atomic weight 238.03 amu (the
heaviest natural element)
melting point 1132º
boiling point 3818º C.
Uranium is highly reactive, and
it combines with most other elements to form
chemical compounds. These compounds are always
All isotopes of
uranium are radioactive.
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
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 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 ore is taken from the mine to a uranium-concentrating
plant, where sulfuric acid is used to
extract an oxide of uranium called yellowcake.
The yellowcake is then combined with fluorine to
produce uranium hexafluoride, which is
subsequently refined into pure 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
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