Characterization of the Modes of Occurrence of Mercury and Their

Nov 5, 2015 - ABSTRACT: The utilization of coal gangue in a power plant has attracted ... occurrence of mercury in coal gangue is crucial for developi...
1 downloads 0 Views 529KB Size
Download PDF
Article pubs.acs.org/EF

Characterization of the Modes of Occurrence of Mercury and Their Thermal Stability in Coal Gangues Jindong Zhai, Shaoqing Guo,* Xian-Xian Wei, Yanzhi Cao, and Libing Gao School of Environment and Safety, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030024, People’s Republic of China ABSTRACT: The utilization of coal gangue in a power plant has attracted wide interest in China; however, coal gangue represents a new anthropogenic source of mercury pollution due to its high mercury content. Understanding the modes of occurrence of mercury in coal gangue is crucial for developing the mercury control technology used during coal gangue combustion. In this study, the mercury in four typical coal gangues in China was characterized by a sequential extraction procedure (SEP) coupled with a temperature-programmed decomposition (TPD) method. The method is proved to be an effective approach in studying the modes of occurrence of mercury as well as the thermal stability of coal gangues by distinguishing the characteristic release temperature during the thermal decomposition process. The iron−manganese oxidebound Hg releases at a temperature range of 200−600 °C, while the carbonate-bound Hg releases at a temperature range of 250−300 °C. The organic-bound Hg, sulfide-bound Hg, and silicate-bound Hg release at temperature ranges of 200−400, 400− 600, and above 1200 °C, respectively. Furthermore, the sulfide-bound Hg is found to be the dominant form of mercury in the four coal gangue samples.

1. INTRODUCTION Coal gangue is an industrial residue of coal mining and coal washing in China.1 Large quantities of coal gangue cause serious environmental problems by polluting the air, water, and soil as well as occupying a tremendous amount of land.2−4 Therefore, coal gangue utilization is a matter of great concern and has attracted wide interest in China.5−7 Recently, due to the lack of energy resources in China, coal gangue has been extensively utilized as a raw material for power plants to effectively utilize its calorific value.8−10 However, the utilization of coal gangue in power plants has become a new anthropogenic discharge source of mercury attributable to the high mercury content in coal gangue.11 Mercury (Hg) is a toxic element that is hazardous to the environment and all living organisms, including human beings.12,13 Due to its high toxicity, a series of strict policies to control Hg emissions has been established,14 including the emission standard of air pollutants for thermal power plants in China (GB-13223-2011). To satisfy the standard of Hg emission for power plants, effective Hg control technology should be introduced to reduce the emissions of Hg. Consequently, it is crucial to develop effective Hg control technologies. Therefore, it is of great importance to understand the Hg release behavior during the coal gangue combustion, especially the modes of occurrence of Hg in coal gangue and their thermal stability. In recent years, extensive studies have been focused on the environmental effect and transformation behavior of some trace elements during coal gangue combustion.5,6 However, very few reports considered the characterization of Hg in coal gangue. The modes of occurrence of Hg have been analyzed for various types of coal, but little attention has been paid to the coal gangues.15−18Although coal gangue is slightly similar to coal because of its association with coal in a coal mine, it has a higher content of mineral and lower content of organic material © 2015 American Chemical Society

than coal. In addition, coal gangue has a higher content of Hg than coal. As a result, the modes of occurrence of Hg in coal gangue should be studied. The goal of this study is to characterize the modes of occurrence of Hg in coal gangue. According to the literature, two methods have been used to study the modes of occurrence of Hg in coals.16,17,20,21 One method is the sequential extraction procedure (SEP), which was originally developed to analyze soil samples.19 This method identifies Hg species on the basis of the chemical leaching of the complex substrate. Generally, Hg in coal can be classified into six modes of occurrence: water-leachable Hg, ionexchangeable Hg, carbonate-bound Hg, organic-bound Hg, sulfide-bound Hg, and silicates-bound Hg.16 The other method is temperature-programmed decomposition (TPD).22−25 In the TPD method, the modes of occurrence of Hg are identified based on the relationship between the specified modes of occurrence of Hg and the specified release temperatures during thermal treatment of samples. In the TPD technique, the modes of occurrence of Hg in coals are correlated with their thermal stability.15,23,25 Although the two methods are both effective in determining the modes of occurrence of Hg in the solids, it is difficult to clarify the relationship between the modes of occurrence of Hg and their thermal stability if they are used separately. In the present work, with four Chinese coal gangues as the typical samples, the SEP was innovatively coupled with the TPD to characterize the modes of occurrence of Hg and their thermal stability simultaneously to provide insight for developing advanced Hg control technologies for use during coal gangue utilization. Received: June 24, 2015 Revised: November 5, 2015 Published: November 5, 2015 8239

