Chemical Reactions in the Reduction of Iron from Oxides

Abstract

In this paper, we simulated the chemical process accompanied by the reduction of iron from hematite using the Terra computer program (the product from Bauman Moscow State Technical University). Carbon, hydrogen, and methane were taken as reducing agents. The equilibrium concentrations of the system components were determined by varying the consumption of reducing agents and the process temperature. The change in these concentrations at the boundaries of individual temperature regions was regarded as a result of the passage of corresponding chemical reactions in them. At the same time, it was noted that reactions of the non-variant type begin and end at the same fixed temperatures. Calculations showed that the Fe₂O₃ → Fe₃O₄ transformation in all cases was thermodynamically possible at temperatures exceeding 65°C. Consequently, it will be realized without complications at the furnace operating temperatures. The second stage of reduction also proceeded according to the unified scheme Fe₃O₄ → Fe, bypassing the participation of FeO oxide in it. The temperature of the beginning of the iron reduction by the C, H₂, and CH₄ components was 680, 350, and 520°C, respectively. In this case, only direct reduction of iron by the indicated components took place. An attempt to record the fact of indirect reduction using carbon monoxide as a reducing agent was unsuccessful even at its high consumption. Carbon monoxide decomposed at low temperatures according to the Boudouard-Bell reaction. Therefore, iron was reduced by “sooty” carbon, i.e., also by a direct method. At the final stage of the carbon-thermal process, depending on the composition of the system, the formation of iron carbide at 720°C can occur with its possible subsequent transformation back into iron, as well as the secondary oxidation of iron with the formation of wustite. Carbon dioxide takes an active part in these reactions. The reduction (or oxidative) efficiency of all elements and components of the Fe–O–C–H system is numerically estimated based on the calculation results of chemical processes at high temperatures. With a high degree of reliability, this allowed predicting the phase composition of the reaction products at the maximal process temperature (1500°C).