Where Found (Encyclopedia of Global Resources)
Chromium is a moderately abundant element that does not occur free in nature. Its principal ore is known as chromite, (Fe,Mg) (Cr,Al)2O4. The world’s chromite resources are concentrated in the Eastern Hemisphere, with major producers including South Africa, Kazakhstan, India, Zimbabwe, Turkey, Finland, and Brazil.
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Primary Uses (Encyclopedia of Global Resources)
Chromium is a strategic and critical resource used principally in the production of alloys and superalloys, stainless steel, refractory materials, pigments, and chemicals. It is used for dyeing textiles and leather tanning and as a laboratory glassware cleanser. Furthermore, chromium in its trivalent oxidation state is an essential trace nutrient for humans and other mammals.
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Technical Definition (Encyclopedia of Global Resources)
Chromium (abbreviated Cr), atomic number 24, is a metallic chemical element belonging to Group VIB of the periodic table of the elements. It has four naturally occurring isotopes and an average molecular weight of 51.996. Pure chromium is silver-gray, brittle, and hard. Its specific gravity is 7.19 at 20° Celsius, its melting point is approximately 1,890° Celsius, and its boiling point is 2,200° Celsius. This lustrous metal will take a high polish and does not tarnish in air. In chemical compounds chromium may have oxidation states ranging from -2 to +6, but in most compounds it is trivalent (+3) or hexavalent (+6). The trivalent state is more common in naturally occurring compounds, while hexavalent chromium is frequently found in industrial applications.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Chromium is a commercially important metallic element. Forming compounds with brilliant red, yellow, and green hues, it derives its name from the Greek chroma (color). Its concentration in the lithosphere is 100 grams per metric ton. Total world production of chromite is about 20 million metric tons. Trivalent chromium, the form most often found in nature, is a trace element in the human body; by contrast, hexavalent chromium is a highly toxic substance whose concentrations in the environment are regulated by law.
Approximately 95 percent of the world’s chromium resources are found in southern Africa, with South Africa the leading producer in the region. Other world producers include Kazakhstan, India, Turkey, Finland, Brazil, and Russia. Chromium is present in a number of minerals, but chromite is its only commercial ore. Primary deposits of chromite occur as stratiform and podiform ores found in certain types of ultrabasic (low-silica) rocks. Secondary alluvial deposits of chromite are formed by the weathering of stratiform (layered) and podiform ores.
Stratiform chromite deposits are often several meters thick, extend over large areas, have a relatively uniform composition, and frequently include platinum-bearing zones. They formed as chromite crystallized and precipitated from silicate melts. Examples include the Bushveld igneous Complex in Transvaal, South Africa; the Great Dyke in...
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History (Encyclopedia of Global Resources)
Chromium appears to have been unknown to ancient civilizations. It was discovered in 1797 by Louis-Nicolas Vauquelin, a French chemist, when he found that the lead in a sample of crocoite (PbCrO4) from Siberia was combined with an unknown oxide mineral. Between the time of chromium’s discovery and 1827, the primary source of chromite was the Ural Mountains of Russia. In 1827, the discovery of chromite in Maryland moved the United States to the forefront of world production. Large Turkish deposits were developed in the 1860’s; after this time, the Eastern Hemisphere became the chief source of chromite. The chemical manufacturing industry was the main consumer of chromium until the early 1900’s, when the element found increasing use in metallurgical and refractory products. During World Wars I and II, the United States increased its domestic production of the metal, and during the 1950’s it stockpiled domestic ores. International political conflicts have often led to interruptions in chromium supply.
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Obtaining Chromium (Encyclopedia of Global Resources)
Sodium dichromate, from which most commercial chromium compounds are made, is produced by roasting chromite with sodium carbonate, leaching the resulting product with water, and concentrating and acidifying the leachate to cause sodium dichromate to precipitate. Ferrochromium is prepared from chromite by reducing the ore with carbon in a blast furnace. Metallic chromium is obtained by reducing chromium oxide with aluminum or carbon, or by electrolyzing a solution of ferrochromium dissolved in sulfuric acid after the iron has been removed from the solution as ferrous ammonium sulfate. Chromium metal in its purest form is produced in small quantities by vapor deposition from anhydrous chromium iodide.
