Periodic Table -> Cadmium
Cadmium DetailsCadmium Symbol:
CdCadmium Atomic Number:
48Cadmium Atomic Weight:
112.41What is Cadmium?
Cadmium (atomic number 48, symbol Cd)
is a chemical element similar to mercury and zinc, which are stable metals. It is a blue-white, soft metal similar to mercury in that it has a lower melting point than the group of transition metals. Being a soft metal, cadmium can be cut with a knife, and is soluble in acids. However, it is not soluble in alkalis and tarnishes in air. Because cadmium does not have partly filled f or d electron shells in common oxidation or elemental states, it is not considered a transition metal in every case. In the Earth’s crust, cadmium is found in concentrations of 0.1 – 0.5 ppm.
Cadmium is a byproduct of zinc extraction, occurring as a component of many zinc ores. It is a rare element compared to zinc and also occurs as a byproduct of copper and lead extraction. After application, it is present in the environment because cadmium is found in pesticides and manures. A large amount of cadmium is released every year or some 25,000 tons. Half of it is released through weathering rocks into the rivers and some through volcanoes and forest fires into the air. Cadmium is also released through manufacturing and other human activities. Because sufficient quantities of cadmium are produced as a byproduct, cadmium ores are not explored. The mining sites are those where zinc is extracted, and the smelting of this metallic element from sphelerite, which is its ore, produces cadmium as a byproduct. The main producers of cadmium are Canada, the United States, Japan, Mexico, Australia, and Peru.
Cadmium can enter the body through food, which is rich in cadmium and increases its concentration in the body. Foods that are rich in it are mussels, shellfish, cocoa powder, mushrooms, liver, and dried seaweed. People who smoke are exposed to higher levels of cadmium. The blood stream transports cadmium to other parts of the body, augmenting the effects of cadmium already supplied with cadmium-rich food.
In terms of applications, cadmium is mostly used in the production of Ni-Cd batteries as well as stabilizers for plastics, plating and coatings, and pigments. Another application of the element is in electroplating steel, with cadmium film providing a good protection against the sea. It is also used as a barrier for controlling nuclear fission because of its ability to absorb neutrons.
Cadmium oxide is a compound used in the production of green and blue phosphors for picture tubes in color television and phosphors in black and white television. Cadmium sulfide is another compound used as a photoconductive coating in the production of photocopier drums.
The element forms different salts in paint pigments, including CdS, which is the most common. Cadmium selenide is a pigment known as cadmium red. Cadmium reds, oranges, and yellows are used by painters working with this pigment. The colors are considerably toned down during production before they are blended into acrylics, gouaches, and other pigments and paint formulations.
In higher organisms, the element has no known beneficial role. It has been discovered recently that cadmium plays role in lower life forms. A cadmium-dependent carbonate dehydratases has been observed in marine diatoms, through which a group of enzymes are formed. They act to catalyze the interconversion of water and carbon dioxide to protons and bicarbonate.
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