Tellurium (Te)
Tellurium (Te) is a chemical element with the atomic number 52, found in small amounts in the Earth's crust, primarily in the form of various compounds. It resembles selenium and is typically encountered in ores associated with copper, lead, and gold. Discovered in 1782, tellurium was not isolated until 1798 and has since become valuable in multiple industrial applications. It is primarily utilized as an additive to improve the properties of metals, such as enhancing the machinability of steel and copper alloys. Tellurium compounds are also essential in the production of thermoelectric devices, which convert temperature differences into electrical energy, and are increasingly important in solar cell manufacturing. While tellurium is toxic, significant poisonings are rare, with symptoms often characterized by a distinctive garlic breath odor. Its recovery from ore is an ongoing area of research, reflecting its nonrenewable nature and rising demand in various technological applications.
Tellurium (Te)
Where Found
Tellurium is uncommon but widely distributed in the Earth’s crust. It has been found in small amounts as an uncombined element but is most often found in various compounds. These compounds occur in sulfide deposits or in ores of gold, copper, and lead.
Primary Uses
Tellurium is used in small amounts to improve the properties of other metals. Tellurium compounds are used to manufacture thermoelectric devices.
Technical Definition
Tellurium (abbreviated Te), atomic number 52, belongs to Group VIA of the periodic table of the elements and resembles selenium in its chemical and physical properties. It has eight stable isotopes and an average atomic weight of 127.6. Pure tellurium exists as brittle, silver-white crystals or as a dark gray or brown powder. Its density is 6.24 grams per cubic centimeter; it has a melting point of 449.8° Celsius and a boiling point of 989.9° Celsius.
Description, Distribution, and Forms
Tellurium is a widely distributed element resembling selenium. It usually occurs in compounds with copper, lead, silver, gold, iron, or bismuth. The most important sources of tellurium are ores mined for copper, lead, and gold. The most important producers of tellurium are Canada, the western United States, and Peru. Tellurium is nonrenewable, and investigations into the recovery of tellurium from gold and lead-zinc ores is ongoing.
History
Tellurium was discovered in 1782 by the Austrian mining inspector Franz Joseph Müller von Reichenstein. It was not isolated as a free element until 1798 and not used for practical purposes until the middle of the twentieth century.
Obtaining Tellurium
Tellurium is usually obtained as a by-product of copper production. After copper is removed from processed ore by electrolysis, the remaining material contains tellurium as well as silver, gold, and selenium. The tellurium is separated out by treating the material with a base, then neutralizing it. This produces impure tellurium dioxide. This compound can be purified by repeatedly dissolving it and recrystallizing it. Free tellurium metal may be obtained by electrolysis.
Uses of Tellurium
Tellurium is added to steel to improve its machinability and added to copper to create an alloy with good machinability and high electrical and thermal conductivity. It also increases the ductility of aluminum alloys, the hardness and strength of tin alloys, and the resistance to corrosion of lead alloys. Rubber may be treated with tellurium to improve its aging and mechanical properties. Tellurium has also been used alone or with platinum as a catalyst for chemical reactions.
Tellurium compounds are used in thermoelectric devices. Lead telluride is used to make devices that produce electricity when heated. Bismuth telluride is used to manufacture devices that transfer heat when electricity passes through them.
Tellurium is most important as a steel additive and secondarily as an alloy in copper (to improve its machinability while maintaining conductivity), lead (to dampen vibration and lessen metal fatigue), and cast iron (to reduce depth of chill). It is also used in photoreceptors, in blasting caps, in thermal cooling devices, and as a catalyst in the production of synthetic fibers. Tellurium has been added to glass and ceramics to alter the pigments of these products. An increasingly important application is in the manufacture of solar cells, accounting for an increased demand for high-grade tellurium.
Although tellurium is a toxic substance, serious poisonings are rare. Symptoms caused by tellurium include nausea, headache, sleepiness, and dry mouth. The most distinctive feature of tellurium ingestion is a strong garlic breath odor, which may persist for several days. Tellurium toxicity rarely requires treatment. Vitamin C has been used to treat the breath odor.
Bibliography
Natural Resources Canada.
U.S. Geological Survey.