Isothermal reduction behavior of Fe2O3/MnO composite materials with solid carbon

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Abstract

Compacts of pure and 2% MnO doped iron oxide were reduced isothermally at 800–1100 °C by solid carbon. The reduction behavior was investigated using advanced quadrupole mass spectrometer. XRD and SEM analysis were used to characterize the reduced samples. The aim of this work is to clarify the reduction behavior of Fe2O3/MnO composite materials with solid carbon. The influence of reduction conditions on the structural characteristics of the products was extensively studied to get clear comprehension of reduction process. It was found that the reduction rate increases with temperature and decreases with the presence of MnO. The experimental measurements were used to elucidate the carbothermic reduction mechanism of iron oxide doped with MnO. The reactions proceeded in a stepwise manner and Boudouard reaction is the rate controlling step. The calculated values of activation energy revealed that solid state diffusion mechanism had a significant role in the reduction process.

Introduction

Blast furnace technology is still the main source of hot metal production, over 95% of the total iron in the world is produced using iron blast furnace. Most of the research on blast furnace operation is designed to improve both productivity and cost of production. The most powerful means for reducing energy consumption and increase productivity in the blast furnace is the improvement in the composition of burdens. However, many iron ores are characterized by relatively high contents of impurities such as barite, alkali and manganese. These impurities play an important role in the blast furnace operation because the flow of molten burdens has an influence on the gas permeability, heat transfer, and reduction processes. For example, in Egypt, the molten pig iron is produced at Egyptian Iron and Steel Company (EISCO, Egypt) using Egyptian iron ore which is rich in BaO, MnO, and alkalis. Accordingly, the hot metal produced at EISCO contains high percent of manganese, sulphur and silicon (Mn ∼2.4, S ∼0.06, and Si ∼0.7%, respectively). The average coke consumption is over 500 kg/tHM and the productivity of the furnace is about 1500–1600 kg/day. This high rate of coke consumption and low productivity can be attributed to the characterization of iron ore sinter and also to the operation parameters which control the efficiency of the blast furnace.

However, manganese is considered one of the most iron ore impurities where it forms strong oxides which partially reduced in blast furnace and part of them enter in the composition of slag. Manganese exists in iron ores in the form of oxides as MnO2, MnO and sometimes in the form of carbonates as MnCO3 which easily dissociate to MnO and CO2. Higher oxides as MnO2, Mn2O3 and Mn3O4 are reduced at lower temperature (<900 °C) to MnO. The reduction of MnO is taken place by solid carbon in blast furnaces at relatively high temperatures.

The kinetics and mechanism of reduction process of iron oxides with solid carbon have been investigated by many researchers from different view points [1], [2], [3], [4], [5], [6], [7]. Few researches have been carried out to investigate the carbothermic reduction of MnO [8], [9], [10]. Reduction mechanism of iron-manganese oxide (MnFe2O4, Jacobsite) with carbon was investigated by an effluent gas analysis method [8]. Manganese carbide was formed at the early stage of reduction and the reaction between manganese oxide and carbide occurred to yield ferro-manganese. Singleton et al. [10] investigated the high temperature kinetics of the carbothermic reduction of MnO and determined the loss of manganese through volatilization. The isothermal gaseous reduction of MnO2-doped Fe2O3 compacts was studied at 700–1100 °C using CO and H2 gas [11]. It was found that the addition of MnO2 has a significant effect on the reduction of iron oxide due to the formation of hard reducible phases of Jacobsite (MnFe2O4) and manganese wüstite (FeO, MnO).

The present study is designated to investigate the isothermal reduction behavior of Fe2O3/MnO composite materials with solid carbon using advanced quadrupole mass spectrometer. The microstructures of the reduced compacts together with the kinetics data obtained from reduction process were used to elucidate the reduction mechanism under isothermal conditions.

Section snippets

Experimental work

Reagent grade iron oxide (99.5% Fe2O3) and manganese oxide (99% MnO) were used as starting materials together with ultra pure solid carbon (>99% C). MnO was mixed with Fe2O3 in 2% weight concentration. Both pure Fe2O3 and Fe2O3/2% MnO were mixed with excess solid carbon in a fixed composition (31 wt% C, C/O = 2). The excess carbon content was adapted to grantee the complete reduction of MnO and compensates the consumption of carbon in the gas-solid reactions. The produced powders were thoroughly

Reduction behavior

In the present study, two different kinds of compacts namely pure Fe2O3/C and Fe2O3/C doped with 2% MnO were prepared. Reduction experiments were carried out isothermally using both thermo-gravimetric experiment and effluent gas analysis method. The influence of reduction conditions on the structural characteristics of the products was extensively studied to get clear comprehension of reduction process. The experimental measurements were used to elucidate the carbothermic reduction mechanism of

Conclusion

Pure Fe2O3/C and Fe2O3/C doped with 2% MnO compacts were prepared and isothermally reduced using two different techniques, thermo-gravimetric technique was used to measure the weight loss as a function of time while effluent gas analysis method was applied to follow the outlet gases. The effect of reduction temperature and MnO content on the reduction behavior and structural characteristics of the reduced compacts was investigated. It was observed that the reduction rate increases with

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