Application of coal-based direct reduction-magnetic separation process for recycling of high-iron-content non-ferrous metallurgical wastes: Challenges and opportunities

Non-Ferrous Metallurgical Wastes, including copper slag, red mud, jarosite residue, zinc-bearing dust, pyrite cinder, and nickel slag, are hazardous waste products released during the metal extraction process. Metallurgical solid wastes pose significant risks to the environment due to their content of hazardous elements, which may impact the quality of surface water and groundwater. However, the iron content in non-ferrous metallurgical solid wastes such as copper slag, red mud and zinc-containing dust can often reach 30-50%, which is higher than the average iron grade (27%) of the iron ores found in China and has a high utility value. In this manuscript, we summarize the primary optimization process of the coal-based direct reduction-magnetic separation method for metallurgical recovery and further purification of metallurgical solid waste. We discuss technological advancements, including rotary kiln, rotary bottom furnace, and tunnel kiln methods, and address environmental and economic aspects, especially in coal-rich regions with limited natural gas resources. Additionally, we have highlighted the technical challenges and developmental bottlenecks of the direct reduction-magnetic separation process; our findings reveal that the improved processes, characterized by high recycling efficiency and low energy consumption and secondary environmental pollution, continue to be the focus of research and development for the sustainable utilization of metallurgical solid waste.