Thermodynamic Simulation of Silicothermic Reduction of Chromium

Abstract

Thermodynamic simulation of chromium reduction from the oxide system of the composition (wt %) was conducted as follows: 25.0–37.5 CaO, 25.0–12.5 SiO2, 25.0 Cr2O3, 5.0 FeO, 14.0 MgO, 3.0 MnO, and 3.0 Al2O3. Silicon of FeSi20, FeSi45, and FeSi65 ferrosilicon grades was used as a reducing agent in an amount of 110% for the quantity stoichiometrically required for the reduction of iron, manganese, and chromium. The simulation was performed using the HSC Chemistry 6.12 software package developed from Outokumpu, Finland. Calculations were performed using the “Equilibrium Compositions” module in the initial nitrogen atmosphere at a total pressure of 0.1 MPa within the temperature range 1500–1700°C at a temperature increment of 50°C. The thermodynamic characteristics of the CrO(II) compound were entered into the software package’s database. The thermodynamic constants of CaCr2O4 available in the database were adjusted. The calculated results are represented in the graphic dependence form of changes in the reduction degree of chromium ηCr on the temperature T, the slag basicity (CaO)/(SiO2), and the silicon concentration in ferrosilicon [Si]FeSi. It is shown that the increase in the process temperature from 1500 to 1700°C at (CaO)/(SiO2) = 2 decreases ηCr by 1.87, 6.04, and 7.38% when FeSi20, FeSi45, and FeSi65, respectively, are used as reducing agents. It has been found that the increase in (CaO)/(SiO2) from 1 to 3 at a temperature of 1600°C results in an increase in ηCr by 17.3, 14.2, and 12.5% when FeSi20, FeSi45, and FeSi65, respectively, are used as reducing agents. The increase in the silicon concentration in ferrosilicon from 20 to 65% [Si]FeSi increases ηCr by 9.5, 5.9, and 4.2% at a slag basicity of 1, 2, and 3, respectively, at a temperature of 1600°C. The metal’s chemical composition has been determined. The thermodynamic simulation results can be used to calculate the reduction degree of chromium from the reduction period slags of the argon–oxygen refining during stainless steel production.