Magnesium is a Group IIA element of the third cycle of the Periodic Table of the Elements. The element symbol Mg, atomic number 12, atomic weight 24.305. The electrons in the magnesium atom are arranged in the order of ls ^{2 ₂} s ² 2p ⁶ 3s ² , and when they become ions, they generally have a valence of +2, that is, Mg ²⁺ .
Magnesium metal is silver, the thermal conductivity and good electrical conductivity. Magnesium is relatively light, with a density of about 2/3 of aluminum and 115 of iron , which is a light metal. The main physical properties of magnesium are listed in Table 1.

Magnesium has good mechanical properties, can be cast, rolled and machined, can cast thin-walled parts, and the surface of castings is smooth and smooth, suitable for high-speed cutting, easy to finish, good welding performance, can produce a variety of mechanical zeros The part is the lightest structural material. The mechanical properties of magnesium are listed in Table 2. Magnesium can be alloyed with metals such as A1, Cu, Zn, Mn, Zr, Th, and Li to form a magnesium-based alloy. Magnesium based alloys are lighter than aluminum based alloys. The mechanical properties of magnesium-based alloys are superior to those of pure magnesium. [next]

Magnesium reacts with oxygen in the air at room temperature to form a dense magnesium oxide film. This oxide film prevents oxidation from proceeding. Therefore, magnesium is stable in the air. Magnesium powder and magnesium chips can be burned in the air, giving off dazzling white light, which is the raw material for making fireworks. At temperatures above 300 °C, magnesium reacts with nitrogen to form Mg ₂ N ₂ , which is intense at temperatures above 670 °C. At temperatures above 500 ° C, magnesium reacts with sulfur to form MgS. When heated in a chlorine gas medium, magnesium reacts violently with chlorine to form M ₉ Cl ₂ . At room temperature, magnesium reacts with water to form Mg(OH) ₂ and H ₂ , which forms a layer of insoluble Mg(OH) ₂ , which hinders and slows down the reaction. Magnesium reactive with the acid, salt and H _2, and hydrofluoric acid, phosphoric acid and chromic acid reaction rate is very slow, with hydrochloric acid, nitric acid and sulfuric acid the reaction is very strong. Magnesium can reduce TiCl ₄ to metallic titanium . The reduction of TiCl ₄ with magnesium is the main method for the industrial production of titanium metal. Magnesium oxide (MgO), melting point up to 2802 ° C, can be used as a refractory material. Magnesium oxide as a refractory material is called magnesia. Light magnesium oxide is often used as a filler for rubber. MgO easily absorbs moisture and CO ₂ and acts as a CO ₂ absorbent in desiccants and spacecraft. At room temperature, MgO is dissolved in water to form Mg(OH) ₂ . MgO is easily soluble in acid; it is soluble in hydrochloric acid to form MgCl ₂ . Industrial production of MgO is obtained by calcining Mg(OH) ₂ or MgCO ₃ . Magnesium carbonates, phosphates and fluorides are hardly soluble in water and are easily soluble in strong acids such as hydrochloric acid; sulfates, nitrates, chlorides, chlorates, perchlorates and acetates are readily soluble in water and acid. The most important salts are magnesium chloride and magnesium carbonate. Magnesium chloride is a raw material for electrolytic magnesium smelting. MgCl _{2 is} colorless and easily soluble in water. The solubility increases with increasing temperature. The saturated solution at 20 ° C contains 35.5% MgCl ₂ . Since MgCl _{2 is} easily soluble in water, there is no separate magnesium chloride ore in nature. Magnesium chloride is present in salt lakes and sea, in water, or combined with potassium chloride to form double salt potassium carnallite (KC1·MgCl ₂ ·6H ₂ O) Exist in underground deposits. The ore formed by magnesium carbonate is magnesite . Magnesite is calcined at a high temperature to obtain magnesium oxide. Magnesite is obtained by adding carbon chloride to the magnesite at a high temperature. Dolomite is a double salt of magnesium carbonate and calcium carbonate (CaCO ₃ ·MgCO ₃ ). Dolomite is the raw material for magnesium smelting by thermal reduction. [next]
Magnesium is mainly used in aluminum alloy, magnesium alloy die casting, steel desulfurization and ductile iron.
