Manganese

Notable Characteristics Manganese is a gray-white metal, resembling iron. It is a hard metal and is very brittle, fusible with difficulty, but easily oxidized. Manganese metal is ferromagnetic only after special treatment.

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from +1 to +7 are observed. Mn⁺² often competes with Mg⁺² in biological systems, and manganese compounds where manganese is in oxidation state +7 are powerful oxidizing agents.

Applications Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking, including its ironmaking component, has accounted for most domestic 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 certain widely used aluminum alloys and is used in oxide form in dry cell batteries. The overall level and nature of manganese use in the United States is expected to remain about the same in the near term. No practical technologies exist for replacing manganese with other materials or for using domestic deposits or other accumulations to reduce the complete dependence of the United States on foreign countries for manganese ore.

Substitutes: Manganese has no satisfactory substitute in its major applications.

History Manganese was in use in prehistoric times. Paints that were pigmented with manganese dioxide can be traced back 17,000 years. The Egyptians and Romans used manganese compounds in glass-making, to either remove color from glass or add color to it. Manganese can be found in the iron ores used by the Spartans. Some speculate that the exceptional hardness of Spartan steels derives from the inadvertant production of an iron-manganese alloy.

In the 17th century, the German chemist Glauber first produced permanganate, a useful laboratory reagent. By the mid 18th century, manganese oxide was in use in the manufacture of chlorine. The Swedish chemist Scheele was the first to recognize that manganese was an element, and his colleague, J. G. Gahn, isolated the pure element in 1774 by reduction of the dioxide with carbon. Around the beginning of the 19th century, scientists began exploring the use of manganese in steelmaking, with patents being granted for its use at the time. In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle.

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 such classes as oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The best known manganese containing polypeptides may be arginase[?], Mn containing superoxide dismutase, and the diphtheria toxin. Occurrence Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. South Africa and Ukraine account for more than 80% of the world’s identified resources; South Africa accounts for more than 80% of the total exclusive of China and Ukraine.

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%.

Manganese is mined in Burkina Faso.

Vast quantities of manganese exist in manganese nodules[?] on the ocean floor[?]. Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.

Compounds Potassium permanganate 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).

Manganese dioxide is used in dry cells, and can be used to decolorize glass that is colored green by trace amounts of iron. Manganese compounds can color glass an amethyst color, and is responsible for the color of true amethyst. Manganese dioxide is also used in the manufacture of oxygen and chlorine, and in drying black paints.

Isotopes Naturally occurring manganese is composed of 1 stable isotope; 55-Mn. 18 radioisotopes have been characterized with the most stable being 53-Mn with a half-life of 3.7 million years, 54-Mn with a half-life of 312.3 days, and 52-Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lifes that are less than 3 hours and the majority of these have half lifes 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 supernova explosion. Manganese-53 decays to ⁵³Cr with a half-life of 3.7 million years. Because of its relatively short half-life, ⁵³Mn is an extinct radionuclide. Manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology[?]. Mn-Cr isotopic ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotopic systematics must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. 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 amu (46-Mn) to 65 amu (65-Mn). The primary decay mode before the most abundant stable isotope, 55-Mn, is electron capture and the primary mode after is beta.

Precautions Manganese in excess is toxic. 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.

Acidic permanganate solutions will destroy any organic material they come in contact with, and can set them on fire.

External Links

• WebElements.com - Manganese (http://www.webelements.com/webelements/elements/text/Mn/index)
• EnvironmentalChemistry.com - Manganese (http://environmentalchemistry.com/yogi/periodic/Mn)
• International Manganese Institute (http://www.manganese.org)