Manganese as a chemical element. Interaction with others. Chemical properties of manganese

Chemistry of metals

Lecture 2

Metals of VIIB-subgroup

General characteristics of metals of the VIIB-subgroup.

Chemistry of manganese

Natural Mn compounds

Physical and chemical properties of metal.

Mn compounds. The redox properties of the compound

Brief description of Tc and Re.

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Metals of VIIB-subgroup

general characteristics

						The VIIB subgroup is formed by d-elements: Mn, Tc, Re, Bh.
						Valence electrons are described by the general formula:
						(n–1)d 5 ns2
							Simple substances - metals, silver grey,
			manganese
						heavy, with high melting points, which
						increase during the transition from Mn to Re, so that
						the fusibility of Re is second only to W.
							Mn is of the greatest practical importance.
			technetium				Elements Tc, Bh - radioactive elements, artificial
						directly obtained as a result of nuclear fusion; Re-
						rare item.
							The elements Tc and Re are more similar to each other than
						with manganese. Tc and Re have a more stable higher
						oxidation stump, so these elements are common
						compounds in oxidation state 7 are strange.
							Mn is characterized by oxidation states: 2, 3, 4,
							More stable -				2 and 4. These oxidation states

appear in natural compounds. The most

strange minerals Mn: pyrolusite MnO2 and rhodochrosite MnCO3.

Mn(+7) and (+6) compounds are strong oxidizers.

The greatest similarity of Mn, Tc, Re is highly oxidized

tion, it is expressed in the acidic nature of higher oxides and hydroxides.

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The higher hydroxides of all elements of the VIIB subgroup are strong

acids with the general formula HEO4.

In the highest degree of oxidation, the elements Mn, Tc, Re show similarities with the element of the main subgroup chlorine. Acids: HMnO4 , HTcO4, HReO4 and

HClO4 are strong. The elements of the VIIB-subgroup are characterized by a noticeable

similarity with its neighbors in the series, in particular, Mn shows similarity with Fe. In nature, Mn compounds always coexist with Fe compounds.

Marganese

Characteristic oxidation states

			Valence electrons Mn - 3d5 4s2 .
			Most Common Degrees
	3d5 4s2	manganese	the oxidations at Mn are 2, 3, 4, 6, 7;
			more stable - 2 and 4. In aqueous solutions
			oxidation state +2 is stable in acidic, and +4 - in

neutral, slightly alkaline and slightly acidic environment.

Mn(+7) and (+6) compounds exhibit strong oxidizing properties.

The acid–base character of oxides and hydroxides of Mn is naturally

varies depending on the oxidation state: in the +2 oxidation state, the oxide and hydroxide are basic, and in the highest oxidation state, they are acidic,

moreover, HMnO4 is a strong acid.

In aqueous solutions, Mn(+2) exists in the form of aquacations

2+ , which for simplicity denote Mn2+ . Manganese in high oxidation states is in solution in the form of tetraoxoanions: MnO4 2– and

MnO4 - .

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Natural compounds and metal production

The element Mn is most abundant in the earth's crust among heavy metals.

The catch follows iron, but is noticeably inferior to it: the content of Fe is about 5%, and Mn is only about 0.1%. In manganese, oxide-

nye and carbonate and ores. Minerals are of the greatest importance: pyrolu-

zit MnO2 and rhodochrosite MnCO3 .

to get Mn

In addition to these minerals, hausmannite Mn3 O4 is used to obtain Mn

and hydrated psilomelane oxide MnO2. xH2 O. In manganese ores, all

Manganese is mainly used in the production of special grades of steels with high strength and impact resistance. Therefore, os-

a new amount of Mn is obtained not in pure form, but in the form of ferromanganese

tsa - an alloy of manganese and iron containing from 70 to 88% Mn.

The total volume of the annual world production of manganese, including in the form of ferromanganese, ~ (10 12) million tons/year.

To obtain ferromanganese, manganese oxide ore is reduced

coal.

MnO2 + 2C = Mn + 2CO

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Together with Mn oxides, Fe oxides contained in ru-

de. To obtain manganese with a minimum content of Fe and C, compounds

Fe is preliminarily separated and mixed oxide Mn3 O4 is obtained

(MnO . Mn2 O3 ). It is then reduced with aluminum (pyrolusite reacts with

Al is too violent).

3Mn3 O4 + 8Al = 9Mn + 4Al2 O3

Pure manganese is obtained by hydrometallurgical method. After preliminary preparation of the MnSO4 salt, through a solution of Mn sulfate,

start an electric current, manganese is reduced at the cathode:

Mn2+ + 2e– = Mn0 .

simple substance

Manganese is a light gray metal. Density - 7.4 g / cm3. Melting point - 1245O C.

	It is a fairly active metal, E(Mn		/ Mn) \u003d - 1.18 V.
		It is easily oxidized to the Mn2+ cation in dilute
		ny acids.
		Mn + 2H+ = Mn2+ + H2
		Manganese is passivated in concentrated
		nitric and sulfuric acids, but when heated
	Rice. Manganese - se-	begins to interact with them slowly, but
	rye metal, similar	even under the influence of such strong oxidizing agents
	for iron
		Mn goes into a cation

Mn2+ . When heated, powdered manganese interacts with water with

release of H2.

