manganese dioxide

[èr yǎng huà měng]

inorganic compound

Collection

zero Useful+1

zero

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Manganese dioxide is an inorganic compound with the chemical formula MnO two , black amorphous powder or black rhombic crystal, insoluble in water weak acid 、 weak alkali 、 nitric acid Cold sulfuric acid, soluble in Concentrated hydrochloric acid Resulting in chlorine 。 It is used for the preparation of manganese salt and also for Oxidant Rust remover and catalyst.

Chinese name: manganese dioxide^[2]
Foreign name: Manganese dioxide^[2]
chemical formula: MnO two^[2]
molecular weight: eighty-six point nine three seven^[2]
CAS login number: 1313-13-9^[2]
EINECS login number: 215-202-6^[2]
Melting point: 535 ℃^[2]

Water solubility: Insoluble
Density: 5.02 g/cm³^[2]
Appearance: Black amorphous powder or black rhombic crystal
Application: Preparation of manganese salt, oxidant and rust remover
Security description: S25^[2]
Hazard symbol: Xn^[2]
Hazard description: R20/22^[2]
UN dangerous goods number: three thousand one hundred and thirty-seven^[2]

catalog

▪ Safety terminology
▪ Risk terminology

Physical and chemical properties

Announce

edit

physical property

Melting point: 535 ℃

Density: 5.03g/cm three

Appearance: black amorphous powder or black rhombic crystal

Water solubility: insoluble in water

chemical property

Acidity and alkalinity: manganese dioxide is an amphoteric oxide, which is a very stable black powder solid at room temperature and can be used as a dry battery Depolarizer 。 It is often used in the laboratory to react with concentrated HCl to produce chlorine ：

Manganese dioxide is a strong oxidant in acidic medium.

Manganese dioxide structure

Manganese dioxide has an octahedral structure. The oxygen atom is on the octahedral corner top, and the manganese atom is in the octahedron. The octahedron is connected with each other to form a single chain or double chain. These chains have the same top with other chains, forming a tunnel structure of voids. The octahedron is packed in a hexagonal manner, or Cubic dense packing 。

Manganese dioxide is a kind of Amphoteric oxide , there is corresponding BaMnO three Or SrMnO three Salts in the form of such perovskite structure (obtained through the combination reaction in the molten alkali system)^[1] , also exists Manganese tetrachloride 。

When encountering reducing agent, it is oxidizing. If manganese dioxide is put into hydrogen Obtained by heating to 1400K in the stream Manganese oxide ； Put manganese dioxide in ammonia Heat in the stream to obtain brownish black Manganese trioxide ； React manganese dioxide with concentrated hydrochloric acid to obtain Manganese chloride 、 chlorine And water.

When encountering strong oxidant, it also shows reducibility. If manganese dioxide is added, Potassium carbonate and potassium nitrate or Potassium chlorate The dark green melt can be obtained by mixing and melting, and the hexavalent manganese compound can be obtained by dissolving the melt in water and cooling it Potassium manganate 。 It is a strong oxidant in acidic medium.

Strong oxidant, which does not burn but supports combustion, should not be placed together with combustibles.

In potassium chlorate [KClO three ]Decomposition hydrogen peroxide solution (Hydrogen peroxide, H two O two ）Catalysis in decomposition reaction^[1] Chemicals:

Preparation method

Announce

edit

Mainly from natural minerals Pyrolusite 。 High temperature is widely used Manganese sulfate Prepared by solution electrolysis, Manganese carbonate And pyrolusite can be used as raw materials. The preparation of manganese sulfate solution includes leaching, iron removal, neutralization, heavy metal removal, filtration, static removal of calcium and magnesium and other processes. After high temperature electrolysis, crude products are produced, and then processed, including stripping, crushing, washing, neutralization and drying, to produce qualified crystals. When manganese chloride solution is used for electrolysis, fibrous manganese dioxide can be obtained. There are also manganese carbonate and manganese nitrate thermal decomposition, which are produced by direct oxidation of manganese oxide with oxidants such as sodium chlorate, chlorine, oxygen, etc.

