Magnesium in its purest form. Magnesium is an important metal for industry and human life
MAGNESIUM(lat. Magnesium), Mg (read "magnesium"), a chemical element of group IIA of the third period of the periodic system of Mendeleev, atomic number 12, atomic mass 24.305. Natural magnesium consists of three stable nuclides: 24 Mg (78.60% by mass), 25 Mg (10.11%) and 26 Mg (11.29%). The electronic configuration of a neutral atom is 1s 2 2s 2 p 6 3s 2, according to which magnesium in stable compounds is divalent (oxidation state +2). The simple substance magnesium is a light, silvery-white lustrous metal.
Physical and chemical properties: metallic magnesium has a hexagonal crystal lattice. Melting point 650°C, boiling point 1105°C, density 1.74 g/cm 3 (magnesium is a very light metal, only calcium and alkali metals are lighter). The standard electrode potential of magnesium Mg / Mg 2+ is -2.37V. In a series of standard potentials, it is located behind sodium in front of aluminum.
The surface of magnesium is covered with a dense film of MgO oxide, which, under normal conditions, reliably protects the metal from further destruction. Only when the metal is heated to a temperature above about 600°C does it ignite in air. Magnesium burns with the emission of bright light, the spectral composition close to that of the sun. Therefore, in the past, photographers in low light shot in the light of a burning magnesium tape. When magnesium is burned in air, a loose white powder of magnesium oxide MgO is formed:
2Mg + O 2 \u003d 2MgO.
Simultaneously with the oxide, magnesium nitride Mg 3 N 2 is also formed:
3Mg + N 2 \u003d Mg 3 N 2.
Magnesium does not react with cold water (or, more precisely, it reacts, but extremely slowly), but it interacts with hot water, and a loose white precipitate of magnesium hydroxide Mg (OH) 2 is formed:
Mg + 2H 2 O \u003d Mg (OH) 2 + H 2.
If a magnesium strip is set on fire and lowered into a glass of water, then the burning of the metal continues. In this case, the hydrogen released during the interaction of magnesium with water immediately ignites in air. The combustion of magnesium continues in an atmosphere of carbon dioxide:
2Mg + CO 2 \u003d 2MgO + C.
The ability of magnesium to burn both in water and in an atmosphere of carbon dioxide significantly complicates the extinguishing of fires in which structures made of magnesium or its alloys burn.
Magnesium oxide MgO is a white friable powder that does not react with water. It used to be called burnt magnesia or just magnesia. This oxide has basic properties, it reacts with various acids, for example:
MgO + 2HNO 3 \u003d Mg (NO 3) 2 + H 2 O.
The base Mg (OH) 2 corresponding to this oxide is of medium strength, but practically insoluble in water. It can be obtained, for example, by adding alkali to a solution of any magnesium salt:
2NaOH + MgSO 4 \u003d Mg (OH) 2 + Na 2 SO 4.
Since magnesium oxide MgO does not form alkalis when interacting with water, and the magnesium base Mg (OH) 2 does not have alkaline properties, magnesium, unlike its “companions” - calcium, strontium and barium, is not among the alkaline earth metals.
Metal magnesium at room temperature reacts with halogens, for example, with bromine:
Mg + Br 2 \u003d MgBr 2.
When heated, magnesium reacts with sulfur, giving magnesium sulfide:
If a mixture of magnesium and coke is calcined in an inert atmosphere, then magnesium carbide of the composition Mg 2 C 3 is formed (it should be noted that the nearest neighbor of magnesium in the group - calcium - under similar conditions forms a carbide of the composition CaC 2). When magnesium carbide is decomposed with water, an acetylene homologue is formed - propyne C 3 H 4:
Mg 2 C 3 + 4H 2 O \u003d 2Mg (OH) 2 + C 3 H 4.
Therefore, Mg 2 C 3 can be called magnesium propylene.
The behavior of magnesium has similarities with the behavior of the alkali metal lithium (an example of the diagonal similarity of elements in the periodic table). So, magnesium, like lithium, reacts with nitrogen (the reaction of magnesium with nitrogen occurs when heated), resulting in the formation of magnesium nitride:
3Mg + N 2 \u003d Mg 3 N 2.
Like lithium nitride, magnesium nitride is easily decomposed by water:
Mg 3 N 2 + 6H 2 O \u003d 3Mg (OH) 2 + 2NH 3.
Magnesium is also similar to lithium in that its carbonate MgCO 3 and phosphate Mg 3 (PO 4) 2 are poorly soluble in water, as are the corresponding lithium salts.
Magnesium is similar to calcium in that the presence of soluble bicarbonates of these elements in water determines the hardness of water. As with calcium bicarbonate, the hardness caused by magnesium bicarbonate Mg(HCO 3) 2 is temporary. When boiling, magnesium bicarbonate Mg (HCO 3) 2 decomposes and its main carbonate precipitates - magnesium hydroxocarbonate (MgOH) 2 CO 3:
2Mg (HCO 3) 2 \u003d (MgOH) 2 CO 3 + 3CO 2 + H 2 O.
Practical application still has magnesium perchlorate Mg(ClO 4) 2 , which interacts vigorously with water vapor, well drying air or other gas passing through its layer. In this case, a strong crystalline hydrate of Mg(ClO 4) 2 ·6H 2 O is formed. This substance can be dehydrated again by heating in vacuum at a temperature of about 300°C. Magnesium perchlorate was given the name "anhydrone" for its desiccant properties.
Of great importance in organic chemistry are organomagnesium compounds containing the Mg-C bond. A particularly important role among them is played by the so-called Grignard reagent - magnesium compounds of the general formula RMgHal, where R is an organic radical, and Hal \u003d Cl, Br or I. These compounds are formed in ether solutions by the interaction of magnesium and the corresponding organic halide RHal and are used for the most various syntheses.
Opening history: magnesium compounds have been known to man for a long time. The Latin name of the element comes from the name of the ancient city of Magnesia in Asia Minor, in the vicinity of which there are deposits of the mineral magnesite. Metallic magnesium was first obtained in 1808 by the English chemist G. Davy. As in the case of other active metals - sodium, potassium, calcium, Davy used electrolysis to obtain metallic magnesium. He subjected to electrolysis a moistened mixture of white magnesia (its composition, apparently, included magnesium oxide MgO and magnesium hydroxide Mg (OH) 2) and mercury oxide HgO. As a result, Davy received an amalgam - an alloy of a new metal with mercury. After the distillation of mercury, a powder of a new metal remained, which Davy called magnesium.
Magnesium Davy was rather dirty, pure metallic magnesium was obtained for the first time in 1828 by the French chemist A. Bussy.
Finding in nature: magnesium is one of the ten most common elements in the earth's crust (8th place). It contains 2.35% magnesium by weight. Due to the high chemical activity in free form, magnesium does not occur, but is part of many minerals - silicates, aluminosilicates, carbonates, chlorides, sulfates, etc. Thus, magnesium contains widespread silicates olivine (Mg, Fe) 2 and serpentine Mg 6 (OH) 8 . Of great practical importance are such magnesium-containing minerals as asbestos, magnesite, dolomite MgCO 3 CaCO 3, bischofite MgCl 2 6H 2 O, carnallite KCl MgCl 2 6H 2 O, epsomite MgSO 4 7H 2 O, kainite KCl MgSO 4 3H 2 O, astrakhanite Na 2 SO 4 MgSO 4 4H 2 O, etc. Magnesium is found in sea water (4% Mg in the dry residue), in natural brines, and in many underground waters.
Receipt: the usual industrial method for obtaining metallic magnesium is the electrolysis of a melt of a mixture of anhydrous magnesium chlorides MgCl 2 , sodium NaCl and potassium KCl. In this melt, magnesium chloride undergoes electrochemical reduction:
MgCl 2 (electrolysis) \u003d Mg + Cl 2.
The molten metal is periodically taken from the electrolysis bath, and new portions of magnesium-containing raw materials are added to it. Since the magnesium obtained in this way contains a relatively large amount - about 0.1% of impurities, if necessary, "raw" magnesium is subjected to additional purification. For this purpose, electrolytic refining, vacuum remelting with the use of special additives - fluxes, which “take away” impurities from magnesium, or distillation (sublimation) of the metal in vacuum are used. The purity of refined magnesium reaches 99.999% and higher.