Magnesium is an important component of aluminum alloys. It can improve the thermal strength of aluminum, enhance weldability, corrosion resistance and improve mechanical properties. Aluminum alloy profiles, sheets and castings are used in a wide range of applications. Aluminum alloys are used in various industries such as automobile manufacturing, aerospace, electric power, construction (aluminum doors and windows) and food packaging (cans). Many aluminum alloys contain magnesium, and the magnesium content is generally 0.5% to 5%, and individual amounts are as high as 10%. Thus, 50% of the magnesium is used in aluminum alloys, which are the largest users of magnesium.
Magnesium is used as a desulfurizer for steel, and the sulfur content of steel can reach 0.003%-0.001%. It can greatly improve the castability, ductility, weldability and toughness of steel. Compared with other desulfurizing agents, the time for desulfurization with magnesium is short, the temperature drop of molten iron is small, the iron loss is small, and the waste residue is also small. 1t steel desulfurization consumes 0.5-1.0 kg of magnesium. In the 1980s, North America and European countries switched to magnesium as a steel desulfurizer. US steel desulfurization uses magnesium. Desulfurization of steel has become one of the main users of magnesium. The amount of magnesium used in steel desulfurization has accounted for about 14% of total magnesium consumption. Steel mills in the CIS, Japan and China have also started using magnesium as a steel desulfurizer.
Adding magnesium to the pig iron can spheroidize the scaly graphite in the iron. This kind of pig iron is called ductile iron. The ductile iron has better fluidity than ordinary cast iron and the mechanical strength is increased by 1-3 times. Due to the excellent performance of ductile iron, it is widely used. The amount of magnesium used in ductile iron accounts for about 5% of total magnesium consumption.
Magnesium alloy die castings are the main form of magnesium as a structural material. Magnesium alloy die-casting parts have the characteristics of large strength-to-mass ratio, lighter than aluminum alloy, good shock absorption, high precision of castings and the ability to be cast into thin-walled parts. Magnesium alloy die castings are used more and more widely. In the 1990s, the application of magnesium alloy die castings in the car manufacturing industry developed rapidly. Energy conservation and environmental protection are becoming more and more important to humans. Some countries have stipulated the mileage and exhaust emissions of cars that consume 3.79dm ^{3 of} gasoline. To this end, the body weight must be reduced to reduce fuel consumption. The world's major automobile manufacturing companies began to use magnesium alloy die-casting parts as car parts, and used magnesium die-casting parts to make steering wheel, frame, cylinder head and wheel. Due to the application of magnesium alloy die-casting parts in cars, magnesium alloy die-casting parts have become the second largest consumer of magnesium, accounting for 25% of total magnesium consumption.
In addition, magnesium can also be used as a sacrificial anode for corrosion protection. The welding of large steel tanks and underground steel pipes with magnesium or magnesium alloy blocks can delay the corrosion and extend the life of steel tanks and underground steel pipes. Magnesium is a reducing agent for the production of metals such as titanium, zirconium and hafnium . At present, the world's titanium metal is produced by magnesium reduction of TiCl ₄ . There is an electrolytic magnesium workshop in the titanium plant. The magnesium-reduced reduction furnace reduces the TiC1 ₄ and produces titanium and MgCl ₂ . The MgCl _{2 is} returned to the electrolytic magnesium workshop and added to the electrolysis tank. Magnesium can also be used to make fireworks and artificial light sources. In recent years, magnesium has also been widely used in communications, electronic instrumentation and computer industries.
