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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]

In this study, carbon-13 cross-polarization magic-angle-spinning solid-state nuclear magnetic resonance ( 13 C CP-MAS SS NMR) was undertaken on a parent coal sample and its density-fractionated derivatives, an inertinite-rich and a vitrinite-rich sample, obtained from the Witbank Coalfield of South Africa (medium rank C bituminous coal). The formation of inertinite macerals has been extensively researched and the conclusions remain largely controversial. However, most research has been confined to northern hemisphere coals, which are typically dominated by vitrinite. South African coals are widely known for their high inertinite content. Earlier workers have ascribed the inertinite macerals, in their diversity, to aerial oxidation. However, this oxidation-only pathway fails to recognize that inertinite macerals can form through other processes such as charring of plant matter. Microscopically, charred matter possesses anatomical structures that closely resembles those observed in inertinite macerals, with lignin and/or cell walls largely preserved, perhaps mechanically fragmented or compressed in some instances. Based on the NMR structural parameters, the average aromatic cluster size in the inertinite-rich sample (petrographically dominated by fusinite, semifusinite of varying reflectance, and inertodetrinite) corresponds to monocyclic, 6-aromatic carbon rings. In the vitrinite-rich sample of the same coal, the cluster sizes are larger, corresponding to multi-ring aromatic hydrocarbons. The 6-carbon rings in the inertinite-rich sample are interpreted to correspond to guaiacol and syringol, the principal products of low-temperature (below 400 °C) lignin pyrolysis. Since charring depletes cellulose and moisture, fire-affected plant matter is interpreted to have a lower compaction potential than vitrinite-forming material, sustaining 6-aromatic carbon ring isolation in the former. Lignin-derived aromatic rings in compactable plant matter merge to form the multi-ring clusters present in the collotelinite- and collodetrinite-rich sample of the same coal. [ABSTRACT FROM AUTHOR]

Petrological and mineralogical features are key for inferring palaeoenvironmental and sedimentary conditions of coal-bearing sediments. Following the logging of a borehole core, this study reports on the organic petrology and mineralogy of the A and B Seams, Ermelo Coalfield, Main Karoo Basin (MKB), South Africa. Seventeen coal samples collected from the core, differentiated based on changes in lithotypes, were assessed using detailed petrography (macerals, microlithotypes, and mean random vitrinite reflectance), quality analyses (proximate, elemental, and gross calorific value), and mineralogy in order to deduce depositional environments for the Ermelo coals. The lithologies present in the core were typical of the MKB, and the coals were inertinite- and mineral matter-rich, apart from samples occurring at the base of the seams. The latter samples also had a higher proportion of structured inertinite macerals (fusinite and semifusinite) and lower ash yields. The rest of the samples had higher inertodetrinite contents, occurring in association with detrital quartz and kaolinite, resulting in higher ash yields. The formation of each coal seam thus commenced with the prevailing conditions conducive to the preservation of structured macerals and concluded with the accumulation of predominantly inertodetrinite. Select samples from the B Seam also had durite, an association of inertodetrinite and liptinite (including alginite). The co-occurrence of inertodetrinite and the detrital minerals alongside alginite suggests two depositional episodes. The first episode relates to the formation of primary inertinite macerals through charring, followed by fragmentation and redeposition as inertodetrinite. This latter process likely also reflects seasonal flooding, resulting in fluctuating water levels within the palaeomire. The second episode was quieter, occurring in deeper waters, and conducive for the growth of algae. An allochthonous origin is thus proposed for inertodetrinite and the associated detrital minerals, whereas alginite deposition was autochthonous. The cyclical upward-fining and upward-coarsening facies of the MKB were observed in the core, indicative of fluvial and deltaic palaeoenvironments, respectively. The fluvial facies were generally associated with the occurrence of structured vitrinite and inertinite macerals, suggesting in-situ formation, and mostly occur at the base of the coal seams. In contrast, the inertodetrinite-rich samples appear to be related to the overlying deltaic deposits. • An Ermelo core intersecting the A and B Seams is described. • Inertinite is common in the coals, though vitrinite is higher at the base of the seams. • In some B Seam samples, alginite occurs with inertodetrinite reflecting autochthonous and allochthonous deposition. • Structured macerals are associated with fluvial facies and inertodetrinite with deltaic facies. [ABSTRACT FROM AUTHOR]

