Quantitative coal characterisation by means of microfocus X-ray computer tomography, colour image analysis and back-scattered scanning electron microscopy

Abstract

Microfocus computer tomography is a non-destructive technique enabling virtual slicing of opaque objects. Stacking several slices enables 3D visualisation of the object. To extract quantitative information, a thorough calibration with data obtained by classical microscopy techniques is needed. Correlation of microfocus computer tomography data with colour image analysis data of reflected-light microscopy and with back-scattered electron microscopy is worked out. SEM EDX is also used to identify mineralogical phases. Compared to former studies, much better resolutions were achieved in the order of 185 μm. Moreover, a dual energy technique is presented allowing the measurement of the density of all components. It is shown that macerals, which are abundant in the studied coal sample (i.e. vitrinite and liptinite in this study), can be quantified by microfocus computer tomography. However, no significant information on other components like pyrite and inertinite, which have surface percentages of less than 2%, could be retrieved from this sample. Finally, a close interrelation between liptinite and clay is demonstrated. With this information a 3D maceral and mineral visualisation and quantification is performed. In the studied sample 23% of the volume of the sample contains 90% of vitrinite together with 10% of another constituent. A 3D coal characterisation is thus possible.