Magnesium is one of the most abundant elements in the earth's crust, ranking eighth in terms of quantity, accounting for 2.1% of the earth's crust. Magnesium is widely distributed in the earth's crust, with more than 1,500 kinds of minerals in the earth's crust and about 200 kinds of magnesium minerals. In nature, magnesium is present in the form of carbonates, silicates, sulfates, halides and hydroxides. Commonly distributed minerals, carbonates such as magnesite (MgCO ₃ ) and dolomite (MgCO ₃ · CaCO ₃ ): silicates with olives (MgFe ₂ SiO ₄ ), talc (3MgO·4SiO _{2 )} · 2H ₂ O) and serpentine (3MgO · 2SiO ₂ · 2H ₂ O); sulfates with magnesium sulphate (MgSO ₄ · H ₂ O), diarrhea salt (MgSO ₄ · 7H ₂ O) and potassium magnesium alum _{(MgSO 4 · KCl · 6H 2} O); halide with a magnesium chloride (MgCl _2), magnesium bromide (MgBr ₂₎ and carnallite _{(KCl · MgCl 2 · 6H 2} O), magnesium chloride and magnesium bromide in the presence of Salt Lake In water and sea water. [next]
At present, the raw materials used in the industrial production of magnesium in the world are magnesite, dolomite, carnallite, salt lake water and sea water.
Magnesite is a carbonate mineral with a chemical formula of MgCO ₃ , which theoretically contains 47.82% of MgO and 52.18% of CO ₂ . Magnesite often contains impurities such as CaCO ₃ , MgCO ₃ and SiO ₂ , and the color is mostly white and light yellow. China, Russia, North Korea, the United States, Canada, Australia, Brazil, Yugoslavia, Slovakia, Austria and Greece have magnesite. The world's largest and best quality magnesite is the Dashiqiao magnesium mine in Liaoning, China. Most of the magnesite mined in the world is used to produce refractory materials, and only a small part of it is used to produce magnesium. Magnesite used for magnesium smelting requires higher purity. The use of magnesite as a raw material for magnesium smelting is carried out by electrolysis, and it is necessary to convert magnesium carbonate in magnesite into electrolytic raw material magnesium chloride. The method of transformation is to react magnesite with chlorine gas to obtain anhydrous magnesium chloride at a high temperature, or to dissolve magnesite in hydrochloric acid to obtain magnesium chloride, and dehydrate to obtain anhydrous magnesium chloride.
Dolomite is a double salt of magnesium carbonate and calcium carbonate, and its chemical formula is CaCO ₃ ·MgCO ₃ , which theoretically contains MgO 21.8 %, CaO ₃ 0.4%, and CO ₂ 47.68. Theoretically, the mass ratio of CaO to MgO is 1.39, but the mass ratio of CaO to MgO in most dolomite is 1.4-1.70. Dolomite contains impurities such as A1 ₂ O ₃ , Fe ₂ O ₃ and SiO ₂ , and the color is mostly white and gray. Dolomite is widely distributed in the earth's crust, almost as extensive as limestone , and is available in almost every country. Many countries have large-scale high-quality dolomite mines such as China, Russia, the United States, Canada, France, the United Kingdom, Germany, Austria, Italy and Brazil. There are dolomite mines in almost all provinces of China, and the famous large-scale dolomite mines include Nanjing Dolomite Mine. Most of the dolomite mines produced in the world are used as refractory materials and iron-making fluxes, and dolomite for magnesium smelting accounts for a small portion. The purity of dolomite for magnesium smelting is relatively high. Dolomite can be used as a raw material for smelting magnesium by thermal reduction or as a raw material for smelting magnesium by electrolysis. In the electrolytic method of smelting magnesium, it is necessary to convert MgO in dolomite into electrolytic raw material MgC1 ₂ .