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels Table 1. Proximate and Ultimate Analyses of the Coal Gangues (wt %)a proximate analysis, db

a

ultimate analysis, daf

coal gangue

Hg in coal ganguec

VM

A

FC

C

H

N

S

Ob

ED GD PL TX

1897 2016 1435 1272

0.87 1.86 0.93 0.76

70.33 66.94 71.02 77.81

0.87 1.86 0.93 0.76

56.70 63.01 50.45 48.20

5.80 5.19 7.02 6.49

0.80 0.96 0.64 0.93

13.06 12.37 8.95 15.77

23.65 18.46 32.94 28.60

db, dry basis; daf, dry ash-free basis; VM, volatile matter; FC, fixed carbon; A, ash. bBy difference. cNanograms per gram.

Table 2. Distribution of the sequential extractions of the coal gangue samples sample

ion-exchangeable, %

carbonate-bound, %

iron−manganese oxide, %

organic-bound, %

sulfide-bound, %

silicate-bound, %

residue,%

total, %

ED GD PL TX

0.91 0.67 0.98 0.27

0.38 1.76 0.08 0.77

undetected 11.48 6.28 undetected

2.41 0.09 0.27 3.40

74.22 51.49 78.88 74.70

10.32 20.81 18.55 21.96

13.85 14.33 9.49 8.39

102.09 100.54 114.77 109.49

of the steps were the same as the preceding ones. The residue was free of ion-exchangeable Hg, carbonate-bound Hg, iron−manganese oxidebound Hg, and organic-bound Hg; this residue was denoted as step-4 coal gangue. (5) The step-4 coal gangue was treated with a 30 mL solution of a mixture (HNO3:H2O = 1:7), covered with a thin film, and then gently boiled for 60 min. The rest of the steps were the same as the preceding ones. The residue was free of ion-exchangeable Hg, carbonate-bound Hg, iron−manganese oxide-bound Hg, organic-bound Hg, and sulfidebound Hg; this residue was denoted as step-5 coal gangue. (6) The step-5 coal gangue was treated with 30 mL of HF (40%), covered with a thin film, and then gently boiled for 60 min. The rest of the steps were the same as the preceding ones. The residue was free of ion-exchangeable Hg, carbonate-bound Hg, iron−manganese oxidebound Hg, organic-bound Hg, sulfide-bound Hg, and silicate-bound Hg; this residue was denoted as step-6 coal gangue. (7) After the step-6 extraction procedure, the content of Hg in the residue was analyzed. 2.4. TPD Experiment. The TPD experiments were conducted in a quartz boat located in a fixed bed quartz tube reactor that was heated in a furnace. The fixed-bed quartz tube reactor with the diameter of 20 mm was directly connected to an online AFS. The temperature of the sample was measured using a thermocouple inserted into the sample, and the data were recorded by a computer. An approximately 0.2 g coal gangue sample in a quartz boat was placed in the quartz tube reactor and then was heated from room temperature to 1200 °C at a heating rate of 20 °C/min under a N2 flow of 300 mL/min. The gas produced during thermal treatment was directly swept to the AFS analyzer via the N2 flow. The intensity of Hg in the gas was recorded continually. Next, the boat with the sample was moved quickly to the cold end of the quartz tube at 1200 °C and then cooled in the N2 flow. The content of Hg in the sample after TPD was analyzed using AFS. The specified Hg free coal gangues obtained after each extraction procedure were the following subsamples: step-1, -2, -3, -4, -5, and -6 coal gangues. To further investigate the modes of occurrence of Hg in the samples, the 0.2 g subsample after each extraction step was also analyzed via TPD experiments. All of the measurements were performed using two replicates of the same sample.

