Pyrometallurgical processing of ferrous slag “co-product” zero waste full utilization: A critical review

The inherent occurrence of slag "co-products" and its utilization during ferrous production are crucial for the industry to ensure greater sustainability. In this work, various research and technological developments to enhance the utilization of ferrous slag co-products and retrieval of thermal energy are reviewed. Ironmaking slag can be utilized as a substitute for cementitious additives or aggregates for construction use. Steelmaking slag contains significant amounts of FetO, MnO and possibly toxic metal oxides, making them difficult for greater utilization. To minimize the ecological hazards and retrieve the value of steelmaking slag, proper treatments are necessary, including reductions of f-CaO (free lime), γ-Ca2SiO4, FeO, and stabilization of toxic metallic elements. In addition, a large amount of under-utilized thermal energy is present within the high-temperature slag but yet to be recovered. To save the thermal energy and retain the added value of slag, dry granulation could be an attractive and eco-friendly option. Among all the possible methods, centrifugal granulation is most economically and environmental beneficial, which is on the edge of industrialization with the potential to integrate with high-grade thermal energy recovery. Compared with the traditional heat carriers, the heat exchange and storage using thermochemical methods through endothermic reactions provides a potential for higher energy density and added values which is yet limited by the reaction kinetics. This work is expected to gain a thorough understanding of ferrous slag and shed light upon the future perspectives of zero waste concept, relieving the environmental burdens for the carbon neutral society in 2050.