Cadmium is toxic metal and its discovery is credited to two scientist, Karl Smuel and Friedrich Strohmeyer, who simultaneously reported its discovery in 1817. Cadmium based pigments and batteries are widely sed since its discovery.
History and Discovery
Cadmium was discovered as an impurity from the ore of zinc carbonate by Friedrich Strohmeyer in 1817 (Germany). Discovery of cadmium is also credited to Karl Smuel who simultaneously discovered cadmium in zinc ore (zinc carbonate) termed as calamine . Both the scientist belonged to Germany, and for many decades, Germany remained the prime producer of cadmium. The name cadmium has been derived from cadmia (Latin) and kadmeia (Greek) that means zinc carbonate. In 1950s, cadmium was widely used in making yellow, orange and red pigments and later as coating agent on the world’s renowned plastic polymer, PVC. But in 1980s, the use of cadmium was greatly reduced due to concerns related to its toxicity and its environmental and health hazards.
|Periodic Table Classification||Group 12
|State at 20C||Solid|
|Color||Silvery bluish-gray metallic|
|Electron Configuration||[Kr] 4d10 5s2|
|Electron Shell||2, 8, 18, 18, 2
|Density||8.65 g.cm-3 at 20°C|
|Atomic Mass||112.41 g.mol -1|
|Electronegativity according to Pauling||1.69|
Cadmium is a rare metal. The concentration of cadmium on the Earth is around 0.5 ppm (parts per million). Mostly it is present in the form of ores of zinc and sulfide. The sulfide ore of cadmium is termed as greenockite (CdS). Currently, cadmium is obtained from the mining, smelting and purification of ores of zinc sulfide, and copper sulfide. Elemental form of cadmium has been found in Siberia. The leading producers of cadmium in the world are Japan, China and South Korea and North America.
Cadmium is whitish blue transition metal. It is soft and malleable and can be cut with a knife. Cadmium is a divalent metal and is insoluble in water. Cadmium is resistant to fire and is inflammable but is flammable in powdered form. Cadmium is an outstanding conductor of electricity. It is resistant to corrosion. Cadmium metal is unreactive with water .
Cadmium is not highly reactive. However, when exposed to air, cadmium undergoes tarnishing. When burned in the presence of air, if forms oxide (cadmium oxide CdO). Cadmium is not soluble in alkalis (such as sodium hydroxide) but is dissolved in acids (such as sulfuric acid). With halogens, cadmium forms compounds with fluorine, iodine and bromine: CdF2, CdI2 and CdBr2 .
Significance and Uses
- Cadmium is widely used in the production of cadmium batteries, such as rechargeable cadmium nickel batteries.
- Cadmium is used as an electroplating agent to protect aircrafts etc. from corrosion.
- It is used in nuclear reactors as control rods.
- Cadmium is used to make lasers and UV lamps.
- Cadmium is used for making bearings and in alloys used in making bearing due to its resistance to high fatigue and low coefficient of friction.
- Various salts of cadmium are used in making pigments, such as cadmium selenide is termed as cadmium red as it is used to make red pigment and cadmium sulfide is used to make yellow pigment.
Cadmium is a highly toxic compound. It is considered as a carcinogenic (cancer causing) element. If inhaled or ingested, cadmium cause toxicity in various organs of the body, such including reproductive, gastrointestinal system, renal and cardiovascular system. Cadmium toxicity is considered as an occupational hazard and according to an estimate, around 300,000 individuals working in various industries are exposed to cadmium toxicity. For instance, personals working in metal smelting and refining plants, and manufacturing of plastic, solar panels and batteries . Cadmium contamination from soil can accumulate in certain crops, such as rice and tobacco plants, which can cause toxicity in humans when consumed .
Isotopes of Cadmium
Cadmium has more than 30 isotopes. There are 8 naturally occurring isotopes in the cadmium element. Two natural isotopes are radioactive, cadmium-113 and cadmium-116, while stable isotopes include cadmium-114, cadmium-108 and cadmium-106, cadmium-110, cadmium-112 and cadmium-111. The most abundant stable isotope is cadmium-114 .
. Friedrich Stromeyer, Annals of Philosophy, edited by Thomas Thomson, Volume XIII, 1819, Robert Baldwin, p108
. Alireza Pourkhabbaz, Hamidreza Pourkhabbaz Investigation of Toxic Metals in the Tobacco of Different Iranian Cigarette Brands and Related Health Issues, Iran J Basic Med Sci. 2012 Jan-Feb; 15(1): 636–644. PMC 3586865