Cadmium (Cd) — properties, uses, and environmental impact

Properties and chemical behavior

Cadmium is typically a bluish-white metal that is relatively soft and has a low melting point compared with many transition metals. In compounds it most often appears in the +2 oxidation state. Its chemistry includes stable oxides, sulfides and various coordination compounds; some cadmium compounds display vivid colors and semiconductor behavior.

Occurrence and production

Cadmium is not usually mined directly. It occurs as a minor component of zinc, lead and copper ores and is recovered mainly as a byproduct of zinc refining. Small quantities are reclaimed from recycled materials and industrial wastes. Because it is dispersed in ores, cadmium production is linked to broader base-metal mining and refining industries.

Uses and applications

• Rechargeable nickel–cadmium batteries (now partly supplanted by other chemistries).
• Pigments and coatings—some cadmium compounds give bright yellow, orange or red colors.
• Cadmium telluride (CdTe) and related materials used in thin-film photovoltaics and electronic components.
• Electroplating and corrosion-resistant coatings in specialized applications.

Health, safety and environmental concerns

Cadmium and many of its compounds are toxic to humans and wildlife. Chronic exposure can damage kidneys and bones and is associated with increased cancer risk; airborne or soluble forms are particularly hazardous. For these reasons many uses have been reduced or replaced, and strict occupational and environmental regulations control emissions, disposal and product contents.

History and notable facts

Cadmium was first isolated in the early 19th century and its name comes from historical terms for zinc ores. Historically valued for its pigments and electrochemical properties, its industrial role has shifted as awareness of its toxicity grew. Today cadmium remains important in niche technologies and in some photovoltaic and electronic applications; ongoing recycling and regulatory efforts aim to limit environmental release.