Due to oxidation in air, manganese becomes covered with brown spots,

In an oxygen atmosphere, manganese forms an oxide

Mn2 O3, and at a higher temperature mixed oxide MnO. Mn2O3

(Mn3 O4 ).

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When heated, manganese reacts with halogens and sulfur. Affinity Mn

to sulfur more than iron, so when adding ferromanganese to steel,

sulfur dissolved in it binds to MnS. Sulfide MnS does not dissolve in the metal and goes into the slag. The strength of steel after the removal of sulfur, which causes brittleness, increases.

At very high temperatures (>1200 0 C), manganese, interacting with nitrogen and carbon, forms non-stoichiometric nitrides and carbides.

Manganese compounds

Manganese compounds (+7)

All Mn(+7) compounds exhibit strong oxidizing properties.

Potassium permanganate KMnO 4 - the most common compound

Mn(+7). In its pure form, this crystalline substance is dark

purple. When crystalline permanganate is heated, it decomposes

		2KMnO4 = K2 MnO4 + MnO2 + O2
		This reaction can be obtained in the laboratory
		Anion MnO4 - stains solutions of permanent
		ganata in raspberry-violet color. On the
		surfaces in contact with the solution
Rice. The KMnO4 solution is pink		KMnO4, due to the ability of permanganate to oxidize
purple		pour water, thin yellow-brown
		MnO2 oxide films.
	4KMnO4 + 2H2O = 4MnO2 + 3O2 + 4KOH

To slow down this reaction, which is accelerated by light, KMnO4 solutions are stored

yat in dark bottles.

When adding a few drops of concentrated

sulfuric acid, permanganic anhydride is formed.

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2KMnO4 + H2 SO4 2Mn2 O7 + K2 SO4 + H2 O

Oxide Mn 2 O 7 is a heavy oily liquid of dark green color. This is the only metal oxide that, under normal conditions, is

ditsya in a liquid state (melting point 5.9 0 C). The oxide has a mole-

cular structure, very unstable, at 55 0 C it decomposes with an explosion. 2Mn2O7 = 4MnO2 + 3O2

Oxide Mn2 O7 is a very strong and energetic oxidizing agent. Many or-

organic substances are oxidized under its influence to CO2 and H2 O. Oxide

Mn2 O7 is sometimes called chemical matches. If a glass rod is soaked in Mn2 O7 and brought to a spirit lamp, it will light up.

When Mn2 O7 is dissolved in water, permanganic acid is formed.

HMnO 4 acid is a strong acid, exists only in water

nom solution, was not isolated in the free state. Acid HMnO4 decomposes -

Xia with the release of O2 and MnO2.

When a solid alkali is added to a solution of KMnO4, the formation of

green manganate.

4KMnO4 + 4KOH (c) = 4K2 MnO4 + O2 + 2H2 O.

When KMnO4 is heated with concentrated hydrochloric acid, it forms

Cl2 gas is present.

2KMnO4 (c) + 16HCl (conc.) = 2MnCl2 + 5Cl2 + 8H2 O + 2KCl

In these reactions, the strong oxidizing properties of permanganate are manifested.

The products of the interaction of KMnO4 with reducing agents depend on the acidity of the solution in which the reaction takes place.

In acidic solutions, a colorless Mn2+ cation is formed.

MnO4 – + 8H+ +5e–  Mn2+ + 4H2 O; (E0 = +1.53 V).

A brown precipitate of MnO2 precipitates from neutral solutions.

MnO4 – +2H2 O +3e–  MnO2 + 4OH– .

In alkaline solutions, the green anion MnO4 2– is formed.

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Potassium permanganate is commercially obtained either from manganese

(oxidizing it at the anode in an alkaline solution), or from pyrolusite (MnO2 pre-

oxidized to K2 MnO4, which is then oxidized to KMnO4 at the anode).

Manganese compounds (+6)

Manganates are salts with the anion MnO4 2– , have a bright green color.

The anion MnO4 2─ is stable only in strongly alkaline media. Under the action of water and, especially, acid, manganates disproportionate to form compounds

of Mn in oxidation states 4 and 7.

3MnO4 2– + 2H2 O= MnO2 + 2MnO4 – + 4OH–

For this reason, the acid H2 MnO4 does not exist.

Manganates can be obtained by fusing MnO2 with alkalis or carbonate-

mi in the presence of an oxidizing agent.

2MnO2 (c) + 4KOH (l) + O2 = 2K2 MnO4 + 2H2 O

Manganates are strong oxidizing agents , but if they are affected

with an even stronger oxidizing agent, they turn into permanganates.

Disproportionation

Manganese compounds (+4)

is the most stable Mn compound. This oxide is found in nature (the mineral pyrolusite).

MnO2 oxide is a black-brown substance with a very strong crystalline

cal lattice (same as that of rutile TiO2). For this reason, despite the fact that MnO 2 is amphoteric, it does not react with alkali solutions and dilute acids (just like TiO2). It dissolves in concentrated acids.