Another method for obtaining magnesium has also been developed - thermal. In this case, coke is used to reduce magnesium oxide at high temperature:
MgO + C = Mg + CO
or silicon. The use of silicon makes it possible to obtain magnesium from raw materials such as CaCO 3 ·MgCO 3 dolomite without preliminary separation of magnesium and calcium. With the participation of dolomite, reactions occur:
CaCO 3 MgCO 3 \u003d CaO + MgO + 2CO 2,
2MgO + 2CaO + Si = Ca 2 SiO 4 + 2Mg.
The advantage of the thermal process is that it makes it possible to obtain higher purity magnesium. To obtain magnesium, not only mineral raw materials are used, but also sea water.
Application: the bulk of the mined magnesium is used to produce various light magnesium alloys. The composition of these alloys, in addition to magnesium, includes, as a rule, aluminum, zinc, zirconium. Such alloys are strong enough and are used in aircraft construction, instrument making and for other purposes.
The high chemical activity of metallic magnesium makes it possible to use it in the magnesium-thermal production of metals such as titanium, zirconium, vanadium, uranium, etc. In this case, magnesium reacts with oxide or fluoride of the resulting metal, for example.
The predominant industrial method for obtaining magnesium is the electrolysis of a melt of a mixture of MgCl 2
MgCl 2 Mg 2+ 2Cl -
Mg 2+ +2e Mg 0 2Cl - -2e Cl 2 0
2MgCl 2 2Mg+ 2Cl 2
melt
in anhydrous MgCl 2 , KCl, NaCl. To obtain the melt, dehydrated carnallite or bimophyte is used, as well as MgCl 2 obtained by chlorination of MgO or as a waste in the production of Ti.
Electrolysis temperature 700-720 o C, graphite anodes, steel cathodes. The content of MgCl 2 in the melt is 5-8%, with a decrease in concentration to 4%, the output of magnesium by current decreases, with an increase in the concentration of MgCl 2 above 8%, the consumption of electricity increases. To ensure the optimal content of MgCl 2 periodically select part of the spent electrolyte and add fresh carnallite or MgCl 2 . Liquid magnesium floats to the surface of the electrolyte, from where it is taken with a vacuum ladle. Extracted magnesium raw contains 0.1% impurities. To remove non-metallic impurities, magnesium is melted down with fluxes - chlorides or fluorides K, Ba, Na, Mg. Deep cleaning is carried out by vacuum distillation, zone melting, electrolytic refining. The result is magnesium with a purity of 99.999%.
In addition to magnesium, electrolysis also produces Cl 2 . In thermal methods for producing magnesium, magnesite or dolomite is used as a raw material, from which MgO is obtained by calcination. 2Mg+O 2 =2MgO. In retort or rotary furnaces with graphite or coal heaters, oxide is reduced to metal with silicon (siliconothermal method) or CaC 2 (carbide thermal method) at 1280-1300 ° C, or carbon (carbothermal method) at temperatures above 2100 ° C. In the carbothermic method ( MgO+C Mg+CO) the resulting mixture of CO and magnesium vapor is quickly cooled when leaving the furnace with an inert gas to prevent a back reaction with magnesium.
properties of magnesium.
Physical properties of magnesium.
Magnesium is a silvery-white lustrous metal, relatively soft and ductile, a good conductor of heat and electricity. Almost 5 times lighter than copper, 4.5 times lighter than iron; even aluminum is 1.5 times heavier than magnesium. Magnesium melts at a temperature of 651 o C, but under normal conditions it is quite difficult to melt it: heated in air to 550 o C, it flares up and instantly burns out with a dazzlingly bright flame. A strip of magnesium foil can be easily set on fire with an ordinary match, and in an atmosphere of chlorine, magnesium ignites spontaneously even at room temperature. When burning magnesium, a large amount of ultraviolet rays and heat is released - to heat a glass of ice water to a boil, you need to burn only 4 g of magnesium.
Magnesium is located in the main subgroups of the second group of the D.I. Periodic Table of Elements. Mendeleev. Its serial number is 12, atomic weight is 24.312. The electronic configuration of the magnesium atom in the unexcited state is 1S 2 2S 2 P 6 3S 2 ; the electrons of the outer layer are valence, in accordance with this, magnesium exhibits valency II. In close connection with the structure of the electron shells of the magnesium atom is its reactivity. Due to the presence of only two electrons in the outer shell, the magnesium atom tends to easily donate them to obtain a stable eight-electron configuration; therefore, magnesium is chemically very active.
Magnesium oxidizes in air, but the resulting oxide film protects the metal from further oxidation. The normal electronic potential of magnesium in an acidic environment is -2.37V, in an alkaline - 2.69V. In dilute acids, magnesium dissolves already in the cold. In hydrofluoric acid, it is insoluble due to the formation of a film of MgF 2 fluoride, which is sparingly soluble in water; almost insoluble in concentrated sulfuric acid. Magnesium dissolves easily under the action of solutions of ammonium salts. Alkali solutions do not work on it. Magnesium enters laboratories in the form of powder or tapes. If you set fire to a magnesium tape, it quickly burns out with a blinding flash, developing a high temperature. Magnesium flashes are used in photography, in the manufacture of lighting rockets. The boiling point of magnesium is 1107 o C, density = 1.74 g / cm 3, atomic radius 1.60 NM.
Chemical properties of magnesium.
The chemical properties of magnesium are quite peculiar. It easily removes oxygen and chlorine from most elements, is not afraid of caustic alkalis, soda, kerosene, gasoline and mineral oils. Magnesium almost does not interact with cold water, but when heated, it decomposes with the release of hydrogen. In this respect, it occupies an intermediate position between beryllium, which generally does not react with water, and calcium, which easily interacts with it. The reaction is especially intense with water vapor heated above 380 ° C:
Mg 0 (tv) + H 2 + O (gas) Mg +2 O (tv) + H 2 0 (gas).
Since the product of this reaction is hydrogen, it is clear that extinguishing burning magnesium with water is unacceptable: an explosive mixture of hydrogen and oxygen can form and explode. It is impossible to put out burning magnesium and carbon dioxide: magnesium restores it to free carbon
2Mg 0 +C +4 O 2 2Mg +2 O+C 0 ,
You can stop the access of oxygen to burning magnesium by filling it with sand, although magnesium interacts with silicon (IV) oxide, but with much less heat release:
2Mg 0 + Si +4 O 2 \u003d 2Mg +2 O + Si 0
this determines the possibility of using sand to extinguish silicon. The danger of magnesium igniting during intense heating is one of the reasons why its use as an engineering material is limited.
In the electrochemical series of voltages, magnesium is much to the left of hydrogen and actively reacts with dilute acids to form salts. In these reactions, magnesium has features. It does not dissolve in hydrofluoric, concentrated sulfuric and in a mixture of sulfuric and in a mixture of nitric acids, which dissolves other metals almost as efficiently as "aqua regia" (a mixture of HCl and HNO 3). The stability of magnesium to dissolution in hydrofluoric acid is explained simply: the surface of magnesium is covered with a film of magnesium fluoride MgF 2 insoluble in hydrofluoric acid. The resistance of magnesium to sufficiently concentrated sulfuric acid and its mixture with nitric acid is more difficult to explain, although in this case the reason lies in the passivation of the magnesium surface. Magnesium practically does not interact with solutions of alkalis and ammonium hydroxide. But with solutions of ammonium salts, the reaction, although slowly, but occurs:
2NH + 4 + Mg \u003d Mg 2+ + 2NH 3 + H 2
This reaction is not surprising. This reaction is essentially the same as the reaction of displacement of hydrogen from acids by metals. In one definition, an acid is a substance that dissociates to form hydrogen ions. This is how the NH4 ion can also dissociate:
NH 4 + NH 3 +H +
Mg 0 + 2HCl \u003d Mg +2 Cl 2 + H 0 2
2H + + Mg Mg 2+ + H 0 2
When magnesium is heated in a halogen atmosphere, ignition and the formation of halide salts occur.
The cause of ignition is a very large heat release, as in the case of the reaction of magnesium with oxygen. Thus, in the formation of 1 mol of magnesium chloride from magnesium and chlorine, 642 kJ is released. When heated, magnesium combines with sulfur (MgS), and with nitrogen (Mg 3 N 2). At elevated pressure and heating with hydrogen, magnesium forms magnesium hydride
Mg 0 + H 2 0 Mg +2 H 2 -.
