A South African chromite sample was subjected to characterisation and physical beneficiation testwork in order to assess its suitability to produce an upgraded chromite product with a silica level of <1 per centsio2 and a chromite level of>46 per cent Cr2O3. Chemical analysis by XRF indicated that the bulk material had a Cr2O3 content of 40.5 per cent w/w and a SiO2 content of 7.5 per cent w/w. Combined XRF analysis with sizing data showed that the majority (~70 per cent) of the siliceous material was present in the +600 m fraction while ~70 per cent of the Cr2O3 was in the -600 m fraction._x000D_
Qualitative mineral phase analysis by XRD indicated that the sample mineralogy was dominated by ferrian-magnesiochromite spinel ([Fe,Mg]Cr2O4) and aluminium-chromite spinel (Fe[Al,Cr]2O4), with enstatite (Mg2Si2O6), haematite (Fe2O3) and anorthite (CaAl2Si2O8) as minor phases. SEM and EMP characterisation showed that the silica was mainly present in discrete enstatite grains but lesser amounts were also present as the high silica phases plagioclase and enstatite on the edge of grains._x000D_
Wet gravity separation performed on sized fractions (-600+106 m size range) from the -2.0 mm (primary) ore as well as the ore that had been crushed to pass 0.6 mm (secondary) showed that stage crushing of the -2 mm +600 m fraction followed by wet gravity separation upgraded the Cr2O3 grade at 70 per cent Cr2O3 recovery from ~44 per cent Cr2O3 in the primary material to 46 per cent Cr2O3 (the target grade specification) in the secondary sample. It also showed that the stage crushing of this +600 m fraction at a cut-off level of one per cent SiO2 increased the cumulative Cr2O3 recovery from ~50 per cent in the primary material to ~63 per cent in the secondary sample in the same size range of -600+106 m. The extent to which additional crushing could lead to improved chromite recoveries at the required chromite and silica grade target specifications was not determined._x000D_
This experience demonstrates that prior to processing test work being conducted, a thorough understanding of the chemistry and mineralogy of the test sample promotes efficient and targeted processing research._x000D_
FORMAL CITATION:McCallum, D A, Bruckard, W J and Pownceby, M I, 2009. Chromite ore - characterisation through to processing, in Proceedings MetPlant 2008, pp 339-352 (The Australasian Institute of Mining and Metallurgy: Melbourne).