Manganese, Mn, atomic number 25
Manganese price, history, occurrence, extraction and application
Manganese [maŋɡaːn] is a chemical element with the element symbol Mn and atomic number 25. In the periodic table it is in the 7. Subgroup (7, IUPAC group), the manganese group. Manganese is a silvery-white, hard, very brittle transition metal that in some ways resembles iron.
Manganese is found in nature primarily as brownstone and is mined in large quantities. 90% of the mined manganese is used in the steel industry in the form of ferromanganese as an alloying constituent of steel. It removes oxygen and sulfur from the steel and at the same time improves through-hardening. Manganese (IV) oxide, which is used as a cathode in alkaline manganese batteries, is also economically important.
The element has a high biological importance as a component of various enzymes. Thus, it acts at a central site in the photosynthesis cycle, where a manganese-calcium cluster is responsible for the oxidation of water to oxygen.
History
Naturally occurring manganese oxides such as manganese dioxide have long been known and used as natural pigments. Black manganese oxide pigments, for example, were found in the 17.000 year old cave paintings in the caves of Ekain and Lascaux. Manganese compounds have been used in glass production since the fourth century BC in the Roman Empire. Manganese has two different functions. If brownstone is used, it colors the glass intensely brown-violet. If, on the other hand, trivalent manganese oxide is added to iron-containing glasses, it discolors them by oxidizing the green-colored divalent iron to the slightly yellow trivalent iron, which together with the violet of the manganese gives a gray "discolored" appearance.
The first extraction of the element probably succeeded 1770 Ignatius Gottfried Kaim (1746-1778), which reduced carbon monoxide with manganese and received impure manganese, which he called Braunsteinkönig. However, this discovery has not become very popular. 1774 recognized Carl Wilhelm Scheele that Braunstein must contain an unknown element, in the same year Johan Gottlieb Gahn made on Scheele's suggestion to manganese by reducing manganese dioxide with carbon. The name Manganesium was first chosen after the Latin name for manganese manganese mangy, but after the discovery of magnesium it was abbreviated to manganese (ium) because of possible confusion. Braunstein was described by Pliny because of the similarity to the magnet iron (or magnes masculini sexus) as magnes feminei sexus (since brownstone is not magnetic), which became manganesia in the Middle Ages.
1839 has been recognized that manganese improves the malleability of iron. When 1856's Robert Forester Mushet (1811-1891) showed that the addition of manganese allows mass production of steel using the Bessemer process, manganese was quickly used in large quantities for steel production. Braunstein also acquired technical importance from 1866, when Walter Weldon developed the Weldon process for chlorine production, in which hydrochloric acid is oxidized to chlorine by means of manganese dioxide.
occurrence
Manganese is a common element on Earth, in the continental crust it contains 0,095%, similar to phosphorus or fluorine. After iron and titanium, it is the third most common transition metal. It is not elementary, but always in connections. In addition to manganese silicates and manganese carbonate, it is mainly bound in oxides. Common minerals are the mineral group of brownstones, manganite, hausmannite, brownite, rhodochrosite and rhodonite. The manganese occurs in different oxidation states as a two-, three- and four-valent manganese, which sometimes occur as in Hausmannite in the same mineral.
While many compounds of divalent manganese are slightly water-soluble, compounds in higher oxidation states are usually sparingly soluble and physically and chemically stable. This is why manganese ores are formed primarily under oxidative conditions. Although iron behaves similarly to manganese and also oxidizes under oxidative conditions from the slightly soluble divalent to the sparingly soluble trivalent iron, there are only a few iron-manganese mixed salts. This is due to the fact that manganese requires much higher oxygen concentrations for oxidation than iron.
Degradable manganese ores can be classified geologically into three groups. The first type are rhodochrosite brownite ores trapped in precambrian volcanic rocks. These ores are found mainly around the southern Atlantic, for example in Brazil, Guyana, the Ivory Coast, Ghana, Burkina Faso or Congo. Ores of the second type are found in strongly oxidized, iron and silicate rich sedimentary rocks from the Proterozoic. The deposits of this type at Hotazel in South Africa and Corumbá in Brazil are among the largest manganese deposits in the world. The third type includes manganese-schist ores formed by sedimentation in shallow shelf seas. This type includes deposits in Gabon, the Ukraine and other countries around the Black Sea.
