Manganese is an important metal with a wide range of applications. Potassium permanganate

Manganese is a chemical element found in periodic system Mendeleev under atomic number 25. Its neighbors are chromium and iron, which causes the similarity of physical and chemical properties these three metals. Its nucleus contains 25 protons and 30 neutrons. Atomic mass element is 54.938.

properties of manganese

Manganese is a transition metal from the d-family. Its electronic formula is as follows: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 . The hardness of manganese on the Mohs scale is estimated at 4. The metal is quite hard, but, at the same time, brittle. Its thermal conductivity is 0.0782 W / cm * K. The element is characterized by a silvery-white color.

There are four known to man, metal modifications. Each of them is characterized by thermodynamic stability under certain temperature conditions. So, a-manganese has a rather complex structure and shows its stability at temperatures below 707 0 C, which determines its fragility. This modification of the metal in its elementary cell contains 58 atoms.

Manganese can have completely different oxidation states - from 0 to +7, while +1 and +5 are extremely rare. When the metal interacts with air, it is passivated. Powdered manganese burns in oxygen:

Mn+O2=MnO2

If the metal is exposed to elevated temperature, i.e. heated, then it will decompose into water with the displacement of hydrogen:

Mn+2H0O=Mn(OH)2+H2

It should be noted that manganese hydroxide, the layer of which is formed as a result of the reaction, slows down the reaction process.

Hydrogen is absorbed by the metal. The higher the temperature rises, the higher becomes its solubility in manganese. If the temperature is exceeded by 12000C, then manganese reacts with nitrogen, as a result of which nitrites are formed, which have a different composition.

The metal also interacts with carbon. The result of this reaction is the formation of carbides, as well as silicides, borides, phosphides.

The metal is resistant to alkaline solutions.

It is able to form the following oxides: MnO, Mn 2 O 3 , MnO 2 , MnO 3 , the last of which has not been isolated in the free state, as well as manganese anhydride Mn 2 O 7 . At normal conditions existence of manganese anhydride is a liquid oily substance of a dark green color, which does not have special stability. If the temperature is raised to 90 0 C, then the anhydride decomposition is accompanied by an explosion. Among the oxides that show the greatest stability, Mn 2 O 3 and MnO 2 are distinguished, as well as the combined oxide Mn 3 O 4 (2MnO·MnO 2, or salt Mn 2 MnO 4).

Manganese oxides:

During the fusion of pyrolusite and alkalis with the presence of oxygen, a reaction occurs with the formation of manganates:

2MnO 2 + 2KOH + O 2 \u003d 2K 2 MnO 4 + 2H 2 O

The manganate solution is characterized by a dark green color. If it is acidified, then the reaction proceeds with tinting the solution in a crimson color. This is due to the formation of the MnO 4 − anion, from which a precipitate of manganese oxide-hydroxide precipitates, which has a brown color.

Permanganic acid is strong, but does not show particular stability, and therefore, its maximum permissible concentration is no more than 20%. The acid itself, like its salts, acts as a strong oxidizing agent.

Salts of manganese do not show stability. Its hydroxides have a characteristic basic character. Manganese chloride decomposes when exposed to it high temperatures. It is this scheme that is used to obtain chlorine.

Application of manganese

This metal is not scarce - it belongs to common elements: its content in the earth's crust is 0.03% of total atoms. He is ranked third among heavy metals, which include all elements of the transition series, skipping ahead of iron and titanium. Heavy metals are those whose atomic weight exceeds 40.

Manganese can be found in trace amounts in some rocks. Basically, localization of its oxygen compounds in the form of pyrolusite mineral - MnO 2 occurs.

Manganese has many uses. It is necessary for the production of many alloys and chemical substances. Without manganese, the existence of living organisms is impossible, as it acts as an active trace element, and is also present in almost all living and plant organisms. Manganese has a positive effect on the processes of hematopoiesis in living organisms. It is also found in many foods.

Metal is an indispensable element in metallurgy. It is manganese that is used to remove sulfur and oxygen from steel during its production. This process requires large volumes of metal. But it is worth saying that not pure manganese is added to the melt, but its alloy with iron, called ferromanganese. It is obtained in the process of the reduction reaction of pyrolusite with coal. Manganese also acts as an alloying element for steels. Thanks to the addition of manganese to steels, their wear resistance is significantly increased, and they also become less susceptible to mechanical stress. The presence of manganese in the composition of non-ferrous metals significantly increases their strength and resistance to corrosion.