2. EXPERIMENTAL SECTION 2.1. Coal Gangue Samples. Four typical coal gangue samples, which can be utilized as part of the raw materials for power plants, were collected from Taiyuan power plant, Gundi coal mine, Pinglu coal preparation plant, and Taiyuan Coal washery in Shanxi Province, and they were labeled as ED, GD, PL, and TX, respectively. The samples were placed in plastic storage bags when they were collected to prevent contamination and minimize oxidation. Next, the coal gangue samples were crushed, sieved to 0.16−0.27 mm, and then dried prior to use. The proximate and ultimate analyses of the coal gangues and the concentration of Hg contents in the coal gangues are shown in Table 1. 2.2. Analysis of Mercury in Samples. The contents of Hg in the coal gangue samples were determined through the following three steps:6 (1) The solids were digested with 10 mL of an oxidizing mixture (HNO3:HCl:HF = 3:1:1, volume ratio) in a Teflon digestion vessel, and then the vessel was transferred into a microwave oven (130 °C, 10 min; 150 °C, 5 min; 180 °C, 5 min; 200 °C, 25 min); after cooling, the digested samples were diluted with double-distilled deionized water. (2) Hg2+ was reduced to Hg0 by the addition of potassium borohydride (KBH4). (3) The content of Hg0 was determined using atomic fluorescence spectroscopy (AFS). 2.3. Sequential Extraction Procedure. Six sequential extraction procedures were performed to identify the modes of occurrence of Hg in the coal gangue according to previous reports.17,21,22 A 5 g amount of each sample was used for the sequential extractions for the four coal gangues. Each sample was introduced into a 100 mL glass reservoir, and then the different extraction solutions were sequentially added. Each fraction was filtered and analyzed using AFS, and then the solid residue was rinsed by pure water between each sequential step. The detailed procedures are as follows: (1) A 5 g amount of fresh coal gangue sample was treated with a 30 mL solution of 1 M NH4Ac (pH = 7) and then shaken for 15 h at room temperature, followed by centrifugation at 4000 rpm for 20 min. The residue was dried at 50 °C for 40 min; the residue was free of ionexchangeable Hg; this residue was denoted as step-1 coal gangue. (2) The step-1 coal gangue was treated with 1 M NH4Ac (pH = 5) and then shaken for 15 h at room temperature. The rest of the steps were the same as those of the preceding procedure. The residue was free of ion-exchangeable Hg and carbonate-bound Hg; this residue was denoted as step-2 coal gangue. (3) The step-2 coal gangue was treated with a 30 mL solution of 0.04 M NH2OH·HCl and 25% (v/v) HOAc and was heated to 96 °C with occasional agitation for 6 h. The rest of the steps were the same as the preceding ones. The residue was free of ion-exchangeable Hg, carbonate-bound Hg, and iron−manganese oxide-bound Hg; this residue was denoted as step-3 coal gangue. (4) The step-3 coal gangue was treated with a 10 mL solution of 0.2 M HNO3 and then a 10 mL solution of 30% H2O2 (pH = 2). The rest

3. RESULTS AND DISCUSSION 3.1. Results of the Sequential Extraction Procedures. The results of the sequential extraction procedures are presented in Table 2. It can be clearly seen that the sulfidebound Hg is the dominant form of Hg in the four coal gangues; the levels of sulfide-bound Hg are 74.22%, 51.49%, 78.88%, and 74.70% for ED, GD, PL, and TX, respectively; this result is similar to the results of other reports on coal.16,26−28 For example, Feng and Hong have reported that sulfide-bound Hg accounted for substantial amounts (av 83%) of the total Hg in 8240

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels

Figure 1. Hg release profiles during TPD of the coal gangue samples.

some high-Hg coals from Huaibei.26 Moreover, Zheng et al. and Palmer et al. also obtained similar results for a subbituminous USA coal.27,28 Table 2 also shows that the second most abundant Hg form is the silicate-bound Hg, accounting for 10.32%, 20.81%, 18.55%, and 21.96% of the total Hg in the coal gangues of ED, GD, PL, and TX, respectively. This result is close to the amount of silicate-bound Hg in the coal considered in other literature reports.29 It was reported that the silicate-bound Hg accounted for 9−31% of the total Hg in the coal samples from southwestern Guizhou Province.29 Iron−manganese oxide-bound Hg accounts for 11.48% and 6.28% in GD and PL coal gangue, whereas it is undetected in ED and TX coal gangues. Moreover, the contents of ionexchangeable Hg for ED, GD, PL, and TX are calculated to be 0.91%, 0.67%, 0.98%, and 0.27%, respectively, being almost negligible at less than 1%. These results agree with the results of Feng and Hong, who observed that ion-exchangeable Hg only accounted for a small amount of the total Hg (average 0.3%) in 32 coal samples from Guizhou Province.26 Similar to ionexchangeable Hg, carbonate-bound Hg is also nearly negligible and accounts for 0.38−1.76% of the total Hg in coal gangue; this result is consistent with the other reports on coals.16,26,27 For example, Palmer et al. found that carbonate-bound Hg was absent in a subbituminous coal from the Powder River basin.27 Feng and Hong reported that negligible carbonate-bound Hg existed in coals from Guizhou Province.26 Zheng et al. also suggested that Hg in carbonate minerals was typically negligible in some coals.16 Organic-bound Hg accounts for approximately 2−4% in ED and TX and less than 0.3% in GD and PL,

