Abstract <p>This study systematically investigated the reduction behavior of copper slag under a hydrogen atmosphere, with a focus on the effects of reduction conditions on the degree of metallization, phase composition, and microstructure. The results indicate that under temperatures of 1000–1150 °C, a reduction time of at least 0.5 h, and a mixture flow rate of 120 mL/min or higher, the reduction rate of iron in the copper slag remains largely stable. Further increases in reduction time or mixture flow rate do not significantly improve reduction efficiency. As the temperature rises, the silicate phase formed during reduction begins to melt and agglomerate. This leads to particle coarsening, which in turn hinders the reduction of Fe and the coalescence of metallic Fe particles. Phase and micro-area composition analyses reveal that the local Fe content in the reduction products can reach 50% to 70%. The remaining phases consist mainly of silicates such as Ca₂Zn(SiO₇), Ca₂(Al₂SiO₇), and Ca(Fe, Zn)(Si₂O₆). Metallic Fe particles are often found intergrown with or included within silicate phases. The maximum degree of metallization of Fe can reach 89.96%. After grinding and crushing, most of the metallic Fe can be separated as individual particles. This study offers a theoretical foundation for optimizing the hydrogen-based reduction of copper slag and the subsequent separation process.</p> Graphical Abstract <p></p>