General overview

Manganese is an element VIIB of the IV period subgroup. Electronic structure atom 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2, the most characteristic oxidation states in compounds are from +2 to +7.

Manganese is a fairly common element, making up 0.1% (mass fraction) of the earth's crust. Found in nature only in the form of compounds, the main minerals are pyrolusite (manganese dioxide MnO2.), gauskanite Mn3O4 and brownite Mn2O3.

Physical properties

Manganese is a silvery-white, hard, brittle metal. Its density is 7.44 g/cm 3, melting point is 1245 o C. Four crystalline modifications of manganese are known.

Chemical properties

Manganese is an active metal; in a number of voltages it is between aluminum and zinc. In air, manganese is covered with a thin oxide film, which protects it from further oxidation even when heated. In a finely crushed state, manganese oxidizes easily.

3Mn + 2O 2 = Mn 3 O 4– when calcined in air

Water at room temperature acts on manganese very slowly, but when heated it acts faster:

Mn + H 2 O = Mn(OH) 2 + H 2

It dissolves in dilute hydrochloric and nitric acids, as well as in hot sulfuric acid (in cold H2SO4 it is practically insoluble):

Mn + 2HCl = MnCl 2 + H 2 Mn + H 2 SO 4 = MnSO 4 + H 2

Receipt

Manganese is obtained from:

1. electrolysis of solution MnSO 4. In the electrolytic method, the ore is reduced and then dissolved in a mixture of sulfuric acid and ammonium sulfate. The resulting solution is subjected to electrolysis.

2. reduction from its oxides with silicon in electric furnaces.

Application

Manganese is used:

1. in the production of alloy steels. Manganese steel, containing up to 15% manganese, has high hardness and strength.

2. manganese is part of a number of magnesium-based alloys; it increases their resistance to corrosion.

Magrane oxides

Manganese forms four simple oxides - MnO, Mn2O3, MnO2 And Mn2O7 and mixed oxide Mn3O4. The first two oxides have basic properties, manganese dioxide MnO2 is amphoteric, and the higher oxide Mn2O7 is an anhydride permanganic acid HMnO4. Manganese(IV) derivatives are also known, but the corresponding oxide MnO3 not received.

Manganese(II) compounds

Oxidation state +2 corresponds to manganese (II) oxide MnO, manganese hydroxide Mn(OH) 2 and manganese(II) salts.

Manganese(II) oxide is obtained in the form of a green powder by reducing other manganese oxides with hydrogen:

MnO 2 + H 2 = MnO + H 2 O

or during thermal decomposition of manganese oxalate or carbonate without air access:

MnC 2 O 4 = MnO + CO + CO 2 MnCO 3 = MnO + CO 2

When alkalis act on solutions of manganese (II) salts, a white precipitate of manganese hydroxide Mn(OH)2 precipitates:

MnCl 2 + NaOH = Mn(OH) 2 + 2NaCl

In air it quickly darkens, oxidizing into brown manganese(IV) hydroxide Mn(OH)4:

2Mn(OH) 2 + O 2 + 2H 2 O =2 Mn(OH) 4

Manganese (II) oxide and hydroxide exhibit basic properties and are easily soluble in acids:

Mn(OH)2 + 2HCl = MnCl 2 + 2H 2 O

Manganese (II) salts are formed when manganese is dissolved in dilute acids:

Mn + H 2 SO 4 = MnSO 4 + H 2- when heated

or by the action of acids on various natural manganese compounds, for example:

MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O

In solid form, manganese (II) salts are pink in color; solutions of these salts are almost colorless.

When interacting with oxidizing agents, all manganese (II) compounds exhibit restorative properties.

Manganese(IV) compounds

The most stable manganese(IV) compound is dark brown manganese dioxide. MnO2. It is easily formed both during the oxidation of lower and during the reduction of higher manganese compounds.

MnO2- an amphoteric oxide, but both acidic and basic properties are very weakly expressed.

