Use of geochemical analysis and vitrinite reflectance to assess different self-heating processes in coal-waste dumps (Upper Silesia, Poland)

Fuel 181 (2016) 102–119

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Full Length Article

Use of geochemical analysis and vitrinite reflectance to assess different self-heating processes in coal-waste dumps (Upper Silesia, Poland) Ádám Nádudvari ⇑, Monika J. Fabian´ska Faculty of Earth Sciences, University of Silesia, Sosnowiec 41-200, Poland

h i g h l i g h t s
Self-heated coal waste analysed by petrographic and geochemical methods.
self-heating and leaching influence on coal waste features found.
applicability of Rock Eval in self-heated coal waste characterization assessed.
abundant phenols and PAHs expelled, hazardous to the environment.

a r t i c l e

i n f o

Article history: Received 17 January 2016 Received in revised form 22 April 2016 Accepted 26 April 2016 Available online 4 May 2016 Keywords: Coal waste Self-heating Pyrolytical conditions Biomarkers Aromatic hydrocarbons GC/MS

a b s t r a c t Coal-waste dumps are sources of a variety of pollutants, especially when coal-waste material undergoes self-heating. For this research, representative samples were taken from four dumps (Wełnowiec, Czerwionka-Leszczyny, Rymer and Anna) in the Rybnik region. The set of samples collected were divided into three subsets, namely, (1) expelled bitumen precipitated on coal waste, (2) thermally-affected coal waste and (3) highly-thermally affected coal waste from active- and inactive sites. To assess the characteristic features and impacts of self-heating, Rock Eval pyrolysis, measured random vitrinite reflectance (Rr %) and gas chromatography–mass spectrometry (GC–MS) of coal waste extracts were applied. Typical features of the bitumen expelled are elevated parameters of S1, PI, BI, and Py. Generally, the bitumen appeared at lower Tmax values. The self-heating in oxygen deficiency, i.e. under pyrolytic conditions caused thermal cracking of organic matter. Later the generated bitumen expelled from the self-heating zone, migrated and accumulated on colder coal-waste surfaces. This expelled bitumen, observed under fluorescence, shows irregular shapes and coats the organic particles with yellowish–greenish colours. Migrated bitumen is also found in highly-thermally affected, where Tmax values are extremely high due to the oxidation and maturation of organic matter (overmatured). R0 % values based on HI–Tmax comparison and the measured Rr % values generally well correlate in the burning coal waste and in highlythermally affected samples. The greatest quantities of phenols (mostly C1–C2) occur in the bituminous subset, samples in which 2–3 ring PAHs also dominate. In addition, high relative percentages of phenols (mostly C1–C2) characterize thermally-affected coal waste, together with heavier pyrolytical PAHs; these samples were closer to the heating zone. In totally burned-out porous waste, the presence of adsorbed short-chain n-alkanes and lighter PAHs, and higher CPI, Pr/n-C17 and Pr/Ph values, reflect migration from an active self-heating zone. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Coal-waste dumps are stores of enormous amounts of material from coal mining and coal production. These dumps are typical of the Upper-Silesian landscape in southern Poland where intense coal exploitation has began in 19th century. At present, despite ⇑ Corresponding author. E-mail address: [email protected] (Á. Nádudvari). http://dx.doi.org/10.1016/j.fuel.2016.04.129 0016-2361/Ó 2016 Elsevier Ltd. All rights reserved.

some decline, caused by mid-90s crisis, Upper Silesia Coal Basin (USCB) remains the most important source of hard coal in Poland, used mainly for heating and energy purposes. The basin productive rocks of the Pennsylvanian age comprise four lithostratigraphic series: Paralic, Upper Silesian Sandstone, Mudstone, and Cracow Sandstone Series [1]. Their total thickness is 8.5 km. The mine typical operating system is longwall coal mining and generally, the excavated coal layer is 2.5 m thick, 250– 400 m long, and about 680 m deep [2,3]. Hard coals in the USCB

´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

vary in rank from subbituminous coals to anthracites, with coal rank increasing westwards of the basin. The coals are mostly of humic type, with rare lenses and lamina of sapropelic coals. The main maceral group is vitrinite; its contents can reach 80%. Vitrinite-maceral contents vary across the basin area, the lowest in the eastern and the highest in the western part. The content of inertinite macerals is usually <32%, rarely close to 55% [1,4]. Most of the organic matter was deposited in an estuarine/deltaic environment with normal- to low water levels. The coals are early matured with similar vitrinite reflectance and thermal maturity corresponding to early- and medium catagenesis [5]. All over the world coal-waste dumps in active mining areas contain appreciable amounts of coal from non-economic seams and other carbonaceous waste [6–8]. On these dumps, secondary processes such as self-heating, water-washing, and biodegradation typically occur [7,8]. The waste usually comprises 8–10 wt% organic matter, in some <30 wt%. It commonly occurs as laminae, lenses and interlayers, and also as dispersed organic matter in, e.g., mudstone and sandstone [7]. This work focuses on one secondary process, i.e. spontaneously occurring coal waste heating (self-heating), which can lead to significant environmental problems around coal-waste dumps [6–8]. During self-heating, high concentrations of toxic, acidic gases and chemical compounds (e.g., PAHs – polycyclic aromatic hydrocarbons) are released [8–10]. The processes of oxidation and self-combustion are responsible for changes in the physical- and chemical properties of coal and coal waste [6,11]. Susceptibility to self-heating is increased by climate-air temperature, wind, organic-matter rank, ash content, surface area exposed, particle size, moisture- and oxygen content, and the shape, layering and compaction of a dump [7,9,12]. Mineral composition (especially pyrite), volatile matter, organicmatter type, contact with water (wetting) and storage time are also important factors affecting self-heating development [12–17] as well as poor compaction of coal wastes which allows easier permeation of air and water, increasing the self-heating process [13]. As a result, thermally active zones within a dump interior develop where, the coal-waste mass may be subjected to heating causing the de-volatilization of coal and mineral matter, and significant emissions of VOCs, H2S, NH3, and a number of volatile elements [18]. One of signs of self-heating ongoing within a coal waste dump are hot spots seen at the dump surface, up to several meters across, located above thermally active zones within the dump. In such places temperature is elevated, vegetation is burned or absent, often plumes of water vapour are visible, and the coal-waste is saturated with bitumen and/or water [6,18,19]. A sulphurous and/or bituminous odour often accompanies self-heating, nuisance for residences nearby leading to environmental and health problems [6–8]. Temperatures of self-heating vary from place to place and change with time at any given site [19]. Such thermally active zones on dumps can be also detected by remote sensing technologies, using surface thermal mapping and snow covering maps (NDSI – Normalised Difference Snow Index). Spatially, the elevated surface temperatures are well correlating with areas where snow is lacking. The indicated anomalies are hot spots potentially related to strong self-heating. Hot spots appear, move and disappear, and increase or decrease in intensity according to the weather conditions [20]. In addition, there are alterations in the organic matter seen under a microscope, such as formation of devolatilisation vacuoles and dark reactions rims (with lower reflectance when oxidation is already severe), numerous fractures, particle relief increased, and reduced anisotropy [6,14]. Such changes have been also described in the case of discarded coals [21]. The aim of the research was to differentiate, using geochemistry, vitrinite reflectance and Rock Eval pyrolysis, between burned-out waste (clinker), moderately burned-out waste and waste with expelled bitumen. Material from different coal-waste

103

dumps (Wełnowiec, Czerwionka-Leszczyny, Rymer, and Anna) in the Katowice and Rybnik industrial regions (Upper Silesia) was analysed. 2. The study area After early 90s, most of the USCB coal (old) mines operating under urbanized areas, or with unfavourable mining and geological conditions were closed to reduce the operating costs of the mining industry [22,23]. However, their long-time operations resulted more than 220 dumps and landfills, and covering over 4000 ha [2,24]. The highest amounts of the dumps occur in the central and south-western part of the USCB, in the areas of the highest population concentration exposing inhabitants to substances emitted from them [24]. Until the late 1980s, under the previous regime, little was done to prevent dump self-heating and negative impact to the environment and health. 2.1. Wełnowiec dump The dump in Wełnowiec, the Katowice district, is surrounded by housing estates and a block of flats (Fig. 1). It is a former urban rubbish dump operating from 1991 to 1996. Approx. 1.6 mln tones of mining, municipal, building and other wastes were deposited there covering the area of 0.16 km2. In 1998 the area of the dump was remediated with a multi-barrier system. The reclamation project assumed several layers, one of them a 0.6 m thick layer of uncompacted coal mine waste (sandstone, shale, mudstone, where a coal content should not exceed 5%). In reality, much more coal wastes were used [25]. The initiation of thermal activity on the dump is unrecorded but it has been thermally active since 2007 at the slopes, where the thickness of the reclamation coal waste layer was exceeded many times that planned. At present, the dump has been undergoing self-heating and self-ignition and has been a source of pollution and unpleasant odours. Thermal activity has been observed mainly on the northern slope of the dump where the fire started at the eastern end and moved westwards [26]. After extinguishing the fire, only a few square meters on the western side is under heating now. Samples were taken from this part of the dump for analysis. 2.2. Czerwionka-Leszczyny dump Here mining companies deposited over 37 million tons of waste rock and tailings on the 140-hectare heap. The main part of the dump used by the closed De˛bien´sko and Czerwionka-Leszczyny mines comprises of two conical heaps, a huge flat heap and 4 tailings ponds [27]. This dump, mostly forested, consists of three cones, the highest of which is 100 m high (Fig. 1). These cones cover a relatively large area of ca. 97 ha with variable morphology. Intensive surface pseudo-fumarolic activity on the top of the highest steep cone is associated with surface gas vents surrounded by sulphate crusts and puddles of bitumen [28]. The scale of this thermal activity, extant for more than 30–40 years, is lessening today [20]. 2.3. Rymer dump The Rymer dump is closed at present (Fig. 1). The original waste material was essentially burnt out. From 1994–1999, the cones were redeveloped and spread out with additional coal-waste materials. During this redevelopment, two cones from three were dismantled and leaving only cone. At present the capacity of the dump is 2.4 million m3 and it covers an area of 0.13 km2. However, as the original burnt-out material was hot, burning restarted in this

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´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

Fig. 1. Sampling points on the coal waste dumps (background map – Google Earth 2014 and Landsat 4-5 TM).

added coal waste [29]. Around the turn of the 21st century, the surface of the dump was covered by concrete panels to block air access. Despite these, self-heating intensified. Finally, the panels were removed from the western part [30]. Today, heating occurs mostly on the eastern slope still covered by panels. Bitumen spillages through cracks in the panels provided most of the samples collected here.

