Manganese is a chemical element with an atomic mass of 54.9380 and atomic number 25, a silvery-white shade, with a large mass, in nature exists in the form of a stable isotope 35 Mn. The first mention of metal was recorded by the ancient Roman scientist Pliny, who called it "black stone". In those days, manganese was used as a glass clarifier, during the melting process manganese pyrolusite MnO 2 was added to the melt.
In Georgia, manganese pyrolusite has long been used as an additive during the production of iron, it was called black magnesia and was considered one of the varieties of magnetite (magnetic iron ore). Only in 1774, the Swedish scientist Scheele proved that this was a compound of a metal unknown to science, and a few years later, Yu. Gan, while heating a mixture of coal and pyrolusite, obtained the first manganese contaminated with carbon atoms.
Natural distribution of manganese
In nature, the chemical element manganese is not widespread, it contains only 0.1% in the earth's crust, 0.06–0.2% in volcanic lava, the metal on the surface in a dispersed state, has the form Mn 2+. On the surface of the earth, under the influence of oxygen, oxides of manganese are quickly formed, minerals Mn 3+ and Mn 4+ are widespread, in the biosphere the metal is inactive in an oxidizing environment. Manganese is a chemical element that actively migrates under reducing conditions; the metal is very mobile in acidic natural tundra reservoirs and forest landscapes, where an oxidizing environment prevails. For this reason, cultivated plants have an excess metal content, ferromanganese nodules, marsh and lake low-percentage ores are formed in soils.
In regions with a dry climate, an alkaline oxidizing environment predominates, which limits the mobility of the metal. In cultivated plants, there is a lack of manganese, agricultural production cannot do without the use of special complex microadditives. In the rivers, the chemical element is not widespread, but the total removal can reach large values. Especially a lot of manganese is available in coastal zones in the form of natural precipitation. At the bottom of the oceans there are large deposits of metal, which were formed in ancient geological periods, when the bottom was dry land.
Chemical properties of manganese
Manganese belongs to the category of active metals; at elevated temperatures, it actively reacts with non-metals: nitrogen, oxygen, sulfur, phosphorus and others. As a result, multivalent oxides of manganese are formed. At room temperature, manganese is an inactive chemical element; when dissolved in acids, it forms divalent salts. When heated in a vacuum to high temperatures, a chemical element is able to evaporate even from stable alloys. Manganese compounds are in many ways similar to compounds of iron, cobalt and nickel, which are in the same oxidation state.
There is a great similarity of manganese with chromium, the metal subgroup also has an increased stability at higher oxidation states with an increase in the element's serial number. Perenates are less powerful oxidizing agents than permanganates.
Based on the composition of manganese (II) compounds, the formation of a metal with higher degrees of oxidation is allowed; such transformations can occur both in solutions and in molten salts.
Stabilization of manganese oxidation states The existence of a large number of oxidation states in the chemical element manganese is explained by the fact that in transition elements, during the formation of bonds with d-orbitals, their energy levels are split in the tetrahedral, octahedral, and square arrangement of ligands. Below is a table of currently known oxidation states of some metals in the first transition period.
Attention is drawn to the low oxidation states that occur in a large number of complexes. The table contains a list of compounds in which the ligands are chemically neutral molecules of CO, NO, and others.
Due to complexation, high oxidation states of manganese are stabilized, the most suitable ligands for this are oxygen and fluorine. If we take into account that the stabilizing coordination number is six, then the maximum stabilization is five. If the chemical element manganese forms oxo complexes, then higher oxidation states can be stabilized.
Stabilization of manganese in lower oxidation states
The theory of soft and hard acids and bases makes it possible to explain the stabilization of different oxidation states of metals due to complex formation when exposed to ligands. Soft type elements successfully stabilize low oxidation states of the metal, while hard elements positively stabilize high oxidation states.
The theory fully explains metal-metal bonds, formally these bonds are considered as acid-base mutual influence.
Alloys of manganese The active chemical properties of manganese allow it to form alloys with many metals, while a large number of metals can dissolve in individual modifications of manganese and stabilize it. Copper, iron, cobalt, nickel, and some other metals are capable of stabilizing the γ-modification; aluminum and silver are capable of expanding the β- and σ-regions of magnesium in binary alloys. These characteristics play an important role in metallurgy. Manganese is a chemical element that makes it possible to obtain alloys with high ductility values; they can be stamped, forged and rolled.