The high affinity of magnesium to chlorine made it possible to create a new metallurgical production - "magnesium" - the production of metals as a result of the reaction
MeCln + 0.5nMg \u003d Me + 0.5nMgCl 2
this method produces metals that play a very important role in modern technology - zirconium, chromium, thorium, beryllium. Lightweight and durable "space age metal" - almost all titanium is obtained in this way.
The essence of production is as follows: in the production of metallic magnesium by electrolysis of a melt of magnesium chloride, chlorine is formed as a by-product. This chlorine is used to obtain titanium (IV) chloride TiCl 4, which is reduced by magnesium to metallic titanium
Ti +4 Cl 4 + 2Mg 0 Ti 0 +2Mg +2 Cl 2
The resulting magnesium chloride is reused for the production of magnesium, etc. Based on these reactions, titanium-magnesium plants work. Along with titanium and magnesium, other products are also obtained, such as Bertolet's salt KClO 3 , chlorine, bromine and products - fiberboard and xylitic plates, which will be discussed below. In such an integrated production, the degree of use of raw materials, the profitability of production is high, and the mass of waste is not large, which is especially important for protecting the environment from pollution.
The name magnesia is found in the Leiden papyrus, which dates back to the third century. Davy in 1808, obtained a small amount of impure magnesium metal by electrolyzing white magnesia. In its pure form, this metal was obtained only in 1829 by Bussy.
The main field of application of magnesium is the use of metal as a lightweight structural material. Alloys of this element are increasingly being used in the automotive, printing, and textile industries. These alloys can be used in the production of car engine cases, chassis and aircraft fuselages. Magnesium is used not only in aviation, it is also used in the manufacture of ladders, cargo platforms, walkways in docks, lifts and conveyors, in the production of optical and photographic equipment.
Magnesium plays an important role in metallurgy. It is used as a reducing agent in the production of some valuable and rare metals - titanium, vanadium, zirconium, chromium. Sources of electric current, created on the basis of magnesium, are distinguished by a rather high value of the specific energy characteristic, high discharge voltages.
Magnesium, as a macroelement, plays a huge role in life, which is manifested in the fact that the element acts as a universal regulator of physiological and biochemical processes in a living organism. Forming reversible bonds with a huge number of organic substances, magnesium provides the ability to metabolize about three hundred enzymes, namely phosphofructokinase, creatine kinase, adenylate cyclase, protein synthesis enzymes, K-Na-ATPase, Ca-ATPase, transmembrane ion transport, glycolysis, and others. Magnesium is also necessary to maintain the structure of nucleic acids, some proteins and ribosomes. The microelement takes part in protein synthesis, oxidative phosphorylation reactions, the formation of energy-rich phosphates, in the exchange of nucleic acids and lipids.
Biological properties
As you know, green leaves of plants contain chlorophylls. They are nothing more than magnesium-containing porphyrin complexes involved in photosynthesis.
Magnesium, among other things, is also very closely involved in the biochemical processes of animal organisms. Enzyme initiation requires magnesium ions, which are responsible for the conversion of phosphates, as well as for the metabolism of carbohydrates and for the transmission of nerve impulses. In addition, they are also involved in the process of muscle contraction, which is initiated by calcium ions.
Magnesium, as a macroelement, plays a huge role in life, which is manifested in the fact that the element acts as a universal regulator of physiological and biochemical processes in a living organism. Forming reversible bonds with a huge number of organic substances, magnesium provides the ability to metabolize about three hundred enzymes, namely phosphofructokinase, creatine kinase, adenylate cyclase, protein synthesis enzymes, K-Na-ATPase, Ca-ATPase, transmembrane ion transport, glycolysis, and others. Magnesium is also necessary to maintain the structure of nucleic acids, some proteins and ribosomes. The microelement takes part in protein synthesis, oxidative phosphorylation reactions, the formation of energy-rich phosphates, in the exchange of nucleic acids and lipids.
Magnesium controls the normal functioning of myocardiocytes. The trace element is of great importance in the regulation of the contractile function of the myocardium. Magnesium is of particular importance in the functioning of the conduction system of the heart and nervous system. A sufficient supply of magnesium to the body contributes to the easy tolerance of stressful situations, as well as the suppression of depression. Magnesium is also very important for the metabolism of sodium, calcium, phosphorus, vitamin C, and potassium. Magnesium interacts well with A-vitamin. So you can see that magnesium monitors the normal functioning of not only individual cells, but also the whole parts of the heart - the ventricles, the atria.
Quite a significant amount of magnesium is found in cereals (coarse flour, wheat bran) and in nuts, apricots, dried apricots, dates, cocoa (powder), plums (prunes). Fish (especially salmon), bread with bran, soybeans, nuts, chocolate, watermelons, fresh fruits (particularly bananas) are also rich in magnesium. Magnesium is found in cereals (buckwheat, oatmeal, millet), legumes (peas, beans), seaweed, squid, eggs, meat, bread (especially coarse rye), herbs (spinach, parsley, lettuce, dill), lemons, grapefruits , almonds, nuts, halva (sunflower and tahini), apples.
The body of a healthy adult contains approximately 140 g of magnesium (which is 0.2% of body weight). The accepted intake of magnesium for adults is 4 mg/kg. On average, this is 350 mg/day for men and 280 mg/day for women. The daily requirement of the human body for magnesium is about 280-500 mg. Magnesium deficiency in the body will be caused by drinking alcohol, hyperthermia, taking diuretic drugs.
Magnesium is non-toxic. The lethal dose has not been determined in humans. As a result of excessive overdoses of magnesium compounds (for example, antacids), there is a risk of poisoning. Upon reaching magnesium concentrations in the blood of 15-18% mg, anesthesia occurs.
If you wish, you can extract magnesium even from ordinary cobblestone: each kilogram of stone that is used for paving roads, the magnesium content is approximately 20 grams. But in such production, however, there is no need yet, because. magnesium, mined from road stone, would become too costly.
In one cubic meter of sea water, the magnesium content is approximately 4 kilograms. In general, more than 6·10 16 tons of this chemical element are dissolved in the waters of the world's oceans.
Approximately 90% of patients who have had a myocardial infarction have magnesium deficiency, which increases in the most acute period of the disease.
During physical exertion, the human body's need for magnesium increases significantly, for example, in athletes during intense and long training, during responsible sports competitions, and in stressful situations. The loss of magnesium by the human body in such situations is comparable to the degree of emotional or physical stress.
To set fire to magnesium, you just need to bring a lit match to it, in an atmosphere of chlorine, magnesium begins to heat up even while maintaining room temperature. When magnesium is burned, a huge amount of heat and ultraviolet rays begin to be released: four grams of this “fuel” is enough to bring a glass of ice water to a boil.
Experiments conducted by Hungarian scientists on animals provided the following information. The lack of magnesium in a living organism increases the creature's predisposition to heart attacks. One part of the dogs was given food that was rich in salts of this element, and the other was poor. At the end of the experiment, dogs that had too little magnesium in their diets were stricken with myocardial infarction.
Magnesium is responsible for protecting the body from the processes associated with aging and disease.
In experiments with wheat crops, it was noted that the influence of psychics contributed to an increase in the amount of magnesium in the seeds.
The more magnesium is contained in the diet, the lower the likelihood of oncological diseases of the colon and rectum. Scientists believe that this microelement is able to act on intestinal cells, while they do not allow them to grow and degenerate.
The ratio of men and women who suffer from magnesium deficiency is 1:3.
Research scientists have shown that daily intake of magnesium in the amount of 500-700 milligrams reduces the level of triglycerides, as well as cholesterol in the blood. The most digestible drug in this area is magnesium glycinate, its absorption is not dependent on the acidity of the stomach, the drug does not cause diarrhea, irritates the intestines.
With magnesium deficiency, the body “takes” the microelement from the bones, which is why after prolonged magnesium deficiency there is a strong deposition of calcium salts on the walls of arterial vessels, in the kidneys and heart muscle.
