Manganese

Manganese

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. 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 magnesium, Mg, and magnetite, an ore of the element iron, Fe. By the mid-18th century, Swedish chemist Carl Wilhelm Scheele had 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. 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. The permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in zinc-carbon and alkaline batteries.

In biology, manganese(II) ions function as cofactors for a large variety of enzymes with many functions. 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. In larger amounts, and apparently with far greater activity by inhalation, manganese can cause a poisoning syndrome in mammals, with neurological damage which is sometimes irreversible.

Occurrence and production

Manganese makes up about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant element there. Soil contains 7–9000 ppm of manganese with an average of 440 ppm. Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3. Manganese occurs principally as pyrolusite (MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20] psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3).


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 in Ukraine, Australia, India, China, Gabon and Brazil. In 1978, 500 billion tons of manganese nodules were estimated to exist on the ocean floor. Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s. For a Cold War ruse, the CIA had had billionaire Howard Hughes commission a ship, the Hughes Glomar Explorer to go to Hawaii to harvest manganese nodules. That ship started a rush of people who wanted to collect manganese nodules from the bottom of the sea, which is impractical. The Hughes Glomar Explorer was actually built to raise a sunken Russian submarine, the K-129. Sadly for the CIA, the part of the submarine containing the code books broke off while it was being raised, so they did not get what they wanted.

Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan. 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%.

For the production of ferromanganese, the manganese ore is 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 noniron alloys is produced by leaching manganese ore with sulfuric acid and a subsequent electrowinning process.

Symbol		Mn
Atomic Number		25
Atomic Weight		54.93805
Oxidation States		+2,+3,+4,+7
Electronegativity, Pauling		1.55
State at RT		Solid, Metal
Melting Point, K		1517
Boiling Point, K		2235

Interesting Facts about Manganese

• Manganese is an essential element in photosynthesis. Without it, there would be no free oxygen on earth.
• Human bodies contain a tiny amount of manganese: about 10 – 20 mg. If you chopped a 10c coin into 100 equal pieces, each piece would weigh more than the weight of manganese in an average human. Despite this, we cannot survive without it; manganese performs vital metabolic functions.
• Manganese in humans needs to be topped up frequently because our bodies cannot store it.
• Neanderthals may have used black manganese dioxide as a cosmetic 50 000 years ago. 

Appearance and Characteristics

Harmful effects:

Excess manganese, particularly inhalation of the powder/dust, is toxic. Exposure to manganese or manganese oxide(s) dust can result in a medical condition called manganism; symptoms resemble those of Parkinson’s disease. Workers at particular risk of exposure include miners and welders.

Characteristics:

• Manganese is a gray-white, hard, brittle, metal that can take a high polish. It is not magnetic. The metal tarnishes on exposure to air and, when heated, oxidizes to manganese(II, III) oxide (Mn3O4).
• Like other transition metals, manganese has more than one common oxidation state. The most stable is +2, which is a pale pink color in aqueous solutions. Also important is +4, brown/black, which is found in manganese dioxide; and +7 found in the purple permanganate anion MnO4-. Manganese’s +6 oxidation state is green.

Uses of Manganese

• For over 2000 years manganese dioxide has been used to make colorless glass. Glass is made from sand (silica) and most sand contains iron (II) oxide, which naturally gives glass a green color. It is sometimes incorrectly stated that the manganese dioxide oxidizes the iron (II) oxide to iron (III) oxide; with a corresponding color change from intense green to pale yellow – and the pale yellow is too faint to be seen.
• In fact, the real reason the glass decolorizes is complementary colors. Colors that are directly opposite one another on the color wheel (image: left) cancel one another out, to leave a pale gray.
• In glass the manganese dioxide forms a violet silicate which cancels the green color of Iron (II). 
• Manganese dioxide is also used as a black-brown pigment in paint and as a filler in dry cell batteries.
• The great majority of manganese ore ends up in steel production where the manganese desulfurizes and deoxidizes the steel.
• It is also is used extensively to produce a variety of important alloys. For example, the aluminum used to make most soft drinks cans contains about 1% manganese to improve the cans’ stiffness and corrosion resistance.
• Organo-manganese compounds can be added to gasoline to increase its octane rating and reduce engine knock.
• Manganese is the twelfth most abundant element in the earth’s crust and it is an essential trace element for all life on earth.
• In the human body several manganese-containing enzymes are need to metabolize carbohydrates, cholesterol, and amino acids. Typically our bodies have about 10 – 20 mg manganese. This needs to be topped up frequently because our bodies cannot store it. About a quarter of the manganese in our bodies is in bone, while the rest is evenly distributed through our tissues.