2.4. Anna dump This dump stores wastes from the Ruch-Anna Coal Mine opened in 1954 (Fig. 1). There is only one cone covering an area of 0.43 km2. The oldest part is 0.20 km2 and 50 m above surface level. The planned capacity was >3  106 m3 [31]. Burnt-out material from here is used for road construction. However, exploitation

´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

of the waste allowed oxygen to enter the interior of the dump, resulting in intensive burning which has started in 2000 y. Toxic fumes and odorous gases reach distance higher than 3 km and are a problem in the nearby Pszów town. Recent intensive burning has obstructed current exploitation of the waste [30]. Landsat images reveal intensive fire on the western side of the dump around the year 2010 [20]. Burned-out samples were taken from this side of the dump where large amounts of melted rock and breccias also occur.

105

in the electron impact ionisation mode at 70 eV and scanned from 50–650 da. Data were acquired in a full scan mode and processed with the Hewlett Packard Chemstation software. The compounds were identified by using their mass spectra, comparison of peak retention times with those of standard compounds, interpretation of mass spectra and literature data [35]. The aim of GC–MS analysis was to define the geochemical characteristics of the coal waste extracts. All biomarker parameters were calculated using peak areas acquired in the manual integration mode. The analyses were carried out in the Faculty of Earth Sciences, University of Silesia.

3. Methodology 4. Results and discussion 3.1. Coal waste sampling and preparation 4.1. Coal waste division All 41 samples of 500–1000 g were taken from the dump surface to represents variability of coal waste material, with 14 samples from the Czerwionka-Leszczyny, 11 from the Anna, 11 from the Rymer Cones, and 5 from the Wełnowiec coal waste dump. In the study 34 samples were investigated and seven samples among the analysed coal waste material from the CzerwionkaLeszczyny dump was already published in [43]. To prevent organic matter contamination samples were stored in alumina foil during transport. Samples were manually cleaned from surface contamination and a dried at room temperature (ca 22 °C) for ca 5 days, crushed to fragments of 0.5–2 cm, uniformed and about 200 g was powdered in a rotary mill to 0.2 mm grain size.

For random reflectance measurements the samples were crushed to <1 mm, embedded in epoxy resin and polished blocks were prepared. Measurements were conducted at the University of Silesia on a Zeiss Axioplan2 microscope, at 100 points on thirty-seven samples according to ISO 7404-5 [32] and at 50 points on four samples because of presence of poor amount of organic particles.

The coal-waste sample set was divided into three subsets, namely, (1) coal waste samples composed of expelled bitumen precipitated on coal waste, in the following text called ‘‘bituminous” coal waste, (2) moderately thermally-affected coal waste, and (3) highly-thermally affected coal waste (from active- and inactive sites on the dumps). The criteria of samples division included: (1) physical features of coal wastes as colour, texture, smell, and bitumen stain, (2) extract yields, (3) Rock–Eval results (Table 1). The bituminous subset (1) was smelly, sticky with a blackish or greyish colour (Fig. 2) Samples in the second subset had been affected by initial and moderate stages of self-heating. They are black or dark gray, with relatively high content of organic matter still showing geochemical features of sedimentary organic matter. The third subset comprises highly-thermally affected coal waste with very low carbon content or with highly carbonized organic matter from sites where thermal activity was waning or totally extinguished. Their colour was black, reddish or whitish and they consisted mostly of solid powder or reddish–whitish larger pieces (Fig. 2). This dehydrated highly-fractured material (clinker) was very hard, with the variety of different colours reflecting oxidation and reduction [16,36].

3.3. Rock–Eval pyrolysis

4.2. Vitrinite-reflectance measurements

The analysis was performed on a Delsi Model VI Rock–Eval instrument equipped with a total organic-carbon module with a computer program to process results. Each sample was heated up to 300 °C for 3 min followed by a programmed pyrolysis at 25 °C/min up to 600 °C under a He flow. Each was then oxidized at 600 °C for 7 min under an oxygen flow. Each analytical cycle begun from IFP (Institut Français du Pétrole) 55000 applied as a standard. Total organic carbon (TOC), thermally released bitumen (S1), the pyrolysate (S2), carbon dioxide (S3) and temperature at maximum pyrolysate yield (Tmax – peak temperature of S2 peak) were measured. The Hydrogen Index (HI in mg/g TOC), the Oxygen Index (OI in mg/g TOC), (S1/TOC) ⁄ 100 – Bitumen Index (BI), S1 + S2 – Potential Yield (Py) and S1/(S1 + S2) – Production Index (PI) were calculated [33,34].

Vitrinite reflectance (Ro %) provides a good basis for evaluating organic maturity; both increase in tandem with Tmax values from Rock–Eval Pyrolysis [37–39]. Measured random vitrinite reflectances Rr % varying from 0.28 to 0.70–3.79 reveal a fairly diverse picture of unaltered- to strongly-altered by heat oxidized organic material. The highest reflectances of samples An 1 and An 3, and the lowest (0.28) Rr % in the bituminous Rc 4, probably reflect the expulsion of copious amounts of bitumen. Generally, there is little difference in Rr % between the bituminous (ave. 1.09) and the thermally-affected coal waste (ave. 1.15); the highlythermally affected coal waste (ave. 2.08) characterized by strongly-altered organic matter is exceptional. This is opposite to Rock–Eval results which well differentiated all samples subsets (see Section 4.3). In addition, the calculated vitrinite reflectance (Rc, see Table 1 footnote) does not agree with the measured random vitrinite reflectance (Rr %) (Table 1). Reflectances of unaltered organic matter in coal-waste dumps in Poland is 0.60–0.76% and increase in bituminous coals with increasing temperature [40– 42]. Vitrinite reflectance of unaltered coal waste in the region is 0.80–0.90 Rr % [43]. Representative reflectograms (Fig. 3) used to show the variously-altered organic material and the heating processes on the dumps; some reflectograms, e.g., We 5, Cz 10 and Cz 12, show bimodal distribution that clearly mirror temperature-related changes in the organic-matter with lower reflectance values likely characterizing organic particles from colder parts of a dump.

3.2. Vitrinite-reflectance measurement

3.4. Gas chromatograpy–mass spectrometry Powdered coal wastes were extracted in dichloromethane (DCM) in the Dionex 350 apparatus dedicated for accelerated solvent extraction. An Agilent gas chromatograph 7890A with a HP– 35 column (60 m  0.25 mm i.d.), coated by a 0.25 lm stationary phase film coupled with an Agilent Technology mass spectrometer 5975C XL MDS was applied. The experimental conditions were as follows: carrier gas – He; temperature – 50 °C (isothermal for 2 min); heating rate – up to 175 °C at 10 °C/min, to 225 °C at 6 °C/min and, finally, to 300 °C at 4 °C/min. The final temperature (300 °C) was held for 20 min. The mass spectrometer was operated

106

Table 1 The results of Rock Eval Pyrolysis and measured random vitrinite reflectances. S3

S30

S3CO

S30 CO

PI

PC (wt%)

RC (wt%)

HI

OICO

OI

pyroMINC (wt%)

oxiMINC (wt%)

MINC (wt%)

BI

Py

Rc %

Rr %

r for Rr%

0.54 3.90 3.10 4.80 14.40 0.16 10.00 1.75 2.90 1.39 14.80 15.60

3.30 2.40 2.10 2.20 2.50 3.70 4.00 2.10 3.40 6.40 1.77 0.90

18.00 8.90 9.40 8.10 13.30 32.80 8.90 9.20 7.40 15.60 7.90 4.50

1.35 0.76 1.04 1.02 2.11 2.04 1.33 1.23 1.54 3.01 1.40 1.05

2.00 1.40 2.90 1.60 3.50 1.80 1.50 1.90 1.80 3.50 2.50 2.30

0.94 0.89 0.86 0.80 0.74 1.00 0.16 0.92 0.84 0.95 0.48 0.57

0.93 2.96 2.02 2.19 4.79 4.06 1.19 1.90 1.64 2.66 2.55 3.15

5.60 6.80 15.90 9.40 14.60 8.40 3.90 2.50 5.30 9.70 14.60 12.70

8 40 17 42 75 1 197 40 42 11 87 99

21 8 6 9 11 16 26 28 22 24 8 7

51 24 12 19 13 30 79 47 50 52 10 6

0.53 0.27 0.32 0.26 0.44 0.93 0.27 0.29 0.24 0.50 0.27 0.17

0.06 0.04 0.01 0.92 0.73 0.31 0.12 0.01 0.11 0.02 0.19 0.02

0.59 0.31 0.33 1.18 1.17 1.24 0.39 0.30 0.35 0.52 0.46 0.20

128.31 311.34 108.38 171.55 208.25 368.00 37.45 438.64 211.59 212.20 81.87 132.28

