Manganese, << MANG guh neez, >> is a brittle, silver-gray metallic element. All plants and animals require small amounts of it. Manganese is also an important substance in steel and has many other industrial uses.
Manganese is plentiful in Earth’s crust. It occurs naturally only in combination with other elements, mainly in the minerals braunite, hausmannite, manganite, psilomelane, pyrolusite, and rhodochrosite. It was first isolated in 1774 by Johan Gottlieb Gahn, a Swedish chemist.
In living things, manganese is a part of many proteins and enzymes. An enzyme is a protein that serves as a catalyst, a substance that speeds up chemical reactions. Without enzymes, these reactions would occur slowly or not at all. One manganese enzyme is called superoxide dismutase. This enzyme protects living tissue from superoxide, an electrically charged oxygen molecule. Cells produce superoxide during respiration, the process by which living things obtain and use oxygen. Manganese also plays an important role in photosynthesis, the process by which plants produce food. During photosynthesis, manganese assists in the reaction that produces most of the oxygen gas on the earth.
In human beings and other animals, a lack of manganese disrupts growth and results in disorders of the bones and central nervous system. A diet that includes beans, nuts, green leafy vegetables, or whole grain and cereals provides adequate amounts of manganese.
Industrial uses.
Industry uses most manganese in the form of alloys (metal mixtures) and compounds. About 95 percent of the manganese in ores is used to make ferromanganese. This alloy with iron contains about 80 percent manganese and is used in refining steel. Manganese strengthens steel—itself an alloy—-by removing oxygen and sulfur from it. Bubbles of oxygen weaken steel, and sulfur increases the tendency of steel to break during the forging process, in which the metal is heated and shaped.
All steel has some manganese. Manganese steel contains as much as 14 percent manganese. It is extremely durable, so it is used for heavy-duty machinery and safes. Manganese makes stainless steel and various alloys of aluminum, copper, and magnesium harder and more resistant to rust.
The most widely used compound of manganese is manganese dioxide. Applications include dry cell batteries, paints and dyes, and photographic developer. It also gives bricks a red to brown color. In addition, glassmakers have used manganese dioxide for centuries. Manganese sulfate is used in the production of paint and varnish driers. It is also a key substance in certain kinds of fertilizer.
Another industrially important manganese compound is potassium permanganate. It serves as a disinfectant and deodorizer, and is used in water purification and in the production of the artificial sweetener saccharin. Such compounds as manganous nitrate and manganous oxide act as catalysts in the production of petrochemicals, plastics, and synthetic fibers.
Properties.
Manganese has an atomic number (number of protons in its nucleus) of 25. Its relative atomic mass is 54.938049. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of an atom of carbon 12, the most abundant form of carbon. Manganese melts at 1246 plus or minus 3 °C and boils at 2062 °C. Its chemical symbol is Mn. Chemists classify manganese as a transition metal. For information on the position of manganese on the periodic table, see the article Periodic table.
Manganese can exist in four forms. These forms, called allotropes, have different chemical and physical properties. For example, the allotrope alpha manganese is brittle and has a density of 7.44 grams per cubic centimeter at 20 °C. Another allotrope, gamma manganese, is flexible and has a density of 7.21 grams per cubic centimeter at 20 °C.
Manganese metal tarnishes in dry air and rusts in moist air. In dilute inorganic acids, it forms dissolved manganese salts and hydrogen gas.
Sources.
Most manganese occurs in iron ores. A high manganese content makes the ore more valuable. Australia, China, Gabon, Ghana, and South Africa produce the most manganese ore. The United States, which has few deposits of high-grade manganese ore, imports all of its manganese.
The ocean floor, especially in the Pacific, has large deposits of manganese in the form of round masses called nodules. Erosion of land washes manganese oxide into the sea. Scientists believe action by certain bacteria may help the oxides of manganese, iron, cobalt, nickel, and other metals accumulate into nodules. The nodules are about 20 percent manganese. They may become an important source of manganese and other metals if the technology for mining them economically is developed.
Manganese ores are processed by several methods. The purest manganese is obtained by heating manganese ores to an extremely high temperature. This roasting of the ores produces manganese oxide. Next, mixing this substance with sulfuric acid forms a solution of manganous sulfate. Finally, this solution is purified through electrolysis—that is, an electric current is run through the solution to remove the metal from it.
In another method of purification, manganese ore, aluminum, and silicon are deposited in an electric furnace. There, the ore undergoes a chemical process called reduction to yield manganese (see Reduction).
