Thermodynamic modeling and experimental analysis of reduction of iron and nickel from oxide nickel ore

This study presents the results of thermodynamic modeling and thermal analysis of the reduction roasting process of lateritic nickel ore using coke as a carbonaceous reductant. Thermodynamic modeling was performed using version 10.0 of the HSC Chemistry software package based on the minimization of Gibbs free energy under isobaric-isothermal conditions. To evaluate the thermodynamic stability of phases, predominance diagrams of the Fe-C-O, Ni-C-O, Si-C-O, and Mg-C-O systems were constructed, and the equilibrium phase composition was determined as a function of temperature and carbon consumption. The results showed that increasing temperature and carbon reducing potential promote the sequential reduction of iron-bearing phases according to the scheme Fe₂O₃ → Fe₃O₄ → FeO → Fe. The most favorable conditions for magnetite formation were observed within the temperature range of 700-900 °C at moderate carbon consumption, providing favorable conditions for subsequent magnetic beneficiation. At higher temperatures and elevated carbon consumption, the probability of fayalite (Fe₂SiO₄), FeO, and metallic iron formation increases. Analysis of the Ni-C-O system demonstrated that the reduction of NiO to metallic nickel proceeds most intensively at temperatures of 900-1200 °C and carbon consumption above 0.6 kg. At the same time, the silicate phases CaSiO₃, MgSiO₃, and Mg₂SiO₄ retain high thermodynamic stability within the investigated temperature range. To verify the thermodynamic modeling results, thermal analysis of the lateritic nickel ore-coke mixture was performed using the simultaneous thermal analysis method. TG-DTA-DTG analysis revealed the main physicochemical transformations associated with dehydration, destruction of hydrosilicate mineral structures, reduction of iron-bearing oxides, and partial melting of the material. It was established that the presence of coke shifts several thermal effects toward lower temperatures due to the enhancement of the reducing atmosphere. The formation of a magnetic phase after thermal treatment indicates the possibility of magnetite formation during reduction roasting. The obtained results confirm the potential of reduction roasting followed by magnetic separation for improving nickel recovery from lateritic nickel ore.