8.88 34.10 22.50 24.70 54.80 46.16 11.91 21.05 17.50 27.49 28.80 36.50

0.96 0.85 0.81 0.62 – 0.58 1.28 – – – – 0.95

0.84 1.77 2.46 0.77 0.70 0.28 0.95 1.61 0.96 0.85 1.06 0.77

0.15 0.67 1.22 0.79 0.16 0.08 0.38 1.17 0.42 0.33 0.41 0.46

Averages

21.75

6.11

2.90

12.00

1.49

2.20

0.76

2.50

9.12

55

16

33

0.37

0.21

0.59

200.82

27.87

0.86

1.09

–

2. Thermally affected coal wastes An. 5 30.30 443 An. 6 29.50 434 An. 7 12.70 440 An. 8 16.60 435 An. 9 30.60 432 An. 10 25.50 433 An. 11 24.00 434 Cz. 4a 8.40 437 Cz 7a 2.70 417 a Cz. 8 11.10 436 a Cz. 9 5.90 434 a Cz. 11 8.00 436 Cz. 15 0.53 437

0.02 0.45 0.16 0.97 2.65 0.26 1.02 0.05 0.21 0.11 0.05 0.07 0.02

1.99 14.30 4.50 40.80 57.90 35.20 27.60 7.20 0.95 9.70 2.80 9.31 0.27

1.59 2.40 1.09 0.85 0.62 1.65 0.86 2.60 3.60 3.60 3.50 0.40 0.68

10.30 19.70 7.10 14.30 15.90 12.90 13.60 6.20 15.70 8.80 8.10 16.70 7.10

0.59 2.00 0.92 1.52 1.26 1.47 1.24 1.27 0.69 1.38 1.11 0.67 0.26

1.10 4.00 1.00 4.40 3.30 3.40 3.00 1.90 1.00 1.80 1.40 1.00 0.80

0.01 0.03 0.04 0.02 0.04 0.01 0.04 0.01 0.18 0.01 0.02 0.01 0.08

0.26 1.46 0.48 3.65 5.17 3.12 2.52 0.77 0.25 1.01 0.40 0.84 0.07

30.00 28.00 12.20 12.90 25.40 22.30 21.40 7.70 2.50 10.10 5.50 7.20 0.46

7 48 35 246 189 138 115 85 35 88 46 116 51

2 7 7 9 4 6 5 15 25 12 19 8 49

5 8 9 5 2 6 4 31 131 32 58 5 128

0.30 0.62 0.22 0.48 0.50 0.42 0.44 0.21 0.45 0.28 0.25 0.48 0.21

0.03 0.29 0.01 0.04 0.11 0.28 0.12 0.03 0.10 0.03 0.10 0.07 0.01

0.33 0.92 0.22 0.52 0.62 0.70 0.55 0.24 0.55 0.31 0.35 0.55 0.22

0.07 1.53 1.26 5.84 8.66 1.02 4.25 0.60 7.78 0.99 0.85 0.88 3.77

2.01 14.75 4.66 41.77 60.55 35.46 28.62 7.25 1.16 9.81 2.85 9.38 0.29

0.70 0.76 0.78 0.78 0.61 0.77 0.76 1.03 0.71 0.89 0.96 0.85 0.72

1.68 1.67 2.33 1.13 1.53 0.89 1.33 0.76 0.74 0.76 0.74 0.89

0.67 1.03 1.53 0.28 0.61 0.10 0.48 0.07 0.15 0.08 0.09 0.09

Cz. 16 Rc. 1 Rc. 11 We. 1 We. 2 We. 3 We. 4 We. 5

4.30 3.70 8.70 16.60 11.60 10.60 12.20 12.40

377 437 423 442 409 350 400 423

0.12 0.01 0.22 2.27 3.60 2.80 3.93 1.38

0.71 0.61 2.20 3.98 3.28 3.48 6.13 2.41

2.60 2.10 3.90 8.40 5.90 5.60 7.40 6.20

9.20 16.30 20.00 33.50 25.10 24.60 29.40 31.40

0.92 0.51 1.29 2.75 2.23 2.13 2.84 2.54

1.30 0.90 2.10 5.20 5.20 4.20 5.30 4.90

0.15 0.02 0.09 0.36 0.52 0.45 0.39 0.36

0.21 0.15 0.40 0.98 0.94 0.85 1.27 0.70

4.10 3.50 8.30 15.60 10.70 9.70 11.00 11.70

16 17 25 24 28 33 50 19

21 14 15 17 19 20 23 20

59 57 45 51 51 53 60 50

0.28 0.46 0.59 1.03 0.80 0.76 0.92 0.96

0.06 0.03 0.09 1.00 0.24 0.38 0.44 0.31

0.34 0.49 0.68 2.02 1.04 1.14 1.35 1.27

2.79 0.27 2.53 13.67 31.03 26.42 32.21 11.13

0.83 0.62 2.42 6.25 6.88 6.28 10.06 3.79

0.84 0.68 0.72 0.78 0.78 0.89 0.80 0.80

0.78 1.39 0.98 0.97 1.08 1.07 1.06 1.28 1.08

0.12 0.73 0.21 0.22 0.48 0.20 0.17 0.27 0.30

Averages

13.60

424

0.97

11.21

3.12

16.50

1.41

2.70

0.14

1.21

12.39

67

15

40

0.51

0.18

0.69

7.50

12.18

0.79

1.15

–

3. Highly thermally-affected coal wastes An. 1 13.40 598 – An. 2 3.60 491 – An. 3 21.90 602 – An. 4 0.15 603 –

– 0.50 1.63 0.08

0.92 1.69 1.26 0.55

3.10 10.10 14.40 3.30

0.22 0.42 0.65 –

0.80 0.70 2.20 –

1.00 – – 0.02

0.05 0.12 0.24 0.02

13.40 3.50 21.60 0.13

– 14 7 53

2 12 3 –

7 47 6 367

0.10 0.29 0.44 0.09

0.01 0.22 0.18 0.11

0.11 0.51 0.62 0.20

– – – –

– 0.50 1.63 0.08

– 0.68 – –

3.79 1.03 3.26

1.70 0.40 0.31

Cz. 10a Cz. 13

0.05 0.27

3.50 0.53

18.50 8.40

0.68 0.26

0.70 0.80

0.03 –

0.14 0.07

6.10 0.38

1 60

11 58

56 118

0.52 0.25

0.02 0.01

0.54 0.25

– –

0.05 0.27

0.70 0.67

2.56 1.45

1.04 0.60

1.05

0.24

TOC (wt%)

11.60

6.30 0.45

Tmax (oC)

363

595 604

S1

– –

´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

S2

1. Expelled bitumen precipitated on coal wastes Cz. 5a 6.50 315 8.34 Cz. 12 9.70 313 30.20 Cz. 14 17.90 318 19.40 Rc. 2 11.60 429 19.90 Rc. 3 19.40 426 40.40 Rc. 4 12.50 300 46.00 Rc. 5 5.10 424 1.91 Rc. 6 4.40 329 19.30 Rc. 7 6.90 326 14.60 Rc. 8 12.30 326 26.10 Rc. 9 17.10 426 14.00 Rc. 10 15.80 428 20.90

Sample code

Table 1 (continued)

r for Rr%

Sample code

TOC (wt%)

Tmax (oC)

S1

S2

S3

S30

S3CO

S30 CO

PI

PC (wt%)

RC (wt%)

HI

OICO

OI

pyroMINC (wt%)

oxiMINC (wt%)

MINC (wt%)

BI

Py

Rc %

Rr %

Cz. 17 Cz. 18

0.11 0.23

590 603

– –

0.47 0.66

0.14 0.07

4.40 4.10

0.10 0.15

0.50 0.40

– –

0.06 0.07

0.05 0.16

427 287

91 65

127 30

0.13 0.12

– 0.01

0.14 0.13

– –

0.47 0.66

0.89 0.91

1.16

1.02

2.31

1.35

Averages

5.77

586

–

0.52

1.08

8.30

0.35

0.90

0.35

0.10

5.67

121

35

95

0.24

0.08

0.31

–

0.46

0.77

2.08

–

´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

TOC (wt%): Total Organic Carbon [wt%]. Tmax (°C): temperature of maximal expulsion of pyrolytic hydrocarbons from kerogen. S1: Free hydrocarbons [mg HC/g rock]. S2: Hydrocarbons generated by pyrolytic degradation of kerogen [mg HC/g rock]. S3: CO2 generated by pyrolytic degradation of kerogen [mg CO2/g rock]. S30 : CO2 generated by pyrolytic degradation of mineral substances (carbonates) [mg CO2/g rock]. S3CO: Amount of CO resulting from destruction of organic matter [mg CO/g rock]. S30 CO: Amount of CO formed in the reaction of Boudouard [mg CO/g rock]. PI: Production Index; PI = S1/(S1 + S2). PC: pyrolyzable carbon (wt%). Corresponds to carbon content of hydrocarbons volatilized and pyrolyzed during analysis. RC (wt%): Residual carbon content. HI: Hydrogen Index [mg HC/g TOC]; HI = S2/TOC100. OICO: Ratio of CO [mg CO/g TOC]. OI: Oxygen Index [mg CO2/g TOC]; OI = S3/TOC100. pyroMINC: Pyrolytic carbon content of mineral (wt%). oxiMINC: Indicated oxidative carbon content of the mineral in the oven (wt%). MINC: Total carbon content of the mineral (wt%). BI: Bitumen Index; (S1/TOC) ⁄ 100. Py: Potential Yield; S1 + S2 (mg/g rock). Rc % = 0.6 ⁄ (MPI-1) + 0.4); calculated vitrinite reflectance. Rr %: measured vitrinite reflectance in immersion oil (underlined, bold values – measured only on 50 points). r for Rr %: Standard deviation for Rr (underlined, bold values – measured only on 50 points). ‘‘–” Concentration too low (or nil) to calculate a parameter value. a Data published in [43].

