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Production of Ferro- Manganese
Ferro-manganese (Fe-Mn) is an important additive used as a deoxidizer in the production of steel. It is a master alloy of iron (Fe) and manganese (Mn) with a minimum Mn content of 65 %, and maximum Mn content of 95 %. It is produced by heating a mixture of the oxides of Mn (MnO2) and iron (Fe2O3) with carbon (C) normally as coke or coal.
Fe-Mn in a blast furnace (BF) with considerably higher Mn content than was possible earlier was first produced in 1872 by Lambert Von Pantz. The Fe-Mn produced had 37 % Mn instead of 12 % being obtained earlier. Metallurgical grade Mn ores having Mn content higher than 40 % are usually processed into suitable metallic ferro- alloy forms by pyro-metallurgical processes, which are very similar to the iron pyro-metallurgical processes. In its production process, a mixture of Mn ore, reductant (a form of C) and flux (CaO) are smelted at a temperature which is higher than 1200 deg C to enable reduction reactions and alloy formation. Standard grades of Fe-Mn can be produced either in a BF or in an electric submerged arc furnace (SAF).
The electric SAF process, however, is far more flexible than the BF process, in that slags can be further processed to Si-Mn and refined Fe-Mn. The choice of process is also dependent on the relative price of electric power and coke. In a three-phase SAF, the electrodes are buried in the charge material. The raw materials are heated and the Mn oxides pre-reduced by hot carbon mono oxide (CO) gas form the reaction zones deeper in the furnace. The exothermic reactions contribute favourably to the heat required. Efficient production of HC Fe-Mn depends on the degree of pre-reduction which occurs in the upper region of the furnace.
There are several grades of Fe-Mn which are divided into many groups. The three main groups are high C Fe-Mn, medium C Fe-Mn, and low C Fe-Mn. High C Fe-Mn can be made in BF and in SAF. In SAF it is made by two different practices namely (i) high Mn slag practice, and (ii) discard slag practice. Medium C Fe-Mn can be produced by a de-carbonation process or through a redox (reduction-oxidation) reaction between silicon (Si) in the silico-manganese (Si-Mn) alloy and Mn ores. Low C Fe-Mn is produced by the reaction of Mn ore and low C Si-Mn.
Ferrochrome plants & their annual production capacity
Ferrochrome, or Ferrochromium (FeCr) is a type of ferroalloy
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