Cadmium is a metallic element that is distributed across the world but only in small deposits. It is considered to be rare, which makes it relatively expensive. It has a number of uses, especially in the composition of paints since it is a natural pigment. Cadmium is a toxic metal that accumulates inside the body in time and can’t be eliminated. As a result, it must be handled carefully and people who are exposed to this metal as part of their daily job have to take special protection measures.
In pure metallic form, cadmium has a silvery-white color and a soft texture. It is rarely find in elemental form in nature. The most common sources of cadmium are lead, copper and especially zinc ores, where it is found as oxides, carbonates or sulphides.
This metal is toxic and plays no role inside the human body, unlike other elements. It can cause cancer when inhaled and builds up in the kidneys, bones and liver. The metal continues to have negative effects after it accumulates in these specific parts of the body.
Cadmium is also toxic to most living organisms, from microscopic ones to plants and animals. It is especially dangerous because it doesn’t decay in time, regardless of the environment. This is due to its very simple chemical structure.
Elemental cadmium is very rarely found naturally. It occurs in the ores of other metallic elements (as mentioned earlier), in particular zinc, lead or copper. As a result, cadmium can be extracted as part of the smelting process for these ores, or after reacting with sulfuric acid. The pure form of cadmium is very ductile and has a silver or blue metallic aspect. It is very useful for alloys, improving the characteristics of other metals. In the periodic chemical metal, cadmium is included in the group of transition metals, with the Cd symbol and an atomic number of 48.
Cadmium was discovered in 1817 by German chemist Fredrich Stromeyer, who was researching zinc and the trace metals associated with it. He named it after the ancient god Cadmus, who is colourful figure of Greek mythology. People were not initially aware of the toxicity of cadmium and it was even used as a treatment until its harmful effects were acknowledged. This also happened with other very dangerous chemicals, for example arsenic or lead. They were included in make-ups and other cosmetics, which were extremely toxic.
This metal is part of the very common rechargeable batteries based on nickel-cadmium, and most of the world’s production is used for this purpose. It also continues to be part of some red, orange and yellow pigments, as well as a stabilizing agent in plastics. The element and its compounds have many other uses, as part of alloys and solders, as well as in the production of some types of semiconductors.
Most scientists agree that both cadmium and its compounds are dangerous and cause cancer. When cadmium enters the body through ingestion or inhalation, it builds up in internal organs. It immediately causes irritation in the intestines and lungs; exposure to it can be fatal on the long term. Most people are exposed to cadmium due to air or water pollution, or as part of their daily job. Cadmium is extremely difficult to remove from polluted areas. This is especially true for locations where the metal is extracted or processed, which have been contaminated severely.
How is cadmium produced and used?
Most of the cadmium produced in the world is a by-product of mining and processing of other metals. The most important of these is zinc but cadmium can also be refined from various lead or copper ores. Dedicated cadmium processing is rare and the metal mainly results from the production of zinc. Between the years 1950 and 1990, the global cadmium output has doubled. After 1990, global production has stagnated and remains around 20,000 tons per year. However, the areas where it is produced have changed significantly, with the severe drop in European output being compensated by an increase in Asia. Around 18 percent of the production is now recycled, thanks to improved technology. New methods of melting, smelting and refining have reduced the amount that contaminates the environment.
Nickel-cadmium batteries use more than 80 percent of the total cadmium production and are by far the most important application for this toxic metal. The rest is consumed by various other uses. Refined cadmium serves as a coloring pigment in ceramic, enamel and plastic, an ingredient in copper, tin or lead alloys, as anti-corrosive plating on steel and iron, or as a stabilizing agent in plastics. However, most non-battery uses have dropped sharply in the last two decades.
Health effects and uses
Cadmium is available as a by-product of the non-ferrous industry and results from the processing of other ores. It has several industrial uses.
This metal has a number of important qualities. It is a great conductor of electricity, has a very high resistance to corrosion, it is not affected by high temperatures of high concentrations of other chemicals and has a low melting point. These special properties make cadmium a great material in many industrial applications were very resilient metals are required.
Most of the cadmium produced in the world that is not included in batteries ends up being used in electroplating. This technique uses an electric current to apply a layer of coating on metals.
It is also used in the production of electronics. When included in bearing alloys, cadmium significantly reduces the friction coefficient and improves fatigue resistance.
One of its compounds, cadmium sulphide, is an important material with photosensitive qualities. It used to be very important in the phosphors of black and white TVs and continues to be a part of the green and blue phosphors of color TV tubes. Cadmium sulphide has also been known for a long time as a natural yellow pigment.
Small amounts of this metal have many other niche uses. It forms many salts and it is part of the voltaic cell known as the Weston standard. Photovoltaic cells convert energy from light into electrical power using thin films of either cadmium sulphide or cadmium telluride.
Many research applications, such as infrared imaging techniques, need cadmium mercury telluride as a semiconductor. There are also a large number or organic compounds that are manufactured using organic acids salts of cadmium as a catalyst.
An alloy made from silver, iridium and cadmium is the material of choice for the control rods found in the pressurized water reactors of nuclear power plants. They provide control over the process by absorbing free neutrons.
Due to its ability to absorb neutrons, cadmium is also used to produce sheets needed for shielding and protection in various engineering applications.
Most of the cadmium that ends up inside the human body is ingested from food. Several foods have a higher than average cadmium concentration and allows it to accumulate on the long term. These include liver, cocoa powder, dried seaweed, mushrooms, shellfish and mussels.
Smoking is another common way of exposure to high levels of toxic cadmium. The smoke of tobacco takes this metal directly into the lungs. It then enters the blood stream and reaches all parts of the body, making the effects of the cadmium sourced from food even more dangerous.
It is also possible to become exposed to high cadmium levels if you live near factories that contaminate the air or close to deposits of hazardous waste. People who work in metal refineries are also at risk. Inhaling cadmium will destroy your lungs and trigger conditions that are potentially fatal.
When cadmium enters the blood stream, it is usually transported to the liver. Proteins bind to it in order to create complex chemicals that end up in the kidneys. Kidneys are unable to eliminate this metal, which builds up and harms the normal activities of the organ. The kidneys become damaged and no longer perform their functions well, allowing essential nutrients to be lost. Some of the cadmium is eventually eliminated from the body, but this typically takes a long time.
Almost all of the health and safety agencies in the world list cadmium and its chemicals as carcinogenic compounds. Cadmium poisoning is also considered to be a work hazard and most exposure to it is caused by industrial activities, as well as through air or water pollution. It is inhaled or ingested and starts an irritation of the lungs or digestive system. It is very difficult to remove from the body, where high concentrations cause death, as well as from the environment. Regions where cadmium is extracted or processes are usually highly contaminated.