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Fig. 2. Representative self-heated forms and sampling points from the different dumps. (A–C) Sampling points on the highest, thermally active (smoke, steam) cone of Czerwionka-Leszczyny dump, showing burned out (reddish) and bituminous waste (blackish-sticky mixed with sulphur) – western part of Fig. 1. (D) (Eastern side of Czerwionka-Leszczyny dump on Fig. 1) sample was taken, where the self-heating is in the initial state (Cz. 11), however – (E) (Eastern side of Czerwionka-Leszczyny dump on Fig. 1) is an inactive site of the dump (Cz. 10). (F) Reddish (burned out) – blackish (coked – carbonized coal) layers on the Rymer dump. (G–J) Expelled bitumen leaking between the concrete panels on the Rymer dump (samples were taken from there). (K and L) Intensive self-heating occurring on the Wełnowiec dump after opening of the heating site. (M and N) Pictures also taken on the Wełnowiec dump; typical forms are sulphur crusts and sal-amoniac precipitation on carbonized and/or burned out wastes with elevated temperature.

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Fig. 3. Representative vitrinte reflectograms from bituminous-, burning- and burnt-out coal waste.

4.3. Results of Rock–Eval pyrolysis The parameters S1, Tmax, PI and BI were found to be suitable for characterizing the thermally-affected coal-waste material. The bituminous samples characterized by elevated average values of S1 (21.75), PI (0.76), BI (200.82), Py (27.87) and lower Tmax (363) – see Table 1. Any expulsion of bitumen caused a total change in Tmax values, undermining the validity of this parameter as a maturity indicator for these waste materials. The low Tmax values (<380 °C) may reflect significant amounts of a soluble component such as bitumen rather than kerogen and indicate a lowtemperature pyrolysate [44,45]. Tmax is defined as the pyrolysis temperature at which the maximum amount of hydrocarbon is released by kerogen [33]. Generally, increased values of the Bitumen Index (BI) are used to distinguish the oil generation zone from the immature zone [46]. With increasing thermal maturity, bound biomarker moieties are released as free biomarkers from the polar fraction as the bitumen decomposes to yield free hydrocarbons [47]. Bitumen is a geological equivalent of lipids, consisting in the widest sense of any sedimentary hydrocarbon ranging in state from tarry asphalt to liquid petroleum [48]. The results show that the thermally-affected samples (subset 2) are mostly matured samples where heating had no impact. The

values of Tmax (ave. 424 °C), S1 (0.97) and PI (0.14) in Table 1 correlate with values of the same parameters obtained for carbonaceous shales, claystones, mudstones and coal seams in Upper Silesian coal mines in the Rybnik region [49]. Furthermore, the results for this subset also compare with those from coal-waste material and coaly material from river sediments [43,50]. For kerogen III, Tmax at 434 °C marks the boundary between immature- and mature kerogen; at the oil-generation stage, kerogen generally has Tmax values of 435–450 °C [34,51–53]. The Tmax values for the highly-thermally affected coal waste are extremely high (491–603 °C) and free hydrocarbons (S1) are lacking (Table 1). Very high Tmax values (<600 °C) probably reflect oxidation of organic matter in outcrops and/or, in part, a mineral matrix effect [54]. Furthermore, Tmax at 465 °C is the boundary between mature- and over-mature kerogen (gas-production zone) [34,51–53]. As a general rule, Tmax increases linearly with the degree of maturation degree of organic matter [55,33]. With increasing maturity, the remaining kerogen became more and more resistant to pyrolysis [56]. Because of the intensive heating, the organic material is mostly destroyed and, thus, several parameters, e.g., S1, S2, S3CO, S30 CO, PC, BI and Py are decreased in comparison to the other subsets (Table 1). However, bitumen may migrate from the hot spot to the highly-thermally affected coal

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wastes, which can have a high adsorptive potential for pyrolisates. Thus it may also show elevated values of, e.g., TOC or PI. For example, values of PI (1.00) and TOC (13.4) in sample An 1 are as high as in bituminous samples. The An 1 and An 3 samples comprise totally black, soft material under a reddish burned-out layer. They contain an abundance of coked particles, white under a microscope and deformed due to extreme temperatures. Various discriminating diagrams, e.g., HI–Tmax, S1–TOC, HI–OI, S2–TOC, and Tmax–PI, enable further analysis and comparison of the differently-heated coal wastes (Fig. 4). Based on the HI–Tmax diagram, most of waste from which bitumen was expelled have low values of HI and Tmax and plot on the left side of the diagram, and highly-thermally affected (overmatured) waste on the right. The measured random vitrinite-reflectance (Rr %) values do not correlate with the values suggested by the diagram (Table 1). However, these Rr % values do correlate well with R0 % in case of subsets 2 and 3. According to [34], there is a linear correlation between Tmax and vitrinite reflectance between 0.5 R0 % (Tmax  425 °C) and 1.5 R0 % (Tmax  475 °C), but more scattering is evident at lower maturities. The Wełnowiec samples are probably close to the bitumen generation zone according to the Tmax–PI diagram. It is also possible that slightly elevated PI and lower Tmax values are caused by migrated bitumen or by the different type of organic material dumped there.

On the S1–TOC diagram (Fig. 4), most of the bituminous samples plot on the edge of the epigenetic- and syngenetic-hydrocarbon fields, possibly due to thermal cracking of organic matter. This bitumen expelled from self-heating zones migrated and accumulated on colder coal-waste surfaces. The thermally-affected (2) and highly-thermally affected coal waste (3) shows lower amounts of expelled hydrocarbons (S1); these light hydrocarbons probably devolatilized with increasing temperature. Thermal decomposition of solid oxygenated complexes plays an important role in organicmatter oxidation [57]; the formation of gaseous products and the regeneration of active sites for oxygen adsorption contribute to self-heating [17,58]. The Tmax–PI diagram (Fig. 4) generally serves to show the maturation and nature of the hydrocarbon products [46,59]. The Production Index which should be at low levels (e.g., 0.05) in the immature section starts to increase as the kerogen enters the oil window [46]. Here, the diagram is used to see what happens with the different types of coal waste under pyrolytic conditions. It well reflects thermal cracking in organic material in the case of bituminous samples whereas thermally-affected and highly-thermally affected samples plot in the immature zone. The Py–TOC diagram (Fig. 5) illustrates a general correlation of increasing Py values with increasing TOC. Py is an important parameter in assessing if rocks at depth are mature enough to

Fig. 4. Comparisons of S1–TOC, HI–OI, HI–Tmax, S2–TOC and Tmax–PI values of Rock Eval Pyrolysis.

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Fig. 5. Comparisons of Py–TOC values of Rock Eval Pyrolysis in the different types of self-heated coal waste.

generate hydrocarbons, and their source potential in terms of yield of oil and/or gas [59]. Here, the diagram broadly differentiates between the various self-heated samples on the basis of their contained hydrocarbons, and informs about different thermal processes in the dumps. Most of highly-thermally affected samples are characterized by low Py (<1.0). The Rr %–Tmax diagram (Fig. 6) also clearly discriminates between the three subsets; self-heating changed the reflectances and promoted the expulsion of pyrolytic hydrocarbons from kerogen III. Thus, the HI–Tmax, S1–TOC, and Tmax–PI diagrams clearly identify coal waste differently affected by heating. In contrast, the HI–OI and S2–TOC diagrams indicate only kerogen type (III) and shows that self-heating has not influenced significantly by the original type of organic matter. 4.4. Self-heated forms The various self-heated forms are illustrated in Fig. 7. Palercoloured particles with irregular cracks as shown by We 1 (A) and An 9 (C) are typical of moderately-altered organic material that underwent slow heating [60]. Similar cracks are also present in strongly-heated vitrinite particles in anisotropic layers, e.g., An 3 (F). Oxidation rims around the edges of particles, pores and cracks

were well seen in We 1 (A), We 2 (D, G) and Rc 8 (E), The rims can have paler or darker colours. Rims that are paler in colour have higher reflectance resulting from higher aromaticity [61,62]. They probably formed at 200 °C [63]. The darker rims with plasticised edges in Rc 8 (E) probably formed during oxidation of organic material at high temperatures. In some cases, zoned oxidation rims can form that likely reflect an interrupted heating history [64]. Relatively small devolatilization pores are evident in An 3 (F) and An 2 (R), and larger in Cz 7 (I). These are formed during rapid heating that causes the organic matter to become plastic. Vitrinite macerals mostly show circular- or oval pores surrounded, in some instances, by pale oxidation rims. Though pores rarely occur in liptinite macerals high heating rates can result in rapid devolatilization of liptinite macerals and formation of pores [42]. When together with vitrinite macerals in clarites, liptinites act to increase the plasticity of vitrinite [11]. Expelled bitumen in Rc 3 (K-L) and Cz 5 (M-N) shows typical irregular shapes or coats organic particles. The bitumen fluorescence is fairly high with an intensive yellowish–greenish colour. Exceptionally, in An 3 (O-P), bitumen associated with an anisotropic coked (whitish–yellowish) particle is a good example of bitumen migration. In addition, in-situ bitumens occur within coal-waste fragments or in their pores whereas migrating bitumens are usually on grain surfaces and not bound

Fig. 6. Relationship between measured random vitrinite reflectance (Rr %) and Tmax.

