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Article

Occurrence Modes of Arsenic in Coal: A Case Study from the Hanshuiquan Coal Mine, Santanghu Coalfield, Xinjiang Province, China

by
Bo Zhu
1,2,3,
Wenfeng Wang
1,2,4,*,
Jijun Tian
4,
Wenlong Wang
1,2,
Shuo Feng
1,2,4 and
Meng Wang
1,2,5
1
Key Laboratory of Coalbed Methane Resources & Reservoir Formation Process, Ministry of Education, Xuzhou 221008, China
2
School of Resources and Geosciences, China University of Mining & Technology, Xuzhou 221116, China
3
Satellite Application Center of Xinjiang Uygur Autonomous Region, Urumqi 830000, China
4
College of Geology and Mining Engineering, Xinjiang University, Urumqi 830046, China
5
Carbon Neutrality Institute, China University of Mining and Technology, Xuzhou 221116, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(13), 7092; https://doi.org/10.3390/app15137092
Submission received: 11 April 2025 / Revised: 4 June 2025 / Accepted: 7 June 2025 / Published: 24 June 2025
(This article belongs to the Section Electrical, Electronics and Communications Engineering)
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Abstract

The high concentration of arsenic in coal does great harm to the environment. It is important to research the occurrence mode of As in coal to promote the removal of As in coal and understand the migration and transformation of As in coal. In this work, eleven samples from the Hanshuiquan coal mine, in the Santanghu Coalfield, were tested by X-ray diffraction (XRD) and Scanning Electron Microscopy with an Energy Dispersive Spectrometer (SEM-EDS). The results show that maximum arsenic content in the coal seam was 108.37 μg/g, which was 13 times more than that of the world coal, and 28 times more than that of the Chinese coal. Through X-ray diffraction (XRD) experiments, ojuelaite and scorodite were found in the samples. Scanning Electron Microscopy (SEM) and an Energy Dispersive Spectrometer (EDS) were used to determine the occurrence location of the arsenic elements. In combination with geochemistry and mineralogy theory, the occurrence modes of the arsenic were studied in detail. The occurrence modes of arsenic in coal from the study area are dominated by sulfide-bound arsenic. At the same time, it was found that arsenic in the study area might occur in the form of arsenate containing zinc and organic bound arsenic. Previous studies and this work have shown that (1) arsenic in coal is predominantly in the form of pyrite, and (2) arsenic in coal is associated with organic matter in low-rank coal and to a lesser extent in high-rank coal. Understanding the occurrence modes of arsenic in coal is of great significance because it has significant impacts on coal mining, preparation, combustion, and utilization, and has adverse effects on the environment and human health.

1. Introduction

Coal, as a special sedimentary organic rock, contains almost all the elements found in the Earth’s crust. Research on the elements in the coal-bearing strata is of great significance both theoretically and practically [1,2,3,4,5,6]. Theoretically, an understanding of the content, distribution, origin of enrichment, and occurrence modes of elements in coal is helpful to explain the geological origin of coal seams, the sedimentary environment, the history of geological evolution, and sudden geological events [1,2,3,4,5,6]. Practically, (1) understanding the content of elements in coal could guarantee the national energy strategic needs, and (2) revealing the occurrence modes, migration, and transformation mechanisms of elements in coal and coal by-products may help solve the environmental problems in the process of coal utilization [1,2,3,4,5,6,7]. Twenty-four elements (Sb, As, Ba, Be, B, Cd, Cl, Cr, Co, Cu, F, Pb, Hg, Mn, Ni, Mo, P, Se, Tl, Th, Sn, V, U, and Zn) are defined as hazardous elements. According to their negative influence on the environment, these hazardous elements can be classified into four types, with As, Cd, Cr, Hg, and Se thought to cause the most severe damage to the environment [8]. During the exploitation and utilization of coal, there are large amounts of waste and exhaust gases produced, and these hazardous materials could threaten human health through the air, soil, drinking water, and the food chain. Examples include the endemic coal-fired arsenic poisoning of Guizhou Province in southwest China [9,10], and the poor skeletal growth of children influenced by the discharged As and Pd from the nearby coal-fired power plant in Former Czechoslovakia [11]. In addition, it has also been reported that pollution of the residential water wells in Virginia (USA) is disposal of coal slurry using underground injection [12].
Previous studies have proven that the migration and release of elements from coal during its exploitation, storage, and utilization have a certain influence on the environment, and the occurrence state of various elements determines how difficult it is for them to migrate and be released [13,14]. The poisonousness of As(III) is 60 times that of As(V) [15], and organic-state arsenic is difficult to extracted using physical methods, but arsenic gas can be released during burning [16]. Furthermore, the As in sulfate, carbonates, sulfide, and part-organic matter can be separated easily, while the arsenic in silicate minerals (such as the clay minerals) is quite stable in the surface environment [17]. Therefore, research on the occurrence states of arsenic could have a positive impact on coal exploitation and environmental protection. There have been several large-scale studies on the occurrence states of arsenic in coal. It was found that arsenic could be enriched in pyrite in coal at the beginning of the twentieth century [18], and it can also be divided into two types, the arsenopyrite and pyrite form states [19]. There are some arsenic minerals inclined to accrete with sulfides, such as realgar, orpiment and arsenopyrite. These sulfides mainly contain the elements of Cu, Pb and Zn, such as chalcopyrite, sphalerite and pyrite [20,21]. It has been found that arsenic cannot be enriched as an independent mineral in Guizhou, and that there is a positive relationship between the S and As contents, and that pyrite is the dominant carrier for arsenic [22]. Research on the X-ray absorption fine structure (XAFS) of arsenic has also shown that there is partly organic-state arsenic in coal [23,24].
There has been detailed study of the coal quality in the Hanshuiquan coal mine in the Santanghu Basin, Xinjiang, China, while research on the enrichment and occurrence states of arsenic is still incomplete. With the sequential chemical extraction experiment (SCEE) method, it has been demonstrated that the enrichment state of the arsenic in the coal is mainly in an inorganic state in Hanshuiquan coal mine [25]. The arsenic content in the pyrite is lower in the Hanshuiquan coal mine, and the main occurrence mode of arsenic in the coal is arsenate, as demonstrated with the reduction difference method, but the types of arsenate are unclear [26].