Metal dioxide has found its application in the oxidation of ammonia, and it is also a participant in organic reactions and decomposition reactions of inorganic salts. In this case, manganese dioxide acts as a catalyst.

The ceramic industry also does not do without the use of manganese, where MnO 2 is used as a black and dark brown dye for enamels and glazes. Manganese oxide is highly dispersed. It has a good adsorbing capacity, due to which it becomes possible to remove harmful impurities from the air.

Manganese is introduced into bronze and brass. Some metal compounds are used in fine organic synthesis and industrial organic synthesis. Manganese arsenide is characterized by a gigantic magnetocaloric effect, which becomes much stronger when subjected to high pressure. Manganese telluride acts as a promising thermoelectric material.

In medicine, it is also appropriate to use manganese, or rather its salts. So, an aqueous solution of potassium permanganate is used as an antiseptic, and they can also wash wounds, gargle, lubricate ulcers and burns. In some poisonings with alkaloids and cyanides, its solution is even indicated for oral administration.

Important: Despite great amount positive aspects of the use of manganese, in some cases, its compounds can adversely affect the human body and even have a toxic effect. Thus, the maximum allowable concentration of manganese in the air is 0.3 mg/m 3 . In the case of pronounced poisoning with a substance, the human nervous system is affected, for which the syndrome of manganese parkinsonism is characteristic.

Obtaining manganese

Metal can be obtained in several ways. Among the most popular methods are the following:

aluminothermic. Manganese is obtained from its oxide Mn 2 O 3 by a reduction reaction. The oxide, in turn, is formed during pyrolusite calcination:

4MnO 2 \u003d 2Mn 2 O 3 + O 2

Mn 2 O 3 + 2Al \u003d 2Mn + Al 2 O 3

restorative. Manganese is obtained by reducing the metal with coke from manganese ores, resulting in the formation of ferromanganese (an alloy of manganese and iron). This method is the most common, since the bulk of the total metal production is used during the production of various alloys, the main component of which is iron, in connection with this, manganese is not extracted from ores in pure form, and in an alloy with it;
electrolysis. The pure metal is obtained by this method from its salts.

Designation - Mn (Manganese);
Period - IV;
Group - 7 (VIIb);
Atomic mass - 54.938046;
Atomic number - 25;
Radius of an atom = 127 pm;
Covalent radius = 117 pm;
Electron distribution - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2 ;
t melting = 1244°C;
boiling point = 1962°C;
Electronegativity (according to Pauling / according to Alpred and Rochov) = 1.55 / 1.60;
Oxidation state: +7, +6, +5, +4, +3, +2, +1, 0;
Density (n.a.) \u003d 7.21 g / cm 3;
Molar volume = 7.35 cm 3 / mol.

Manganese compounds:

Pyrolusite (manganese mineral) has been known to people since ancient times, it was used by our ancestors to lighten glass obtained by melting. Until 1774, pyrolusite was considered a type of magnetic iron ore. And only in 1774, the Swede K. Scheele guessed that pyrolusite contained a metal unknown to science at that time, after which Yu. Gan obtained metallic manganese by heating pyrolusite in a coal stove. Manganese got its name at the beginning of the 19th century (from the German Manganerz - manganese ore).

Manganese ranks 14th among all chemical elements distribution in the earth's crust. Most manganese is found in basic rocks. Independent deposits of manganese are extremely rare; more often this metal accompanies iron in many of its ores. Quite a lot of manganese is contained in iron-manganese nodules located in the bottom of the oceans.

Minerals rich in manganese:

pyrolusite - MnO 2 n H2O
manganite - MnO(OH)
manganese spar - MnCO 3
brownite - 3Mn 2 O 3 MnSiO 3

Rice. The structure of the manganese atom.

The electronic configuration of the manganese atom is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2 (see Electronic structure of atoms). In the formation of chemical bonds with other elements, 2 electrons located at the outer 4s level + 5 electrons of the 3d sublevel (7 electrons in total) can participate, therefore manganese can take oxidation states from +7 to +1 in compounds (the most common are +7 , +2). Manganese is chemically active metal. Similar to aluminum at room temperature, it reacts with oxygen contained in atmospheric air, with the formation of a strong protective oxide film, which prevents further oxidation of the metal.

Physical properties of manganese:

silver-white metal;
solid;
fragile at n. y.

Four modifications of manganese are known: α-form; β-form; γ form; δ-form.

