Glossary

Cadmium (chemical symbol Cd) is a soft, bluish-white metallic element with the atomic number 48 and an atomic mass of 112.41. It is located in Group 12 of the periodic table, directly below zinc and above mercury, sharing several chemical similarities with those elements. Cadmium is relatively ductile and malleable, meaning it can be easily shaped, and it has a low melting point of 321°C (610°F) and a boiling point of 767°C (1413°F).

Cadmium is most commonly found in nature associated with zinc ores, particularly sphalerite (zinc sulfide, ZnS). It is produced mainly as a byproduct of zinc refining. Because it rarely occurs in concentrated deposits, cadmium’s availability depends largely on zinc production levels.

Chemically, cadmium is quite reactive. It slowly oxidizes in moist air, forming cadmium oxide (CdO), a compound that can release toxic fumes when heated. It also forms various salts, including cadmium chloride (CdCl₂) and cadmium sulfate (CdSO₄), which are highly soluble and toxic. Cadmium is divalent in nearly all its compounds, meaning it typically exhibits a +2 oxidation state (Cd²⁺).

Historically, cadmium has been valued for several key industrial uses. It was widely used in nickel-cadmium (NiCd) rechargeable batteries, electroplating, pigments, and stabilizers for plastics. Its corrosion resistance made cadmium plating particularly useful for protecting steel fasteners and aerospace components in marine or harsh environments. Cadmium pigments, producing bright yellows, oranges, and reds, were prized for their stability and brilliance in paints, plastics, and ceramics.

However, cadmium and its compounds are now recognized as highly toxic to humans and the environment. Prolonged exposure can cause kidney damage, bone demineralization, and respiratory illness, and cadmium is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). Because of these dangers, cadmium use has been heavily restricted or banned in most consumer applications. NiCd batteries, once common, are being replaced by safer lithium-ion and nickel-metal hydride alternatives, and cadmium pigments have been largely phased out.

In modern applications, cadmium still finds limited, specialized use in aerospace, nuclear, and electronics industries—for instance, in control rods of nuclear reactors due to its strong neutron-absorbing properties, and in infrared detectors and semiconductors.