Story
The name magnesia is found in the Leiden papyrus, which dates back to the third century. The name comes, most likely, from the name of a town in the mountainous landscape of Thessaly, from the city of Magnesia. In ancient times, magnetic iron oxide was called magnesian stone, and a magnet was called magnes. These names eventually passed into Latin and other languages.
Most likely, the external similarity of pyrolusite (manganese dioxide) with magnetic iron oxide led to the fact that magnesian stone, magnetis and magne became the name of minerals and ores of dark brown and dark color, and later other minerals began to be called that.
The word magnes (lat. Magnes) in alchemical literature meant not one, but many substances, for example, Heraclius stone, mercury, Ethiopian stone. Minerals containing magnesium have also been known since ancient times (jade, talc, dolomite, asbestos and others) and already at that time they were widely used.
But they were not considered individual substances, it was believed that these were just modifications of other, much more well-known minerals, and most often lime. Studies of mineral water in the Epsom spring in England, which was discovered in 1618, helped to establish the fact that a special metallic base is present in minerals containing magnesium, as well as salts.
Grew in 1695 from Epsom water, bitter in taste, isolated solid salt, while indicating that this salt, by its nature, is noticeably different from all other salts. In the 18th century, many prominent chemical analysts were engaged in Epsom salt, among them Black, and Bergman, and Neumann, and others. After water sources similar to Epsom were discovered in continental Europe, these studies began to unfold even more widely.
Most likely, it was Neumann who was the first to propose calling Epsom salt (and it was magnesium carbonate) not black (pyrolusite), but white magnesia. The land of white magnesia (At that time the earth is a solid) (or "Magnesia alba"), which had the name of magnesia, appeared in Lavoisier's list of simple bodies, while Lavoisier considered the synonym for this land to be "the base of Epsom salt" (or "base de sel d "Epsom"). In Russian literature of the first half of the 19th century, magnesia was sometimes called bitter earth.
Davy in 1808, obtained a small amount of impure magnesium metal by electrolyzing white magnesia. In its pure form, this metal was obtained only in 1829 by Bussy. At first, Davy suggested calling the new element and the new metal magnesium (lat. Magnium), but by no means magnesia, which in those days meant the metal base of pyrolusite (lat. Magnesium).
However, after the name of black magnesia was changed over time, Davy still preferred to call the metal magnesia again. I would like to note the fact that initially the name "magnesium" survived only in Russian, this happened only thanks to Hess's textbook. Scientists at the beginning of the 19th century proposed several more different variants of the name, for example, magnesia, bitter earth (Shcheglov), magnesia (Fears).
Being in nature
The earth's crust is quite rich in magnesium, the magnesium content in it is more than 2.1% by weight. Only 6 elements of the periodic table of chemical elements of Dmitry Ivanovich Mendeleev are found on our planet more often than magnesium. Magnesium is found in about two hundred minerals. But they get it for the most part from just three - carnallite, magnesite and dolomite.
Magnesium is present in crystalline rocks in the form of insoluble carbonate or sulfate, in addition (but in a much less accessible form) in the form of silicates. The estimation of the total magnesium content depends to a large extent on the geochemical model used in practice, and specifically on the weight ratio of sedimentary and volcanic rocks. At the moment, values of 2% -13.3% are used. Most likely, the value of 2.76% is considered the most acceptable, because it puts magnesium in the sixth most common after calcium, which (4.66%) and before potassium (1.84%) and sodium (2.27%).
The Russian Federation has the richest deposits of magnesite, which are located in the Orenburg region (Khalilovskoye) and in the Middle Urals (Satka deposit). In the area of Solikamsk, the world's largest deposit of one of the most important magnesium minerals, carnallite, is being developed. Dolomite is considered the most common magnesium-containing mineral; it is most often found in the Moscow and Leningrad regions, Donbass, and many other places.
Significant expanses of land, such as the Dolomites in what is now Italy, are composed mostly of a mineral called dolomite MgCa(CO3)2. In such places, one can also meet sedimentary magnesium minerals: carnallite K2MgCl4 6H2O, magnesite MgCO3, langbeinite K2Mg2(SO4)3, epsomite MgSO4 7H2O.
Huge reserves of magnesium are present in the water of the oceans and seas, as well as in the composition of natural brines. In some states, it is these waters that are the most important raw material for the production of magnesium. Among all the metallic elements, magnesium is second only to sodium in terms of content in the water of the seas and oceans. There are approximately four kilograms of magnesium in one cubic meter of sea water. Magnesium is also present in fresh water, along with calcium, which determines its hardness.
The most important types of finding magnesium raw materials are:
- - sea water - (Mg 0.12-0.13%)
- - bischofite - MgCl2. 6H2O (Mg 11.9%)
- - carnallite - MgCl2 KCl 6H2O (Mg 8.7%)
- - brucite - Mg (OH) 2 (Mg 41.6%).
- - epsomite - MgSO4 7H2O (Mg 16.3%)
- - kieserite - MgSO4 H2O (Mg 17.6%)
- - kainite - KCl MgSO4 3H2O (Mg 9.8%)
- - dolomite - CaCO3 MgCO3 (Mg 13.1%)
- - magnesite - MgCO3 (Mg 28.7%)
Magnesian salts are found in huge quantities among the salt deposits of self-sustaining lakes. In many countries, deposits of carnallite are known - fossil sedimentary salts.
Magnesite is predominantly formed under hydrothermal conditions, it belongs to hydrothermal deposits with an average temperature. Dolomite is also a very important magnesium raw material. Dolomite deposits of dolomite are common and their reserves are huge. They are often associated with carbonate strata, most of which are Permian or Precambrian in age. Dolomite deposits are formed by sedimentation, but they can also occur when hydrothermal solutions act on limestones, as well as surface or groundwater.
Types of magnesium deposits
- - Sea water
- - Fossil mineral deposits (potassium-magnesian and magnesian salts)
- - Natural carbonates (magnesite and dolomite)
- - Pickles (brine from salt lakes)
Application
Magnesium is the lightest structural material used on an industrial scale. The density of magnesium (1.7 g/cm3) is less than two-thirds that of aluminium. Magnesium alloys weigh four times less than steel. Among other things, magnesium lends itself well to processing, and can also be cast or reworked by any of the standard metalworking methods (stamping, rolling, drawing, forging, riveting, welding, soldering). That is why the main field of application of magnesium is the use of metal as a lightweight structural material.
The most widely used alloys of magnesium with manganese, aluminum and zinc. Each component of this series makes its own contribution to the general properties of the alloy: zinc and aluminum are able to make the alloy more durable, manganese increases the anti-corrosion properties of the alloy. Magnesium makes the alloy light, parts made of magnesium alloy are 20%-30% lighter than aluminum and 50%-75% lighter than cast iron and steel parts. Alloys of this element are increasingly being used in the automotive, printing, and textile industries.
Magnesium based alloys typically contain more than 90% magnesium, in addition 2% to 9% aluminium, 1% to 3% zinc and 0.2% to 1% manganese. At high temperatures (up to about 450 ° C), the strength of the alloy noticeably improves in the process of alloying with rare earth metals (for example, neodymium and praseodymium) or thorium. These alloys can be used in the production of car engine cases, chassis and aircraft fuselages. Magnesium is used not only in aviation, it is also used in the manufacture of ladders, cargo platforms, walkways in docks, lifts and conveyors, in the production of optical and photographic equipment.
Magnesium alloys are widely used in aircraft construction. Back in 1935, the Sergo Ordzhonikidze aircraft was designed in the Soviet Union, which consisted of almost 80% magnesium alloys. This aircraft successfully withstood all tests, it was operated for a long time in difficult conditions. Nuclear reactors, rockets, engine parts, oil and gasoline tanks, bodies of cars, wagons, buses, wheels, jackhammers, oil pumps, pneumatic drills, cinema and cameras, binoculars - all this is a short list of parts, instruments and assemblies, in the manufacture which use magnesium alloys.
Magnesium plays an important role in metallurgy. It is used as a reducing agent in the production of some valuable and rare metals - titanium, vanadium, zirconium, chromium. If magnesium is introduced into molten cast iron, the cast iron is immediately modified, i.e. its structure improves and mechanical properties increase. Castings can be made from such modified cast iron, which will successfully replace steel forgings. In metallurgy, magnesium is used to deoxidize alloys and steel.
Many magnesium compounds are also widely used, especially its oxide, sulfate and carbonate.
