|
Zinc is a
lustrous bluish-white metal. It is found in group IIb of the
periodic table. It is brittle and crystalline at ordinary
temperatures, but it becomes ductile and malleable when heated between 110°C and 150°C. It is a fairly
reactive metal that will combine with
Oxygen and other non-metals, and will react with dilute acids to
release
Hydrogen.
Applications
It is used
principally for galvanizing Iron, more than 50% of metallic Zinc goes
into galvanizing steel, but is also important in the preparation of
certain alloys. It is used for the negative plates in some electric batteries
and for roofing and gutters in building construction.
Zinc is the primary metal used in making American pennies, is used in
die casting in the automobile industry. Zinc oxide is used as a white
pigment in watercolours or paints, and as an activator in the rubber
industry. As a pigment Zinc is used in plastics, cosmetics, photocopier
paper, wallpaper, printing inks etc, while in rubber production its role
is to act as a catalyst during manufacture and as a heat disperser in
the final product. Zinc metal is included in most single tablet, it is
believed to possess anti-oxidant properties, which protect against
premature aging of the skin and muscles of the body.
Zinc in
the environment
Zinc is a very common substance that occurs
naturally. Many foodstuffs contain certain concentrations of Zinc.
Drinking water also contains certain amounts of Zinc, which may be
higher when it is stored in metal tanks. Industrial sources or
toxic waste sites may cause the Zinc amounts in drinking waterto reach levels that can cause health problems.
Zinc occurs naturally in air, water
and soil, but Zinc concentrations are rising unnaturally, due to
addition of Zinc through human activities. Most Zinc is added
during industrial activities, such as mining, coal and waste
combustion and steel processing. Some soils are heavily
contaminated with Zinc, and these are to be found in areas where Zinc
has to be mined or refined, or were sewage sludge from industrial areas
has been used as fertilizer.
Zinc is
the 23rd most abundant element in the Earth's crust. The dominant ore is
Zinc blende, also known as sphalerite. Other important Zinc ores are
wurzite, smithsonite and hemimorphite. The main Zinc mining areas are
Canada, Russia, Australia, USA and Peru'. World production exceeds 7
million tonnes a year and commercially exploitable reserves exceed 100
million tonnes. More than 30% of the world's need for Zinc is met by
recycling.
Zinc is a trace element that is essential for human health. When
people absorb too little Zinc they can experience a loss of
appetite, decreased sense of taste and smell, slow wound healing
and skin sores. Zinc-shortages can even cause birth defects.
Although humans can handle proportionally large concentrations of
Zinc, too much Zinc can still cause eminent health problems, such
as stomach cramps, skin irritations, vomiting, nausea and anaemia.
Very high levels of Zinc can damage the pancreas and disturb the
protein metabolism, and cause arteriosclerosis. Extensive exposure
to Zinc Chloride can cause respiratory
disorders.
In the work place envIronment Zinc contagion can lead to a
flu-like condition known as metal fever. This condition will pass
after two days and is caused by over sensitivity.
Zinc can be a danger to unborn and newborn children. When their
mothers have absorbed large concentrations of Zinc the children
may be exposed to it through blood or milk of their mothers.
The world's Zinc production is still rising. This basically means
that more and more Zinc ends up in the environment.
Water is polluted with Zinc, due to the presence of large
quantities of Zinc in the wastewater of industrial plants. This
wastewater is not purified satisfactory. One of the consequences
is that rivers are depositing Zinc-polluted sludge on their banks.
Zinc may also increase the acidity of waters.
Some fish can accumulate Zinc in their bodies, when they live in
Zinc-contaminated waterways. When Zinc enters the bodies of these
fish it is able to bio magnify up the food chain.
Large quantities of Zinc can be found in soils. When the soils of
farmland are polluted with Zinc, animals will absorb
concentrations that are damaging to their health. Water-soluble
Zinc that is located in soils can contaminate groundwater.
Zinc cannot only be a threat to cattle, but also to plant
species. Plants often have a Zinc uptake that their systems cannot
handle, due to the accumulation of Zinc in soils.
On Zinc-rich soils only a limited number of plants has a chance of
survival. That is why there is not much plant diversity near
Zinc-disposing factories. Due to the effects upon plants Zinc is a
serious threat to the productions of farmlands. Despite of this
Zinc-containing manures are still applied.
Finally, Zinc can interrupt the activity in soils, as it
negatively influences the activity of microrganisms and
earthworms. The breakdown of organic matter may seriously slow
down because of this.
|
