Cadmium is a relatively abundant metal. In 2007, 20,400 metric tonnes of cadmium were mined. Cadmium has a bad reputation as a toxic metal that can cause cancer.
Physical properties: Cadmium is a malleable, ductile, bluish-white metal that shares many physical properties with zinc. It is soft (2.0 on a 10 point scale) and moderately dense (8.65 gram/cm3). Cadmium melts at 321C, and boils at 767C.
Like chromium, compounds of cadmium form have bright colors. Cadmium Sulfide is yellow, and Cadmium Selenide is red. Painters prefer cadmium-based colors as they are more vibrant and eye-catching than other colors.
Chemical properties: Cadmium reacts easily to form compounds. Many of these compounds are richly colored and are used to make pigments. Due to its toxicity, people are kept away from the metal and its compounds as far as possible. Though cadmium and the compounds it forms are toxic, hospitals in England used it in the early 20th century to treat certain ailments like enlarged joints. A combination of metallic cadmium and nickel oxide is used to make rechargeable batteries.
History: Cadmium was discovered in Germany in 1817 by Friedrich Strohmeyer (1776 - 1835). Strohmeyer found cadmium in zinc carbonate. He noticed that when zinc carbonate containing cadmium was heated, it changed color. However, pure zinc carbonate did not change color. For 100 years, Germany remained the only large producer of the element cadmium. Later, China, Japan and Korea became the main producers of the metal.
Production: Since cadmium often occurs as an impurity in zinc, it is extracted mainly during the processing of ores that contain zinc. Cadmium is then extracted from the rest of the mixture through distillation, or by reacting it with carbon and then separating it as a solid from the liquid impurities. Cadmium is usually found in small quantities in the ore, so large areas of land have to be mined to obtain substantial amounts of the metal. The top producers of cadmium are China, South Korea, Canada, Kazakhstan and Japan. Pie Chart of Top 5 Cadmium Producing Countries...
Uses: Most of the cadmium that the world produces goes into batteries, mainly rechargeable batteries that contain a mix of nickel and cadmium. The European Union banned the use of cadmium in electronics in 2004, with only a few exceptions allowed under the law. Cadmium is also used in making pigments and dyes to color a variety of materials, like plastics. A minor use of cadmium is to make alloys with low melting points, such as solder.
Health: People working in the production of nickel-cadmium batteries, pigments, and plastics are often poisoned by exposure to the toxic metal. Inhaled in gaseous form, it can cause swollen lungs, accumulation of fluid in the lungs, and in serious cases, death. Due to its toxicity, cadmium is one of the six metals banned by the European Union in the making of electronics. A particularly serious case of cadmium poisoning happened in Japan, on the Jinzu River soon after the end of the Second World War Mining corporations had contaminated the river with cadmium, and the crops watered with water from the river had high levels of cadmium in them. The people who ate these crops suffered from the "Itai itai" disease that causes their bones to soften and their kidneys to fail. Children of parents with the disease were often born with deformities. Because cadmium is passed from the soil to the plant, cadmium compounds are never used in fertilizers.
Tobacco smoke contains cadmium, and about 10% of the cadmium content in a cigarette accumulates in the body. Children who are exposed to smoking often have much higher levels of cadmium in the blood than recommended. On average smokers have 4-5 times more cadmium in their blood and 2-3 times more cadmium in their kidneys than the non-smokers. Since cadmium and several of its compounds can cause many different types of cancer in humans, these metals must not come into direct contact with people. They should be kept in sealed containers, during storage and when in use (like in batteries).
Cobb, Alan. Cadmium: The Elements, 2007, Marshall Cavendish, USA.
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