## 3 Results
### EDXRF Results  
Tables 1 and 2 present the concentrations of both major and trace elements in coal ash samples from the five coal mines. Mean values for all samples were calculated and are provided in Table 3 for comparison. The chemical compositions are compared with the compositions of the Clarke value of the crust (CVC) [35; 36; 37; 38] and worldwide hard coal combustion (WHC) [38].  
& +++ & +++ & +++ & +++ \\ \hline Kaolinite & ++ & ++ & ++ & ++ & ++ \\ \hline Pyrite & + & + & + & + & + \\ \hline Chalcopyrite & & & a & a & \\ \hline Rutile & & & a & & a \\ \hline Apatite & a & & & & a \\ \hline \hline \end{tabular}
\end{table}
Table 4: Mineral contents in the five selected coal samples from the five coal mines measured by low-temperature ashing X-ray diffraction (LTA-XRD) and SEM (+++—dominant phase >20 wt%; +++— abundant phase 20–5 wt%; +— minor phase <5 wt%; and a—accessory mineral detected by SEM-EDS).  
Yb's link to rare earth elements emphasizes its presence in accessory minerals like apatite, with a distinct inorganic affinity that underscores its role in trace mineral phases. Zn and Mn are associated with sulfide and oxide minerals, reflecting their roles in less abundant mineral assemblages while maintaining strong inorganic affinities. Many authors emphasize that apatite, a common accessory mineral, is particularly important for hosting REE, especially Yb [47; 48]. Mn in coal primarily occurs in carbonates and silicates [2], while Zn is mainly found as an accessory sulfide mineral [2]. Zn is associated with various mineral phases, including silicate-bound, sulfide-bound, and carbonate-bound fractions [49].  
P is primarily found in phosphate minerals, and its occurrence in sediments highlights its importance in biogeochemical processes. Although it primarily shows an inorganic affinity, it may interact with organic matter in specific environments. [PERSON] et al. (1996) [50] mentioned that P in coal occurs primarily as crystalline mineral particles, mainly apatite and aluminophosphates.  
Ca is commonly found in carbonate minerals, phosphate, and silicates, emphasizing its widespread occurrence in geological settings and its strong inorganic affinity. As noted by [PERSON] et al. (2013) [51], calcium (Ca) in coals is commonly found in carbonate, phosphate, and silicate minerals.  
Figure 6: Dendrogram developed from cluster analysis on the elemental data of the complex Jurassic and Carboniferous coals from five coal mines.  
The grouping of As, Cr, and Ni indicates their associations with sulfide and oxide minerals, reflecting a shared inorganic affinity. While As primarily exhibits inorganic behavior, it may show organic affinity in reducing environments. The organic affinity of As, Cr, and Ni in coal varies by element and coal type, with studies suggesting moderate to strong organic associations for Cr and Ni, while As exhibits variable affinities, ranging from strong organic bonds [52; 53] to inorganic associations [54], influenced by factors such as element abundance, properties, and coal-forming processes [53].  
The analysis indicates that the elements in the dendrogram are predominantly associated with inorganic mineral phases, specifically silicates, oxides, sulfides, and phosphates. Although some elements may exhibit organic affinity under specific conditions, their primary associations are within inorganic mineral frameworks. The use of SEM-EDS further supports these findings, confirming the presence of various minerals, including aluminosilicates (clay minerals), oxides (e.g., quartz and rutile), sulfides (e.g., pyrite and chalcopyrite), and phosphates (e.g., apatite).