Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. It is a soft, silvery-white metal that is found in small amounts in the Earth's crust, usually between 0.1 and 0.5 parts per million. Cadmium was discovered in 1817 by two scientists in Germany, Stromeyer and Hermann, when they found it as an impurity in zinc carbonate.

This metal is often found together with zinc ores and is a byproduct of making zinc. In the past, cadmium was widely used to protect steel from rust and as colorful pigments in paints, glass, and plastics. However, its use has decreased because cadmium is toxic to living things. Today, it is less common, though it still has some important uses, such as in control rods for nuclear reactors and in a type of solar panel called cadmium telluride.

Even though cadmium is harmful to most animals and plants, some tiny ocean organisms called marine diatoms have been found to use it in a special way for a process involving carbon dioxide. This shows that cadmium can play unusual roles in nature, even if it is usually dangerous.

Characteristics

Cadmium is a soft, silvery-white metal that can be bent and stretched easily. It is similar to zinc but can form more complex compounds. Unlike many metals, cadmium does not rust easily and is used to protect other metals from damage. In large pieces, cadmium does not mix with water or catch fire, but when powdered, it can burn and release harmful gases.

Cadmium usually has a chemical state of +2, but it can also exist in the +1 state. It burns in air to make a brown compound, and it mixes with certain acids to form other compounds. Scientists have studied how cadmium connects with important molecules in our bodies.

Naturally occurring cadmium is made of eight different types, called isotopes. Two of these change over very long periods, while three others are expected to change but have not been observed doing so in labs. Three isotopes are stable and do not change. Researchers have also found many other isotopes that do not occur naturally, with most changing very quickly. One special isotope, ¹¹³Cd, can absorb certain types of particles called neutrons very well.

History

Cadmium was discovered in Germany in 1817 by Friedrich Stromeyer. He found it in zinc compounds that were sold in pharmacies. Stromeyer noticed that some zinc samples changed color when heated and worked hard to isolate the new metal. For many years, Germany was the main place where cadmium was produced.

Even though cadmium can be harmful in some forms, it was once used as a medication. Later, cadmium helped scientists measure distances very precisely. In the mid-20th century, cadmium became important for coating metals to protect them from rust and for making bright pigments. Today, cadmium is mostly used in certain types of batteries.

Occurrence

See also: Category:Cadmium minerals

Cadmium is a rare element, making up only about 0.1 parts per million of Earth's crust. It is found mainly alongside zinc, especially in a mineral called greenockite. Because it is so similar to zinc, cadmium is usually obtained when zinc is being mined or processed. Some cadmium also comes from recycling iron and steel.

Small amounts of cadmium can be found in certain rivers, like the Vilyuy River in Siberia. It can also be present in rocks used for phosphate fertilizers and in coal, which leaves cadmium in ash. Crops like rice and chocolate can sometimes contain cadmium, which is why there are limits on how much can be allowed. Some plants, such as willow trees and poplars, can help remove cadmium from soil.

Typical levels of cadmium in the environment are very low, but higher amounts can be hard to remove from water.

Production

Cadmium is often found mixed in zinc ores, so it is usually taken out when making zinc. Some zinc ores can have up to 1.4% cadmium in them. When making zinc from its ores, cadmium can be separated using special heating methods or by mixing it with a liquid and then removing it.

In 2001, China made the most cadmium in the world, followed closely by South Korea and Japan.

Applications

Cadmium is commonly used in electric batteries, coatings, and other special materials.

Batteries

Cadmium is mostly used in rechargeable nickel–cadmium batteries. These batteries have been popular for many years but rules now limit how much cadmium can be used in electronics to keep them safe.

Electroplating

Cadmium is also used to protect steel parts in airplanes from rust. However, this can sometimes make the steel weaker, so special care is needed.

Nuclear technology

In nuclear reactors, cadmium helps control the reaction by absorbing particles that could make the reaction go too fast.

Televisions

Some newer TVs use cadmium in their screens, but efforts are being made to reduce this because of concerns about the material’s impact on the environment.

Anticancer drugs

Scientists have studied cadmium for possible use in treating some diseases, but it can be harmful, so this use is limited.

Compounds

Cadmium is used in old television screens and in paints to make bright yellow, orange, and red colors. Painters often take care to protect their hands when working with these paints.

Semiconductors

Cadmium is part of some materials used in devices that can detect light, like in solar panels and motion sensors.

Laboratory uses

Cadmium is used in special lasers for scientific research and in tools that help scientists study cells and chemicals.

Jewelry

In 2025, tests found that some cheap jewelry sold online contained very high levels of cadmium, which is not safe. This shows that some manufacturers may still be using cadmium in jewelry.

Biological role

Cadmium does not help living things grow and can be harmful. Scientists have found a special kind of tiny water creature called a diatom that can use cadmium when there isn’t enough of another metal called zinc around.

When people are exposed to cadmium, it can stay in their bodies for many years, especially in the kidneys, liver, and bones. Researchers are studying how cadmium might increase the chances of certain health problems later in life.

Safety

Cadmium is a metal that can be harmful to people and the environment. Breathing in cadmium dust or fumes can make people very sick. It can cause problems with the lungs and other parts of the body.

People can come into contact with cadmium from many places, like burning fuels, making steel, and even eating certain foods. In the past, cadmium polluted a river in Japan, making the rice grown there unsafe to eat. This caused health problems for many people who ate the rice.

Cadmium is also found in cigarette smoke. Smoking can bring cadmium into the body more easily than eating it. Foods like some seafood, chocolate, and mushrooms can also contain cadmium, but most people get small amounts from their regular diet.

Because cadmium can be dangerous, there are rules to limit how much of it people can be exposed to. Different countries have set limits on how much cadmium can be in food, water, and products like batteries. These rules help protect people from getting too much cadmium.