MnO2 + 4HCl (conc.) = MnCl2 + Cl2 + 2H2 O

The reaction is used in the laboratory to produce Cl2.

When MnO2 is dissolved in concentrated sulfuric and nitric acid, Mn2+ and O2 are formed.

Thus, in a very acidic environment, MnO2 tends to go into

Mn2+ cation.

MnO2 reacts with alkalis only in melts with the formation of mixed

ny oxides. In the presence of an oxidizing agent, manganates are formed in alkaline melts.

MnO2 oxide is used in industry as a cheap oxidizing agent. In particular, redox interaction

2 decomposes with the release of O2 and forms

oxidation of Mn2 O3 and Mn3 O4 oxides (MnO. Mn2 O3 ).

Hydroxide Mn (+4) is not isolated, during the reduction of permanganate and man-

ganate in neutral or slightly alkaline media, as well as during oxidation

Mn (OH) 2 and MnOOH from solutions a dark brown precipitate of hydrated

of MnO2.

Mn(+3) oxide and hydroxide have a basic character. These are solid

brown, insoluble in water and unstable substances.

When interacting with dilute acids, they disproportionate

they form Mn compounds in oxidation states 4 and 2. 2MnOOH + H2 SO4 = MnSO4 + MnO2 + 2H2 O

They react with concentrated acids in the same way as

MnO2 , i.e. in an acidic medium, they transform into the Mn2+ cation. In an alkaline environment, they are easily oxidized in air to MnO2.

Manganese compounds (+2)

In aqueous solutions, Mn(+2) compounds are stable in an acidic environment.

Oxide and hydroxide Mn (+2) are basic, easily soluble

ionize in acids to form a hydrated Mn2+ cation.

MnO oxide - gray-green refractory crystalline compound

(melting point - 18420 C). It can be obtained by decomposing kar-

bonate in the absence of oxygen.

MnCO3 = MnO + CO2.

MnO does not dissolve in water.

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This element, in the form of pyrolusite (manganese dioxide, MnO 2 ), was used by prehistoric cave artists at the Lascaux Caves, France, as early as 30,000 years ago. In more recent times in ancient Egypt, glass makers used minerals containing this metal to remove the pale greenish tint of natural glass.

Excellent Ores were found in the region of Magnesia, which is in northern Greece, south of Macedonia, and that's when the confusion with the name began. Various ores from the region that included both magnesium and manganese were simply referred to as magnesia. In the 17th century, the term magnesia alba or white magnesia was adopted for magnesium minerals, while the name black magnesia was used for the darker oxides of manganese.

By the way, the famous magnetic minerals found in this region were called magnesia stone, which eventually became today's magnet. The confusion continued for some time until, at the end of the 18th century, a group of Swedish chemists concluded that manganese was a separate element. In 1774, a member of the group presented these findings to the Stockholm Academy, and in the same year, Johan Gottlieb Hahn, became the first person to obtain pure manganese and proved that it is a separate element.

Manganese - chemical element, characteristics of manganese

It is a heavy, silvery-white metal that slowly darkens in the open air. Harder, and more brittle than iron, it has a specific gravity of 7.21 and a melting point of 1244°C. Chemical symbol Mn, atomic weight 54.938, atomic number 25. In formulas read as manganese, for example, KMnO 4 - potassium manganese about four. This is a very common element in rocks, its amount is estimated at 0.085% of the mass of the earth's crust.

There are over 300 different minerals, containing this element. Large terrestrial deposits are found in Australia, Gabon, South Africa, Brazil and Russia. But even more are found on the ocean floor, mostly at depths of 4 to 6 kilometers, so mining there is not commercially viable.

Oxidized iron minerals (hematite, magnetite, limonite and siderite) contain 30% of this element. Another potential source is clay and red mud deposits, which contain nodules up to 25%. The purest manganese obtained by electrolysis of aqueous solutions.

Manganese and chlorine are in group VII of the periodic table, but chlorine is in the main subgroup, and manganese is in the side group, which also includes technetium Tc and rhenium Ke - complete electronic analogues. Manganese Mn, technetium Ts and rhenium Ke are complete electronic analogs with the configuration of valence electrons.

This element is present in small quantities and in agricultural soils. In many alloys of copper, aluminum, magnesium, nickel, its various percentages give them specific physical and technological properties:

• wear resistance;
• heat resistance;
• resistance to corrosion;
• fusibility;
• electrical resistance, etc.

Valencies of manganese

The oxidation states of manganese are from 0 to +7. In the divalent oxidation state, manganese has a distinctly metallic character and a high tendency to form complex bonds. In tetravalent oxidation, an intermediate character between metallic and non-metallic properties prevails, while hexavalent and heptavalent have non-metallic properties.

Oxides:

Formula. Colour

Biochemistry and pharmacology

Manganese is an element widely distributed in nature, it is present in most tissues of plants and animals. The highest concentrations are found:

• in orange peel;
• in grapes;
• in berries;
• in asparagus;
• in crustaceans;
• in gastropods;
• in double doors.

