Direct Carbothermic Reduction of Weathered Ilmenite for Efficient Removal of Iron by Leaching

Abstract

The commercial processes to extract iron from ilmenite (FeTiO3) essentially include energy-intensive methods, such as high-temperature reduction smelting or preoxidation, coupled with reduction by carbon. However, due to altered mineralogy of ilmenite caused by weathering at sea coast, the reduction of iron remains incomplete in either of these processes, demanding a high concentration of acid when used for extraction of high-purity TiO2 for high-end applications. We developed a process for the flux-catalyzed reduction of a partially weathered ilmenite ore of Indian origin. Initially, the effect of flux material and temperature was evaluated using thermogravimetric/diffraction thermal analysis (TG/DTA). The reduction behavior of the fluxed self-reducing pellets of ilmenite was then studied in a raising hearth furnace. The TG/DTA results indicated improved performance of sodium carbonate over lime within a temperature range of 1173 K to 1373 K. Under different reduction conditions in raising hearth furnace experiments, the leaching of reduced ilmenite in diluted hydrochloric acid (6.6 pct concentration) produced different grades of synthetic rutile. The best reduction conditions under optimized parameters enhanced the TiO2 from initial 51 to 93 wt pct in the synthetic rutile. The X-ray diffraction and electron probe microanalysis investigation of the unreduced and reduced ilmenite revealed the conversion of the FexOy-SiO2-Al2O3 system to Na2O-SiO2-Al2O3 by sodium carbonate. The thermochemical analysis further explained the influence of sodium carbonate on the liquidus of Na2O-SiO2-Al2O3 slag. The improved process enables the complete reduction of the iron from weathered ilmenite to produce a high-grade rutile.