Mechanism and Kinetics of PbO–SiO2–CaO Slag Reduction Using Hydrogen

The present study investigates the mechanism and kinetics of hydrogen reduction in PbO–SiO2–CaO slag pellets over a temperature range of 300 to 1200 °C. The phase transformations occurring during reduction at different temperatures were systematically analyzed. In the temperature range of 400 to 600 °C, hydrogen reduction occurred at a microscopic scale, resulting in the formation and aggregation of Pb within the glass structure. The calculated activation energy (Ea) for this process was 63 kJ/mol. The highest extent of solid-state reduction, without formation of a glassy state or significant shrinkage, was observed at 600 °C, reaching 45%. At this temperature, hydrogen diffusion occurred through the amorphous glass structure, targeting preferred sites with a high concentration of PbO. At 800 °C, shrinkage and densification restricted hydrogen diffusion, confining the reduction to the near-surface region and decreasing the overall extent of reduction to 34%. At temperatures above 1000 °C, evaporation had a significant impact on the process. Softening, bubbling, and melting were also observed at 1000 °C and 1200 °C. The findings from this study provide valuable insights into the feasibility of solid-state hydrogen reduction of silicate materials, particularly for applications in blast furnace and hydrogen direct reduction reactors.Graphical Abstract