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RADIOACTIVE WASTE
TREATMENT -
Process effluents bearing radioactive isotopes can be treated through
columns packed with natural zeolites. The zeolites selectively remove cesium
(Cs134, CS137) and Strontium (Sr90) isotopes through the process of
ion-exchange. Effluent liquids are purified to acceptable limits for discharge
as the radioactive isotopes are held within the zeolite cage structure. One
outstanding example of the application is the British Nuclear Fuels, Ltd. Site
Ion Exchange Efficient Plant (SIXEO) at Sellifield, England. The other large
application is for the treatment of low level liquid effluents at the DOE West
Valley, NY site, where Phillipsite was used to selectively remove CS137 and SR90
isotopes. The permanent storage or disposal of the waste is facilitated by the
inorganic and stable structure of the zeolite which can be encapsulated in
cement or glass. |
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SORBENT BARRIERS
FOR RADIOACTIVE WASTE-
Permeable barriers incorporate
sorbent materials, including zeolite, to selectively contain contaminants that
are percolating from shallow land burial sites of low-level radioactive waste.
The zeolites are combined with clays and other materials that retard the
migration of leachate for a period long enough to allow exchange and/or decay of
radioactive ions.Finely crushed zeolites are used in sorbent barrier layers.
Exact specifications are dependent upon the engineered permeability of the
system. |
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Beneficial qualities include:
• High cation exchange capacity • Low cost • Large tonnage reserves - |
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FILLERS
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Zeolites are used extensively in Japan as fillers in the manufacture of paper
These filler grades of zeolite have a large potential for utilization in the
paint and plastics industries. Many deposits of natural zeolites contain
high-brightness reserves and the potential for benefaction is increasing with
improved technology for magnetic separation and bleaching of zeolite. |
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POLLUTION CONTROL
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Natural zeolites are an
adsorbent of choice for many cost effective air pollution control technologies
treating the hazardous air pollutants (HAP) and listed volatile organic
compounds (VOC). The need for technologically improved air purification systems
has been indicated by keen client interest in the use of zeolites in controlling
indoor air pollutants or "sick building syndrome". Existing filtration systems
typically contain activated carbon as the adsorbent media. Because most grades
of activated carbon contain large internal pores, they tend to trap a wide
variety of larger molecules. Zeolites, on the other hand, contain a very small
internal pores, in all cases from 3 to 5 angstroms. For this reason zeolite is a
highly selective adsorbent of specific gas-phase molecules and elements. Many of
the identified indoor air pollutants, including formaldehyde, chloroform,
ammonia and carbon monoxide, are in a size range that is most effectively sieved
by zeolite. Many promising zeolite and zeolite/carbon air purification and odor
controlling systems are being developed to meet the need. |
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Beneficial
qualities include: •
Selectivity for pollutant gases of concern • Inexpensive relative to other
molecular sieves |
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GAS PURIFICATION
AND SEPARATION |
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