IN acidic environment Manganese dioxide is a strong oxidizing agent. When heated with concentrated acids, the following reactions occur:

2MnO 2 + 2H 2 SO 4 = 2MnSO 4 + O 2 + 2H 2 O MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O

Moreover, in the first stage in the second reaction, unstable manganese (IV) chloride is first formed, which then decomposes:

MnCl 4 = MnCl 2 + Cl 2

When fusion MnO2 Manganites are obtained with alkalis or basic oxides, for example:

MnO 2 + 2KOH = K 2 MnO 3 + H 2 O

When interacting MnO2 with concentrated sulfuric acid manganese sulfate is formed MnSO4 and oxygen is released:

2Mn(OH) 4 + 2H2SO 4 = 2MnSO 4 + O 2 + 6H 2 O

Interaction MnO2 with stronger oxidizing agents leads to the formation of manganese (VI) and (VII) compounds, for example, when fused with potassium chlorate, potassium manganate is formed:

3MnO 2 + KClO 3 + 6KOH = 3K2MnO 4 + KCl + 3H 2 O

and when exposed to polonium dioxide in the presence of nitric acid - manganese acid:

2MnO 2 + 3PoO 2 + 6HNO 3 = 2HMnO 4 + 3Po(NO 3) 2 + 2H 2 O

Applications of MnO 2

As an oxidizing agent MnO2 used in the production of chlorine from hydrochloric acid and in dry galvanic cells.

Manganese(VI) and (VII) compounds

When manganese dioxide is fused with potassium carbonate and nitrate, a green alloy is obtained, from which dark green crystals of potassium manganate can be isolated K2MnO4- salts of very unstable permanganic acid H2MnO4:

MnO 2 + KNO 3 + K 2 CO 3 = K 2 MnO 4 + KNO 2 + CO 2

V aqueous solution manganates spontaneously transform into salts of manganese acid HMnO4 (permanganates) with the simultaneous formation of manganese dioxide:

3K 2 MnO 4 + H 2 O = 2KMnO 4 + MnO 2 + 4KOH

in this case, the color of the solution changes from green to crimson and a dark brown precipitate is formed. In the presence of alkali, manganates are stable; in an acidic environment, the transition of manganate to permanganate occurs very quickly.

When strong oxidizing agents (for example, chlorine) act on a manganate solution, the latter is completely converted into permanganate:

2K 2 MnO 4 + Cl 2 = 2KMnO 4 + 2KCl

Potassium permanganate KMnO4- the most famous salt of permanganic acid. It appears as dark purple crystals, moderately soluble in water. Like all manganese (VII) compounds, potassium permanganate is a strong oxidizing agent. It easily oxidizes many organic substances, converts iron(II) salts into iron(III) salts, oxidizes sulfurous acid into sulfuric acid, releases chlorine from hydrochloric acid, etc.

In redox reactions KMnO4(ion MnO4-)can be restored to varying degrees. Depending on the pH of the medium, the reduction product may be an ion Mn 2+(in an acidic environment), MnO2(in a neutral or slightly alkaline environment) or ion MnO4 2-(in a highly alkaline environment), for example:

KMnO4 + KNO 2 + KOH = K 2 MnO 4 + KNO 3 + H 2 O- in a highly alkaline environment 2KMnO 4 + 3KNO 2 + H 2 O = 2MnO 2 + 3KNO 3 + 2KOH– in neutral or slightly alkaline 2KMnO 4 + 5KNO 2 + 3H 2 SO 4 = 2MnSO 4 + K 2 SO 4 + 5KNO 3 + 3H 2 O– in an acidic environment

When heated in dry form, potassium permanganate already at a temperature of about 200 o C decomposes according to the equation:

2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2

Free permanganate acid corresponding to permanganates HMnO4 has not been obtained in the anhydrous state and is known only in solution. The concentration of its solution can be increased to 20%. HMnO4- a very strong acid, completely dissociated into ions in an aqueous solution.

Manganese (VII) oxide, or manganese anhydride, Mn2O7 can be prepared by the action of concentrated sulfuric acid on potassium permanganate: 2KMnO 4 + H 2 SO 4 = Mn 2 O 7 + K 2 SO 4 + H 2 O

Manganese anhydride is a greenish-brown oily liquid. It is very unstable: when heated or in contact with flammable substances, it explodes into manganese dioxide and oxygen.

As an energetic oxidizing agent, potassium permanganate is widely used in chemical laboratories and industries, it also serves as a disinfectant, reaction thermal decomposition Potassium permanganate is used in the laboratory to produce oxygen.

MnО, Mn 2 О 3, MnО 2, Mn 3 О 4, Mn 2 О 7, Mn 5 О 8. Except for Mn 2 O 7, all oxides are crystals, not soluble. in the water. When heated higher oxides, O2 is split off and formed lower oxides:

