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Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis
Accepted Manuscript Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis
Angelina Kosateva, Maya Stefanova, Stefan Marinov, Jan Czech, Robert Carleer, Jan Yperman PII: DOI: Reference:
S0166-5162(17)30524-4 doi:10.1016/j.coal.2017.10.005 COGEL 2904
To appear in:
International Journal of Coal Geology
Received date: Revised date: Accepted date:
29 June 2017 5 October 2017 5 October 2017
Please cite this article as: Angelina Kosateva, Maya Stefanova, Stefan Marinov, Jan Czech, Robert Carleer, Jan Yperman , Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Cogel(2017), doi:10.1016/j.coal.2017.10.005
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ACCEPTED MANUSCRIPT Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis Angelina Kosateva1 , Maya Stefanova1 *, Stefan Marinov1 , Jan Czech2 , Robert Carleer2 , Jan Yperman2
Institute of Organic Chemistry with Centre of Phytochemistry,
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1
Belgium
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Research group of Applied and Analytical Chemistry, Hasselt University, B-3590 Diepenbeek,
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*corresponding author: [email protected]
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2
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Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Abstract
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Lignites from Thrace- and Sofia- coal basins, i.e. “Maritsa-East” and “Stanjanci” mines, were subjected to aqueous sequential extraction at 25 0 C during 10 weeks. Each 7 days leachates were separated and pH and conductivity were measured. According to the extraction curves μS vs. time two portions were prepared, enriched in salts, extracts from the first two weeks (“head” of the elution) and in organic matter, extracts from the rest of time (“tail” of the elution curve). Combined freeze-dried extracts were characterized by yields, technical and elemental analyses. They were studied by X-ray photoelectron spectroscopy (XPS) and Infrared spectroscopy (IR). According to XPS spectra the main species on the leachate surfaces were carbon atoms in aromatic and aliphatic structures, 48-53 at. % from the total C1s signal. The intensive N 1s signal at 400 eV was assigned to pyrroles and amines (1-3 at. %). The most abundant sulphur form was inorganic sulphates while intensities for the other ones were < 1%. Respectively, the sulphatic sulphur content (13.6%) determined for Maritsa leachate was almost seven times higher than the same sulphur for Stanjanci leachate. FTIR spectra gave evidences for oxygen-containing functional groups, i.e. COOH groups in benzene carboxylic acids and their derivatives, in shortchain aliphatic fatty acids and for polyols. The appearance of mineral matter, mainly gypsum and kaolinite, made equivocal the IR spectra interpretation. Acetone soluble portions of “tail” leachates have represented relatively small parts of the organic matter (340 mg/kg Maritsa East and 80 mg/kg Stanjianci lignite) but have assigned reliable evidences for the polar constituents of leachates. Linear fatty acids, nC12 -nC32 , nC16 max , n-alcohols, benzoic acids, i.e. hydroxy-, methoxy-, phthalic acids, were highly abundant. Sterols, stanols, ketosterols were present in both extracts. Phthalates were recognizable as well. AP-TPR-TD-GC/MS technique has proved the presence of phenols, PAHs and heteroatom containing components in leachates flue gases. From an environmental viewpoint it seems that the identified compounds do not represent an acute toxic risk. However, N-containing compounds could raise concerns and further attention is needed to be focused on them. Keywords: lignite, aqueous leachate, organic components, environmental pollutants
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Introduction Bulgarian lignites are the main source for energy production in the thermal power plants of the country (www.fe.doe.gov). During their exploration, incineration and storage of waste products from mining and combustion, i.e. dumps, fly ashes and score, they create environmental problems (Vassilev and Vassileva, 2005, Stefanova et al. 2007, Meawad et al. 2010, Kostova et
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al. 2013). The main disadvantages of Bulgarian lignites are their low calorific value, high ash
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and moisture content and harmful emissions during combustion. One possibility for gradual
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reduction of lignites energy use and finding alternatives is the direct application of lignites in other areas of the economy, i.e. production of humic acids, adsorbents, soil conditioners, etc.
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At present, there is a little information, what and how much harmful to human health persistent organic compounds are leached from lignites, dumps and combustion waste materials by
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rainwater and during irrigation activities. Amounts of leached inorganic substances in dry residues from aqueous leachates of Maritsa East lignite, claystone partings and combustion
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wastes were recently evaluated (Yossifova et al. 2016), while organics therein were not studied. Organic components are of considerable environmental impact and care should be paid on their
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disposal and release in the nature because of the potential toxicity of the infiltrated substances. In Bulgarian legislation there is a regulation norm for the amounts of some organic industrial in
groundwaters,
i.e.
chlorinated
species,
PAHs,
phthalates,
pesticides,
etc.
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pollutants
(Regulation 8, 2004). In order to assess the potential impact of interactions between coal and
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water that might occur in soil systems during the agricultural application of lignite, during their storage in dumps or in the waste water during sorption treatment, it is necessary to have adequate
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information on the composition of lignite water-soluble fractions, the so called “water leachates”. Coals were suspected for many human health problems (Finkelman et al. 2002) and became an object of the new discipline - “medical geology” (Feder et al. 2002). Potential human health risk of organic compounds leached from coal included endocrine disruption, nephrotoxicity, and cancer. With a similar topic of study, to identify potential toxic or environmentally relevant organic compounds in the aquifers of the Amynteo hydrogeological basin, Northern Greece, and to assess a possible link of the identified organic contaminants with the parent lignites was the study of Iordanidis et al. (2012). Therein only anthropogenic pollutants were identified, no coalderived organic compounds were depicted.
ACCEPTED MANUSCRIPT Recently, Zhu et al. (2015) have performed systematic study on water-soluble organic compounds released from black shale and different rank coals, Ro, %=0.3-2.6 with Tmax = 409 o C - 602 °C. A steep decline of extracts yields with maturation and positive correlation with oxygen index OI were determined. Yields and fatty acids amounts, normalized to total organic carbon TOC, were comparable for coals and shales with the same maturity, but differences were depicted in the patterns of the constituent’s distributions. Acetates and formates were the main
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acids in the extracts, accompanied by some low molecular carboxylic and dicarboxylic acids.
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Nowadays, the importance of water-soluble organic components studies gradually increases as it
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is firmly related to PAHs determination in coal leachates (McElmurry and Voice, 2004), as well as to the disposal of produced waters from gas extraction in coal and shale from coalbed methane
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production and from shale hydraulic fracturing (Orem et al. 2014).
The objective of the present study is characterization by chemical, spectral and pyrolytic
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methods of aqueous leachates from two Bulgarian lignites. On the base of the data an attempt for appraisal of environmentally relevant organic compounds in aqueous leachates that could be
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regarded as potential organic pollutants in groundwater will be done. II. Experimental
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II.1. Lignite samples, aqueous leachate preparation and fractionation. Lignites from two coal basins, Thrace- and Sofia-, i.e. Maritsa East (ME) of Early-Middle
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Miocene and Stanjanci (Stan) mines of the Pliocene-Late Miocene geological age, were under study (Šiškov, 1997; Šiškov and Andreev, 1987). ME lignites were characterized by Ro - 0.20 %,
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Wr -64.4 %, Ad - 39.7 %, Cdaf - 65.0 % , VMdaf - 55.8 %, Q daf - 22.3 MJ/kg and the following maceral composition H - 61 %; L - 2 %; I - 1 % and M - 36 %. Stan lignites cover the area of
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Western Bulgaria, between the Balkan and Sredna Gora Mountains. Coal formation lasted till the beginning of the Pliocene. Stan lignite characteristics were: Ro - 0.12 %, Wr - 52.5 %, Ad - 21.9 %, Cdaf - 61.6 %, VMdaf - 61.0 %, Q daf - 19.42 MJ/kg and maceral composition H -74 %, L - 8 %, I - 5 %, M -13 %. Two lignite samples, one from ME and one from Stan lignites, respectively, were grounded to < 0.2 mm and subjected to sequential extraction by distilled water at 25 0 C during 10 weeks. For quality assurance duplicate aqueous extractions under experimental condition were performed. Experimental scheme is illustrated in Fig.1. It was partly adopted from the study of Doskočil et al. (2014) of water-extractable fractions from South Moravian lignite. Briefly, 10 g of lignite
ACCEPTED MANUSCRIPT samples and 150 ml of distilled water were placed into a 200 ml Erlenmeyer flask. The slurry was regularly agitated by magnetic stirrer. Each 7 days, the aqueous extracts were separated from lignite by centrifugation for 10 min at 4000 rpm at 25 0 C. Subsequently, the supernatants were filtered to remove the finest particles possibly penetrated during manipulations. Likewise leachates were isolated and ten aqueous extracts were prepared. Their pH and conductivity were measured and changes with time were illustrated in Fig. 2. According to the conductivity, two
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portions were prepared: - with higher conductivity (“head” of the extraction curve, extracts from
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the first two weeks); - and, with lower conductivity for the “tail” of the curve (Fig. 2).
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Respectively, the total leachate from each one lignite was divided into two portions, “head” and “tail”. They were freeze-dried and kept in refrigerator. Dried leachates were light and
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voluminous. Due to the higher organic content for the “tail” leachates (Table 1) they were further
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studied by chemical, spectral and pyrolytic methods.
II.2. Isolation of acetone soluble (AS) components
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For isolation of material soluble in organic solvents, “tail” freeze-dried leachate portions were refluxed for half an hour with acetone (3x50ml). Acetone solubles (ASs) were combined, dried
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over CaSO 4 , filtrated, concentrated at reduced pressure, silylated and studied by GC-MS.
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II.3. Reductive pyrolysis
Residues after acetone extraction of “tail” leachates were studied by reductive pyrolysis (Fig.1).
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Atmosphere Pressure – Temperature Programmed Reduction (AP-TPR) coupled “off-line” with thermal desorption gas chromatography-mass spectrometry (TD-GC/MS) was used to specify
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volatile organic components in coal and its derivatives (Yperman et al. 1999, Gonsalvesh et al. 2013 and references therein). For reductive pyrolysis ca: 40 mg of sample and 20 mg of fumed silica were placed in the quartz reactor under a 100 ml/min flow of pure H2 . A linear temperature program of 5 °C min-1 from ambient temperature up to 950 °C was applied. The apparatus was adapted to trap volatiles for subsequent GC-MS analysis. The outlet of the AP-TPR reactor is connected to a set of two ice-cooled tubes containing Tenax (Sigma-Aldrich), a porous polymer of 2,6-diphenyl-p-phenylene oxide, as adsorbent. Volatiles were additionally diluted by adding inert gas to the H2 flow in a 5:1 (v/v) ratio in order to prevent break through the adsorption tube. Volatiles were trapped in two separated temperature ranges using two separate adsorption tubes:
ACCEPTED MANUSCRIPT 250o C - 550o C (tube 1) and 550o C - 950o C (tube 2). Later on, adsorption tubes were subsequently desorbed and analyzed by thermal desorption-gas chromatography/mass spectrometry (TDGC/MS) using He as carrier gas at 85 kPa and the following conditions: a) Unity thermal desorber (Marks): primary desorption 20 min at 275ºC; Cold trap at – 10ºC, heated at maximum heating rate up to 320ºC, hold time 15 min; flow path temperature 200ºC; b) Trace GC Ultra-Gas chromatography (Thermo Instruments): capillary column 30m ZB 5-MS x 0.25 mm x 0.25 µm
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Phenomenex; temperature program: 3 min at 30ºC, 30ºC-100ºC (8 ºC/min), 100 ºC-310 ºC (12
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ºC/min), hold time 5 min at 310 °C; c) DSQ-Mass spectrometer (Thermo Instruments): EI
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spectra; Ionization energy: 70 eV; Scan range: m/z 33 - 480 in 0.4s. Deuterated thiophene, Th-d4 , 3 μg, was used as a standard. NIST library spectra were used for peak identification.
