Magnesium (Mg)
Magnesium (Mg) is a vital alkaline-earth metal with the atomic number 12, recognized for its lightweight and highly reactive properties. It is the eighth most abundant element in the Earth’s crust and is primarily extracted from seawater as well as minerals such as magnesite and dolomite. Magnesium is integral to a variety of industries, being used in alloys, refractory materials, fertilizers, and chemicals, and plays a significant role in biological systems as a component of chlorophyll in plants and a crucial element for animals' metabolic processes.
As a metal, magnesium is soft and ductile but, when alloyed with other elements, it becomes much stronger and is commonly utilized in aerospace, automotive, and portable equipment manufacturing due to its favorable strength-to-weight ratio. Additionally, magnesium compounds are employed in various applications, including pharmaceuticals and agriculture. The extraction processes, such as the Dow seawater process and the ferrosilicon method, facilitate the large-scale production of magnesium, with China being the leading global producer. Understanding magnesium's properties and uses can provide insights into its critical role in both industry and ecology.
Magnesium (Mg)
Where Found
Magnesium is a widespread and abundant element. Magnesium chloride and magnesium sulfate are present in dissolved form in seawater and underground brines—these sources accounted for 43 percent of U.S. magnesium compound production in 2008. Magnesium is also found in many minerals, notably magnesite (MgCO3), dolomite (CaMg (CO3)2), and brucite (Mg(OH)2). China, Russia, Israel, Kazakhstan, Canada, and Brazil are among the main producers. For a number of years, the United States has withheld its magnesium production statistics to avoid disclosure of companies’ proprietary data.
Primary Uses
Magnesium is used principally in alloys, refractory materials (60 percent of U.S. use), paper, fertilizer, chemicals, and pyrotechnics. As a compound, it can be used as an additive to food, in medicine, and as a sedative.
Technical Definition
Magnesium (abbreviated Mg), atomic number 12, belongs to Group IIA of the periodic table of the elements (alkaline-earth metals). It has three stable isotopes and an average molecular weight of 24.312. Pure magnesium is a silver-white, ductile metal that is malleable when heated. A chemically active element, magnesium is a potent reducing agent. Its specific gravity is 1.738 at 20° Celsius, its melting point is 651° Celsius, and its boiling point is 1,100° Celsius.
Description, Distribution, and Forms
Magnesium in the form of powder or ribbons readily ignites when heated, burning with an intense white light and releasing large amounts of heat while forming magnesia (magnesium oxide, MgO). Magnesium reacts with organic halides to produce Grignard reagents, an important class of chemical compounds used in the laboratory.
Magnesium is an alkaline-earth metal, a class of hard, heavy metals that are strongly electropositive and chemically reactive. It is the eighth most abundant element; its concentration in the lithosphere is 20,900 grams per metric ton, and the percentage of its ions in seawater is 0.1272. Magnesium’s density (only two-thirds that of aluminum) and the ease with which the element can be machined, cast, forged, and welded contribute to its commercial applications, as do the refractory properties of some of its compounds. China is the leading producer of primary (mined and processed) magnesium (627,000 metric tons in 2007), accounting for nearly 85 percent of magnesium production in the world. Russia and Canada are the world’s other leading producers. However, from 2003 to 2007, Canadian production declined dramatically from 78,000 to 16,300 metric tons.
Magnesium is one of the most common minerals in the Earth’s crust; its principal commercial source, however, is seawater. Extensive terrestrial deposits of magnesium are also found in the form of magnesite and dolomite. Magnesite, a magnesium carbonate, occurs as a hydrothermal alteration of serpentine, (Mg,Fe)3Si2O5(OH)4, a vein filling and a replacement mineral in carbonate rocks such as dolostone. Dolomite, or calcium magnesium carbonate, is the predominant mineral in dolostone, a widespread sedimentaryrock similar to limestone. Most dolomites are thought to have originated from partial replacement of calcium in limestone by magnesium. Magnesium occurs in nature as a component of several common minerals. Important ores include magnesite, a white or grayish mineral found in crystalline or porcelain-like masses; dolomite, a white mineral that resembles limestone; and brucite, a pearly foliated or fibrous mineral that resembles talc. Magnesium silicates are found in asbestos, serpentine, and talc. Magnesium chloride and magnesium sulfate occur in dissolved form in sea water and natural underground brines. Magnesium is also a constituent of chlorophyll in green plants.
