Activation Behavior and Mechanism of Sodium Sulfate for Iron Recovery from Red Mud through Magnetization Roasting–Magnetic Separation

It is a hot topic to recover iron from red mud in the research field of solid waste comprehensive utilization, but high-quality iron concentrate is always difficult to be obtained unless by high-temperature reduction roasting–magnetic separation. In this study, low-temperature magnetization roasting–magnetic separation has been conducted to recover iron from red mud, with carbon monoxide as the reducing agent, and the effect of Na₂SO₄ as an additive and corresponding activation mechanism has been investigated, confirming that Na₂SO₄ can significantly improve the quality of the iron concentrate. Under the optimum conditions, an iron concentrate with a total iron grade of 60.65% and a recovery of 94.01% could be obtained, increased by 3.46% and 2.76%, respectively, compared with that in the absence of Na₂SO₄. This verified that weak-magnetic hematite was transformed into strong-magnetic magnetite by reductive roasting. The iron content in the magnetite was raised from 0.93% in red mud to 80% and 82%, respectively, for the roasted briquettes in the absence and presence of Na₂SO₄. As Na₂SO₄ contributed to not only the reduction and enrichment of iron minerals but also to the decomposition of iron-containing complex oxides, the separation of the iron and the magnetic property intensity of iron concentrate was enhanced.