One of the most important reactions in biology, photosynthesis, is completely dependent on this element. It is the star player in the reaction center of photosystem II, where water molecules are converted into oxygen. Without it, photosynthesis is impossible..

It is an essential element in all known living organisms. For example, the enzyme responsible for converting water molecules into oxygen during photosynthesis contains four manganese atoms.

The average human body contains about 12 milligrams of this metal. We get about 4 milligrams every day from foods like nuts, bran, cereals, tea, and parsley. This element makes the bones of the skeleton more durable. It is also important for the absorption of vitamin B1.

Benefits and harmful properties

This trace element, is of great biological importance: it acts as a catalyst in the biosynthesis of porphyrins, and then hemoglobin in animals and chlorophyll in green plants. Its presence is also a necessary condition for the activity of various mitochondrial enzyme systems, some lipid metabolism enzymes, and oxidative phosphorylation processes.

Vapors or drinking water contaminated with salts of this metal leads to irritative changes in the respiratory tract, chronic intoxication with a progressive and irreversible tendency, characterized by damage to the basal ganglia of the central nervous system, and then a violation of the extrapyramidal type similar to Parkinson's disease.

Such poisoning is often professional character. It affects workers employed in the processing of this metal and its derivatives, as well as workers in the chemical and metallurgical industries. In medicine, it is used in the form of potassium permanganate as an astringent, local antiseptic, and also as an antidote for alkaloid nature poisons (morphine, codeine, atropine, etc.).

Some soils have low levels of this element, so it is added to fertilizers and given as a food supplement for grazing animals.

Manganese: application

As a pure metal, with the exception of limited use in the field of electrical engineering, this element has no other practical applications, while at the same time it is widely used for the preparation of alloys, steel production, etc.

When Henry Bessemer invented the process of making steel in 1856, his steel was destroyed by hot rolling. The problem was solved in the same year when it was discovered that adding small amounts of this element to molten iron solved the problem. Today, in fact, about 90% of all manganese is used for steel production.

True, empirical, or gross formula: Mn

Molecular weight: 54.938

Manganese- an element of a side subgroup of the seventh group of the fourth period of the periodic system of chemical elements of D. I. Mendeleev with atomic number 25. It is designated by the symbol Mn (lat. Manganum, manganum, in Russian formulas it is read as manganese, for example, KMnO 4 - potassium manganese o four). The simple substance manganese (CAS number: 7439-96-5) is a silver-white metal. Along with iron and its alloys, it belongs to ferrous metals. Five allotropic modifications of manganese are known - four with a cubic and one with a tetragonal crystal lattice.

Discovery history

One of the main minerals of manganese - pyrolusite - was known in antiquity as black magnesia and was used in glass melting to clarify it. It was considered a kind of magnetic iron ore, and the fact that it is not attracted by a magnet, Pliny the Elder explained by the female sex of black magnesia, to which the magnet is “indifferent”. In 1774, the Swedish chemist K. Scheele showed that the ore contained an unknown metal. He sent samples of the ore to his friend, the chemist Yu. Gan, who, by heating pyrolusite with coal in an oven, obtained metallic manganese. At the beginning of the 19th century, the name "manganum" was adopted for it (from the German Manganerz - manganese ore).

Distribution in nature

Manganese is the 14th most abundant element on Earth, and after iron, it is the second heavy metal contained in the earth's crust (0.03% of the total number of atoms in the earth's crust). The weight content of manganese increases from acid (600 g/t) to basic rocks (2.2 kg/t). It accompanies iron in many of its ores, but there are also independent deposits of manganese. Up to 40% of manganese ores are concentrated in the Chiatura deposit (Kutaisi region). Manganese, dispersed in rocks, is washed out by water and carried away to the oceans. At the same time, its content in sea water is insignificant (10−7-10−6%), and in deep places of the ocean its concentration increases to 0.3% due to oxidation by oxygen dissolved in water with the formation of water-insoluble manganese oxide, which in hydrated form (MnO2 xH2O) and sinks into the lower layers of the ocean, forming the so-called iron-manganese nodules at the bottom, in which the amount of manganese can reach 45% (they also contain impurities of copper, nickel, cobalt). Such concretions may become a source of manganese for industry in the future.
In Russia, it is an acutely scarce raw material, the following deposits are known: Usinskoye in the Kemerovo region, Polunochnoye in the Sverdlovsk region, Porozhinskoye in the Krasnoyarsk Territory, Yuzhno-Khinganskoye in the Jewish Autonomous Region, Rogachevo-Taininskaya area and Severo-Taininskoye » field on Novaya Zemlya.

manganese minerals

• pyrolusite MnO 2 xH 2 O, the most common mineral (contains 63.2% manganese);
• manganite (brown manganese ore) MnO(OH) (62.5% manganese);
• brownite 3Mn 2 O 3 MnSiO3 (69.5% manganese);
• hausmanite (MnIIMn2III)O 4 ;
• rhodochrosite (manganese spar, raspberry spar) MnCO 3 (47.8% manganese);
• psilomelan mMnO MnO 2 nH 2 O (45-60% manganese);
• purpurite Mn 3 +, (36.65% manganese).

