Mg Name, symbol Magnesium, Mg Appearance Shiny grey solid Atomic number  12 Group, block group 2 (alkaline earth metals) Standard atomic weight  24.305 Phase solid Melting point 923 K ​(650 °C, ​1202 °F) Boiling point 1363 K ​(1091 °C, ​1994 °F) Density  1.738 g/cm3 Heat of fusion 8.48 kJ/mol Heat of vaporization 128 kJ/mol Oxidation states +2, +1 ​(a strongly basic oxide) Crystal structure ​hexagonal close-packed (hcp) Magnetic ordering paramagnetic Young's modulus 45 GPa Shear modulus 17 GPa Brinell hardness 44–260 MPa Discovery Joseph Black (1755)

Magnesium is the lightest structural metal used today, some 30% lighter than aluminium, and is generally used in alloys. Pure magnesium burns vigorously once molten, but magnesium alloys have higher melting points and are widely used in the automotive and aircraft industries. Magnesium is the eighth-most-abundant element in the Earth's crust by mass. Although magnesium is found in more than 60 minerals, only dolomite, magnesite, brucite, carnallite, talc, and olivine are of commercial importance.

Magnesium production (thousand tonnes) Rank Country (2013) Magnesium production (thousand tonnes) —  World 5,960 1  China 4,000 2  Russia 400 3  Turkey 300 4  Austria 250 5  Slovakia 200 6  Korea, North 150 7  Brazil 140 8  Spain 120 9  Greece 100 10  India 11  Australia 90 Other Countries 110 Magnesium has the following three principal uses as well as various other relatively minor uses: The principal constituent in magnesium alloys used chiefly in the production of die-cast parts, mainly for the automobile industry (this is the largest market). A minor constituent of aluminium alloys used in most applications for aluminium (especially beverage cans). A desulphurising agent in the production of steel.

MANUFACTURE OF MAGNESİUM Magnesium is found in solution in sea-water (about 1,3 kg m-3 magnesium) and in natural brines.  It is also found extensively in the ores magnesite (MgCO3) and dolomite (MgCO3.CaCO3). Magnesium is principally produced by two methods a) Thermal reduction of magnesium oxide b) Electrolysis of magnesium chloride Before the expansion of production in China, electrolysis was the more common method of production in countries where electrical energy is produced relatively cheaply.  Most Chinese plants, however, use an updated version of the thermal reduction process originally developed in Canada in the 1940s to boost production during World War II (the 'Pidgeon Process').

(a) Thermal reduction process Dolomite ore is crushed and heated in a kiln to produce a mixture of magnesium and calcium oxides, a process known as calcining:

(Fe,Si)(s) + MgO(s) ↔ Fe(s) + SiO2(s) + Mg(g) The next step is reduction of the magnesium oxide.  The reducing agent is ferrosilicon (an alloy of iron and silicon) which is made by heating sand with coke and scrap iron, and typically contains about 80% silicon. The oxides are mixed with crushed ferrosilicon, and made into briquettes for loading into the reactor. Alumina may also be added to reduce the melting point of the slag. The reaction is carried out at 1500 - 1800 K under very low pressure, close to vacuum. Under these conditions the magnesium is produced as a vapour which is condensed by cooling to about 1100 K in steel-lined condensers, and then removed and cast into ingots: (Fe,Si)(s) + MgO(s) ↔ Fe(s) + SiO2(s) + Mg(g) CaO + SiO2 → CaSiO3

The forward reaction is endothermic and the position of equilibrium is in favour of magnesium oxide.  However, by removing the magnesium vapour as it is produced, the reactiongoes to completion.  The silica combines with calcium oxide to form the molten slag, calcium silicate (CaSiO3) The process gives magnesium with up to 99,99% purity, slightly higher than from the electrolytic processes.

(b) The electrolytic process Outside China, the electrolytic process is usually the preferred choice. The process involves two stages: 1) Production of pure magnesium chloride from sea water or brine 2) Electrolysis of fused magnesium chloride

MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2 The Mg2+ cation is the second-most-abundant cation in seawater (about ⅛ the mass of sodium ions), which makes seawater and sea salt attractive commercial sources for Mg. To extract the magnesium, calcium hdroxide is added to seawater to form magnesium hydroxide precipitate. MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2 Magnesium hydroxide (brucide) is insoluble in water and can be filtered out and reacted with hydrochloric acid to produced concentrated magnesium chloride. Mg(OH)2 + 2 HCl → MgCl2 + 2 H2O From magnesium chloride, elctrolysis produces magnesium.

Figure x Illustrating the electrolysis of magnesium chloride. (ii) The electrolysis of fused magnesium chloride The resulting an hydrous magnesium chloride is fed continuously into electrolytic cells (Figure x) which are hot enough to melt it. On electrolysis, magnesium and chlorine are produced. Figure x  Illustrating the electrolysis of magnesium chloride. The molten metal is removed and cast into ingots.  The chlorine gas is recycled to the chlorination furnace.

Secondary production Only about 3% of the total magnesium used annually is from recycling, an estimated 23 000 tonnes. (2013)