Марганец

Описание

Manganese occurs as a free element in nature and is ubiquitous in the environment. The origin and uses of this black mineral date back to the Greek golden period. Manganese was known as pyrolusite or manganese dioxide. A Swedish chemist, Carl Wilhelm Scheele, used pyrolusite to produce chlorine in the mid-eighteenth century. But not until 1774 was manganese isolated and purified as a metal by Johan Gottlieb Gahn by reducing the dioxide with carbon. Manganese is an essential element for humans and animals.

Химические свойства

Manganese is a combustible, lustrous, brittle, silvery soft metal. It may be found in chunks, powder, or flakes. The most important ore containing manganese is pyrolusite. Manganese may also be produced from ferrous scrap used in the production of electric and open-hearth steel.

Физические свойства

Manganese is a reactive metal that has several oxidation states (2, 3, 4, 6, and 7) thatare responsible for its varied chemical compounds. The chemical and physical properties ofmanganese are similar to the properties of its companions in group 7—technetium (₄₃Tc) andrhenium (₇₅Re).Pure manganese is a gray-white metal that is somewhat similar to iron, located just to theright of it in period 4. Manganese is a reactive element that, over time, will decompose in coldwater and will rust (oxidize) in moist air. It has magnetic properties but is not as magnetic asiron. Its melting point is 1,233°C, its boiling point is 1962°C, and its density is 7.44 g/cm³.

Изотопы

There are 30 isotopes of manganese, ranging from Mn-44 to Mn-69, with onlyone being stable: Mn-55 makes up 100% of the element in the Earth’s crust. All theother isotopes are artificially radioactive with half-lives ranging from 70 nanoseconds to3.7×10⁶ years. Artificial radioisotopes are produced in nuclear reactors, and becausemost radioactive isotopes are not natural, they do not contribute to the element’s naturalexistence on Earth.

Происхождение имени

The name manganese is derived from the mineral magnesite (or dolomite, a compound of magnesium carbonate), which was mined in the region of Magnesia of ancient Greece.

Характеристики

There are four allotropic forms of manganese, which means each of its allotropes has a different crystal form and molecular structure. Therefore, each allotrope exhibits different chemical and physical properties (see the forms of carbon—diamond, carbon black, and graphite).The alpha (α) allotrope is stable at room temperature whereas the gamma (γ) form is soft,bendable, and easy to cut. The delta ? allotrope exists only at temperatures above 1,100°C. Asa pure metal, it cannot be worked into different shapes because it is too brittle. Manganese isresponsible for the color in amethyst crystals and is used to make amethyst-colored glass.

Использование

In manufacture of steel; for rock crushers, railway points and crossings, wagon buffers; as a constituent of several alloys, e.g., ferromanganese, copper manganese, Manganin.

Определение

A transition metal occurring naturally as oxides, e.g. pyrolusite (MnO₂). Nodules found on the ocean floor are about 25% manganese. Its main use is in alloy steels made by adding pyrolusite to iron ore in an electric furnace. Manganese decomposes cold water and dilute acids to give hydrogen and reacts with oxygen and nitrogen when heated. The oxidation states are +7, +6, +4, and (the most stable) +2. Manganese(II) salts are pale pink and with alkali the solutions precipitate manganese(II) hydroxide, which rapidly oxidizes in air to brown manganese(III) oxide. Symbol: Mn; m.p. 1244°C; b.p. 1962°C; r.d. 7.44 (20%C); p.n. 25; r.a.m. 54.93805.

Методы производства

World manganese ore production was estimated to be 13.3 million ton (as manganese) in 2008. Top five manganese-producing countries were South Africa, Australia, China, Gabon, and Brazil. World manganese ferroalloy production in 2008 was 13.2 million ton (MT) (10). Metallurgical applications account for most manganese consumption. In the United States, 85–90% of this is for steelmaking. Manganese is essential in iron and steel production because of its sulfur-fixing, deoxidizing, and alloying properties. As an alloying agent in finished steel, manganese contributes increased strength, hardness, and corrosion resistance. Practically all steels contain manganese; low-carbon steels contain 0.15–0.8% manganese, whereas high-strength steels contain over 1% manganese. Stainless steels typically contain about 1% manganese, but there are manganese-stainless steels (200 series stainless steels) where nickel is replaced partly or entirely by manganese, resulting in manganese content of 4–16%.