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Fig. 7. Self-heated and burnt organic coal-waste materials from Wełnowiec (We), Anna (An), Rymer (Rc) and Czerwionka – Leszczyny (Cz). We 1 (A) paler-coloured oxidation rims around a vitrinite particle. An 9 (B) well-preserved trimacerite particle. An 9 (C) paler-coloured vitrinite particle with irregular cracks occurring with inertinite. We 2 (D) two differently heated particles. One is a paler-colour vitrinite particle with irregular crackes and darker oxidation rims, the second, vitrinite with paler-coloured oxidation rims. Rc 8 (E) whitish heated organic particle with dark plasticised edges and irregular crackes. An 3 (F) heated particle with irregular crackes and slightly porous structure. We 2 (G) vitrinite particle with paler oxidation rims. An 9 (H) different types of heated vitrinite particles. Cz 7 (I) massive heated organic particle with large devolatilisation pores. An 1 (J) heated organic material with coked particles. Rc 3 (K), Rc 3 (L), Cz 5 (M) and Cz 5 (N) expelled bitumen in fluorescent compared to original view. An 3 (O) and An 3 (P) expelled bitumen coating thermally-altered organic particle. An 4 (Q) reddish altered mineral in totally burnt-out waste lacking organic material. An 2 (R) thermallyheated organic particles surrounded by reddish, brownish mineral matter. Rc 3 (S) and Cz 7 (T) porous thermally-altered organic matter from pulverised fluid boiler. All in immersion oil. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

to the organic-matter macromolecule [42]. At Rymer and Czerwionka-Leszczyny, power-plants ash used to extinguish fires was identified in Rc 3 (S); Cz 7 (T). 4.5. Geochemical features of self-heating Bitumen-bearing samples provided the highest (2.64) yield extracts on average, and highly-thermally affected samples the lowest. 4.5.1. The distribution of n-alkanes Generally, n-alkane distributions were monomodal Gaussian and monomodal with additional input of short- and long-chain compounds (Fig. 8). Self-heating strongly affects the distribution of n-alkanes which differs significantly from those of fresh coal wastes [43] and coal of the region [5,49]. The monomodal Gaussian

distribution reflects macromolecule cracking and the expulsion of short-chain n-alkanes (n-C11–n-C18) which migrate to, and precipitate on, the dump surface. Short-chain alkanes also occur in highly-thermally affected waste. The distribution maximum depends on the heating temperature range. These pyrolytical nalkanes may be accompanied by low concentrations of preserved n-alkanes from primary-coal waste organic matter [43]. Coal waste in the initial- or middle advanced stages of heating show distribution- with monomodal Gaussian- to flattened monomodal shapes (Fig. 8). Overlapping peaks, calculation of, e.g., R2/R1, n-C23/n-C31, and CPI, proved problematic in the case of bituminous samples. Generally, average R2/R1 and n-C23/n-C31 values are lower in highlythermally affected samples compared to others (Table 2). The fact that CPI values (ave. 4.61) generally appear higher for subset 3 compared to the others may relate to the marked capacity of this

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Fig. 8. Typical distribution of n-alkanes in bituminous-, thermally affected- and totally burnt-out coal waste.

type of material for adsorbing bitumen migrating from hot spots. The extremely high CPI (84.28) of Cz 12 can be explained by the integration problems caused by overlapping peaks (Table 2). CPI (ave. 1.3) values of subset 2 samples compare with those of fresh- and water-washed coal waste. The CPI of thermallyunchanged coal waste lie close to 1.0 [43]. Pristane and phytane occur in almost all samples (Table 2). In general, subset 2 samples show higher Pr/Ph (ave. 6.87), Pr/n-C17 (ave. 1.31) values. Similar elevated values characterize highlythermally affected waste, i.e., 6.21 (Pr/Ph) and 1.14 (Pr/n-C17) may be due to adsorption of Pr and Ph that had evaporated from burning zones. With increase in heating, values of both ratios tend to decrease significantly as is shown by the Pr/Ph average for bituminous samples, also characterized by increased Ph/n-C18 (Table 2).

Such distributions are typical of bituminous-coal pyrolysates in the Rybnik region [72,73]. Differences in these ratios reflect selfheating temperatures and advancing pyrolytical change [68,74]. Relatively fresh coal wastes from the Trachy coal waste dump [43], investigated previously show Pr/Ph, Pr/n-C17 and Ph/n-C18 values within the range typical for USCB coals [5,43,49]. 4.5.2. Pentacyclic triterpanes and changes due to self-heating The lack of pentacyclic triterpanes in some samples may be apparent only and due to overlapping peaks, especially in the bituminous waste, or they may have been destroyed (subset 3). The self-heating did, however, significantly influenced the general hopane distribution (Table 2). The results may be contrasted with data for unaltered coal waste [43] in the region and distributions of

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Table 2 Distribution of extract yields and n-alkane- and pentacyclic triterpane biomarker parameters. CPI

Pr/nC17

Ph/nC18

Pr/Ph Ts/(Ts + Tm)

C29Ts/ (C29 + C29Ts)

C29ba/(ab + ba)

C30ba/(ab + ba )

C31ba/(ab + ba)

C31S/(S + R)

1.93 84.28 – – 0.93 – 1.48 – – – 1.30 1.53

1.19 – – 1.26 0.40 0.28 0.81 0.88 0.26 0.47 – –

0.39 – – 2.24 6.60 1.41 0.23 1.16 0.20 0.17 – –

3.76 – – 1.38 0.03 0.13 5.37 2.40 2.05 4.7 – –

0.88 – – – 0.74 – 0.73 – 0.58 – – 0.45

0.03 – – – 0.10 – 0.05 – 0.32 – – 0.15

0.26 – – – 0.41 – 0.29 – 0.57 – – 0.44

0.28 – – – 0.40 – 0.62 – 0.64 – – 0.45

0.15 – – – 0.19 – 0.28 – 0.22 – – 0.30

0.55 – – – 0.54 – 0.54 – 0.54 – – 0.55

1.41

15.24 0.69

1.55

2.48

0.68

0.13

0.39

0.48

0.23

0.54

2. Thermally affected coal wastes An. 5 0.47 0.47 An. 6 0.21 0.55 An. 7 0.22 0.61 An. 8 0.31 0.56 An. 9 0.44 0.03 An. 10 0.36 0.69 An. 11 0.38 0.19 a Cz. 4 0.07 0.94 a Cz 7 0.27 0.05 a Cz. 8 0.06 0.53 Cz. 9a 0.04 0.39 Cz. 11a 0.09 0.51 Cz. 15 0.08 0.08 Cz. 16 0.19 0.15 Rc. 1 0.10 0.04 Rc. 11 0.03 0.09 We. 1 0.15 1.67 We. 2 0.05 4.59 We. 3 0.28 1.64 We. 4 0.20 3.88 We. 5 0.10 0.78

14.44 8.49 17.83 15.20 12.26 4.87 8.43 2.41 – 3.68 2.94 3.29 11.48 – 6.11 9.29 11.68 3.10 105.77 38.18 43.74

1.25 1.13 1.19 1.17 1.16 1.16 1.20 1.25 2.39 1.21 1.40 1.20 2.55 1.76 1.34 1.31 1.16 1.11 1.22 1.20 1.31

1.17 0.55 0.48 0.83 0.49 1.98 0.59 5.40 2.29 2.46 2.44 2.62 0.46 0.72 0.69 0.56 0.98 1.11 0.50 0.63 1.53

0.22 0.12 0.08 0.11 0.10 0.21 0.11 0.49 0.42 0.35 0.31 0.38 0.10 0.09 0.06 0.08 0.24 0.14 0.12 0.10 0.10

7.96 4.45 5.05 5.10 5.16 5.78 3.73 10.99 4.63 11.32 9.92 10.07 4.49 2.33 9.90 13.84 1.66 5.84 2.17 4.95 9.55

0.89 0.79 0.73 0.91 0.90 0.90 0.88 0.68 – 0.95 0.87 0.95 0.36 0.45 0.82 0.82 0.54 0.58 0.74 0.72 0.72

0.04 0.04 0.05 0.07 0.07 0.05 0.06 0.02 – 0.05 0.07 0.05 0.05 0.06 0.04 0.09 0.04 0.02 0.06 0.03 0.03

0.15 0.17 0.16 0.13 0.15 0.15 0.15 0.08 – 0.29 0.24 0.12 0.29 0.20 0.27 0.33 0.29 0.36 0.26 0.30 0.27

