Distribution and Mobility Potential of Trace Elements in the Main Seam of the Most Coal Basin
Graphical abstract
Introduction
The study of trace elements in coal provides not only useful data related to the sedimentological environment, but also reveals information required to minimise the environmental impact during the use of coal. Inorganic components in the coal can originate from several sources: 1) original organic matter, 2) formation during the stages of coalification, 3) carrying away by water or wind, 5) products of alteration of primary minerals. Trace elements, as a part of the inorganic components of coals, have deserved much attention and many studies have been done on trace element content and their distribution on sub-bituminous and bituminous coals (Adedosu et al., 2007; Finkelman, 1995; Lewinska-Preis et al., 2009; Ren et al., 1999; Suárez-Ruíz et al., 2006; Swaine, 1990; Zhuang et al., 2012, among many others). On the contrary, such conventional studies are scarce for low-rank coals (Gentzis et al., 1996). The modes of occurrence of trace elements vary greatly among coals. In low-rank coals, elements are usually organically bound, but with the progress of coalification, the elements are removed by expulsion of moisture and by changes in the chemical structure of the organic matter (Ward, 2002; Li et al., 2007; Finkelman et al., 2018). Elements bound with discrete minerals remain unchanged (Ward, 2002). The fate of trace elements during coal conversion processes has become a matter of concern due to the large amount of coal that is often used for energy production. The behaviour of trace elements during coal combustion depends on their concentration, mode of occurrence, and combustion parameters. The organically associated trace elements tend to be vaporised, either escaping into the atmosphere or adsorbed on the fine fly ash particles upon combustion in the furnace. The inorganically associated elements are generally non-volatile and tend to retain in the bottom ash and/or the fly ash particles upon combustion. On the other hand, the presence of trace elements in coal may help in understanding phenomena such as the geological history of coal-bearing sequences in sedimentary basins, the conditions ongoing due to coal seam formation, the depositional environment, and the influence of tectonics (Dai et al., 2012).
The mobility potential has been successfully evaluated in coal by the modified Sequential Extraction Procedure (SEP) (Cabon et al., 2007). The general principle of the method is to gradually leach the elements with a decreasing pH agent. The mobility potential of any trace element increases in the following order: oxidisable, reducible and acid and allows to predict its behaviour in environment under given conditions.
The Most Basin (Late Eocene-Early Miocene) represents an economically significant coal basin for the Czech Republic with only surface mining (Rajchl et al., 2009). The basin belongs to the group of Podkrušnohorská basins (Fig. 1), being a subject of detailed palaeo-environmental and geochemical studies for its unique sedimentary sequence (Havelcová et al., 2012, Havelcová et al., 2013, Havelcová et al., 2015; Mach et al., 2013; Matys Grygar and Mach, 2013; Rajchl et al., 2008; Teodoridis et al., 2011; Teodoridis and Sakala, 2008). The basin formation started during the late Eocene and Oligocene by the intensive volcanic activity. The sedimentation followed by the clastic and organic deposits from the end of the Oligocene to the early Miocene (Mach et al., 2014). During the late Eocene-Oligocene, an intense alkaline volcanism mainly of basaltic character brought the pyroclastic materials and lava thick-bodies into the sedimentary basin, establishing the volcanic Střezov Formation. The following Most Formation is a unique coal-bearing strata (Fig. 2) subdivided to the Duchcov, Holešice, Libkovice and Lom members. The lowermost Duchcov Member contains alluvial sediments, followed by the Holešice Member. The last-mentioned member represents the Main Seam gradually passing to the Libkovice Member. The fine-grained lacustrine clays and lacustrine clay sediments form the uppermost Lom Member (Pešek and Sivek, 2016).
According to the geochemistry and mineralogy, two main complexes were distinguished in the Most Basin. The Lower Bench, including Duchcov Member and lower part of the Holešice Member, contained a higher content of Al, Ti, Nb, Zr, Cr. While the high content of Si, Mg, K, Rb and Cs was typical for the Upper Bench, forming the upper part of the Holešice Member (Elznic et al., 1998). This division was further supported by Mach et al. (2014) with using the significant correlation proxies, e.g. Al, K, Ti.
Taking into account these previous findings, the present work evaluates the mobility potential and the final distribution of V, Cr, Ni, Cu, Zn, Pb, Se, As, Mn in the Lower Bench (Holešice Member) of the Main Seam in the Most Coal Basin.
