## 5 Conclusions  
XRF was selected as a fast and routine tool for analyzing 105 coal ash samples from Jurassic and Carboniferous coals sourced from five mines in Kazakhstan: Lenin, Saradyr, Bogatyr, Maikuben, and Shubarkol. A total of 20 elements were identified in the coal samples, including 9 major elements (Al, Si, P, S, Fe, K, Ca, and Ti) and 11 trace elements (As, Cu, Cr, Zn, Pb, V, Ga, Mn, Ni, Y, Yb, and Zr). Dendrogram analysis shows strong inorganic affinities, with Al and Si linked to aluminosilicates such as quartz and kaolinite, while Fe, Pb, Cu, Zn, and Mn are associated with sulfide minerals. Elements like Ti, Ga, Cu, Yb, V, Zr, and Y are found in accessory minerals, including rutile, zircon, and apatite, contributing to the mineralogical complexity alongside kaolinite. P and As may interact with organic matter. Quartz and kaolinite are the dominant minerals, with minor pyrite present in both euhedral and framboidal forms, accompanied by accessory minerals such as chalcopyrite, rutile, and REE-bearing apatite, as observed through SEM-BSE with EDS analysis. Technological impacts arise from the significant variations in silicon and sulfur content in the coal samples from the five mines, affecting combustion and suitability for industrial use. High Si levels, particularly in Carboniferous coals, may cause abrasion and ash-related issues, though kaolinite could help mitigate these effects. The low S content improves the coals' suitability by reducing emissions. Variations in ash yield and volatile matter highlight the need for customized combustion technologies to optimize performance, minimize slagging, and improve efficiency for both Carboniferous and Jurassic coals. The concentration coefficient (CC) analysis shows that most major elements, including P and Ti, fall within normal concentrations in both Jurassic and Carboniferous coal ash samples. Mn is depleted in Jurassic samples but normal in Carboniferous ones. Trace elements like Yb are slightly enriched, while Cu, As, and Y show normal levels. Elements such as Cr, Pb, and Zn are depleted in both coal types, highlighting differences in elemental distribution with potential environmental and industrial implications. Moreover, EDS anal  
Figure 8: Comparative environmental impact assessment of selected potentially toxic elements in three coal mines against standard harmful thresholds (referred to as impact value) (impact value for comparison as per [62; 63; 64]). ysis revealed additional rare-earth elements (La, Ce, and Nd), as identified in unchanged coal matrices using SEM-EDS, while Yb was detected in coal ash samples via XRF. The comparison of trace element concentrations in coal ash samples from the five mines against harmful environmental thresholds suggests minimal environmental impact. Potentially toxic elements such as As, Pb, Cu, Zn, and Cr, including the highest levels of Mn, are found in concentrations significantly below harmful thresholds, often ten times lower. These findings indicate that the coal ash from the studied samples poses a low risk of environmental contamination. XRF analysis may prove to be highly effective for large-scale studies involving multiple coal samples, as demonstrated by the successful analysis of 105 samples in 1.5 days using automated overnight measurements. This efficiency greatly exceeds that of traditional digestion-derived techniques, which require longer processing times. Additionally, the XRF results highlight the potential for further detailed investigations, particularly focused on trace elements, including REE. Methodology, M.J.; Investigation, M.J.; Resources, M.J.; Writing--original draft, M.J.; Writing--review & editing, M.J.; Visualization, M.J. and S.M. ; Funding acquisition, S.M. All authors have read and agreed to the published version of the manuscript. This study was supported by Sathayev University (Almaty, Kazakhstan), project no. AP14871618 \"Major boundaries of the Lower Carboniferous in the sections of Central Kazakhstan: development of a zonal standard\". Not applicable.