Evaluation of mineral liberation and stereological bias based on X-ray microtomography and scanning electron microscopy for an iron ore tailing

A key factor in mineral concentration is mineral liberation. Scanning electron microscope-based (SEM-based) automated image analysis systems have been used to obtain information concerning liberation. One of the limitations of SEM-based techniques is the unavoidable loss of 3D information, leading to significant stereological errors. X-ray microtomography (μCT) emerges as an alternative that permits three-dimensional imaging and direct measurement of spatial characteristics of particles, eliminating stereological issues. We used high-resolution μCT and a microscope-based system to evaluate the characteristics of liberation of an iron ore waste. Grade and surface exposure have been overestimated by the 2D assessment. The stereological effect was more pronounced in surface exposure quantification. We found a linear relationship between (i) grade and surface exposure and (ii) particle size and surface exposure. A comparison of SEM-based and μCT techniques showed that a 3D technique is better for the purpose of particulate systems characterisation.