is necessary. The zeolites
can be used in various steps of the purification process: as a secondary
filtration unit after biological purification and/or aeration; as a
support material for bacteria; as a filter medium for the removal of solid
and suspended particles and removal of unwanted ions at the same time.
Household
products:
- Household odour control
- Pet odour control
Domestic uses relate primarily to the
odour and liquid adsorbing characteristics of zeolite. A range of gases
including formaldehyde, hydrogen sulphide has been shown to be adsorbed by
zeolite.
In the USA, zeolite is routinely added to small air filters to adsorb such
gases and reduce allergy problems. It can be used to dry sports shoes,
reduce moisture in wardrobes and is commonly used to adsorb cigarette
odours. A very useful carpet cleaner had zeolite as its base material.
The most common use for zeolite around the home is as kitty litter and as
a fat absorber for barbecues. It is also used in fish tanks to adsorb
ammonia. When fully utilised the spent product makes an ideal addition to
composts where it will assist in conditioning and eventually contribute to
soil moisture and nutrient holding capacity. |