About 75% of the known resources of manganese are in the Kalahari of South Africa. In the Ukraine, Brazil, Australia, India, Gabon and China are also larger manganese deposits. The largest manganese producing countries are Australia, China and South Africa, with world total production 2009 at 10,8 million tons.
In larger quantities manganese occurs in so-called manganese nodules, bulbous, up to 20 centimeters large, porous concretions of heavy metal oxides in the deep sea, which can consist up to 50% of manganese. Particularly high concentrations of manganese nodules are found in the Pacific Ocean south of Hawaii and in the Indian Ocean. A reduction of manganese nodules, especially for the extraction of copper, cobalt and nickel, has been intensively studied at times, but has so far failed due to high technical requirements and high mining costs, while maintaining comparatively low prices for land-based metals.
Extraction and presentation
Degradable manganese ores contain at least 35% manganese. Depending on the content and other elements contained, the ores are preferably used for various applications. Metallurgically used manganese ore contains between 38 and 55% manganese and is mined underground or in the chamber construction process underground. In addition, there is battery-grade ore, which contains at least 44% manganese and may contain only a small proportion of copper, nickel and cobalt, so that it is suitable for the production of alkali-manganese batteries, and chemical-grade ore, which is used for the production of pure manganese and manganese compounds.
For a large part of the applications, no pure manganese is needed. Instead, ferromanganese, an iron-manganese alloy containing 78% manganese, is extracted. This is made by reducing oxide manganese and iron ores with coke in an electric furnace. Another alloy made in this way is the manganese-iron-silicon alloy silicomanganese. Here, quartz is additionally introduced as a silicon source into the furnace.
Pure manganese can not be obtained technically by reduction with carbon, since in addition to manganese there are also stable carbides, in particular Mn7C3. Only at temperatures above 1600 ° C, pure manganese is formed, but at this temperature, some of the manganese already evaporates, so that this route is not economical. Instead, manganese is extracted by hydrometallurgy. Here, manganese ore is oxidized, leached and subjected to electrolysis. In the latter case, as pure a manganese sulfate solution as possible is used, which is electrolysed with stainless steel electrodes at 5-7 V. Pure manganese is produced at the cathode and oxygen at the anode, which reacts with manganese ions to form brownstone.
To reduce energy consumption, smaller quantities of sulfur or selenium dioxide are added to the electrolyte.
In addition, the production of manganese by the reduction of manganese oxides with aluminum (aluminothermie) or silicon are possible.
Physical Properties
Manganese is a silvery-white, hard, very brittle heavy metal. It melts at 1246 ° C and boils at 2100 ° C. In contrast to most other metals, manganese does not crystallize at room temperature in a dense spherical packing or in the cubic-body-centered crystal structure, but in the unusual α-manganese structure. Overall, four different modifications are known which are stable at different temperatures. Manganese is paramagnetic at room temperature, the α-modification becomes antiferromagnetic under a Néel temperature of 100 K, while β-manganese shows no such behavior.
Up to a temperature of 727 ° C, the α-manganese structure is thermodynamically stable. It is a distorted, cubic structure with 58 atoms in the unit cell. The manganese atoms of the structure can be divided into four groups with different environments and coordination numbers between 12 and 16. Above 727 ° C to 1095 ° C is another unusual structure, which also thermodynamically more favorable cubic β-manganese structure, with 20 formula units per unit cell and coordination numbers of 12 and 14 for the manganese atoms. Only above 1095 ° C the metal crystallizes in a densest sphere packing, the cubic-face-centered crystal structure (γ-manganese, copper type). At 1133 ° C, this finally transforms into a cubic-centered structure (δ-manganese, tungsten-type).
