The recent demand on global steel production has prompted the development of new techniques for the reliable measurement and characterisation of iron ore minerals such as hematite (Fe2O3), magnetite (Fe3O4), goethite (FeO(OH)), and limonite (FeO(OH).n(H2O)). While magnetite and hematite can be distinguished qualitatively using optical microscopy, quantitative characterisation using SEM-based Automated Mineralogy solutions, is challenging due to the similar BSE and EDS response of these two minerals. A new MLA measurement workflow has been developed by FEI to discriminate iron oxides by taking full advantage of the subtle difference in backscatter intensities between hematite and magnetite.The workflow involves three steps:1.Stretching BSE brightness and contrast to effectively double the grey level contrast for iron oxides. As a result two separate peaks emerge, representing hematite (~200) and magnetite (~210). This allows for reliable phase separation at the image segmentation stage
2.Energy-dispersive X-ray (EDX) spectra acquisition combining two measurement settings. Single EDX spectra are collected from centre points of unsaturated segmented phases (including hematite and magnetite). Saturated segments, comprising multiple bright mineral phases, are mapped using a regular grid with further phase discrimination based on EDX spectra
3.Mineral identification is performed by a classification algorithm combining BSE thresholds and EDX spectra.
This advanced approach to magnetite and hematite as been applied to several iron ore samples from different locations worldwide. The results show successful discrimination of iron oxides into hematite and magnetite, with identification based on a combination of modified backscatter intensities and EDX spectral matching, FEI reports.