When exposed to air or in an O2 atmosphere above 300 °C, MnO and Mn2O3 are oxidized to MnO2. Anhydrous and hydrated. Mn oxides are included in the composition of manganese and ferromanganese ores in the form of the minerals pyrolusite b-MnO 2, psilomelane mMO.nMnO 2 .xH 2 O [M = Ba, Ca, K, Mn(H)], manganite b-MnOOH (Mn 2 O 3 .H 2 O), groutite g-MnOOH, braunite 3Mn 2 O 3 .MnSiO 3, etc. with a MnO 2 content of 60-70%. Processing of manganese ores includes wet concentration and subsequent processing. chem. separation of oxides MnO 2 or Mn 2 O 3 by methods of sulfitization and sulfatization, carbonization, reduction. roasting, etc. Monoxide MnO (mineral manganosite). Hexagon is stable up to 155.3 °C. modification, above - cubic (see table). Semiconductor. Antiferromagnet with Néel point 122 K; mag. susceptibility + 4.85.10 - 3 (293 K). Possesses weakly basic properties; is reduced to Mn by hydrogen and active metals when heated. When interacting MnO with compounds form Mn(II) salts, with a melt of NaOH at 700-800°C and excess O 2 - Na 3 MnO 4, under the action of (NH 4) 2 S - MnS sulfide. Obtained by the decomposition of Mn(OH) 2, Mn(C 2 O 4), Mn(NO 3) 2 or MnCO 3 in an inert atmosphere at 300 °C, controlled by the reduction of MnO 2 or Mn 2 O 3 with hydrogen or CO at 700-900 ° WITH. Component of ferrites and other ceramics. materials, slag for metal desulfurization, microfertilizers, piperidine dehydrogenation catalyst, antiferromagnetic. material. Sesquioxide Mn 2 O 3 exists in two modifications - rhombic. a (mineral kurnakite) and cubic. b (bixbyite mineral), transition temperature a: b 670 °C; paramagnetic, magnetic susceptibility +1.41X10 - 5 (293 K); is reduced by H 2 at 300°C to MnO, by aluminum upon heating. - to Mn.


Under the influence of dil. H 2 SO 4 and HNO 3 transform into MnO 2 and Mn(II) salt. Get Mn 2 O 3 thermal. decomposition of MnOOH. Manganese (II, III) oxide Mn 3 O 4 (hausmannite mineral); a-Mn 3 О 4 at 1160°С transforms into b-Mn 3 О 4 с cubic. crystalline grate; DH 0 transition a: b 20.9 kJ/mol; paramagnetic, magnetic susceptibility + 1.24.10 - 5 (298 K). Shows chemical properties inherent in MnO and Mn 2 O 3. MnO 2 dioxide is the most common compound. Mn in nature; max. b-modification (mineral pyrolusite) is stable. Known rhombus. g-MnO 2 (mineral ramsdelite, or polyanite), as well as a, d and e, considered as solid solutions decomposition forms MnO 2. Paramagnetic, magnetic susceptibility + 2.28.10 - 3 (293 K). Mn dioxide - non-stoichiometric. conn., there is always a lack of oxygen in its lattice. Amphoteric. H2 is reduced to MnO at 170°C. When interacting with NH 3 H 2 O, N 2 and Mn 2 O 3 are formed. Under the influence of O 2 in the melt, NaOH gives Na 2 MnO 4, in a conc. kit - the corresponding salts of Mn(IV), H 2 O and O 2 (or Cl 2 in the case of hydrochloric acid). MnO 2 is obtained by the decomposition of Mn(NO 3) 2 or Mn(OH) 2 at 200°C in air, the reduction of KMnO 4 in a neutral environment, and the electrolysis of Mn(II) salts. Used for the production of Mn and its compounds, driers, as a depolarizer in dry elements, a component of brown pigment (umber) for paints, for glass brightening, as a reagent for the detection of Cl -, an oxidizing agent in hydrometallurgy of Zn, Cu, U, a catalyst component in hopcalite cartridges, etc. Active MnO 2, the resulting interaction. aqueous solutions MnSO 4 and KMnO 4, oxidizing agent in org. chemistry. Manganese (VII) oxide Mn 2 O 7 (dimanganese heptaoxide, manganese anhydride) - oily green liquid; m.p. 5.9 °C; dense 2.40 g/cm3; DH 0 sample -726.3 kJ/mol. Above 50 °C, with slow heating, it begins to decompose with the release of O 2 and the formation of lower oxides, and at more tall tits or high heating rates explodes; extremely sensitive to fur. and thermal effects. Strong oxidizing agent; upon contact with Mn 2 O 7, flammable substances ignite. M. b. received during interaction KMnO 4 with H Z SO 4 in the cold. Oxide Mn 5 O 8, or Mn 2 II (Mn IV O 4) 3, is a solid substance; not sol. in water; m.b. obtained by oxidation of MnO or Mn 3 O 4 ; easily decomposes into MnO 2 and O 2. Of the Mn hydroxides, stoichiometric. conn. are only Mn(OH) 2 , MnO(OH) and HMnO 4 , others are hydrate. oxides of variable composition, similar in chemical St. you corresponding oxides. The acid properties of hydroxides increase with increasing oxidation state of Mn: Mn(OH) 2< MnО(ОН) (или Mn 2 O 3 .xH 2 O) < MnO 2 .xН 2 О < Mn 3 О 4 .xН 2 О < Н 2 MnО 4 < НMnО 4 . Гидроксид Мn(II) практически не раств. в воде (0,0002 г в 100 г при 18 °С); основание средней силы; раств. в р-рах солей NH 4 ; на воздухе постепенно буреет в результате окисления до MnО 2 .xН 2 О. Гидроксиоксид Mn(III) MnO(OH) известен в двух модификациях; при 250 °С в вакууме обезвоживается до g-Mn 2 О 3 ; в воде не раств. Прир. манганит не разлагается HNO 3 и разб. H 2 SO 4 , но медленно реагирует с H 2 SO 3 , искусственно полученный легко разлагается минер. к-тами; окисляется О 2 до b-MnО 2 . См. также Manganates. M. o. toxic; MPC see Art. Manganese. Lit.: Pozin M.E.. Technology of mineral salts, 4th ed., part 1 2, L., 1974. P. M. Chukurov.

