Toward Low-Carbon Metallurgy: Sustainable Iron Recovery from Copper Slag Using Hydrogen Reduction

Copper slag contains abundant iron resources but has long been difficult to utilize efficiently due to its complex mineralogical composition and fine particle size. In this study, a process of hydrogen-based non-melting reduction followed by melting separation was proposed for the green and efficient recovery of iron from copper slag. Through thermodynamic analysis and systematic experimental investigations, the hydrogen reduction behavior of iron-bearing phases and the effects of key operational parameters, including temperature, reduction time, hydrogen partial pressure, and gas-to-material ratio, were clarified. The results indicate that the reduction of fayalite (Fe 2 SiO 4 ) requires elevated temperature and high hydrogen partial pressure. Under optimized conditions (950 °C, 6 h, H 2 > 80%, gas-to-material ratio ≥ 10.8 L·g −1 ), iron-bearing phases in copper slag can be efficiently transformed into metallic iron, achieving an iron recovery exceeding 99%. Subsequent melting separation enabled significant enrichment of iron, increasing the iron content in the resulting ferroalloy to approximately 96.6 wt %. Energy consumption and carbon emission calculations demonstrate that, compared with conventional carbothermic reduction, the hydrogen-based process reduced cumulative energy consumption and greenhouse gas emissions by 91.5 and 94.9%, respectively. This study provides a novel low-carbon, high-efficiency, and high-value utilization route for iron resources in copper slag.