CALCULATION OF THERMODYNAMIC TEMPERATURES OF CHEMICAL REACTIONS OF STEPWISE IRON REDUCTION PROCESS FROM HEMATITE BY SOLID CARBON

The results of thermodynamic analysis of chemical reactions of stepwise reduction of iron from hematite by solid carbon are presented. The aims of the work are to obtain our own expressions for calculating the numerical values of Gibbs free energy depending on temperature using tabular values of standard enthalpies of formation and entropies of inorganic substances, as well as graphical dependences of Gibbs energy on temperature using formulas from literary sources and using the obtained expressions. Numerical values of boundary temperatures are obtained, above which chemical reactions of stepwise reduction of iron from hematite by solid carbon can thermodynamically proceed. It has been established that: the reduction of magnetite (Fe3O4) from hematite (Fe2O3) by solid carbon C is thermodynamically possible above the boundary temperature, the numerical value of which, according to the obtained formula, is 270°; the reduction of wustite (FeO) from magnetite (Fe3O4) by solid carbon C is thermodynamically possible above the boundary temperature, the numerical value of which, according to the obtained formula, is 658°C; the reduction of iron (Fe) from wustite (FeO) by solid carbon C is thermodynamically possible above the boundary temperature, the numerical value of which, according to the obtained formula, is 703°C, and according to formulas, taken from literary sources, is 774°C, 690°C, 680°C and 609°C, respectively, for each formula. Despite the fact that thermodynamics allows all these chemical reactions to occur above the certain above-mentioned temperature values, each of the reactions of stepwise reduction of iron from its oxides by solid carbon in a shaft reduction furnace either occurs at higher temperatures, and, which is quite obvious, with a change in the aggregate state of the reacting (initial) substances or at least one of them (given that FeO forms low-melting compounds with SiO2, this will be the reaction of reduction of iron from wustite), or does not occur at all (given that Fe2O3 and Fe3O4 do not form low-melting compounds with SiO2, and their melting temperatures are greater than 1500°C, these will be the reactions of reduction of magnetite from hematite and reduction of wustite from magnetite).