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Manganese dioxide (MnO2) or manganese (IV) oxide is a dark gray substance. When heated in air to 530 degrees. C manganese dioxide decomposes, releasing oxygen, as shown above. In a vacuum or in the presence of a reducing agent, this reaction proceeds much more intensely.

When manganese dioxide is boiled with concentrated nitric acid, a manganese (II) salt is formed and oxygen is released:

2 MnO 2 + 4 HNO 3 = 2 Mn(NO 3) 2 + 2 H 2 O + O 2.

Manganese dioxide in an acidic environment exhibits oxidizing properties:

MnO 2 + 4 HCl = MnCl 2 + Cl 2 + 2 H 2 O;

MnO 2 + 2 FeSO 4 + 2 H 2 SO 4 = MnSO 4 + Fe 2 (SO 4) 3 + 3 H 2 O.

When manganese (IV) oxide is fused with alkalis without air access, manganite or manganate (IV) is formed:

2 MnO 2 + 2 KOH = K 2 MnO 3 + H 2 O.

In the presence of atmospheric oxygen, which plays the role of an oxidizing agent, a manganate salt (VI) is formed during fusion:

2 MnO 2 + 4 KOH + O 2 = 2 K 2 MnO 4 + 2 H 2 O.

Potassium manganate (K 2 MnO 4) spontaneously decomposes into potassium permanganate and manganese dioxide:

3 K 2 MnO 4 + 2 H 2 O = 2 KMnO 4 + MnO 2 + 4 KOH.

Potassium permanganate (KMnO4) is widely used in laboratory practice, industry, medicine and everyday life. It is a very strong oxidizing agent. Depending on the environment, manganese in the presence of a reducing agent can be reduced to different oxidation states. In an acidic environment it is always reduced to Mn(II):

2 KMnO 4 + 10 KVr + 8 H 2 SO 4 = 2 MnSO 4 + 6 K 2 SO 4 + 5 Br 2 + 8 H 2 O.

Potassium manganate (K 2 MnO 4) and manganese dioxide behave similarly.

In an alkaline environment, potassium permanganate is reduced to manganate:

2 KMnO 4 + K 2 SO 3 + 2 KOH = K 2 SO 4 + 2 K 2 MnO 4 + H 2 O.

In a neutral or slightly alkaline environment, potassium permanganate is reduced to manganese dioxide:

2 KMnO 4 + C 6 H 5 CH 3 = 2 KOH + 2 MnO 2 + C 6 H 5 COOH;

2 KMnO 4 + 3 MnSO 4 + 2 H 2 O = 5 MnO 2 + K 2 SO 4 + 2 H 2 SO 4.

Last reaction used in analytical chemistry in the quantitative determination of manganese.

Previously, potassium permanganate was prepared by the oxidation of either manganese dioxide or potassium manganate. Manganese dioxide was oxidized with nitrate when fused with alkali:

MnO 2 + KNO 3 + 2 KOH = K 2 MnO 4 + KNO 2 + H 2 O.

The resulting potassium manganate in solution spontaneously decomposed into potassium permanganate and manganese dioxide:

3 K 2 MnO 4 + 2 H 2 O = 2 KMnO 4 + MnO 2 + 4 KOH.

According to the second method, potassium manganate was oxidized with chlorine:

2 K 2 MnO 4 + Cl 2 = 2 KMnO 4 + 2 KCl.

Currently, potassium permanganate is obtained by electrolytic oxidation of manganate:

MnO 4 2- — e — = MnO 4 — .

