Morphological Changes and Reduction Mechanism for the Weak Reduction of the Preoxidized Panzhihua Ilmenite

Morphological changes and phase transition behaviors were investigated for the weak reduction (reduction of ferric iron-to-ferrous state) of preoxidized Panzhihua ilmenite by hydrogen at 873 K to 1073 K (600 °C to 800 °C). Ilmenite was preoxidized for 4 hours at 1023 K and 1173 K (750 °C and 900 °C), respectively, before the reduction. The results revealed that there were two competing reduction routes. At high reduction temperatures, e.g., 1023 K and 1073 K (750 °C and 800 °C), ferric irons from both hematite and pseudobrookite would combine with rutile grains as formed in the preoxidation to form homogeneous ilmenite phase with pores immingled. However, at lower reduction temperatures, e.g., 873 K (600 °C), hematite and pseudobrookite are reduced mainly through direct reduction without the participation of rutile. As a result, the as-reduced ilmenites show great differences in their phase components and microstructure, especially for the Ti species. For ilmenites preoxidized at 1023 K (750 °C), most of the Ti ions present in the needlelike rutile network, but for ilmenites preoxidized at 1173 K (900 °C), Ti distributed in both irregular rutile grains and ilmenite matrix.