Production of high-carbon ferromanganese in electric furnace (1)

A, furnace grade carbon ferromanganese furnace uses high-carbon manganese and iron containing small amounts of silicon, phosphorus, sulfur impurities in the Mn-Fe-C alloy three yuan, ferromanganese and manganese to iron is about 92%, containing Carbon 6% to 7%. Manganese, iron, and carbon are usually present in the alloy in the form of Mn ₃ C, FeC. The melting point of high carbon ferromanganese is 1220~1270°C, the density is 7.1~7.4g/cm ³ , and the compressive strength is 70~90MPa. The manganese and iron in the alloy can be mutually soluble in any ratio, but when the manganese content exceeds 82%, It is easily dissipated into powder by the erosion of moisture in the air; therefore, when the product containing more than 82% manganese should be protected from moisture during transportation.
Electric furnace high carbon ferromanganese is mainly used for steelmaking as a deoxidizer, desulfurizer and alloy additive. Adding steel as an alloying additive can improve the mechanical properties of steel and increase the strength, ductility, toughness and wear resistance of steel. With the advancement of medium and low carbon ferromanganese production processes, high carbon ferromanganese can also be used to produce low carbon ferromanganese.
The electric furnace high carbon manganese iron grade and its chemical composition are shown in Table 1.

Second, the electric furnace method high carbon ferromanganese smelting principle
The electric furnace method for producing high-carbon ferromanganese is a method for producing high-carbon ferromanganese in a reduction electric furnace with electric energy as a heat source and coke as a reducing agent.
Smelting principle: High-carbon ferromanganese smelting is mainly a process in which high-valent oxides of manganese are thermally decomposed into low-valent oxides of low-oxides and further reduced into manganese metal.
MnO _{2 is} easily decomposed after being heated. When the temperature is higher than 753 K, MnO _{2 is} decomposed into Mn ₂ O ₃ .

In the normal production process, the high-valence oxide of manganese can also be reduced to low-oxide by the CO formed by the reaction in the furnace. The reaction formula is as follows:

MnO is relatively stable and is not easily decomposed under normal conditions (contact with oxygen is easily reoxidized under certain conditions).
At the smelting temperature, MnO cannot be reduced by CO. Thus, the manganese oxide entering the high temperature zone of the furnace exists in the form of MnO, and can only be reduced to manganese by direct contact with MnO by carbon.
The reaction formula of carbon reduction of MnO is as follows:

It can be seen from the above reaction formula that the temperature required for carbon reduction of MnO to form Mn ₃ C is lower than the temperature required for manganese production. Therefore, when ferromanganese is produced by using carbon as a reducing agent, not only elemental manganese but manganese carbide is obtained. (Mn ₃ C); the carbon content of the alloy is usually 6% to 7%. [next]
MnO is a metal oxide and easily combines with SiO2 in the charge to form a silicate:
MnO+SiO ₂ ===MnO · SiO ₂
2MnO+SiO ₂ ===2MnO · SiO ₂
These reactions reduce the concentration of free MnO in the slag, making it difficult to sufficiently reduce MnO.
In order to reduce the loss of MnO in the slag and increase the recovery rate of manganese, a metal oxide having a basicity greater than MnO, such as lime, dolomite, etc., may be added to the charge to combine CaO with SiO ₂ in the lime to form The corresponding silicate replaces MnO:
MnO · SiO ₂ +CaO===CaSiO ₂ +MnO
2MnO · SiO ₂ +2CaO===2CaSiO ₂ +2MnO
The replaced MnO is in a free state and is easily reduced by carbon.
Manganese ore used for smelting is usually accompanied by oxides of elements such as iron, silicon, calcium, magnesium , aluminum , and phosphorus. In the process of heating and reducing manganese oxide, the oxides of iron, phosphorus, and silicon introduced by the charge are also Restored by carbon:
FeO+C===Fe+CO

The reduced Fe and Mn constitute the binary carbide of ferromanganese [(MnFe) ₃ C], which greatly improves the reduction condition of MnO; in the presence of iron, when the temperature is close to 1100 ° C, the reduction of MnO Can be carried out.
Phosphorus oxide (P ₂ O ₅ ) in the charge can be fully reduced by carbon and manganese:

About 75% of the reduced phosphorus enters the alloy, 5% remains, and the rest evaporates.
The SiO ₂ introduced in the charge is more stable than MnO and can only be reduced by carbon at higher temperatures.

Control HCFeMn smelting temperature does not exceed 1550 deg.] C, can be effectively suppressed reduction of SiO ₂ in the slag into the most SiO _2.
Other oxides in the charge, such as CaO, Al ₂ O ₃ , MgO, etc., are more stable than MnO, and it is impossible to be reduced by carbon under high carbon ferromanganese smelting conditions, and almost all enter the slag.
The sulfur in the charge is mainly from coke. Organic sulfur volatilizes at high temperatures. The sulfur in the sulfate is generally melted in the slag in the form of MnS or CaS. Usually only about 1% of the sulfur in the charge is melted in the alloy.

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