Hydrolysis of TiOCl₂ solution from ilmenite HCl leaching: Controlled synthesis of coarse metatitanic acid with predictable D₅₀ and growth modeling

Titanium metal is critical for aerospace and biomedical applications, yet its widespread use is severely hindered by the high cost of the conventional Kroll process. Thermoreduction offers an alternative route but requires a stable and economically viable supply of coarse metatitanic acid (H₂TiO₃) feedstock. This study develops a process for synthesizing coarse H₂TiO₃ via controlled hydrolysis of titanium oxychloride (TiOCl₂) solution derived from hydrochloric acid leaching of ilmenite. By optimizing key parameters: reaction temperature, titanium concentration, feeding time, and initial water volume, H₂TiO₃ particles with a median diameter (D₅₀) of 28.2 μm were obtained. A semi-empirical growth model for H₂TiO₃ particles was established, which can be used to describe the evolution of particle size within the investigated experimental range. Thermal decomposition of H₂TiO₃ shows that adsorbed water and hydroxyl groups are partially removed below 300 °C, mostly eliminated at 600 °C, and completely removed at 700 °C, with phase transformation occurring between 300 and 800 °C. Nearly pure rutile is obtained above 800 °C. This process provides coarse H₂TiO₃ feedstock for thermal reduction-based titanium production.