Up to 710°C, the α-form is stable, which, upon further heating, successively passes through all modifications to the δ-form (1137°C).

Chemical properties of manganese

manganese (powder) easily reacts with oxygen, forming oxides, the type of which depends on the reaction temperature:
- 450°C - MnO 2 ;
- 600°C - Mn 2 O 3 ;
- 950°C - Mn 3 O 4 ;
- 1300°C - MnO.
finely divided manganese, when heated, reacts with water to release hydrogen:
Mn + 2H 2 O \u003d Mn (OH) 2 + H 2;
manganese (powder) when heated, reacts with nitrogen, carbon, sulfur, phosphorus:
Mn + S = MnS;
actively reacts with dilute hydrochloric and sulfuric acids with the release of hydrogen:
Mn + 2HCl \u003d MnCl 2 + H 2;
reacts with dilute nitric acid:
3Mn + 8HNO 3 \u003d 3Mn (NO 3) 2 + 2NO + 4H 2 O.

The use and production of manganese

Obtaining manganese:

pure manganese is obtained by electrolysis of aqueous solutions of MnSO 4 with the addition of (NH 4) 2 SO 4 at pH=8-8.5: anode - lead; cathode - stainless steel (manganese flakes are removed from the cathodes);
less pure manganese is obtained from its oxides by metallothermic methods:
- aluminothermy:
  4Al + 3MnO 2 = 3Mn + 2Al 2 O 3;
- siliconthermia:
  Si + MnO 2 \u003d Mn + SiO 2.

Application of manganese:

in metallurgy, manganese is used to bind sulfur and oxygen:
Mn + S = MnS; 2Mn + O 2 \u003d 2MnO;
as an alloying additive in the smelting of various alloys (manganese gives corrosion resistance, toughness, hardness):
- manganin- an alloy of manganese with copper and nickel;
- ferromanganese- an alloy of manganese with iron;
- manganese bronze- an alloy of manganese with copper.
Potassium permanganate has long been used as an antiseptic agent that acts only on the surface of the skin and mucous membranes.

The biological role of manganese:

Manganese is one of the ten "metals of life" necessary for the normal functioning of animal and plant cells.

The body of an adult contains about 12 mg of manganese, which is involved in the formation of protein complexes, and is also part of some nucleic acids, amino acids, enzymes (arginase and cholinesterase).

Manganese, along with magnesium, is involved in the activation of ATP hydrolysis, thereby ensuring the energy vitality of a living cell.

Manganese ions are involved in the activation of nuclease - this enzyme is necessary for the decomposition of nucleic acids to nucleotides.

Manganese is found in all types of steel and cast iron. The ability of manganese to produce alloys with most known metals is used to obtain not only various grades of manganese steel, but also a large number of non-ferrous alloys (manganines). Of these, alloys of manganese with copper (manganese bronze) are especially remarkable. It, like steel, can be hardened and at the same time magnetized, although neither manganese nor copper show noticeable magnetic properties.

Manganese in the form of ferromanganese is used to "deoxidize" steel during its melting, that is, to remove oxygen from it. In addition, it binds sulfur, which also improves the properties of steels. The introduction of up to 12-13% Mn into steel (the so-called Hadfield Steel), sometimes in combination with other alloying metals, greatly strengthens the steel, makes it hard and resistant to wear and impact (this steel is sharply hardened and becomes harder on impact). Such steel is used for the manufacture of ball mills, earth-moving and stone-crushing machines, armor elements, etc. Up to 20% Mn is introduced into "mirror cast iron".

An alloy of 83% Cu, 13% Mn, and 4% Ni (manganin) has a high electrical resistance that changes little with temperature. Therefore, it is used for the manufacture of rheostats, etc.

According to the standards adopted in our country, all steel alloying elements have their own letter. So, the steel grade containing silicon necessarily includes the letter C, chromium is denoted by the letter X, nickel is denoted by the letter H, vanadium is denoted by the letter F, tungsten is denoted by the letter B, aluminum is denoted by the letter Y, molybdenum is denoted by the letter M. Manganese is assigned the letter G. Only carbon does not have a letter, and for most steels, the numbers at the beginning of the grade indicate its content, expressed in hundredths of a percent. If there are no numbers behind the letter, it means that the element indicated by this letter is contained in steel in an amount of about 1%. Let us decipher, for example, the composition of structural steel 30KhGS: the indices show that it contains 0.30% carbon, 1% chromium, 1% manganese and 1% silicon.

