Where Is Cobalt Used?
Can you think of any connection between a delicate Ming vase and a nuclear explosion? Difficult, isn’t it? And yet there is a connection in the sense that different types of one particular substance – cobalt have been used in the production of both.
In ancient China the beautiful blues used in the finest porcelains came from a cobalt ore dating from the Tang dynasty (618–907 AD) and the Ming dynasty (1368–1644 AD). Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed in 79 AD).
Until the early years of this century most of the world’s production of cobalt went to provide color for the porcelain and glass industries. Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes, and ceramics since the Bronze Age.
Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth’s crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
Today, some cobalt is produced specifically from various metallic-lustered ores, for example cobaltite (CoAsS), but the main source of the element is as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo, Central African Republic and Zambia yields most of the cobalt mined worldwide.
Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were so named because they were poor in known metals, and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.
Today, cobalt, which in its natural state is a hard silvery-white metallic substance, serves many purposes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high energy gamma rays. A “cobalt bomb” can be a terrible weapon capable of distributing lethal radioactive cobalt-60 through a nuclear explosion. It can also be the means of treating certain illnesses by deep X-rays.
Cobalt is primarily used in the preparation of magnetic, wear-resistant and high-strength alloys. The compounds, cobalt silicate and cobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. About a quarter of the output of cobalt goes into the making of magnets, since the metal has a high magnetic quality. It has many engineering uses. It can be employed to take away the slightly yellow tint of the iron in plate-glass windows. There is a call for it in dentistry and bone surgery.
Cobalt is the active center of coenzymes called cobalamins, the most common example of which is vitamin B12. As such, it is an essential trace dietary mineral for all animals. Cobalt in inorganic form is also a micronutrient for bacteria, algae and fungi.
In Australia and New Zealand ranchers were puzzled by the poor condition of sheep and cattle grazing on apparently good pasture land. Eventually it was discovered that the land did not have enough cobalt. Today small quantities of a cobalt-based compound are added either to the water supplies serving the cattle or to the land itself in the form of fertilizers.
Cobalt is also an essential food ingredient for human beings. Liver, cabbage, spinach, lettuce and watercress all contain comparatively high levels of it. About 20,000 tons of cobalt is produced every year.