Manganese sulfate

take Rhodochrosite The powder and sulfuric acid are mixed according to the mass ratio of 1: 1.8~1: 2.0 to produce manganese sulfate. Normally, the circulating acid of the electrolytic cell is used, and some sulfuric acid is supplemented. When pH=4, a small amount of manganese dioxide is added, and the Fe in the solution is 2+ Oxidation to Fe 3+ , plus Lime milk Neutralize to near neutral pH, add Barium sulfide Saturated solution, making heavy metal ions generate sulfide precipitation, and then filtering to prepare electrolyte composition: MnSO four =120±20 g/L、H two SO four =At a temperature of 93 ± 5 ℃ and a cell voltage of 2 ～ 3 V, 30 ± 10 g/L, after 20 ～ 30 days of electrolysis, the crude products are generally deposited on the anode to form blocky crude products. The crude products are stripped, crushed, rinsed with water for many times, neutralized with sodium bicarbonate to pH=5 ～ 7, and then filtered, dried and crushed to produce electrolytic manganese dioxide products.

The chemical equation is:

Manganese chloride method reacts rhodochrosite with excessive hydrochloric acid to generate Manganese chloride After the reaction is completed, add lime for neutralization, control pH=4 or so, and add oxidant hydrogen peroxide to make Fe 2+ It is oxidized to form ferric hydroxide precipitation and removed, and purified manganese chloride solution is added Manganese nitrate Prepare electrolyte to make the concentration of manganese chloride 0.5~2.0 mol/L and the concentration of HCl 0.01~1.0 mol/L. Manganese nitrate with the content of 10%~15% can be added to the electrolyte and electrolyzed at 85~95 ℃, which can solve the air pollution and corrosion problems caused by the reaction of trace chlorine emission in the electrolysis process. The fibrous manganese dioxide is obtained by electrolysis, and then the electrolytic manganese dioxide product is obtained by stripping, crushing, neutralization rinsing, filtering, drying and crushing of crude products.

The chemical equation is:

Most of them are underground mining, and the general process flow is the same as "phosphorite". Commonly used mineral processing methods include manual separation, magnetic separation, flotation, gravity separation, etc. In addition, chemical beneficiation and bacterial leaching methods have been widely used for manganese ores.

Beneficiation process flow:

The pyrolusite is mixed with coal powder by the manganese nitrate method, and the high valence manganese is reduced to Manganous oxide , using nitric acid and sulphuric acid Leaching, filtration and purification Manganese nitrate The solution is then concentrated and thermally decomposed to obtain manganese dioxide, and finally refined by dilute nitric acid, activated by sulfuric acid, washed and dried to obtain manganese dioxide products.

The chemical equation is:

Fine grinding of manganese carbonate pyrolusite and mixing with coal powder, reduction roasting to produce manganese oxide, leaching with sulfuric acid, neutralizing the obtained manganese sulfate solution to pH 4~6, precipitating impurities, filtering and removing slag, adding filtrate Sodium sulfide Purified, filtered by pressure, added Ammonium bicarbonate And crystal seeds to generate manganese carbonate precipitation, which is calcined and thermally decomposed at about 450 ℃ with water vapor in the air to generate manganese dioxide Manganese carbonate And manganese dioxide of low valence, dissolved in sulfuric acid, sodium chlorate, washed and dried to obtain manganese dioxide.

The chemical equation is:

Natural manganese ore activation method

High quality pyrolusite is heated to 600-800 ℃ in air, or heated to 300 ℃ in the presence of reducing agents (such as pulverized coal and natural gas) for reduction roasting, so that manganese dioxide is reduced to manganese trioxide, and the reduction products are treated with hot sulfuric acid and disproportionated Manganese trioxide High activity γ - MnO was obtained two And manganese sulfate, after acid leaching, the slurry is filtered, washed, dried and prepared into active manganese dioxide.

