Integrated carbothermic smelting – Acid baking – Water leaching process for extraction of scandium, aluminum, and iron from bauxite residue

Abstract

A closed-loop valorization process, combining carbothermic smelting and acid baking – water leaching was developed to recover scandium, aluminum, and iron from bauxite residue, a major side product of aluminum production. This process employs carbothermic smelting to recover 99% of the iron in the starting residue as crude metallic iron, which can be separated from slag that contains aluminum and scandium. Composition of slag was found to be primarily dependent on the smelting temperature and amount of smelting flux added. At high smelting temperatures (1600 °C), sodium was found to evaporate from slag, potentially enabling sodium separation and recovery. The slag was treated by acid baking – water leaching, to convert scandium and aluminum to soluble sulfate species, allowing recovery. The single-pass acid baking – water leaching was optimized to achieve 99% scandium and 47% aluminum extraction by employing sulfuric acid at a ratio of 1.25 gH₂SO₄/g, baking at 150 °C for 2 h, and water leaching at ratio of 7.5 mLH₂O/g for 210 min. The production of solid leaching residue was avoided by employing thermal desulfation at 1400 °C to remove 84% of leaching residue sulfur content thereby potentially allowing regeneration of sulfuric acid for acid baking and producing a recycled smelting flux that would reduce reagent consumption and would allow recapturing the scandium and aluminum not recovered during leaching. This closed-loop process enables efficient and sustainable recovery of scandium, iron, and aluminum from bauxite residue, and constitutes first steps in an integrated process for sustainable valorization of bauxite residue, supporting efforts to develop a zero-waste economy.