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6 décembre 2011 2 06 /12 /décembre /2011 02:33

Production

Approximately 4.4 million metric tons of marketable chromite ore were produced in 2000, and converted into ~3.3 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.HP Pavilion DV4-1254TX Battery

The largest producers of chromium ore have been South Africa (44%) India (18%),Kazakhstan (16%) Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world production.

The two main products of chromium ore refining are ferrochromium and metallic chromium.HP Pavilion DV4-1255TX Battery

For those products the ore smelter process differs considerably. For the production of ferrochromium, the chromite ore (FeCr2O4) is reduced in large scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reaction.HP Pavilion DV4-1256TX Battery

For the production of pure chromium, the iron has to be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with a mixture of calcium carbonateand sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe2O3.HP Pavilion DV4-1257TX Battery

The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves the insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate.

4 FeCr2O4 + 8 Na2CO3 + 7 O2 ? 8 Na2CrO4 + 2 Fe2O3 + 8 CO2

2 Na2CrO4 + H2SO4 ? Na2Cr2O7 + Na2SO4 + H2O

The dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.HP Pavilion DV4-1258TX Battery

Na2Cr2O7 + 2 C ? Cr2O3 + Na2CO3 + CO

Cr2O3 + 2 Al ? Al2O3 + 2 Cr

Metallurgy

The strengthening effect of forming stable metal carbides at the grain boundaries and the strong increase in corrosion resistance made chromium an important alloying material for steel.HP Pavilion DV4-1259TX Battery

The high speed tool steels contain between 3 and 5% chromium. Stainless steel, the main corrosion-proof metal alloy, is formed when chromium is added to iron in sufficient concentrations, usually above 11%. For its formation, ferrochromium is added to the molten iron.HP Pavilion DV4-1260TX Battery

Also nickel-based alloys increase in strength due to the formation of discrete, stable metal carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromium. Because of the excellent high temperature properties of these nickel superalloys, they are used in jet engines and gas turbines in lieu of common structural materials.HP Pavilion DV4-1265DX Battery

The relative high hardness and corrosion resistance of unalloyed chromium makes it a good surface coating, being still the most "popular" metal coating with unparalleled combined durability. A thin layer of chromium is deposited on pretreated metallic surfaces by electroplating techniques.HP Pavilion DV4-1272CM Battery

There are two deposition methods: Thin, below 1 µm thickness, layers are deposited bychrome plating, and are used for decorative surfaces. If wear-resistant surfaces are needed then thicker chromium layers are deposited. Both methods normally use acidic chromate or dichromate solutions.HP Pavilion DV4-1275MX Battery

To prevent the energy consuming change in oxidation state, the use of Chromium(III) sulfate is under development, but for most applications, the established process is used.

In the chromate conversion coating process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc and cadmium.HP Pavilion DV4-1280US Battery

This passivation and the self healing properties by the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.[31] Because of environmental and health regulations on chromates, alternative coating method are under development.HP Pavilion DV4-1281US Battery

Anodizing of aluminium is another electrochemical process, which does not lead to the deposition of chromium, but uses chromic acid as electrolyte in the solution. During anodization, an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.HP Pavilion DV4-1282CM Battery

The high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium or at least a change to less toxic chromium(III) compounds.HP Pavilion DV4-1283CL Battery

Dye and pigment

The mineral crocoite (lead chromate PbCrO4) was used as a yellow pigment shortly after its discovery. After a synthesis method became available starting from the more abundant chromite, chrome yellow was, together with cadmium yellow, one of the most used yellow pigments.HP Pavilion DV4-1287CL Battery

The pigment does not photo degrade and has a strong color, and was used for school buses in the US and for Postal Service (for example Deutsche Post) in Europe. The use of chrome yellow declined due to environmental and safety concerns and was replaced by organic pigments or other lead-free alternatives.HP Pavilion DV4-1290BR Battery

Other pigments based on chromium are, for example, the bright red pigment chrome red, which is a basic lead chromate (PbCrO4·Pb(OH)2). Chrome green is a mixture of Prussian blue and chrome yellow, while the chrome oxide green is Chromium(III) oxide.HP Pavilion DV4-1290EL Battery