The chemical equation is:

Preparation type

Announce

edit

High activity (YE-A01) natural manganese dioxide (YE-A09) is directly used as the cathode material of batteries. With the passage of time, its resources have become increasingly exhausted. The research on the use of low activity and high grade natural manganese dioxide has always been a hot topic for the scientific and technological workers in the manganese industry and battery industry. On the basis of a large number of tests, it was proposed that "electrolytic manganese dioxide (EMD) electrolyte is used as the acid medium for disproportionation activation, and a small amount of NaClO is added three The calcination, disproportionation activation and the optimal combination of activation system for the preparation of active manganese dioxide were studied in depth.

On the basis of previous research work, the chemical manganese dioxide process technology is used for reference, and the "particle electrolytic manganese dioxide (CEMD) electrolyte is used as the acid medium for disproportionation activation, NaClO three It is a new activation system of oxidation and heavy quality of oxidant and impregnation of aluminum containing polychloride, which activates the calcined powder (Mn) of low activity and high grade natural manganese dioxide two O three ）The positive material of crystalline high activity manganese dioxide battery is made. It has rich liquid absorption capacity, large specific surface area and excellent discharge performance, especially 2 Ω heavy load continuous discharge and 3.9 Ω light load intermittent discharge. The physical and chemical properties and electrochemical properties of the developed samples are close to or tend to be close to EMD. In battery production, the expensive electrolytic manganese dioxide can be partially or completely replaced. The potential economic benefits appear and the development and application prospects are broad.

Preparation of manganese trioxide powder

Take a certain amount of natural manganese dioxide ore, dry it, grind it until it passes 100 mesh sieve, and then calcine it for 1.5h in a 700 ℃ converter to make MnO in natural manganese dioxide ore powder two Convert to Mn two O three , take out the powder, cool it to normal temperature, and grind it fully to obtain Mn two O three Powder.

Preparation of active manganese dioxide

Take a certain amount of Mn two O three The powder is placed in "particle electrolytic manganese dioxide (CEMD) electrolyte+NaClO three In the new activation system with oxidant+aluminum containing polychloride as the medium, the activation temperature is controlled at about 80 ℃, and the disproportionation activation time is 2h. After activation, neutralize and wash with 10% NaOH solution, adjust the pH value to about 6, and obtain crystalline active manganese dioxide after stirring, filtering and drying.

Activation mechanism of new activation system

In acid medium, Mn two O three The powder is disproportionated and activated into active manganese dioxide, and the main reaction formula is:

Mn two O three + 2H + →MnO two + Mn 2+ + H two O

According to the chemical reaction formula, sulfuric acid (H two SO four ）It is an acidic medium. When activated, Mn two O three The powder itself undergoes redox reaction, that is, disproportionation reaction. The solid material generated is active manganese dioxide, and the solution material is Manganese sulfate 。 Some literatures suggest that the manganese sulfate solution is purified to prepare solid manganese sulfate. A large number of tests found that H two SO four Activate Mn for acid medium two O three MnSO produced in powder process four Not many, but with H two SO four It is possible to activate the system for acidic medium. Therefore, on the basis of a large number of tests and with reference to chemical manganese dioxide process technology, it is proposed that "CEMD electrolyte is used as acid medium for disproportionation activation, NaClO three It is a new activation system of oxidation and heavy quality of oxidant and impregnation of aluminum containing polychloride.

Mn two O three + H two SO four = MnO two ↓ + MnSO four + H two O

MnSO four +2NaClO three =MnO two ↓+Na two SO four +Cl two ↑+2O two ↑

5MnSO four + 2NaClO three + 4H two O = 5MnO two ↓ + Na two SO four + 4H two SO four + Cl two ↑

4MnSO four + 4MnO four - + 2H two O = 8MnO two ↓ + 4HSO four - + O two ↑

2MnSO four + O two + 2H two O = 2MnO two ↓ + 2H two SO four

Fe two O three + 3H two SO four = Fe two (SO four ) three + 3H two O

Fe two (SO four ) three + 6H two O = 2Fe(OH) three ↓ + 3H two SO four

MeO + H two SO four →MeSO4 + H two O (Me is a metal element)