Potassium permanganate is widely used both in industry and in laboratory practice. It is used to bleach cotton, wool, spinning fibers, clarify oils and oxidize various organic substances. In laboratory practice, it is used to produce chlorine and oxygen:

2 KMnO 4 + 16 HCl = 2 KCl + 2 MnCl 2 + 5 Cl 2 + 8 H 2 O;

2 KMnO 4 = K 2 MnO 4 + MnO 2 + O 2.

In analytical chemistry, potassium permanganate is used for quantification substances with reducing properties (Fe 2+, Sn 2+, AsO 3 3+, H 2 O 2, etc.). This analysis method is called permanganatometry.

Receipt

• · Minerals found in nature braunite, kurnakite and bixbyite - manganese oxide with various impurities.
• · Oxidation of manganese(II) oxide:
• Reduction of manganese(IV) oxide:

Physical properties

Manganese(III) oxide forms brown-black crystals of several modifications:

• · b-Mn2O3, rhombic system, kurnakite mineral;
• · β-Mn2O3, cubic system, space group I a3, cell parameters a = 0.941 nm, Z = 16, mineral bixbyite;
• · g-Mn2O3, tetragonal system, cell parameters a = 0.57 nm, c = 0.94 nm.

Does not dissolve in water.

Paramagnetic.

Chemical properties

Decomposes when heated:

• Reduced by hydrogen:
• · When dissolved in acids, it disproportionates:
• · When fused with metal oxides, it forms manganite salts:

Manganese(IV) oxide

Table 6. Manganese(IV) oxide.

Chemical properties

Under normal conditions it behaves quite inertly. When heated with acids, it exhibits oxidizing properties, for example, it oxidizes concentrated hydrochloric acid to chlorine:

With sulfuric and nitric acids, MnO2 decomposes with the release of oxygen:

When interacting with strong oxidizing agents, manganese dioxide is oxidized to Mn7+ and Mn6+ compounds:

Manganese dioxide exhibits amphoteric properties. Thus, when a sulfuric acid solution of the salt MnSO4 is oxidized with potassium permanganate in the presence of sulfuric acid, a black precipitate of the salt Mn(SO4)2 is formed.

When alloying with alkalis and basic oxides, MnO2 acts as acid oxide, forming manganite salts:

Is a catalyst for the decomposition of hydrogen peroxide:

Receipt

In laboratory conditions obtained by thermal decomposition potassium permanganate:

It can also be prepared by reacting potassium permanganate with hydrogen peroxide. In practice, the resulting MnO2 catalytically decomposes hydrogen peroxide, as a result of which the reaction does not proceed to completion.

At temperatures above 100 °C, reduction of potassium permanganate with hydrogen:

Manganese(VII) oxide

• · Manganese(VII) oxide Mn2O7 - greenish-brown oily liquid (tmelt=5.9 °C), unstable at room temperature; a strong oxidizer, upon contact with flammable substances it ignites them, possibly with an explosion. Explodes from a push, from a bright flash of light, when interacting with organic substances. Manganese(VII) oxide Mn2O7 can be obtained by the action of concentrated sulfuric acid on potassium permanganate:
• · The resulting manganese(VII) oxide is unstable and decomposes into manganese(IV) oxide and oxygen:
• At the same time, ozone is released:
• Manganese(VII) oxide reacts with water to form permanganic acid:

Manganese(VI) oxide

Table 7. Manganese(VI) oxide.

Manganese(VI) oxide -- inorganic compound, manganese metal oxide with the formula MnO3, dark red amorphous substance, reacts with water.

manganese dioxide production chemical

Receipt

· Formed by the condensation of violet vapors released when the solution is heated potassium permanganate in sulfuric acid:

Physical properties

Manganese(VI) oxide forms a dark red amorphous substance.

Chemical properties

• · Decomposes when heated:
• Reacts with water:
• With alkalis it forms salts - manganates:

Patterns of changes in the properties of manganese oxides

The most stable are MnO2, Mn2O3 and Mn3O4 (mixed oxide - trimanganese tetroxide).