A red color is achieved by doping chromium(III) into the crystals of corundum, which are then called ruby. Therefore, chromium is used in producing synthetic rubies.[36]

Chromium oxides are also used as a green color in glassmaking and as a glaze in ceramics.HP Pavilion DV4-1292CM Battery

Wood preservative

Because of their toxicity, chromium(VI) salts are used for the preservation of wood. For example, chromated copper arsenate (CCA) is used in timber treatment to protect wood from decay fungi, wood attacking insects, including termites, and marine borers.HP Pavilion DV4-1299EE Battery

The formulations contain chromium based on the oxide CrO3 between 35.3% and 65.5%. In the United States, 65,300 metric tons of CCA solution have been used in 1996.[38]

Tanning

Chromium(III) salts, especially chrome alum and chromium(III) sulfate, are used in the tanning of leather.HP Pavilion DV4-1300 CTO Battery

The chromium(III) stabilizes the leather by cross linking the collagen fibers.  Chromium tanned leather can contain between 4 and 5% of chromium, which is tightly bound to the proteins. Although the form of chromium used for tanning is not the toxic hexavalent variety,HP Pavilion DV4-1301TU Battery

there remains interest in management of chromium in the tanning industry such as recovery and reuse, direct/indirect recycling, use of less chromium or "chrome-less" tanning are practised to better manage chromium in tanning.HP Pavilion DV4-1301TX Battery

Refractory material

The high heat resistivity and high melting point makes chromite and chromium(III) oxide a material for high temperature refractory applications, like blast furnaces, cement kilns, molds for the firing of bricks and as foundry sands for the casting of metals.HP Pavilion DV4-1302TU Battery

In these applications, the refractory materials are made from mixtures of chromite and magnesite. The use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).

Catalysts

Several chromium compounds are used as catalysts for processing hydrocarbons.HP Pavilion DV4-1302TX Battery

For example the Phillips catalysts for the production of polyethylene are mixtures of chromium and silicon dioxide or mixtures of chromium and titanium and aluminium oxide.[41] Fe-Cr mixed oxides are employed as high-temperature catalysts for thewater gas shift reaction. Copper chromite is a useful hydrogenation catalyst.HP Pavilion DV4-1303TU Battery

Other use

  • Chromium(IV) oxide (CrO2) is a magnetic compound. Its ideal shape anisotropy, which imparts high coercivity and remanent magnetization, made it a compound superior to the ?-Fe2O3. Chromium(IV) oxide is used to manufacture magnetic tape used in high-performance audio tape and standard audio cassettes.HP Pavilion DV4-1303TX Battery
  • Chromates can prevent corrosion of steel under wet conditions, and therefore chromates are added to drilling muds.
  • Chromium(III) oxide is a metal polish known as green rouge.HP Pavilion DV4-1304TU Battery
  • Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. It is prepared in situ by dissolving potassium dichromate in concentrated sulfuric acid, which is then used to wash the apparatus.HP Pavilion DV4-1304TX Battery
  • Sodium dichromate is sometimes used because of its higher solubility (50 g/L versus 200 g/L respectively). Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.HP Pavilion DV4-1305TU Battery

Biological role

Chromium has no verified biological role and has been classified as not essential for mammals. (Cr(III) or Cr3+) occurs in trace amounts and appears to be benign. Chromium deficiency is controversial or is at least extremely rare.HP Pavilion DV4-1305TX Battery

It has been attributed to only three people on parenteral nutrition, which is when a patient is fed a liquid diet through intravenous drips. In contrast, hexavalent chromium (Cr(VI) or Cr6+) is very toxic and mutagenic when inhaled. Cr(VI) has not been established as a carcinogen when in solution, although it may cause allergic contact dermatitis (ACD).HP Pavilion DV4-1306TU Battery

Although no biological role for chromium has ever been demonstrated, dietary supplements for chromium include chromium(III) picolinate, chromium(III) polynicotinate, and related materials. The benefit of those supplements is still under investigation and is questioned by some studies.HP Pavilion DV4-1306TX Battery

The use of chromium-containing dietary supplements is controversial owing to the absence of any verified biological role, the expense of these supplements, and the complex effects of their use.  The popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells.HP Pavilion DV4-1307TU Battery

In the United States the dietary guidelines for daily chromium uptake were lowered from 50–200 µg for an adult to 35 µg (adult male) and to 25 µg (adult female).