In chemical compounds, the valency of manganese varies within 2–7, an increase in the degree of oxidation causes an increase in the oxidizing and acidic characteristics of manganese. All Mn(+2) compounds are reducing agents. Manganese oxide has reducing properties, gray-green in color, does not dissolve in water and alkalis, but is highly soluble in acids. Manganese hydroxide Mn (OH) 3 does not dissolve in water, the color is white. The formation of Mn(+4) can be both an oxidizing agent (a) and a reducing agent (b).
MnO 2 + 4HCl \u003d Cl 2 + MnCl 2 + 2H 2 O (a)
This reaction is used when it is necessary to obtain chlorine in the laboratory.
MnO 2 + KClO 3 + 6KOH = KCl + 3K 2 MnO 4 + 3H 2 O (b)
The reaction proceeds during the fusion of metals. MnO 2 (manganese oxide) has a brown color, the corresponding hydroxide is somewhat darker in color.
Physical properties of manganese Manganese is a chemical element with a density of 7.2–7.4 g/cm 3 , melting point +1245°C, boils at a temperature of +1250°C. The metal has four polymorphic modifications:
- α-Mn. It has a cubic body-centered lattice, 58 atoms are located in one unit cell.
- β-Mn. It has a cubic body-centered lattice, 20 atoms are located in one unit cell.
- γ-Mn. It has a tetragonal lattice, 4 atoms in one cell.
- δ-Mn. It has a cubic body-centered lattice.
Temperature transformations of manganese: α=β at t°+705°C; β=γ at t°+1090°C; γ=δ at t°+1133С. The most brittle modification α is rarely used in metallurgy. Modification γ is distinguished by the most significant indicators of plasticity; it is most often used in metallurgy. The β-modification is partially ductile and is rarely used in industry. The atomic radius of the chemical element manganese is 1.3 A, the ionic radii, depending on the valence, range from 0.46 to 0.91. Manganese is paramagnetic, coefficients of thermal expansion are 22.3×10 -6 deg -1 . Physical properties may vary slightly depending on the purity of the metal and its actual valency.
Method for obtaining manganese Modern industry receives manganese according to the method developed by the electrochemist V.I. Agladze by electrohydrolysis of aqueous solutions of the metal with the addition of (NH 4) 2SO 4, during the process, the acidity of the solution should be in the range of pH = 8.0–8.5. Lead anodes and cathodes made of an alloy based on AT-3 titanium are immersed in the solution, it is allowed to replace titanium cathodes with stainless ones. The industry uses manganese powder, which after the end of the process is removed from the cathodes, the metal settles in the form of flakes. The method of obtaining is considered energy-consuming, this has a direct impact on the increase in cost. If necessary, the collected manganese is further remelted, which makes it easier to use it in metallurgy.
Manganese is a chemical element that can also be obtained by the halogen process due to ore chlorination and further reduction of the formed halides. This technology provides the industry with manganese with the amount of extraneous technological impurities not more than 0.1%. A more contaminated metal is obtained during the aluminothermic reaction:
3Mn 3 O 4 + 8Al \u003d 9Mn + 4A l2 O 3
Or electrothermal. To remove harmful emissions in the production workshops, powerful forced ventilation is installed: PVC air ducts, centrifugal fans. The frequency of air exchange is regulated by regulations and must ensure the safe stay of people in work areas.
The use of manganese The main consumer of manganese is ferrous metallurgy. The metal is also widely used in the pharmaceutical industry. For one ton of smelted steel, 8–9 kilograms are needed; before introducing a chemical element into the manganese alloy, it is preliminarily alloyed with iron to obtain ferromanganese. In the alloy, the proportion of the chemical element manganese is up to 80%, carbon up to 7%, the rest is occupied by iron and various technological impurities. Due to the use of additives, the physical and mechanical characteristics of steels smelted in blast furnaces are significantly increased. The technology is also suitable for the use of additives in modern electric steel furnaces. Due to the addition of high-carbon ferromanganese, steel is deoxidized and desulfurized. With the addition of medium and low-carbon ferromanganese, metallurgy receives alloyed steels.
