Preparation of TiO2 and Fe2O3 Pigments from Sri Lankan Natural Ilmenite

Abstract

Mineral sands deposits represent the most promising and profitable future resources for the country. The crude heavy minerals at Pulmudai-Sri Lanka contain about 60% to 70% of heavy minerals having composition of 70% to 75% ilmenite (about 52% of titanium dioxide and 48 % iron oxide), 10% rutile (about 95% titanium dioxide) and 8 to 10% zircon (65% zirconium dioxide and 35% silica). Titanium dioxide is an important inorganic chemical material, especially the best-quality white pigment. The objective of this project was to apply a simple and very effective method to produce nano particles of titanium dioxide and iron oxide powders from beach mineral sands. Low cost environmental friendly hydrothermal technique was used to breakdown well structured mineral of Ilmenite, with a composition of FeTiO3. Breaking down of ilmenite structure into TiO2 is normally done at 850 C using 70% H2SO4. It is assumed that this can be done at a relatively low temperature with saturated vapor pressure or high pressure under hydrothermal conditions since near critical state condition of water which facilitate to fabricate most of inorganic compounds. In the acidic media, ilmenite could was mixed with a strong acid such as HCl or H2SO4 in different ratios of ilmenite to water then the mixture was reacted under hydrothermal conditions at different temperatures and pressures. Ilmenite was decomposed completely after several hours. Nano-particles of TiO2 could be obtained by hydrolysis and low temperature calcinations of the hydrothermally derived product. The effect of pH on the size and morphology of particles in nano-powders were also investigated. Our results showed after the hydrothermal treatment of ilmenite, black-colored granules changed into swelled yellowish-white product. The HCl solution was also colored yellowish, indicating the Fe-ion leaching from the natural source. This phenomenon implies the hydrothermal treatment for natural rutile can be used not only as a reaction step but also as a semi-purification step. The further research on evaluation and optimization should be conducted in detail; this preliminary results are encouraging toward the present cost-effective process. The results demonstrated that the process is inexpensive, environment friendly and promising in preparing high-purity TiO2 from ilmenite with a high content of gangues.