Characterization of superhigh-organic-sulfur Raša coal, Istria, Croatia, and its environmental implication

Towards Consistent Interpretations of Coal Geochemistry Data on Whole-Coal versus Ash Bases through Machine Learning

“…For example, based on selective leaching, Wang et al [39] found that F is elevated in the similar coals in the Haerwusu coals in the Jungar coalfield, which is closely located to the south of the Daqingshan coalfield, and occurs mainly in boehmite and kaolinite. High gallium concentration is these coals is also associated with these two minerals [30][31][32][33][34][35][36][37][38][39][40][41][42]. However, other associations such as Sc-Tl and F-Tl need further investigation.…”

“…In either case of basis, it would be expected that the REY should generally be clustered together if a method is effective. On the basis of trace-elements' geochemical nature and on the investigations by Zhao et al [15] and Dai et al [13] using directed analysis (such as SEM-EDS, XRD), the geochemical nature of the two elements in each pair of the following elements, i.e., Sr versus Ba, Sn versus Hg, Cd versus Zn, and As with other elements, concentrations of rare earth elements and yttrium (REY) could be reported either on ash basis or on whole-coal basis [31][32][33][34][35][36], and the ash basis is particularly suitable for REY potential recovery evaluation in coal combustion products [8,9]. In either case of basis, it would be expected that the REY should generally be clustered together if a method is effective.…”

“…All the hierarchy clustering results from different transformation methods are shown in Figures 1 and 2. As with other elements, concentrations of rare earth elements and yttrium (REY) could be reported either on ash basis or on whole-coal basis [31][32][33][34][35][36], and the ash basis is particularly suitable for REY potential recovery evaluation in coal combustion products [8,9]. In either case of basis, it would be expected that the REY should generally be clustered together if a method is effective.…”

“…The correlation between different element concentrations based on our proposed improved alr is the same, regardless of ash or whole-coal bases. Elemental concentrations based either on ash basis or on whole-coal basis have been reported by a number of authors [31][32][33][34][35][36], and either reported basis is correct, because the concentrations of elements in coal ash can be converted back to the whole-coal basis by using the equation [E i ] coal = ([E i ] ash × ash%). The transformed data with improved alr on whole-coal and ash bases can be described as ialr(X) wc = ialr(X) ash .…”

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“…SHOS coals show extreme enrichment in organic sulfur, but the pyritic S is variable; Croatian Raša coal, and Chinese Yanshan and Guiding coals (see Figure 1c) have low pyritic sulfur content (up to 1.1%), the lowest values (up to 0.3%) reported for Raša coal. Moreover, Raša coal is enriched with selenium, uranium, vanadium, and molybdenum (Medunić et al, 2018a(Medunić et al, , 2020. Similarly, U-Se-Mo-Re-V assemblage was found in Chinese SHOS Guiding coals (Dai et al, 2015), and Yishan coals (Dai et al, 2017), while increased S, F, V, Cr, Ni, Mo, and U were found in Yanshan SHOS coal .…”