Low-alloy steel contains 0.9-1.6% manganese, high-alloyed up to 15%. Steel containing 15% manganese and 14% chromium has high physical strength and corrosion resistance. The metal is wear-resistant, can work in harsh temperature conditions, is not afraid of direct contact with aggressive chemical compounds. Such high characteristics make it possible to use steel for the manufacture of the most critical structures and industrial units operating in difficult conditions.
Manganese is a chemical element used in the smelting of iron-free alloys. During the production of high-speed industrial turbine blades, an alloy of copper and manganese is used, for propellers, bronzes containing manganese are used. In addition to these alloys, manganese as a chemical element is present in aluminum and magnesium. It greatly improves the performance of non-ferrous alloys, makes them well deformable, not afraid of corrosion processes and wear-resistant.
Alloy steels are the main material for heavy industry, indispensable during the production of various types of weapons. Widely used in shipbuilding and aircraft construction. The presence of a strategic reserve of manganese is a condition for the high defense capability of any state. In this regard, metal mining is increasing every year. In addition, manganese is a chemical element used during glass production, agriculture, printing, etc.
Manganese in flora and fauna
In wildlife, manganese is a chemical element that plays an important role in development. It affects the characteristics of growth, the composition of the blood, the intensity of the process of photosynthesis. In plants, its amount is ten-thousandths of a percent, and in animals, hundred-thousandths of a percent. But even such minor content has a noticeable impact on most of their functions. It activates the action of enzymes, affects the function of insulin, mineral and hematopoietic metabolism. The lack of manganese causes the appearance of various diseases, both acute and chronic.
Manganese is a chemical element widely used in medicine. The lack of manganese reduces physical endurance, causes some types of anemia, disrupts metabolic processes in bone tissues. The disinfecting characteristics of manganese are widely known, and its solutions are used during the treatment of necrotic tissues.
An insufficient amount of manganese in the diet of animals causes a decrease in daily weight gain. For plants, this situation causes spotting, burns, chlorosis and other diseases. If signs of poisoning are detected, special drug therapy is prescribed. Severe poisoning can cause the appearance of manganese parkinsonism syndrome - an intractable disease that has a negative effect on the human central nervous system.
The daily requirement of manganese is up to 8 mg, the main amount a person receives from food. In this case, the diet should be balanced in all nutrients. With increased load and insufficient sunlight, the dose of manganese is adjusted based on a complete blood count. A significant amount of manganese is found in mushrooms, water chestnuts, duckweed, mollusks and crustaceans. The manganese content in them can reach several tenths of a percent.
When manganese enters the body in excessive doses, diseases of muscle and bone tissues can occur, the respiratory tract is affected, the liver and spleen suffer. It takes a long time to remove manganese from the body, during this period the toxic characteristics increase with the effect of accumulation. The concentration of manganese in the air allowed by the sanitary authorities must be ≤ 0.3 mg/m 3 , the parameters are controlled in special laboratories by air sampling. The selection algorithm is regulated by state regulations.
Salts of manganese (II)
Chemical properties
Receipt
Manganese(II) hydroxide
Chemical properties
Manganese oxide (II) belongs to the main oxides, has all their properties. It corresponds to the unstable hydroxide Mn(OH) 2 .
Manganese hydroxide (II) - Mn (OH) 2 - a water-insoluble substance of a light pink color.
The main production method is alkaline treatment of manganese (II) salts:
MnSO 4 + 2NaOH → Mn(OH) 2 ↓ + Na 2 SO 4
In air, it oxidizes to manganese (IV) hydroxide:
2Mn(OH) 2 ↓ + O 2 + 2H 2 O → 2Mn(OH) 4 ↓
Shows all the properties of water-insoluble bases.
All salts of manganese (II) in redox reactions occurring in solutions are reducing agents:
3Mn(NO 3) 2 + 2KMnO 4 + 2H 2 O → 5MnO 2 + 4HNO 3 + 2KNO 3
Salts of manganese (II) are not hydrolyzed, forming strong aqua complexes:
Mn 2+ + 6H 2 O → 2+
MnCl 2 + 6H 2 O → Cl 2
Salts of manganese (II) form complexes.
Mn(CN) 2 is an insoluble white compound, due to complexation it dissolves in the presence of KCN:
4KCN + Mn(CN) 2 = K 4 potassium hexocyanomanganate
Similarly:
4KF + MnF 2 = K 4
2KCl + MnCl 2 = K 2
Manganese(III) compounds
Mn 2 O 3 - amphoteric oxide, with a predominance of basic properties.