Chemical properties
As a base metal, manganese reacts with many non-metals. With oxygen, compact manganese reacts slowly and superficially, while finely divided manganese is pyrophoric in the air and quickly reacts with manganese (II, III) oxide. Manganese also reacts with fluorine, chlorine, boron, carbon, silicon, phosphorus, arsenic and sulfur, whereby the reactions take place only slowly at room temperature and are faster only at elevated temperature. With nitrogen, the element reacts only at temperatures above 1200 ° C to manganese nitride Mn3N2, with hydrogen it does not react.
Like other non-noble elements, manganese dissolves in dilute acids under hydrogen evolution, unlike chromium it is not passivated by a dense oxide layer. This reaction also takes place slowly in water. If it is dissolved in concentrated sulfuric acid, sulfur dioxide is formed. In aqueous solution, Mn2 + ions, which are pink in the complex [Mn (H2O) 6] 2 +, are particularly stable to oxidation or reduction. Responsible for this is the formation of an energetically favored semi-filled d-shell (d5). Manganese ions in other oxidation states also have characteristic colors, such as trivalent manganese ions red, tetravalent brown, pentavalent (hypomanganate, MnO43) blue, hexavalent (manganate, MnO42) green, and pentavalent (permanganate, MnO4) violet.
isotope
There are a total of 28 isotopes and eight other core isomers of manganese between 44Mn and 72Mn known. Of these, only one, 55Mn, is stable, making manganese one of the pure elements. Furthermore, 53Mn has a long half life with 3,74 millions of years ago. All other isotopes have short half-lives, with 54Mn having the longest 312,3 days.
The longest-lived radioactive manganese isotope 53Mn is found in nature. It is formed by spallation reactions in iron-containing rocks. 54Fe reacts with 3He from the cosmic radiation and the short-lived 53Fe is formed, which decays to 53Mn.
Usage
Pure manganese is only used to a very limited extent. 90% of the mined manganese is used as ferromanganese, mirror iron or silica manganese in the steel industry. Since manganese forms very stable manganese-oxygen compounds, it acts as deoxidizing aluminum and silicon and enhances the effect of these elements. In addition, it prevents the formation of easily melting iron sulfide and thus acts desulfurizing. At the same time, the solubility of nitrogen in the steel is increased, which promotes austenite formation. This is important for many stainless steels. Another important property of manganese in steel is that it increases the hardenability of the steel.
Also in alloys with non-ferrous metals, especially copper alloys and aluminum-manganese alloys, manganese is used. It increases the strength, corrosion resistance and ductility of the metal. The alloy manganin (83% copper, 12% manganese and 5% nickel), similar to Konstantan or better yet Isaohm, has a low electrical temperature coefficient, ie the electrical resistance is only slightly dependent on the temperature. These materials are therefore widely used in electrical meters.
Manganese is also used as an activator in phosphors. Depending on the oxidation state, the wavelength of the emitted light is, according to the current state of knowledge, between 450 and 750 nm (Mn2 +) or 620 and 730 nm (Mn4 +). Of particular importance are BaMgAl10O17: Eu2 +, Mn2 + (green emitter) and Mg14Ge5O24: Mn4 + (red emitter) as phosphors in white LEDs.
YInMn Blue is a mixed oxide of yttrium, indium and manganese oxides that shows a very pure and brilliant blue.
Pure manganese is produced in the order of about 140.000 tons per year. It is used to a large extent for the production of special steels and aluminum alloys. It also produces zinc-manganese ferrites for electronic components.
Biological significance
Manganese is an essential element and component of various enzymes for all living beings. There it acts in different ways among other things as Lewis acid, for the formation of the enzyme structure and in redox reactions. In some bacteria it is also used for energy production. For example, Shewanella putrefaciens, a marine bacterium, performs anaerobic respiration with Mn4 + as the terminal electron acceptor, which is reduced to Mn2 +.
Manganese plays an essential role in photosynthesis, namely in the oxidation of water to oxygen in photosystem II. The central component of the photosystem is a complex of four manganese atoms and one calcium atom linked together by oxygen bridges, the oxygen-evolving complex complex, OEC). Here, in a multi-stage cycle, the Kok cycle, in which the manganese alternates between the three- and four-valent oxidation state, sunlight splits water and releases oxygen, electrons and protons.