Receipt

• Aluminothermic method, reducing oxide Mn 2 O 3 formed during pyrolusite calcination.
• Recovery of iron-containing manganese oxide ores with coke. Ferromanganese (~80% Mn) is usually obtained in this way in metallurgy.
• Pure metallic manganese is produced by electrolysis.

Physical properties

Some properties are shown in the table. Other properties of manganese:

• Electron work function: 4.1 eV
• Coefficient of linear thermal expansion: 0.000022 cm/cm/°C (at 0°C)
• Electrical conductivity: 0.00695 106 ohm -1 cm -1
• Thermal conductivity: 0.0782 W/cm K
• Enthalpy of atomization: 280.3 kJ/mol at 25°C
• Enthalpy of fusion: 14.64 kJ/mol
• Enthalpy of vaporization: 219.7 kJ/mol
• Hardness
• Brinell scale: MN/m²
• Mohs scale: 4
• Vapor pressure: 121 Pa at 1244 °C
• Molar volume: 7.35 cm³/mol

Chemical properties

Typical oxidation states of manganese: 0, +2, +3, +4, +6, +7 (oxidation states +1, +5 are uncharacteristic). When oxidized in air, it is passivated. Powdered manganese burns in oxygen.
Manganese, when heated, decomposes water, displacing hydrogen. In this case, the layer of manganese hydroxide formed slows down the reaction. Manganese absorbs hydrogen, with increasing temperature its solubility in manganese increases. At temperatures above 1200 °C, it interacts with nitrogen, forming nitrides of various composition.
Carbon reacts with molten manganese to form Mn 3 C carbides and others. It also forms silicides, borides, phosphides. Manganese is stable in alkaline solution.
Manganese forms the following oxides: MnO, Mn 2 O 3 , MnO 2 , MnO 3 (not isolated in the free state) and manganese anhydride Mn 2 O 7 .
Mn 2 O 7 under normal conditions, a liquid oily substance of a dark green color, very unstable; in a mixture with concentrated sulfuric acid ignites organic substances. At 90 °C Mn2O7 decomposes with an explosion. The most stable oxides are Mn 2 O 3 and MnO 2 , as well as the combined oxide Mn 3 O 4 (2MnO·MnO 2 , or Mn 2 MnO 4 salt). When manganese (IV) oxide (pyrolusite) is fused with alkalis in the presence of oxygen, manganates are formed. Manganate solution has a dark green color. The solution turns crimson due to the appearance of the MnO 4 − anion, and a brown precipitate of manganese (IV) oxide-hydroxide precipitates from it.
Permanganic acid is very strong, but unstable, it cannot be concentrated to more than 20%. The acid itself and its salts (permanganates) are strong oxidizing agents. For example, potassium permanganate, depending on the pH of the solution, oxidizes various substances, being reduced to manganese compounds of different oxidation states. In an acidic environment - to manganese (II) compounds, in a neutral one - to manganese (IV) compounds, in a strongly alkaline environment - to manganese (VI) compounds.
When calcined, permanganates decompose with the release of oxygen (one of the laboratory methods for obtaining pure oxygen). Under the action of strong oxidizing agents, the Mn 2+ ion passes into the MnO 4 - ion. This reaction is used for the qualitative determination of Mn 2+ (see section "Determination by chemical analysis methods").
When solutions of Mn (II) salts are alkalized, a precipitate of manganese (II) hydroxide precipitates out of them, which quickly turns brown in air as a result of oxidation. For a detailed description of the reaction, see the section "Determination by chemical analysis methods".
Salts MnCl 3 , Mn 2 (SO 4) 3 are unstable. Hydroxides Mn (OH) 2 and Mn (OH) 3 are basic, MnO (OH) 2 - amphoteric. Manganese (IV) chloride MnCl 4 is very unstable, decomposes when heated, which is used to obtain chlorine. The zero oxidation state of manganese manifests itself in compounds with σ-donor and π-acceptor ligands. So, for manganese, a carbonyl of the composition Mn 2 (CO) 10 is known.
Other manganese compounds with σ-donor and π-acceptor ligands are also known (PF 3 , NO, N 2 , P(C 5 H 5) 3).

Application in industry

Application in metallurgy

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, strongly 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”. In the 1920s-40s, the use of manganese made it possible to smelt armored steel. In the early 1950s, a discussion arose in the journal Stal on the possibility of reducing the manganese content in cast iron, and thereby refusing to support a certain manganese content in the process of open-hearth melting, in which, together with V.I. Yavoisky and V.I. Baptizmansky was attended by E.I. Zarvin, who, on the basis of production experiments, showed the inexpediency of the existing technology. Later, he showed the possibility of conducting an open-hearth process on low-manganese cast iron. With the launch of ZSMK, the development of the conversion of low-manganese cast iron in converters began. 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. Manganese is introduced into bronze and brass.

Application in chemistry

A significant amount of manganese dioxide is consumed in the production of manganese-zinc galvanic cells, MnO 2 is used in such cells as an oxidizing agent-depolarizer. Manganese compounds are also widely used both in fine organic synthesis (MnO 2 and KMnO 4 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 that increases under pressure. Manganese telluride is a promising thermoelectric material (thermoelectric power with 500 μV/K).

