Application of a complex Si–Al–Fe reducing agent for the production of a nickel-containing alloy

To address the significant environmental challenges and technological limitations of conventional carbothermic ferronickel production, this study presents and optimizes an innovative metallothermic smelting process employing a complex silicon-aluminum-iron reducing agent (ferrosilicoaluminum, FeSiAl). For the first time, a comprehensive methodology integrating thermodynamic analysis, kinetic modeling, experimental design, and pilot-scale validation smelting has been applied to optimize the production of a nickel-containing alloy from lateritic ores of the Batamsha deposit (Kazakhstan). Thermodynamic modeling (HSC Chemistry) demonstrated that the combined use of Si and Al creates more favorable conditions for NiO reduction compared with their separate application, as evidenced by more negative ΔG values and higher equilibrium constants over the investigated temperature range (100-1600 °C). Kinetic analysis based on non-isothermal thermogravimetric and differential thermal analysis (TG-DTA) revealed a pronounced synergistic effect: the FeSiAl system exhibits the lowest apparent activation energy (16.15 kJ mol^-1, which is 57% and 68% lower than those for ferrosilicon and aluminum-containing slag, respectively. This indicates a substantially enhanced reducibility and lower kinetic limitations. Process optimization was achieved through thermodynamic modeling in FactSage combined with a second-order rotatable central composite design (CCD). This approach enabled the development of predictive response surface models and the determination of optimal process parameters: smelting temperature of 1300-1350 °C, FeSiAl addition of 10 wt%, and lime flux addition of 38-40 wt%. Validation smelting experiments conducted in a laboratory ore-thermal electric furnace confirmed the accuracy of the model, yielding 9.5 kg of a multicomponent alloy with the following composition (wt%): Fe 70.0, Ni 8.0, Si 17.0, Cr 3.5, and Al 0.8. The accompanying slag exhibited a technologically favorable composition (wt%): SiO₂ 48.6, CaO 36.4, Al₂O₃ 10.2, and MgO 4.5, with a very low residual nickel oxide content (NiO 0.1%), confirming the high reduction efficiency. The recovery rates of iron and chromium into the metallic phase were 71% and 83%, respectively. The resulting Fe-Ni-Si-Cr-Al alloy is proposed as a potential master alloy for steelmaking or as a reducing agent in metallurgical processes. The developed FeSiAl-based metallothermic process represents an energy-efficient and environmentally more sustainable alternative to conventional carbothermic technology.