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II.4. Instrumental techniques used for aqueous leachates characterization Leachates were analyzed and characterized by yield (wt. %), proximate, ultimate analyses and by
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a set of analytical techniques, i.e. XPS and IR spectroscopy, GC-MS and pyrolysis. Proximate analysis, i.e. moisture (W), volatile matter (VM), fixed carbon (C fix ) and ashes, were determined
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by thermogravimetrical analyser using DuPont Instrument 951. For determination of elemental composition, i.e. C, H, N and S, was used a Thermo Electron Flash EA1113 elemental analyzer
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according to Warne method (Warne, 1991).
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II.4.1. Analytical techniques, i.e. X-ray photoelectron spectroscopy (XPS) and Infrared spectroscopy (IR)
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The XPS measurements were carried out in the analysis chamber of the electron spectrometer ESCALAB-MkII (VG Scientific) at a base pressure of 5x10 -8 Pa. The spectra were excited with
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an Mg-K α radiation at instrumental resolution of ≈ 0.9 eV. The base C 1s line had a binding energy of 284.6 +/- 0.1 eV and no charge effects were observed. The acquisition time for C 1s, N 1s and S 2p spectra were in the interval 30 ~ 5 min. The FTIR spectra were recorded on dried spectrometry grade KBr pellets using a Tensor 27 Spectrophotometer in the range 4000–400 cm–1 within a 2 cm-1 resolution. On each sample 256 scans were accumulated.
II.4.2. GC-MS analyses of acetone extract of leachate
ACCEPTED MANUSCRIPT GC-MS analyses was carried out on a Hewlett-Packard 6890 GC system plus HP 5973 MSD equipped with a HP-5 MS column (0.25mm×30m×0.25μ film thickness) with flame ionization detector (300o C). A split/splitless capillary injector (300o C) is used in the splitless mode (valve reopened 1 min after injection). After 0.5 min isothermal period at 85 o C the oven temperature was increased to 200o C at 20o C/min and then to 320o C at 5o C/min. The MSD was operated in the electron impact (EI) mode with energy of 70 eV and scan range from 50 to 650 Daltons. AS were
converted
to
trimethylsilyl
derivatives
by
reaction
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extracts
with
N,O-bis-
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(trimethylsilyl)trifluoroacetamide (BSTFA) and pyridine in sealed vials for 3h at 70°C. The MS data were acquired and processed with the HP software. Individual compounds were determined by comparison of mass spectra (MS) with literature and library data, comparison of
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MS and GC retention times with those of authentic standards or interpretation of mass spectra. For MS tracking Xcalibur software was used. MS were quantitatively interpreted by internal
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standard application, deuterated nC24 . Amounts were normalized in μg/kg coal. The following specific fragments were tracked (some were silylated derivatives): m/z 57 - for n-alkanes, m/z
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117 – for n-fatty acid, m/z 75 – for n-alcohols, m/z 129 – for sterols, m/z 215 – for stanols, m/z
III. Results and discussion
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174 –for ketosterols, and m/z 204 – for mono saccharides.
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III.1 Yields and bulk characteristics
Leachates conductivity (2000-4000 μS, Fig. 2) has proved that extracts from the first two weeks
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(“head” portions) were characterized by high amount of salts, 60-70% ash (Table 1). Data were in accordance with results for leaching of South Moravian lignites where leachates conductivity
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from the first weeks was very high (Doskočil et al. 2014). Based on conductivity measured in our experiments and literature data, only leachate portions relatively enriched in TOCs and with lower ash content were further studied. Respectively, leachates from the third to tenth weeks (“tail” portions) were combined, freeze-dried and analyzed by instrumental and spectral methods as shows in Fig.1. In Table 1 were present yields of leachates, in %. Data were recalculated on “dry, ash free basis” and amounts of organic matter in leachates, in % daf, were obtained. Leachates acetone extractability was 340 mg/kg for ME lignite and 80 mg/kg for Stan lignite. Data for elemental analyses have confirmed the observation done on the base of conductivity: - “head” portions were highly enriched in ash, 63-70% gradually reduced to 32-
ACCEPTED MANUSCRIPT 35% in “tail” portions; - the tendency has mimicked VM amounts; - “tail” portion were partly enriched in C, H and O comparing to their counterparts of “head” portions; - sustainable decrease in S content for “tail” fraction was depicted. III. 2. Spectral analyses X-ray photoelectron spectroscopy (XPS) was used to receive qualitative information for C, N and S compounds on the surface of freeze-dried lignite water-extractable fractions. In order to
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provide a general picture of the distribution of several functional groups on the surface of the
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sample, curve-fitting method of the XPS spectra was applied. Chemical structural assignments of
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each component were made taking into account the binding energies reported for C, N and S functional groups (Marinov et al. 2004, Lorenc-Grabowska et al. 2013, Doskočil etal. 2014). The
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XPS data of organic functional oxygen atoms were not presented because the general oxygen signal of samples under study was due to predominantly of Si, Al, Ca, Mg, Na and other
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inorganic oxides. The XPS signal of organic oxides was negligible, almost compared to a signal from the inorganic oxides.
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XPS C1s spectra obtained by a deconvolution procedure of the Maritsa-East and Stanjanci portions were presented in Fig .3. For both samples four different structural groups of the organic
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carbon atoms with binding energies occurred at 284.6, 286.3, 288.4 and 292.3 eV were registered (Table 2). They were assigned as follow:
the 284.6 eV peak represented the contribution from aromatic and aliphatic carbon
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(i)
(C-C, C=C, C-H);
the carbon bound by a single bond to oxygen (i.e., C-O, C-OH, etc.) and to nitrogen
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(ii)
or sulphur (C-N, C-S) corresponded to signal at 286.3 eV; the 288.4 eV peak concerned mainly carbon bound by three bonds to oxygen as in
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(iii)
carboxyl and ester functional groups; (iv)
shake-up satellite peak at 292.3 eV was attributed to π-π transitions in aromatic rings (Kelemen and Kwiatek, 1995).
III.2.1. Organic carbon containing compounds According to the XPS spectra illustrated in Fig. 3 carbon atoms in aromatic and aliphatic structures were the main surface species in the both leachates with contribution of 48-53 at. % from the total C1s signal. Carbon atoms in carboxylic and ester groups were in subordinary
ACCEPTED MANUSCRIPT amounts, 11-14 at. % (Table 2). The lowest C1s signal was measured for π-π satellite peak, < 2 at. %. III.2.2. Organic nitrogen containing compounds Based on N 1s spectrum the organic nitrogen species were mainly assigned as pyrrolic nitrogen and amines, followed by quaternary and pyridine nitrogen (Fig.3). The peak at 398.4 eV was assigned to N in pyridine, while the peaks at 400 eV and 402.3 eV, respectively to nitrogen
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in pyrroles, pyridones, secondary and tertiary amines, imides, protonated amines, N-quaternary atoms and oxidized nitrogen (N-O) (Kelement et al. 1994, Pels et al. 1995, Cagniant et al. 1998,
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Straka et al. 2000, Xiao et al. 2005, Doskočil et al. 2014). In samples under study the most intensive N 1s signal was for pyrroles and amines at 400 eV (1-3 at. %) (Table 2). Amino
(Finkelman et al. 2002).
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III.2.3. Organic sulphur containing species
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containing functional groups were also determined in the aqueous leachate from lignite
The XPS signal of a sulphur single species was composed by two representing 2 p 3/2 and 2 p1/2
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components having a 2:1 relative intensity ratio and separated in energy by 1.2 eV. For each sulphur species a peak synthesis for S 2p by mixed Gaussian and Lorentzian line shapes was
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performed with full width at half maximum of 2.60 eV. XPS spectra obtained by a deconvolution procedure were shown in Fig. 3. The assignments of sulphur forms were based on references and
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previous studies (Kelemen et al. 1990, Gorbaty et al. 1990, Marinov et al. 2004, Doskočil et al. 2014). The relative atomic concentrations in XPS spectra were determined using peak values
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fixed at 163.3, 164.1, 165.5, 168.4, and 169.1 eV of binding energies for inorganic (pyritic) and organic sulphidic, thiophenic, sulphoxidic, sulphonic and sulphatic sulphur forms, respectively.
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The most abundant sulphur form was for inorganic sulphates while the other ones were ≤ 1%. In this respect for Maritsa East leachate sulphatic sulphur content of 13.6% was almost seven times higher than for Stanjanci leachate. This peculiariry could be explained by the higher sulphur content of parent Maritsa-East lignite (Marinov et al. 2004, Gonsalvesh et al. 2013). III.2.4 FTIR spectra A comparison of the FTIR spectra for the wave number region 4000 to 400 cm−1 for the leachates of lignites samples was shown in Fig. 4. Gypsum was revealed by the bands at 3543 cm-1 , 671 cm-1 and 603 cm-1 (Painter et al. 1978). Kaolinite was related to bands at 534 cm-1 and 470 cm-1 (Iordanidis et al. 2012). The FTIR spectra of the fractions have shown absorbance in
ACCEPTED MANUSCRIPT the region of 4000-3000 cm−1 due to vibrations of OH groups (H-bonded). The sharp intense bands at 2920 cm-1 and 2850 cm−1 have represented the valency oscillations of -CH3 and -CH2 aliphatic groups and that at 1622 cm−1 have corresponded to aromatic C=C structure. Bending vibrations of phenols OH groups were observed at 1384 cm–1 . The vibrational frequencies of oxygen in C-O-R structure were spread from 1143 cm-1 to 1016 cm−1 . III.3. Composition of acetone soluble (AS) extracts
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XPS and FTIR spectra have denoted the presence of a variety of functional groups for
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aqueous leachates under study. Information for the compositions at a molecular level was
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received by GC-MS study of AS extracts. Generally, ASs have represented relatively small portions of leachates (80-340 mg/kg lignite) but have depicted reliable evidences for the polar
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constituents. There were certain similarities in AS extracts compositions, i.e. predominance of linear fatty acids, comparable amounts of alcohols and considerable phthalates presence, as well
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as differences, i.e. traces of hydrocarbons and rests of saccharides for Stanjanci leachates and appreciable amounts of aromatic acids and rests of lignins for Maritsa East leachates (Fig. 5,
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Table 3). For both AS extracts a particularity in molecular compositions was the high amount of steroid structures, especially for Stanjanci leachates, 10.03 µg/kg coal, with well-expressed
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doublets for sterols/stanols counterparts (Fig, 6). Sterols, stanols and ketosterols were described in previous study on polar constituents of Bulgarian lignites (Stefanova et al. 2016b). The ratio
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5α(H)-stanol/Δ5 sterol (stanol/sterol ratio), was calculated as the ratio of the amounts of stigmastanol/sitosterol (Fig. 6). Magnitudes of ~ 1 were calculated for Maritsa East leachates and
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> 1 for Stanjanci leachates. The higher value indicated an enhanced microbial reduction of organic matter under reducing (anoxic) conditions in the Stanjanci leachates palaeomire. By GC-
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MS in both leachates were determined 24-n-Pr-sterols, C29 M+396 and C30 , M+410 (Fig. 6). The distribution of n-alkanoic (fatty) acids in Bulgarian lignites generally has shown a maximum at the ubiquitous nC16 homologue. In AS extracts n-fatty acids ranged from nC12 to nC32 , with the “even” numbered homologues being dominant. Shorter homologues have strongly prevailed fatty acids distribution signature and attested predominant aquatic origin for the parent material. For both leachates distributions with two maxima, centered at nC16 and subordinated at nC22 , nC24 , with a strong dominance of the shorter homologues, were determined.