Manganese is usually introduced into steel along with other elements - chromium, silicon, tungsten. However, there is steel, which, apart from iron, manganese and carbon, contains nothing. This is the so-called Hadfield steel. It contains 1...1.5% carbon and 11...15% manganese. Steel of this brand has great wear resistance and hardness. It is used to make crushers that grind the most hard rocks, details of excavators and bulldozers. The hardness of this steel is such that it cannot be machined; parts from it can only be cast.

The use of manganese for the purification of metal from sulfur.

Sulfur is an element, of course, useful. But not for metallurgists. Getting into cast iron and steel, it becomes almost the most harmful impurity. Sulfur actively reacts with iron, and FeS sulfide lowers the melting point of the metal. Because of this, during rolling, gaps and cracks appear on the hot metal.

In metallurgical production, sulfur removal is entrusted to blast furnace workers. "Bind", turn into a fusible compound and remove sulfur from the metal is easiest in a reducing atmosphere. It is this atmosphere that is created in a blast furnace. But sulfur is also introduced into the metal during blast-furnace smelting along with coke, which usually contains 0.7 ... 2% sulfur. Cast iron produced in our country should contain no more than 0.05% sulfur, and at advanced plants this limit has been reduced to 0.035% or even less.

Manganese is introduced into the blast mine precisely in order to remove sulfur from pig iron. The affinity for sulfur in manganese is greater than that of iron. Element No. 25 forms with it a strong low-melting sulfide MnS. Sulfur bound by manganese turns into slag. This method of cleaning cast iron from sulfur is simple and reliable.

The ability of manganese to bind sulfur, as well as its analogue - oxygen, is widely used in steel production. Even in the last century, metallurgists learned how to melt "mirror" cast iron from manganese iron ore. This cast iron, containing 5 ... 20% manganese and 3.5 ... 5.5% carbon, has a remarkable property: if it is added to liquid steel, then oxygen and sulfur are removed from the metal. The inventor of the first converter, G. Bessemer, used mirror cast iron to deoxidize and carburize steel.

In 1863, the production of ferromanganese, an alloy of manganese with iron, was organized at the Fonica plant in Glasgow. The content of element No. 25 in such an alloy is 25 ... 35%. Ferromanganese turned out to be a better deoxidizer than mirror cast iron. Steel, clad with ferromanganese, becomes flexible and elastic.

Now ferromanganese containing 75...80% Mn is being produced. This alloy is smelted in blast and electric arc furnaces and is widely used for the production of manganese steels, which are still to be discussed.

Manganese is introduced into bronze and brass.

A significant amount of manganese dioxide is consumed in the production of manganese-zinc galvanic cells, MnO2 is used in such cells as an oxidizing agent-depolarizer.

Manganese compounds are also widely used both in fine organic synthesis (MnO2 and KMnO4 as oxidizing agents) and industrial organic synthesis (components of hydrocarbon oxidation catalysts, for example, in the production of terephthalic acid by oxidation of p-xylene, oxidation of paraffins to higher fatty acids).

Manganese arsenide has a gigantic magnetocaloric effect (increasing under pressure). Manganese telluride is a promising thermoelectric material (thermo-emf with 500 μV/K).

Interesting properties have an alloy called normal manganin, containing 11-13% manganese, 2.5-3.5% nickel and 86% copper. Characterized by high electrical resistance and low thermal electromotive force paired with copper, this alloy is especially suitable for the manufacture of resistance coils. The ability of manganin to change resistance depending on the pressure under which the alloy is located is used in the manufacture of electrical pressure gauges. Indeed, how to measure pressure, for example, in 15-25-30 thousand atmospheres? No ordinary pressure gauge can withstand such pressure. The liquid or gas escapes through the walls of the tube, no matter how strong they are, with the force of an explosion. Sometimes it is not even possible to find micro-holes through which the contents of the manometric tube break through. In these cases, manganin is indispensable. measuring electrical resistance manganin, which is under a determined pressure, it is possible to calculate the latter with any degree of accuracy from a pre-drawn graph of the dependence of resistance on pressure.

Of the manganese compounds that have found application in practical activities man, one should point to manganese dioxide and potassium permanganate (potassium permanganate), the best known, especially among physicians, under the name "potassium permanganate". Manganese dioxide is used in galvanic cells of the Leclanchet type, in the production of chlorine, in the preparation of catalytic mixtures (hopcalite in gas masks). Potassium permanganate is widely used in medicine as an antiseptic for washing wounds, lubricating burns, etc., for washing the stomach in case of poisoning with phosphorus, alkaloids, hydrocyanic acid salts. Potassium permanganate is also widely used in chemistry for analytical studies, obtaining chlorine, oxygen, etc.

