Automated and Quantitative Mineralogy Applied to Chromite Ore Characterization and Beneficiation

A characterization study of chromite ore from South Africa was conducted using bulk assays, X-ray diffraction, optical, scanning electron microscopy (SEM), automated probe microanalysis (EPMA) and quantitative evaluation mineral by (QEMSCAN) mineralogical techniques, EPMA. The aim to identify all major gangue impurities, the degree liberation, possible beneficiation options. material assayed 40.5% Cr2O3 with impurities being Al2O3 (13.2%), MgO (12.1%), SiO2 (7.5%). Quantitative phase analysis showed that sample mineralogy dominated a chrome-rich spinel an average chemical composition (in wt.%) of: Cr2O3—47.8; FeO—26.0; Al2O3—15.4; MgO—11.0. Contaminant phases included siliceous minerals enstatite, anorthite-rich plagioclase (bytownite), Cr-rich diopside (containing 1–2 wt.% Cr2O3), phlogopite mica. QEMSCAN sized fractions indicated (a) most silicate species were in +850 μm fractions, (b) >80% liberated, (c) common association for enstatite. Based on results, upgrading test work demonstrated stage crushing followed wet gravity concentration produced chemical–metallurgical-grade ‘chromite’ product containing >46% <1% SiO2.