ACCEPTED MANUSCRIPT Long chain “even” carbon numbered n-alkanols ranging from nC22 to nC28 (Cmax at nC22 , nC24 ) were identified in both leachates. The distribution signature was broader for Maritsa East leachate where the span has covered the interval nC12 -nC28 . Concerning linear lipid structures in AS extracts, a considerable amount of n-alkanes, 10.58µg/kg lignite was characteristic for Maritsa East leachates while only traces for Stanjanci
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leachates were determined (Table 3). In addition, n-alkanes distribution for Maritsa East
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leachates was differed from the parent lignite. Namely, it was like a “bell” centered at nC25 ,
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without “odd” numbered homologues recognizable predominance, all reflecting in CPI 1.09. For Maritsa East parent lignite was published a prevalence of long-chain members (> nC27 , maximizing at nC27 and nC29 ), with a marked ”odd” over “even” predominance and CPI in the
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range 2.8-4.2 (Bechtel et al. 2005). The mid-chain n-alkanes (nC21 -nC25 with an assigned origin from aquatic macrophytes) were pointed as a possible source for n-alkanes with “bell”
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distribution signature. Actually, high amounts of nC21 -nC25 were determined ibidem and an assumption for the higher contribution of macrophytes to parent vegetation comparing to the
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vascular plants has been done. This view was supported by our data, specifically, by leachate nalkanes distribution with Paq = 0.75 ratio, falling in the range for submerged/floating
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macrophytes (Ficken et al. 2000).
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Aromatic acids, i.e. m-, p- hydroxy benzoic, o-phthalic, t-phthalic acids, as well as marks for a survived gymnosperm lignin, i.e. 3-methoxy, 4-hydroxy benzoic acid, dehydroabietic acid,
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were highly abundant in AS extracts of Maritsa East leachate (Table 3). Due to the parent lignites low maturity, Ro ~ 0.20 (Šiškov, 1997), products of East
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carbohydrates diagenetic transformation were recognizable in AS extracts. By m/z 204 in Maritsa leachate
some
mono
saccharides derived
from hemicellulose,
i.e.
D-xylose,
D-
xylopyranose, D-arabinose, and by m/z 217 - D-xylofuranose and arabinofuranose, were depicted. These compounds have denoted that some small portions of carbohydrates have been incorporated in the Miocene-aged lignites and became extractable in aqueous media. In both AS extracts were determined appreciable amounts of phthalates (Table 3). They are ubiquitous pollutant of our civilization. In Bulgarian legislation there is a norm for their amount in groundwaters and they are under surveillance, Regulation 8 (2004). According to Maharaj et
ACCEPTED MANUSCRIPT al. (2014) the phthalate esters represent contamination of the coal prior to processing in the laboratory. Only in AS extract of Stanjanci leachate there were some tentative MS indications for the presence of alkaloids, i.e. 2-ethyl-acridone, M+223, C15 H13 NO (0.4μg/kg Stanjanci lignite) and harmol, M+198, C12 H10 N2 O (2.5 µg/kg Stanjanci lignite). Harmol is abundant in seeds of Peganum harmala, a widespread species growing wild and used as an antiheamoroidal,
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helmicide, and central nervous system stimulating agent in folk medicine (Kartal et al. 2003). It
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is toxic β-carboline indoleamine alkaloid amounting up to 2.5 μg/kg Stanjanci lignite. The
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problem with alkaloids in groundwaters is not in their absolute concentrations therein but in the
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long term exposure to their harmful action with deleterious effect on the human health.
III.4. Reductive pyrolysis
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Pyrolysis gas chromatography/mass spectrometry (Pyr-GC/MS) is an effective approach in the study of coal organic matter using thermal degradation for bonds cleavage and enables a
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sensitive and rapid characterization of organic constituents. It aids the molecular characterization of microbial and plant-derived biomass and generates valuable data on the degradation and
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conservation rates of organic debris. Pyrolysis of aqueous leachate organic matter has started at 250°C. In pyrograms two distinct and separated maxima were distinguished. Leachates
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pyrograms were shown in Supplementary Material [SM]. Volatiles in flue gases were trapped in two temperature intervals - “low”, 250o C-550o C and “high”, 550o C -950o C. Compounds were
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identified by TD-GC/MS, quantified, normalized to mg/kg parent lignite and data were shown in Table 4. Ten series of compounds were tracked and following compounds were identified:
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aliphatics, i.e. nC6 ÷nC14 , mono unsaturated/ saturated pairs, benzene, alkylated benzenes, styrenes, naphthalenes, biphenyls, fluorene, acenaphthylene; oxygen containing compounds, i.e. phenols, methoxy phenols, furans, benzofurans; sulphur containing compounds, i.e. sulphides, thiophenes,
benzothiophenes;
nitrogen
containing
compounds,
i.e.
pyrroles,
pyridine,
benzonitrile, etc. Considerable amount of sesquiterpenoids was identified in both leachates, ~ 20 rel.%. These biomarkers for conifer vegetation were already characterized in lignites chloroform bitumens, humic acids and in AP-TPR pyrolysates of Maritsa East lithotypes and Stanjanci lignites (Stefanova et al. 2002, 2005, 2016, 2016a). There was a variety of unsaturated/saturated sesquiterpenoids but the most abundant were longifolene/isolongifolene (M+ 204, m/z 95, 100%),
ACCEPTED MANUSCRIPT α-cedrene (M+ 204, m/z 119, 100%); cuparene (M+ 202, m/z 132, 100%), cadalene (M+ 198, m/z 183, 100%), etc. In the high temperature regions of the pyrograms elemental sulphur was recognizable as well. Distributions of tracked series, present in pyrolysates flue gases were illustrated in Fig.7, were amounts were expressed in rel. %. Alkyl benzenes, i.e. C 6 - C10 , were the main compounds in the Stanjanci leachate
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pyrograms (30.8 rel.%, Fig. 7). In the low temperature region the distribution was dominated by
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toluene, while benzene has predominated in the flue gases in the high temperature range (SM 3).
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There was a considerable decrease by14 rel.% in the amount of alkylbenzenes comparing to the pyrolysate of the parent Stanjanci lignites (Stefanova et al, 2016a). Alkylbenzenes were considered as a product of humification of the primary plant materials and microbial metabolites.
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The highest amount of phenols, a half of the total volatiles, 46.2 rel.%, Fig. 7, was measured for pyrolysate of Maritsa East leachate, while no change in phenols for Stanjanci
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leachates comparing to the initial lignite was recognized. With the additional amount of 11.8 rel.% of methoxy phenols for Maritsa East leachate the amount of phenols/methoxy phenols has
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increased to the enviable 58 rel.%. The presence of phenol and its derivatives in groundwaters could be a serious threat to human health, toxic even at low concentrations.
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In pyrolysate of Maritsa East leachate considerable of amount furans, with furfural the most abundant compound in the high temperature pyrogram was identified (SM 2). Actually
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furans and furaldehydes were considered as typical products for carbohydrates pyrolysis. The cellulose in lignite may survive for millions of years if has been deposited under favorable
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palaeoenvironmen (Fabbri et al. 2008). One possible way for cellulose preservation is its incorporated by sulphur bridges in coal organic matter. In a suite of studies devoted to the
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determination of organic sulphur forms in Maritsa East lignites by AP-TPR pyrolysis were able to determined high amounts of dimethyl di- and trisulphids (Gonsalvesh et al. 2013), which a proof for a possible way of preservation of certain molecules in bound form during diagenetic transformation of coal precursors. In the pyrolysate flue gases of both leachates significant amounts of polycyclic aromatic hydrocarbons (PAHs) were determined. Inasmuch as only data for PAHs in parent Stanjanci lignite were available (Stefanova et al. 2016a) an increase by10 rel.% for this leachate was appraised. In the national legislation there are limits for the amounts of 2-3 cyclic PAHs in
ACCEPTED MANUSCRIPT surface/underground waters, i.e. for acenaphthene, acenaphthylene, fluorine, phenanthrene. In general, amount of PAHs in Stanjanci pyrolysates was 2-3 folds higher than the amount in Maritsa East leachate (Table 4). The threat for human health is not in the absolute sum of PAHs but in their signature. According to the PAH position paper of EC 2-3 ring PAHs are not priority environmental pollutants and their TEFEPA values are negligible in comparison to benz[a]pyrene equivalent carcinogenic power (Cecinato, 1997). PAHs distribution signatures for both leachate
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samples [SM] were dominated by naphthalene and its methylated homologues and the danger of
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considerable pollution seems insignificant as for naphthalene was determined a negligible
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TEFEPA value. However, it should be taken into consideration that in geology the time scale is different and during the long exposure to PAHs infiltration the risk might become noteworthy.
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Other identified compounds in pyrolysates with potential ecological concern were Ncontaining species. By AP-TPR in leachate of Stanjanci lignites was registered their increase by
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3.8 rel.% in comparison with the reductive pyrolysis of the parent lignite (Stefanova et al. 2016a). Systematically in flue gases of products from Stanjanci lignites were estimated high
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amounts of pyrroles, pyridines, quinolones, etc., i.e. in bitumens, humic acids and the data should not be regarded as random. In addition, exactly in AS of Stanjanci lignites were tentative GC-MS
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indications for alkaloids and XPS spectra gave evidences for N-containing compounds (Table 2, Fig.3). Therefore, the hints for their presence in Stanjanci aqueous leachates should not be
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ignored. For information, one launched assumption for the Balkan Endemic Nephropathy (BEN), a disease lethal, is the presence of aristolochic acid, C 17 H11 NO 7 , M+ 341in the groundwater and long
consumption,
regardless
at
low
concentration
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its
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(https://en.wikipedia.org/wiki/Aristolochic_acid).
