Enhanced Scandium Recovery from Red Mud Using Two-stage Acid Baking and Water Leaching Process

Red Mud, a byproduct of bauxite processing via the Bayer process, has emerged as a potential secondary source of the critical rare earth element (REE) Scandium. Previous research using direct acid leaching or acid baking and water leaching processes achieved limited Scandium recoveries of up to 60%. Improved recovery has been reported when using high-temperature pretreatments or extended leaching time with associated energy costs. This study aims to develop a more efficient H₂SO₄ acid baking and water leaching process to achieve higher Scandium recovery without using high temperatures or excess acid. Scanning Electron Microscopy – Energy Dispersive Spectroscopy analysis to visualize the depth of sulfation of the baked sample showed that Scandium recovery was limited by the mass diffusion of acid through the sulfated layer formed during baking. An efficient two-stage acid baking and water-leaching process was developed to reduce mass transfer limitations, achieving Scandium recovery exceeding 75%. Baking with H₂SO₄ at 200°C for two hours and water leaching at 75°C for two hours at each stage offered a 20% improvement in recovery while employing the same acid concentration as in the single-stage process. The improved recovery is attributed to the enhanced Scandium accessibility due to improved porosity and surface area as measured by N₂ adsorption in the two-stage process.