whereas the content of organic-bound Hg almost exceeded 40% in coal.16,27 This result indicates that a small portion of organicbound Hg exists in coal gangue because of the high content of minerals and low content of organic matter in coal gangue. However, a portion of Hg remains in the residue after the step6 extraction procedure. According to some literature, the Hg in the residue is possibly insoluble Hg, such as HgSO4 or HgS.18,25 As a result, the SEP shows that the modes of occurrence of Hg in the four coal gangues is generally in the order of sulfidebound Hg > silicate-bound Hg > iron−manganese oxide-bound Hg > organic-bound Hg > carbonate-bound Hg ≈ ionexchangeable Hg. Although both the content of sulfide-bound Hg and the sulfur contents are higher in coal gangue, the content of sulfide-bound Hg has no clear positive relationship with the sulfur content in the coal gangue listed in Table 1; this result agrees with the results of other literature reports on coal.16,18,30,31 Note that the ratios of the modes of the aforementioned occurrence of Hg in the four coal gangues are in accordance with those in some coals reported by Zheng et al. and Feng and Hong.16,26 This finding could be explained by the fact that coal gangue is a byproduct during coal mining and undoubtedly exhibits mineral composition similar to that of coal, resulting in similar ratios of the modes of the occurrence of Hg. However, note that the organic-bound Hg in the four coal gangues used in this study is less than that in the coal reported in the literature.16,27 This difference can be attributed to the higher content of minerals and lower content of organic matter of coal gangue compared to coal. 8241

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels 3.2. Results of TPD. 3.2.1. Results of TPD for the Original Samples. The dynamic Hg release profiles versus the increase of temperature for the four coal gangues were measured using the TPD technique; the results are shown in Figure 1. Figure 1 indicates that there are several well-resolved peaks in the profiles for the four coal gangues. According to the literature, the modes of occurrence of Hg can be distinguished according to the well-resolved peaks during thermal-programmed decomposition.15,17,18 Therefore, the several Hg peaks shown in Figure 1 for each coal gangue indicate the several modes of occurrence of Hg in coal gangue, such as organic-bound Hg, pyrite-bound Hg, and silicate-bound Hg, which are released at the specified temperature range during the temperatureprogrammed decomposition of coal gangue. Although the peak patterns are not the same for the four coal gangues, they have some similarities in the Hg release temperature range. For example, Hg starts to release at 150− 170 °C, which somewhat agrees with the Hg release behavior in coals.18,25 Meanwhile, as shown in Figure 1, two typical peaks can be observed for all of the samples. One peak was located in the range of 200−400 °C, and the peak reaches the maximum intensity at 250−300 °C, especially for GD, and the other sharp peak of Hg release appeared at 400−600 °C, with the highest intensity at 500−550 °C. The profile also shows a tendency for Hg release at approximately 1200 °C for three coal gangues (GD, PL, and TX). This result indicates that the stable Hg must exist in GD, PL, and TX coal gangues. According to Guo et al., the silicatebound Hg is the most stable form of Hg in coal.25 Therefore, the stable Hg in GD, PL, and TX is probably silicate-bound Hg. In addition, the SEP results shown in Table 2 prove that part of the Hg (approximately 14−19%) in GD, PL, and TX gangues exists in the silicate-bound form, whereas the ED coal gangue contains less silicate-bound Hg (approximately 8%) than the other coal gangues, leading to an unclear Hg release pattern at approximately 1200 °C. 3.2.2. Results of TPD for the Subsamples after Each Extraction Step. 3.2.2.1. Results of TPD for the Subsample of Step-1 Coal Gangue. As stated earlier, the step-1 coal gangue is free of ion-exchangeable Hg. The dynamic Hg release profiles during the TPD of step-1 coal gangue show that the Hg release behavior for all of the coal gangues is similar to that of the original samples. The behavior is probably correlated with the SEP result that only 0.3−0.9% of ion-exchangeable Hg exists in all of the coal gangues. As a result, there is no obvious change for Hg release profiles after the step-1 extraction procedure. 3.2.2.2. Results of TPD for the Subsample of Step-2 Coal Gangue. The step-2 coal gangue is free of ion-exchangeable and carbonate-bound Hg. The dynamic Hg release profiles during TPD of step-2 coal gangue also show that the Hg release profiles of ED, PL, and TX have no change relative to the original samples. This result may be related to the SEP result that only 0.1−0.7% of carbonate-bound Hg is detected for the three coal gangues. However, the GD exhibits 1.8% carbonatebound Hg, and the Hg release profiles for GD before and after the step-2 extraction procedure are shown in Figure 2. As seen in Figure 2, the peak during 250−300 °C for step-2 coal gangue becomes lower than that in step-1 coal gangue of GD after carbonate-bound Hg leaching out, which should be attributable to the removal of carbonate-bound Hg. Hence, it is inferred that carbonate-bound Hg releases approximately at the range of 250−300 °C, which is analogous to the result of Ohki et al. in the study for coals.32 It was reported that the carbonate-bound