In different laboratories with the aim to simulate groundwater leaching of Pliocene lignites samples were extracted with distilled water (Orem et al. 1999, Maharaj et al. 2014, Doskočil et al. 2014) and instrumental techniques were used for structural elucidation of aqueous extracts.
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C NMR spectra of the leachates have determined high degree of condensed aromatic
character consistent with polycyclic aromatic structures. Of special concern were lignites from BEN endemic regions, where using GC/MS well water samples were analyzed for dissolved aromatic compounds (Orem et al. 1999). Fourteen compounds at the low concentration level were identified. With the exception of phenol, all the identified compounds were PAHs, some of
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human carcinogens. MS separations of the Pliocene lignite extracts were
characterized by aromatic hydrocarbons mainly in the benzene and naphthalene category, rich in functional groups: methoxy, acetyl, keto, hydroxy. It was assumed that some of these compounds could
be
nephrotoxic/carcinogenic.
In
conclusion
the
authors
have
pointed
out
that
functionalized compounds were sufficiently hydrophilic to be leached into the groundwater. Other compounds identified in the Pliocene lignite extract were terpanes and steranes as well as derivatives. These compounds might have been generated by fungi
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their functionalized
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degradation of the precursor organic matter. They have revealed the immature state of the coal,
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where in many ways the fossil wood could be macroscopically recognized (Feder et al. 2002). In our study by AS extraction we were able to isolate and identified variety of streroids (Fig. 6),
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functionalized by carbonyl or hydroxyl groups, making them enough polar to become soluble in water. Data for their effect on human health are missing, or could become a subject of the new
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discipline “medical geology” (Maharaj et al. 2014), as coal “human health” impact may be in part due to mobilization of organic components from coal organic matter.
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Doskocil et al. (2014) have improved the protocol for analyses of lignite water-soluble component by applying fractionation and pyrolytic technique in view to receive as much as
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possible information for aqueous leachates. In products of TMAH thermochemolysis of South Moravian lignite leachate the most abundant were methyl esters of 3,4-dimethoxy-3,4,5-
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trimethoxy- and 4-methoxybenzoic acids. There were low amounts of methoxy benzenes as well. Fatty acids, as methyl ester, were identified in minor portion among thermochemolysis products
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and they consisted of short chain nC14 and nC16 . Actually, in our study were identified the same series of organic compounds. Our separation scheme, very simple, gave us ground to isolate,
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identify and quantify more components, some of them potential pollutants or of human health impact. There was a good coherence of our data with the published on the topic. Present results have confirmed and enriched the knowledge on the aqueous leachate composition and have proposed the presence of some heteroatom containing compounds. In the present study were depicted the main differences in the compositions of flue gases from pyrolysis of Stanjanci lignite itself (Stefanova et al. 2016a) and its aqueous leachate. The following peculiarities were determined: leachate volatiles were characterized by a strong decrease in the amounts of hydrocarbons (-20.6 rel.%) and alkyl benzenes (-14 rel.%) and an increase in the amounts of PAHs (+10 rel.%) and N-containing compounds (+3.8 rel.%).
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CONCLUSIONS The present study could be regarded as a first attempt to assess the mobile contaminants in some Bulgarian lignites aqueous leachates. Although a very simplified separation procedure based on conductivity was applied some fractionation has been achieved. Portions relatively enriched in C, H, N and O were isolated and characterized by spectral methods. The sulphur in
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leachates the most likely was of pyrite type and concentrated in the “head” portions, with high
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ash content, 60-70%. Fractions relatively enriched in organic matter, “tail” portions, were
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characterized by chromatographic and spectral methods and the following information was obtained:
XPS and FTIR spectra have attested a great variety of functional group on the surface of
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aqueous leachates;
GC-MS study of acetone extracts has supplied data for the individual compositions at a
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molecular level. Extracts, although representing small portions of leachates (340 mg/kg
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Maritsa East lignite and 80 mg/kg Stanjianci lignite), gave reliable evidences for the polar constituents, i.e. fatty acids, alcohols, sterols, saccharides, etc. There were tentative
-
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MS indications for alkaloids in Stanjanci extract. AP-TPR-TD-GC/MS technique gave unequivocal evidences for the presence of PAHs
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and heteroatom containing components in leachates flue gases. The main differences in the compositions of flue gases from reductive pyrolysis of Stanjanci lignite and leachate
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were depicted: leachate volatiles were characterized by a strong decrease in the amounts of hydrocarbons (-20.6 rel.%) and alkyl benzenes (-14 rel.%) and an increase in the
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amounts of PAHs (+10 rel.%) and N-containing compounds (+3.8 rel.%). At the moment, it seems that the identified compounds do not represent an acute toxic risk from an environmental viewpoint. However, N-containing compounds could raise concerns and further attention is needed to be focused on them. In progress, the study could be developed by the appraisal of the influence of different extractants, i.e. acidic leaching liquor, alkaline leaching solution and other experimental parameters (liquor: solid ratio, pH, temperature, time, etc.) on the yields and compositions of leachates.
Acknowledgements
ACCEPTED MANUSCRIPT The study was performed in the frame of FWO-Belgium and BAS-Bulgaria collaboration. The financial support of the National Scientific Fund, Ministry of Education and Science, Bulgaria under Project DN 04/5 is highly acknowledged. REFERENCES
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Fig.1. Scheme of leachable preparation and analyses
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Fig.2. Leachables curves tracked by conductivity and pH. (Values measured for the 5and 6 weeks have overlapped)
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Fig. 3. XPS spectra C 1s, N 1s and S 2p deconvolution included the Maritsa East and Stanjanci leachables.
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3410
0.3
1143
1622
3548 0.2
Stanjanci 1407 670 603 470
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1142 1.0
Maritsa-East
3408 3545 0.5
670 603
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Absorbance units
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1686 0.0
3000
2500 2000 -1 Wavenumber, cm
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Fig. 4. FTIR spectra of leachables
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Fig. 5. GC-MS separation of acetone extract of Maritsa East leachables
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Fig. 6. Sterols in GC-MS separations of Maritsa East (ME) and Stanjanci (Stan) leachables
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50 45 40 35 30 % 25 20 15 10 5 0
Fig.7. Distribution of compounds in AP-TPR flue gases of leachables, in rel. %
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(grey – Maritsa East; black – Stanjanci)
Abbreviations: AlkBz - alkyl benzenes; PAH - polycyclic aromatic hydrocarbons;
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Sesqui-T - sesqui terpenoids; S-containing – sulphur-containing compounds;
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N-containing - nitrogen-containing compounds;
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Table 1. Ultimate (ad) and proximate analyses of leachable fractions, in wt.% Proximate analysis Fraction
Stanjanci
Ash
VM
Cfix
C
H
N
“Front”
21.62
70.26
6.85
1.27
1.22
2.79
0.15 14.38
11.2
“Tail”
15.93
35.93
43.44
4.7
10.91 3.10
0.39
6.76
42.91
“Front”
19.92
63.09
11.1
5.89
7.11
0.27
9.08
17.65
“Tail”
11.45
32.82
31.67
24.06
28.86 3.58
1.24
2.20
31.30
2.80
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ad-air dried; W-moisture; VM—volatile matter; Cfix—fixed carbon; Odiff=100%-(∑(C+H+N+S)+Ash
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Maritsa-East
Ultimate analysis
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Lignite
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Table 2. Distribution of carbon, nitrogen and sulphur forms in leachables determined by XPS. Atomic %
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Maritsa 48.27 19.87 11.96 2.04 0.59 1.19 0.65 1.03 0 0.79 0 13.62
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284.6 286.3 288.4 292.3 398.4 400 402.3 163.3 164.1 165.5 168.4 169.1
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S 2p
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N 1s
Aromatic and aliphatic Single C-O, C-OH, C-N bond Carboxyl, ester π-π satellite N-pyridinic Pyrroles, pyridones, sec./tert. amines, imides N-quaternary, protonated amines, N-O Organic/inorganic sulphidic Thiophene Sulphoxide Sulphone Inorganic sulphate
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C 1s
Binding energies, (eV)
Functionality
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Elemental peak
Stanjanci 53.57 23.37 14.82 0.2 0.52 3.4 0.3 0.37 0.26 0.3 0.47 2.42
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Leachable ME Stan 10.59 tr.
n-Alkanes, nC21 -nC31 , (nC25 max) Fatty acids, i.e.
12.91 18.16 0.97
unsaturated nC18:ω9
0.88
dicarboxylic, nC7 -nC10
0.23
sterols, C27 - C30 , C29 max ketosterols, C 29 Industrial pollutants, i.e. phthalates
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Total, in μg/kg lignite
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stanols, C28 ,C29
1.02 1.52
3.95 6.89 1.53 10.00 2.93
4.63 0.96 n.d. 1.91 10.04
2.00
7.27
0.90
2.32
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n-Alcohols, , nC12 -nC26 (even), nC22 , nC24 max Aromatic acids Residues of saccharides Residues of lignins Steroids, i.e.
