Tellurium is very rare in the crust of the Earth. Although it occurs in minute quantities in soil, most of its ore is obtained as an anode derivative during the oxygen refining of copper and other sulfide ores. It is estimated that the average content of tellurium in the earth’s crust is 0.001 ppm or less. In a sulfide ore such as pyrite, the content of tellurium would be about 0.02-0.03 ppm.
Tellurium also occurs as a natural compound. One such telluride mineral is meneghinite (Au, Cu, Ag Te), which has been found in several places in the world. It was first discovered in 1827 in Meneghino near Ferrara, Italy. Other telluride minerals include calaverite (Au, Ag Te2), sylvanite (Au, Ag Te4) and krennerite (Au, Ag Te4).
Tellurium is mined as either a primary mineral or as a by-product from other ores such as copper, lead, silver and zinc. The primary ore of tellurium is calaverite (Au, Ag Te2), which is found in hydrothermal deposits. Other tellurium-bearing ore deposits include fault fissures and quartz veins.
Tellurium is also recovered from roasting sulfide ores. During this process, oxides of tellurium and other metals are formed along with the tellurium dioxide (TeO2). The oxides and ores are heated to temperatures of 932-1022°F (500-550°C) in an oxidizing atmosphere. This results in the formation of metallic tellurium, which is then purified and filtered.
Tellurium is used in many industries, including electronics, automotive and aerospace. It is also used to produce optical glass, ceramics, polymers and semiconductor material.
In electronics, it is used to produce transistors, integrated circuits, logic chips and memory chips. These are essential for modern electronic devices. Tellurium is also used as an alloying agent in producing automobile parts such as engine bearings, spark plug electrodes and clutch plates. In aerospace, it is employed in the manufacture of turbine blades, rocket nozzles and pressure vessels.
In addition, tellurium is used as a catalyst in the production of synthetic rubber and plastic, and as an oxidizing agent in medicine and chemistry.
The production of tellurium is estimated to be about 3,000 metric tonnes per year, with about two-thirds of the production coming from processing ores and the remaining one-third coming from the recycling of waste products.
There are few known health risks associated with tellurium, but studies have found that it is toxic when inhaled or ingested. It is also a powerful oxidant which can have harmful effects on the environment.
The main producers of tellurium are Canada, US, Mexico and Sweden. The largest deposits of tellurium are located in Canada and the US.
Tellurium is an important, but often overlooked, raw material and is an integral part of modern society. Its applications in electronics, automotive and aerospace industries, as well as in medicine and chemistry, make it a crucial asset for mankind.