The response of inertinite-rich Witbank coals (South Africa) to rapid heating was evaluated using petrography, selected Nuclear Magnetic Resonance (NMR) and X-Ray Diffraction (XRD) structural parameters. A total of thirteen (13) coal samples were collected from the No. 2 Seam; a set of six (6) samples from the western and the eastern sides of a ~ 0.4 m thick dolerite dyke emplaced into the coal seam at 0.25 m intervals. An unaltered coal (Un-C; the 13th sample), collected away from the dyke but within the same seam at the mine, was included for comparison. All 13 coal samples were dominated by inertinite. Semifusinite was most abundant in the samples from the western side of the dyke, whereas the proportion of inertodetrinite was highest in samples from the eastern side. Due to very low vitrinite contents, mean random total reflectance (%RoTmr) was used to compare the maturity of the inertinite-rich coals. A decrease in volatile matter was correlated with an increase in mean random total reflectance (%RoTmr; measured on semifusinite, inertodetrinite, and vitrinite), the latter used as a potential maturity indicator for the thermally altered inertinite-rich coals. Mean random total reflectance rose from a background value of 1.52%RoTmr (for Un-C) to 2.83%RoTmr for the coal sample at the western coal-dyke contact (0.0 m). The corresponding reflectance values for the thermally altered coals from the eastern side were less consistent, decreasing closest to the dyke (1.93%RoTmr for the sample at 0.0 m); this trend is also reflected in the NMR and XRD parameters. Eight (8) samples were selected for the NMR analysis, representative of the maceral composition and maturities of the coals investigated. For Un-C, the fraction of aromatic carbons (fa) was 0.88 (average number of carbons per aromatic cluster (C) = 17), and the interplanar spacing (d002) was 3.48 Å (with a crystallite height of 22.09 Å). For the thermally altered coals from the western side, fa decreased from 0.96 at the coal-dyke contact (C = 26 for sample at 0.0 m) to 0.92 for the sample at 1.25 m from the dyke (C = 20). For samples from the eastern side, fa increased from 0.91 (C = 19 for the sample at 0.25 m) to 0.93 (C = 23 for sample at 0.5 m), before decreasing to 0.89 further from the dyke (C = 18 for sample at 1.25 m). In general, the d002 values for the thermally altered coal samples were larger than for graphite. Similarly, only marginal increases in crystallite heights were observed. Although the dyke induced coal maturation and the resultant increase in fa , the overall lack of graphitic order in the thermally altered coals was ascribed to the limited thermal energy provided by the relatively thin dyke; increased heat input would be required to effect significant structural changes in the inertinite-rich coals. Differences between the two sets of thermally altered coal samples were attributed to the emplacement dynamics of the igneous intrusion, which require further investigation. [ABSTRACT FROM AUTHOR]

• Nine articles are reviewed for the VSI of the 38th Annual Conference of The Society for Organic Petrology [ABSTRACT FROM AUTHOR]

The increased global demand for rare earth elements (REEs) from unconventional sources has led to increased interest and research in coal deposits. South Africa has extensive coal resources, but understanding of the concentration, mode of occurrence, and distribution of REEs in the coals and associated sediments is limited. This study aims to assess selected coal samples obtained from an exploration project underway in the Waterberg Coalfield (South Africa) to determine the concentration and mode of occurrence of REEs, and to gain insight into the behaviour of REEs during density fractionation. Density fractionation of coal is considered a pre-concentration method prior to REE extraction. Samples were selected from zones 8, 7, 4, and 3, spanning the Grootegeluk and Vryheid Formations of the Waterberg Coalfield. Density fractionation was conducted at relative densities (RD) of 1.3 to 1.8, providing float (F) and sink (S) products. Five parent and thirty density-fractionated coal samples were characterized using proximate analysis, petrography, X-ray diffraction (XRD), and the concentration of REEs determined using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS) (after microwave digestion). The samples are classified as medium-rank C bituminous coals with variable maceral composition. The dominant minerals are kaolinite and quartz, occurring as both syngenetic and epigenetic phases. The total REY (REEs + yttrium) concentrations range from 45.1 to 389.2 ppm, higher than for world coals (except sample 8H F1.30, REY = 45.1 ppm), and generally higher than the average for Chinese coals. Float products obtained at 1.40 to 1.80 RD show greater variation of light REY (LREY) compared to medium REY (MREY) and heavy REY (HREY), whereas float fractions at 1.30 and sink fractions at 1.80 RD show no distinct enrichment patterns. Although the results suggest a relationship between the concentration of LREY with float fractions obtained between 1.40 and 1.80 RD, pre-concentration using density fractionation generally shows limited benefits for these coals. Ashing of the coals may be more effective in concentrating the REEs and further investigations are therefore required. • The REY concentrations range from 45.1 to 389.2 ppm, comparable to or higher than that of world coal average values. • Density fractionated 1.4–1.8 float products show a greater variation of light REY (LREY) compared to medium REY (MREY) and heavy REY (HREY). • Pre-concentration by density fractionation may not be the best REY concentration process for these Waterberg coal samples. [ABSTRACT FROM AUTHOR]