A cleaner-sustainable process for recovering valuable elements from steel slag with acetic acid: Leaching studies and multi-value-added products

Steel slag (SS), a hazardous solid waste produced by the steelmaking industry, contains a large number of valuable metals but generates a potential threat to the environment. This research focuses on a cleaner-sustainable process to recover valuable elements, including calcium (Ca), magnesium (Mg), aluminium (Al), and iron (Fe), from SS by acetic acid leaching and develop new products. The single-factor experiment and kinetic analysis were employed to determine the leaching characteristics of SS, optimize the leaching processes, investigate the influence of various leaching conditions, and clarify the constraints of leaching kinetics. The results indicated that the leaching rate of Ca, Mg, Al, and Fe was 76.24%, 67.19%, 54.97%, and 28.91%, respectively, under the optimal leaching conditions. Besides, the apparent activation energies of Ca, Mg, Al, and Fe were 26.20 kJ/mol, 26.26 kJ/mol, 23.37 kJ/mol, and 14.76 kJ/mol, respectively, and the whole leaching process was found to be controlled by the diffusion and interfacial chemical reaction. Meanwhile, a residue with admirable surface areas was obtained after the leaching stage. The leachate was co-precipitated by sodium hydroxide (NaOH), and multi-value-added Mg-Fe layered double hydroxide (Mg-Fe LDH) was synthesized. This work demonstrates the potential of hydrometallurgical processes for the treatment of SS, which is of great considerable importance to the harmless treatment of industrial solid waste and provides insights into strategies for the utilization of secondary resources.