Biological role and content in living organisms

Manganese is found in the organisms of all plants and animals, although its content is usually very low, on the order of thousandths of a percent, it has a significant impact on vital activity, that is, it is a trace element. Manganese affects growth, blood formation, and gonadal function. Beet leaves are especially rich in manganese - up to 0.03%, and large amounts of it are found in the organisms of red ants - up to 0.05%. Some bacteria contain up to several percent manganese. Excessive accumulation of manganese in the body affects, first of all, the functioning of the central nervous system. This is manifested in fatigue, drowsiness, deterioration of memory functions. Manganese is a polytropic poison that also affects the lungs, cardiovascular and hepatobiliary systems, causes an allergic and mutagenic effect.

Toxicity

The toxic dose for humans is 40 mg of manganese per day. The lethal dose for humans has not been determined. When taken orally, manganese is one of the least toxic trace elements. The main signs of manganese poisoning in animals are growth inhibition, decreased appetite, impaired iron metabolism, and altered brain function. There are no reports of cases of manganese poisoning in humans caused by ingestion of foods high in manganese. Basically, poisoning of people is observed in cases of chronic inhalation of large amounts of manganese at work. It manifests itself in the form of severe mental disorders, including hyperirritability, hypermotility and hallucinations - "manganese madness". In the future, changes in the extrapyramidal system develop, similar to Parkinson's disease. It usually takes several years for the clinical picture of chronic manganese poisoning to develop. It is characterized by a rather slow increase in pathological changes in the body caused by an increased content of manganese in the environment (in particular, the spread of endemic goiter, not associated with iodine deficiency).

Field

Usinsk manganese deposit

Manganese (lat. - Manganum, Mn) in our body is contained in a small amount. Therefore, it is classified as a micronutrient. The content of this trace element in our body is small. Nevertheless, manganese, along with other substances, is involved in the metabolism of fats, carbohydrates, and proteins.

Manganese was discovered in the 18th century, which by historical standards is not so long ago. However, man has been familiar with manganese compounds since ancient times. One of these compounds is manganese dioxide or pyrolusite, MnO 2 . It was used in glass and leather business. At that time, many mineral compounds were called magnesia. So MnO 2 was called black magnesia due to its similarity with another mineral, magnetite.

However, these minerals had differences. Magnetite is iron oxide, Fe 3 O 4 , and was attracted by a magnet. In contrast, the magnet did not work on black magnesia, and iron could not be extracted from it. Therefore, this mineral received another name - manganesium from the ancient Greek word for deceit. This term has migrated to many European languages.

In German, the mineral was called Mangan or Manganerz. This is where the Russian name manganese comes from. However, manganese itself was obtained only in 1778. Then the Swedish chemist Scheele concluded that instead of iron pyrolusite contains another hitherto unknown metal. In the same year, Gan

also a Swedish scientist, isolated manganese from pyrolusite.

Properties

In the periodic system of elements of Mendeleev, Mn is located in group VII of period IV, and is listed under number 25. This means that 25 electrons revolve around the atomic nucleus of Mn, and 7 of them are in the outer orbit.

When interacting with various substances, manganese is able to donate these electrons, or attach others to itself. Accordingly, its valency is variable, and ranges from 1 to 7. Most often it is 2, 4, and 7. At a minimum valence, the properties of manganese as a reducing agent predominate, and at a maximum, an oxidizing agent.

In many of its features, manganese is similar to iron, and, along with iron, it is classified as a ferrous metal. It is a silvery-white metal with an atomic mass of 55. This metal is quite heavy, its density is 7.4 g/cm 3 . The melting and boiling points are also high - 1245 0 С, and 2150 0 С. Manganese easily reacts with oxygen to form oxides.

Since the valency of manganese is changeable, its oxides differ from each other. One of them is pyrolusite mentioned above. An oxide film forms on the surface of metallic manganese, which protects it from further oxidation. Since manganese, depending on its valence, can be both an oxidizing agent and a reducing agent, it reacts with both metals and non-metals, and its compounds are diverse.

Together with oxygen, it forms an acidic residue of permanganous acid. This residue is part of the salts of this acid, manganates. One of these salts is potassium permanganate, KMnO 4, the well-known potassium permanganate. In general, manganese compounds are quite common in nature. There are especially many of them at the bottom of the oceans, where manganese is combined with iron. The share of manganese accounts for about 0.1% of the mass of the earth's crust. According to this indicator, among all the elements of the periodic system of Mendeleev, he takes 11th place.

Physiological action

The content of manganese in the body of an adult is small, 10-20 mg. This is much less than the content of other metals - potassium, calcium, iron, sodium, copper, zinc. Therefore, Mn was not initially classified as a vital element, and it was believed that its presence in the body was not at all mandatory. Indeed, not all varieties of this trace element are of interest to us. Divalent and trivalent manganese, Mn (II) and Mn (III) are involved in physiological processes.

