Ferromanganese Nodules
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Ferromanganese is an alloy of
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
, with other elements such as
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
,
carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
,
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
,
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
and
phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
. The primary use of ferromanganese is as a type of processed manganese source to add to different types of steel, such as
stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...
. Global production of low-carbon ferromanganese (i.e. alloys with less than 2% carbon content) reached 1.5 megatons in 2010.


Physical and chemical properties

The properties of ferromanganese vary considerably with the precise type and composition of the alloy. The melting point is generally between and . The density of the alloy depend slightly on the types of impurities present, but is generally around .


Production

Sources of manganese ore generally also contain iron oxides. As manganese has a more negative free energy of oxidation than iron, i.e. is chemically harder to reduce, during the reduction of manganese ore, iron is also reduced and mixed with the manganese in the melt. This is unlike other oxides such as SiO2, Al2O3 and
CaO Cao or CAO may refer to: Mythology *Cao (bull), a legendary bull in Meitei mythology Companies or organizations * Air China Cargo, ICAO airline designator CAO * CA Oradea, Romanian football club * CA Osasuna, Spanish football club * Canadian ...
, which are more stable as oxides than manganese. Reduction is achieved using a submerged arc furnance. There are two main industrial procedures to perform the reduction, the discard slag method (or flux method) and the duplex method (or fluxless method). Despite the name, the differences in the method are not in the addition of
flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...
, but rather in the number of stages required. In the flux method,
basic Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...
fluxes such as CaO are added in order to electrolytically reduce the manganese ore: 2MnO + C -> 2Mn + CO2 The remaining slag after the reduction process has approximately 15-20% manganese content, which is usually discarded. In the fluxless method,
carbon reduction Climate change mitigation (or decarbonisation) is action to limit the greenhouse gases in the atmosphere that cause climate change. Climate change mitigation actions include conserving energy and replacing fossil fuels with clean energy sour ...
is also used in the first stage, but the fluxes added do not necessarily increase the activity of the manganese. As a result, the remaining slag has a concentration of 30% to 50% of the manganese. This is then reprocessed with
quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...
to make silicomanganese alloys. The resultant discarded slag has a manganese content of less than 5%, increasing the yield. As a result, this method is used more often in industry. In both methods, due to the addition of carbon as an reducing agent, the alloy produced is referred to as high-carbon ferromanganese (HCFM), with a carbon content of up to 6%. A correct mix of coke, flux and ore composition is required to give high yield and reliable furnance operation, by achieving the desired chemical properties, viscosity and smelting temperature in the resulting melt. Since the iron to manganese ratio of natural manganese sources vary greatly, mixing ores from several sources is sometimes done to give a certain desired ratio. In the manufacture of steel, low-carbon ferromanganese (LCFM) is preferred due to the ability to accurately control the amount of carbon in the resultant steel. To arrive at LCFM from HCFM, there are also two main methods: silicothermal reduction and oxygen refinement. In silicothermal reduction, silicomanganese from the second step of the duplex process is used as a reductant. After a variety of mixing and melting steps to reduce the silicon content, a low-carbon alloy with less than 0.8% carbon and 1% silicon by weight can be obtained. In the oxygen refinement method, HCFM is melted and heated to a high temperature of . Oxygen is then blown in to oxidise the carbon into CO and CO2. The disadvantage of this process is that the metal is also oxidised at these high temperatures. Manganese oxide collects mainly in the form of Mn3O4 in the dust blown out from the crucible.


History

350px, lang=en, Evolution of global manganese production, by processes. In 1856,
Robert Forester Mushet Robert Forester Mushet (8 April 1811 – 29 January 1891) was a British metallurgist and businessman, born on 8 April 1811, in Coleford, in the Forest of Dean, Gloucestershire, England. He was the youngest son of Scottish parents, Agnes Wilso ...
"used manganese to improve the ability of steel produced by the Bessemer process to withstand rolling and forging at elevated temperatures."Downing, James H
"Manganese processing"
Encyclopedia Britannica, 23 August 2013
In 1860,
Henry Bessemer Sir Henry Bessemer (19 January 1813 – 15 March 1898) was an English inventor, whose steel-making process would become the most important technique for making steel in the nineteenth century for almost one hundred years. He also played a sig ...
invented the use of ferromanganese as a method of introducing manganese in controlled proportions during the production of steel. The advantage of combining powdered iron oxide and manganese oxide together is the lower melting point of the combined alloy compared to pure manganese oxide. In 1872,
Lambert von Pantz Lambert may refer to People *Lambert (name), a given name and surname * Lambert, Bishop of Ostia (–1130), became Pope Honorius II * Lambert, Margrave of Tuscany (fl. 929–931), also count and duke of Lucca *Lambert (pianist), stage-name of Ger ...
produced ferromanganese in a blast furnace, with significantly higher manganese content than was previously possible (37% instead of the previous 12%). This won his company international recognition, including a gold medal at the
1873 World Exposition The 1873 Vienna World's Fair () was the large world exposition that was held from 1 May to 31 October 1873 in the Austria-Hungarian capital Vienna. Its motto was "Culture and Education" (). History As well as being a chance to showcase Austro-Hu ...
in Vienna and a certificate of award at the 1876
Centennial Exposition The Centennial International Exhibition, officially the International Exhibition of Arts, Manufactures, and Products of the Soil and Mine, was held in Philadelphia, Pennsylvania, from May 10 to November 10, 1876. It was the first official wo ...
in Pennsylvania. In an 1876 article, MF Gautier explained that the magnetic oxide needs to be slagged off by the addition of manganese (then in the form of spiegel iron) in order to befit it for rolling.


Gallery


References

{{reflist Ferroalloys Deoxidizers Manganese