Producing green rutile from secondary ilmenite via hydrogen reduction

Abstract

The use of coal for ilmenite reduction to produce synthetic rutile is widespread in industry. However, the carbon dioxide emissions associated with coal combustion pose significant environmental concerns. Alternative reductants such as hydrogen have the potential to promote environmentally friendly production of green rutile. This study aimed to assess the technical feasibility of reducing an Australian secondary (weathered) ilmenite using hydrogen, focusing on the effects of reduction temperature and time. The ilmenite was composed of 65 % titanium dioxide, 29 % iron oxide, and 6 % impurities. Samples at each stage of the processing were analysed using X-ray fluorescence spectrometry (XRF) and scanning electron microscopy (SEM). The results revealed that both temperature and time impacted ilmenite reduction, with increasing values of both parameters leading to higher reduction percentages. The maximum reduction percentages were obtained for a reduction time of 240 min at all temperatures, and there was an increase from 62 % at 973 K to 99 % at 1273 K for this reduction time. A reduction percentage of 90 % was obtained at 1273 K with a holding time of 60 min. This study indicates that a minimum temperature of 1073 K is required to achieve a reduction exceeding 90 % for secondary ilmenite. The SEM analysis showed that fine, discrete, metallised iron particles were present on the surface of the reduced secondary ilmenite. The investigation into hydrogen as an alternative reductant demonstrated improved iron–titanium separation in acid leaching compared with the conventional reduction method using coal and resulted in green rutile products with titanium dioxide grades exceeding 96 %, and iron oxide content below 1 %.