Synergistic Utilization of Basic Oxygen Furnace Slag and Coal Gangue: Modified Slag and Metal Extraction

The comprehensive utilization of basic oxygen furnace (BOF) slag and coal gangue has always been a significant research interest in alleviating environmental pollution and solid waste, owing to their substantial content of exploitable materials. This research investigates the impact of temperature and the ratio of coal gangue incorporation on the modification of BOF slag, the dissolution of free CaO (f-CaO), and the process of metal extraction. The rules of mineral phase transformation in the mixture were obtained by combining thermodynamic calculations and experiments, and the metal reduction mechanism was analyzed. The results demonstrate that adding coal gangue can increase the solubility of f-CaO, reaching a peak solubility of 85.8 pct at 1550 °C, which is related to the significant formation of Ca₃MgSi₂O₈. The reduction rate of metal oxides is optimal at 1550 °C, and it is further enhanced when coal gangue is added at 1600 °C. The recovered metals mainly consist of iron, manganese, phosphorus, and chromium, although their concentrations vary, indicating their potential as raw materials for steelmaking. For the efficient utilization of these two materials, it is recommended to conduct slag modification and metal recovery simultaneously at 1550 °C. This technical method can transform two types of industrial solid waste into eco-friendly products, with the potential to achieve comprehensive utilization of steel slag residual heat, BOF slag, and coal gangue. The resulting modified mixture is an ideal material for infrastructure construction (with f-CaO content meeting the standard: DB 13/T 5643—2022), realizing the goal of “zero waste”.