Research progress of technologies for iron resource recovery from nonferrous metallurgical waste slags

As the utilization of nonferrous metals increases, the generation of nonferrous metallurgy waste slags (NMWSs) has also escalated. NMWSs, such as red mud, copper slag, pyrite roasting slag, zinc leaching residues, ferrous sulfate byproducts from titanium dioxide production, and acidic leaching residues from laterite nickel ores, are typically enriched in iron and other valuable metals, presenting a compelling opportunity for high-grade secondary iron recovery. The long-term storage of these waste materials not only occupies land but also heightens the safety risks associated with the management of tailings and poses considerable threats to soil and water resources as a result of heavy metal leaching. Therefore, developing efficient, environmentally friendly, and value-adding technologies for iron resource recovery is urgently needed. This review systematically examines the iron occurrence characteristics and recovery challenges encountered in various NMWSs. By focusing on process methodologies, it articulates the reaction mechanisms and technological advancements related to prominent recovery techniques, including magnetic separation, reduction roasting followed by magnetic separation, hydrometallurgical approaches, and the integration of extraction and metallurgy processes. This paper provides a comparative analysis of the process configurations, critical parameters, and applicable scopes of these diverse methodologies. Furthermore, it evaluates typical waste slags, highlighting their resource characteristics and the adaptability of recovery processes. This review summarizes the advantages and limitations of different recovery pathways in terms of iron recovery rates, concentrate grades, synergistic multimetal utilization, and harmful element management. This analysis aims to offer insightful references for optimizing the recovery and selection of iron resources from NMWSs.