1.67
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i, ai C15 , C17
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10.83 13.95
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linear, nC12 -nC30 ,( nC16 max)
0.03 0.45 3.35 1.90 42.22 35.64
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Hydrocarbons Phenols Benzenes/Alkyl benzenes Methoxy phenols Furans PAHs Residue of saccharides Sesquiterpenoids S-containing compounds N-containing compounds Total, in µg Normalized in mg/kg lignite
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Leachable ME Stan 0 0.86 27.64 11.37 5.47 23.56 7.06 5.79 1.98 0.09 5.46 13.8 0.75 0.14 11.38 16.6 0.14 1.11 0 3.27 59.88 76.58 30.5 32.8
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Table 4. Compounds in flue gases of leachables reductive pyrolysis
ACCEPTED MANUSCRIPT Highlights Composition of organic components in Miocene/Pliocene lignite leachate was studied (85)
Based on conductivity two portions were prepared, enriched in salts or in organics (85)
XPS and FTIR evidences for variety of functional groups in organic rich portions (84)
GC-MS data for the presence of carboxyl containing compounds in acetone extracts (83)
Proves for PAHs and N-containing compounds in flue gases from reductive pyrolysis (85)
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Angelina Kosateva, Maya Stefanova, Stefan Marinov, Jan Czech, Robert Carleer, Jan Yperman PII: DOI: Reference:
S0166-5162(17)30524-4 doi:10.1016/j.coal.2017.10.005 COGEL 2904
To appear in:
International Journal of Coal Geology
Received date: Revised date: Accepted date:
29 June 2017 5 October 2017 5 October 2017
Please cite this article as: Angelina Kosateva, Maya Stefanova, Stefan Marinov, Jan Czech, Robert Carleer, Jan Yperman , Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Cogel(2017), doi:10.1016/j.coal.2017.10.005
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ACCEPTED MANUSCRIPT Characterization of organic components in leachables from Bulgarian lignites by spectroscopy, chromatography and reductive pyrolysis Angelina Kosateva1 , Maya Stefanova1 *, Stefan Marinov1 , Jan Czech2 , Robert Carleer2 , Jan Yperman2
Institute of Organic Chemistry with Centre of Phytochemistry,
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1
Belgium
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Research group of Applied and Analytical Chemistry, Hasselt University, B-3590 Diepenbeek,
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*corresponding author: [email protected]
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Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Abstract
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Lignites from Thrace- and Sofia- coal basins, i.e. “Maritsa-East” and “Stanjanci” mines, were subjected to aqueous sequential extraction at 25 0 C during 10 weeks. Each 7 days leachates were separated and pH and conductivity were measured. According to the extraction curves μS vs. time two portions were prepared, enriched in salts, extracts from the first two weeks (“head” of the elution) and in organic matter, extracts from the rest of time (“tail” of the elution curve). Combined freeze-dried extracts were characterized by yields, technical and elemental analyses. They were studied by X-ray photoelectron spectroscopy (XPS) and Infrared spectroscopy (IR). According to XPS spectra the main species on the leachate surfaces were carbon atoms in aromatic and aliphatic structures, 48-53 at. % from the total C1s signal. The intensive N 1s signal at 400 eV was assigned to pyrroles and amines (1-3 at. %). The most abundant sulphur form was inorganic sulphates while intensities for the other ones were < 1%. Respectively, the sulphatic sulphur content (13.6%) determined for Maritsa leachate was almost seven times higher than the same sulphur for Stanjanci leachate. FTIR spectra gave evidences for oxygen-containing functional groups, i.e. COOH groups in benzene carboxylic acids and their derivatives, in shortchain aliphatic fatty acids and for polyols. The appearance of mineral matter, mainly gypsum and kaolinite, made equivocal the IR spectra interpretation. Acetone soluble portions of “tail” leachates have represented relatively small parts of the organic matter (340 mg/kg Maritsa East and 80 mg/kg Stanjianci lignite) but have assigned reliable evidences for the polar constituents of leachates. Linear fatty acids, nC12 -nC32 , nC16 max , n-alcohols, benzoic acids, i.e. hydroxy-, methoxy-, phthalic acids, were highly abundant. Sterols, stanols, ketosterols were present in both extracts. Phthalates were recognizable as well. AP-TPR-TD-GC/MS technique has proved the presence of phenols, PAHs and heteroatom containing components in leachates flue gases. From an environmental viewpoint it seems that the identified compounds do not represent an acute toxic risk. However, N-containing compounds could raise concerns and further attention is needed to be focused on them. Keywords: lignite, aqueous leachate, organic components, environmental pollutants
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Introduction Bulgarian lignites are the main source for energy production in the thermal power plants of the country (www.fe.doe.gov). During their exploration, incineration and storage of waste products from mining and combustion, i.e. dumps, fly ashes and score, they create environmental problems (Vassilev and Vassileva, 2005, Stefanova et al. 2007, Meawad et al. 2010, Kostova et
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al. 2013). The main disadvantages of Bulgarian lignites are their low calorific value, high ash
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and moisture content and harmful emissions during combustion. One possibility for gradual
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reduction of lignites energy use and finding alternatives is the direct application of lignites in other areas of the economy, i.e. production of humic acids, adsorbents, soil conditioners, etc.
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At present, there is a little information, what and how much harmful to human health persistent organic compounds are leached from lignites, dumps and combustion waste materials by
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rainwater and during irrigation activities. Amounts of leached inorganic substances in dry residues from aqueous leachates of Maritsa East lignite, claystone partings and combustion
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wastes were recently evaluated (Yossifova et al. 2016), while organics therein were not studied. Organic components are of considerable environmental impact and care should be paid on their
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disposal and release in the nature because of the potential toxicity of the infiltrated substances. In Bulgarian legislation there is a regulation norm for the amounts of some organic industrial in
groundwaters,
i.e.
chlorinated
species,
PAHs,
phthalates,
pesticides,
etc.
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pollutants
(Regulation 8, 2004). In order to assess the potential impact of interactions between coal and
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water that might occur in soil systems during the agricultural application of lignite, during their storage in dumps or in the waste water during sorption treatment, it is necessary to have adequate
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information on the composition of lignite water-soluble fractions, the so called “water leachates”. Coals were suspected for many human health problems (Finkelman et al. 2002) and became an object of the new discipline - “medical geology” (Feder et al. 2002). Potential human health risk of organic compounds leached from coal included endocrine disruption, nephrotoxicity, and cancer. With a similar topic of study, to identify potential toxic or environmentally relevant organic compounds in the aquifers of the Amynteo hydrogeological basin, Northern Greece, and to assess a possible link of the identified organic contaminants with the parent lignites was the study of Iordanidis et al. (2012). Therein only anthropogenic pollutants were identified, no coalderived organic compounds were depicted.
ACCEPTED MANUSCRIPT Recently, Zhu et al. (2015) have performed systematic study on water-soluble organic compounds released from black shale and different rank coals, Ro, %=0.3-2.6 with Tmax = 409 o C - 602 °C. A steep decline of extracts yields with maturation and positive correlation with oxygen index OI were determined. Yields and fatty acids amounts, normalized to total organic carbon TOC, were comparable for coals and shales with the same maturity, but differences were depicted in the patterns of the constituent’s distributions. Acetates and formates were the main
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acids in the extracts, accompanied by some low molecular carboxylic and dicarboxylic acids.
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Nowadays, the importance of water-soluble organic components studies gradually increases as it
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is firmly related to PAHs determination in coal leachates (McElmurry and Voice, 2004), as well as to the disposal of produced waters from gas extraction in coal and shale from coalbed methane
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production and from shale hydraulic fracturing (Orem et al. 2014).
The objective of the present study is characterization by chemical, spectral and pyrolytic
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methods of aqueous leachates from two Bulgarian lignites. On the base of the data an attempt for appraisal of environmentally relevant organic compounds in aqueous leachates that could be
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regarded as potential organic pollutants in groundwater will be done. II. Experimental
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II.1. Lignite samples, aqueous leachate preparation and fractionation. Lignites from two coal basins, Thrace- and Sofia-, i.e. Maritsa East (ME) of Early-Middle
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Miocene and Stanjanci (Stan) mines of the Pliocene-Late Miocene geological age, were under study (Šiškov, 1997; Šiškov and Andreev, 1987). ME lignites were characterized by Ro - 0.20 %,
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Wr -64.4 %, Ad - 39.7 %, Cdaf - 65.0 % , VMdaf - 55.8 %, Q daf - 22.3 MJ/kg and the following maceral composition H - 61 %; L - 2 %; I - 1 % and M - 36 %. Stan lignites cover the area of
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Western Bulgaria, between the Balkan and Sredna Gora Mountains. Coal formation lasted till the beginning of the Pliocene. Stan lignite characteristics were: Ro - 0.12 %, Wr - 52.5 %, Ad - 21.9 %, Cdaf - 61.6 %, VMdaf - 61.0 %, Q daf - 19.42 MJ/kg and maceral composition H -74 %, L - 8 %, I - 5 %, M -13 %. Two lignite samples, one from ME and one from Stan lignites, respectively, were grounded to < 0.2 mm and subjected to sequential extraction by distilled water at 25 0 C during 10 weeks. For quality assurance duplicate aqueous extractions under experimental condition were performed. Experimental scheme is illustrated in Fig.1. It was partly adopted from the study of Doskočil et al. (2014) of water-extractable fractions from South Moravian lignite. Briefly, 10 g of lignite
ACCEPTED MANUSCRIPT samples and 150 ml of distilled water were placed into a 200 ml Erlenmeyer flask. The slurry was regularly agitated by magnetic stirrer. Each 7 days, the aqueous extracts were separated from lignite by centrifugation for 10 min at 4000 rpm at 25 0 C. Subsequently, the supernatants were filtered to remove the finest particles possibly penetrated during manipulations. Likewise leachates were isolated and ten aqueous extracts were prepared. Their pH and conductivity were measured and changes with time were illustrated in Fig. 2. According to the conductivity, two
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portions were prepared: - with higher conductivity (“head” of the extraction curve, extracts from
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the first two weeks); - and, with lower conductivity for the “tail” of the curve (Fig. 2).
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Respectively, the total leachate from each one lignite was divided into two portions, “head” and “tail”. They were freeze-dried and kept in refrigerator. Dried leachates were light and
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voluminous. Due to the higher organic content for the “tail” leachates (Table 1) they were further
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studied by chemical, spectral and pyrolytic methods.
II.2. Isolation of acetone soluble (AS) components
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For isolation of material soluble in organic solvents, “tail” freeze-dried leachate portions were refluxed for half an hour with acetone (3x50ml). Acetone solubles (ASs) were combined, dried
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over CaSO 4 , filtrated, concentrated at reduced pressure, silylated and studied by GC-MS.
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II.3. Reductive pyrolysis
Residues after acetone extraction of “tail” leachates were studied by reductive pyrolysis (Fig.1).
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Atmosphere Pressure – Temperature Programmed Reduction (AP-TPR) coupled “off-line” with thermal desorption gas chromatography-mass spectrometry (TD-GC/MS) was used to specify
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volatile organic components in coal and its derivatives (Yperman et al. 1999, Gonsalvesh et al. 2013 and references therein). For reductive pyrolysis ca: 40 mg of sample and 20 mg of fumed silica were placed in the quartz reactor under a 100 ml/min flow of pure H2 . A linear temperature program of 5 °C min-1 from ambient temperature up to 950 °C was applied. The apparatus was adapted to trap volatiles for subsequent GC-MS analysis. The outlet of the AP-TPR reactor is connected to a set of two ice-cooled tubes containing Tenax (Sigma-Aldrich), a porous polymer of 2,6-diphenyl-p-phenylene oxide, as adsorbent. Volatiles were additionally diluted by adding inert gas to the H2 flow in a 5:1 (v/v) ratio in order to prevent break through the adsorption tube. Volatiles were trapped in two separated temperature ranges using two separate adsorption tubes:
ACCEPTED MANUSCRIPT 250o C - 550o C (tube 1) and 550o C - 950o C (tube 2). Later on, adsorption tubes were subsequently desorbed and analyzed by thermal desorption-gas chromatography/mass spectrometry (TDGC/MS) using He as carrier gas at 85 kPa and the following conditions: a) Unity thermal desorber (Marks): primary desorption 20 min at 275ºC; Cold trap at – 10ºC, heated at maximum heating rate up to 320ºC, hold time 15 min; flow path temperature 200ºC; b) Trace GC Ultra-Gas chromatography (Thermo Instruments): capillary column 30m ZB 5-MS x 0.25 mm x 0.25 µm
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Phenomenex; temperature program: 3 min at 30ºC, 30ºC-100ºC (8 ºC/min), 100 ºC-310 ºC (12
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ºC/min), hold time 5 min at 310 °C; c) DSQ-Mass spectrometer (Thermo Instruments): EI
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spectra; Ionization energy: 70 eV; Scan range: m/z 33 - 480 in 0.4s. Deuterated thiophene, Th-d4 , 3 μg, was used as a standard. NIST library spectra were used for peak identification.
