Cd - Cadmium
|Chemical Element||Cadmium||Melting Point °C||321|
|Chemical Symbol||Cd||Boiling Point °C||756|
|Atomic Number||48||Density g/cm3||8.7|
Cadmium is a very soft, silvery metal whose surface has a bluish tinge. The pure metal is, in fact, soft enough to cut with a knife. It is a member of Group 12 of the Periodic Table and is the 65th most abundant element within the Earth’s crust. Chemically, cadmium resembles zinc in its properties and, like zinc, it tarnishes in air. Cadmium is soluble in acids but not alkalis. The most notable feature of cadmium is its toxicity, which accumulates both in the environment and living organisms.
Cadmium was discovered in 1817 by Freidrich Stromeyer, a Professor at the University of Göttingen, whilst heating samples of cadmia to produce the white compound, zinc oxide. He observed that occasionally the product he obtained had a yellow colour instead of pure white. An impurity in the mineral was discovered to be the source, and Stromeyer deduced that this was a previously unknown element. By separating this new element into its oxide form, he was able to produce a sample of a blue grey metal, which he named cadmium after the mineral in which it was found. This was achieved in the year of 1817. Stromeyer was only just able to claim the discovery, as the following year Karl Meissner and Karl Karsten announced their discoveries of the same element.
The first true cadmium mineral to be discovered came to light when the Bishopton Railway Tunnel was being bored near port Glasgow in Scotland in 1841. This mineral, cadmium sulfide (CdS), was named greenockite after Lord Greenock, who was in charge of the project, although the substance had been used for more than 2,000 years as a yellow pigment, when it had been mined in Greece and Bohemia. Other cadmium ores are known, such as cadmoselite (CdSe) and otavite (CdCO3), but no ore is mined specifically for its cadmium. More than enough is produced as a by-product of the smelting of zinc, in which CdS is a significant impurity, making up as much as 3%. Consequently, the main mining areas are those associated with zinc.
The total world production from the 1990s has remained relatively stable, at 20,000 – 22,000 mts per year. In 2008, China was the biggest producer with 4,300mts produced that year. Due to cadmium’s toxicity, particularly in its oxide form, recycling is a necessity and is included in the above figures. The largest cadmium recycling project is SAFT in France.
The main use of cadmium since the mid 20th Century has been for the production of nickel-cadmium (NiCd) batteries. Nickel-cadmium (NiCd) batteries are rechargeable and are used to power a variety of electrical goods, from toys and electrical appliances to electric vehicles. China and Japan are the biggest consumers of cadmium, mainly due to their prominence in the electrical goods market with companies such as Sony, Panasonic, Samsung and Fujitsu, being large producers. Another large use of cadmium is for the production of pigments. Despite many attempts at substitutes due to issues of toxicity, cadmium oxide is still used for a true cadmium yellow for applications such as yellow car paint. Today the newest application for cadmium is as an alloy with tellurium to produce cadmium-telluride (CdTe) used in thin-film photovoltaic solar technology. There is also increasing demand for cadmium in storage batteries for solar arrays.
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