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Zirconium
is a very strong, malleable, ductile, lustrous silver-gray metal. Its
chemical and physical properties are similar to those of
titanium. Zirconium is extremely resistant to heat and
corrosion. Zirconium is lighter than steel and its hardness is similar
to
copper. When it is finely divided, the metal can spontaneously
ignite in air, especially at high temperatures. Zirconium powder is
black and is regarded as very dangerous fire hazard. Zirconium does not
dissolve in acids and alkalis.
Applications
Zirconium
is used in alloys
such as zircaloy, which is used in nuclear applications since it does
not readily absorb neutrons. Also used in catalytic converters,
percussion caps and furnace bricks. Baddeleyite and impure zirconium
(zirconia) are used in lab
crucibles.
The major end uses of zircon (ZrSiO4) are refractories,
ceramic opacification and foundry sands.
Zircon is also marketed as a natural gemstone used in jewelry. The metal
also has many other uses, among them in photographic flashbulbs and
surgical instruments, to make the glass for television, in the removal
of residual gases from electronic vacuum tubes, and as a hardening agent
in alloys, especially steel. The paper and packaging industries are
finding that zirconium compounds make good surface coatings because they
have excellent water resistance and strength.
Zirconium in the environment
Zirconium is not a particularly rare element but because its most common
mineral, zircon, is highly resistant to weatering it is only slightly
mobile in the environment. Zirconium is more than twice as abundant as
copper and zinc and more than 10 times more abundant than lead.
The chief ores are zircon (ZrSiO4), which is mined in Australia, USA and
Sri Lanka, and baddeleyite (Zirconium oxide ZrO2) which is mined in
Brasil. World production is in excess of 900.000 tonnes per year of
zircon, and 7000 tonnes of the metal are produced. The estimated
reserves exceed a billion tonnes. Australia, South Africa, India, Sri
Lanka and the USA have vast deposits of zircon and zirconia sands.
Health
effects of zirconium
Zirconium
and its salts generally have low systemic toxicity.
The estimated dietary intake is about 50 microg. Most passes through the
gut without being adsorbed, and that which is adsorbed tends to
accumulate slightly more in the skeleton than in tissue.
Zirconium 95 is one of the
radionuclides involved in atmospheric testing of nuclear weapons. It is
among the long-lived radionuclides that have produced and will continue
to produce increased cancers risk for decades and centuries to come.
Zirconium is unlikely to present a
hazard to the environment.
While aquatic plants have a rapid uptake of soluble
zirconium, land plants have little tendency to adsorb it, and indeed 70%
of plants that have been tested showed no zirconium to be present at
all.
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periodic elements.
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