Description
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Tellurium is a metalloid with a shiny sliver grey color in its natural solid state. Tellurium is one of the rarest element on earth, and it is a brittle metal that has semi-conductive traits. Tellurium has an atomic weight of 127.60, a melting point of 841.12 °F, and a boiling point of 1810 °F. Tellurium metal is commonly used in alloys to strengthen lead and increase the workability of stainless steel and copper; it is also used in ceramics, and as a semiconductor.
Isolation
As a rare substance, tellurium is usually only isolated on a commercial basis. The isolation process used depends on which compounds are present with the tellurium.
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Tellurium does exist in nature in its free form, but it is very rarely found this way. Most tellurium in nature occurs in nature and gold tellurides such as calaverite, krennerite, petzite, and sylvanite. Additional sources of tellurium can be used for isolation. One isolation process uses treatment of copper ore; this treatment process using electrolytic refining of copper forms anode sludges of tellurium. Tellurium can also be collected and isolated from dust that is emitted from the process of refining lead using a blast furnace.
Another isolation method which extracts tellurium from copper uses a multi-step chemical reaction process. The first step of the isolation process is to oxidize the tellurium-copper complex using sodium carbonate and oxygen to produce tellurite. The tellurite is then acidified with sulphuric acid to precipitate out of the solution in its dioxide form. The tellurium dioxide is then dissolved in sodium hydroxide, and electrolytic reduction is used to produce pure tellurium.