Tellurium and Sélénium are rare elements seldom found in their native state and are widely dispersed in the earth´s crust at average levels less abundant than silver (they rank 69th and 75th respectively, in order of abundance). Tellurium was discovered in 1782 by Franz Muller von Reichenstein and was named by M. H. Klaproth, who isolated it in 1798. Sélénium was discovered by Berzelius in 1817. There are no ores from which Tellurium and Sélénium can be mined as primary products. Tellurium is usually associated with gold, silver, copper, lead, and bismuth ores. One of the most common Tellurium minerals is sylvanite, a complex gold silver telluride. Sélénium is found principally in sulfide minerals of copper, iron, and is most common in chalcopyrite, bornite, and pyrite.
The extraction of Tellurium and Sélénium from ore is a complex process involving numerous hydro- and pyro-metallurgical treatments. Flotation concentrates are smelted to remove sulfur, iron, and other impurities. Treatment of 200 MTs of copper ore typically yields one pound of Tellurium. Sélénium and Tellurium are considered as impurities in typical copper production and are separated in electrolytic copper refineries, where impure copper anodes are dissolved electrolytically and redeposited as high purity copper cathodes. The impurities, which include Tellurium and Sélénium, either dissolve in the electrolyte, or settle as slimes to the bottom of the electrolytic cells. They are subsequently recovered through various extraction technologies, and further refined into commercial product forms and compounds.