Journal of Chemical Technology and Applications

Editorial - Journal of Chemical Technology and Applications (2017) Volume 1, Issue 1

Practical reduction of manganese oxide

*Corresponding Author:
Fikri Erdem Şeşen
Metallurgical and Materials Engineering Department, Istanbul Technical University, Istanbul, Turkey
Tel: 00905334172455
E-mail: [email protected]

Accepted date: August 16, 2017

Citation: Şeşen FE. Practical reduction of manganese oxide. J Chem Tech App. 2017;1(1):1-2.

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Abstract

Manganese is an important metal used in steel industry. It is abundant in steel as an alloying element. Additionally, it is used as a deoxidiser in steel production. In steel industry, manganese metal is used as an intermediate product of ferromanganese. Ferromanganese is generally produced by reduction of oxidised manganese. Reduction is in the form of either metalothermic reduction or carbothermic reduction. Practically, metallographic reduction is performed with silicon or aluminium which form more stable oxides than magnesium. Carbothermic reduction means reduction with carbon. All of the reduction reactions are highly endothermic and a high amount of thermal energy is required for the accomplishment of these reactions [1, 2]. The most abundant forms of the manganese oxides are MnO2, Mn2O3, Mn3O4 and MnO. These compounds dissociate during heating.

Editorial

Manganese is an important metal used in steel industry. It is abundant in steel as an alloying element. Additionally, it is used as a deoxidiser in steel production. In steel industry, manganese metal is used as an intermediate product of ferromanganese. Ferromanganese is generally produced by reduction of oxidised manganese. Reduction is in the form of either metalothermic reduction or carbothermic reduction. Practically, metallographic reduction is performed with silicon or aluminium which form more stable oxides than magnesium. Carbothermic reduction means reduction with carbon. All of the reduction reactions are highly endothermic and a high amount of thermal energy is required for the accomplishment of these reactions [1,2]. The most abundant forms of the manganese oxides are MnO2, Mn2O3, Mn3O4 and MnO. These compounds dissociate during heating.

2MnO2 = Mn2O3+1/2O2

3Mn2O3 = 2Mn3O4+1/2O2

Mn3O4= 3MnO+1/2O2

Therefore, different oxide phases are formed dependent on the temperature and partial oxygen pressure. Mn-O-C system is given in Figure 1 in different partial oxygen pressures and different temperatures for equation.

chemical-technology-applications-partial-oxygen

Figure 1: Mn-O-C system in different partial oxygen pressures and different temperatures equation

Reduction of manganese oxides is considered in two steps. The first step is the reduction of oxygen-rich oxides to MnO and the second one is the reduction of Mn to metallic manganese. Reduction starts with the transformation of MnO2 into Mn2O3 and Mn2O3 into Mn3O4 at temperatures over 450°C, then these two phases are reduced by either carbon or carbon monoxide in the system of Mn-C-O. The reduction reactions of manganese oxides and the standard free energies of formation of these chemical reactions are given in Table 1 [3-8].

Reactions ΔGo. kJ/mol T (°C)
Reduction reactions of oxygen-rich oxides to MnO
3Mn2O3 + C = 2Mn3O4 + CO ΔGo = - 0.25 ? 0.17T 25-1100
3Mn2O3 + CO = 2Mn3O4 + CO2 ΔGo = -170.71 ? 0.004T 25-1100
Mn3O4 + C = 3MnO + CO ΔGo = 110.96 ? 0.21T 25-1244
ΔGo = 84.35 ? 0.20T 1244-1700
M3O4 + CO = 3MnO + CO2 ΔGo = 110.96 ? 0.21T 25-1244
ΔGo = 84.35 ? 0.20T 1244-1700
Reduction reaction of MnO with carbon monoxide
MnO + CO = Mn + CO2 ΔGo = 102.38 + 0.01T 25-1227
ΔGo = 116.73 + 0.01T 1227-1727
Boudouard reaction
CO2 + C = 2CO ΔGo = 170.82 ? 0.18T 25-1727
Reduction reactions of MnO with carbon or iron carbide
MnO + C = Mn + CO ΔGo = 287.6  ? 0.16T 25-1227
MnO + 10/7C = 1/7Mn7C3 + CO ΔGo = 284.22 ? 0.18T 717-1087
ΔGo = 282.01 ? 0.18T 1087-1137
ΔGo = 280.22 ? 0.18T 1137-1244
ΔGo = 280.35? 0.18T 1244-1700
MnO + 10/7Fe3C = 1/7Mn7C3 + 30/7Fe + CO ΔGo = 246.09 ? 0.15T 717-840
ΔGo = 269.42 ? 0.17T 840-1087
ΔGo = 267.42 ? 0.17T 1087-1137
ΔGo = 265.42 ? 0.17T 1137-1244

Table 1: Reduction reactions of manganese oxides in different types and the standard free energies of formation of these chemical reactions in different temperature ranges.

A very high carbon monoxide pressure is required for the reduction of MnO with carbon monoxide. Change of ratio of partial equilibrium pressures of carbon monoxide and carbon dioxide with temperature is presented in a diagram given in Figure 2 related to the reduction reaction of MnO with carbon monoxide and Boudouard reaction [3].

chemical-technology-applications-partial-equilibrium

Figure 2: Change of ratio of partial equilibrium pressures of carbon monoxide and carbon dioxide with temperature related to the reduction reaction of MnO with carbon monoxide and Boudouard reaction.

As understood from the diagram, the reduction of MnO with carbon monoxide can only be achieved at temperatures over 1430°C at which the ratio P_CO/P_([CO]_2 ) is 7400. Since the reduction, if done with carbon monoxide, can only be achieved in the abundance of carbon, at temperatures over 1430°C and at an extremely high carbon monoxide pressure, the reduction of MnO with carbon monoxide can not be accomplished in many industrial applications. For this reason, reduction of MnO with solid carbon or iron carbide, as given in Table 1, comes forward [3-9]. Furthermore, manganese carbides are also formed during the carbothermic reduction of manganese oxides. The temperature required for manganese carbide formation (1280°C) is lower than that required for metallic manganese formation (1430°C). Therefore, formation of metallic manganese is inevitable.

References