Magnesium in the form of pure metal and its chemical compounds (perchlorate, bromide) are used in the production of very powerful electrical backup batteries (for example, sulfur-magnesium cell, magnesium-perchlorate cell, copper-magnesium chloride cell, magnesium-vanadium cell, lead-magnesium chloride cell , chloride-silver-magnesium element, etc.), as well as dry elements (bismuth-magnesium element, manganese-magnesium element, etc.). Sources of electric current, created on the basis of magnesium, are distinguished by a rather high value of the specific energy characteristic, high discharge voltages. Recently, in a number of states, the problem of creating a rechargeable battery with a long service life has become aggravated. Empirical data allowed us to assert that magnesium provides great prospects for its wide use (availability of raw materials, high energy, environmental friendliness).
Production
Metal magnesium is obtained in two ways: electrolytic and electrothermal (or metallothermic). As the names of the methods imply, an electric current is present in both processes. But in the second case, the role of electricity is reduced only to heating the reaction apparatus, while magnesium oxide, which was obtained from minerals, is reduced by one of the reducing agents, for example, aluminum, coal, silicon. This method is quite promising, in recent years it has been increasingly used. Nevertheless, the first method remains the main industrial method for obtaining magnesium, i.e. electrolytic.
Magnesium is produced in large quantities by electrolysis of a melt of mixtures of magnesium, sodium and potassium chlorides or by silicon-thermal reduction. The electrolytic process uses either anhydrous molten magnesium chloride MgCl2 (at 750°C) or (at a lower temperature) magnesium chloride partially hydrated and isolated from sea water. The percentage of magnesium chloride in this melt is about 5-8%. Along with a decrease in concentration, the output of magnesium by electric current also decreases, with an increase in concentration, the consumption of electricity consumed increases. The process takes place in specially prepared electrolytic baths. Molten magnesium floats to the surface of the bath, and from there it is taken out with a vacuum ladle from time to time, and then magnesium is poured into molds.
After all this, magnesium is purified by remelting with fluxes, as well as by zone melting or sublimation in vacuum. There is a possibility of magnesium in two ways: sublimation in vacuum or remelting and fluxes. The meaning of the latter method is well known: fluxes, i.e. special additives that interact with impurities, as a result, turn them into compounds that are easily separated mechanically from the metal. On a vacuum sublimation, i.e. the first method requires much more advanced equipment, however, using this method, much purer magnesium can be obtained.
Sublimation is carried out in special devices under vacuum, these are steel cylindrical retorts. "Chernovoi", i.e. the metal that has undergone primary processing is placed on the bottom of such a retort, then it is closed, after which the air is pumped out. After that, the lower part of the retort is heated, while the upper part is cooled all the time with the help of outside air. The action of high temperature affects the fact that magnesium begins to sublimate, i.e. to pass into the gaseous state, while the substance bypasses the liquid state. Magnesium vapor rises and begins to condense on the cold walls at the top of the retort. This method makes it possible to obtain especially pure metallic magnesium, the magnesium content of which exceeds 99.99%.
Thermal methods for producing magnesium require dolomite or magnesite as a raw material, from which MgO oxide is obtained by calcination. In rotary or retort furnaces with carbon or graphite heaters, this oxide is reduced by silicon to metal (with the silicothermal method) or to Ca2 (with the carbide-thermal method) at a temperature of 1280-1300 ° C, or with carbon (with the carbothermal method) at a temperature above 2100 ° C . In the last carbothermal process (MgO + C = Mg + CO), a mixture of carbon monoxide and magnesium vapor is formed, which is quickly cooled with an inert gas during its exit from the furnace in order to prevent the reverse reaction of magnesium with carbon monoxide (CO).
Physical Properties
Magnesium is a lustrous, silvery-white metal, ductile and malleable, and comparatively soft. The strength and hardness of magnesium for cast samples are minimal in prevalence, higher for pressed samples. Magnesium is almost five times lighter than copper and four and a half times lighter than iron. Even, as it is called, the “winged” metal aluminum is one and a half times heavier than magnesium.
The melting point of magnesium is not as high as that of some other metals and is only 650 ° C, however, it is quite difficult to melt magnesium under normal conditions: when heated in an air atmosphere to a temperature of 550 ° C, magnesium flares up and immediately burns out with a very bright dazzling flame ( This property of magnesium is very widely used in the manufacture of pyrotechnics). To set fire to this metal, you just need to bring a lit match to it; in an atmosphere of chlorine, magnesium begins to heat up even while maintaining room temperature. When magnesium is burned, a huge amount of heat and ultraviolet rays begin to be released: four grams of this “fuel” is enough to bring a glass of ice water to a boil.
Metallic magnesium has a hexagonal crystal lattice. The boiling point of magnesium is 1105 ° C, the density of the metal is 1.74 g / cm3 (thus, magnesium is a very light metal, lighter than only calcium, as well as alkali metals). Magnesium has a standard electrode potential Mg/Mg2+ of -2.37V. Among a number of standard potentials, it is located in front of aluminum and behind sodium. The atomic radius of magnesium is 1.60Å and the ionic radius is Mg2+ 0.74Å.
The surface of magnesium is always covered with a dense oxide film of MgO oxide, which under normal conditions protects the metal from destruction. Only when heated to temperatures above 600°C does it begin to burn in air. Magnesium burns emitting bright light, which in its spectral composition is close to the sun. That is why photographers in low light used to shoot in the light of burning magnesium tape.
The thermal conductivity of metal at room temperature 20 °C is 156 W/(m.K). Highly pure magnesium is ductile, it is well pressed, the metal is excellent for cutting and rolling. The specific heat capacity of the metal (at room temperature 20 °C) is 1.04 103 J/(kg K), or 0.248 cal/(g °C).
For magnesium, the thermal coefficient of linear expansion (range from 0 to 550 ° C) is determined by the equation 25.0 10-6 + 0.0188 t. The metal has a specific electrical resistance (at room temperature 20 °C) equal to 4.5 10-8 ohm m (4.5 μΩ cm). Magnesium is a paramagnetic metal, its specific magnetic susceptibility is +0.5·10-6.
Magnesium is a relatively ductile and soft metal, the mechanical properties of magnesium are largely dependent on the method of processing this metal. For example, at a room temperature of 20 ° C, the properties of deformed and cast magnesium, respectively, can be characterized by the following indicators: Brinell hardness 35.32 107 n/m2 (30 and 36 kgf/mm2) and 29.43 107, yield strength 8.83 107 n/m2 (2.5 and 9.0 kgf/mm2) and 2.45 107, tensile strength 19.62 107 n/m2 (11.5 and 20.0 kgf/mm2) and 11.28 107, elongation 11.5% and 8.0.
Magnesium vapor pressure (in mm Hg) is:
- - 0.1 (at 510°C)
- - 1 (at 602°C)
- - 10 (at 723°C)
- - 100 (at 892°C)
- - 0.983 (at 25°C)
- - 1.6 (at 100°C)
- - 1.31 (at 650°C)
The standard enthalpy of formation is ΔH (298 K, kJ/mol): 0 (t) and the standard Gibbs energy of formation is ΔG (298 K, kJ/mol): 0 (t). The standard entropy S of formation is (298 K, J/mol K): 32.7 (t), while the standard molar heat capacity of magnesium Cp (298 K, J/mol K) is 23.9 (t). The enthalpy of melting of the metal ΔHm (kJ/mol) is 9.2, and the enthalpy of boiling ΔHboil (kJ/mol) is 131.8.
Chemical properties
The surface of magnesium is always covered with a dense oxide film of MgO oxide, which under normal conditions protects the metal from destruction. Only when heated to temperatures above 600°C does it begin to burn in air. Magnesium burns emitting bright light, which in its spectral composition is close to the sun. That is why photographers in low light used to shoot in the light of burning magnesium tape. During the combustion of magnesium in air, a white loose powder of MgO oxide begins to form:- 2Mg + O2 = 2MgO.
- 3Mg + N2 = Mg3N2.
- Mg + 2H2O = Mg(OH)2 + H2.
- 2Mg + CO2 = 2MgO + C.
The ability of magnesium to continue burning both in an atmosphere of carbon dioxide and in water greatly complicates attempts to extinguish fires in which structures made of magnesium or its alloys begin to burn.
