Article
Mineralogical and Geochemical Compositions of the No. 5 Coal in Chuancaogedan Mine, Junger Coalfield, China Ning Yang, Shuheng Tang *, Songhang Zhang and Yunyun Chen Received: 21 September 2015; Accepted: 17 November 2015; Published: 25 November 2015 Academic Editor: Shifeng Dai School of Energy Resources, China University of Geosciences, Beijing 100083, China;
[email protected] (N.Y.);
[email protected] (S.Z.);
[email protected] (Y.C.) * Correspondence:
[email protected]; Tel./Fax: +86-10-8232-2005
Abstract: This paper reports the mineralogy and geochemistry of the Early Permian No. 5 coal from the Chuancaogedan Mine, Junger Coalfield, China, using optical microscopy, scanning electron microscopy (SEM), Low-temperature ashing X-ray diffraction (LTA-XRD) in combination with Siroquant software, X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The minerals in the No. 5 coal from the Chuancaogedan Mine dominantly consist of kaolinite, with minor amounts of quartz, pyrite, magnetite, gypsum, calcite, jarosite and mixed-layer illite/smectite (I/S). The most abundant species within high-temperature plasma-derived coals were SiO2 (averaging 16.90%), Al2 O3 (13.87%), TiO2 (0.55%) and P2 O5 (0.05%). Notable minor and trace elements of the coal include Zr (245.89 mg/kg), Li (78.54 mg/kg), Hg (65.42 mg/kg), Pb (38.95 mg/kg), U (7.85 mg/kg) and Se (6.69 mg/kg). The coal has an ultra-low sulfur content (0.40%). Lithium, Ga, Se, Zr and Hf present strongly positive correlation with ash yield, Si and Al, suggesting they are associated with aluminosilicate minerals in the No. 5 coal. Arsenic is only weakly associated with mineral matter and Ge in the No. 5 coals might be of organic and/or sulfide affinity. Keywords: early Permian coals; minerals; trace elements; Junger Coalfield
1. Introduction Coal is responsible for about 65% of electricity generation in China. The large abundance of coal makes it a reliable, long-term fuel source for both in China and in other coal-rich countries like Australia, Turkey and South Africa. With the increasing use of coal, a large amount of pollutants are produced, not only gas emissions (SOx, NOx and CO2 ) but also ash residues. Environmental impact of coal and coal combustion are generally associated with the minerals and the trace elements in coal. Studies on the mineralogy and geochemistry of coal are the basic work for researching environmental impact of coal and coal combustion. Dai et al. [1,2], Gürdal [3], Yang [4] Wang [5], Kolker [6], Finkelman [7] and Tang et al. [8] have done much research on mineralogical and geochemical characteristics of the coal in many areas. The Ordos basin is the most important energy base in China. Late Paleozoic coals from the Ordos basin have attracted much attention. Dai et al. [9–11], and Wang et al. [12] have studied the geochemistry and mineralogy of the coal and its coal combustion products from the Heidaigou, Guanbanwusu, and Haerwusu Surface Mines in the Junger Coalfield. The previous studies mostly focused on the No. 6 coals in Junger Coalfield. In this paper, we report the data on the mineralogy and elemental geochemistry of the No. 5 Coals in the Chuancaogedan mine, Junger coalfield, China.
Minerals 2015, 5, 788–800; doi:10.3390/min5040525
www.mdpi.com/journal/minerals
Minerals 2015, 5, 788–800 Minerals 2015, 5, page–page
2. Geological Setting
2. Geological Setting
The Junger Coalfield is located on the northeastern margin of the Ordos Basin. The coalfield is The Junger Coalfield is located on the northeastern margin of the Ordos Basin. The coalfield is 2 The geological setting of 65-km longlong (N–S) and 26-km withaatotal total area of 1700 65-km (N–S) and 26-kmwide wide (W–E), (W–E), with area of 1700 km2.km The .geological setting of the the area in detail detailby byDai Daietetal.al.[9]. [9].The The Chuancaogedan is situated area has has been been described described in Chuancaogedan MineMine is situated in thein the southeastern partpart of the Junger Coalfield southeastern of the Junger Coalfield(Figure (Figure 1). 1).
Figure 1. Location of the Chuancaogedan Mine in the Junger Coalfield, northern China (modified
Figure 1. Location of the Chuancaogedan Mine in the Junger Coalfield, northern China (modified after Dai et al. [10]). after Dai et al. [10]).