Precautions

Water insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.HP Pavilion DV4-1307TX Battery

Because of the specific transport mechanisms, only limited amounts of chromium(III) enter the cells. Several in vitro studies indicated that high concentrations of chromium(III) in the cell can lead to DNA damage.[57] Acute oral toxicity ranges between 1.5 and 3.3 mg/kg.HP Pavilion DV4-1308TU Battery

The proposed beneficial effects of chromium(III) and the use as dietary supplements yielded some controversial results, but recent reviews suggest that moderate uptake of chromium(III) through dietary supplements poses no risk.

The acute oral toxicity for chromium(VI) ranges between 50 and 150 µg/kg.HP Pavilion DV4-1308TX Battery

In the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells. The chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also sulfate and phosphate ions enter the cell.HP Pavilion DV4-1309TU Battery

The acute toxicity of chromium(VI) is due to its strong oxidational properties. After it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions. Hemolysis, renal and liver failure are the results of these damages. Aggressive dialysis can improve the situation.HP Pavilion DV4-1309TX Battery

The carcinogenity of chromate dust is known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company. Three mechanisms have been proposed to describe the genotoxicity of chromium(VI).HP Pavilion DV4-1310TU Battery

The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the DNA.HP Pavilion DV4-1310TX Battery

The last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.

Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives.HP Pavilion DV4-1311TU Battery

Contact with products containing chromates can lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.HP Pavilion DV4-1311TX Battery

Environmental issues

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, now needing environmental cleanup and remediation per the treatment of brownfield land.HP Pavilion DV4-1312TU Battery

Primer paint containing hexavalent chromium is still widely used foraerospace and automobile refinishing applications.

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature (often in combination with iron), and in many minerals.HP Pavilion DV4-1312TX Battery

As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.

Historically, manganese is named for various black minerals (such as pyrolusite) from the same region of Magnesia in Greece which gave names to similar-sounding magnesia and magnetite, which are ores of different elements.HP Pavilion DV4-1313DX Battery

By the mid-18th century the Swedish chemist Carl Wilhelm Scheele used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite (now known to be manganese dioxide) contained a new element, but they were not able to isolate it.HP Pavilion DV4-1313TU Battery

Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

Manganese phosphating is used as a treatment for rust and corrosion prevention on steel. Depending on their oxidation state, manganese ions have various colors and are used industrially as pigments. HP Pavilion DV4-1313TX Battery

The permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in standard and alkaline disposable dry cells and batteries.

Manganese(II) ions function as cofactors for a large variety of enzymes with many functions.HP Pavilion DV4-1314TU Battery

Manganese enzymes are particularly essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the oxygen evolving complex of photosynthetic plants. The element is a required trace mineral for all known living organisms.HP Pavilion DV4-1314TX Battery

In larger amounts, and apparently with far greater activity by inhalation, manganese can cause apoisoning syndrome in mammals, with neurological damage which is sometimes irreversible.

Manganese is a silvery-gray metal resembling iron. It is hard and very brittle, difficult to fuse, but easy to oxidize.[1] Manganese metal and its common ions are paramagnetic.HP Pavilion DV4-1315TU Battery

Naturally occurring manganese is composed of 1 stable isotope, 55Mn. Eighteen radioisotopeshave been characterized with the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a half-life of 5.591 days.HP Pavilion DV4-1315TX Battery

All of the remaining radioactive isotopes have half-lives that are less than 3 hours and the majority of these have half-lives that are less than 1 minute. This element also has 3 meta states.

Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before thesupernova explosion.?HP Pavilion DV4-1316TU Battery

53Mn decays to 53Cr with a half-life of 3.7 million years. Because of its relatively short half-life,53Mn occurs only in tiny amounts due to the action of cosmic rays on iron in rocks.  Manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology and radiometric dating.HP Pavilion DV4-1316TX Battery

Mn–Cr isotopic ratios reinforce the evidence from 26Al and 107Pd for the early history of the solar system. Variations in53Cr/52Cr and Mn/Cr ratios from several meteorites indicate an initial 53Mn/55Mn ratio that suggests Mn–Cr isotopic composition must result from in–situ decay of 53Mn in differentiated planetary bodies.HP Pavilion DV4-1317TU Battery

Hence 53Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system.

The isotopes of manganese range in atomic weight from 46 u (46Mn) to 65 u (65Mn). The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay.HP Pavilion DV4-1317TX Battery

Chemical properties

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from ?3 to +7 are observed. Mn2+ often competes with Mg2+ in biological systems.HP Pavilion DV4-1318TU Battery

Manganese compounds where manganese is in oxidation state +7, which are restricted to the unstable oxide Mn2O7 and compounds of the intensely purple permanganate anion MnO4?, are powerful oxidizing agents.  Compounds with oxidation states +5 (blue) and +6 (green) are strong oxidizing agents and are vulnerable todisproportionation.HP Pavilion DV4-1318TX Battery

The most stable oxidation state for manganese is +2, which has a pale pink color, and many manganese(II) compounds are known, such as manganese(II) sulfate (MnSO4) and manganese(II) chloride(MnCl2). This oxidation state is also seen in the mineral rhodochrosite, (manganese(II) carbonate).HP Pavilion DV4-1319TU Battery

The +2 oxidation state is the state used in living organisms for essential functions; other states are toxic for the human body. The +2 oxidation of Mn results from removal of the two 4s electrons, leaving a "high spin" ion in which all five of the 3d orbitals contain a single electron.HP Pavilion DV4-1319TX Battery

Absorption of visible light by this ion is accomplished only by a spin-forbidden transition in which one of the d electrons must pair with another, to give the atom a change in spin of two units. The unlikeliness of such a transition is seen in the uniformly pale and almost colorless nature of Mn(II) compounds relative to other oxidation states of manganese.HP Pavilion DV4-1320CA Battery

The +3 oxidation state is known in compounds like manganese(III) acetate, but these are quite powerfuloxidizing agents and also prone to disproportionation in solution to manganese(II) and manganese(IV). Solid compounds of manganese(III) are characterized by their preference for distorted octahedral coordination due to the Jahn-Teller effect and its strong purple-red color.HP Pavilion DV4-1320TX Battery

The oxidation state 5+ can be obtained if manganese dioxide is dissolved in molten sodium nitrite. Manganate (VI) salts can also be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air.

Permanganate (+7 oxidation state) compounds are purple, and can give glass a violet color. HP Pavilion DV4-1321TX Battery

Potassium permanganate, sodium permanganateand barium permanganate are all potent oxidizers. Potassium permanganate, also called Condy's crystals, is a commonly used laboratory reagent because of its oxidizing properties and finds use as a topical medicine (for example, in the treatment of fish diseases).HP Pavilion DV4-1322TX Battery

Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy.

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece, were both called magnes from their place of origen, but were thought to differ in gender.HP Pavilion DV4-1322US Battery

The male magnes attracted iron, and was the iron ore we now know as lodestone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolorize glass. This feminine magnes was later called magnesia, known now in modern times as pyrolusiteor manganese dioxide.HP Pavilion DV4-1323TX Battery

Neither this mineral nor manganese itself is magnetic. In the 16th century, manganese dioxide was called manganesum (note the two n's instead of one) by glassmakers, possibly as a corruption and concatenation of two words, since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba HP Pavilion DV4-1324TX Battery

(a white ore, also from Magnesia, also useful in glassmaking). Michele Mercati called magnesia negra Manganesa, and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated, much later.HP Pavilion DV4-1325TX Battery

Several oxides of manganese, for example manganese dioxide, are abundant in nature and due to color these oxides have been used as since the Stone Age. The cave paintings in Gargas contain manganese as pigments and these cave paintings are 30,000 to 24,000 years old.HP Pavilion DV4-1326TX Battery

