Production, modification and application of biochar in iron and steel metallurgy

The iron and steel industry emits large amounts of CO₂. It relies heavily on fossil fuels. Therefore, energy saving and carbon reduction are urgent. Biochar offers great potential. It can replace fossil fuels and sequester carbon. However, steelmaking processes are complex. Different routes require different biochar properties.This paper reviews sustainable biochar production strategies. These include torrefaction, pyrolysis, supercritical CO₂ treatment, flash carbonization, gasification, hydrothermal carbonization, and microwave-assisted pyrolysis. We also review biochar modification methods. We focus on ball-milling and steam activation. Multidimensional analysis reveals key parameters: surface area, pore structure, and density. We then classify structure-activity relationships.Finally, we compare biochar with traditional fossil fuels in steelmaking and evaluate feasible blending ratios for each application: 20–30% for blast furnace pulverized coal injection, 10–20% for structural coke replacement in large blast furnaces, 2–10% for biocoke in coking blends, 20–40% for iron ore sintering, and variable partial replacement in electric arc furnaces depending on the function (slag foaming, carburization, or reduction).