Sulfidising roast treatment for the removal of chrome spinels from murray basin ilmenite concentrates

The Murray Basin region of southeastern Australia represents the remains of a shallow inland sea and contains heavy mineral sand placer deposits typically comprising the primary economic minerals ilmenite (FeTiO3), altered ilmenite, rutile (TiO2), and zircon (ZrSiO4). Rutile and zircon are easily separable from the bulk heavy mineral concentrate and are currently extracted from deposits. The ilmenite component remains largely unexploited due to its wide spectrum of chemical alteration (making a clean separation difficult) and the presence of impurity mineral grains; mainly, chrome spinel (general formula AB2O4; A2+ = divalent cation e.g. Fe, Mg, Mn; B3+ = trivalent cation e.g. Cr, Al, Fe3+). The presence of even a minor amount of chromia (Cr2O3 <0.05%) in the ilmenite product downgrades its market value. While magnetic separation is usually an effective method to achieve a clean separation between ilmenite and chrome spinel, this procedure is not effective for the Murray Basin material as there is a considerable overlap in the magnetic susceptibility properties of both mineral phases [1]. Pownceby et al. [2] recently suggested a potential method for separating chrome spinels from ilmenite which involved changing the physical properties of the individual chrome spinel grains through a sulphidising roast treatment. The aim of the current work is to analyse the sulfidation treatment of chrome spinel as a new route for chrome spinel removal from the Murray Basin ilmenite concentrates. This study comprises two phases of investigation: (1) a systematic thermodynamic assessment of equilibrium reactions in the Fe-Cr-Ti-O-S system to evaluate the effect of composition, temperature, and partial pressures of sulfur and oxygen, and, (2) selected experimental investigations using natural ilmenite and chromite samples to test the findings from the thermodynamic calculations.