Magnesium [Mg]

Characteristics

An: 12 N: 13

Am: 24.3050 g/mol

Group No: 2

Group Name: Alkaline earth metal

Block: s-block Period: 3

State: solid at 298 K

Colour: silvery white Classification: Metallic

Boiling Point: 1363K (1090^oC)

Melting Point: 923K (650^oC)

Density: 1.738g/cm³

Availability: Magnesium is the eight most abundant element in the Earth’s crust, about 2% by weight.

Discovery Information

Who: Sir Humphrey Davy

When: 1808

Where: England

Name Origin

From Magnesia ancient city in Asia Minor. " Magnesium" in different languages.

Some crystals of dolomite from the Tri-State mining district near Joplin, Missouri USA.

Dolomite is an commercially important source of magnesium.

Sources

Although magnesium is found in over 60 minerals, only dolomite (CaMg(CO₃)₂), magnesite (MgCO₃), brucite (Mg(OH)₂), carnallite (KMgCl₃ - ₆(H2O)), talc, and olivine ((Mg,Fe)₂SiO₄) are of commercial importance. Usually obtained by electrolysis of melted magnesium chloride found in sea water.

China produces around 60% of the world’s magnesium, other important producers are Austria, Poland, Russia, the USA, India, Greece and Canada. Annual production is around 350 thousand tons.

Abundance

Universe: 600 ppm (by weight)

Sun: 700 ppm (by weight)

Carbonaceous meteorite: 1.2 x 10⁵ ppm

Earth’s Crust: 23000 ppm

Seawater: 1200 ppm

Human: 270000 ppb by weight; 70000 ppb by atoms

Uses

Used in alloys to make airplanes, missiles, car engine parts, racing bikes and other things that need light metals. Also used in fireplace bricks, flashbulbs, pigments and filters. Magnesium powder is still used in the manufacture of fireworks and marine flares where a brilliant white light is required.

Magnesium oxide and other compounds also are used in agricultural, chemical, and construction industries. As a metal, this element’s principal use is as an alloying additive to aluminium with these aluminium-magnesium alloys being used mainly for beverage cans.

Magnesium carbonate (MgCO₃) powder is also used by athletes, such as gymnasts and weightlifters, to improve the grip on objects - the apparatus or lifting bar.

Magnesium stearate is a slightly flammable white powder with lubricative properties. In pharmaceutical technology it is used in the manufacturing of tablets, to prevent the tablets from sticking to the equipment during the tablet compression process (i.e., when the tablet’s substance is pressed into tablet form).

History

The name originates from the Greek word for a district in Thessaly called Magnesia. It is related to magnetite (Fe₃O₄) and manganese, which also originated from this area, and required differentiation as separate substances. See manganese for this history.

Magnesium is the eighth most abundant element in the earth’s crust. It is found in large deposits of magnesite, dolomite, and other minerals, and in mineral waters, where magnesiumion is soluble. In 1618 a farmer at Epsom in England attempted to give his cows water from a well. This they refused to drink because of the water’s bitter taste. However the farmer noticed that the water seemed to heal scratches and rashes. The fame of Epsom salts spread. Eventually they were recognised to be hydrated magnesium sulphate, MgSO₄.

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Sir Humphry Davy electrolytically isolated pure magnesium metal in 1808 from a mix of magnesia and HgO, and A. A. B. Bussy prepared it in coherent form in 1831. Davy’s first suggestion for a name was magnium, but the name magnesium is now used.

Notes

Organic magnesium is important in both plant and animal life.

Hazards

Magnesium metal and alloys are highly flammable in their pure form when molten, as a powder, or in ribbon form. Burning or molten magnesium metal reacts violently with water. Once ignited it is difficult to extinguish, being able to burn in both nitrogen (forming magnesium nitride), and carbon dioxide (forming magnesium oxide and carbon). Magnesium powder is an explosion hazard. Magnesium reacts violently with halogens.

Magnesium Compounds

Magnesium carbonate MgCO₃

Used in flooring, fireproofing, fire extinguishing compositions, cosmetics, dusting powder, and toothepaste. Other applications are as filler material, smoke suppressant in plastics, a reinforcing agent in neoprene rubber, a drying agent, and colour retention in floods. In addition, high purity magnesium carbonate is used as antacid and as an additive in table salt to keep it free flowing.

Magnesium chloride MgCl₂

It is used in the manufacture of textiles, paper, fireproofing agents, cements and refrigeration brine.

Magnesium chloride is an important coagulant used in the preparation of tofu from soy milk. In Japan it is sold as nigari (the term is derived from the Japanese word for "bitter"), a white powder produced from seawater after the sodium chloride has been removed, and the water evaporated. Nigari consists mostly of magnesium chloride, with some magnesium sulfate and other trace elements.

Magnesium diboride MgB₂

An inexpensive and simple superconductor that can be synthesized by high temperature reaction between boron and magnesium.

Magnesium hydroxide Mg(OH)₂

Otherwise known as milk of magnesia, is commonly used as an antacid or a laxative. The mineral form of magnesium hydroxide is known as brucite. Magnesium hydroxide interferes with the absorption of folic acid and iron. The diarrhea caused by magnesium hydroxide carries away much of the body’s supply of potassium, and failure to take extra potassium will lead to muscle cramps.