0.22 0.49 0.43 0.19 0.16 0.24 0.25 0.23 – 0.46 0.33 0.23 0.82 0.86 0.48 0.44 0.39 0.49 0.33 0.40 0.37

0.11 0.17 0.18 0.14 0.16 0.15 0.20 – – 0.07 0.20 0.12 0.41 0.27 0.13 0.25 0.23 0.28 0.19 0.26 0.19

0.59 0.57 0.55 0.57 0.60 0.58 0.62 0.54 – 0.52 0.63 0.61 0.55 0.62 0.53 0.56 0.54 0.49 0.62 0.51 0.58

Averages

16.23

1.30

1.31

0.18

6.87

0.77

0.05

0.22

0.38

0.19

0.57

3. Highly–thermally affected coal wastes An. 1 0.02 – An. 2 0.01 0.27 An. 3 0.04 0.01 An. 4 0.55 0.14 a Cz. 10 0.01 0.47 Cz. 13 0.01 0.36 Cz. 17 0.01 0.20 Cz. 18 0.01 0.26

– – – – 1.38 4.28 5.52 7.38

– 16.18 – 1.76 2.01 3.08 1.89 2.72

– 1.18 1.07 0.82 2.11 0.92 0.79 1.10

– 0.42 0.33 0.17 0.42 0.29 0.15 0.26

– 4.69 8.62 6.57 6.32 5.09 4.99 7.22

– – – – 0.58 0.55 – –

– – – – 0.16 0.13 – –

– – – – 0.14 0.19 – –

– – – – 0.32 0.56 – –

– – – – 0.11 0.35 – –

– – – – 0.48 0.49 – –

Averages

4.64

4.61

1.14

0.29

6.21

0.57

0.15

0.17

0.44

0.23

0.49

Sample code 1. Expelled Cz. 5a Cz. 12 Cz. 14 Rc. 2 Rc. 3 Rc. 4 Rc. 5 Rc. 6 Rc. 7 Rc. 8 Rc. 9 Rc. 10 Averages

Extracted yields (wt R2/ %) R1 bitumen precipitated on coal 0.42 0.07 5.12 2.49 2.98 1.95 2.91 – 4.78 – 4.49 0.01 0.37 0.03 2.63 – 1.67 – 2.20 – 1.86 0.05 2.28 0.02 2.64

0.20

0.08

0.66

0.91

0.24

n-C23/nC31 wastes – – – – – – 1.41 – – – – –

R2/R1 = [R (from n-C23 to n-C37)]/[R (from n-C11 to n-C22) ]; m/z = 71, source indicator [37]. n-C23/n-C31; m/z = 71 source indicator [65]. CPI = 0.5[(n-C25 + n-C27 + n-C29 + n-C31 + n-C33)/(n-C24 + n-C26 + n-C28 + n-C30 + n-C32)] + [(n-C25 + n-C27 + n-C29 + n-C31 + n-C33)/(n-C26 + n-C28 + n-C30 + n-C32 + n-C34)]; Carbon Preference Index; m/z = 71; thermal maturity parameter [66]. Pr/n-C17 = pristane/n-heptadecane; m/z = 71 [67]. Ph/n-C18 = phytane/n-octadecane; m/z = 71 [67]. Pr/Ph = pristane/phytane; parameter of environment oxicity (with exception of coals); m/z = 71 [68]. Ts/(Ts + Tm) = C2718a(H)-22,29,30-trisnorneohopane/(C2718a(H)-22,29,30-trisnorneohopane + C2717a(H)-22,29,30-trisnorhopane); m/z = 191; thermal maturity parameter [69]. C29Ts/(C29 + C29Ts) = 18a-30-norneohopane/(17a-hopane + 18a-30-norneohopane); m/z = 191 [58,59]. C29ba/(ab + ba) = C2917b(H),21a(H)-30-norhopane/(C2917a(H),21b(H)-30-norhopane + C2917b(H),21a(H)-30-norhopane) [69,70]. C30ba/(ab + ba) = C3017b(H),21a(H)-hopane C30/(C3017a(H),21b(H)-hopane + C3017b(H),21a(H)-hopane); m/z = 191 [71]. C31ba/(ab + ba) = C3117b(H),21a(H)-homohopane/(C3117a(H),21b(H)-homohopane + C3117b(H),21a(H)-homohopane); m/z = 191 [69,70]. C31S/(S + R) = C3117a(H),21b(H)-homohopane 22S/(C3117a(H),21b(H)-homohopane 22S + 17a(H),21b(H)-homohopane 22R); m/z = 191; thermal maturity parameter [69]. ‘‘–” Concentration was too low (or nil) to calculate a parameter value. a Data published in [43].

pentacyclic triterpanes in bituminous coal of the region [5,49]. The low Ts/(Ts + Tm) values point to partial destruction of Ts due to lower heat resistance. The hopane C29ba/(ab + ba), C30ba/(ab + ba) and C31ba/(ab + ba) thermal-maturity parameters are greatly increased. Most C31S/(S + R) values are unchanged.

4.5.3. Distribution of aromatics and alkyl-aromatics Various types of aromatic- and alkyl aromatic compounds were detected in the coal waste, e.g., methyl-, dimethyl-, trimethylnaphthalenes, methylphenanthrenes and methylbiphenyls. Unsubstituted PAHs such as naphthalene (m/z = 128), phenanthrene and

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Table 3 Various calculated alkylnaphthalene- and alkylphenanthrene ratios. Sample code

2-MP/2-MA

DNR

TNR-1

TNR-2

TNR-5

MPI-1

MPI-3

MB/DBF

P/A

PHENOLS in %

1. Expelled bitumen precipitated on coal wastes Cz. 5a 3.75 1.41 Cz. 12 0.27 0.61 Cz. 14 1.95 0.45 Rc. 2 4.59 0.83 Rc. 3 – 0.52 Rc. 4 2.10 – Rc. 5 – 2.41 Rc. 6 – 1.43 Rc. 7 – 2.56 Rc. 8 – 2.69 Rc. 9 2.25 1.63 Rc. 10 1.80 3.01

1.07 1.84 2.02 0.49 0.43 2.69 7.35 0.57 2.52 4.09 3.92 1.93

0.18 1.84 – 0.78 0.90 1.74 0.70 0.59 0.62 1.05 0.50 1.46

0.23 1.35 – 0.52 0.85 1.08 0.73 0.49 0.74 0.99 0.60 1.17

0.48 0.31 – 0.35 0.32 0.27 0.56 0.40 0.37 0.55 0.23 0.17

0.93 0.75 0.68 0.37 – 0.31 1.47 – – – 0.91 1.56

1.27 0.61 1.20 1.55 – 1.93 0.98 – – – 1.14 1.04

– – – – – – 0.28 – – – – –

3.95 0.06 0.22 18.9 – 7.61 – – – – 3.75 –

1.24 2.87 1.97 30.12 35.56 13.97 14.96 16.67 9.11 15.88 5.32 4.20

Averages

1.60

2.41

0.94

0.80

0.36

0.87

1.22

0.28

5.75

12.66

2. Thermally affected coal wastes An. 5 5.01 An. 6 2.59 An. 7 3.54 An. 8 2.52 An. 9 4.91 An. 10 2.03 An. 11 3.19 Cz. 4a 9.59 a Cz 7 0.33 a Cz. 8 31.93 a Cz. 9 2.24 Cz. 11a 12.76 Cz. 15 3.47 Cz. 16 17.82 Rc. 1 – Rc. 11 4.72 We. 1 3.32 We. 2 1.43 We. 3 2.68 We. 4 0.96 We. 5 8.34

1.17 2.12 1.90 1.74 2.19 1.57 1.94 1.06 1.24 1.01 1.28 1.86 1.47 2.19 1.95 1.28 1.91 1.49 2.11 1.65 1.45

2.09 7.38 5.67 5.15 8.61 5.23 7.11 3.12 2.20 3.09 3.50 4.94 3.95 4.26 4.13 2.50 4.23 3.82 5.20 5.45 2.92

0.75 1.11 1.08 1.00 0.76 0.91 1.05 0.37 0.17 0.31 0.32 0.72 1.04 0.82 0.74 0.76 1.30 1.13 1.40 1.22 1.21

0.72 0.89 0.87 0.84 0.85 0.84 0.86 0.54 0.42 0.48 0.42 0.65 0.87 0.77 0.80 0.82 0.92 0.87 0.95 0.92 0.90

0.62 0.61 0.66 0.70 0.58 0.66 0.62 0.58 0.55 0.59 0.48 0.58 0.58 0.56 0.51 0.58 0.65 0.59 0.63 0.55 0.62

0.51 0.59 0.63 0.63 0.35 0.62 0.60 1.04 0.51 0.81 0.93 0.75 0.54 0.74 0.47 0.53 0.63 0.64 0.81 0.66 0.67

0.79 1.10 1.32 1.35 1.06 0.91 1.11 1.31 0.58 1.23 0.84 1.33 1.28 1.33 1.49 1.16 1.12 0.83 1.20 0.78 1.27

0.59 0.43 0.32 0.35 0.52 0.44 0.37 0.60 0.43 0.86 0.56 0.20 0.19 0.09 0.43 0.50 0.10 0.25 0.14 0.23 0.11

26.83 7.67 10.11 7.10 15.90 6.17 9.46 13.97 0.09 10.75 0.67 14.43 4.69 8.93 12.42 8.98 6.39 2.97 4.53 1.86 13.82