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Uses of Chromium (Encyclopedia of Global Resources)
The principal use of chromium is as an alloy metal, particularly in the steel industry. Combined with other metals, it imparts hardness, strength, and resistance to corrosion and heat. Chromium facilitates the hardening of steel and, if the alloy’s carbon content is high, enables it to withstand extreme abrasion and wear. In ball-bearing steel, chromium improves the elastic limit and imparts an evenly distributed hardness. Chromium increases the corrosion resistance of stainless steel and is an important alloy metal in heat-resisting steels. High-chromium steel, with its high resistance to wear, is used for making items such as die blocks, press plates, chisels, hacksaw blades, and circular steel saws. Nichrome, an alloy of nickel and chromium, is used as a heating element in household appliances such as electric toasters and coffeepots. Stellite, an extremely hard alloy of cobalt, chromium, and tungsten with minor amounts of iron, silicon, and carbon, is used in metal cutting tools and wear-resistant surfaces. A similar alloy, which employs molybdenum rather than tungsten, is used in surgical tools. With its hardness and nontarnishing properties, chromium is also an ideal electroplating metal. Chromium’s uses in alloys and plating make it an important strategic and critical metal.
Chromite is a valuable raw material for the manufacture of refractory materials such as refractory bricks, foundry sand, and casting items...
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Further Reading (Encyclopedia of Global Resources)
Adriano, Domy C. “Chromium.” In Trace Elements in Terrestrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals. 2d ed. New York: Springer, 2001.
Greenwood, N. N., and A. Earnshaw. “Chromium, Molybdenum, and Tungsten.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Guertin, Jacques, et al., eds. Chromium (VI) Handbook. Boca Raton, Fla.: CRC Press, 2005.
Independent Environmental Technical Evaluation Group. Chromium (VI) Handbook. Edited by Jacques Guertin, James A. Jacobs, and Cynthia P. Avakian. Boca Raton, Fla.: CRC Press, 2005.
Katz, Sidney A., and Harry Salem. The Biological and Environmental Chemistry of Chromium. New York: VCH, 1994.
Kogel, Jessica Elzea, et al., eds. “Chromite.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: Society for Mining, Metallurgy, and Exploration, 2006.
Manning, D. A. C. Introduction to Industrial Minerals. New York: Chapman & Hall, 1995.
Nriagu, Jerome O., and Evert Nieboer, eds. Chromium in the Natural and Human Environments. New York: Wiley, 1988.
Udy, Marvin J. Chemistry of Chromium and Its Compounds. Vol 1 of Chromium. New York: Reinhold, 1956.
Natural Resources Canada. Canadian Minerals Yearbook, Mineral and Metal Commodity...
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Chromium (Chemical Elements)
Chromium is found in the center of the periodic table, a chart that shows how chemical elements are related to each other. Elements in Groups 3 through 12 are known as the transition metals. These elements all have similar physical and chemical properties. They have a bright, shiny surface and high melting points.
Chromium was discovered in 1797 by French chemist Louis-Nicolas Vauquelin (1763-1829). The name comes from the Greek word chroma, meaning "color," because chromium compounds are many different colors.
About three-quarters of chromium produced today is used in alloys, including stainless steel. An alloy is made by melting and mixing two or more metals. The mixture has different properties than the individual metals. Chromium is also used to cover the surface of other metals. This technique protects the base metal and gives the surface a bright, shiny appearance at a low cost.
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Chromium (Encyclopedia of Alternative Medicine)
Chromium is a mineral that is essential to humans. It is found naturally in a variety of foods, and supplements are available in capsules or tablets. Supplements are prepared using a number of formulas, including chromium (III), chromium aspartate, chromium chloride, chromium citrate, chromium nicotinate, chromium picolinate, GTF chromium, and trivalent chromium.
Chromium supports the normal function of insulin, which is a hormone secreted by the pancreas. Insulin helps transport glucose from the bloodstream into liver, muscle, and fat cells. Once it is inside these cells, the sugar is metabolized into a source of energy. Insulin is also involved in regulating protein, fat, and catalytic enzyme processes. People with diabetes do not produce insulin (or produce very little) or their bodies cannot properly use the insulin that is produced. As a result, sugar builds up in the bloodstream, causing serious health effects. Numerous scientific studies have shown that chromium is useful in treating insulin resistance (metabolic syndrome) and diabetes. Diabetic peripheral neuropathy, a form of nerve damage that is a direct result of diabetes, is indirectly related to a lack of sufficient chromium.
Several studies have shown that chromium supplements may improve insulin sensitivity, and...
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