Clean dealkalization technology from aluminum industry hazardous tailings-red mud by displacement with Mg-based agent

Red mud is a kind of strong alkaline hazardous slag discharged from aluminum metallurgy industry. In this study, the water immersion with high temperature and high pressure was developed for the selective dealkalization from red mud by adding Mg-based additives. The removal efficiency of alkali could reach 92% by using 12% MgCl₂ with 9 mL/g at 250 °C for 60 min. The MgCl₂ was the most effective leaching reagent to promote the decomposion of cancrinite lattice. The new minerals bearing Mg, i.e., chlorite (Mg₅Al₂Si₃O₁₀(OH)₈) and pyrope (Mg₃Al₂Si₃O₁₂) could be formed, which was in favor of transforming the structural alkali into the free alkali by the analysis and validation of XRD and SEM-EDS. The dealkalization process was mainly controlled by chemical reactions according to the analysis of unreacted shrinking core model (USCM) of leaching kinetics. The leaching kinetics equation of 1 - (1 - x)^1/3 = 32.2 × exp[4582.6 / T] × t was built and the apparent activation energy of 38.1 kJ/mol was obtained. This method may provide a new and cleaner way for the efficient dealkalization of red mud and a basis for the utilization of leaching residue as the soil amendment.