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Zinc

 

Zinc

Zinc is also one of the elements whose compounds have been known to mankind from time immemorial. Its best known mineral was calamine (zinc carbonate). Upon calcination it yielded zinc oxide, which was widely used, for instance, for treating eye diseases.

Although zinc oxide is comparatively easily reduced to free metal, it was obtained in a metal state much later than copper, iron, tin, and lead. The explanation is that reduction of zinc oxide with coal requires high temperature (about 1100oC). The boiling point of the metal is 906oC; therefore, highly volatile zinc vapour escapes from the reaction zone. Before metallic zinc was isolated, its ores were used for making brass, an alloy of zinc and copper. Brass was known in Greece, Rome, India, and China. It is an established fact that Romans produced brass for the first time during the reign of Augustus (B.C.20-A.D.14). Interestingly, the Roman method of preparing brass was still used up to the 19th century.

It is impossible to establish when metallic zinc was obtained. In ancient Dacian ruins an idol was found containing 27.5 percent of zinc. Zinc was possibly obtained during brass production as a side product.

In the 10-11th centuries the secret of zinc production was lost in Europe and zinc had to be imported from India and China. It is believed that China was the first country to produce zinc on a large scale. The production process was extremely simple. Earthenware filled with calamine were tightly closed and piled into a pyramid. The gaps between the posts were filled with coal and the posts were heated to red heat. After cooling the pots, where zinc vapours condensed, were broken and metal ingots were extracted.

Europeans rediscovered the secret of zinc production in the 16th century when zinc had already been recognized as an independent metal. During the next two centuries many chemists and metallurgists worked on with methods of zinc extraction. A great deal of credit should go to a. Marggraf who published in 17

46 a large treatise, Methods of Extraction of Zinc from Its Native Mineral Calamine. He also found that lead ores from Rammelsberg (Germany) contained zinc and that zinc could be obtained from sphalerite, natural zinc sulphide.

The name “zinc” originates from the Latin word denoting leucoma or white deposit. Some scholars relate “zinc” to the German word zink, which means lead.