Research frontier of steel slag recycling in carbon emission reduction

Metallurgical slag is a waste or by-product of the metallurgical process, and its improper disposal can pose negative environmental impacts, including groundwater and soil contamination. The composition and properties of metallurgical slag are complex, which is usually difficult to use or process directly and requires special treatment and utilization methods. Taking converter slag and blast furnace slag as examples, the research frontiers and development potential were primarily discussed and analyzed in three aspects: the recycling within and outside metallurgical slag plants, the extraction and utilization of thermal energy from metallurgical slag, and the functionalization and social application of metallurgical slag. The metallurgical slag waste heat recovery includes chemical methods and physical methods. Among them, the physical method currently most used was centrifugal granulation to recover heat. Chemical laws could recover hydrogen through the waste heat of metallurgical slag, which could save fuel and reduce CO₂ generated by fuel combustion. Metallurgical slag is rich in alkaline metal oxides, which can undergo a carbonation reaction with CO₂ to achieve carbon sequestration in metallurgical slag. Elements such as iron, phosphorus, and silicon contained in metallurgical slag could be used in soil conditioners, cement raw materials, and wastewater treatment. For example, the phosphorus element in the slag could be extracted by melt modification followed by acid leaching and used as a raw material for phosphate fertilizer. Therefore, under the background of China’s carbon neutrality goal, it is important to develop the key technologies of waste heat utilization of metallurgical slag and carbon sequestration of metallurgical slag.