Sources of Cesium
Cesium is a soft white alkali metal, atomic number 55 on the periodic table of the elements. In its "family" are the other alkali metals, lithium, sodium, potassium and rubidium. In nature, it exists as isotope 133, but a number of man-made radioactive isotopes are known to exist. Of these isotopes, Cesium-137 is commercially important.
Some Important Properties
Cesium is the most electropositive of the elements. Although a solid at room temperature, with a melting point of 28 degrees C it is very easily melted. When burned, its spectrum contains two bright blue lines, hence its name (Latin: caesius which means sky blue). Cesium has the strongest alkaline hydroxide of the alkali metals, and readily reacts with glass, etching it.
Uses
As a result of cesium's great reactivity, it is used as a "getter" in removing final traces of oxygen from inside electron tubes. Besides electronics uses, cesium is used in glasses, ceramics and pyrotechnics. Special low-temperature alkali batteries employ cesium in their construction. Of special note, the metal is used in the extremely accurate "cesium clock," or "atomic clock." The cesium clock is accurate to within five seconds in 300 years. Finally, the radio-isotope, Cesium-137, is used in the treatment of cancers in brachytherapy. Perhaps most curious of all, it is hoped one day cesium will be used in ion-propulsion for spacecraft.
Ore Sources
Cesium is found in two well-known ores, lepidolite and pollucite. One of the world's richest sources of cesium is tanco pegmatite located at Bernic Lake, Lac-du-Bonnet, Manitoba, Canada. The deposits are estimated to contain 300,000 tons of pollucite, averaging 20 percent cesium. The United States imports all the cesium it uses, mostly from Canada. Zimbabwe and Southwest Africa are also sources.
Isolation of the Metal from Compounds
Cesium can be isolated by electrolysis of the fused cyanide and by vacuum distillation of the metal formed by the reaction of cesium chloride with either calcium or sodium metals. Very pure, gas-free cesium can be prepared by thermal decomposition of cesium azide.
Produced by Fission
When Uranium 235 undergoes fission, a number of fragments result. Some have fairly long half-lives. Two of these fragments are Strontium-90 and Cesium-137. Living organisms assimilate Cesium-137, becoming part of the body's fluid electrolytes. This being the case, Cesium-137 presents a considerable risk to the environment.
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