MgO - magnesium oxide, is a loose white powder that does not react with water. Once it was called burnt magnesia or simply magnesia. This oxide has the most important properties, it reacts with a variety of acids, for example:
- MgO + 2HNO3 = Mg(NO3)2 + H2O.
- 2NaOH + MgSO4 = Mg(OH)2 + Na2SO4.
Because magnesium oxide in interaction with water does not form alkalis, and the base Mg (OH) 2 does not have alkaline properties, magnesium does not belong to alkaline earth metals, in contrast to such elements of its group as calcium, strontium barium.
Metallic magnesium reacts with halogens at room temperature, such as bromine:
- Mg + Br2 = MgBr2.
- Mg + S = MgS.
- Mg2C3 + 4Н2О = 2Mg(OH)2 + С3Н4.
That is why Mg2C3 is often referred to as magnesium propylene.
The behavior of magnesium has similar features with the behavior of such an alkali metal as lithium (for example, the diagonal similarity of elements in the table of Dmitry Ivanovich Mendeleev). Both magnesium and lithium react with nitrogen (magnesium reacts with nitrogen after heating), and the result is the formation of magnesium nitride:
- 3Mg + N2= Mg3N2.
- Mg3N2 + 6H2O \u003d 3Mg (OH) 2 + 2NH3.
In magnesium, the similarity with lithium is also manifested in the fact that magnesium carbonate MgCO3 and magnesium phosphate Mg3 (PO4) 2 in water are poorly soluble, just like lithium salts corresponding to these compounds.
Magnesium brings calcium closer to the fact that the presence of soluble bicarbonates of these elements in water affects the hardness of water. The hardness caused by Mg(HCO3)2 - magnesium bicarbonate is temporary. In the process of boiling, magnesium bicarbonate decomposes, as a result of which its main carbonate - (MgOH) 2CO3 - magnesium hydroxocarbonate precipitates:
- 2Mg(HCO3)2 = (MgOH)2CO3 + 3CO2 + H2O
Magnesium - (lat. Magnesium), Mg (read "magnesium"), a chemical element of group IIA of the third period of the Mendeleev periodic system, atomic number 12, atomic mass 24.305. Natural magnesium consists of three stable nuclides: 24 Mg (78.60% by mass), 25 Mg (10.11%) and 26 Mg (11.29%). The electronic configuration of a neutral atom is 1s 2 2s 2 2p 6 3s 2, according to which magnesium in stable compounds is divalent (oxidation state +2). Magnesium belongs to the alkaline earth metals.
The history of the discovery of magnesium
Magnesium compounds have been known to man for a long time. The Latin name of the element comes from the name of the ancient city of Magnesia in Asia Minor, in the vicinity of which there are deposits of the mineral magnesite.
In the 17th century a new period began in the history of chemical science. It was during this period that a discovery occurred that largely anticipated the discovery of the element magnesium. In 1695, N. Gro, evaporating the mineral water of the Epsom spring (England), obtained a salt that had a bitter taste and a laxative effect. A few years later, it turned out that when interacting with “permanent alkali” (as soda and potash were called in those days), this salt forms a white friable powder. Exactly the same powder was obtained by calcining a mineral found in the vicinity of the Greek city of Magnesia. For this similarity, Epsom salt is called white magnesia.
In 1808, Humphry Davy, by electrolysis of slightly moistened white magnesia with mercury oxide, obtained an amalgam of a new metal, which was soon isolated from it and named magnesium. True, the magnesium received by Davy was contaminated with impurities; the first truly pure magnesium was obtained by A. Bussy in 1829
Finding magnesium in natureThe earth's crust is rich in magnesium - it contains more than 2.1% of this element. Only six elements of the periodic table are found on Earth more often than magnesium. It is part of almost two hundred minerals. But they get it mainly from three - magnesite, dolomite and carnallite.
Large amounts of magnesium are found in sea water. The main types of finding magnesian raw materials are:
- sea water - (Mg 0.12-0.13%),
- carnallite - MgCl 2 KCl 6H 2 O (Mg 8.7%),
- bischofite - MgCl 2 6H 2 O (Mg 11.9%),
- kieserite - MgSO 4 H 2 O (Mg 17.6%),
- epsomite - MgSO 4 7H 2 O (Mg 16.3%),
- kainite - KCl MgSO 4 3H 2 O (Mg 9.8%),
- magnesite - MgCO 3 (Mg 28.7%),
- dolomite - CaCO 3 MgCO 3 (Mg 13.1%),
- brucite - Mg (OH) 2 (Mg 41.6%).
Magnesian salts are found in large quantities in the salt deposits of self-sustaining lakes. Deposits of fossil salts of carnallite of sedimentary origin are known in many countries.
Magnesite is formed predominantly under hydrothermal conditions and belongs to medium-temperature hydrothermal deposits. Dolomite is also an important magnesium raw material. Dolomite deposits are widespread, their reserves are huge. They are associated with carbonate strata and most of them are of Precambrian or Permian age. Dolomite deposits are formed by sedimentation, but can also occur when limestone is exposed to hydrothermal solutions, groundwater or surface water.
Magnesium is found in the following types of deposits:- Fossil mineral deposits (magnesian and potassium-magnesian salts)
- Sea water
- Pickles (brine of salt lakes)
- Natural carbonates (dolomite and magnesite)
Metal is obtained in two ways - electrothermal (or metallothermic) and electrolytic. As the names suggest, both processes involve electricity. But in the first case, its role is reduced to heating the reaction apparatus, and magnesium oxide obtained from minerals is reduced with some kind of reducing agent, such as coal, silicon, aluminum. This method is quite promising, in recent years it has been increasingly used. However, the main industrial method for obtaining magnesium is the second, electrolytic.
The electrolyte is a melt of anhydrous chlorides of Mg, potassium and sodium; metallic magnesium is released on the iron cathode, and chloride ions are discharged on the graphite anode. The process takes place in special electrolytic baths. The molten magnesium floats to the surface of the bath, from where it is taken from time to time with a vacuum ladle and then poured into molds.
But the process does not end there: there are still too many impurities in such magnesium.
Therefore, the second stage is inevitable - the purification of magnesium. Magnesium can be refined in two ways - by remelting and fluxing or by sublimation in a vacuum. The meaning of the first method is well known: special additives - fluxes - interact with impurities and turn them into compounds that are easy to separate from the metal mechanically. The second method - vacuum sublimation - requires more sophisticated equipment, but it produces more pure magnesium. Sublimation is carried out in special vacuum apparatus - steel cylindrical retorts. The "draft" metal is placed at the bottom of the retort, it is closed and the air is pumped out. Then the lower part of the retort is heated, while the upper part is constantly cooled by outside air. Under the action of high temperature, magnesium sublimates - it passes into a gaseous state, bypassing the liquid state. Its vapor rises and condenses on the cold walls of the upper part of the retort.
In this way, a very pure metal containing over 99.99% magnesium can be obtained.
Physical Properties magnesiumThe metal is 5 times lighter than copper, 4.5 times lighter than iron; even aluminum is 1.5 times heavier than magnesium.
Magnesium is a silver-white metal with a hexagonal lattice (a=3.21 Å c=5.21 Å). Under normal conditions, the surface of magnesium is covered with a strong protective film of magnesium oxide MgO, which is destroyed when heated in air to about 600 ° C, after which the metal burns with a dazzling white flame to form magnesium oxide and nitride Mg 3 N 2 .
The density of magnesium at 20 ° C is 1.74 g / cm³, the melting point of the metal t pl \u003d 650 ° C, the boiling point is t kip \u003d 1105 ° C, thermal conductivity at 20 ° C is 156 W / (m K). High purity magnesium is ductile, well pressed, rolled and machinable.
When burning magnesium, a large amount of ultraviolet rays and heat is released - to heat a glass of ice water to a boil, you need to burn only 4 g of magnesium.
Magnesium is explosive and flammable
Working with magnesium alloys sometimes causes a lot of trouble - magnesium is easily oxidized. Melting and casting of these alloys have to be carried out under a layer of slag - otherwise the molten metal may catch fire from contact with air.
When grinding or polishing magnesium products, a dust extraction device must be installed above the machine, because the smallest particles of magnesium sprayed in the air create an explosive mixture.