The coal-bearing sequences include Benxi Formation and Taiyuan Formation (both Pennsylvanian) and the Shanxi Formation with aand collective thickness of 134 m;(both The coal-bearing sequences include (Lower BenxiPermian) Formation Taiyuan Formation 110–150 m of which is mainly the Taiyuan and Shanxi formation (Figure 2). The Taiyuan Formation, Pennsylvanian) and the Shanxi Formation (Lower Permian) with a collective thickness of 134 m; withma of thickness 52 m, is made of sandstone, mudstone coals.Taiyuan In the Shanxi 110–150 which isofmainly themainly Taiyuan andupShanxi formation (Figureand 2). The Formation, Formation, which has a thickness of 67 m, there are five coal seams, named No. 1, No. 2, No. 3, No. 4 with a thickness of 52 m, is mainly made up of sandstone, mudstone and coals. In the Shanxi and No. 5 Coals in order from top to bottom. Formation, which has a thickness of 67 m, there are five coal seams, named No. 1, No. 2, No. 3, No. 43.and No. 5and Coals in orderProcedures from top to bottom. Samples Analytical Fifteen samples of the No. 5 Coal were collected from the Chuancaogedan Mine, Junger 3. Samples andbench Analytical Procedures Coalfield following the Chinese Standard Method GB 482-2008 [13], the cumulative thickness of the
Fifteen bench samples ofFrom the No. 5 Coal were fromsamples the Chuancaogedan Mine,All Junger No. 5 Coal is about 4.0 m. bottom to top, thecollected fifteen bench are ZG501 to ZG517. Coalfield following the Chinese Method GBto482-2008 [13], the cumulative samples were air-dried, sealedStandard in polyethylene bags prevent oxidation, and parts ofthickness them wereof the to about pass 200 and stored in brown chemical analyses. No. 5ground Coal is 4.0mesh, m. From bottom to top,glass the bottles fifteenfor bench samples are ZG501 to ZG517. All Proximate analyses were measured in accordance with ASTM standards D3173-11 [14], were samples were air-dried, sealed in polyethylene bags to prevent oxidation, (ASTM and parts of them ASTM D3175-11 [15], and ASTM D3174-11 [16],glass respectively). Total sulfur was determined following ground to pass 200 mesh, and stored in brown bottles for chemical analyses. the ASTMD 3177-02 [17]. Proximate analyses were measured in accordance with ASTM standards (ASTM D3173-11 [14], Mineralogical analyses of the coal samples were performed by means of Powder X-ray ASTM D3175-11 [15], and ASTM D3174-11 [16], respectively). Total sulfur was determined following diffraction (XRD), optical microscopy and scanning electron microscopy (SEM). the ASTMD 3177-02 [17]. ashing of the powdered coal samples was carried out using an EMITECH Low-temperature Mineralogical of the coal samples wereto performed by means of Powder K1050X plasma analyses asher (Quorum, Lewes, UK) prior XRD analysis. XRD analysis of theX-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM). low-temperature ashes was performed on a D/max-2500/PC powder diffractometer (Rigaku, Tokyo, Low-temperature ashing ofradiation the powdered coal samples wasEach carried using EMITECH Japan) with Ni-filtered Cu-Kα and a scintillation detector. XRD out pattern wasan recorded K1050X plasma asher (Quorum, Lewes, UK) 2prior to XRD analysis. XRD analysis of the low-temperature ashes was performed on a D/max-2500/PC powder diffractometer (Rigaku, Tokyo, Japan) with Ni-filtered Cu-Kα radiation and a scintillation detector. Each XRD pattern was recorded 789
Minerals 2015, 5, 788–800
over a 2θ interval of 2.6˝ –70˝ , with a step size of 0.01˝ . X-ray diffractograms of the Low-temperature Minerals 2015, 5, page–page ashings (LTAs) and non-coal samples were subjected to quantitative mineralogical analysis using the Siroquant™ software (Sietronics, Mitchell, Australia). More analytical details over a 2θinterpretation interval of 2.6°–70°, with system a step size of 0.01°. X-ray diffractograms of the Low-temperature are given by Dai et al. [18,19] and Wang et al. [20]. ashings (LTAs) and non-coal samples were subjected to quantitative mineralogical analysis using X-ray fluorescence (XRF) spectrometry (ARL ADVANT’XP+, the Siroquant™ interpretation software system (Sietronics, Mitchell, ThermoFisher, Australia). MoreWaltham, analytical MA, are given by Dai et al. the [18,19] and Wang et al.oxides [20]. in high-temperature ashed coal samples, USA)details was used to determine major element ADVANT’XP+, ThermoFisher, Waltham, MA, includingX-ray SiO2 ,fluorescence Al2 O3 , CaO,(XRF) K2 O,spectrometry Na2 O, Fe2 O(ARL , MnO, MgO, TiO2 and P2 O5 . Trace elements within 3 USA) was used to determine the major element oxides in high-temperature ashed coal samples, acid-digested ashed coal samples, except for As, Se, Hg and F, were determined by conventional including SiO2, Alplasma 2O3, CaO, K2O, Na2O, Fe2O3, MnO, MgO, TiO2 and P2O5. Trace elements within inductively coupled mass spectrometry (ICP-MS). For its analysis, samples were digested acid-digested ashed coal samples, except for As, Se, Hg and F, were determined by conventional using an UltraClave Microwave High Pressure Reactor (Milestone, Sorisole, Italy). The basic load for inductively coupled plasma mass spectrometry (ICP-MS). For its analysis, samples were digested , and The 2-mL 98% H SO4 . the digestion tank was composed of 330-mL distilled H O, 30-mL 30% H2 O2Italy). using an UltraClave Microwave High Pressure Reactor2 (Milestone, Sorisole, basic load2 ˝ C that lasted Initialfornitrogen pressure was set at 50 bars and the highest temperature was set at 240 the digestion tank was composed of 330-mL distilled H2O, 30-mL 30% H2O2, and 2-mL 98% for 75Hmin. reagents 50-mgwas sample were mL 40% HF, 2 mL 65% HNO and 2SO4. The Initial nitrogenfor pressure set atdigestion 50 bars and the5 highest temperature was set at 3240 °C1 mL 30% H . Multi-element were calibration of trace concentrations. that for 75 min. standards The reagents for used 50-mgfor sample digestion wereelement 5 mL 40% HF, 2 mL 65%More 2 O2lasted HNO and 1 by mL Dai 30%etHal. 2O2[21] . Multi-element standards used by for more calibration of trace element details are3 given Arsenic and Sewere were analyzed advanced ICP-MS which concentrations. More details are given by Dai et al. [21] Arsenic and Sewere analyzed by more utilized collision/reaction cell technology (ICP-CCT-MS) as outlined by Li et al. [22]. Fluorine was advanced which utilized collision/reaction cellMercury technology (ICP-CCT-MS) outlined by determined byICP-MS an ion-selective electrode (ISE) method. was determined as using a Milestone Li et al. [22]. Fluorine was determined by an ion-selective electrode (ISE) method. Mercury was DMA-80 Hg analyzer (Milestone, Sorisole, Italy). determined using a Milestone DMA-80 Hg analyzer (Milestone, Sorisole, Italy). The quantitative analysis of minerals and determinations of elements were completed at the State The quantitative analysis of minerals and determinations of elements were completed at the Key Laboratory of Coal Resources and Safe Mining of China University of Mining and Technology State Key Laboratory of Coal Resources and Safe Mining of China University of Mining and (Beijing, China).(Beijing, China). Technology
Figure 2. Stratigraphic sequence of the Junger Coalfield [9].
Figure 2. Stratigraphic sequence of the Junger Coalfield [9]. 3
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Minerals 2015, 5, page–page Minerals 2015,and 5, 788–800 4. Results Discussion
4.1. Coal Chemistry 4. Results and Discussion The results of the total sulfur and proximate analysis of samples from the No. 5 coal are 4.1. Coal presentedChemistry in Table 1. Ash yields of the Chuancaogedan No. 5 coal range from 5.95% to 60.70% (Figure 3), with The an results average indicating a high analysis ash coalofaccording to Chinese Standard of of the32.69%, total sulfur and proximate samples from the No. 5National coal are presented (GB/T 15224.1-2004, 10.01% to 16.00% for low ash coal, 16.01% to 29.00% for medium ash coal, and in Table 1. Ash yields of the Chuancaogedan No. 5 coal range from 5.95% to 60.70% (Figure 3), >29.00% for highofash coal) indicating [23]. The ash yields tendaccording to increase theNational bottom to the top(GB/T in the with an average 32.69%, a high ash coal to from Chinese Standard coal seam. 10.01% to 16.00% for low ash coal, 16.01% to 29.00% for medium ash coal, and >29.00% 15224.1-2004, Theash contents of volatile of thetoNo. 5 coal varies from 32.57% through for high coal) [23]. The ashmatter yields tend increase from the bottom to the to top50.30% in the coal seam.the coal-seam section (Figure 3), with a mean 37.22%, suggesting that32.57% the Chuancaogedan coals the are The contents of volatile matter of theofNo. 5 coal varies from to 50.30% through medium-high volatile bituminous coals based on MT/T 849-2000 (28.01% to 37.00% for coal-seam section (Figure 3), with a mean of 37.22%, suggesting that the Chuancaogedan coals are medium-high volatile volatilebituminous coal, 37.01% to based 50.00% high849-2000 volatile(28.01% coal and >29.00% super high medium-high coals onfor MT/T to 37.00% forfor medium-high volatile coal) [24]. volatile coal, 37.01% to 50.00% for high volatile coal and >29.00% for super high volatile coal) [24]. The No. No. 55 coals of 2.22% 2.22% to to 5.61% (Figure 3), 3), with with an an average average of of 3.81%, 3.81%, The coals have have aa moisture moisture content content of 5.61% (Figure indicating aa low-medium low-medium rank rank coal coal in in accordance accordance of of MT/T MT/T 850-2000 5% indicating 850-2000 (≤5% (ď5%for for low low moisture moisture coal, coal, 5% to 15% for medium moisture coal, and >15% for high moisture coal) [25]. to 15% for medium moisture coal, and >15% for high moisture coal) [25]. The total total sulfur sulfur of of No. No. 55 coals 3), averaging averaging 0.40%, 0.40%, which which The coals changes changes from from 0.12% 0.12% to to 0.83% 0.83% (Figure (Figure 3), corresponds to to ultra-low-sulfur ultra-low-sulfur coal coal according according to to Chinese Chinese National National Standard Standard (GB/T (GB/T 15224.2-2010) 15224.2-2010) corresponds (