Manganese compounds were used by Egyptian and Roman glassmakers, to either remove color from glass or add color to it. The use as glassmakers soap continued through the middle ages until modern times and is evident in 14th century glass from Venice.HP Pavilion DV4-1327TX Battery

Because of the use in glassmaking, manganese dioxide was available to alchemists, the first chemists, and was used for experiments. Ignatius Gottfried Kaim (1770) and Johann Glauber(17th century) discovered that manganese dioxide could be converted to permanganate, a useful laboratory reagent.HP Pavilion DV4-1328TX Battery

By the mid-18th century the Swedish chemist Carl Wilhelm Scheele used manganese dioxide to produce chlorine. First hydrochloric acid, or a mixture of dilutesulfuric acid and sodium chloride was reacted with manganese dioxide, later hydrochloric acid from the Leblanc process was used and the manganese dioxide was recycled by the Weldon process.HP Pavilion DV4-1329TX Battery

The production of chlorine and hypochlorite containing bleaching agents was a large consumer of manganese ores.

Scheele and other chemists were aware that manganese dioxide contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.HP Pavilion DV4-1330TX Battery

The manganese content of some iron ores used in Greece led to the speculations that the steel produced from that ore contains inadvertent amounts of manganese making the Spartan steel exceptionally hard. Around the beginning of the 19th century, manganese was used in steelmaking and several patents were granted.HP Pavilion DV4-1331TX Battery

In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle. In 1837, British academic James Couper noted an association between heavy exposures to manganese in mines with a form of Parkinson's Disease.HP Pavilion DV4-1332TX Battery

In 1912, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.

The invention of the Leclanché cell in 1866 and the subsequent improvement of the batteries containing manganese dioxide as cathodic depolarizer increased the demand of manganese dioxide.HP Pavilion DV4-1365DX Battery

Until the introduction of the nickel-cadmium battery and lithium containing batteries, most batteries contained manganese. The zinc-carbon battery and the alkaline battery normally use industrially produced manganese dioxide, because natural occurring manganese dioxide contains impurities.HP Pavilion DV4-1400 CTO Battery

In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (zinc-carbon) and alkaline types.

Occurrence and production

Manganese makes up about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant element there.HP Pavilion DV4-1404TX Battery

Soil contains 7–9000 ppm of manganese with an average of 440 ppm.[19] Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3.[19] Manganese occurs principally as pyrolusite (MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20] psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3).HP Pavilion DV4-1405TX Battery

The most important manganese ore is pyrolusite (MnO2). Other economically important manganese ores usually show a close spatial relation to the iron ores. Land-based resources are large but irregularly distributed. About 80% of the known world manganese resources are found in South Africa, other important manganese deposits are inUkraine, Australia, India, China, Gabon and Brazil.HP Pavilion DV4-1406TX Battery

In 1978 it was estimated that 500 billion tons ofmanganese nodules exist on the ocean floor.[22] Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.[23]

Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan.HP Pavilion DV4-1407TX Battery

US Import Sources (1998–2001): Manganese ore: Gabon, 70%; South Africa, 10%; Australia, 9%; Mexico, 5%; and other, 6%. Ferromanganese: South Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%. Manganese contained in all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico, 8%; and other, 27%.HP Pavilion DV4-1408TX Battery

For the production of ferromanganese, the manganese ore are mixed with iron ore and carbon and then reduced either in a blast furnace or in an electric arc furnace.The resulting ferromanganese has a manganese content of 30 to 80%. Pure manganese used for the production of non-iron alloys is produced by leachingmanganese ore with sulfuric acid and a subsequent electrowinning process.HP Pavilion DV4-1409TX Battery

Applications

Manganese has no satisfactory substitute in its major applications, which are related to metallurgical alloy use. In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are viable substitutes.HP Pavilion DV4-1413LA Battery

In disposable battery manufacture, standard and alkaline cells using manganese will be generally replaced in the future with lithium battery technology.