Mn 2 O 3 + 6HF \u003d 2MnF 3 + 3H 2 O
Mn +3 2 O 3 + NaOH \u003d 2NaMnO 2 + H 2 O (t)
Mn(OH) 3 - hydroxide Mn 3+- amphoteric compound, with a predominance of basic properties:
Mn(OH) 3 ↔ HMnO 2
Manganese(IV) compounds
The main compounds of tetravalent manganese include manganese (IV) oxide MnO2, as well as permanganic acid H2MnO3- very unstable, easily decomposed into manganese (IV) oxide and water.
The strongest compound of manganese (IV) is a water-insoluble dark brown oxide. This is an amphoteric compound, but the corresponding properties are extremely weakly expressed.
|
MnO 2 + 2NaOH \u003d Na 2 MnO 3 + H 2 O
Depending on the nature of the partner, MnO 2 can exhibit both oxidizing and reducing properties (redox duality) in OB reactions.
Much more often, manganese (IV) oxide is used as an oxidizing agent, carrying out reactions in an acidic environment:
MnO 2 + 4HCl \u003d MnCl 2 + Cl 2 + 2H 2 O
In an alkaline environment, manganese (IV) oxide can also be a reducing agent, turning into manganese (VI) compounds, for example, salts of manganese acid - manganates:
3MnO 2 + KClO 3 + 6KOH = 3K 2 MnO 4 + KCl + 3H 2 O
Influence of pH on the RH Reactions of MnO 2
Manganese(VI) compounds
MnO 3 - oxide, has acidic properties.
H 2 MnO 4 - manganese acid- exists only in solution.
Salts of this acid manganates.
Manganates can be obtained by calcining dry permanganates:
Manganates are stable in a strongly alkaline medium; in a neutral medium, the disproportionation reaction occurs:
3Na 2 MnO 4 + 2H 2 O → 2NaMnO 4 + MnO 2 + 4NaOH
Manganese(VII) compounds
The highest oxidation state of manganese +7 corresponds to acid oxide Mn 2 O 7, permanganic acid HMnO 4 and its salts - permanganates.
Manganese(VII) compounds are strong oxidizers. Mn 2 O 7 is a greenish-brown oily liquid, upon contact with which alcohols and ethers ignite. Oxide Mn(VII) corresponds to permanganic acid HMnO 4 . It exists only in solutions, but is considered one of the strongest (α - 100%). The maximum possible concentration of HMnO 4 in solution is 20%. Salts HMnO 4 - permanganates - the strongest oxidizing agents; in aqueous solutions, like the acid itself, they have a crimson color.
In redox reactions, permanganates are strong oxidizing agents. Depending on the reaction of the environment, they are reduced either to salts of divalent manganese (in an acidic environment), manganese (IV) oxide (in a neutral one) or manganese (VI) compounds - manganates - (in an alkaline one). Obviously, in an acidic environment, the oxidative abilities of Mn +7 are most pronounced.
2KMnO 4 + 5Na 2 SO 3 + 3H 2 SO 4 → 2MnSO 4 + 5Na 2 SO 4 + K 2 SO 4 + 3H 2 O
2KMnO 4 + 3Na 2 SO 3 + H 2 O → 2MnO 2 + 3Na 2 SO 4 + 2KOH
2KMnO 4 + Na 2 SO 3 + 2KOH → 2K 2 MnO 4 + Na 2 SO 4 + H 2 O
Permanganates, both in acidic and alkaline media, oxidize organic substances:
2KMnO 4 + 3H 2 SO 4 + 5C 2 H 5 OH → 2MnSO 4 + K 2 SO 4 + 5CH 3 COH + 8H 2 O
alcohol aldehyde
4KMnO 4 + 2NaOH + C 2 H 5 OH → MnO 2 ↓ + 3CH 3 COH + 2K 2 MnO 4 +
Na 2 MnO 4 + 4H 2 O
When heated, potassium permanganate decomposes (this reaction is used to produce oxygen in the laboratory):
2KMnO 4 K 2 MnO 4 + MnO 2 + O 2
Thus, for manganese, the same dependences are typical: in the transition from the lowest oxidation state to the highest, the acidic properties of oxygen compounds increase, and in the OB reactions, the reducing properties are replaced by oxidizing ones.