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II.4. Instrumental techniques used for aqueous leachates characterization Leachates were analyzed and characterized by yield (wt. %), proximate, ultimate analyses and by
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a set of analytical techniques, i.e. XPS and IR spectroscopy, GC-MS and pyrolysis. Proximate analysis, i.e. moisture (W), volatile matter (VM), fixed carbon (C fix ) and ashes, were determined
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by thermogravimetrical analyser using DuPont Instrument 951. For determination of elemental composition, i.e. C, H, N and S, was used a Thermo Electron Flash EA1113 elemental analyzer
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according to Warne method (Warne, 1991).
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II.4.1. Analytical techniques, i.e. X-ray photoelectron spectroscopy (XPS) and Infrared spectroscopy (IR)
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The XPS measurements were carried out in the analysis chamber of the electron spectrometer ESCALAB-MkII (VG Scientific) at a base pressure of 5x10 -8 Pa. The spectra were excited with
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an Mg-K α radiation at instrumental resolution of ≈ 0.9 eV. The base C 1s line had a binding energy of 284.6 +/- 0.1 eV and no charge effects were observed. The acquisition time for C 1s, N 1s and S 2p spectra were in the interval 30 ~ 5 min. The FTIR spectra were recorded on dried spectrometry grade KBr pellets using a Tensor 27 Spectrophotometer in the range 4000–400 cm–1 within a 2 cm-1 resolution. On each sample 256 scans were accumulated.
II.4.2. GC-MS analyses of acetone extract of leachate
ACCEPTED MANUSCRIPT GC-MS analyses was carried out on a Hewlett-Packard 6890 GC system plus HP 5973 MSD equipped with a HP-5 MS column (0.25mm×30m×0.25μ film thickness) with flame ionization detector (300o C). A split/splitless capillary injector (300o C) is used in the splitless mode (valve reopened 1 min after injection). After 0.5 min isothermal period at 85 o C the oven temperature was increased to 200o C at 20o C/min and then to 320o C at 5o C/min. The MSD was operated in the electron impact (EI) mode with energy of 70 eV and scan range from 50 to 650 Daltons. AS were
converted
to
trimethylsilyl
derivatives
by
reaction
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extracts
with
N,O-bis-
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(trimethylsilyl)trifluoroacetamide (BSTFA) and pyridine in sealed vials for 3h at 70°C. The MS data were acquired and processed with the HP software. Individual compounds were determined by comparison of mass spectra (MS) with literature and library data, comparison of
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MS and GC retention times with those of authentic standards or interpretation of mass spectra. For MS tracking Xcalibur software was used. MS were quantitatively interpreted by internal
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standard application, deuterated nC24 . Amounts were normalized in μg/kg coal. The following specific fragments were tracked (some were silylated derivatives): m/z 57 - for n-alkanes, m/z
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117 – for n-fatty acid, m/z 75 – for n-alcohols, m/z 129 – for sterols, m/z 215 – for stanols, m/z
III. Results and discussion
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174 –for ketosterols, and m/z 204 – for mono saccharides.
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III.1 Yields and bulk characteristics
Leachates conductivity (2000-4000 μS, Fig. 2) has proved that extracts from the first two weeks
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(“head” portions) were characterized by high amount of salts, 60-70% ash (Table 1). Data were in accordance with results for leaching of South Moravian lignites where leachates conductivity
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from the first weeks was very high (Doskočil et al. 2014). Based on conductivity measured in our experiments and literature data, only leachate portions relatively enriched in TOCs and with lower ash content were further studied. Respectively, leachates from the third to tenth weeks (“tail” portions) were combined, freeze-dried and analyzed by instrumental and spectral methods as shows in Fig.1. In Table 1 were present yields of leachates, in %. Data were recalculated on “dry, ash free basis” and amounts of organic matter in leachates, in % daf, were obtained. Leachates acetone extractability was 340 mg/kg for ME lignite and 80 mg/kg for Stan lignite. Data for elemental analyses have confirmed the observation done on the base of conductivity: - “head” portions were highly enriched in ash, 63-70% gradually reduced to 32-
ACCEPTED MANUSCRIPT 35% in “tail” portions; - the tendency has mimicked VM amounts; - “tail” portion were partly enriched in C, H and O comparing to their counterparts of “head” portions; - sustainable decrease in S content for “tail” fraction was depicted. III. 2. Spectral analyses X-ray photoelectron spectroscopy (XPS) was used to receive qualitative information for C, N and S compounds on the surface of freeze-dried lignite water-extractable fractions. In order to
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provide a general picture of the distribution of several functional groups on the surface of the
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sample, curve-fitting method of the XPS spectra was applied. Chemical structural assignments of
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each component were made taking into account the binding energies reported for C, N and S functional groups (Marinov et al. 2004, Lorenc-Grabowska et al. 2013, Doskočil etal. 2014). The
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XPS data of organic functional oxygen atoms were not presented because the general oxygen signal of samples under study was due to predominantly of Si, Al, Ca, Mg, Na and other
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inorganic oxides. The XPS signal of organic oxides was negligible, almost compared to a signal from the inorganic oxides.
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XPS C1s spectra obtained by a deconvolution procedure of the Maritsa-East and Stanjanci portions were presented in Fig .3. For both samples four different structural groups of the organic
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carbon atoms with binding energies occurred at 284.6, 286.3, 288.4 and 292.3 eV were registered (Table 2). They were assigned as follow:
the 284.6 eV peak represented the contribution from aromatic and aliphatic carbon
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(i)
(C-C, C=C, C-H);
the carbon bound by a single bond to oxygen (i.e., C-O, C-OH, etc.) and to nitrogen
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(ii)
or sulphur (C-N, C-S) corresponded to signal at 286.3 eV; the 288.4 eV peak concerned mainly carbon bound by three bonds to oxygen as in
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(iii)
carboxyl and ester functional groups; (iv)
shake-up satellite peak at 292.3 eV was attributed to π-π transitions in aromatic rings (Kelemen and Kwiatek, 1995).
III.2.1. Organic carbon containing compounds According to the XPS spectra illustrated in Fig. 3 carbon atoms in aromatic and aliphatic structures were the main surface species in the both leachates with contribution of 48-53 at. % from the total C1s signal. Carbon atoms in carboxylic and ester groups were in subordinary
ACCEPTED MANUSCRIPT amounts, 11-14 at. % (Table 2). The lowest C1s signal was measured for π-π satellite peak, < 2 at. %. III.2.2. Organic nitrogen containing compounds Based on N 1s spectrum the organic nitrogen species were mainly assigned as pyrrolic nitrogen and amines, followed by quaternary and pyridine nitrogen (Fig.3). The peak at 398.4 eV was assigned to N in pyridine, while the peaks at 400 eV and 402.3 eV, respectively to nitrogen
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in pyrroles, pyridones, secondary and tertiary amines, imides, protonated amines, N-quaternary atoms and oxidized nitrogen (N-O) (Kelement et al. 1994, Pels et al. 1995, Cagniant et al. 1998,
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Straka et al. 2000, Xiao et al. 2005, Doskočil et al. 2014). In samples under study the most intensive N 1s signal was for pyrroles and amines at 400 eV (1-3 at. %) (Table 2). Amino
(Finkelman et al. 2002).
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III.2.3. Organic sulphur containing species
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containing functional groups were also determined in the aqueous leachate from lignite
The XPS signal of a sulphur single species was composed by two representing 2 p 3/2 and 2 p1/2
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components having a 2:1 relative intensity ratio and separated in energy by 1.2 eV. For each sulphur species a peak synthesis for S 2p by mixed Gaussian and Lorentzian line shapes was
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performed with full width at half maximum of 2.60 eV. XPS spectra obtained by a deconvolution procedure were shown in Fig. 3. The assignments of sulphur forms were based on references and
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previous studies (Kelemen et al. 1990, Gorbaty et al. 1990, Marinov et al. 2004, Doskočil et al. 2014). The relative atomic concentrations in XPS spectra were determined using peak values
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fixed at 163.3, 164.1, 165.5, 168.4, and 169.1 eV of binding energies for inorganic (pyritic) and organic sulphidic, thiophenic, sulphoxidic, sulphonic and sulphatic sulphur forms, respectively.
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The most abundant sulphur form was for inorganic sulphates while the other ones were ≤ 1%. In this respect for Maritsa East leachate sulphatic sulphur content of 13.6% was almost seven times higher than for Stanjanci leachate. This peculiariry could be explained by the higher sulphur content of parent Maritsa-East lignite (Marinov et al. 2004, Gonsalvesh et al. 2013). III.2.4 FTIR spectra A comparison of the FTIR spectra for the wave number region 4000 to 400 cm−1 for the leachates of lignites samples was shown in Fig. 4. Gypsum was revealed by the bands at 3543 cm-1 , 671 cm-1 and 603 cm-1 (Painter et al. 1978). Kaolinite was related to bands at 534 cm-1 and 470 cm-1 (Iordanidis et al. 2012). The FTIR spectra of the fractions have shown absorbance in
ACCEPTED MANUSCRIPT the region of 4000-3000 cm−1 due to vibrations of OH groups (H-bonded). The sharp intense bands at 2920 cm-1 and 2850 cm−1 have represented the valency oscillations of -CH3 and -CH2 aliphatic groups and that at 1622 cm−1 have corresponded to aromatic C=C structure. Bending vibrations of phenols OH groups were observed at 1384 cm–1 . The vibrational frequencies of oxygen in C-O-R structure were spread from 1143 cm-1 to 1016 cm−1 . III.3. Composition of acetone soluble (AS) extracts
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XPS and FTIR spectra have denoted the presence of a variety of functional groups for
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aqueous leachates under study. Information for the compositions at a molecular level was
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received by GC-MS study of AS extracts. Generally, ASs have represented relatively small portions of leachates (80-340 mg/kg lignite) but have depicted reliable evidences for the polar
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constituents. There were certain similarities in AS extracts compositions, i.e. predominance of linear fatty acids, comparable amounts of alcohols and considerable phthalates presence, as well
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as differences, i.e. traces of hydrocarbons and rests of saccharides for Stanjanci leachates and appreciable amounts of aromatic acids and rests of lignins for Maritsa East leachates (Fig. 5,
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Table 3). For both AS extracts a particularity in molecular compositions was the high amount of steroid structures, especially for Stanjanci leachates, 10.03 µg/kg coal, with well-expressed
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doublets for sterols/stanols counterparts (Fig, 6). Sterols, stanols and ketosterols were described in previous study on polar constituents of Bulgarian lignites (Stefanova et al. 2016b). The ratio
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5α(H)-stanol/Δ5 sterol (stanol/sterol ratio), was calculated as the ratio of the amounts of stigmastanol/sitosterol (Fig. 6). Magnitudes of ~ 1 were calculated for Maritsa East leachates and
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> 1 for Stanjanci leachates. The higher value indicated an enhanced microbial reduction of organic matter under reducing (anoxic) conditions in the Stanjanci leachates palaeomire. By GC-
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MS in both leachates were determined 24-n-Pr-sterols, C29 M+396 and C30 , M+410 (Fig. 6). The distribution of n-alkanoic (fatty) acids in Bulgarian lignites generally has shown a maximum at the ubiquitous nC16 homologue. In AS extracts n-fatty acids ranged from nC12 to nC32 , with the “even” numbered homologues being dominant. Shorter homologues have strongly prevailed fatty acids distribution signature and attested predominant aquatic origin for the parent material. For both leachates distributions with two maxima, centered at nC16 and subordinated at nC22 , nC24 , with a strong dominance of the shorter homologues, were determined.
