Ferromanganese, a ferroalloy with high content of manganese, is made by heating a mixture of the oxides MnO2 and Fe2O3, with carbon, usually as coal and coke, in either a blast furnace or an electric arc furnace-type system, called a submerged arc furnace. The oxides undergo carbothermal reduction in the furnaces, producing the ferromanganese. Ferromanganese is used as a deoxidizer for steel.
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Ferro Manganese is a hard, silvery white metal with a melting point of 1060-1220 0C. Ordinarily to brittle to be of structural value itself, it is an essential agent in steelmaking, in which it removes impurities such as sulfur and oxygen and adds important physical properties to the metal.
Due to ASTM 99, this commodity has been classified into 3 categories:
- Low carbon ferromanganese
- Medium carbon ferromanganese
- High carbon ferromanganese
Raw Materials
The raw materials needed for the production of FeMn are Mn ores, coke and fluxes such as limestone, dolomite and quartzite. The raw materials are often stored outdoor, and the water content, including chemically bound water in the Mn ores, may therefore be high, up to 10 %.
Production
Blast furnaces were widely used in developed countries for the production of FeMn, up to the end of World War II. Normally, integrated steel plants destined their smaller BF for the production of high C FeMn. Low grade Mn ores with a Mn content of minimum 28 % can be used for smelting in the BF. High C Fe-Mn is produced in a BF in a process which is similar to the process of producing hot metal (HM) in BF. Hence, the production of Fe-Mn in a BF needs larger amounts of coke than needed for HM production in the BF. Preheating of the blast and oxygen (O2) enrichment are usually used to reduce the requirement of coke. Dolomite or limestone added to the charge raises the activity of MnO for reduction. Small slag volume, basic slag and high blast temperature are required for the higher recovery of Mn. By careful control and a more uniform charge mix in the shaft of the BF, recoveries of Mn over 90 % and coke rates of 1530 kg/t have been achieved. Top gas in BF producing the FeMn entrained excessive fines. SAF has replaced BF because of smaller coke rate, longer refractory life, no need of hot blast, and reuse of MnO-rich slag for the production of SiMn ferroalloy.