The physiological value of manganese lies in the fact that it regulates the absorption of many other useful substances (nutrients). Among these nutrients are copper, B vitamins, in particular, vit. B 1 (Thiamin) and vit. B 4 (choline). In addition, manganese has a positive effect on the absorption of vit. E (Tocopherol) and Vit. C (ascorbic acid). These vitamins are powerful antioxidants.

Accordingly, manganese also has an antioxidant effect. As an antioxidant, it binds free radicals and prevents them from damaging cells. Thus, manganese strengthens the immune system and prevents the formation of malignant neoplasms.

In addition, manganese is part of many enzyme systems. Most of this microelement is in mitochondria, where it is involved in the accumulation of energy in the form of ATP molecules. In addition, manganese provides the metabolism (exchange) of carbohydrates, proteins and lipids (fats). It stimulates catabolic processes with the breakdown of substances and the acceleration of metabolic reactions.

During the utilization of proteins under the action of manganese, they are split with the formation of final nitrogenous products, urea and creatinine. As a result, energy is released. This process is of great practical importance in the performance of physical work.

Manganese promotes the synthesis of fatty acids, facilitates the absorption of lipids, and is involved in their breakdown. Lipids are energy-intensive compounds, and thanks to manganese they are fully consumed with the release of the maximum amount of energy. At the same time, manganese prevents the deposition of fat masses in the subcutaneous layer with the development of obesity.

With the consumption of fats, the production of low-density cholesterol decreases, and it is not deposited on the walls of blood vessels in the form of atherosclerotic plaques. In addition, manganese largely prevents fatty infiltration of the liver (fatty liver). Thanks to Mn, the function of the liver is improved by binding and excreting many toxic compounds with bile.

In addition, Mn carries out the deposition, accumulation, of glycogen in the liver and skeletal muscles. In general, the effect of manganese on carbohydrate metabolism is diverse. Manganese has an insulin-like effect, promotes the transport of glucose into the cell and its subsequent breakdown with the formation of ATP. That is why it is concentrated in the mitochondria.

At the same time, according to some data, with glucose deficiency, it is able to trigger the processes of gluconeogenesis, the synthesis of glucose from protein and lipid compounds. Manganese also contributes to the spread of nerve impulses, tk. participates in the synthesis of neurotransmitter substances.

Stimulation of metabolic processes in muscle tissue by manganese leads to an increase in muscle strength and endurance. In addition, manganese strengthens bones. It also forms cartilage, regulates the composition of intra-articular or synovial fluid. Thus, Mn improves the condition and function of the joints, prevents the development of degenerative and inflammatory processes in them.

Together with copper, manganese is involved in hematopoiesis, stimulates blood clotting. And this microelement has a rejuvenating effect. The skin under its influence becomes firm and elastic. The natural processes associated with aging slow down. In addition, manganese increases skin resistance to ultraviolet rays and prevents the development of malignant skin cancers.

The influence of manganese on the state of organs and systems is to a large extent realized through the endocrine system. It enhances the action of insulin. It is thanks to this that glucose is absorbed and the risk of diabetes is reduced. This trace element also has a stimulating effect on the pituitary-adrenal system. Manganese increases the production of thyroid hormones.

Similarly, Mn acts on male and female sex hormones. It activates spermatogenesis in men, participates in the regulation of the menstrual cycle in women, and prevents infertility in both sexes. With advanced pregnancy, manganese, along with other nutrients, forms organs and tissues in the fetus. After childbirth, manganese stimulates lactation.

daily requirement

The need for Mn depends not only on age, but also on a number of other factors.

With physical exertion, severe diseases, the need for manganese increases to 11 mg per day.

Causes and signs of deficiency

Manganese deficiency is said to be in cases where its daily intake in the body of an adult is less than 1 mg. The main reason is the low content of natural foods containing manganese in the diet, the predominance of refined foods or foods containing a large amount of synthetic ingredients.

In addition, with many diseases of the gastrointestinal tract (gastrointestinal tract), the absorption of manganese in the small intestine will deteriorate. This also contributes to the intake of drugs containing calcium and iron. The fact is that these two minerals impair the absorption of manganese. With age, the absorption of manganese deteriorates, and deficiency of this trace element is often observed in the elderly.

Some conditions are accompanied by an increased consumption of manganese:

• physical activity (hard work, sports)
• mental and mental stress
• diabetes
• chronic intoxication in hazardous industries, living in ecologically unfavorable regions
• alcoholism
• pregnancy
• period of rapid growth
• "Female" diseases with a violation of the hormone-producing function of the ovaries.

By themselves, these conditions do not always lead to manganese deficiency. However, if they are combined with each other, as well as with poor nutrition, gastrointestinal disease, then most likely the content of manganese in the body will be reduced.

Signs of manganese deficiency are nonspecific, and in many respects are similar to signs of deficiency of other nutrients. There is a general weakness, deterioration of mental functions, mental instability. Patients complain of dizziness, poor coordination of movements. Muscle tone is reduced, in some cases muscle cramps are noted.

In bone tissue, changes occur similar to those with calcium deficiency. Bone density decreases, osteoporosis develops, and the risk of fractures increases. Arthrosis is formed in the joints, due to the degeneration of the articular cartilage. Among other pathological conditions associated with manganese deficiency: anemia, atherosclerosis, decreased immunity.