Selection of CEMD electrolyte

When studying EMD electrolyte as an activation system, it was found that H two SO four Concentration (about 0.5mol/L) is too low, affecting Mn two O three Powder disproportionation activation requires more concentrated H during the activation process two SO four While CEMD electrolyte contains 2.5~3.2 mol/L H two SO four The concentration just meets the requirements of disproportionation activated Mn two O three Acid medium required for powder. Some scholars said that when the medium H two SO four When the concentration exceeds 3mol/L two SO four Increase of concentration, Mn 3+ At H two SO four Increased stability in media, Mn two O three Powder disproportionation and activation to produce MnO two The speed is slow and the crystallinity of the product increases, which makes the capacitance of the active manganese dioxide product easy to decline when it is made into a solid battery. Therefore, CEMD electrolyte contains 2.5~3.2 mol/L H two SO four The concentration is just the ideal activation system concentration. During the activation process, new concentrated H is no longer needed two SO four 。

About the addition of sodium hypochlorite oxidant

Add NaClO three Oxidant, mainly oxidation activation disproportionation Mn two O three Micro amount of MnSO produced in the powder process four And inherent abundance MnSO in CEMD electrolyte four , oxygen in the air is also associated with MnSO four Weak oxidation reaction occurs, and trace MnO exists in the electrolyte four - Ions are also associated with MnSO four Chemical reaction occurs. The product of these chemical reactions is crystalline chemical manganese dioxide, whose particle size is generally about 5 μ m. Some of these grains are filled in the micropores of active manganese dioxide, some are adsorbed on the surface of active manganese dioxide particles, and the rest are evenly and orderly arranged between the active manganese dioxide particles. Grain type chemical manganese dioxide and activated manganese dioxide infiltrate, absorb, bond and sort each other, so that the "activators" can "develop their strengths and circumvent their weaknesses and complement each other" in terms of chemical, physical and electrochemical properties. Therefore, the developed "activator" is called "crystalline active manganese dioxide" for short.

Final conclusion

1. Disproportionation activation with "particle electrolytic manganese dioxide (CEMD) electrolyte as acid medium, NaClO three It is a new activation system of oxidation and heavy quality of oxidant and impregnation of aluminum containing aggregated chlorides, activating NMD baking powder (Mn two O three The method of producing crystalline high activity manganese dioxide is feasible.

2. A series of "actions", such as disproportionation, adsorption, filling, rearrangement, texturing and impregnation, occur in the new activation system, so that the "activated samples" can "develop their strengths, circumvent their weaknesses and complement each other" in terms of chemical, physical and electrochemical properties, and fundamentally improve the physical, chemical and electrochemical properties of the "activated samples".

3. The sample developed by the new activation system has rich liquid absorption capacity (0.249 cm three /g) And larger specific surface area (58.93cm two /g) , and excellent discharge performance.

4. The physical and chemical properties and electrochemical properties of the samples prepared by the new activation system are close to or tend to be close to electrolytic manganese dioxide. In the battery production process, the activation sample can partially or completely replace the expensive Electrolytic manganese dioxide The potential economic benefits are obvious, and the prospect of development and application value is broad.

Application

Announce

edit

application area

Used as depolarizer for dry battery, catalyst and oxidant for synthesis industry, glass industry and enamel industry Colorant , achromatic agent, iron remover, etc. It is used to manufacture metal manganese, special alloy, ferromanganese castings, gas masks, electronic materials, ferrite, etc. In addition, it can also be used in the rubber industry to increase the viscosity of rubber. It can also be used as a catalyst in chemical experiments.

Organic synthesis use

Manganese dioxide is very useful in organic chemistry. The forms of manganese dioxide used for oxides are different, because manganese dioxide has multiple crystalline forms, and the chemical formula can be written as MnO two · x (H two O) n , where x Between 0 and 0.5, and n It can be greater than 0. Manganese dioxide can be produced in the reaction of potassium permanganate (KMnO ₄) and manganese sulfate (MnSO ₄) at different pH.