Steel

Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties.HP Pavilion DV4-1414LA Battery

Steelmaking, including its ironmaking component, has accounted for most manganese demand, presently in the range of 85% to 90% of the total demand. Among a variety of other uses, manganese is a key component of low-cost stainless steelformulations.HP Pavilion DV4-1416LA Battery

Small amounts of manganese improve the workability of steel at high temperatures, because it forms a high melting sulfide and therefore prevents the formation of a liquid iron sulfide at the grain boundaries. If the manganese content reaches 4% the embrittlement of the steel becomes a dominant feature.HP Pavilion DV4-1425LA Battery

The embrittlement decreases at higher manganese concentrations and reaches an acceptable level at 8%. Steel containing 8 to 15% of manganese can have a high tensile strength of up to 863 MPa. Steel with 12% manganese was used for the British steel helmets. This steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield steel.HP Pavilion DV4T Battery

Aluminium alloys

The second large application for manganese is as alloying agent for aluminium. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion due to the formation of grains absorbing impurities which would lead to galvanic corrosion.HP Pavilion DV4T-1000 CTO Battery

The corrosion resistant aluminium alloy 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloy used for most of the beverage cans. Before year 2000, in excess of 1.6 million tonnes have been used of those alloys, with a content of 1% of manganese this amount would need 16,000 tonnes of manganese.HP Pavilion DV4T-1100 CTO Battery

Other uses

Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost octane rating and reduce engine knocking. The manganese in this unusual organometallic compound is in the +1 oxidation state.HP Pavilion DV4T-1200 CTO Battery

Manganese(IV) oxide (manganese dioxide, MnO2) is used as a reagent in organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring). Manganese dioxide has been used since antiquity to oxidatively neutralize the greenish tinge in glass caused by trace amounts of iron contamination.HP Pavilion DV4T-1200SE CTO Battery

MnO2 is also used in the manufacture of oxygen and chlorine, and in drying black paints. In some preparations it is a brown pigment that can be used to make paint and is a constituent of natural umber.

Manganese(IV) oxide was used in the original type of dry cell battery as an electron acceptor from zinc, and is the blackish material found when opening carbon–zinc type flashlight cells.HP Pavilion DV4T-1300 CTO Battery

The manganese dioxide is reduced to the manganese oxide-hydroxide MnO(OH) during discharging, preventing the formation of hydrogen at the anode of the battery.

MnO2 + H2O + e? ? MnO(OH) + OH?

The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction, but a different electrolyte mixture.HP Pavilion DV4T-1300SE CTO Battery

In 2002 more than 230,000 tons of manganese dioxide was used for this purpose.

The metal is very occasionally used in coins; until 2000 the only United States coin to use manganese was the "wartime" nickel from 1942–1945.HP Pavilion DV4T-1400 CTO Battery

An alloy of 75% copper and 25% nickel was traditionally used for the production of nickel coins. However, because of shortage of nickel metal during the war, it was substituted by more available silver and manganese, thus resulting in an alloy of 56% copper, 35% silver and 9% manganese.HP Pavilion DV4Z Battery

Since 2000, dollar coins, for example the Sacagawea dollar and the Presidential $1 Coins, are made from a brass containing 7% of manganese with a pure copper core. In both cases of nickel and dollar, the use of manganese in the coin was to duplicate the electromagnetic properties of a previous identically sized and valued coin, for vending purposes.HP Pavilion DV4Z-1000 CTO Battery

In the case of the later U.S. dollar coins, the manganese-alloy was an attempt to duplicated properties of the copper/nickel alloy used in the previous Susan B. Anthony dollar.