ACCEPTED MANUSCRIPT Long chain “even” carbon numbered n-alkanols ranging from nC22 to nC28 (Cmax at nC22 , nC24 ) were identified in both leachates. The distribution signature was broader for Maritsa East leachate where the span has covered the interval nC12 -nC28 . Concerning linear lipid structures in AS extracts, a considerable amount of n-alkanes, 10.58µg/kg lignite was characteristic for Maritsa East leachates while only traces for Stanjanci
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leachates were determined (Table 3). In addition, n-alkanes distribution for Maritsa East
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leachates was differed from the parent lignite. Namely, it was like a “bell” centered at nC25 ,
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without “odd” numbered homologues recognizable predominance, all reflecting in CPI 1.09. For Maritsa East parent lignite was published a prevalence of long-chain members (> nC27 , maximizing at nC27 and nC29 ), with a marked ”odd” over “even” predominance and CPI in the
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range 2.8-4.2 (Bechtel et al. 2005). The mid-chain n-alkanes (nC21 -nC25 with an assigned origin from aquatic macrophytes) were pointed as a possible source for n-alkanes with “bell”
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distribution signature. Actually, high amounts of nC21 -nC25 were determined ibidem and an assumption for the higher contribution of macrophytes to parent vegetation comparing to the
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vascular plants has been done. This view was supported by our data, specifically, by leachate nalkanes distribution with Paq = 0.75 ratio, falling in the range for submerged/floating
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macrophytes (Ficken et al. 2000).
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Aromatic acids, i.e. m-, p- hydroxy benzoic, o-phthalic, t-phthalic acids, as well as marks for a survived gymnosperm lignin, i.e. 3-methoxy, 4-hydroxy benzoic acid, dehydroabietic acid,
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were highly abundant in AS extracts of Maritsa East leachate (Table 3). Due to the parent lignites low maturity, Ro ~ 0.20 (Šiškov, 1997), products of East
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carbohydrates diagenetic transformation were recognizable in AS extracts. By m/z 204 in Maritsa leachate
some
mono
saccharides derived
from hemicellulose,
i.e.
D-xylose,
D-
xylopyranose, D-arabinose, and by m/z 217 - D-xylofuranose and arabinofuranose, were depicted. These compounds have denoted that some small portions of carbohydrates have been incorporated in the Miocene-aged lignites and became extractable in aqueous media. In both AS extracts were determined appreciable amounts of phthalates (Table 3). They are ubiquitous pollutant of our civilization. In Bulgarian legislation there is a norm for their amount in groundwaters and they are under surveillance, Regulation 8 (2004). According to Maharaj et
ACCEPTED MANUSCRIPT al. (2014) the phthalate esters represent contamination of the coal prior to processing in the laboratory. Only in AS extract of Stanjanci leachate there were some tentative MS indications for the presence of alkaloids, i.e. 2-ethyl-acridone, M+223, C15 H13 NO (0.4μg/kg Stanjanci lignite) and harmol, M+198, C12 H10 N2 O (2.5 µg/kg Stanjanci lignite). Harmol is abundant in seeds of Peganum harmala, a widespread species growing wild and used as an antiheamoroidal,
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helmicide, and central nervous system stimulating agent in folk medicine (Kartal et al. 2003). It
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is toxic β-carboline indoleamine alkaloid amounting up to 2.5 μg/kg Stanjanci lignite. The
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problem with alkaloids in groundwaters is not in their absolute concentrations therein but in the
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long term exposure to their harmful action with deleterious effect on the human health.
III.4. Reductive pyrolysis
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Pyrolysis gas chromatography/mass spectrometry (Pyr-GC/MS) is an effective approach in the study of coal organic matter using thermal degradation for bonds cleavage and enables a
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sensitive and rapid characterization of organic constituents. It aids the molecular characterization of microbial and plant-derived biomass and generates valuable data on the degradation and
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conservation rates of organic debris. Pyrolysis of aqueous leachate organic matter has started at 250°C. In pyrograms two distinct and separated maxima were distinguished. Leachates
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pyrograms were shown in Supplementary Material [SM]. Volatiles in flue gases were trapped in two temperature intervals - “low”, 250o C-550o C and “high”, 550o C -950o C. Compounds were
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identified by TD-GC/MS, quantified, normalized to mg/kg parent lignite and data were shown in Table 4. Ten series of compounds were tracked and following compounds were identified:
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aliphatics, i.e. nC6 ÷nC14 , mono unsaturated/ saturated pairs, benzene, alkylated benzenes, styrenes, naphthalenes, biphenyls, fluorene, acenaphthylene; oxygen containing compounds, i.e. phenols, methoxy phenols, furans, benzofurans; sulphur containing compounds, i.e. sulphides, thiophenes,
benzothiophenes;
nitrogen
containing
compounds,
i.e.
pyrroles,
pyridine,
benzonitrile, etc. Considerable amount of sesquiterpenoids was identified in both leachates, ~ 20 rel.%. These biomarkers for conifer vegetation were already characterized in lignites chloroform bitumens, humic acids and in AP-TPR pyrolysates of Maritsa East lithotypes and Stanjanci lignites (Stefanova et al. 2002, 2005, 2016, 2016a). There was a variety of unsaturated/saturated sesquiterpenoids but the most abundant were longifolene/isolongifolene (M+ 204, m/z 95, 100%),
ACCEPTED MANUSCRIPT α-cedrene (M+ 204, m/z 119, 100%); cuparene (M+ 202, m/z 132, 100%), cadalene (M+ 198, m/z 183, 100%), etc. In the high temperature regions of the pyrograms elemental sulphur was recognizable as well. Distributions of tracked series, present in pyrolysates flue gases were illustrated in Fig.7, were amounts were expressed in rel. %. Alkyl benzenes, i.e. C 6 - C10 , were the main compounds in the Stanjanci leachate
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pyrograms (30.8 rel.%, Fig. 7). In the low temperature region the distribution was dominated by
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toluene, while benzene has predominated in the flue gases in the high temperature range (SM 3).
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There was a considerable decrease by14 rel.% in the amount of alkylbenzenes comparing to the pyrolysate of the parent Stanjanci lignites (Stefanova et al, 2016a). Alkylbenzenes were considered as a product of humification of the primary plant materials and microbial metabolites.
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The highest amount of phenols, a half of the total volatiles, 46.2 rel.%, Fig. 7, was measured for pyrolysate of Maritsa East leachate, while no change in phenols for Stanjanci
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leachates comparing to the initial lignite was recognized. With the additional amount of 11.8 rel.% of methoxy phenols for Maritsa East leachate the amount of phenols/methoxy phenols has
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increased to the enviable 58 rel.%. The presence of phenol and its derivatives in groundwaters could be a serious threat to human health, toxic even at low concentrations.
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In pyrolysate of Maritsa East leachate considerable of amount furans, with furfural the most abundant compound in the high temperature pyrogram was identified (SM 2). Actually
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furans and furaldehydes were considered as typical products for carbohydrates pyrolysis. The cellulose in lignite may survive for millions of years if has been deposited under favorable
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palaeoenvironmen (Fabbri et al. 2008). One possible way for cellulose preservation is its incorporated by sulphur bridges in coal organic matter. In a suite of studies devoted to the
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determination of organic sulphur forms in Maritsa East lignites by AP-TPR pyrolysis were able to determined high amounts of dimethyl di- and trisulphids (Gonsalvesh et al. 2013), which a proof for a possible way of preservation of certain molecules in bound form during diagenetic transformation of coal precursors. In the pyrolysate flue gases of both leachates significant amounts of polycyclic aromatic hydrocarbons (PAHs) were determined. Inasmuch as only data for PAHs in parent Stanjanci lignite were available (Stefanova et al. 2016a) an increase by10 rel.% for this leachate was appraised. In the national legislation there are limits for the amounts of 2-3 cyclic PAHs in
ACCEPTED MANUSCRIPT surface/underground waters, i.e. for acenaphthene, acenaphthylene, fluorine, phenanthrene. In general, amount of PAHs in Stanjanci pyrolysates was 2-3 folds higher than the amount in Maritsa East leachate (Table 4). The threat for human health is not in the absolute sum of PAHs but in their signature. According to the PAH position paper of EC 2-3 ring PAHs are not priority environmental pollutants and their TEFEPA values are negligible in comparison to benz[a]pyrene equivalent carcinogenic power (Cecinato, 1997). PAHs distribution signatures for both leachate
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samples [SM] were dominated by naphthalene and its methylated homologues and the danger of
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considerable pollution seems insignificant as for naphthalene was determined a negligible
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TEFEPA value. However, it should be taken into consideration that in geology the time scale is different and during the long exposure to PAHs infiltration the risk might become noteworthy.
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Other identified compounds in pyrolysates with potential ecological concern were Ncontaining species. By AP-TPR in leachate of Stanjanci lignites was registered their increase by
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3.8 rel.% in comparison with the reductive pyrolysis of the parent lignite (Stefanova et al. 2016a). Systematically in flue gases of products from Stanjanci lignites were estimated high
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amounts of pyrroles, pyridines, quinolones, etc., i.e. in bitumens, humic acids and the data should not be regarded as random. In addition, exactly in AS of Stanjanci lignites were tentative GC-MS
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indications for alkaloids and XPS spectra gave evidences for N-containing compounds (Table 2, Fig.3). Therefore, the hints for their presence in Stanjanci aqueous leachates should not be
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ignored. For information, one launched assumption for the Balkan Endemic Nephropathy (BEN), a disease lethal, is the presence of aristolochic acid, C 17 H11 NO 7 , M+ 341in the groundwater and long
consumption,
regardless
at
low
concentration
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its
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(https://en.wikipedia.org/wiki/Aristolochic_acid).