Section snippets
Samples and methods
Fifty-one samples were collected from the Bílina Mine in the Most Basin. The evaluated set represents a continuous vertical profile of the Holešice Member in the Lower Bench (Fig. 2). The proximate (moisture content Wa, volatile matter content Vd and ash yield content Ad) and ultimate analyses (CHNS), together with the calorific value Qsd, were conducted in all samples according to ISO 17246, 17247 and ISO 1928. The element migration potential in environment was evaluated based on the
Ultimate and proximate analyses
The ultimate and proximate analyses illustrated the variability of a vertical profile (Table 1, Fig. 3). The ash yield (Ad) significantly fluctuated with depth, ranging from 17.4 to 87.7 wt% throughout and reflected the varying amount of the detritus at the time of the deposition. The samples with the ash yield content higher than 50% were according to the ISO 11760 (2005) classified as coaly claystones. The study set of coaly claystones showed the variable Vd content, varying from 11.6 to
Mode of occurrence of trace elements
The results of the PCA revealed that 62.85% of the dispersed variable could be assigned to two factors (Fig. 5). The high positive loadings for Ti (0.84), Cd (0.80), V (0.91), Cr (0.90), Ni (0.85), Cu (0.71) and Pb (0.88) displayed a high positive Factor 1. The elements were probably organically associated and/or originated from Ti-bearing minerals.
In contrast, a high positive loading for As (0.79) and Sd (0.52) have been found in the Factor 2. Therefore, the origin of As from sulphide minerals
Conclusions
Our results have provided a detailed distribution of trace elements within the Lower Bench of the Holešice Member (Most Formation). The dominant maceral group is huminite with mean random reflectance Rr = 0.32%. The mean of huminite reflectance does not show a significant trend throughout the profile of the Lower Bench. The study samples are classified as lignites and coaly claystones.
Ash yield (Ad), a general parameter of coal, cannot be used to estimate trace element content in the study
Acknowledgements
We would like to thank Erasmus+ HE-2015 for supporting the research at the National Institution of Coal in Oviedo. Our thanks also go to the Operational Program Prague – Competitiveness, more specifically, the Centre for Texture Analysis project (project ID: CZ.2.16/3.1.00/21538) and the long-term conceptual development of the research organization RVO: 67985891. This work was financially supported by the RECETOX Research Infrastructure (LM2015051 and CZ.02.1.01/0.0/0.0/16_013/0001761). It is
References (40)
- et al.
Quality parameters of lignite of the north Bohemian Basin in the Czech Republic in comparison with the world average lignite
Int. J. Coal Geol.
(1999) - et al.
Study of trace metal leaching from coals into seawater
Chemosphere
(2007) - et al.
Reconstructing chemical weathering, physical erosion nad monsoon intensity since 25 MA in the northern South China Sea: a review of competing proxies
Earth Sci. Rev.
(2014) - et al.
Geochemistry of trace elements in Chinese coal: a review of abundances, genetic types, impact of human health, and industrial utilization
Int. J. Coal Geol.
(2012) - et al.
Quantification of the modes of occurrence of 42 elements in coal
Int. J. Coal Geol.
(2018) - et al.
Petrology, mineralogy and geochemistry of lignites from Crete, Greece
Int. J. Coal Geol.
(1996) - et al.
Identification of organic matter in lignite samples from basins in the Czech Republic: geochemical and petrographic properties in relation to lithotype
Fuel
(2012) - et al.
“Stump Horizon” in the Bílina Mine (Most Basin, Czech Republic) — GC–MS, optical and electron microscopy in identification of wood biological origin
Int. J. Coal Geol.
(2013) - et al.
Petrology and organic geochemistry of the lower Miocene lacustrine sediments (the NBBCB, Eger Graben, Czech Republic)
Int. J. Coal Geol.
(2015) - et al.
Geochemical signature and related climatic-oceanographic processes for early Albian black shales: site 417D, North Atlantic Ocean
Cretac. Res.
(2001)
Geochemical distribution of trace elements in Kaffioyra and Longyearbyen coals, Spitsbergen, Norway
Int. J. Coal Geol.
Occurrence of non-mineral inorganic elements in low-rank coal macerals as shown by electron microprobe element mapping techniques
Int. J. Coal Geol.
Effect of relative lake-level changes in mire–lake system on the petrographic and floristic compositions of a coal seam, in the NBBCB (Miocene), Czech Republic
Int. J. Coal Geol.
Classification of liptinite – ICCP system 1994
Int. J. Coal Geol.
Distribution of minor and trace elements in Chinese coals
Int. J. Coal Geol.
Arsenic in iron disulfides in a brown coal from the North Bohemian Basin, Czech Republic
Int. J. Coal Geol.
Concentration and association of minor and trace elements in Mukah coal from Sarawak, Malaysia, with emphasis on the potentially hazardous trace elements
Int. J. Coal Geol.
Geochemistry, mineralogy and technological properties of coals from Rio Maior (Portugal) and Penarroya (Spain) basins
Int. J. Coal Geol.
Classification of huminite–ICCP system 1994
Int. J. Coal Geol.
Regininy CLAMP — instigations towards improving the climate leaf analysis multivariate program
Palaeogeogr. Palaeoclimatol. Palaeoecol.
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