1.17 4.73 8.28 5.79 26.99 4.23 7.02 – 0.61 – 0.03 1.92 3.11 0.43 3.67 1.66 1.47 0.90 2.86 2.18 0.88

Averages

6.17

1.65

4.50

0.87

0.77

0.60

0.65

1.11

0.37

8.94

4.10

3. Highly-thermally An. 1 An. 2 An. 3 An. 4 Cz. 10a Cz. 13 Cz. 17 Cz. 18

affected wastes – 4.58 – – 5.20 4.53 35.12 27.23

– – 0.97 – – 1.62 1.23 0.90

– 2.47 5.00 – 0.76 2.88 4.13 5.61

– 0.47 0.51 0.76 0.76 0.93 1.07 1.22

– 0.60 0.70 0.68 0.59 0.80 0.87 0.88

– 0.56 0.55 0.65 0.59 0.53 0.66 0.52

– 0.47 – – 0.49 0.45 0.82 0.85

– 0.85 – – 1.63 0.98 0.94 0.99

– 0.30 0.77 – 0.13 0.36 0.36 0.27

– 12.64 – 18.10 37.81 5.04 8.73 7.76

– – 2.14 1.54 – 1.18 0.42 –

Averages

15.33

1.18

3.48

0.82

0.73

0.58

0.44

1.08

0.37

15.01

1.32

2.39

MNR

2-MP/2-MA = 2-MP/2-MA = 2-methylphenanthrene/2-methylanthracene; m/z = 192. MNR = 2-methylnaphthalene/1-methylnaphthalene, m/z = 142 [75]. DNR = (2,6-dimethylnaphthalene + 2,7-dimethylnaphthalene)/1,5-dimethylnaphthalene, m/z = 156 [76]. TNR-1 = 2,3,6-trimethylnaphthalene/(1,3,6-trimethylnaphthalene + 1,4,6-trimethylnaphthalene), m/z = 170 [75]. TNR-2 = (1,3,7-trimethylnaphthalene + 2,3,6-trimethylnaphthalene)/(1,3,5-trimethylnaphthalene + 1,4,6-trimethylnaphthalene + 1,3,6-trimethylnaphthalene), [75]. TNR-5 = 1,2,5-trimethylnaphthalene/(1,2,5-trimethylnaphthalene + 1,2,7-trimethylnaphthalene + 1,6,4-trimethylnaphthalene), m/z = 170 [77]. MPI-1 = 1.5(2 methylphenanthrene + 3 methylphenanthrene)/(phenanthrene + 1 methylphenanthrene + 9 methylphenanthrene) [78]. MPI-3 = (2-methylphenanthrene + 3-methylphenanthrene)/(1-methylphenathrene + methylphenanthrene), m/z = 192 [78]. MB/DBF = (3-methylbiphenyl + 4 methylbiphenyl)/dibenzofurane, m/z = 168 [77]. P/A = phenanthrene/anthracene, m/z 178. Phenols in %: Calculated relative % comparing to the whole area of the chromatograms. ‘‘–” Concentration was too low (or nil) to calculate a parameter value. a Data published in [43].

anthracene (m/z = 178), fluoranthene and pyrene (m/z = 202), benzo[a]anthracene and chrysene (m/z = 228), benzo[a]fluoranthene, benzo[k]fluoranthene, benzo[e]fluoranthene, benzo[e]pyrene, benzo[a]pyrene and perylene (m/z = 252), indeno[1,2,3-cd] pyrene and benzo[ghi]perylene (m/z = 276) are also present. Alkylnaphthalene- and alkylphenanthrene thermal-maturity parameters calculated to assess degrees of self-heating alteration included 2-MP/2-MA (Methylphenanthrene ratio) MNR (Methyl-

m/z = 170

naphthalene ratio), DNR (Dimethylnaphthalene ratio), TNR-1, TNR-2 and TNR-5 (Trimethylnaphthalene ratios), MPI-1 and MPI3 (Methylphenanthrene ratio), MB/DBF (Methylbiphenyl/Dibenzofurane ratio) and P/A (Phenanthrene/Anthracene ratio) – see Table 3. MNR, DNR, MPI-3, MPI-1, TNR-1, TNR-2, TNR-5 and MB/DBF do not show significant changes in values nor any evident trends (Table 3). Low values of MNR and DNR may indicate leaching in

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´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

Fig. 9. Relative percentages of phenols in bituminous-, thermally affected- and totally burnt-out coal waste compared to total phenols.

some samples [43]. Trimethylnaphthalenes and methylphenanthrenes were used to assess thermal maturity as they are less water-soluble than methyl- and dimethylnaphthalenes and, in addition, the self-heating did not greatly influence parameter values. 2-MP/2-MA and P/A decreased in subsets 1 and 2 and increased in burnt-out samples. The increase in the ratios values is linked to increases in phenanthrene- and anthracene relative contents [79]. P/A distinguishes between pyrogenic origin (P/A < 10) and petrogenic origin (P/A > 10) in some samples [80]. Amounts of phenols are highest in the bituminous samples (ave. 12.66 rel.%) and in the thermally-affected samples (ave. 4.1) samples, and lower in burnt-out waste. (ave. 1.32%) – see Table 3. The elevated phenol amounts in subsets 1 and 2 may well reflect the thermal destruction of vitrinite, releasing these compounds in quantity. Vitrinite is formed from a lignin macromolecule and the major chemical structural elements in vitrinites are simple phenols with a high contribution of para alkyl-substituted derivatives [81,82]. The dominant (30–40 rel.%) phenols in subsets 1 and 2 are C1–C2. whereas, among highly-thermally affected samples, C2 phenols are the most dominant (ave. 1.32 rel.%; Fig. 9). The low presence of phenols in subset 3 is related to the total destruction of vitrinites and their ease of leaching and evaporation. Comparing to fresh coal waste material analysed previously, whose extracts had only traces of phenolic compounds, the self-heated coal wastes investigated here contain large quantities of them [43]. In the bituminous subset, 2–3 ring PAHs dominate (avg  93%) due to precipitation of lighter PAHs. That naphthalene is the most dominant (83–99%) in the Rymer samples may be related to the concrete covering there which, despite the intensive pyrolysis in the dump, limited water leaching and evaporation of naphthalene, and phenols. The ash covering on the dumps is also highly absorbent. Phenanthrene and anthracene are also dominant in all three subsets (Table 4); these are structural isomers, of which phenanthrene is the more thermodynamically stable [83]. Lower-weight PAHs and substituted PAHs are typical components of petroleum and coals [84,85]. In subset 2, the general distribution of 2–3 ring PAHs (avg 62%) and 4–5 ring PAHs (avg 36.6%) has changed in comparison to the bituminous samples (Table 4). The domination of heavier PAHs with higher boiling temperatures indicates that these lay closer to the heating zone. As self-heating, which occurs in oxygen-depleted settings, is rather more similar to pyrolysis than combustion, the mechanism of PAHs fractionation is probably temperature-related. Heavy PAHs are mainly associated with incomplete combustion of organic materials. Typical combustion PAHs are (pyrogenic) anthracene, fluoranthene, pyrene, indeno [1,2,3-cd]pyrene and benzo[ghi]perylene [86,87]. In case of subset

3, the burned-out material remaining after the fire is extinguished can also contain lighter PAHs, reflecting its adsorption capacity; these compounds, like n-alkanes, migrate and precipitate in colder sites. The heavier PAHs, e.g., benzo[a]anthracene, chrysene, benzo [a]fluoranthene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene, formed even closer to the heating zone and, thus, are mostly absent in these samples. 5. Conclusions 1. Elevated extraction yields are typical of bituminous waste (subset 1). Heating under pyrolytic conditions caused thermal cracking of the coal-waste organic-matter macromolecule. The resulting bitumen migrated from the self-heating zone to accumulate on colder coal-waste surfaces. That increased Rock Eval pyrolysis values of S1, PI, BI and Py and generally lowered Tmax values in this waste. Tmax values are extremely high in subset 3 waste due to oxidation of organic matter without any free hydrocarbons. Thus, Rock Eval pyrolysis can be used to characterize bulk changes in organic matter due to selfheating. 2. Expelled bitumen, under fluorescence, has irregular shapes and coats organic particles with yellowish–greenish rims. Migrated bitumen may also coat anisotropic coked (whitish–yellowish) particles in inactive burnt-out waste. Characteristic of moderately-altered particles that underwent slow heating are a paler colour with irregular cracks, and oxidation rims (paler and darker) around particles and pores. Devolatilisation pores in organic parts are indicative of plasticity and faster heating. 3. In bituminous waste (subset 1), measured vitrinite randomreflectance (Rr %) values do not correlate well with values of R0 % indicated on HI–Tmax diagrams. In subsets 2 and 3, they do. 4. In subset 1 waste, increased temperatures link to decreases in both Pr/Ph and Pr/n-C17 and an increase Ph/n-C18. In both subsets 2 and 3, the pattern is the opposite. In subset 3, the presence of short chain n-alkanes (n-C11–n-C23) and elevated values of CPI, Pr/n-C17 and Pr/Ph reflect the adsorption characteristics of this material. The migrated n-alkanes originated as a consequence of macromolecule cracking in the core of the self-heating zone. 5. High contents of phenols, mostly substituted with C1–C2 groups, in subsets 1 and 2 waste are the result of the thermal destruction of vitrinite. Generally, the lowest phenol (mostly C2 phenols) contents occur in the highly-thermally affected coal waste total destruction of vitrinite particles, and easy leaching and evaporation of phenols is the cause.