For the body, permanganates are poisonous due to their strong oxidizing properties.
In case of permanganate poisoning, hydrogen peroxide in an acetic acid medium is used as an antidote:
2KMnO 4 + 5H 2 O 2 + 6CH 3 COOH → 2(CH 3 COO) 2 Mn + 2CH 3 COOK + 5O 2 + 8H 2 O
KMnO 4 solution is a cauterizing and bactericidal agent for treating the surface of the skin and mucous membranes. The strong oxidizing properties of KMnO 4 in an acidic environment underlie the analytical method of permanganatometry used in clinical analysis to determine the oxidizability of water, uric acid in urine.
The human body contains about 12 mg of Mn in various compounds, with 43% concentrated in bone tissue. It affects hematopoiesis, bone tissue formation, growth, reproduction and some other body functions.
Topic: D-elements of group VIII
Keywords:d-elements, iron, cobalt, nickel, triads - d-elements, the iron family, ferromagnetic compounds, complexing ability, cold passivation with acids, iron carbonyls, crystalline hydrates, yellow and red salts, ferrates, Mohr's salt, iron acid.
A feature of the VIII B-group is that it combines 3 triads of d-elements of large periods that have no electronic analogues in small periods.
Elements of the first triad - Fe, Co, Ni called the iron family. Elements of the second and third triads, that is Ru(ruthenium), Rh(rhodium), Pd(palladium), Os(osmium), Ir(iridium), Pt(platinum) are called platinum metals.
The atoms of elements of the iron family, in contrast to the atoms of platinum metals, do not have a free f-sublevel.
This fact determines the chemical features of the elements of the iron family.
Platinum metals, very similar in properties and difficult to separate from each other, differ sharply from the metals of the iron family and never occur together with them in the lithosphere.
In the elements of the VIII B-group, the d-sublevel of the preexternal level is almost completely completed. However, not all electrons of the d-sublevel participate in the formation of chemical bonds. Only about 10 years ago, an iron compound with an oxidation state of +8 was obtained, but more often in complex compounds for iron, oxidation states of +3 and +2 are characteristic; Co +3, and Ni +2. Metals of the VIII B-group are characterized by high densities and melting points. Fe, Co, Ni are ferromagnets; all elements of the VIII B-group are good complexing agents.
Elements of the iron family are metals with medium chemical activity. In a series of standard electrode potentials, they are located to the left of hydrogen. Platinum metals are located at the end of a series of standard electrode potentials and are characterized by low chemical activity.
Platinum metals are used in instrument making, as catalysts in organic synthesis, and for the preparation of corrosion-resistant alloys.
The elements of the iron family are located in the fourth period of the periodic table of chemical elements. Fe, Co are silvery-white metals, Ni has a yellowish-white color.
For iron and cobalt in complex substances, the oxidation states +2 and +3 are most characteristic, and for nickel +2. Like the elements of the manganese subgroup, they are able to form compounds with an oxidation state of 0 (carbonyls):
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 were 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
Ministry of Education and Science of Ukraine
National Mining University
Department of Ecology
Search and analytical work
By discipline: "Human Ecology"
On the topic: "Manganese"
Performed:
Art. group GEK-02-1
Filonenko E. S.
Checked:
Bogdanov V.K.
Dnepropetrovsk
Introduction
1. Historical background ............................................... ..........................4
2. The use of manganese.............................................. ..........................5
3. Obtaining manganese ............................................... .............................5
4. Manganese compounds in biological systems...............................................5
5. The volume of production of manganese ore by enterprises ............... 6
6. Manganese fertilizers............................................... .......................6
7. Disease caused by manganese toxin .............................................. 7
Bibliography
Introduction
In the second half of the 20th century, non-communicable diseases, primarily diseases of the central nervous system and the cardiovascular system, began to pose a major threat to public health and a public health problem.
In this search and analytical robot, we will talk about a chemical element Manganese .
I took this topic because today it is relevant. Every third person is sick with some kind of disease associated with some elements of the periodic system of Mendeleev.
