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Uranium (U)

a silvery-white, radioactive metal

pure uranium
pure uranium


atomic number 92
atomic weight 238.03 amu (the heaviest natural element)

melting point 1132º C
boiling point 3818º C.

Uranium is highly reactive, and it combines with most other elements to form chemical compounds. These compounds are always extremely poisonous.

All isotopes of uranium are radioactive.

Occurence and Sources

Uranium is more plentiful than such "common" elements as iodine, mercury, and silver, but only tiny amounts of uranium are present in most of the rocks in which it is found.

Many rocks contain bits of uranium, but large amounts occur only in such minerals as pitchblende and carnotite. Pitchblende, which contains various uranium oxides, is the richest uranium ore. Carnotite is the most important uranium ore mined in the United States. It consists of uranium, oxygen, potassium, and vanadium. Uranium also occurs in seawater, and could be recovered from the oceans if prices rose significantly.

The United States produces more uranium oxide than any other country, followed by Canada and South Africa. The chief deposits of uranium ore in the United States are in Wyoming, New Mexico, Texas, Colorado, and Utah, in that order. About 85 per cent of Canada's uranium comes from the province of Ontario. Much of South Africa's uranium is a by-product of gold mining. The gold mines in the Witwatersrand area, near Johannesburg, provide large amounts of uranium.

uranium-producing areas of the world
world map showing major uranium deposits

Uranium near the earth's surface is mined by a process called strip mining. Huge power shovels remove the rocks and soil that cover the deposits, and smaller shovels then dig out the uranium ore. Miners use explosives and drills to excavate uranium ore that lies deep below the ground.

uranium mine in Australia
a uranium mine

The uranium ore is taken from the mine to a uranium-concentrating plant, where sulfuric acid is used to extract an oxide of uranium called yellow cake. The yellow cake is then combined with fluorine to produce uranium hexafluoride, which is subsequently refined into pure uranium.

yellow cake
yellowcake, a form of processed uranium


Uranium and its compounds have been used for various purposes for more than 2,000 years. Colored glass produced about A.D. 79 contains uranium oxide, and this substance has continued to be used through the centuries to color glass. For nearly 100 years after the discovery of uranium it continued to be used chiefly as a pigment in glass manufacturing, as well as a pigment in painting china and as a chemical for processing photographs.

In 1896, the French physicist Antoine Henri Becquerel discovered that uranium is radioactive. In 1938, the German chemists Otto Hahn and Fritz Strassman used uranium to produce the first artificial nuclear fission. In 1942, the Italian-born physicist Enrico Fermi and his co-workers at the University of Chicago produced the first artificial nuclear chain reaction, using uranium as the fissionable material.

Today, uranium is used primarily as a fuel for nuclear reactors, which in turn produce electricity. About 1 pound of uranium produces as much energy as 3 million pounds of coal. Uranium is also used in making atomic bombs and some other nuclear weapons. Medical researchers use uranium to produce radiation for certain experiments. In addition, uranium is used in scientific research to produce various radioactive isotopes and such artificial elements as neptunium and plutonium.

The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding.


Uranium was discovered in 1789 by the German chemist Martin H. Klaproth, who found it in pitchblende, a dark bluish-black mineral. Klaproth named the element in honor of the planet Uranus, which had been discovered eight years earlier. In 1841, pure uranium was isolated from the other elements in pitchblende by the French chemist Eugène Péligot.

See Also

Antoine Henri Becquerel

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The Robinson Library >> Chemical Elements

This page was last updated on 10/15/2018.