Figure 2. Release profiles of the step-2 coal gangues for GD.

Hg started to decompose at a relatively low temperature of 200 °C.32 3.2.2.3. Results of TPD for the Subsample of Step-3 Coal Gangue. After step-3 of the extraction procedure, the iron− manganese oxide-bound Hg has been leached out. The step-3 coal gangue is free of ion-exchangeable, carbonate-bound, and iron−manganese oxide-bound Hg. Because the iron−manganese oxide-bound Hg in ED and TX are not detected (Table 2), it is reasonable that the Hg release profiles of step-3 coal gangue for ED and TX are consistent with the step-2 samples. For GD and PL, the Hg release profiles changed substantially, as shown in Figure 3. After the step-3 extraction procedure, the two peaks at 200−400 and 400−600 °C become lower than that of step-2. Furthermore, the content of iron−manganese

Figure 3. Release profiles of the step-3 coal gangues for GD and PL. 8242

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels

the peak at 200−400 °C almost disappeared for the step-4 coal gangue, which implies that the organic-bound Hg for ED, PL, and TX releases at the temperature range of 200−400 °C. This result is similar to the organic-bound Hg in some coals and soil,18,33 which releases at 200−400 °C and is associated with the organic moiety of coal gangue, probably as CH3Hg+ and CH3 HgCH3 type species.33,34 3.2.2.5. Results of TPD for the Subsample of Step-5 Coal Gangue. Compared with the step-4 coal gangue, the step-5 coal gangue is free of sulfide-bound Hg. The sulfide-bound Hg can be identified by comparing the profiles of the step-4 and step-5 coal gangues; the results are shown in Figure 5. Note that the resolved peaks at 400−600 °C for all of the samples of step-4 almost completely disappear for all of the samples of step-5. This result indicates that the sulfide-bound Hg for the coal gangue probably releases in the temperature range of 400−600 °C, in good agreement with the results on coal.25,35,36 It is reported that the sulfide-bound Hg in coal releases at 400−600 °C during thermal-programmed decomposition, which is associated with pyrite-bound Hg, sulfides, thiosulfate, and sulfite, etc.27,31 3.2.2.6. Results of TPD for the Subsample of Step-6 Coal Gangue. Compared with the step-5 coal gangue, the step-6 coal gangue is free of silicate-bound Hg. In addition, the silicatebound Hg is identified by comparing the profiles of step-5 and step-6 coal gangues. Table 2 shows that the content of silicatebound Hg is approximately 10−22% in the four coal gangues. However, the dynamic Hg release profiles of the step-6 coal gangue have no change compared with the step-5 samples. This result implies that most of the silicate-bound Hg is released above 1200 °C. Note that all of the samples after the step-6 extraction procedure are free of ion-exchangeable, carbonate-bound, iron−manganese oxide-bound, organic-bound, sulfide-bound, and silicate-bound Hg. However, there is still one small peak approximately between 200 and 400 °C for ED, GD, and TX. According to the literature, the pure HgS releases in the temperature range of 200−400 °C during thermal desorption.15,17,23 Generally, HgS is insoluble in the leaching agent and is difficult to leach out with the treatment from the step-1 to step-6 extraction procedure.18,25 Therefore, it is inferred that the peak is possibly attributable to the release of Hg from HgS in the coal gangue.