Manganese
History reference
Manganese minerals have been known for a long time. The ancient Roman naturalist Pliny mentions a black stone, which was used to decolorize a liquid glass mass; it was about the mineral pyrolusite MnO 2 . In Georgia, pyrolusite has served as a filler material in the production of iron since ancient times. For a long time, pyrolusite was called black magnesia and was considered a type of magnetic iron ore. In 1774, K. Schelle proved that this was a compound of an unknown metal, and another Swedish scientist, J. Gai, by strongly heating a mixture of pyrolusite with coal, obtained carbon-contaminated manganese. The name Manganese is traditionally derived from the German Marganerz- manganese ore.
Manganese- silvery-white hard brittle metal. Four crystalline modifications of manganese are known, each of which is thermodynamically stable in a certain temperature range. Below 707 0 C, a-manganese is stable, having a complex structure - its unit cell includes 58 atoms. The complexity of the structure of manganese at temperatures below 707 0 С causes its fragility.
Some physical constants of manganese are given below:
Density, g / cm 3 .............................. ........... 7.44
T. pl., 0 C .................................. ...................... 1245
Boiling point, 0 С............................... ................... ~2080
S 0 298 , J / deg mol .......................................... ................. 32.0
DH air 298, kJ / mol ............................................... ......... 280
E 0 298 Mn 2+ + 2e = Mn, V .............................. ..... -1.78
Manganese is a d-element of group VII of the periodic system, with a configuration of valence electrons 3d 5 4s 2 .
Some information about this item is given below:
Atomic mass................................................ .... 54.9380
Valence electrons.............................................. 3d 5 4s 2
Metallic atomic radius, nm ............................. 0.130
Conditional radius of the Mn 2+ ion, nm .............................. 0.052
Conditional radius of the Mn 7+ ion, nm .............................. 0.046
Ionization energy Mn 0 ® Mn + , eV ........................ 7.44
Application of manganese
Manganese belongs to a very common element, accounting for 0.03% of the total number of atoms in the earth's crust. Among the heavy metals (atomic weight over 40), which include all elements of the transition series, manganese occupies the third place in terms of abundance in the earth's crust, after iron and titanium. Many rocks contain small amounts of manganese. At the same time, there are also accumulations of its oxygen compounds, mainly in the form of the mineral pyrolusite - MnO 2.
Manganese is used in large quantities in metallurgy in the process of obtaining steels to remove sulfur and oxygen from them. However, not manganese is added to the melt, but an alloy of iron and manganese - ferromanganese, which is obtained by reducing pyrolusite with coal. Additives of manganese to steels increase their resistance to wear and mechanical stress. In non-ferrous alloys, manganese increases their strength and resistance to corrosion.
Manganese dioxide is used as a catalyst in ammonia oxidation processes, organic reactions, and decomposition reactions of inorganic salts. In the ceramic industry, MnO 2 is used to color black and dark brown enamels and glazes. Highly dispersed MnO 2 has a good adsorption 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 of an aqueous solution, for washing wounds, gargling, lubricating ulcers and burns. A solution of KMnO 4 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.
Do not forget that manganese compounds can have toxic action on the human body. The maximum permissible concentration of manganese in the air is 0.3 mg/m 3 . In severe poisoning, damage to the nervous system is observed with a characteristic syndrome of manganese parkinsonism .
Obtaining manganese
Pure manganese can be obtained by electrolysis of solutions of its salts. However, since 90% of all manganese production is consumed in the manufacture of various iron-based alloys, it is usually smelted from the ores directly into its high-percentage alloy with iron - ferromanganese.
Manganese compounds in biological systems
Manganese is very interesting in biochemical terms. Accurate analyzes show that it is present in the organisms of all plants and animals. Its content usually does not exceed thousandths of a percent, but sometimes it is much higher.
Manganese is one of the few elements that can exist in eight different oxidation states. However, only two of these states are realized in biological systems: Mn (II) and Mn (III).
Production volume of manganese ore by enterprises
| - Marganetsky GOK - Ordzhonikidzevsky GOK |
Marganetsky GOK
The deposit of manganese ores was discovered in 1883. In 1985, the Pokrovsky mine began mining ore on the basis of this deposit. With the development of the mine and the emergence of new quarries and mines, the Marganetsky GOK was formed.
The production structure of the plant includes: two open pit mines for manganese ore, five mines for underground mining, three processing plants, as well as the necessary auxiliary shops and services, incl. repair and mechanical, transport, etc.
