A Review of the Solid-State Reduction Aspects of Ilmenite for Efficient and Sustainable Production of TiO2 Slag

Various pyrometallurgical processes to produce TiO2 slag have been reviewed, focusing on the solid-state reduction aspects of ilmenite. Most of the upgradation processes from ilmenite to titania slag involve direct smelting of ilmenite and, therefore, are generally considered energy-intensive and not environmentally friendly. On the other hand, the pre-reduction of ilmenite, followed by the smelting processes, is advantageous because of its low energy consumption, furnace stability, and negligible slag foaming. In this paper, the impact of different reducing agents on the ilmenite reduction kinetics has been reviewed. The gas-based reduction techniques, primarily with hydrogen or hydrogen-enriched syngas as reductants, show better reaction kinetics and are more environment-friendly than the carbon-based reduction of ilmenite. Hence, the titania slag production from ilmenite can be made efficient and sustainable by incorporating the pre-reduction concept and gas-based reduction for the pre-reduction step. Numerous ways of improving ilmenite pre-reduction have been investigated intensively, featuring pre-oxidation, additives, mechanical activation, and microwave-assisted reduction. Since ilmenite is a good microwave absorber and the microwave-assisted reduction process provides faster kinetics, the method is also very promising for large-scale applications.