Optimization of Mineralogy and Microstructure of Solidified Basic Oxygen Furnace Slag Through SiO₂ Addition or Atmosphere Control During Hot-Stage Slag Treatment

Valorization of basic oxygen furnace (BOF) slag is of significant importance for mitigation of the steel production’s environmental impact. The present work aims to investigate the influence of SiO₂ addition and oxygen partial pressure on the mineralogical modification of a typical industrial BOF slag. The slag basicity (mass ratio of CaO/SiO₂) was varied from 1.8 to 4.4 by mixing specific amounts of SiO₂ with the master BOF slag. The original and modified slags were remelted and solidified under argon or air atmosphere followed by slow cooling. The experimental observations were then compared with the results of thermodynamic modeling to achieve a thorough understanding. With decreasing the basicity, free lime was eliminated, as it forms dicalcium silicate (Ca₂SiO₄). With increasing oxygen partial pressure, wustite was oxidized to hematite, which combined with free lime to form calcium aluminoferrite (C₂AF). The effects of SiO₂ addition and oxygen partial pressure were finally evaluated with respect to the energy consumption for the BOF slag valorization. The modified slag is suitable as a precursor for construction applications as binders.