Thermodynamics and kinetics of FeO transferred to Fe₃O₄ in modified nickel slag during molten oxidation process

In view of the utilization of iron resources in nickel slag, water-quenched nickel slag from flash furnace was treated by using a molten oxidation method. During this process, the iron components in the nickel slag were melted and oxidized, finally transferred to magnetite phases (Fe₃O₄). In this paper, the thermodynamic analysis and calculation of the Fe-containing phase evolution during the molten oxidation process were carried out, the transfermation possibility of iron component as magnetite phase was analyzed, and the kinetics of FeO transfermation to Fe₃O₄ in modified nickel slag during molten oxidation process was studied. The study results show that the use of CaO in oxidizing process favors the decomposition of fayalite phase and formation of magnetite phase. The Fe₃O₄ spinel solid solution precipitated from the CaO-FeO-MgO-SiO₂ system under the conditions of slag basicity of 0.90 and oxygen partial pressure of 0.21 atm. With the extension of oxidizing time, FeO transferred to Fe₃O₄ in modified nickel slag during molten oxidation process. The magnetite crystals gradually change from fine dendritic shape to granular shape at lower oxidizing temperature. But dendrites exist during the oxidization at the higher oxidizing temperature. The formation rate constant and apparent activation energy of magnetite crystals is calculated to be 0.0183 and 68.17 kJ mol⁻¹, respectively. (paper)