The minerals like Spessartite and Manganese Garnate also contains sufficient amount of manganese and can be used for extraction of manganese. Manganese oxide minerals are formed by breaking of manganese bearing silicates. Large deposits of ferro manganese nodules occur in the basins of pacific ocean, Atlantic ocean and Indian ocean. These nodules are found at depth of 5 km. The origin of these nodules are biological and chemical. Manganese ores are grouped into different grades as per their contents of manganese and iron.
| Battery grade | MnO2(72% and more),Fe(less than 7%) |
| Chemical grade | MnO2(75% and more),Fe(less than 1.5%) |
| Ferromanganese grade | Mn(46% and more), Mn/Fe(4.6 % minimum),P(0.2% or less) |
| Blastfurnace grade | Mn( 25-35%),Al2O3(7.5% or less),SiO2(13% or less),P(0.2% or less |
| Ferrosilicon | Silicon(50%-90%), Iron(18%-48%), Carbon(up to 2%) |
| Ferromanganese | Silicon(78%-82%), Iron(10%-15%), Carbon(up to 7%) |
| Silicomanganese | Silicon(56%-66%), Iron(28%-32%), Carbon(up to 1%) |
Ferromanganese and its uses: Ferromanganese, silicomanganese and ferrosilicon are used as deoxidizers in the iron and steel production. These ferroalloys are also used as alloying additions with non-ferrous metal. Different type of ferromanganese is produced for special grade steel. The manufacture of highly strong steel such as Hadfield manganese steel requires significant addition of ferromanganese. The ferromanganese with desired composition is to be produced for making of special steel. The ferroalloys are produced in various grades. These gradations of ferroalloys are given as follows:
In addition to ferroalloy & manganese ore is used in refining of pig iron. Manganese oxide is the most stable oxide produced during refining of pig iron.
Iron and manganese form ideal solutions and even in the presence of other solutes, ideal behaviour is assumed. Manganese oxide is soluble in slags.
FeO + Mn = MnO + Fe
FeS + Mn = MnS + Fe
Similarly, silicon content decides the grade of pig iron. It strongly interacts with iron to produce appreciable quality of pig iron. Ferromanganese, ferrosilicon and silicomanganese are produced in submerged electric arc furnace. In case of ferromanganese, the raw material is manganese oxide ore, iron ore and coke. The charge is put in the furnace. Current is switched on. After some time, the coke starts burning and produce carbon monoxide and carbon dioxide. The reduction process starts and oxygen is separated from the manganese and iron. To remove impurities like silica, limestone is added as flux. Oxygen is blown to the furnace. The impurities form the slag with lime and moves to the surface of the molten ferromanganese. The ferromanganese is separated for future use. The slag is removed to the dumping site. The silicomanganese is produced by the use of manganese ore, silica and coke as the raw materials. The process is similar to ferromanganese production. The ferrosilicon is produced with raw material as iron ore, silica and coke