Mn - Manganese

Properties

Manganese is a hard, brittle, silvery metal belonging to Group 7 of the Periodic Table, and it is the 12th most abundant element in the Earth’s crust. When in its pure form, manganese is reactive and as a powder will burn in oxygen. It reacts with water (rusting similarly to iron) and dissolves in dilute acids. Manganese has many similar properties to that of its neighbour, iron. Manganese is not found in its pure form in nature and is usually found combined with oxygen. The name manganese comes from the Latin word magnes, meaning magnet, as the mineral in which it is mainly found has magnetic properties.

History

Long before manganese was first isolated as an element, it was used by pre-historic cave painters of the Lascaux region of France (c.30,000 years ago). The cave painters would use the black ore, manganese dioxide, to paint. More recently, its minerals were mined in Germany, Italy and England, and were used commercially by glass makers for hundreds of years, in order to remove the pale greenish tint of natural glass, caused by traces of iron ions (Fe2+) in the sand from which it is made. This mineral was called pyrolusite (manganese dioxide).  Pyrosulite was thought to contain iron, due to its magnetic properties, but in 1740, a glassmaker discovered that this was not the case, and was able to isolate potassium permanganate (KMnO4), one of the strongest oxidising agents known to early chemists. In the 1700’s, many chemists tried and failed to isolate manganese from its ore, pyrolusite. It was eventually achieved by Gottlieb Gahn from Sweden in 1774. Some argued that he should not have been given credit, as 3 years earlier, a dissertation had been published by Ignatius Kaim outlining the exact same method of producing manganese.

Sources

Manganese occurs in many mineral ores, such as, bixbyite, manganite, pyrolusite, rhodochrosite, rhodonite and romanochite, although only pyrolusite, romanachite and manganite are the chief ores.  The main mining regions for these ores are South Africa, Russia, Gabon, Australia, Brazil, Georgia and the Ukraine.  Of these countries, South Africa produces 80% of manganese resources, Ukraine produces 10%, while the other nations together make up the rest.  Over 25 million mts per year of manganese ores are mined to reach the world production figure of manganese metal at 6.2 million mts per year, with global reserves of 3.2 billion mts.

Manganese ores were mined in Germany, England and Italy as early as in Roman times, when manganese was used by glass makers to remove the pale green tint of natural glass.

Uses

Pure manganese is too brittle for many modern commercial applications, and today 90% of manganese goes into steel and cast iron production.  Of this 90%, about 70% is for alloy making, where only 1% of manganese alloys (FeMn, SiMn) are added to steel to improve strength, working properties and wear resistance.  There is also an alloy called ‘manganese steel’, which contains about 13% manganese and is strong enough to be used for railway tracks, earth-moving machinery, safes, helmets, rifle barrels and bars in prison cells.  The other 30% is used for its properties as a sulphide former and deoxidant.

The 10% of non-iron/steel manganese consumption goes into making dry cell batteries (20 billion produced per year) where manganese dioxide is used as a polariser, and also aluminium cans, electronic circuits, fungicides, pesticides and animal feeds.