Manganese compounds have been used as pigments and for the coloring of ceramics and glass. The brown color of ceramic is sometimes based on manganese compounds.HP Pavilion DV4Z-1100 CTO Battery

In the glass industry manganese compounds are used for two effects. Manganese(III) reacts with iron(II). The reaction induces a strong green color in glass by forming less-colored iron(III) and slightly pink manganese(II), compensating the residual color of the iron(III). Larger amounts of manganese are used to produce pink colored glass.HP Pavilion DV4Z-1200 CTO Battery

Biological role

Manganese is an essential trace nutrient in all forms of life. The classes of enzymes that have manganese cofactors are very broad and include oxidoreductases, transferases, hydrolases, lyases,isomerases, ligases, lectins, and integrins.HP Pavilion DV4 Battery

The reverse transcriptases of many retroviruses (though notlentiviruses such as HIV) contain manganese. The best known manganese-containing polypeptides may bearginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).[HP Pavilion DV4-1000 Battery

Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide, formed from the 1-electron reduction of dioxygen.HP Pavilion DV4-1000EA Battery

Exceptions include a few kinds of bacteria such as Lactobacillus plantarum and related lactobacilli, which use a different non-enzymatic mechanism, involving manganese (Mn2+) ions complexed with polyphosphate directly for this task, indicating how this function possibly evolved in aerobic life.HP Pavilion DV4-1000ET Battery

The human body contains about 12 mg of manganese, which is stored mainly in the bones; in the tissue, it is mostly concentrated in the liver and kidneys. In the human brain the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes.HP Pavilion DV4-1001 Battery

Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants. The oxygen evolving complex (OEC) is a part of Photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal photooxidation of waterduring the light reactions of photosynthesis and has a metalloenzyme core containing four atoms of manganese.HP Pavilion DV4-1001AX Battery

For this reason, most broad-spectrum plant fertilizers contain manganese.

Precautions

Manganese compounds are less toxic than those of other widespread metals such as nickel and copper. However, exposure to manganese dusts and fumes should not exceed the ceiling value of 5 mg/m3 even for short periods because of its toxicity level.HP Pavilion DV4-1001TU Battery

Manganese poisoning has been linked to impaired motor skills and cognitive disorders.

The permanganate exhibits a higher toxicity than the manganese(II) compounds. The fatal dose is about 10 g, and several fatal intoxications have occurred. The strong oxidative effect leads to necrosis of the mucous membrane.HP Pavilion DV4-1001TX Battery

For example, the esophagus is affected if the permanganate is swallowed. Only a limited amount is absorbed by the intestines, but this small amount shows severe effects on the kidneys and on the liver.

In 2005, a study suggested a possible link between manganese inhalation and central nervous system toxicity in rats.HP Pavilion DV4-1002 Battery

It is hypothesized that long-term exposure to the naturally occurring manganese in shower water puts up to 8.7 million Americans at risk.

A form of neurodegeneration similar to Parkinson's Disease called "manganism" has been linked to manganese exposure amongst miners and smelters since the early 19th century.HP Pavilion DV4-1002AX Battery

Allegations of inhalation-induced manganism have been made regarding the welding industry. Manganese exposure in United States is regulated byOccupational Safety and Health Administration.

According to results from a 2010 study, higher levels of exposure to manganese in drinking water are associated with increased intellectual impairment and reduced intelligence quotients in school-age children.HP Pavilion DV4-1002TU Battery

Clinical toxicity

Manganism has occurred in persons employed in the production or processing of manganese alloys, patients receiving total parenteral nutrition, workers exposed to manganese-containing fungicides such as maneb, and abusers of drugs such as methcathinone made with potassium permanganate.HP Pavilion DV4-1002TX Battery

Excessive exposure may be confirmed by measurement of blood or urine manganese concentrations.

Chronic exposure to excessive Mn levels can lead to a variety of psychiatric and motor disturbances, termed manganism.HP Pavilion DV4-1003AX Battery

Generally, exposure to ambient Mn air concentrations in excess of 5 ?g Mn/m3 can lead to Mn-induced symptoms. Increased ferroportin protein expression in human embryonic kidney (HEK293) cells is associated with decreased intracellular Mn concentration and attenuated cytotoxicity,HP Pavilion DV4-1003TU Battery

characterized by the reversal of Mn-reduced glutamate uptake and diminishedlactate dehydrogenase (LDH) leakage.HP Pavilion DV4-1003TX Battery,HP Pavilion DV4-1004AX Battery,HP Pavilion DV4-1004TU Battery,HP Pavilion DV4-1004TX Battery,HP Pavilion DV4-1005TX Battery,HP Pavilion DV4-1006TX Battery

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