However, this does not mean that any work with magnesium is fraught with the danger of fire or explosion. Magnesium can be ignited only by melting it, but it is not so easy to do this under normal conditions - the high thermal conductivity of the alloy will not allow a match or even a torch to turn cast products into white oxide powder. But with shavings or a thin tape of magnesium, you really need to handle it very carefully.
Chemical properties of magnesiumThe chemical properties of magnesium are quite peculiar. It easily removes oxygen and chlorine from most elements, is not afraid of caustic alkalis, soda, kerosene, gasoline and mineral oils. At the same time, it does not tolerate the action of sea and mineral water at all and quickly dissolves in them. Almost without reacting with cold fresh water, it vigorously displaces hydrogen from hot water.
A mixture of powdered magnesium with potassium permanganate KMnO 4 - explosive
Hot magnesium reacts with water:
Mg (decay) + H 2 O \u003d MgO + H 2;
Alkalis do not act on magnesium, it dissolves easily in acids with the release of hydrogen:
Mg + 2HCl \u003d MgCl 2 + H 2;
When heated in air, magnesium burns to form an oxide; a small amount of nitride can also form with nitrogen:
2Mg + O 2 \u003d 2MgO;
3Mg + N 2 \u003d Mg 3 N 2
Since magnesium oxide MgO does not form alkali when interacting with water, and the magnesium base Mg (OH) 2 does not have alkaline properties, magnesium, unlike its “companions” - calcium, strontium and barium, is not among the alkaline earth metals.
Metal magnesium at room temperature reacts with halogens, for example, with bromine:
Mg + Br 2 \u003d MgBr 2.
When heated, magnesium reacts with sulfur, giving magnesium sulfide:
If a mixture of magnesium and coke is calcined in an inert atmosphere, then magnesium carbide of the composition Mg 2 C 3 is formed (it should be noted that the nearest neighbor of magnesium in the group - calcium - under similar conditions forms a carbide of the composition CaC2). When magnesium carbide is decomposed with water, an acetylene homologue is formed - propyne C 3 H 4:
Mg 2 C 3 + 4H 2 O \u003d 2Mg (OH) 2 + C 3 H 4.
Therefore, Mg 2 C 3 can be called magnesium propylene.
The behavior of magnesium has similarities with the behavior of the alkali metal lithium (an example of the diagonal similarity of elements in the periodic table). So, magnesium, like lithium, reacts with nitrogen (the reaction of magnesium with nitrogen occurs when heated), resulting in the formation of magnesium nitride:
3Mg + N 2 \u003d Mg 3 N 2.
Like lithium nitride, magnesium nitride is easily decomposed by water:
Mg 3 N 2 + 6H 2 O \u003d 3Mg (OH) 2 + 2NH 3.
Magnesium is also similar to lithium in that its carbonate MgCO 3 and phosphate Mg 3 (PO 4) 2 are poorly soluble in water, as are the corresponding lithium salts.
Magnesium is similar to calcium in that the presence of soluble bicarbonates of these elements in water determines the hardness of water. As with calcium bicarbonate, the hardness caused by magnesium bicarbonate Mg(HCO3) 2 is temporary. When boiling, magnesium bicarbonate Mg (HCO 3) 2 decomposes and its main carbonate precipitates - magnesium hydroxocarbonate (MgOH) 2 CO 3:
2Mg (HCO 3) 2 \u003d (MgOH) 2 CO 3 + 3CO 2 + H 2 O.
Magnesium perchlorate Mg(ClO 4) 2, which interacts vigorously with water vapor, well drying air or other gas passing through its layer. In this case, a strong crystalline hydrate of Mg(ClO 4) 2 ·6H 2 O is formed. This substance can be dehydrated again by heating in vacuum at a temperature of about 300°C. Magnesium perchlorate was given the name "anhydrone" for its desiccant properties.
The effect of magnesium on the human bodyMagnesium is one of the important biogenic elements found in significant quantities in the tissues of animals and plants. Magnesium is a cofactor in many enzymatic reactions. Magnesium is necessary for the conversion of creatine phosphate into ATP - a nucleotide that is a universal energy supplier in living cells of the body. Therefore, magnesium is the element that controls the energy of the body. Magnesium is essential at all stages of protein synthesis. It has also been established that 80-90% of modern people suffer from magnesium deficiency. This can manifest itself in many ways: insomnia, chronic fatigue, osteoporosis, arthritis, fibromyalgia, migraine, muscle cramps and spasms, cardiac arrhythmia, constipation, premenstrual syndrome (PMS) and other symptoms and illnesses. And with frequent use of laxatives, alcohol, great mental and physical stress, the need for magnesium increases.
Statistics say that residents of areas with a warmer climate experience spasms of blood vessels less often than northerners. Medicine explains this by the nutritional characteristics of both. After all, it is known that intravenous and intramuscular infusions of solutions of certain magnesium salts relieve spasms and convulsions. Fruits and vegetables help to accumulate in the body the necessary supply of these salts. Apricots, peaches and cauliflower are especially rich in magnesium. There is it in ordinary cabbage, potatoes, tomatoes.
According to the results of recent studies, magnesium citrate is found to be the most digestible magnesium-containing product.
The body needs magnesium to absorb calcium. One of the most biologically appropriate sources of magnesium for transcutaneous (percutaneous) absorption is the mineral bischofite, which is widely used for medical rehabilitation, physiotherapy and spa treatment.
A few years ago, scientists at the University of Minnesota in the United States chose eggshells as the object of scientific research. They were able to establish that the shell is stronger, the more magnesium it contains. This means that by changing the composition of the feed for laying hens, it is possible to increase the strength of the shell.
French biologists believe that magnesium will help physicians in the fight against such a serious illness of the 20th century as overwork. Studies show that the blood of tired people contains less magnesium than healthy people, and even the most insignificant deviations of “magnesium blood” from the norm do not pass without a trace.
It is important to remember that in cases where a person is often and for any reason irritated, the magnesium contained in the body “burns out”. That is why in nervous, easily excitable people, disturbances in the functioning of the heart muscles are observed much more often.
Magnesium(lat. Magnesium), Mg, a chemical element of group II of the Mendeleev periodic system, atomic number 12, atomic mass 24.305. Natural Magnesium consists of three stable isotopes: 24 Mg (78.60%), 25 Mg (10.11%) and 26 Mg (11.29%). Magnesium was discovered in 1808 by G. Davy, who subjected moistened magnesia (a long-known substance) to electrolysis with a mercury cathode; Davy received an amalgam, and from it, after distillation of mercury, a new powdered metal called magnesium. In 1828, the French chemist A. Bussy, by reducing molten magnesium chloride with potassium vapor, obtained magnesium in the form of small balls with a metallic sheen.
Distribution of magnesium in nature. Magnesium is a characteristic element of the Earth's mantle; its ultramafic rocks contain 25.9% by weight. Magnesium is less in the earth's crust, its average clarke is 1.87%; Magnesium predominates in basic rocks (4.5%), in granites and other acidic rocks it is less (0.56%). In magmatic processes, Mg 2+ is an analogue of Fe 2+, which is explained by the proximity of their ionic radii (0.74 and 0.80 Å, respectively). Mg 2+ together with Fe 2+ is a part of olivine, pyroxenes and other igneous minerals.
Magnesium minerals are numerous - silicates, carbonates, sulfates, chlorides and others. More than half of them were formed in the biosphere - at the bottom of the seas, lakes, in soils, etc.; the rest are associated with high-temperature processes.
Vigorous migration and differentiation of Magnesium is observed in the biosphere; here the main role belongs to physicochemical processes - dissolution, precipitation of salts, sorption of magnesium by clays. Magnesium is slightly retained in the biological cycle on the continents and enters the ocean with river runoff. In sea water, on average, 0.13% Magnesium is less than sodium, but more than all other metals. Sea water is not saturated with Magnesium and precipitation of its salts does not occur. When water evaporates in marine lagoons, magnesium sulfates and chlorides accumulate in sediments along with potassium salts. Dolomite accumulates in the silts of some lakes (for example, in Lake Balkhash). In industry, magnesium is obtained mainly from dolomites, as well as from sea water.