oxide-bound Hg listed in Table 2 is approximately 6−12% for the GD and PL coal gangues. This result implies that the decrease of the two Hg peaks is attributed to the leaching out of iron−manganese oxide-bound Hg and further indicates that the iron−manganese oxide-bound Hg probably releases in the temperature ranges of 200−400 and 400−600 °C. 3.2.2.4. Results of TPD for the Subsample of Step-4 Coal Gangue. Compared with the step-3 coal gangue, the step-4 coal gangue is free of organic-bound Hg. Therefore, the organicbound Hg is identified by comparing the profiles of the step-3 and step-4 coal gangues; the results are shown in Figure 4. An obvious change is observed from the Hg profiles of ED, PL, and TX after performing step-4, whereas GD remained nearly unchanged. Note that the content of organic-bound Hg in GD is 0.27%, which is far less than that of ED, PL, and TX, causing the unchangeable profile of Hg release. For ED, PL, and TX,

4. CONCLUSIONS In summary, it is demonstrated that SEP coupled with TPD technique is effective in studying the modes of occurrence of Hg and their thermal stability in coal gangues. According to the different extraction procedures of SEP, quantitative analysis of six Hg-bound species in the four coal gangues were obtained. With the aid of the TPD technique, the release temperature ranges of the different modes of occurrence of Hg were also obtained. According to the results of the four test coal gangues, the sulfide-bound Hg, which releases at 400−600 °C, is the dominant form of Hg in the four coal gangues. The silicatebound Hg is the second abundant form and releases above 1200 °C. The iron−manganese oxide-bound Hg varies in different coal gangues and probably releases at 200−400 and 400−600 °C. The content of the organic-bound Hg is low and releases in the temperature range of 200−400 °C. The carbonate-bound Hg releases in the temperature range of 250−300 °C. The content of ion-exchangeable and carbonatebound Hg is negligible in the four coal gangues.

Figure 4. Release profiles of the step-4 coal gangues for ED, PL, and TX. 8243

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels

Figure 5. Release profiles of the step-5 coal gangues for ED, GD, PL, and TX.

■

(12) Swain, E. B.; Jakus, P. M.; Rice, G.; Lupi, F.; Maxson, P. A.; Pacyna, J. M.; Penn, A.; Spiegel, S. J.; Veiga, M. M. Ambio 2007, 36, 45−61. (13) Sundseth, K.; Pacyna, J. M.; Pacyna, E. G.; Munthe, J.; Belhaj, M.; Astrom, S. J. J. Cleaner Prod. 2010, 18, 386−394. (14) Pavlish, J. H.; Sondreal, E. A.; Mann, M. D.; Olson, E. S.; Galbreath, K. C.; Laudal, D. L.; Benson, S. A. Fuel Process. Technol. 2003, 82, 89−165. (15) Lopez-Anton, M. A.; Yuan, Y.; Perry, R.; Maroto-Valer, M. M. Fuel 2010, 89, 629−34. (16) Zheng, L.; Liu, G.; Qi, C.; Zhang, Y.; Wong, M. Int. J. Coal Geol. 2008, 73 (2), 139−55. (17) Rumayor, M.; Diaz-Somoano, M.; Lopez-Anton, M. A.; Martinez-Tarazona, M. R. Chemosphere 2015, 119, 459−465. (18) Luo, G.; Yao, H.; Xu, M.; Gupta, R.; Xu, Z. Proc. Combust. Inst. 2011, 33 (2), 2763−9. (19) Biester, H.; Scholz, C. Environ. Sci. Technol. 1997, 31 (1), 233− 239. (20) Liu, R.; Yang, J.; Xiao, Y.; Liu, Z. Energy Fuels 2009, 23, 2013− 2017. (21) Khodadoust, A. P.; Naithani, P.; Theis, T. L.; Murarka, I. P. Ind. Eng. Chem. Res. 2011, 50 (4), 2204−13. (22) Wichliński, M.; Kobyłecki, R.; Bis, Z. Fuel Process. Technol. 2014, 119, 92−7. (23) Rallo, M.; Lopez-Anton, M. A.; Meij, R.; Perry, R.; MarotoValer, M. M. J. Hazard. Mater. 2010, 174, 28−33. (24) Ozaki, M.; Uddin, M. A.; Sasaoka, E.; Wu, S. Fuel 2008, 87 (17), 3610−5. (25) Guo, S.; Yang, J.; Liu, Z. Energy Fuels 2012, 26 (6), 3388−3392. (26) Feng, X.; Hong, Y. Fuel 1999, 78 (10), 1181−1188. (27) Palmer, C. A.; Mroczkowski, S. J.; Kolker, A. U.S. Geological Survey, Open-File Report 02-331; U.S. Geological Survey: Reston, VA, USA, 2002; 52. (28) Zheng, L.; Liu, G.; Chou, C.-L.; Qi, C.; Zhang, Y. J. Asian Earth Sci. 2007, 31 (2), 167−176.