However, manganese improves the properties of not only iron. Thus, manganese-copper alloys have high strength and corrosion resistance. Turbine blades are made from these alloys, and aircraft propellers and other aircraft parts are made from manganese bronzes.

The use of manganese dioxide and potassium permanganate

Manganese dioxide is used as a catalyst in ammonia oxidation processes, organic reactions, and decomposition reactions of inorganic salts. In the ceramics industry, MnO2 is used to color black and dark brown enamels and glazes. Highly dispersed MnO2 has a good adsorbing capacity and is used to purify the air from harmful impurities.

Potassium permanganate is used for bleaching linen and wool, bleaching process solutions, as an oxidizing agent for organic substances.

Some salts of manganese are used in medicine. For example, potassium permanganate is used as an antiseptic in the form aqueous solution, for washing wounds, gargling, lubricating ulcers and burns. A solution of KMnO4 is also used orally in some cases of poisoning with alkaloids and cyanides. Manganese is one of the most active trace elements and is found in almost all plant and living organisms. It improves the processes of hematopoiesis in organisms.

Manganese fertilizers are manganese slags containing up to 15% manganese, as well as manganese sulfate. But the most widely used is manganese superphosphate containing about 2-3% manganese.

Microfertilizers are also used in the form of foliar dressings, spraying plants with an appropriate solution or soaking seeds in it before sowing.

Manganese compounds used in many industries can have toxic effect on the body. Entering the body mainly through Airways, Manganese accumulates in parenchymal organs (liver, spleen), bones and muscles and is excreted slowly over many years. The maximum permissible concentration of manganese compounds in the air is 0.3 mg/m3. In case of severe poisoning, damage is observed nervous system with the characteristic syndrome of manganese parkinsonism. Treatment: vitamin therapy, anticholinergics and others. Prevention: observance of the rules of occupational health.

Prices for metallic manganese in ingots with a purity of 95% in 2006 averaged $2.5 per kg. In 2010, a kilogram of metal cost $4-4.5

In the general structure of manganese consumption, over 90% of it is used in ferrous metallurgy for steelmaking in the form of various manganese ferroalloys, as well as in the form of metallic manganese of technical purity (96-99% Mn). The average consumption of manganese in ferrous metallurgy is 7-9 kg per 1 ton of steel. A wide variety of steel grades and alloys necessitates the production of manganese and manganese ferroalloys of a wide range. The standard for metallic manganese and manganese alloys is based on carbon content, while low carbon alloys also have a low phosphorus content. The silicomanganese standard is based on silicon content, and alloys richer in silicon are characterized by lower carbon and phosphorus content. The content of phosphorus and sulfur in ferromanganese is strictly limited. The most common manganese alloys are as follows:

Ferromanganese:

carbon ferromanganese FMn75 and FMn78 (the numbers in the brand indicate the percentage of manganese) contains > 70% Mn and< 7% С;

medium-carbon ferromanganese FMn1.0, FMn1.5 and FMn2.0 (the numbers in the grade indicate the percentage of carbon) contains > 85% Mn and, accordingly,< 1,0; 1,5 и 2,0 %С;

low-carbon ferromanganese FMn 0.5 (> 85% Mn,< 0,5 %С).

Silicomanganese grades SMn10, SMn14, SMn17, SMn20 and SMn26 (numbers indicate the silicon content in percent), the manganese content in hard grade silicomanganese is > 60%.

Metal manganese - contains 95.0 - 99.85% Mn and 0.04 - 0.20% C. Phosphorus content< 0,01 % для Мр00 и Мр0 и 0,07 % для остальных марок. Выплавляется следующие марки металлического марганца:

Electrothermal Mr2, Mr1, Mr1C;

Electrolytic Mr0, Mr00.

Nitrided metallic manganese containing 2-6% nitrogen.

Ferromanganese is used for deoxidation of boiling and calm steel of almost all grades, as well as for alloying some grades of special steel. For deoxidation of boiling steel, carbon ferromanganese with a normal or reduced silicon content is used, for deoxidation of calm steel, carbon ferromanganese or silicomanganese is used. Special steel is alloyed with carbon or low-carbon ferromanganese or metallic manganese.

In medicine, some manganese salts (for example, KMnO4) are used as disinfectants.