The properties of manganese oxides depend on the oxidation state of the metal: with increasing oxidation degree, the acidic properties increase:

MnO > Мn2О3 > MnO2 > Мn2О7

Manganese oxides exhibit oxidizing or reducing properties depending on the degree of oxidation of the metal: higher oxides are oxidizing agents and are reduced to MnO2, lower oxides are reducing agents, and when oxidized, form MnO2. Thus, MnO2 is the most stable oxide.

methods for producing manganese dioxide

The invention relates to the field of metallurgy, more specifically, to the production of high-quality manganese oxides, which can be widely used in the chemical and metallurgical industries. A method for producing manganese dioxide involves dissolving manganese-containing raw materials in nitric acid to obtain a solution of manganese nitrates and nitrates of calcium, potassium, magnesium, and sodium impurities present in the ore. Then thermal decomposition of nitrates is carried out in an autoclave. Thermal decomposition is carried out with a constant decrease in pressure in the autoclave, starting from a pressure of 0.6 MPa and reducing it to 0.15 MPa at the end of the process. In this case, during thermal decomposition, the pulp is continuously stirred with a stirrer rotating at a speed of 1-15 rpm and vibration is applied to it with a frequency of 20-50 hertz. The method can be implemented at chemical enterprises that have autoclaves operating under pressure. The technical result of the invention is the production of manganese dioxide of improved quality. 2 tab., 2 pr.

The invention relates to the field of ferrous metallurgy, more specifically, to the production of high-quality manganese dioxide, which can be widely used in the chemical and metallurgical industries, in particular in the production of electrolytic and electrothermal manganese, medium-carbon ferromanganese, and low-phosphorus alloys based on it.

Several methods for producing pure manganese dioxide are known from the technical literature: chemical, hydrometallurgical, pyrohydrometallurgical and pyrometallurgical.

The main requirements for chemical methods obtaining manganese dioxide are:

• - efficiency of phosphorus and waste rock removal;
• - simplicity of hardware design;
• - high productivity;
• - availability and low cost of reagents.

There is a known method for producing pure manganese dioxide using the sulfuric acid method. The essence of the method is as follows: sulfur dioxide containing sulfur dioxide (SO2) and sulfuric anhydride (SO3) is passed through a suspension (S:L = 1:4) prepared from ore and a solution of calcium dithionate. The dissolution of these gases in water leads to the formation of sulfurous and sulfuric acids. Manganese oxides intensively dissolve in sulfurous acid to form manganese salt of dithionate acid and manganese sulfate according to the reactions: MnO2+2SO2 = MnS2O6; MnO2+SO2 = MnSO4.

In the presence of excess calcium dithionate, calcium sulfate precipitates and manganese dithionate forms: MnSO4+CaS2O6=MnS2O6+CaSO4

The leached pulp is neutralized with lime milk to pH 4-5, then it is aerated to oxidize ferrous oxide and remove sulfur dioxide. The following precipitates: ferric iron, phosphorus, aluminum, silica. The precipitate is filtered off, washed hot water and sent to the dump. From the purified solution, by adding quicklime, manganese is precipitated in the form of hydroxide, and calcium dithionate is again obtained, which is returned to the process:

MnS2O6+Ca(OH)2=Mn(OH) 2+CaS2O6.

The precipitate of manganese hydroxide is filtered off, washed, dried and calcined. The calcined concentrate contains, %: 92 - MnO2, 1.5 - SiO2, 4.0 - CaO, 0.02 - P2O5 and 0.5-3 - SO 2 (M.I. Gasik. Metallurgy of manganese. Kyiv: Technology, 1979, pp.55-56).

The disadvantages of the known method for producing manganese dioxide are:

• - complexity of hardware design;
• - the product is contaminated with waste rock (SiO2, CaO, etc.);
• - high concentration of sulfur in the final product (from 0.5 to 3%).

The closest to the proposed one in terms of technical essence and achieved effect is the method of producing manganese dioxide by thermal decomposition of manganese nitrate in the presence of calcium, magnesium, potassium and sodium nitrates, according to which the decomposition is carried out at a pressure of 0.15-1.0 MPa (Author’s certificate No. 1102819, cl. C22B 47/00; C01G 45/02, priority dated 05/20/83, published 07/15/84, bulletin No. 26).

According to the prototype method, manganese dioxide is produced in the presence of calcium, magnesium, potassium and sodium nitrates, decomposition is carried out at a pressure of 0.15-1.0 MPa.

Technological parameters and properties of the prototype method:

• - decomposition temperature, °C - 170-190;
• - rate of formation of manganese dioxide, kg/m3h - 500-700;
• - degree of decomposition of Mn(NO3)2,% of the original amount - 78-87;
• - conditions for unloading pulp from the reactor - by gravity;
• - moisture content in nitrogen oxides, % - 19-25;
• - energy consumption, MJ/kg - 1.7-2.2;
• - MnO2 content in manganese dioxide, % - 99.5.