In different laboratories with the aim to simulate groundwater leaching of Pliocene lignites samples were extracted with distilled water (Orem et al. 1999, Maharaj et al. 2014, Doskočil et al. 2014) and instrumental techniques were used for structural elucidation of aqueous extracts.
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C NMR spectra of the leachates have determined high degree of condensed aromatic
character consistent with polycyclic aromatic structures. Of special concern were lignites from BEN endemic regions, where using GC/MS well water samples were analyzed for dissolved aromatic compounds (Orem et al. 1999). Fourteen compounds at the low concentration level were identified. With the exception of phenol, all the identified compounds were PAHs, some of
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human carcinogens. MS separations of the Pliocene lignite extracts were
characterized by aromatic hydrocarbons mainly in the benzene and naphthalene category, rich in functional groups: methoxy, acetyl, keto, hydroxy. It was assumed that some of these compounds could
be
nephrotoxic/carcinogenic.
In
conclusion
the
authors
have
pointed
out
that
functionalized compounds were sufficiently hydrophilic to be leached into the groundwater. Other compounds identified in the Pliocene lignite extract were terpanes and steranes as well as derivatives. These compounds might have been generated by fungi
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their functionalized
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degradation of the precursor organic matter. They have revealed the immature state of the coal,
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where in many ways the fossil wood could be macroscopically recognized (Feder et al. 2002). In our study by AS extraction we were able to isolate and identified variety of streroids (Fig. 6),
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functionalized by carbonyl or hydroxyl groups, making them enough polar to become soluble in water. Data for their effect on human health are missing, or could become a subject of the new
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discipline “medical geology” (Maharaj et al. 2014), as coal “human health” impact may be in part due to mobilization of organic components from coal organic matter.
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Doskocil et al. (2014) have improved the protocol for analyses of lignite water-soluble component by applying fractionation and pyrolytic technique in view to receive as much as
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possible information for aqueous leachates. In products of TMAH thermochemolysis of South Moravian lignite leachate the most abundant were methyl esters of 3,4-dimethoxy-3,4,5-
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trimethoxy- and 4-methoxybenzoic acids. There were low amounts of methoxy benzenes as well. Fatty acids, as methyl ester, were identified in minor portion among thermochemolysis products
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and they consisted of short chain nC14 and nC16 . Actually, in our study were identified the same series of organic compounds. Our separation scheme, very simple, gave us ground to isolate,
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identify and quantify more components, some of them potential pollutants or of human health impact. There was a good coherence of our data with the published on the topic. Present results have confirmed and enriched the knowledge on the aqueous leachate composition and have proposed the presence of some heteroatom containing compounds. In the present study were depicted the main differences in the compositions of flue gases from pyrolysis of Stanjanci lignite itself (Stefanova et al. 2016a) and its aqueous leachate. The following peculiarities were determined: leachate volatiles were characterized by a strong decrease in the amounts of hydrocarbons (-20.6 rel.%) and alkyl benzenes (-14 rel.%) and an increase in the amounts of PAHs (+10 rel.%) and N-containing compounds (+3.8 rel.%).
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CONCLUSIONS The present study could be regarded as a first attempt to assess the mobile contaminants in some Bulgarian lignites aqueous leachates. Although a very simplified separation procedure based on conductivity was applied some fractionation has been achieved. Portions relatively enriched in C, H, N and O were isolated and characterized by spectral methods. The sulphur in
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leachates the most likely was of pyrite type and concentrated in the “head” portions, with high
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ash content, 60-70%. Fractions relatively enriched in organic matter, “tail” portions, were
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characterized by chromatographic and spectral methods and the following information was obtained:
XPS and FTIR spectra have attested a great variety of functional group on the surface of
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aqueous leachates;
GC-MS study of acetone extracts has supplied data for the individual compositions at a
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molecular level. Extracts, although representing small portions of leachates (340 mg/kg
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Maritsa East lignite and 80 mg/kg Stanjianci lignite), gave reliable evidences for the polar constituents, i.e. fatty acids, alcohols, sterols, saccharides, etc. There were tentative
-
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MS indications for alkaloids in Stanjanci extract. AP-TPR-TD-GC/MS technique gave unequivocal evidences for the presence of PAHs
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and heteroatom containing components in leachates flue gases. The main differences in the compositions of flue gases from reductive pyrolysis of Stanjanci lignite and leachate
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were depicted: leachate volatiles were characterized by a strong decrease in the amounts of hydrocarbons (-20.6 rel.%) and alkyl benzenes (-14 rel.%) and an increase in the
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amounts of PAHs (+10 rel.%) and N-containing compounds (+3.8 rel.%). At the moment, it seems that the identified compounds do not represent an acute toxic risk from an environmental viewpoint. However, N-containing compounds could raise concerns and further attention is needed to be focused on them. In progress, the study could be developed by the appraisal of the influence of different extractants, i.e. acidic leaching liquor, alkaline leaching solution and other experimental parameters (liquor: solid ratio, pH, temperature, time, etc.) on the yields and compositions of leachates.
Acknowledgements
ACCEPTED MANUSCRIPT The study was performed in the frame of FWO-Belgium and BAS-Bulgaria collaboration. The financial support of the National Scientific Fund, Ministry of Education and Science, Bulgaria under Project DN 04/5 is highly acknowledged. REFERENCES
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ACCEPTED MANUSCRIPT Yossifova, M., Dimitrova, D., Iliev, T. 2016. Maritsa East Lignite Basin, Bulgaria. Phase Composition of Dry Residues from Water Leachates of Coal. Comptes rendus de l'Académie bulgare des Sciences 69, 1611-1620. Yperman, J., Maes, I., Rul, H.V.D., S. Mullens, Aelst, J.V., Franco, D.V., Mullens, J., Poucke, L.C.V., 1999. Sulphur group analysis in solid matrices by atmospheric pressure-temperature programmed reduction. Analytica Chimica Acta 395, 143-155.
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Fig.1. Scheme of leachable preparation and analyses
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Fig.2. Leachables curves tracked by conductivity and pH. (Values measured for the 5and 6 weeks have overlapped)
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Fig. 3. XPS spectra C 1s, N 1s and S 2p deconvolution included the Maritsa East and Stanjanci leachables.
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3410
0.3
1143
1622
3548 0.2
Stanjanci 1407 670 603 470
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1142 1.0
Maritsa-East
3408 3545 0.5
670 603
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Absorbance units
0.1
1686 0.0
3000
2500 2000 -1 Wavenumber, cm
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Fig. 4. FTIR spectra of leachables
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4000
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470
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Fig. 5. GC-MS separation of acetone extract of Maritsa East leachables
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Fig. 6. Sterols in GC-MS separations of Maritsa East (ME) and Stanjanci (Stan) leachables
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50 45 40 35 30 % 25 20 15 10 5 0
Fig.7. Distribution of compounds in AP-TPR flue gases of leachables, in rel. %
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(grey – Maritsa East; black – Stanjanci)
Abbreviations: AlkBz - alkyl benzenes; PAH - polycyclic aromatic hydrocarbons;
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Sesqui-T - sesqui terpenoids; S-containing – sulphur-containing compounds;
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N-containing - nitrogen-containing compounds;
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Table 1. Ultimate (ad) and proximate analyses of leachable fractions, in wt.% Proximate analysis Fraction
Stanjanci
Ash
VM
Cfix
C
H
N
“Front”
21.62
70.26
6.85
1.27
1.22
2.79
0.15 14.38
11.2
“Tail”
15.93
35.93
43.44
4.7
10.91 3.10
0.39
6.76
42.91
“Front”
19.92
63.09
11.1
5.89
7.11
0.27
9.08
17.65
“Tail”
11.45
32.82
31.67
24.06
28.86 3.58
1.24
2.20
31.30
2.80
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ad-air dried; W-moisture; VM—volatile matter; Cfix—fixed carbon; Odiff=100%-(∑(C+H+N+S)+Ash
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Odiff
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Maritsa-East
Ultimate analysis
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Table 2. Distribution of carbon, nitrogen and sulphur forms in leachables determined by XPS. Atomic %
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Maritsa 48.27 19.87 11.96 2.04 0.59 1.19 0.65 1.03 0 0.79 0 13.62
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284.6 286.3 288.4 292.3 398.4 400 402.3 163.3 164.1 165.5 168.4 169.1
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S 2p
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N 1s
Aromatic and aliphatic Single C-O, C-OH, C-N bond Carboxyl, ester π-π satellite N-pyridinic Pyrroles, pyridones, sec./tert. amines, imides N-quaternary, protonated amines, N-O Organic/inorganic sulphidic Thiophene Sulphoxide Sulphone Inorganic sulphate
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C 1s
Binding energies, (eV)
Functionality
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Elemental peak
Stanjanci 53.57 23.37 14.82 0.2 0.52 3.4 0.3 0.37 0.26 0.3 0.47 2.42
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Leachable ME Stan 10.59 tr.
n-Alkanes, nC21 -nC31 , (nC25 max) Fatty acids, i.e.
12.91 18.16 0.97
unsaturated nC18:ω9
0.88
dicarboxylic, nC7 -nC10
0.23
sterols, C27 - C30 , C29 max ketosterols, C 29 Industrial pollutants, i.e. phthalates
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Total, in μg/kg lignite
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stanols, C28 ,C29
1.02 1.52
3.95 6.89 1.53 10.00 2.93
4.63 0.96 n.d. 1.91 10.04
2.00
7.27
0.90
2.32
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n-Alcohols, , nC12 -nC26 (even), nC22 , nC24 max Aromatic acids Residues of saccharides Residues of lignins Steroids, i.e.
1.67
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i, ai C15 , C17
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10.83 13.95
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linear, nC12 -nC30 ,( nC16 max)
0.03 0.45 3.35 1.90 42.22 35.64
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Hydrocarbons Phenols Benzenes/Alkyl benzenes Methoxy phenols Furans PAHs Residue of saccharides Sesquiterpenoids S-containing compounds N-containing compounds Total, in µg Normalized in mg/kg lignite
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Leachable ME Stan 0 0.86 27.64 11.37 5.47 23.56 7.06 5.79 1.98 0.09 5.46 13.8 0.75 0.14 11.38 16.6 0.14 1.11 0 3.27 59.88 76.58 30.5 32.8
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Table 4. Compounds in flue gases of leachables reductive pyrolysis
ACCEPTED MANUSCRIPT Highlights Composition of organic components in Miocene/Pliocene lignite leachate was studied (85)
Based on conductivity two portions were prepared, enriched in salts or in organics (85)
XPS and FTIR evidences for variety of functional groups in organic rich portions (84)
GC-MS data for the presence of carboxyl containing compounds in acetone extracts (83)
Proves for PAHs and N-containing compounds in flue gases from reductive pyrolysis (85)
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