Manganese
Manganese is a metal element denoted by the atomic symbol Mn. Its atomic number is 25 and its atomic weight is 54.93805. It is a silver-grey metal that has a melting point of 2274.8°F (1246°C) and a boiling point of 3741.8°F (2061°C). Manganese is one of the transition metals on the periodic table. It falls between iron and chromium and shares some properties with these metals. It reacts in air and in water, and it combines easily with other elements to form many compounds. The most common of these compounds is manganese dioxide (MnO2), which is found in pyrolusite ore. A less abundant ore, rhodochrosite, contains manganese carbonate (MnCO3). Pure manganese, which does not exist in nature, is rarely used.
When added to steel, manganese increases the strength of the alloy, or mixture of metals. Manganese also cleanses the steel by removing oxygen and sulfur impurities. This is an essential steelmaking step, and manganese has few effective substitutes as a cleansing agent. About 14 lbs, (6.4 kg) of manganese are consumed for every ton of steel produced.
Manganese is usually alloyed with iron before being added to the molten steel. These alloys, called ferromanganese, contain up to 90 percent manganese. Some of the manganese combines with oxygen and sulfur in the steel to form compounds that separate out into the slag, which is poured off. The rest remains in the steel to improve its strength. Manganese steel is so strong that it can be used to make mining machinery, rock crushers, and other heavy-duty equipment. Aluminum and other nonferrous metals are also purified and strengthened using manganese. When alloyed with aluminum, manganese increases the hardness, stiffness, and strength of the metal. It also makes magnesium alloys more resistant to corrosion.
Until the mid-1700s, scientists believed that the manganese ore pyrolusite was composed of iron oxides. Then Carl Wilhelm Scheele and other chemists began to suspect that the ore contained not iron, but a new metallic element. Acting upon this clue, Swedish mineralogist Johann Gottlieb Gahn (1745-1818) produced a small amount of metallic manganese in 1774 by burning the ore with charcoal. Gahn was a friend and colleague of Scheele and had studied under Torbern Olof Bergman (1735-1784), a Swedish chemist and physicist who also suggested the existence of manganese.
During the 1800s, scientists began to appreciate and exploit the properties of manganese. It was first used as an additive in steel manufacturing as early as 1839. Then in the mid-1850s, ferromanganese was introduced, which ensured the practical success of the Bessemer steelmaking process. English metallurgist Robert Abbott Hadfield (1858-1949) produced a very hard steel alloy containing as much as 13 percent manganese in 1882, leading to the growth of the heavy-duty machine industry.
Although by far the greatest use of manganese is still in steelmaking, manganese compounds have a variety of other industrial purposes. The dioxide, for example, is used in dry-cell batteries to keep them from polarizing. It is also used in manufacturing a photograph-developing chemical called hydroquinone and in the production of zinc, uranium, and organic chemicals.
Manganese oxide is added to many animal and poultry feeds for nutritional purposes. As an enzyme activator, manganese is required by all plants and animals. In living tissue, manganese concentrates in the cell 's mitochondria, where biochemical energy is produced. Some fertilizers contain manganese sulfate to supply trace amounts of the metal to deficient soils. Growing citrus fruit in Texas and Florida, for example, requires the addition of manganese to the soil. Manganese oxide is also a component in welding rods and fluxes. Glassmakers formally used the oxide to remove iron impurities that gave glass a yellowish tinge. When exposed to the sun, however, glass treated with manganese turned purple, and selenium is now used instead. Pure manganese is responsible for the purple color of amethyst gemstones. Another important compound is potassium permanganate (KMnO4), a powerful oxidizing agent used in bleach, medicine, and water purification chemicals.
In the future, world supplies of manganese could be increased by mining deposits on the ocean floor, where the metal is found in potato-shaped lumps called manganese nodules. These were discovered during the 1870s by the English research ship, the HMS Challenger. Scientists think that the nodules begin to form layers around a pebble or shark tooth, just as pearls form around grains of sand. It is estimated that the Pacific Ocean floor contains 31,000 tons (31,496 t) of these nodules per square mile.
Besides manganese, the nodules contain significant amounts of more valuable metals-- nickel, copper, and cobalt. The highest percentages of these metals occurs in nodules that lie very deep underwater, while the shallower nodules contain less of the metals. Mining technology will have to be improved before manganese and other metals can be economically recovered from the ocean.
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