Manganese [Mn]

Characteristics

An: 25 N: 30

Am: 54.938049 g/mol

Group No: 7

Group Name: Transition metals

Block: d-block Period: 4

State: solid at 298 K

Colour: silvery metallic Classification: Metallic

Boiling Point: 2234K (2061^oC)

Melting Point: 1519K (1246^oC)

Density: 7.21g/cm³

Discovery Information

Who: Johann Gahn

When: 1774

Where: Sweden

Name Origin

Latin: mangnes (magnet); Ital. manganese. "Manganese" in different languages.

Sources

Most abundant ores are pyrolusite (MnO₂), braunite (Mn²⁺Mn³⁺₆SiO₁₂), psilomelane [(BaH₂O)₂Mn₅O₁₀] and rhodochrosite (MnCO₃). Manganese is mined in South Africa, Russia, Ukraine, Georgia, Gabon and Australia. 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.

Psilomelane is one of the most abundant manganese ores.

Pyrolusite is one of the most abundant manganese ores.

Annual production is around 6.2 million tons.

Abundance

Universe: 8 ppm (by weight)

Sun: 10 ppm (by weight)

Carbonaceous meteorite: 2800 ppm

Earth’s Crust: 1100 ppm

Seawater: Atlantic surface: 1 x 10^-4 ppm; Atlantic deep: 9.6 x 10^-5 ppm; Pacific surface: 1 x 10^-4 ppm; Pacific deep: 4 x 10^-5 ppm

Human: 200 ppb by weight; 23 ppb by atoms

Uses

Manganese is essential to iron and steel production, it also used in some aluminium alloys. It is also used in making; batteries, axles, rail switches, safes, ploughs and ceramics.

Manganese is used to decolourize glass (removing the greenish tinge that presence of iron produces) and, in higher concentration, make violet-coloured glass.

Potassium permanganate (KMnO₄) is a potent oxidizer and used in chemistry and in medicine as a disinfectant.

History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece were both called magnes, but were thought to differ in gender. The male magnes attracted iron, and was the iron ore we now know as loadstone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolourize glass. This feminine magnes was later called magnesia, known now in modern times as Pyrolusite (MnO₂) or manganese dioxide. This mineral is never magnetic (although manganese itself is paramagnetic). In the 16th century, it was called manganesum by glassmakers, possibly as a corruption of two words since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Mercati called magnesia negra Manganesa, and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated,much later.

Manganese compounds were 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 colour from glass or add colour 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 inadvertent production of an iron-manganese alloy.

In the 17th century, German chemist Johann Glauber first produced permanganate, a useful laboratory reagent (although some people believe that it was discovered by Ignites Kaim in 1770). By the mid-18th century, manganese dioxide was in use in the manufacture of chlorine (which it produces when mixed with hydrochloric acid (HCl), or commercially with a mixture of dilute sulfuric acid and sodium chloride). The Swedish chemist Scheele was the first to recognize that manganese was an element, and his colleague, Johan Gottlieb 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. In 1837, British academic James Couper noted an association between heavy exposure to manganese in mines with a form of Parkinson’s Disease. In 1912, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.

In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (carbon-zinc) and alkaline type.

Notes

More than 25 million tonnes of manganese ores are mined every year, representing 5 million tons of the metal, reserves of manganese are estimated to exceed 3 billion tonnes.

Hazards

Manganese is one out of three toxic essential trace elements, which means that it is not only necessary for humans to survive, but it is also toxic when too high concentrations are present in a human body. When people do not live up to the recommended daily allowances their health will decrease. But when the uptake is too high health problems will also occur.

Manganese Compounds

Manganese(II) carbonate MnCO₃

It is widely used as an additive to plant fertilizers to cure manganese deficient crops. It is also used in many health foods. It is also used in ceramics as a glaze colourant and flux.

Manganese(IV) oxide MnO₂

The principal use for MnO₂ is for dry-cell batteries, such as the alkaline battery and the zinc-carbon battery.

Reactions of Manganese

Reactions with water

Manganese does not react with water under normal conditions

Reactions with air

When finely divided, manganese metal burns in air. It burns in oxygen to form the oxide Mn₃O₄ and in nitrogen to form the nitride Mn₃N₂.

3Mn_(s) + 2O_2(g) --> Mn₃O_4(s)

3Mn_(s) + N_2(g) --> Mn₃N_2(s)

Reactions with halogens

Manganese burns in chlorine to form manganese(II) chloride.

Mn_(s) + Cl_2(g) --> MnCl_2(s)

Manganese burns in bromine to form manganese(II) bromide.

Mn_(s) + Br_2(g) --> MnBr_2(s)

Manganese burns in iodine to form manganese(II) iodide.

Mn_(s) + I_2(g) --> MnI_2(s)

The corresponding reaction between the metal and fluorine yields the manganese(II) fluoride and manganese(III) fluoride.

Mn_(s) + F_2(g) --> MnF_2(s)
2Mn_(s) + 3F_2(g) --> 2MnF_3(s)

Reactions with acids

Manganese metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Mn(II) ion together with hydrogen gas.

Mn_(s) + H₂SO_4(aq) --> Mn²⁺_(aq) + SO₄^2-_(aq) + H_2(g)

Occurrence of Manganese

Manganese occurs principally as Pyrolusite (MnO₂), and to a lesser extent as rhodochrosite (MnCO₃). Land-based resources are large but irregularly distributed; those of the United States are very low grade and have potentially high extraction costs. Over 80% of the known world manganese resources are found in South Africa and Ukraine. Other important manganese deposits are in China, Australia, Brazil, Gabon, India, and Mexico. 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%.

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. Manganese is mined in Burkina Faso and Gabon.

Isotopes of Manganese

⁵²Mn [27 neutrons]

Abundance: Synthetic

Half life: 5.591 days [ Electron Capture ]

Decay Energy: ? MeV

Decays to ⁵²Cr.

Half life: 5.591 days [ beta+ ]

Decay Energy: 0.575 MeV

Decays to ⁵²Cr.

Half life: 5.591 days [ Gamma Radiation ]

Decay Energy: 0.7, 0.9, 1.4 MeV

Decays to ?. 

⁵³Mn [28 neutrons]

Abundance: Synthetic

Half life: 3.74 x 10⁶ years [ Electron Capture ]

Decay Energy: ? MeV

Decays to ⁵³Cr.

⁵⁴Mn [29 neutrons]

Abundance: Synthetic

Half life: 312.3 days [ Electron Capture ]

Decay Energy: ? MeV

Decays to ⁵⁴Cr.

Half life: 312.3 days [ Gamma Radiation ]

Decay Energy: 0.834 MeV

Decays to ?. 

⁵⁵Mn [30 neutrons]

Abundance: 100%

Stable with 30 neutrons

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