Magnesium oxide Mg(OH)₂

It is used by many libraries for preserving/deacidifying books, and as an insulator in industrial cables. It is also used as a medication to relieve heartburn, sour stomach, or acid indigestion. Medical uses of Magnesium oxide also include using it as a short-term laxative, or used to supplement a diet with magnesium. Magnesium oxide is a principle ingredient in construction materials used for fireproofing.

Magnesium peroxide MgO₂

Magnesium peroxide being environmentally benign and its stable oxygen release are used widely in the cosmetic, agricultural, pharmaceutical, and environmental industries. It is used to reduce contaminant levels in groundwater. Magnesium peroxide is used in the bioremediation of contaminated soil and can improve the soil quality for plant growth and metabolism. It also used in the aquaculture industry for bioremediation.

Magnesium stearate C₃₆H₇₀MgO₄

It is often used as a filling agent in the manufacture of medical pills. In this regard, the substance is also useful because it has lubricating properties, preventing ingredients from sticking to manufacturing equipment during the compression of chemical powders into solid pills. It is also a common ingredient in baby powders. In pure powder form, the substance can be a dust explosion hazard, although this issue is effectively moot beyond the manufacturing plants using it.

Magnesium sulfate (Epsom Salt) MgSO₄.7H₂O

Epsom salt was originally prepared by boiling down mineral waters at Epsom, England and afterwards prepared from sea water.

In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil (magnesium is an essential element in the chlorophyll molecule). It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, and tomatoes. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.

Locally it may be used as a treatment of an ingrown nail. Oral magnesium sulfate, or magnesium oxide, is used as a laxative. Epsom salts are also available in a gel form for topical application in treating aches and pains. Intravenous use is broadening, as magnesium sulfate reduces striated muscle contractions and blocks peripheral neuromuscular transmission by reducing acetylcholine release at the myoneural junction, as well as other effects.

Reactions of Magnesium

Reactions with water

Although magnesium does not react with water to any significant extent it does react with steam to yield magnesium oxide, or magnesium hydroxide with excess steam, and hydrogen gas.

Mg _(s) + H₂O _(g) --> MgO _(aq) + H₂ _(g)

Mg _(s) + excess 2H₂O _(g) --> Mg(OH)₂ _(aq) + H_{2 (g)}

Reactions with air

A thin layer of oxide helps to protect magnesium from attack by air. However, once ignited magnesium burns in air with its characteristic intensely bright white flame. This yields magnesium oxide and magnesium trioxide.

2Mg _(s) + O_{2 (g)} -- >2MgO _(s)

3Mg _(s) + N₂ _(g) --> Mg₃N₂ _(s)

Reactions with halogens

Magnesium will react with chlorine and bromine to form magnesium(II) dihalides.

Mg _(s) + Cl_{2 (g)} --> MgCl_{2 (s)}

Mg _(s) + Br_{2 (g)} --> MgBr_{2 (s)}

Reactions with acids

Magnesium will dissolve readily in dilute sulphuric acid, as will as other acids, to form solutions containing the Mg(II) ion and hydrogen gas.

Mg _(s) + H₂SO_{4 (aq)} --> Mg²⁺_(aq) + SO₄^2-_(aq) + H_{2 (g)}

Mg _(s) + 2HCl _(aq) --> Mg²⁺ _(aq) + 2Cl^- _(aq) + H_{2 (g)}

Reactions with bases

Magnesium appears not to react with dilute alkalis.

Occurrence and Production of Magnesium

From the ground

Although magnesium is found in over 60 minerals, but only dolomite (CaMg(CO₃)₂), magnesite (MgCO₃), brucite (Mg(OH)₂), carnallite (KMgCl₃.6(H₂O)), talc (Mg₃Si₄O₁₀(OH)₂), and olivine ((Mg,Fe)₂SiO₄) are of commercial importance.

In the United States this metal is principally obtained by electrolysis of fused magnesium chloride from brines, wells, and sea water:

cathode: Mg²⁺ + 2e^- --> Mg

anode: 2Cl^- --> Cl_{2 (g)} + 2e^-

The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a company born from now-defunct Magcorp. As of 2005 China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995. Unlike the above described electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon).

From the Sea

Sea water contains magnesium salts, such as magnesium chloride. To extract the magnesium, calcium carbonate is added to sea water to form magnesium carbonate.

MgCl₂ + CaCO₃ --> MgCO₃ + CaCl₂

Magnesium carbonate is insoluble in water so it can be filtered out, and reacted with hydrochloric acid to obtain concentrated magnesium chloride.

MgCO₃ + 2HCl --> MgCl₂ + CO₂ + H₂O

From magnesium chloride, electrolysis produces magnesium.

Isotopes of Magnesium

²⁴Mg [12 neutrons]

Abundance: 78.99%

Stable with 12 neutrons

²⁵Mg [13 neutrons]

Abundance: 10%

Stable with 13 neutrons

²⁶Mg [14 neutrons]

Abundance: 11.01%

Stable with 14 neutrons

Large enrichments of stable ²⁶Mg have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite meteorites. The anomalous abundance of ²⁶Mg is attributed to the decay of its parent ²⁶Al in the inclusions.

Therefore, the meteorite must have formed in the solar nebula before the ²⁶Al had decayed. Hence, these fragments are among the oldest objects in the solar system and have preserved information about its early history.