Recycling of iron from red mud by magnetic separation after co-roasting with pyrite

• Pyrite thermo-decomposes to iron monosulfide, pyrrhotite and sulfur.
• Iron monosulfide, pyrrhotite or sulfur reduces hematite to magnetite.
• Red mud is co-roasted with pyrite.
• Iron in red mud is recovered by magnetic separation after roasting.

A recycling process of iron from red mud by magnetic separation is proposed, in which iron oxide (Fe2O3) in red mud transforms to magnetite (Fe3O4) by anaerobic co-roasting with pyrite (FeS2). TG-DTA and XRD results showed that hematite was reduced to magnetite by the thermo-decomposed compounds (iron monosulfide, pyrrhotite and element sulfur) of pyrite. The mole ratio of pyrite to hematite and the roasting temperature effected the transformation. In the simulated experiment, 30 g red mud containing 9.24% of iron (13.2% in Fe2O3) mixed with 0.74 g pyrite were roasted at 600 °C under N2 atmosphere for 30 min. 4.5 g magnetic material (with Fe content of 36.9%) was magnetically separated, and the remaining solid only containing 0.61% of Fe (0.87% in Fe2O3), being able to meet the stipulated standard of 2% for refractory material manufacture.