Physical properties of magnesium. Compact Magnesium is a lustrous silvery-white metal that tarnishes in air due to the formation of an oxide film on the surface. Magnesium crystallizes in a hexagonal lattice, a = 3.2028Å, c = 5.1998Å. Atomic radius 1.60Å, ionic radius Mg 2+ 0.74Å. The density of Magnesium is 1.739 g / cm 3 (20 ° C); t pl 651 °C; t kip 1107 °C. Specific heat capacity (at 20 °C) 1.04 10 3 J/(kg K), i.e. 0.248 cal/(g °C); thermal conductivity (20 ° C) 1.55 10 2 W / (m K), that is, 0.37 cal / (cm sec ° C); the thermal coefficient of linear expansion in the range of 0-550 ° C is determined from the equation 25.0 10 -6 + 0.0188 t. Electrical resistivity (20 °C) 4.5·10 -8 ohm·m (4.5 μΩ·cm). Magnesium is paramagnetic, specific magnetic susceptibility is +0.5·10 -6, Magnesium is a relatively soft and ductile metal; its mechanical properties are highly dependent on the processing method. For example, at 20 ° C, the properties of cast and deformed Magnesium, respectively, are characterized by the following values: Brinell hardness 29.43 10 7 and 35.32 10 7 n / m 2 (30 and 36 kgf / mm 2), yield strength 2, 45 10 7 and 8.83 10 7 n / m 2 (2.5 and 9.0 kgf / mm 2), tensile strength 11.28 10 7 and 19.62 10 7 n / m 2 (11 .5 and 20.0 kgf / mm 2), elongation 8.0 and 11.5%.
Chemical properties of magnesium. The configuration of the outer electrons of the magnesium atom is 3s 2 . In all stable compounds, magnesium is bivalent. Chemically, magnesium is a very active metal. Heating to 300-350 °C does not lead to significant oxidation of compact Magnesium, since its surface is protected by an oxide film, but at 600-650 °C Magnesium ignites and burns brightly, giving magnesium oxide and partly Mg 3 N 2 nitride. The latter is also obtained by heating Magnesium to about 500 °C in a nitrogen atmosphere. With cold water, not saturated with air, magnesium almost does not react, slowly displacing hydrogen from boiling water; the reaction with steam starts at 400°C. Molten Magnesium in a humid atmosphere, releasing hydrogen from H 2 O, absorbs it; when the metal solidifies, hydrogen is almost completely removed. In a hydrogen atmosphere, magnesium forms MgH 2 at 400-500 ° C.
Magnesium displaces most metals from aqueous solutions of their salts; the standard electrode potential of Mg at 25 °C is 2.38 V. Magnesium reacts with dilute mineral acids in the cold, but does not dissolve in hydrofluoric acid due to the formation of a protective film of insoluble MgF 2 fluoride. In concentrated H 2 SO 4 and its mixture with HNO 3 Magnesium is practically insoluble. Magnesium does not interact with aqueous solutions of alkalis in the cold, but dissolves in solutions of alkali metal bicarbonates and ammonium salts. Caustic alkali precipitates magnesium hydroxide Mg(OH) 2 from salt solutions, the solubility of which in water is negligible. Most magnesium salts are highly soluble in water, such as magnesium sulfate, slightly soluble MgF 2 , MgCO 3 , Mg 3 (PO 4) 2 and some double salts.
When heated, magnesium reacts with halogens to give halides; with wet chlorine, MgCl 2 is formed already in the cold. When magnesium is heated to 500-600 ° C with sulfur or with SO 2 and H 2 S, MgS sulfide can be obtained, with hydrocarbons - MgC 2 and Mg 2 C 3 carbides. Silicides Mg 2 Si, Mg 3 Si 2, phosphide Mg 3 P 2 and other binary compounds are also known. Magnesium is a strong reducing agent; when heated, it displaces other metals (Be, Al, alkali) and non-metals (B, Si, C) from their oxides and halides. Magnesium forms numerous organometallic compounds, which determine its great role in organic synthesis. Magnesium alloys with most metals and is the basis for many technically important light alloys.
Getting Magnesium. In industry, the largest amount of Magnesium is obtained by electrolysis of anhydrous MgCl 2 chloride or dehydrated carnallite KCl MgCl 2 6H 2 O. The electrolyte also contains Na, K, Ca chlorides and a small amount of NaF or CaF 2 . The content of MgCl 2 in the melt is not less than 5-7%; as the electrolysis proceeds at 720-750 ° C, the composition of the bath is adjusted by removing part of the electrolyte and adding MgCl 2 or carnallite. Cathodes are made of steel, anodes are made of graphite. Molten Magnesium, which floats to the electrolyte surface, is periodically removed from the cathode space, which is separated from the anode space by a partition that does not reach the bottom of the bath. The composition of crude Magnesium includes up to 2% impurities; it is refined in crucible electric furnaces under a layer of flux and poured into molds. The best grades of primary Magnesium contain 99.8% Mg. The subsequent purification of Magnesium is carried out by vacuum sublimation: 2-3 sublimations increase the purity of Magnesium to 99.999%. Anode chlorine after purification is used to obtain anhydrous MgCl 2 from magnesite, titanium tetrachloride TiCl 4 from TiO 2 oxide and other compounds.
Other methods of obtaining Magnesium are metal-thermal and carbon-thermal. According to the first, briquettes from calcined to complete decomposition of dolomite and a reducing agent (ferrosilicon or silicoaluminum) are heated at 1280-1300 ° C in vacuum (residual pressure 130-260 N/m 2 , i.e. 1-2 mm Hg). Magnesium vapor condenses at 400-500 °C. For purification, it is melted down under a flux or in a vacuum, after which it is poured into molds. According to the carbon-thermal method, briquettes from a mixture of coal with magnesium oxide are heated in electric furnaces above 2100 ° C; Magnesium vapor is distilled off and condensed.
The use of magnesium. The most important field of application of metallic magnesium is the production of alloys based on it. Magnesium is widely used in metallothermic processes for obtaining hard-to-recover and rare metals (Ti, Zr, Hf, U and others), Magnesium is used for deoxidation and desulfurization of metals and alloys. Mixtures of magnesium powder with oxidizing agents serve as lighting and incendiary compositions. Magnesium compounds are widely used.
Magnesium in the body. Magnesium is a constant part of plant and animal organisms (in thousandths - hundredths of a percent). Magnesium concentrators are some algae that accumulate up to 3% Magnesium (in ash), some foraminifera - up to 3.5%, calcareous sponges - up to 4%. Magnesium is part of the green pigment of plants - chlorophyll (the total mass of chlorophyll of Earth's plants contains about 100 billion tons of Magnesium), and is also found in all cell organelles of plants and ribosomes of all living organisms. Magnesium activates many enzymes, together with calcium and manganese, it ensures the stability of the structure of chromosomes and colloidal systems in plants, and is involved in maintaining turgor pressure in cells. Magnesium stimulates the intake of phosphorus from the soil and its absorption by plants; in the form of a salt of phosphoric acid, it is part of phytin. Magnesium deficiency in soils causes marbling of leaves in plants, plant chlorosis (in such cases, magnesium fertilizers are used). Animals and humans get Magnesium from food. Daily human need for Magnesium - 0.3-0.5 g; in childhood, as well as during pregnancy and lactation, this need is higher. The normal content of Magnesium in the blood is approximately 4.3 mg%; with an increased content, drowsiness, loss of sensitivity, and sometimes paralysis of skeletal muscles are observed. In the body, magnesium accumulates in the liver, then a significant part of it passes into the bones and muscles. In muscles, magnesium is involved in the activation of anaerobic carbohydrate metabolism. Antagonist of magnesium in the body is calcium. Violation of the magnesium-calcium balance is observed in rickets, when magnesium passes from the blood into the bones, displacing calcium from them. Lack of magnesium salts in food disrupts the normal excitability of the nervous system, muscle contraction. Cattle with a lack of magnesium in feed become ill with the so-called herbal tetany (muscle twitching, stunting of the limbs). Magnesium metabolism in animals is regulated by the parathyroid hormone, which lowers the magnesium content in the blood, and prolane, which increases the magnesium content. Of the magnesium preparations in medical practice, they use: magnesium sulfate (as a sedative, anticonvulsant, antispasmodic, laxative and choleretic agent), burnt magnesia (magnesium oxide) and magnesium carbonate (as an alkali, a mild laxative).
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