AUTHOR INFORMATION

Corresponding Author

*Phone: +86-0351-6698326. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully acknowledge the financial support from the Natural Science Foundation of China (Grant 41372350).

■

REFERENCES

(1) Ren, J.; Xie, C.; Lin, J.; Li, Z. Process Saf. Environ. Prot. 2014, 92, 896−902. (2) Querol, X.; Izquierdo, M.; Monfort, E.; Alvarez, E.; Font, O.; Moreno, T.; Alastuey, A.; Zhuang, X.; Lu, W.; Wang, Y. Int. J. Coal Geol. 2008, 75, 93−104. (3) Zhou, B.; Shao, M. a.; Wen, M.; Wang, Q.; Horton, R. Clean: Soil, Air, Water 2010, 38, 1031−1038. (4) Bell, F. G.; Stacey, T. R.; Genske, D. D. Environ. Geol. 2000, 40, 135−152. (5) Zuo, T. F. Coal Technol. 2009, 28, 186−189 [in Chinese with English abstract]. (6) Yan, Y. X.; Wang, X. F.; Wang, X. Q. J. Anhui Univ. Sci. Technol., Nat. Sci. 2006, 26, 9−11 [in Chinese with English abstract]. (7) Liu, G. J.; Xu, G. Q.; Cui, S. J. Coal Geol Explor. 1996, 25, 21−24 [in Chinese with English abstract].. (8) Meng, F.; Yu, J.; Tahmasebi, A.; Han, Y. Energy Fuels 2013, 27, 2923−32. (9) Chugh, Y. P.; Patwardhan, A. Resour. Conserv. Recycl. 2004, 40, 225−243. (10) Zhou, C.; Liu, G.; Yan, Z.; Fang, T.; Wang, R. Fuel 2012, 97, 644−650. (11) Jang, J.; Park, J. J. J. Hazard. Mater. 2014, 273 (30), 1−6. 8244

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245

Article

Energy & Fuels (29) Zhang, J.; Ren, D.; Zhu, Y.; Chou, C. L.; Zeng, R.; Zheng, B. Int. J. Coal Geol. 2004, 57 (1), 49−61. (30) Iwashita, A.; Tanamachi, S.; Nakajima, T.; Takanashi, H.; Ohki, A. Fuel 2004, 83, 631−638. (31) Demir, I. Prepr. Symp. - Am. Chem. Soc., Div. Fuel Chem. 2001, 46, 289−291. (32) Ohki, A.; Sagayama, K.; Tanamachi, S.; Iwashita, A.; Nakajima, T.; Takanashi, H. Powder Technol. 2008, 180 (1−2), 30−4. (33) Wang, Q.; Ma, Z.; Shen, W.; Feng, F.; Liu, R. China Environ. Sci. (Chin. Ed.) 2001, 21 (1), 54−57. (34) Zheng, L.; Liu, G.; Chou, C. Sci. Total Environ. 2007, 384, 374− 383. (35) Biester, H.; Scholz, C. Environ. Sci. Technol. 1996, 31 (1), 233− 239. (36) Luo, G.; Yao, H.; Xu, M.; Gupta, R.; Xu, Z. P. Proc. Combust. Inst. 2011, 33, 2763−69.

8245

DOI: 10.1021/acs.energyfuels.5b01406 Energy Fuels 2015, 29, 8239−8245