Mechanism and Kinetics Study on Sulfuric Acid Leaching of Titanium from NaOH Roasting Ilmenite

Based on the difficulty of extracting titanium from ilmenite, this study modified ilmenite by alkali roasting to improve the leaching rate of titanium. The leaching behaviour and kinetics of titanium in pretreated slag and the mechanism of limiting titanium leaching were studied. The results indicate that alkaline roasting pre-treatment of the ilmenite ore can transform acid-resistant FeTiO₃ into more reactive Na₂TiO₃ and NaFeO₂, which are more amenable to leaching. Simultaneously, under the following pre-treatment conditions—a sodium hydroxide to ilmenite ore mass ratio of 1.5:1, roasting temperature of 1123.15 K and roasting time of 1 h—the optimal leaching conditions are found to be a leaching temperature of 363.15 K, sulphuric acid mass fraction of 60% and liquid–solid mass ratio of 6:1. Under these conditions, the titanium extraction was most efficient, achieving a titanium leaching rate of 97.36%. The leaching reaction of titanium in the pre-treated slag follows the shrinking core model of the internal diffusion-controlled step. The apparent activation energy for the leaching reaction is determined to be 77.45 kJ/mol. Analysis through XRD, XPS and SEM–EDS reveals the formation of silica gel during leaching, which also has an adsorption effect, preventing complete titanium leaching.