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Industrial applications of coal rely on understanding its macromolecular structure, which is primarily controlled by coal type and rank. The present study assessed five (5) samples from different collieries extracting coal from the No. 4 Seam of the Highveld Coalfield and their float products, produced at relative densities (RD) of 1.7 and 1.9 g/cm3. The aim was to assess changes in maceral composition and coal quality following the density fractionation, and to use Raman Spectroscopy to compare differences in macromolecular structures between the parent samples and the float products. Raman parameters were also determined for specific macerals, i.e., semifusinite and collotelinite. Mean random vitrinite reflectance (%RoV) values for the studied coals range between 0.57 and 0.60% (medium rank D/C bituminous) and the parent coals are inertinite-rich (70.3 to 88.7 vol% mmf), enriched in semifusinite and inertodetrinite. Following density fractionation, reactive macerals (a combination of liptinite, vitrinite, and reactive semifusinite) are enriched in the float products (designated by "F"), specifically in the products obtained at the 1.7 RD. In comparison, the proportion of inert macerals is higher in the F1.9 samples. These differences in maceral composition are reflected in the Raman spectra and parameters. Although the G and D1 bands for the parent coals and F1.9 samples are similar, these bands are narrower than for the F1.7 samples, indicative of greater aromaticity. The G FWHM values for the F1.9 samples are comparable to those for the parent coal samples, and lower than for the F1.7 samples. This reflects larger differences in maceral composition between the parent coals and the F1.7 samples. In contrast, the D1 FWHM values for the float products, particularly the F1.7 samples, are slightly higher than the parent coals, reflecting a disordered aromatic character mainly related to the presence of aliphatic chains. The Raman spectra for the F1.7 samples are more like that for collotelinite. In contrast, the Raman spectra and parameters (G and D1 FWHM) for the F1.9 samples are more comparable to semifusinite. Thus, the increased aliphaticity for the F1.7 samples is attributed to the relative enrichment of reactive macerals, whereas higher aromaticity for the F1.9 samples reflects a larger proportion of inert macerals. Raman spectroscopy expanded on the petrographic data by interrogating the macromolecular structure of the isorank Highveld coals and their float products. This may assist in predicting the behaviour of the coals during industrial applications (i.e., liquefaction, gasification, combustion, and carbon fibre production). [Display omitted] [ABSTRACT FROM AUTHOR]

The emplacement of igneous intrusions into coal alters both the organic and inorganic components, and may result in the addition of specific components, including rare earth elements (REEs), into the country rock. Previous studies on the intruded coals of the Main Karoo Basin (South Africa) have mainly focused on understanding changes to their organic fraction despite the likelihood that the inorganic composition is also affected, as demonstrated by others studying intruded coals elsewhere in the world. This study reports on the effects of a 0.4 m thick dolerite dyke on the mineralogy and geochemistry of Witbank coals, South Africa. Coal samples were collected at 0.25 m intervals on both sides of the dyke (west and east); in addition to the intruded coals, an unaltered coal from the same seam and a sample of the dolerite were included. The samples were assessed using petrography, X-Ray Diffraction, X-Ray Fluorescence, Scanning Electron Microscopy, and Inductively Coupled Plasma Mass Spectrometry following sequential leaching, focusing on REEs for the latter analysis. Inertinite is the main maceral group in the coal samples; as a result, the impact of the intrusion on the organic fraction is compared using mean random total reflectance (%RoTmr). Total reflectance increases from 1.65 %RoTmr (for the unaltered coal) to 4.17 %RoTmr closer to the dyke on the western side. In contrast, the eastern side reports lower values (max. 1.94 %RoTmr). Similar to reflectance, dolomite is higher in samples from the western side of the dyke. Dolomite is also found in the unaltered coal (4 wt%) and the dolerite sample (15 wt%). Syngenetic dolomite and a weak positive Gd anomaly for the unaltered coal (ΣREE = 83.7 μg/g) suggest the presence of acidic groundwaters during peatification. Subsequently, the coals were also affected by hydrothermal activity, related to the intrusion of the dolerite dyke. For the intruded coals, dolomite (fracture-infilling) and ΣREEs are higher on the western side, at a maximum of 24 wt% and 153.0 μg/g, respectively. Carbonate associated REEs are higher for the intruded coals than the total for the dolerite (ΣREE = 23.3 μg/g). This reflects the incompatibility of REEs with early-formed minerals in the dolerite, concentrating them in the residual melt. Increased reflectance and dolomite (and associated REEs) in coals from the western side suggest pronounced hydrothermal activity, related to the availability of accommodation space (i.e., fractures). [Display omitted] • Two sets of intruded Witbank coals were studied. • Dolomite is a significant epigenetic phase. • A high proportion of REEs is associated with carbonates. • Reflectance, dolomite, and ΣREEs are higher in the west of dyke. [ABSTRACT FROM AUTHOR]