Converting Iron-Bearing Tailings from Recycling of Urban Steel Scrap to Direct Reduced Iron via Magnetic Separation Followed by Hydrogen Reduction Under Microwave Irradiation

In this study, the feasibility of converting iron-bearing tailings from urban steel scrap recycling to value-added direct reduced iron (DRI) via magnetic separation followed by hydrogen reduction under microwave irradiation was investigated, with an emphasis on the effect of reduction temperature. The experimental results showed that by magnetic separation, the tailings sample with an iron content of 15.42 wt% could transit to a high-grade magnetic concentrate with an iron content of 60.04 wt% and good microwave absorption capability, as revealed by its short microwave penetration depth (Dp). After hydrogen reduction under microwave irradiation, the main iron-bearing phases, including magnetite, hematite, limonite, and martite, had stepwise deoxidation into metallic iron. As the reduction temperature increased from 750 °C to 1050 °C, the total iron content (TFe), reduction degree and iron metallization degree of the product increased rapidly and then became stable due to difficult reduction of FeO. As the reduction process proceeded, the dispersed iron particles gradually aggregated. At the optimum temperature of 950 °C, the reduction degree and iron metallization degree reached 90.10% and 88.71%, respectively. Meanwhile, the pore size, microporous volume, and specific surface area of the product were 1.943 nm, 1.767 × 10−5 cm3/g, and 0.3961 m2/g, respectively. The saturation magnetization (MS) and coercivity (HC) of the product remained 170.94 emu/g and 46.25 Oe, respectively. The product can act as a potential feedstock for electric arc furnace (EAF) steelmaking.