ZINC

Zinc:    

Brass, which is an alloy of copper and zinc, has been used since at least the 10th century BC. Impure zinc metal was not produced in large scale until the 13th century in India, while the metal was unknown to Europe until the end of the 16th century. Alchemists burned zinc in air to form what they called "philosopher's wool" or "white snow.  A variety of zinc compounds are commonly used, such as zinc carbonate and zinc (as dietary supplements), zinc chloride (in deodorants), zinc pyrithione (anti-dandruff shampoos), zinc sulphide (in luminescent paints), and zinc methyl or zinc diethyl in the organic laboratory. Zinc, in commerce also spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element of group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2.

Zinc is the 24th most abundant element in the Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blend), a zinc sulphide mineral. The largest mineable amounts are found in Australia, Asia, and the United States. Zinc production includes froth flotation of the ore, roasting, and final extraction using electricity (electro winning)

The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has relatively low melting (419.5 °C, 787.1 F) and boiling points (907 °C). Its melting point is the lowest of all the transition metals aside from mercury and cadmium.

The element is normally found in association with other base metals such as copper and lead in ores. Zinc is achalcophile, meaning the element has a low affinity for oxides and prefers to bond with sulphides. Chalcophiles formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, which is a form of zinc sulphide, is the most heavily mined zinc-containing ore. Other minerals from which zinc is extracted include smithsonite (zinc carbonate), hemimorphite (zinc silicate),wurtzite (anotherzinc sulphide), and sometimes hydro incite (basic zinc carbonate). With the exception of wurtzite, all these other minerals were formed as a result of weathering processes on the primordial zinc sulphides.

Availability:

  Identified world zinc resources total about 1.9 billion tonnes. Large deposits are in Australia, Canada and the United States with the largest reserves in Iran. At the current rate of consumption, these reserves are estimated to be depleted sometime between 2027 and 2055. About 346 million tonnes have been extracted throughout history to 2002, and one estimate found that about 109 million tonnes of that remains in use.

Many alloys contain zinc, including brass, an alloy of copper and zinc. Other metals long known to form binary alloys with zinc are aluminium, antimony, bismuth, gold, iron, lead, mercury, silver, tin, magnesium, cobalt, nickel, tellurium and sodium.While neither zinc nor zirconium are ferromagnetic, their alloy ZrZn₂ exhibits ferromagnetism below 35 K.

Environmental impacts:

Zinc is an essential mineral of "exceptional biologic and public health importance". Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children it causes growth retardation, delayed sexual maturation, infection susceptibility, and diarrheal, contributing to the death of about 800,000 children worldwide per year. Enzymes with a zinc atom in the reactive centre are widespread in biochemistry, such as alcohol dehydrogenise in humans.                                          

 The production for sulphuric zinc ores produces large amounts of sulphur dioxide and cadmium vapour. Smelter slag and other residues of process also contain significant amounts of heavy metals. About 1.1 million tonnes of metallic zinc and 130 thousand tonnes of lead were mined and smelted in the Belgian towns of La Calamine and plombiã¨res between 1806 and 1882. The dumps of the past mining operations leach significant amounts of zinc and cadmium, and, as a result, the sediments of the Geul River contain significant amounts of heavy metals. About two thousand years ago emissions of zinc from mining and smelting totalled 10 thousand tonnes a year. After increasing 10-fold from 1850, zinc emissions peaked at 3.4 million tonnes per year in the 1980s and declined to 2.7 million tonnes in the 1990s, although a 2005 study of the Arctic troposphere found that the concentrations there did not reflect the decline. Anthropogenic and natural emissions occur at a ratio of 20 to 1.

Advantages:

·         Light in weight and Good in strength.

·         Induces hardness used in casting.

·         Hard and brittle.

·          Good wear and corrosion resistance

Disadvantages:         

Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption. Consumption of excess zinc can cause ataxia, lethargy and deficiency. It’s toxic. Effective sewage treatment greatly reduces this; treatment along the Rhine, for example, has decreased zinc levels to 50 ppb. Concentrations of zinc as low as 2 ppm adversely affects the amount of oxygen that fish can carry in their blood.