The disadvantages of this known method are the low rate of decomposition of manganese nitrate, high energy consumption, and the high amount of water in the resulting nitrogen oxides.

The objective of the present invention is to simplify the technology for producing manganese dioxide, increasing the rate of decomposition and product yield.

The goal is achieved by the fact that the process of thermal decomposition is carried out with a gradual decrease in pressure in the autoclave, starting from a pressure of 0.6 MPa and reducing it to 0.15 MPa at the end of the process, while the pulp is continuously processed with a stirrer rotating at a speed of 1-15 rpm /min; in this case, during the process of thermal decomposition, vibration with a frequency of 20-50 hertz is applied to the rotating stirrer.

The upper pressure value for the thermal decomposition of nitrates is determined by the conditions for processing nitrogen oxides into acid (it is carried out at a pressure not exceeding 0.6 MPa), and the lower limit is determined by practical expediency. A gradual decrease in pressure to 0.15 MPa ensures more complete thermal decomposition of manganese nitrates.

Reducing the mixer rotation speed below 1 rpm does not provide a homogeneous pulp solution. Increasing the rotation speed above 15 rpm leads to pulp separation and the appearance of areas with a higher water concentration (due to differences in densities).

Lower vibration frequencies - below 20 hertz, imposed on the mixer, have virtually no effect on the thermal decomposition of manganese nitrate. Increasing the vibration frequency above 50 hertz is not economically justified.

If these conditions are met, not only the rate of decomposition of manganese nitrate increases, but the process itself as a whole becomes more technologically advanced. It has been established that in the proposed process, the pulp yield does not greatly depend on its physical properties, which greatly simplifies the process of unloading it from the reactor, while nitrogen oxides contain lower concentrations of water and can be easily processed back into acid. Table 1 presents comparative data on the technological parameters for producing manganese dioxide using the known and proposed methods. The indicators (averaged) for the proposed method for producing manganese dioxide, presented in Table 8, are taken based on the results of the experiments (example 1).

Table 8

Technological parameters and properties
Famous	Proposed
Decomposition temperature, °C
Pressure, MPa		Gradual decrease in pressure from 0.6 to 0.15
Rate of formation of manganese dioxide, kg/m3h
Time required to form 200 kg of manganese dioxide, h
Degree of decomposition of Mn(NO3)2, % of the original amount
Conditions for unloading pulp from the reactor	By gravity	By gravity
Energy consumption, MJ/kg MnO2
Mixer rotation speed, rpm.

During thermal decomposition, vibration with a frequency of 30 hertz was applied to the rotating stirrer - the degree of decomposition of Mn(NO3)2 increases by 2-3.5%.

Physico-chemical properties of the powder:

• - density - 5.10 g/cm3;
• - MnO2 content - 99.6 wt.%;
• - Fe content - less than 3×10-4 wt.%,
• - P content - no more than 5H10-3 wt.%;
• - H 2O - no more than 3×10-2 wt.%.

Below are examples, not exclusive of others, within the scope of the claims.

1.5 kg of nitrate solution of the following composition, wt.%: 40.15 Mn(NO3)2; 25.7 Ca(NO3) 2; 7.3 Mg(NO3)2; 9.2 KNO3; 5.7 NaNO3; 15.0 H2O.

The weight of water removed during thermal decomposition was determined by the difference in its weight in the initial solution and in the liquid phase of the pulp. The amount of released nitrogen oxides was determined by the stoichiometry of the reaction of thermal decomposition of manganese nitrate in accordance with the amount of MnO2 obtained. The main results of the experiments are presented in Table 9.

Table 9

Options	Examples of concrete implementation
Known method	Suggested method
Decomposition temperature, C°
Pressure, MPa*
Mixer rotation speed, rpm
Vibration frequency, Hz
Decomposition time, min
MnO2 formation rate, kg/m3h
Volume of released gases, m3 per 1 kg MnO2
Yield of dry manganese dioxide, %
The upper pressure limit for the thermal decomposition of nitrates is determined by the conditions for processing nitrogen oxides into acid

Manganese dioxide was obtained with the following composition, wt.%: MnO2 - 99.6; R<0,005; S<0,05; SiO2<0,1; (К, Mg, Na, Ca)<0,1.

Thus, the proposed method provides not only faster decomposition of manganese nitrate, but also significantly simplifies the technology for the production of MnO2, both at the unloading stage and at the stage of regeneration of nitrogen oxides; at the same time, redistribution costs are significantly reduced. The yield of the resulting dry manganese dioxide is 84-92% versus 78% (according to a known method) of the theoretically possible.

