Phase transition pathways and volatilisation kinetics of PbO-Fe₂O₃ in vacuum carbon thermal reduction

Electric arc furnace dust （EAFD） is typical hazardous solid waste generated during the steelmaking process in electric arc furnaces. Because it is rich in valuable metals such as lead, zinc, and iron, it holds high potential for resource utilization. This study aims for the efficient recovery of lead from EAFD. It focused on the interaction within the PbO-Fe₂O₃ system, specifically investigating the lead reduction and volatilization behavior during vacuum carbon thermal reduction at molar ratio of PbO and Fe₂O₃ was 1∶1. The FactSage 8.0 thermodynamic software was used to calculate the system's saturated vapor pressure, equilibrium phase composition, and Gibbs free energy changes. Combined with characterization methods such as X-ray diffraction analysis （XRD） and scanning electron microscope energy dispersive spectrometer （SEM-EDS）, the study systematically analyzed the effects of carbon addition, reduction temperature, and holding time on phase evolution, microstructure, and the lead volatilization rate. Thermodynamic results show that vacuum conditions significantly lower the initial reaction temperature of the system, favoring the reduction of PbO and the volatilization of metallic lead. The reduction of iron oxides mainly follows the stepwise transformation path of Fe₂O₃→Fe₃O₄→FeO→Fe, while lead primarily undergoes the reduction and volatilization process of PbO（s）→Pb（l）→Pb（g）. Experimental results demonstrate that under the conditions of reduction temperature of 1 150 ℃, carbon addition （mass fraction） of 16%, and holding time of 60 min, the system achieves the best lead volatilization effect, with a lead volatilization rate exceeding 99%, realizing efficient separation of lead from the iron phase. Kinetic analysis further reveals that the vacuum carbon thermal reduction process of PbO can be divided into different controlling stages. The early stage of the reaction is mainly controlled by interfacial chemical reactions, with the apparent activation energy increasing from 123.60 kJ/mol to 152.17 kJ/mol. The later stage gradually transitions to gas diffusion control, with the apparent activation energy stabilizing within the range of 150.33 to 155.49 kJ/mol. The findings elucidate the phase transformation regularities and lead volatilization mechanism in the PbO-Fe₂O₃ system during vacuum carbon thermal reduction, providing a theoretical basis and process reference for the selective separation and efficient recovery of lead from electric arc furnace dust.