Cadmium

Cadmium (chemical symbol Cd) is a soft metal with atomic number 48. It is ductile, pale white in colour, and readily malleable. It has a lower melting point than most other metals, which makes it useful for alloys and platings.

Cadmium is obtained chiefly as a byproduct during zinc refining, since cadmium occurs alongside zinc ore. For this reason, cadmium production is tied to zinc smelting activity. It is important to note that cadmium is toxic to humans, leading many countries to regulate its use.

Chemical and physical properties

Cadmium belongs to group 12 of the periodic table, alongside zinc and mercury. Its common oxidation state is +2. It forms compounds such as cadmium sulfide (a yellow pigment formerly used in paint) and cadmium oxide. When burned, cadmium releases toxic fumes.

Uses

The largest use of cadmium was in rechargeable nickel-cadmium batteries (NiCd), which have largely been replaced by nickel-metal-hydride and lithium-ion batteries. It is also used in metal plating to prevent corrosion, in yellow and red pigments and plastics, and in some semiconductor devices and solar cells (CdTe).

Health and environment

Cadmium accumulates progressively in the body, particularly in the kidneys, and is associated with kidney and bone damage. It is classified as a carcinogenic substance. People not occupationally exposed typically acquire cadmium through contaminated food and tobacco smoking, as tobacco plants absorb cadmium from soil. Industrial exposure occurs in zinc mining, certain agricultural practices, and battery recycling.