cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. It is a soft, bluish-white metal in the periodic table's group 12, closely related to zinc and mercury. Cadmium has a melting point of 321.9°C and a boiling point of 767°C, and a density of 8.65 g/cm3. It occurs mainly as a byproduct of zinc refining and is chiefly extracted from zinc sulfide ores such as sphalerite.

Most cadmium production arises during zinc processing, and the refined metal is used as a material or as a source for compounds. The element typically exhibits the +2 oxidation state and forms compounds such as cadmium oxide (CdO) and cadmium chloride (CdCl2); cadmium sulfide (CdS) is a well-known pigment and has applications in electronics and solar cells.

Discovered in 1817 by Friedrich Stromeyer, cadmium has found uses in nickel-cadmium batteries, electroplating, pigments, stabilizers for plastics, and as a semiconductor in CdTe and CdS-based devices.

Cadmium and many of its compounds are highly toxic. Chronic exposure can damage the kidneys and bones, and cadmium is classified as a human carcinogen by international agencies. Itai-itai disease in the mid-20th century highlighted its hazards. Environmental concerns include persistence and bioaccumulation; cadmium is restricted in many products and is subject to recycling and safe handling regulations.