Cadmium Cd

Discovery

In 1817 Friedrich Stromeyer, a professor at Göttingen who also inspected pharmacies, noticed something odd. Zinc carbonate should turn into white zinc oxide when heated, yet some samples turned yellow even though they contained no iron.

Tracing the cause of the colour, he isolated a new metal. Other German chemists found the same element in zinc compounds at about the same time, but Stromeyer is generally credited with the discovery.

Cadmium use expanded greatly in the twentieth century for electroplating, pigments and nickel–cadmium batteries. From the 1960s onward, as its health effects became clear, many countries began to restrict it.

Origin of the name

The name comes from the Latin cadmia, a term for the zinc ore calamine, from the Greek kadmeia. The word is often linked to Cadmus, the legendary founder of Thebes. The symbol is Cd.

Main uses

• Batteries: nickel–cadmium rechargeable cells were once standard in cordless tools and appliances, but nickel–metal hydride and lithium-ion batteries have largely replaced them.
• Pigments: cadmium sulfide and selenide give vivid, lightfast yellows, oranges and reds that are still used in artists' paints.
• Solar power: cadmium telluride thin-film panels are deployed in large solar farms.
• Reactor control: cadmium absorbs thermal neutrons very strongly and is used in control rods and shielding.
• Plating: it protects certain steel parts, for example in aerospace, against corrosion.

Isotopes

Natural cadmium has eight isotopes, cadmium-106, -108, -110, -111, -112, -113, -114 and -116, with cadmium-114 the most abundant. Cadmium-113 and cadmium-116 are radioactive but have half-lives of quadrillions of years or more, so they are effectively stable. Cadmium-113 has an enormous appetite for thermal neutrons, which is why cadmium works as a neutron absorber. Cadmium-109, with a half-life of about 1.3 years, is a source in handheld X-ray fluorescence analysers.

In everyday life

Once absorbed, cadmium accumulates mainly in the kidneys and stays in the body for decades. Long-term exposure can impair kidney function and weaken bones.

From the 1910s, cadmium from an upstream mine contaminated rice paddies along the Jinzū River in Toyama Prefecture, Japan. Residents suffered brittle bones and severe pain, and the condition, called itai-itai ("it hurts, it hurts") disease, was officially recognised as a pollution disease by the Japanese government in 1968.

Today tobacco smoke is a major source of cadmium exposure for smokers. Regulations such as the EU's RoHS directive restrict cadmium in electronics, and spent nickel–cadmium batteries should always be recycled separately.