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Zeolite
ZeoliteThe zeolites are a group of more than 35 soft, white minerals comprised mostly of aluminum, silicon , and oxygen and having a crystal structure featuring spacious pores or rings. Zeolites often form as crystals in small cavities in basaltic rocks or as volcanic tuffs altered by water . They are also synthesized industrially. The pores of a natural zeolite crystal are filled with water that can be driven off by heating. The result is a honeycomb-like structure penetrated by openings on the order of a few atoms in width (2–8 angstroms). This structure can act as a hyperfine filter or molecular sieve. For example, nitrogen binds to some zeolites, so forcing ordinary air (which consists mostly of nitrogen) through such crystals yields an output of up to 95% oxygen. Equally useful is the ability of zeolites to capture large positively-charged ions from aqueous solution. This capture process is reversible; that is, an ion adsorbed by a zeolite can generally be driven off again by heat. This property allows many zeolite-based molecular sieves to be reused indefinitely. Such sieves—often consisting of tanks filled with tons of crushed zeolitic tuff—have been used to filter radioactive cesium and strontium from nuclear waste, to remove ammonia from sewage, to scrub sulfur dioxide (SO2) from coal-fired electric power station emissions, to purify landfill gas for household utility use, to filter mercury and other heavy metals from industrial wastewater, to remove calcium from water in water-softening systems, and for many other purposes. Zeolites were first identified in 1756, but their molecular sieve properties were not observed until the mid 1920s. Even then they remained a mere curiosity for some time, as geologists still argued that natural zeolites were too rare to be commercially useful. Attention turned instead to zeolite synthesis. It was not until the 1950s that geologists discovered that million-ton deposits of volcanic tuff consisting mostly of zeolite are not, in fact, uncommon. See also Crystals and crystallography; Minerology |
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"Zeolite." World of Earth Science. 2003. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "Zeolite." World of Earth Science. 2003. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1G2-3437800661.html "Zeolite." World of Earth Science. 2003. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3437800661.html |
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zeolite
zeolite Group of alumino-silicates that contain sodium, calcium or barium, and loosely held water that can be continuously expelled on heating. Some zeolites occur as fibrous aggregates, while others form robust, non-fibrous crystals. Zeolites vary in hardness from 3 to 5 and in specific gravity from 2 to 2.4. They include analcime, NaAlSi2O6H2O, stilbite, NaCa2(Al5Si13)O36.14H2O, and natrolite, Na2Al2Si3O10.2H2O.
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"zeolite." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "zeolite." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-zeolite.html "zeolite." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-zeolite.html |
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zeolite
ze·o·lite / ˈzēəˌlīt/ • n. any of a large group of minerals consisting of hydrated aluminosilicates of sodium, potassium, calcium, and barium. They can be readily dehydrated and rehydrated, and are used as cation exchangers and molecular sieves. DERIVATIVES: ze·o·lit·ic / ˌzēəˈlitik/ adj. |
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"zeolite." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "zeolite." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O999-zeolite.html "zeolite." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-zeolite.html |
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zeolites
zeolites Group of hydrated alumina silicates of sodium, potassium, calcium, and barium, which occur in geodes, altered igneous rocks, hydrothermal veins, and some sediments. The water molecules are weakly held and the hydration-dehydration reaction has some useful applications, as do the ion-exchange properties of zeolites.
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AILSA ALLABY and MICHAEL ALLABY. "zeolites." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "zeolites." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O13-zeolites.html AILSA ALLABY and MICHAEL ALLABY. "zeolites." A Dictionary of Earth Sciences. 1999. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-zeolites.html |
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zeolites
zeolites A group of naturally occurring hydrated alumina silicates of sodium, potassium, calcium, and barium, in which the water molecules are weakly held. The hydration–dehydration reaction has some useful applications, as do the ion-exchange properties of zeolites.
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MICHAEL ALLABY. "zeolites." A Dictionary of Ecology. 2004. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "zeolites." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O14-zeolites.html MICHAEL ALLABY. "zeolites." A Dictionary of Ecology. 2004. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-zeolites.html |
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zeolite
zeolite (min.) generic name of a group of minerals consisting of hydrous silicates, characterized by swelling up and fusing under the blowpipe. XVIII. — Sw., G., etc. zeolit, f. Gr. zeîn boil + lithos -LITE.
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T. F. HOAD. "zeolite." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "zeolite." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O27-zeolite.html T. F. HOAD. "zeolite." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-zeolite.html |
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