In manganese-containing superoxide dismutases found in mitochondria and peroxisomes, the reaction of superoxide to oxygen and hydrogen peroxide is catalyzed by redox reactions with di- and trivalent manganese ions.
Dioxygenases, which incorporate molecular oxygen into specific organic molecules, usually contain iron, but several manganese-containing dioxygenases are also known from, among others, the bacteria Arthrobacter globoformis and Bacillus brevis. Manganese peroxidase, an enzyme found in the fungus Phanerochaete chrysosporium, is one of the few known enzymes that allows degradation of lignin. Furthermore, manganese is involved in the reaction of arginases, hydrolases, kinases, decarboxylases and transferases such as pyruvate carboxylase, mevalonate kinase and glycosyltransferase, as well as certain ribonucleotide reductases and catalases.
Manganese is absorbed by humans via the small intestine and stored mainly in the liver, bones, kidneys and the pancreas. Inside the cell, the element is mainly found in mitochondria, lysosomes and in the cell nucleus. In the brain, manganese is bound to specific proteins, mainly glutamate-ammonium ligase in astrocytes. The total amount of manganese in the human body is about 10 to 40 mg, the daily requirement is about 1 mg and the average manganese intake in Germany is about 2,5 mg.
Manganese deficiency is rare, in manganese poor fed animals occurred skeletal changes, neurological disorders, defects in carbohydrate metabolism and growth and fertility disorders. Especially manganese-rich foods are black tea, wheat germ, hazelnuts, oatmeal, soybeans, linseeds, blueberries, aronia berries and wholemeal rye bread.
Safety and toxicity
Like many other metals, manganese is finely flammable and reacts with water. Therefore only metal fire extinguishers (class D) or sand can be used for extinguishing. In contrast, compact manganese is not flammable.
If manganese-containing dust is inhaled in high doses, it has a toxic effect. This causes damage in the lungs with symptoms such as cough, bronchitis and pneumonitis. Furthermore, manganese is neurotoxic and damages the central nervous system. This manifests itself in Manganism, a disease with Parkinson-like symptoms such as motor disorders. Manganese dust therefore has a MAK value of 0,02 mg / m3 for particularly fine dusts that can penetrate into the alveoli and 0,2 mg / m3 for inhalable dusts.
Diseases caused by manganese or its compounds are included in the occupational disease list as no. 1105 in Germany. Exposure may result from the extraction, transport, processing and use of manganese or its compounds, provided that they are inhaled as dust or smoke. This also applies to the electric welding with manganese-containing coated electrodes.
proof
The qualitative chemical detection of manganese ions can be provided by formation of violet permanganate after reaction with lead (IV) oxide, ammonium peroxodisulfate (with silver ions as catalyst) or hypobromite in alkaline solution.
Reaction of manganese with lead (IV) oxide in acid solution
For a separation in the context of the cation separation, the so-called alkaline fall can be used in which manganese is oxidized by a mixture of hydrogen peroxide and sodium hydroxide to solid manganese (IV) oxide hydroxide and precipitates.
Reaction of manganese with hydrogen peroxide and sodium hydroxide solution to manganese (IV) oxide hydroxide
Further possible detection reactions which can also be used as a pretreatment are the phosphorus salt pearl, which turns violet by the formation of manganese (III) ions, and the oxidation melt, in which, by reaction with nitrate ions, a green melt of manganate (VI) (MnO42-), with low oxygen supply also blue manganate (V) (MnO43-) is formed. When an acid is added, violet permanganate forms.
Quantitatively, manganese can be determined by atomic absorption spectroscopy (at 279,5 nm), by photometric determination of permanganate, with the absorption maximum at 525 nm, or by titration. In the manganometric method according to Vollhard-Wolff, Mn2 + ions are titrated with permanganate, whereby manganese dioxide forms. The end point is recognizable by the pink coloration by remaining permanganate.
Addition of formaldoxime reagent to a solution of manganese (II) salts produces an orange to red-brown colored metal complex.
