Selenium and Tellurium
Statistics and Information
Commercial quantities of selenium are recovered as a byproduct of the electrolytic refining of copper where it accumulates in anode residues. Growth in consumption was driven by the development of new uses, including applications in rubber compounding, steel alloying, and selenium rectifiers. By 1970, selenium in rectifiers had largely been replaced by silicon, but its use as a photoconductor in plain paper copiers had become its leading application. During the 1980's, the photoconductor application declined (although it was still a large end-use) as more and more copiers using organic photoconductors were produced. In 1996, continuing research showed a positive correlation between selenium supplementation and cancer prevention in humans, but widespread direct application of this important finding would not add significantly to demand owing to the small doses required. In the late 1990's, the use of selenium (usually with bismuth) as an additive to plumbing brasses to meet no-lead environmental standards became important. The average price for selenium in 2000 was $3.82 per pound.
Tellurium is a relatively rare element, in the same chemical family as oxygen, sulfur, selenium, and polonium: oxygen and sulfur are nonmetals, polonium is a metal, and selenium and tellurium are semiconductors (i.e., their electrical properties are between those of a metal and an insulator). Nevertheless, tellurium, as well as selenium, is often referred to as a metal when in elemental form. Tellurium production is mainly a byproduct of copper processing. The 1960's brought growth in thermoelectric applications for tellurium, as well as its use in free-machining steel, which became the dominant use. The use of high-purity tellurium in cadmium telluride solar cells is very promising. Some of the highest efficiencies for electric power generation have been obtained by using this material, but this application has not yet caused demand to increase significantly. Commercial-grade tellurium, which is not toxic, is usually marketed as minus 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The yearend price for tellurium in 2000 was $14 per pound.