Effect of mechanical activation and HNO3 pre-treatment of Pulmoddai ilmenite for the extraction of Ti and TiO2 using H2SO4, HCl, and KOH-assisted leaching

Abstract

Mild leaching with HNO₃ acid can be suggested as a potential pre-treatment technique for removing most impurities found in ilmenite which has not been properly investigated yet. This study examines the mild HNO₃ leaching behavior of ball-milled ilmenite as a novel pre-treatment method to produce high-purity synthetic rutile. Ilmenite was mechanically activated for 1 h at 500 rpm which was then reacted with 1 M HNO₃ acid solution in the solid-to-liquid ratio (S/L) of 1:5 (w/v) at 90 °C, 300 rpm, for 2 h to obtain pretreated (ball-milled and ball-milled-mild-leached) ilmenite. The ball-milled ilmenite and ball-milled-mild-leached ilmenite were then reacted with varying concentrations of H₂SO₄, HCl, and KOH solutions at predetermined conditions. Titanium and iron extraction, TiO₂ purity, phase transformations, surface morphologies, and relative elemental abundances were determined by atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy (SEM/EDX), respectively. The initial mild leaching process removed V₂O₅, MgO, MnO, CaO, and Al₂O₃ impurities. The crystallinity indices of ball-milled ilmenite (39.7%) and ball-milled-mild-leached ilmenite (56.7%) indicate the effect of ball milling and mild leaching, respectively. The maximum Ti extraction of ball-milled-mild-leached ilmenite obtained from the sulfate method, chloride method, and alkaline method were 62.1%, 13.2%, and 41.8%, respectively. However, the Ti extraction of ball-milled-mild-leached ilmenite is relatively low compared to ball-milled ilmenite based on percentage extractions. Therefore, the HNO₃ mild leaching process is important to remove impurities, and mechanical activation is more suitable for efficient Ti extraction than a combined step with leaching.