The resulting manganese dioxide is used for the smelting of metallic manganese by an extra-furnace process.

The charge had the following composition, kg:

• - MnO2 - 10;
• - Al - 4.9;
• - CaO - 0.6.

Only 15.5 kg.

The mixture was mixed, loaded into the smelting shaft and set on fire using a fuse. The melting time was 2.4 minutes. We obtained 5.25 kg of manganese metal composition. % Mn 98.9; Al 0.96; P - traces (less than 0.005%) and 9.3 kg of slag composition, wt.%: MnO 14.6; Al2O3 68.3; CaO 18.0.

The extraction of manganese into the alloy was 85.0%.

Slag from the smelting of manganese metal can be used as a feedstock (instead of bauxite) in the production of aluminum.

The application of the proposed invention will solve the problem of using significant reserves of low-grade manganese ores, in particular carbonate ores of the Usinsk deposit or ferromanganese nodules, the enrichment of which by any other means is currently unprofitable.

The resulting manganese alloys are characterized by a high concentration of the leading element (manganese) and a low content of harmful impurities (phosphorus and carbon).

The use of manganese ferroalloys in the smelting of high-quality steel grades leads to a reduction in the metal consumption of structures, simplifies the alloying process and provides a significant economic effect.

The production of manganese concentrates by chemical methods will significantly reduce the country's shortage of manganese ferroalloys, and its production can be organized at chemical plants.

The proposed method for producing manganese dioxide can be organized at enterprises that have the ability to utilize nitrogen oxides.

FORMULA OF THE INVENTION

A method for producing manganese dioxide by thermal decomposition, including dissolving manganese-containing raw materials in nitric acid to obtain a solution of manganese nitrates and nitrates, impurities of calcium, potassium, magnesium, sodium present in the ore, and subsequent thermal decomposition of nitrates in an autoclave, characterized in that thermal decomposition is carried out at a constant decrease in pressure in the autoclave, starting from a pressure of 0.6 MPa and reducing it by the end of the process to 0.15 MPa, while the pulp is continuously processed with a mixer rotating at a speed of 1-15 rpm and vibrating it at a frequency of 20 -50 Hz.

Experimental part

The above experiences are applied in large enterprises.

I want to consider a laboratory method for producing manganese dioxide in tin dioxide.

Accessories:

• 1. Porcelain crucible:
• 2. Glass filter.

The essence of the method: Preparation of solid oxides by thermal decomposition of a mixture of SnC2O4*H2O and MnSO4*5H2O, calcination in air.

Preliminary synthesis of SnC2O4*H2O.

To obtain tin oxalate, we took 10 g of tin sulfate and 4.975 g of ammonium oxalate. Solutions of both substances were prepared; for this purpose, tin sulfate was dissolved in 100 ml of water, and ammonium oxalate was dissolved in 50 ml of water. Then, a solution of ammonium oxalate was added to the tin sulfate solution. Active precipitation of white fine sediment (SnC2O4*H2O) was observed. The resulting suspension was filtered on a thick glass filter.

Reaction equation:

SnSO4* H2O +(NH4)2C2O4*H2O>SnC2O4*H2Ov+(NH4)2SO4 + H2O

The result was 7.934 g of tin oxalate, with an estimated mass of 9.675. The reaction yield was 82.0%.

According to the reaction equations

MnSO4*5H2O >MnO + SO3 (g)+ 5 H2O(g) >MnO2.

SnC2O4*H2O >SnO + CO2 + H2O >SnO2

A) 7.5% MnO2 / 92.5% SnO2.

To obtain it, we took: 0.75 g. SnC2O4 * H2O, 0.07 g. MnSO4 * 5H2O. (Since the amount of manganese sulfate was significantly less than the amount of ammonium oxalate, to achieve greater homogeneity of the mixture, after placing it in a porcelain crucible, a few drops of water were added. Then the mixture was calcined on a burner.). The calcination mode at 900 °C for 2 hours did not give any result (the grayish-cream color of the mixture remained). As a result of calcination at 1200 °C for 2 hours, the sample acquired a bright red color. Sample weight 0.5 g.

• B) 15% MnO2 / 85% SnO2. (0.761 g SnC2O4*H2O, 0.088 g MnSO4*5H2O) Sample weight 0.53 g.
• B) 22% MnO2 / 78% SnO2. (0.67 g SnC2O4*H2O, 0.204 g MnSO4*5H2O). Sample weight 0.52 g.
• D) 28% MnO2 / 72% SnO2 (0.67 g. SnC2O4 * H2O, 0.2911 g. MnSO4 * 5H2O). Sample weight 0.56 g.