´ ska / Fuel 181 (2016) 102–119 Á. Nádudvari, M.J. Fabian

117

Table 4 The distribution of PAHs in bituminous-, thermally affected- and totally burnt-out coal waste. N – naphthalene. P – phenanthrene. A – anthracene. Fl – fluoranthene. Pyr – pyrene. B(a)A – benzo[a]anthracene. Ch – chrysene. B(a)Fl – benzo[a]fluoranthene. B(k)Fl – benzo[k]fluoranthene. B(e)Fl – benzo[e]fluoranthene. B(e)Pyr – benzo[e]pyrene. B(a)Pyr – benzo[a]pyrene. Per – perylene. IndPyr – indeno[1,2.3-cd]pyrene. B(ghi)per – benzo[ghi]perylene. Sample code

Pyr

B(a)A

Ch

B(a)Fl

B(k)Fl

B(e)Fl

B(e)Pyr

B(a)Pyr

Per

IndPyr

B(ghi)per

2–3 ring

4-5 ring

6 ring

1. Expelled bitumen precipitated on coal wastes Cz. 5a 9.88 70.71 19.85 1.09 Cz. 12 0.31 5.34 86.38 5.07 Cz. 14 0.70 10.32 47.34 24.11 Rc. 2 93.45 5.93 4.79 0.17 Rc. 3 – – – – Rc. 4 0.32 88.10 11.62 – Rc. 5 89.62 – – 0.41 Rc. 6 99.78 – – – Rc. 7 99.30 – – – Rc. 8 94.75 – – 1.00 Rc. 9 76.11 15.37 17.14 2.08 Rc. 10 98.65 – – 0.48

N

0.24 2.74 9.84 0.13 – – 0.49 – – 0.92 2.11 0.41

0.03 0.29 5.51 – – – 0.67 – – – – –

0.06 0.14 2.51 – – – 0.85 – – – – –

0.03 – – – – – 0.85 0.02 0.09 0.38 0.01 0.06

0.01 – – – – – 0.73 0.01 0.09 0.45 0.01 0.03

0.01 – – – – – 0.53 0.01 0.07 0.34 0.01 0.02

0.04 – – – – – 1.30 0.04 0.14 0.68 0.03 0.07

0.02 – – – – – 1.05 0.03 0.09 0.48 0.02 0.06

– – – – – – 0.26 – – – – –

– – – – – – 1.32 0.05 0.11 0.46 0.04 0.06

– – – – – – 1.92 0.05 0.12 0.55 0.12 0.16

98.51 91.78 58.16 99.71 – 100.00 89.62 99.78 99.30 94.75 96.09 98.65

1.49 8.22 41.84 0.29 – – 7.14 0.11 0.48 4.24 3.77 1.13

– – – – – – 3.24 0.10 0.22 1.01 0.14 0.22

Averages

4.30

2.11

1.63

0.89

0.21

0.19

0.14

0.33

0.25

0.26

0.34

0.49

93.30

6.87

0.82

2. Thermally affected coal wastes An. 5 3.03 39.72 1.53 An. 6 27.24 32.41 5.81 An. 7 17.82 52.68 6.34 An. 8 11.48 49.51 7.88 An. 9 91.68 6.74 5.09 An. 10 38.83 24.72 6.55 An. 11 26.20 35.74 5.12 a Cz. 4 0.53 23.20 1.67 a Cz 7 2.11 7.97 90.25 Cz. 8a – 40.43 3.76 Cz. 9a 0.88 23.90 36.04 Cz. 11a 64.49 18.64 3.64 Cz. 15 0.71 52.60 11.30 Cz. 16 2.61 63.61 7.31 Rc. 1 16.19 66.42 6.38 Rc. 11 0.67 70.36 7.89 We. 1 1.56 47.22 7.50 We. 2 1.30 10.11 3.45 We. 3 2.69 32.48 7.37 We. 4 2.48 10.48 5.79 We. 5 – 60.07 4.35

6.26 5.67 4.49 4.27 0.19 3.98 3.59 8.11 0.61 11.79 18.64 2.19 10.31 16.16 5.38 5.86 15.31 12.13 26.87 22.74 21.58

10.78 7.80 7.32 8.34 0.29 7.42 6.42 10.23 0.97 13.52 13.99 3.24 11.05 8.68 4.05 7.55 13.00 16.74 22.58 31.96 9.82

5.15 5.02 2.87 4.59 0.15 5.26 4.92 7.92 – 5.12 1.02 2.11 3.29 0.93 0.54 1.65 3.87 15.13 3.41 12.3 1.10

9.11 7.12 3.76 5.23 0.23 6.29 6.18 13.29 – 12.04 2.91 2.80 6.78 0.61 0.68 1.97 7.84 20.84 4.30 12.72 1.67

2.44 1.15 0.77 1.41 0.03 1.23 1.58 5.65 – 2.84 0.83 0.94 0.75 0.04 0.33 1.22 1.07 3.13 0.14 0.45 0.28

3.01 1.34 0.64 0.69 0.07 1.51 1.2 1.91 – 1.37 0.35 0.42 1.23 0.11 0.33 0.49 0.83 5.71 0.09 0.35 0.39

1.03 0.57 0.27 0.39 0.02 0.47 0.60 2.86 – 1.50 0.17 0.32 0.36 0.02 0.11 0.12 0.28 1.26 0.05 0.12 0.11

8.49 3.68 1.93 2.75 0.12 2.80 4.30 10.13 – 5.44 1.31 1.64 1.70 0.11 0.34 1.49 1.48 7.24 0.15 0.46 0.47

3.11 1.75 0.95 2.11 0.07 1.64 2.62 4.41 – 2.18 0.28 0.85 – – 0.27 0.79 0.15 1.84 0.02 0.10 0.15

– – – – – – – – – – – – – – – – – – – – –

0.82 0.47 0.27 0.51 – 0.45 0.48 1.65 – – – 0.25 – – – – – 0.32 0.01 0.05 –

5.57 1.54 1.03 1.74 – 1.38 2.41 8.44 – – – 0.83 – – – – – 0.84 0.03 0.14 –

44.26 64.44 75.98 68.26 98.90 68.36 66.17 25.40 98.45 44.20 60.63 84.78 64.56 73.39 88.08 78.88 56.22 14.86 42.46 18.72 64.41

49.35 33.58 22.73 29.52 1.10 29.86 30.98 64.51 1.55 55.8 39.37 14.17 35.44 26.61 11.92 21.12 43.78 83.97 57.50 81.08 35.59

6.39 1.98 1.29 2.22 – 1.79 2.85 10.10 – – – 1.05 – – – – – 1.17 0.03 0.19 –

Averages

9.82

10.27

4.32

6.32

1.31

1.10

0.53

2.80

1.29

–

0.48

2.18

61.97

36.64

2.64

3. Highly-thermally affected wastes An. 1 – – – An. 2 – 36.50 2.89 An. 3 – 100.00 – An. 4 – 62.59 3.46 Cz. 10a – 72.99 1.93 Cz. 13 0.76 54.20 10.84 Cz. 17 – 31.34 3.59 Cz. 18 – 26.45 3.41

– 22.52 – 16.44 7.50 15.86 31.21 29.08

– 38.09 – 17.50 6.21 9.83 33.86 41.07

– – – – 1.51 4.65 – –

– – – – 3.38 3.94 – –

– – – – 2.69 – – –

– – – – 0.94 – – –

– – – – 0.55 – – –

– – – – 1.92 – – –

– – – – 0.38 – – –

– – – – – – – –

– – – – – – – –

– – – – – – – –

– 39.38 100.00 66.05 74.92 65.75 34.93 29.85

– 60.62 – 33.95 25.08 34.25 65.07 70.15

– – – – – – – –

Averages

20.44

24.43

3.08

3.66

2.69

0.94

0.55

1.92

0.38

–

–

–

58.70

48.19

–

60.26

16.45

0.76

P

32.63

36.62

54.87

A

31.19

11.19

4.35

Fl

‘‘–” Concentration was too low (or nil) to calculate a parameter value. a Data published in [43].

6. Precipitated 2–3 ring PAHs are prominent in waste of subsets 2 and 3. In addition, naphthalene, and phenols, appear in enriched concentrations in Rymer bituminous waste; adsorbing ash covering the waste inhibited leaching and evaporation of the naphthalene and phenols. Heavier 4-, 5- or 6-ring PAHs, in subset 2 waste may indicate that it formed closer to a heating zone. Light PAHs in extinguished, burnt-out material likely relate to its porous structure and adsorption capacity. 7. Abundant organic compounds generated in self-heating should be considered a serious environmental hazard since many of them show high mobility. This concerns particularly phenols which are relatively well soluble in water thus can be transported easily to the coal waste dumps outside contaminating soils and water. As previous studies indicated leached

compounds may include also PAHs, particularly those with 2– 4 rings. Moreover, light-weight compounds may evaporate from the self-heated dump surface to add to the general background of organic contaminants in Upper Silesia.

Acknowledgements The research was funded by a Grant for Young Scientists from the University of Silesia for the project. The authors are grateful to Dr. hab. Magdalena Misz-Kennan for her help with the petrographical analysis. Dr. Pádhraig Kennan (University College, Dublin, Ireland) helped with language correction.

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