The risk of diabetes mellitus, cardiovascular and oncological diseases, allergic reactions with skin rash, edema and bronchospasm increases. Early signs of aging appear; flabby wrinkled skin with age spots, hair loss, slow nail growth. Infertility often occurs due to hormonal imbalance.

In children, manganese deficiency is most often of a nutritional nature, and is often combined with other nutrient deficiencies. Such children lag behind in mental and physical development. They often suffer from infectious diseases, suffer from allergies. Sometimes there is a convulsive syndrome.

Sources of income

Manganese comes to us mainly with plant products. In animal food, its amount is small.

Product	Content, mg/100 g
wheat germ	12,3
Whole flour bread	1,9
Hazelnut	4,9
Almond	1,92
pistachios	3,8
Soya	1,42
Rice	1,1
Peanut	1,93
cocoa beans	1,8
polka dots	0,3
Walnut	1,9
Spinach	0,9
Garlic	0,81
Apricot	0,2
A pineapple	0,75
Beet	0,66
Pasta	0,58
White cabbage	0,35
Potato	0,35
Rose hip	0,5
Champignon	0,7

It should be taken into account that a significant amount of manganese is lost during refining. The same goes for heat treatment, especially boiling. Therefore, preference should be given to raw products containing manganese.

Synthetic analogs

The most famous manganese-containing pharmaceutical is potassium permanganate, KMnO 4, or simply, potassium permanganate. True, potassium permanganate is used only as an external antiseptic for the treatment of wounds, skin burns, oropharyngeal rinses for colds.

Sometimes potassium permanganate is taken as an emetic during gastric lavages for certain poisonings. Although the use of the drug in this capacity is highly controversial. First, it is very difficult to find the optimal concentration. Concentrated potassium permanganate can cause burns of the oral mucosa, esophagus and stomach. And secondly, some of the manganese is absorbed when taken orally, and you can get manganese poisoning.

As for manganese-containing preparations for oral administration in the form of capsules and tablets, these are not pharmaceuticals, but dietary supplements.

Here, manganese compounds are often combined with other minerals and vitamins. These drugs are taken as adjuvants for immunodeficiency, osteoporosis, anemia, mental and physical overwork, and other conditions associated with an increased need for manganese.

Metabolism

Absorption of ingested Mn (II) is carried out throughout the small intestine. It is characteristic that absorption is small, about 5%. The rest is excreted in the feces. The absorbed manganese enters the liver through the portal vein, where it is in free form or in globulins associated with plasma proteins.

A certain amount of Mn (II) is oxidized to Mn (III), and in combination with a carrier protein is transported to organs and tissues. Here, its content can vary significantly. The maximum manganese is in the tissues of organs, the cells of which contain a large number of mitochondria. These are the liver, pancreas, kidneys.

Myocardium, brain structures also contain a significant amount of manganese. Meanwhile, its level in the blood plasma is low, because. manganese is quickly transported from the blood to the tissues. Manganese is excreted mainly in the feces, and to a lesser extent in the urine. It enters the intestines mainly with bile. In this case, some part can be reabsorbed in the intestine.

In addition, Mn from blood plasma can be secreted directly into the intestine. In diseases accompanied by cholestasis (stagnation of bile), the release of manganese is difficult. In these cases, it is secreted into the duodenum with pancreatic juice. A small amount of the trace element is lost in breast milk during lactation.

Interaction with other substances

Mn improves the absorption of many B vitamins, as well as vit. E and C. It enhances the effects of copper and zinc. Together with copper and iron, manganese is involved in hematopoiesis. However, in large quantities, it hinders the absorption of iron. In turn, iron impairs the absorption of manganese. The same goes for calcium and phosphorus. From food products, sweets, caffeine, and alcohol negatively affect the content of Mn. They impair its absorption or increase consumption.

signs of excess

We can talk about excess intake of manganese if its daily dosage exceeds 40 mg. To achieve this through a single meal rich in manganese is unrealistic. An overdose of manganese-containing products - too. After all, Mn is represented by dietary supplements, and the content of the trace element in them is low.

True, in rare cases, acute poisoning with potassium permanganate is possible. Basically, manganese poisoning is chronic. The main reason is industrial inhalation poisoning, when compounds containing manganese are inhaled. Drinking water contaminated with manganese compounds can also lead to poisoning.

Manganese intoxication is manifested by general weakness, decreased muscle tone, and coordination disorders. Anemia often develops. There is no appetite, digestion is disturbed, the liver is enlarged. Neurological disorders are of the same nature as in Parkinson's disease. In severe poisoning, the so-called. manganese madness - inadequacy, irritability and hallucinations with motor excitation.

Another characteristic feature of chronic manganese intoxication is manganese rickets. It is formed due to the fact that manganese, being in the bone tissue in excess, displaces calcium from there. This condition is treated with vit. D and calcium preparations.

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• 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 in terms of abundance 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 a reactive metal. Similar to aluminum at room temperature, it reacts with oxygen contained in atmospheric air to form 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.