21.2: Occurrence, Extraction, and Uses

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Occurrence

Manganese is the 12th most abundant element and 3rd most abundant transition metal (cf. Fe, Ti). A number of forms of manganese occur in nature (~ 300 minerals) giving an overall abundance of 0.106%. 12 of these minerals are economically viable including: pyrolusite (MnO₂), manganite (Mn₂O₃.H₂O), hausmannite (Mn₃O₄) rhodochrosite (MnCO₃) and Mn-nodules. The main deposits are found in South Africa and the Ukraine (> 80%) and other important manganese deposits are in China, Australia, Brazil, Gabon, India, and Mexico.

Extraction

The metal is obtained by reduction with Al, or in a Blast furnace. The metal resembles iron in being moderately reactive and at high temperatures reacts vigorously with a range of non-metals. For example it burns in N₂ at 1200 °C to form Mn₃N₂ and roasting in air gives Mn₃O₄

Uses

85-90% of the Manganese produced goes in to the fabrication of ferromanganese alloys. The 1 and 2 Euro coins contain manganese since there it is more abundant and cheaper than nickel. Manganese dioxide has been used in the cathodes of dry cell batteries and is used in newer alkaline batteries as well. Manganese salts have been used in glass making since the Eygyptian and Roman times and found in paints from as early as 17,000 years ago. Its use in glass is either to add color or to reduce the effect iron impurities have on the color of glass, see below.

Manganese in Biology

Manganese is an essential trace element for all forms of life. It accumulates in mitochondria and is essential for their function. The manganese transport protein, transmanganin, is thought to contain Mn(III). Several metalloenzymes are known: arginase, pyruvate carboxylase and superoxide dismutase. Humans excrete roughly 10 kg of urea per year, this results from the hydrolysis of arginine by the enzyme arginase found on the liver which is the final step of the urea cycle. This reaction allows for the disposal of nitrogenous waste from the breakdown of proteins.

In mammalian arginases I and II, binuclear manganese clusters are present at the active site. In the structure 1rla the Manganese nearest neighbours were identifed as: Asp124, Asp128, Asp232, Asp234, His101, His126.

Contributors and Attributions

Prof. Robert J. Lancashire (The Department of Chemistry, University of the West Indies)