Biomass ironmaking is crucial for carbon reduction in the ironmaking industry. To understand this process better, the iron production capacity and energy requirements of biomass were studied. A thermodynamic equilibrium model and energy consumption model for the biomass and iron oxide reduction system at 100–1300 °C was established by the minimum free Gibbs energy method. The effects of factors such as biomass type, temperature, and initial amount of iron oxide on the system were analyzed. The research results indicated that the maximum ironmaking capacity of biomass was determined by the element content of carbon, hydrogen and oxygen in biomass and temperature. The equilibrium H₂/(H₂ + H₂O) and CO/(CO + CO₂) at the maximum iron yield were affected not by the biomass species and element content, but by temperature. The reduction capacity of the ten selected biomass types decreased with a temperature increase from 700 °C to 1300 °C. For the 1 kg of pine sawdust and iron oxide system, the maximum equilibrium state amount of metallic iron was 23.05 mol at 718 °C, and the minimum system energy consumption per ton Fe was 1.16 GJ at 800 °C and 1.18 GJ at 900 °C. These research results will provide a key basis for a deeper understanding of the intrinsic mechanism of biomass ironmaking.

Sulfate roasting is a critical pyrometallurgical pre-treatment for extracting Cu and Co from low-grade Cu–Co–Fe sulfide ores, yet conventional phase diagrams provide limited quantitative guidance for process control. To address this gap, a multicomponent/multiphase thermodynamic equilibrium model based on Gibbs free energy minimization was developed to systematically investigate the oxidative roasting behavior of single sulfides (Cu₂S, CoS₂, FeS₂) and their ternary mixture, with respect to air supply, temperature, and total pressure. The model reveals that each sulfide follows distinct, temperature-dependent phase transformation pathways: Cu₂S forms the acid-leachable product CuO·CuSO₄ at temperatures ≤ 588 °C with a stoichiometric air supply of 11.9 mol, transitioning to oxides at ≥800 °C; CoS₂ converts completely to CoSO₄ below 727 °C and to CoO at higher temperatures; FeS₂ yields sulfate phases at low temperatures and iron oxides above 654 °C. In the ternary Cu₂S–CoS₂–FeS₂ system, competitive oxidation reactions produce refractory mixed oxides (CuO·Fe₂O₃, CoO·Fe₂O₃) whose formation is governed by temperature, air supply, and sulfide molar ratios. The results demonstrate that low-temperature roasting (≤641 °C) with precisely controlled air supply maximizes the formation of water-soluble sulfates, providing a quantitative thermodynamic basis for process optimization and enhanced recovery of Cu and Co from complex sulfide ores.