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The mineral rhodochrosite is a manganese carbonate. |
Manganese
| Atomic Number: | 25 | Atomic Radius: | 197 pm (Van der Waals) |
| Atomic Symbol: | Mn | Melting Point: | 1246 °C |
| Atomic Weight: | 54.94 | Boiling Point: | 2061 °C |
| Electron Configuration: | [Ar]4s23d5 | Oxidation States: | 7, 6, 5, 4, 3, 2, 1, −1, −2, −3 acidic, basic or amphoteric; depending on the oxidation state |
History
From the Latin word magnes, magnet, from magnetic properties of pyrolusite. Recognized by Carl Wilhelm Scheele, Torbern Olof Bergman, and others as an element and isolated by Gahn in 1774 by reduction of the dioxide with carbon.
Sources
Manganese minerals are widely distributed, with oxides, silicates, and carbonates being the most common. Large quantities of manganese nodules are found on the ocean floor and may become a source of manganese. These nodules contain about 24% manganese, together with many other elements in lesser abundance.
Most manganese today is obtained from ores found in Russia, Brazil, Australia, South Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by electrolysis.
Properties
It is gray-white, resembling iron, but is harder and very brittle. The metal is reactive chemically and decomposes slowly in cold water. Manganese is used to form many important alloys. Manganese improves rolling and forging qualities in steel, along with adding strength, stiffness, wear resistance, hardness.
With aluminum and antimony, and especially with small amounts of copper, it forms highly ferromagnetic alloys.
Manganese metal is ferromagnetic only after special treatment. The pure metal exists in four allotropic forms. The alpha form is stable at ordinary temperature; gamma manganese, which changes to alpha at ordinary temperatures, is said to be flexible, soft, easily cut, and capable of being bent.
Uses
The dioxide (pyrolusite) is used as a depolarizer in dry cells and is used to "decolorize" glass that is colored green by impurities of iron. Manganese by itself colors glass an amethyst color and is responsible for the color of true amethyst. The dioxide is also used in the preparation of oxygen and chlorine and in drying black paints. The permanganate is a powerful oxidizing agent and is used in quantitative analysis and in medicine.
Manganese is widely distributed throughout the animal kingdom. It is an important trace element and may be essential for utilization of vitamin B1.
Handling
Exposure to manganese dusts, fume, and compounds should not exceed the ceiling value of 5 mg/m3 for even short periods because of the element's toxicity level.