Общее описание

A lustrous brittle silvery solid.

Реакции воздуха и воды

During a fire in an industrial bag filter, a mixture of aluminum and Manganese dusts was released and an explosion resulted [Occ. Haz. 28:185-7. 1946-47].

Профиль реактивности

Manganese dust(finely divided) has been known to be pyrophoric. Powdered Manganese ignites in chlorine and burns brilliantly; with fluorine the reaction takes place with incandescence [Mellor 12:185, 344. 1946-47]. Concentrated nitric acid reacts with Manganese with incandescence and a feeble explosion [Mellor 12:188. 1946-47]. Manganese or potassium ignites in nitrogen dioxide [Ann. Chim. et Phys.(2) 2:317]. Manganese burns with a brilliant flame when heated in sulfur dioxide vapor [Mellor 12:187. 1946-47]. Contact with conc. hydrogen peroxide causes violent decomposition and/or ignition.

Опасность

Dust or powder is flammable. Use dry chemical to extinguish. Toxic. Central nervous system impairment. Questionable carcinogen.

Профиль безопасности

Human systemic effects by inhalation: degenerative brain changes, change in motor activity, muscle weakness. A skin and eye irritant. Questionable carcinogen with experimental tumorigenic data. Flammable and moderately explosive in the form of dust or powder when exposed to flame. The dust ma)' be pyrophoric in air and may explode when heated in carbon dioxide. Murtures of aluminum dust and manganese dust may explode in air. mxtures with ammonium nitrate may explode when heated. The powdered metal igmtes on contact with fluorine, chlorine + heat, hydrogen peroxide, bromine pentafluoride, sulfur dioxide + heat. Violent reaction with NO2 and oxidants. Incandescent reaction with phosphorus, nitryl fluoride, nitric acid. Wdl react with water or steam to produce hydrogen; can react with oxidizing materials. To fight fire, use special dry chemical. See also MANGANESE COMPOUNDS.

Возможный контакт

Manganese is used in the production of steel; and in the manufacture of welding rod coatings and fluxes; in the iron and steel industry in steel alloys, e.g., ferro-manganese, silico-manganese, manganin, spiegeleisen; and as an agent to reduce oxygen and sulfur content of molten steel. Other alloys may be formed with copper, zinc, and aluminum. Manganese and its compounds are utilized in the manufacture of dry cell batteries (MnO2), paints, varnishes, inks, dyes, matches, and firework; as a fertilizer, disinfectant, bleaching agent; laboratory reagent; drier for oils; an oxidizing agent in the chemical industry particularly in the synthesis of potassium permanganate; and as a decolorizer and coloring agent in the glass and ceramics industry. Exposure may occur during the mining, smelting, and refining of manganese; in the production of various materials; and in welding operations with manganese-coated rods. Manganese normally is ingested as a trace nutrient in food. The average human intake is approximately 10 mg/day

Перевозки

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN3077Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous hazardous material, Technical Name Required

Несовместимости

Dust, powder, or finely divided material has been known to be pyrophoric or explosive in air. Compact, solid metallic magnesium is nonflammable. Reacts with water (slowly), steam, or acid producing flammable hydrogen gas. Reacts violently with concentrated hydrogen peroxide. Incompatible with nitrogen gas above 200C. Oxidizers, nitric acid; nitrogen, finely divided aluminum and other metals; sulfur dioxide; carbon dioxide 1 heat may cause fire and explosions

Утилизация отходов

Generators of waste (equal to or greater than 100 kg/mo) containing this contaminant, EPA hazardous waste number N450, must conform to USEPA regulations for storage, transportation, treatment, and disposal of waste. Dispose of waste material as hazardous waste using a licensed disposal contractor to an approved landfill. Dispose of contents and container to an approved waste disposal plant. Containers must be disposed of properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office. All federal, state, and local environmental regulations must be observed. Do not discharge into drains or sewers. Manganese metal-sanitary landfill. Manganese chloride or sulfate-chemical conversion to the oxide followed by land filling, or conversion to the sulfate for use in fertilizer. Consult with environmental regulatory agencies for guidance on acceptable disposal practices.