Connections
There are known manganese compounds in the oxidation states between -3 and + 7. The most stable are divalent, trivalent and tetravalent manganese compounds, the lower ones are found mainly in complexes, the higher ones in compounds with oxygen.
oxygen compounds
With oxygen manganese forms compounds in the oxidation states + 2 to + 7, whereby in the higher stages + 5, + 6 and + 7 above all anionic manganates as well as manganese halogen oxides, but also the green, oily, explosive liquid manganese (VII) oxide are known are. Of importance are predominantly the seven-valued, purple permanganates (MnO4-), with potassium permanganate in particular having an economic importance. This is used, inter alia, as a strong oxidizing agent in organic reactions, detection reactions in the context of manganometry and medically as an astringent and disinfectant. The pentavalent blue hypomanganates (MnO43-) and hexavalent green manganates (MnO42-) are more unstable and intermediates in permanganate production. There are also complex permanganates such as hexamanganato (VII) manganese (IV) acid, (H3O) 2 [Mn (MnO4) 6] .11H2O, a deep violet compound stable only at low temperatures. Manganese (IV) oxide is mainly used in alkaline manganese batteries as cathode material. When discharging the battery, manganese oxide hydroxide and manganese (II) hydroxide are formed. Furthermore, the divalent manganese (II) oxide, the trivalent manganese (III) oxide and manganese (II, III) oxide are also known.
As manganese hydroxides, manganese (II) hydroxide, manganese (III) oxide hydroxide and manganese (IV) oxide hydroxide are known. However, white manganese (II) hydroxide precipitated from manganese (II) salts with caustic soda is unstable and is easily oxidized by atmospheric oxygen to manganese (III, IV) oxide hydroxide. Because of its ease of oxidation, manganese (II) hydroxide is used for oxygen fixation in the Winkler method.
halogen compounds
The halides fluorine, chlorine, bromine and iodine in each case the divalent compounds and manganese (III) and manganese (IV) fluoride and manganese (III) chloride are known. Corresponding bromine and iodine compounds do not exist because Br and I ions reduce Mn (III) to Mn (II). The most technically important manganese halide is manganese (II) chloride, which can be obtained by reaction of manganese (IV) oxide with hydrochloric acid, which is used, among other things, for the production of dry batteries, corrosion-resistant and hard magnesium alloys and the synthesis of the anti-knock agent (methylcyclopentadienyl) manganese tricarbonyl (MMT) becomes.
Further manganese compounds
Manganese does not form a stable, binary compound with hydrogen at room temperature, only manganese (II) hydride could be prepared at low temperatures in an argon matrix.
Many complexes of manganese are known, predominantly in the oxidation state + 2. These are predominantly as high-spin complexes with five unpaired electrons and a correspondingly strong magnetic moment. The crystal field and ligand field theory predicts no preferred geometry here. Accordingly, depending on the ligand, tetrahedral, octahedral, square-planar or even dodecahedral geometries of Mn2 + complexes are known. The complexes show a faint coloration by (quantum-mechanically forbidden) dd-transitions, whereby octahedral Mn2 + -complexes are usually pale pink, tetrahedral yellow-green colored. With very strong ligands such as cyanide, there are also low-spin complexes with only one unpaired electron and strong ligand-field splitting. Complexes in lower oxidation states include dimangandecacarbonyl Mn2 (CO) 10 with the 0 oxidation state of manganese and a manganese-manganese single bond. Other similar complexes such as Mn (NO) 3CO with the lowest known oxidation state -3 in manganese are also known.
Mangafodipir is a liver-specific paramagnetic contrast agent approved for magnetic resonance imaging (MRI). The contrast-enhancing effect is based on the paramagnetic properties of Mn2 + ions, which are due to the five unpaired electrons. The toxic effect of Mn2 + ions is suppressed in mangafodipir by complexation with the ligand dipyridoxyl diphosphate (DPDP, or fodipir). For liver imaging, it is superior to standard gadolinium-based MRI contrast agents.
The metallocene of manganese is manganocene. This has one electron less than ferrocene and thus, contrary to the 18 electron rule, only 17 electrons. Nevertheless, due to the favorable high-spin d5 configuration, it can not be reduced to Mn + and is present in the solid state in a polymeric structure.
Manganese prices
