Selective sulfidising roasting for the removal of chrome spinel impurities from weathered ilmenite ore

• The paper evaluates a selective sulfidation route as a new approach to separate the chrome spinel from weathered ilmenite
• It has shown that there are two windows of operation (Area-1 and Area-2) where chrome spinel could be selectively sulfidised
• Conditions for Area-1 varies from pO2 ≈ 2.37 × 10− 09 to 5.01 × 10− 15 atm and Area-2 is pO2 ≤ 6.92 × 10− 19 atm and pS2 ≤ 1 × 10− 06 atm
• This approach could be used to remove other impurities such as Mn and Mg

With high-grade ilmenite (FeTiO3) ores becoming scarce, there is a need to process lower-grade and more weathered ilmenite ores. These alternative sources provide complexities in terms of physical characteristics, mineral compositions, and impurity levels, all of which can significantly affect the subsequent processing route. In the production of high purity white pigment from ilmenite, chromia (Cr2O3)-containing impurities such as chrome-rich spinels need to be removed from the ilmenite concentrates down to commercially accepted levels. Existing magnetising roast processes currently used in the industry do not allow a clean separation of the chrome-rich spinels from the ilmenite due to overlapping physical properties. It has been suggested that selective sulfidation of chrome-rich spinels could be a potential route for chromia separation from ilmenite. However, the detailed conditions under which the selective sulfidation can occur are not well known. This work focuses on a systematic study of selective sulfidation of chromite FeCr2O4 (one end member of the spinel series) for the purpose of chromia impurity removal from a weathered ilmenite concentrate. Detailed thermodynamic assessment and experimental studies have been carried out to determine the conditions at which selective chrome spinel sulfidation occurs. The results suggest that there are two regimes (Area-1 and Area-2) where selective chrome spinel sulfidation is possible. Area-1 is in the range of pO2 ≈ 2.37 × 10− 09 atm to 5.01 × 10− 15 atm, while Area-2 is at lower pO2 (≤ 6.92 × 10− 19 atm) and pS2 (≤ 1 × 10− 06 atm) region relative to Area-1. Targeted experimental analyses of the two regimes revealed that selective sulfidation of chrome spinel occur only under the reaction conditions at Area-2. It is suggested that the lack of selective chrome spinel sulfidation under Area-1 conditions is the change in activity of iron (aFe) due to weathering action on chrome spinel grain.