Ordzhonikidzevsky GOK
The main type of manufactured products is manganese concentrate of various grades with pure manganese content from 26% to 43% (depending on grade). By-products - expanded clay and sludge.
The enterprise extracts manganese ore from the ore fields assigned to it. The ore reserves will last for more than 30 years. Reserves of manganese ore in Ukraine in total for Ordzhonikidzevsky and Manganese mining and processing plants make up one third of all world reserves.
Manganese fertilizers
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 actively affects the metabolism of proteins, carbohydrates and fats. The ability of manganese to enhance the action of insulin and maintain a certain level of cholesterol in the blood is also considered important. In the presence of manganese, the body uses fats more fully. Cereals (primarily oatmeal and buckwheat), beans, peas, beef liver and many bakery products are relatively rich in this trace element, which practically replenish the daily human need for manganese - 5.0-10.0 mg.
Disease caused by manganese toxin
As mentioned above, manganese compounds cause toxic effects on humans. The most common disease is Parkinson's syndrome. Also a consequence of these toxins are diseases: Central - Nervous System, pneumonia, stomach cancer and lethargy.
Parkinson's disease
Parkinson's disease- this is a hereditary disease in connection with the defeat (degeneration of neurons) of the subcortical formation of the brain - the "black substance" due to the lack of an enzyme (L-tyrosine hydrogenase) and a decrease in dopamine. Suffering from "trembling paralysis", James Parkinson, a doctor, described "his disease" in the literature in 1818, and one of the most famous neuropathologists, Charcot, called it "Parkinson's disease." The frequency of the disease up to 70 years is 180 patients per 100,000 population. after 70 years - 1800 patients per 100,000 population. Men get sick 1.6 times more often than women.
History of manganese
The Swedish chemists K. Scheele and J. Gan are considered to be the discoverers of manganese, the first of whom in 1774 discovered an unknown metal in the widely used iron ore, called in ancient times black magnesia, the second, by heating a mixture of pyrolusite (the main mineral of manganese) with coal, received metallic manganese (calorizator). The name of the new metal received from the German Manganerz, i.e. manganese ore.
Manganese is an element of a side subgroup of the VII group of the IV period of the Periodic Table of Chemical Elements of D.I. Mendeleev, has an atomic number of 25 and an atomic mass of 54.9380. The accepted designation is Mn(from Latin Manganum).
Being in nature
Manganese is quite common, it is in the second ten elements in terms of abundance. In the earth's crust, it is most often found together with iron ores, but there are also deposits of manganese, for example, in Georgia and Russia.
Manganese is a heavy, silvery-white metal, the so-called black metal. When heated, it tends to decompose water, displacing hydrogen. Normally, it absorbs hydrogen.
daily requirement for manganese
For a healthy adult, the daily requirement for manganese is 5-10 mg.
Manganese enters the human body with food, so it is imperative to eat one or more foods from the following list every day:
- nuts ( , )
- cereals and cereals (, wheat)
- legumes ( , )
- vegetables and greens ( , )
- berries and fruits ( , )
- mushrooms ( , )
Useful properties of manganese and its effect on the body
Functions of manganese in the human body:
- regulation of blood glucose levels, stimulation of production
- prevention of diabetes mellitus by lowering blood sugar levels
- normalization of brain activity and processes in the nervous system
- participation in the work of the pancreas and the synthesis of cholesterol
- promoting the growth of connective tissues, cartilage and bones
- influence on lipid metabolism and prevention of excessive deposition of fat in the liver
- involved in cell division
- a decrease in the activity of "bad" cholesterol and a slowdown in the growth of cholesterol plaques.
Interaction with others
Manganese helps to activate the enzymes necessary for proper use by the body, and. The interaction of manganese with and is a recognized antioxidant agent. Large doses will delay the absorption of manganese.
Manganese has found the greatest use in metallurgy, as well as in the production of rheostats and galvanic cells. Manganese compounds are used as thermoelectric material.
Manganese Deficiency Signs
With a diet weighted with a large amount of carbohydrates, an excess of manganese occurs in the body, which is manifested by the following symptoms: anemia, reduced bone strength, growth retardation, and atrophy of the ovaries in women and testicles in men.
Signs of excess manganese
Excess manganese is also not good for the body, its manifestations can be drowsiness, muscle pain, loss of appetite and changes in bone formation - the so-called "manganese" rickets.