One of them is dedicated to manganese dioxide chemical reaction It is to convert alcohols into aldehydes. Even if the alcohol has double bonds, it will not be oxidized by manganese dioxide: cis RCH=CHCH two OH + MnO two → cis-RCH=CHCHO + H two O + MnO

The product will not be oxidized even if it is more active. Diols can be oxidized to dialdehyde by manganese dioxide. There are many other manganese dioxide reactions, which can be used to oxidize amine, aromatics and triols.

Laboratory use

Used as a catalyst for hydrogen peroxide decomposition to produce oxygen; Used as catalyst for heating potassium chlorate decomposition to produce oxygen; It reacts with aluminum powder to produce manganese. Used as pigment, yellow glass, etc; React with hot concentrated hydrochloric acid to produce chlorine; Reaction with molten caustic potassium (potassium hydroxide) in air to produce potassium manganate; In the decomposition reaction of potassium permanganate, manganese dioxide acts as the self catalyst of potassium permanganate.

matters needing attention

Announce

edit

Hazard Overview

Health hazard: excessive manganese entering the body can cause poisoning. It mainly damages the central nervous system, especially acute poisoning is rare in the industrial production of extracorporeal cone system. If a large amount of smoke and dust of the product is inhaled in a short time, "metal smoke heat" may occur, and the patient may have headache, nausea, chills, high fever, and sweating. Chronic poisoning shows neurasthenic syndrome, autonomic nerve dysfunction, and mental symptoms of imbalance between excitation and inhibition. In severe cases, toxic psychosis occurs; The manifestations of extrapyramidal system damage include increased muscle tension, tremor, speech disorder, abnormal gait, etc.

Flammability hazard: This product is incombustible and irritant.

First aid measures

Skin contact: Take off contaminated clothes and wash with flowing water.

Eye contact: Lift the eyelid and flush with flowing water or physiological saline. Get medical attention.

Inhalation: quickly leave the site to a place with fresh air. If breathing is difficult, give oxygen. Get medical attention.

Ingestion: drink enough warm water to induce vomiting. Get medical attention.

Fire fighting measures

Hazard characteristics: no special combustion and explosion characteristics. Toxic gas is released due to high thermal decomposition.

Hazardous combustion products: Natural decomposition products are unknown.

Extinguishing method: firefighters must wear full body fire and gas protective clothing and extinguish the fire upwind. When putting out a fire, try to move the container from the fire site to an open place.

Leakage emergency treatment

Emergency treatment: isolate the leakage contaminated area and restrict access. It is recommended that emergency personnel wear dust masks (full face masks) and gas suits. Avoid flying dust, sweep it carefully, put it in a bag and transfer it to a safe place. In case of large leakage, cover it with plastic cloth and canvas. Collect and recycle or transport to waste disposal site for disposal.

Handling storage

Precautions for operation: close operation and strengthen ventilation. Operators must be specially trained and strictly abide by the operating procedures. It is recommended that operators wear self-priming filter type dust mask, chemical safety goggles, anti poison penetration work clothes and rubber gloves. Keep away from flammable and combustible materials. Avoid dust generation. Avoid contact with reducing agents and acids. Load and unload gently during transportation to prevent damage to packaging and containers. Provide leakage emergency treatment equipment. Empty containers may leave harmful substances.

Precautions for storage: store in a cool and ventilated warehouse. Keep away from kindling and heat sources. It shall be stored separately from combustibles, reducing agents and acids, and mixed storage is strictly prohibited. The storage area shall be equipped with appropriate materials to contain leakage.

security information

Announce

edit

Safety terminology

S25：Avoid contact with eyes.

Avoid eye contact.

Risk terminology

R20/22：Harmful by inhalation and if swallowed.

Harmful if inhaled or swallowed.

Novice on the road

Growth task Getting Started with Editing Edit Rule Edit by myself

I have questions

Content query Online Service Official post bar Feedback

Complaints and suggestions

Report bad information Failed to appeal through entries Complaint of infringement information Blocking query and unblocking

Jinggong Network Anbei No. 1100000200001