History
Sir Humphry Davy discovered magnesia in 1808. In 1828, Antoine Bussy isolated pure magnesium by chemical reduction of the chloride, and in 1833, Michael Faraday isolated magnesium electrolytically. The earliest commercial production of the metal may have been in France during the first half of the nineteenth century, where a modification of the Bussy method was employed. At this time, magnesium metal was used primarily in photography. Around 1886, Germany developed an improved production process based on an electrolytic cell method devised by Robert Bunsen in 1852. Germany became the world’s sole source for elemental magnesium. Magnesium alloys were used in Germany in the early 1900’s in aircraft fuselages, engine parts, and wheels. In 1915, when a wartime blockade of Germany by the British interrupted the elemental magnesium trade, magnesium production began in the United States. Large-scale use of dolostone as a refractory material also commenced during World War I. In 1941, Dow Chemical Corporation introduced its process for extracting magnesium from seawater.
Obtaining Magnesium
Magnesium is obtained principally from seawater through theDow seawater process. The water is treated with lime to produce magnesium hydroxide as a precipitate. This precipitate is mixed with hydrochloric acid to form magnesium chloride; the chloride, in turn, is fused and electrolyzed, producing magnesium metal and chlorine gas. From a liter of seawater, approximately 10 milligrams of magnesium can be extracted. Another common method for obtaining magnesium is the ferrosilicon (Pidgeon) process, which uses dolomite as a raw material. The dolomite is heated to produce magnesia, which is then reduced with an iron-silicon alloy.
Uses of Magnesium
Dead-burned magnesite, produced by heating the mineral in a kiln at 1,500° to 1,750° Celsius until it contains less than 1 percent carbon dioxide, is a refractory material. Able to withstand contact with often corrosive substances at high temperatures, refractory materials are used to line furnaces, kilns, reaction vessels, and ladles used in the cement, glass, steel, and metallurgical industries. Magnesia refractories are materials particularly suited for the basic oxygen furnaces used in steelmaking. Dead-burned dolomite, produced by heating dolostone or dolomitic limestone at about 1,500° Celsius, is also a refractory material used for lining metallurgical furnaces.
In its elemental state, magnesium is soft and weak; its alloys, however, are sturdier and have a variety of uses. Magnesium is used extensively as an alloy metal, particularly in combination with aluminum, zinc, cadmium, and manganese. Magnesium alloys in general are lightweight, fatigue-resistant, free from brittleness, and able to withstand bending stresses; these qualities make magnesium alloys ideal for jet-engine parts, rockets and missiles, luggage frames, cameras, optical instruments, scientific equipment, and portable power tools. Duralumin, a lightweight alloy of aluminum, copper, magnesium, and manganese, is ductile and malleable before its final heat treatment; afterward, its hardness and tensile strength are increased. Its properties make duralumin especially useful to the aircraft industry. Magnalium, an alloy of aluminum and magnesium that is lighter and easier to work than aluminum, is used in metal mirrors and scientific instruments.
Pure magnesium is used in incendiary bombs, signals and flares, thermite fuses, and other pyrotechnic devices. It is an important component of photographic flashbulbs, a deoxidizing agent used in the preparation of some nonferrous metals, a rocket and missile fuel additive, and an agent for chemical synthesis. Magnesium reacts with organic halides to form Grignard reagents, an important class of extremely reactive chemical compounds that are used in synthesizing hydrocarbons, alcohols, carboxylic acids, and other compounds. Magnesium compounds are used in chemicals, ceramics, cosmetics, fertilizer, insulation, paper, leather tanning, and textile processing. Epsom salts (magnesium sulfate heptahydrate), milk of magnesia (magnesium hydroxide), and citrate of magnesium are used in medicines. Caustic-calcined magnesia (magnesite heated to between 700° and 1,000° Celsius to drive off 2 to 10 percent of its carbon dioxide) is mixed with magnesium chloride to create oxychloride (sorel) cement. This cement is used for heavy-duty floorings, stucco, and fireproof building materials. Dolostone, a rock composed chiefly of dolomite, is used as a building stone as well as a refractory material.
Magnesium is an essential element in all plants and animals. In green plants, it is a component of chlorophyll; in animals, it plays a role in carbohydrate metabolism and is an important trace element for muscle, nerve tissue, and skeletal structure. Serious dietary deficiencies of magnesium can bring on such symptoms as hyperirritability and soft-tissue calcification.
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