Thermodynamic simulation of silicothermal process of nickel and iron reduction from oxides

Abstract

For stainless steel production, chromium and nickel-containing ferroalloys are used. Oxidized nickel ores are reduced by carbo- and metal-thermic methods for obtaining ferronickel. The nickel and iron reduction process from oxide system studied by method of thermodynamic simulation. The system composition was as follows, %: 1.5 CaO, 53.6 SiO 2 , 18.4 MgO, 4.8 Al 2 O 3 , 20 FeO, 1.5 NiO, 0.05 P 2 O 5 , 0.15 SO 3 . As the reducing agent the composition of the iron-containing alloy with a silicon content of from 5 to 65% was used. The flow rate was calculated by stoichiometry for the full reduction of Ni and Fe. The HSC Chemistry 6.12 software package developed by Outokumpu (Finland) was used for the thermodynamic simulation. The chemical compounds Ni 3 Si and Ni 5 Si 2 were added into the database. The calculation was accomplished by application the “Equilibrium Compositions” subroutine at a gas pressure of 1 atm, containing 2.24 m 3 of N 2 . The simulation results indicate the thermodynamic possibility of nickel and iron reduction from the CaO-SiO 2 -MgO-Al 2 O 3 -FeO-NiO system by silicon of ferrosilicon. It was found that increasing the silicon concentration in [Si] FeSi ferrosilicon from 5 to 65% results in increasing the nickel content in the [Ni] alloy from 1.24 to 6.55% at t = 1500°C, increasing the degree of iron reduction η Fe from 88.8 to 91.4%, and nickel η Fe remaining almost unchanged, in the amount 99.8-99.7%. The Gibbs energy of the reactions ∆ r G°( T ) of NiO and FeO reduction by silicon was calculated at temperatures of 1500, 1600 and 1700°C using the “Reaction Equations” subroutine. The change in the degree of silicon helpful usage φ Si on the temperature at various Si concentrations in ferrosilicon was studied. The highest value of φ Si of 94.5% was obtained at t = 1500°C and FeSi65, and the lowest of 89.4% at t = 1700°C and FeSi5. The TM results of the NiO reduction process with iron (at 0% Si) were obtained at other factors being equal. The degrees of nickel reduction η Fe i of 56.6% and iron η Fe of 0.68% were calculated at consumption of the reducing agent by stoichiometry. The degree of nickel reduction η Fe was 80.6% and iron - 2.13% at the increase of the consumption of the reducing agent - iron - 1.5 times. The chemical composition of the alloy was as follows, %: 1.24-6.55 Ni, 98.3-91.7 Fe, 0.35-1.28 Si, 0.063-0.334 S, 0.023-0.122 P. The results of simulation can be used for elaborating a technology of Fe-Si-Ni production from oxidized nickel ore by silicothermic method.