The carnallite is a double salt of magnesium chloride and potassium chloride, and has a chemical formula of KCl·MgCl ₂ ·6H ₂ O, which theoretically contains 34.5% of MgCl ₂ , 26.7% of KCl, and 38.896 of H ₂ O. Natural carnallite contains impurities such as NaCl, NaBr, MgSO ₄ and FeSO ₄ . Pure carnallite is colorless and transparent. It usually has pink or yellowish color due to impurities. The distribution of carnallites is relatively concentrated, and only a few countries have carnallite mines. Russia, Germany, Spain, the United States, the Congo (Brazzaville) and other countries have carnallite mines. The Sorekham mine in Russia is a world-famous large-scale high-quality carnallite mine. China has not found any carnallite mines.
Both the salt lake and the seawater contain MgCl ₂ , which is enriched and decontaminated to become a raw material for magnesium smelting. Seawater contains more than 80 elements, the highest content of which is sodium, followed by magnesium. 1m ³ sea ​​water contains MgCl ₂ 3.8 kg, and the total amount of MgCl _{2 in the} earth Shanghai water is about 7.9×10 ¹⁵ t, so sea water is the largest magnesium resource. The coastline of China is about 18,000km, and the sea water resources are very rich. The salt lake water contains MgCl ₂ 3%-11%. The salt lake is not much on earth. The Great Salt Lake in Utah, USA covers an area of ​​2,890 km ² . The Rowley Magnesium Plant uses magnesium from the Great Salt Lake to make magnesium. The Dead Sea in the Middle East is 75km long, 15km wide and 390m deep. The lake contains 10.1% MgCl ₂ . The Dead Sea Magnesium Plant in Israel uses the Dead Sea Lake water as raw material for magnesium smelting. There are several salt lakes in Russia, the largest of which is the Karapogaz Lake, which is close to the Caspian Sea, with an area of ​​18,000 km ² . China has dozens of Qaidam Basin in Qinghai Salt Lake, MgCl ₂ total reserves of 3.65 billion tons; the largest of which Kranjcar Han Salt Lake area of 5800km ^_2, MgCl ² reserves of 1.62 billion tons. [next]
Magnesium metal was first isolated from magnesium oxide by British H. David in 1808. In 1830, the British M. Faraday electrolytically melted magnesium chloride to produce magnesium. In 1886, the German electrolytic molten magnesium chloride began industrial production of magnesium metal. Later, thermal reduction magnesium smelting was developed. This forms two major methods of industrial production of magnesium metal - molten salt electrolysis and thermal reduction. In the molten salt electrolysis method, the magnesium chloride-containing raw material is purified into anhydrous magnesium chloride or the magnesium-containing raw material is converted into anhydrous magnesium chloride, and the metallic magnesium is electrolyzed in a molten state. Electrolysis method according to the raw materials and the method of preparing anhydrous magnesium chloride is divided into brine dehydration electrolytic magnesium smelting, referred to as brine smelting magnesium; carnallite dehydration electrolytic smelting magnesium, referred to as carnallite smelting magnesium; magnesium oxide chlorination electrolytic magnesium smelting, which Divided into magnesium oxide into spherical chlorinated electrolytic magnesium and magnesite chlorinated electrolytic magnesium. The thermal reduction method is to obtain magnesium metal by reduction and calcination with a reducing agent (CaO·MgO after calcination of dolomite) at a high temperature. The reducing agent used in industrial production is ferrosilicon, also referred to as silicon thermal method. The silicon thermal method is divided into a Pijiang method and a semi-continuous method according to a reduction furnace.
Electrolytic magnesium smelting, low energy consumption, low production cost, suitable for large magnesium plants, most of the world's magnesium is produced by electrolysis. However, the electrolytic magnesium smelting production process is long, the investment in the construction of the plant is large, and the construction area must have sufficient electricity. The sales of Cl2 must be considered. The production process includes Cl ₂ and acidic wastewater, which must be properly disposed to meet environmental protection requirements. Magnesium smelting by thermal reduction method has a wide range of raw materials, short production process, gas, liquid and solid fuels can be used, investment is small, construction is easy, no toxic waste is discharged, and environmental protection conditions are better. However, due to the use of ferrosilicon as a reducing agent, the total energy consumption (including ferrosilicon) is higher.

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