Application of multispectral computed tomography for the characterisation of natural graphite

Abstract

The established mineralogical and chemical analysis methods for graphite ores require complex sample preparation. Moreover, they do not produce 3D images of the polymineralic rock structure and texture. The lack of 3D information can lead to an erroneous assessment of the quality-determining properties of graphite ores, such as graphite flake size (grain size), graphite flake size distribution, and impurities. Therefore, there is a need to obtain 3D information from graphite ores and concentrates. Industrial computed tomography (CT or single-spectrum CT) is a unique technique that enables the examination of rocks in the 3D regime. The challenge in CT analysis of ores is the different absorption properties of mineral phases present. Low X-ray tube generator voltages lead to pronounced artefacts (volume defects) if highly absorbing gangue phases (e.g. iron sulfides) are present. Therefore, high X-ray tube voltages must be applied. However, graphite and associated gangue minerals, as well as contained cracks and voids in the ore, can exhibit similar absorption properties at higher generator energies (above 120 kV). Multispectral CT (MSP-CT) measurements offer a minimisation of CT artefacts and an increase in grey value contrasts. This work investigates the application of the MSP-CT measurements, significantly improving mineral differentiation.