Sulfuric Acid Leaching of Altered Ilmenite Using Thermal, Mechanical and Chemical Activation

The kinetics of the sulfuric acid leaching of altered ilmenite, mechanisms, and process intensification methods were studied. The effect of changing the chemical composition during grinding was determined. The content of ilmenite and pseudorutile decreased from 5.3% to 3.1% and from 90.2% to 63.1%, respectively. Rutile increased from 4.5% to 28.7%, while a pseudobrookite new phase appeared in the amount of 5.1% after 2 h of grinding. It was found that the modification of raw material by sulfuric acid led to the increase of the decomposition rate, and at the same time, decreased when the ore was utilized due to an increase of insoluble TiO2 content. Isothermal conditions were evaluated with H2SO4 concentration varying from 50 to 96%. The data obtained were described with the approximation of the contracting sphere model. It was shown for the first time that H2SO4 > 85 wt% causes a sharp constant decrease of titanium. Correlating these phenomena allows for the consideration of H2SO4·H2O as reagents, rather than H2SO4 molecules. It was experimentally proven that at a temperature above 190 °C, the Ti leaching degree dropped, which is explained by the formation of polymerized TiOSO4. Finally, it was shown that adding NaF reduced the activation energy to 45 kJ/mol.