Extracting Al2O3 and TiO2 from Red Mud Smelting Separation Slag by Alkali and Acid Leaching Methods

Recovery of valuable metals from red mud smelting separation slag is important for environmental protection and saving of natural resources. In this paper, we propose a recycling process of red mud smelting separation slag by mineral phase reconstruction conducted under an air atmosphere. In this process, NaOH and Ca(OH)2 roasting of Al2O3 and NaAlSiO4 was performed, and Al2O3 and SiO2 were converted into alkaline-soluble NaAlO2 and Ca2SiO4, respectively. In the consequent steps, more than 80% of Al2O3 was selectively dissolved into a leaching solution using a NaOH solution under 95 °C, and the obtained NaAlO2 solution can be used as a source for extracting alumina. Then, a 20 wt.% HCl solution was used to remove SiO2 from the residue, obtaining a SiO2-containing solution and a concentrated residue of undissolved TiO2 and CaO. Finally, this mineral phase reconstruction process can enable a higher metal leaching rate, and this study provides a novel, clean, and sustainable method for recycling valuable metals from red mud smelting separation slag.