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

Automated summary

A characterization study was conducted to identify the impurities, liberation degree of chromite, and possible beneficiation options of chromite ore from South Africa. The study used various techniques including bulk assays, X-ray diffraction, optical and scanning electron microscopy, and quantitative evaluation of mineral by scanning electron microscopy (QEMSCAN) and electron probe microanalysis (EPMA). The results showed that the ore contained 40.5% Cr2O3 with major impurities being Al2O3, MgO, and SiO2. The dominant mineral phase was chrome-rich spinel, and contaminant phases included siliceous minerals, plagioclase, Cr-rich diopside, and phlogopite mica. Upgrading test work demonstrated that stage crushing followed by wet gravity concentration produced a high-quality chromite product.