2. Geological Setting

The Santanghu Coalfield, located at the northern foot of the east Tianshan Mountain, Xinjiang, is the biggest equipped coalfield reconnaissance and survey area, and it is a typical land-phase coalfield. The research area is located in the northwest of the Hanshuiquan depression in Santanghu Basin (Figure 1); the Hanshuiquan depression has a length of approximately 60 km from east to west, and the width from the north to south is about 10 km, with an area of approximately 750 km2. The Santanghu Basin is a peripheral foreland basin which emerged during the middle Jurassic period in China, and the coal-bearing formation is a subsequent development. The Jurassic strata are a set of sedimentary strata mainly composed of braided rivers, braided river deltas, and fan deltas. The strata, from bottom to top, are the Badaowan Formation, the Sangonghe Formation, the Xishanyao Formation, the Toutunhe Formation, the Qigu Formation, and the Kalaza Formation. Among them, the main coal-bearing strata are the Badaowan Formation and the Xishanyao Formation. The Xishanyao Formation is conformity deposited on the Sangonghe Formation. Celadon, fluidity mudstone, and coal seams are the main lithologies in Xishanyao Formation; and the bottom of the stratum mainly consists of sandstone and conglomerate. There are 22 coal seams in the Xishanyao Formation with thicknesses ranging from 20 m to 50 m, and the coal seams mainly developed at the bottom of the Xishanyao Formation (Figure 1).

3. Samples and Methods

The coal samples were collected based on the sampling of coal seams. According to the characteristics of the development and distribution of the main mining coal seam in the Xishanyao Formation and arsenic content in coal from the Hanshuiquan coal mine, 11 coal samples were collected, three (Sample STH7-1~3), one (STH8-1), and seven (STH9-1~7) coal samples corresponding to the 7#, 8#, and 9# coal seams, respectively. Notably, the samples are the same as those studied by Feng et al. (2018) [26], and were collected not far from the sampling location of Zhang et al. (2018) [25].
Low-Temperature Ashing (LTA) was used to remove organic matter from raw coal in order to improve the accuracy of the X-ray diffraction (XRD). The LTA of the coal samples was performed with a K1050X (Emitech, Chelmsford, UK) oxygen plasma low-temperature ashing instrument. The mass of an approximately 1 g coal sample with the grain size of 200 mesh was balanced, and then was put into the vacuum reaction cavity. The power was set to 70 W with a vacuity of 6 kPa for 1.5 h per time, and the whole LTA procedure was carried out 8 times (12 h). After the LTA, measurements of samples were carried out with XRD. The XRD was performed on a D/max-2500/PC powder diffractometer (Rigake, Tokyo, Japan), and the Cu target and scintillation detector were used. The XRD was measured with diffraction angle (2θ) ranges from 3.00° to 64.99°, and an interval step of 0.02° per 2 s.
Meanwhile, the microstructure and element distribution information of the raw coal were collected by examining the coal with the use of a scanning electron microscopy–energy dispersive spectrometer (SEM-EDS, Zeiss, Oberkochen, Germany). All the coal samples were crushed into 100–200 mesh, then these samples were bonded on to conductive tape for the SEM-EDS measurements.

4. Results

The results show that the main minerals in the coal of the Xishanyao Formation from the Hanshuiquan mine are kaolinite, quartz, and illinite, and there is also a certain amount of pyrite. Some of the coal samples also contain a few arsenate minerals, mainly ojuelaite and scorodite (Figure 2). Kaolinite is the most common mineral in the coal. Under an oil immersion lens, the kaolinite mainly occurs as lumps and infillings of fusinite (Figure 3a,b), indicating that the kaolinite is an autogenous mineral. Pyrite is the most common mineral in the coal, and it presents extremely high reflectivity, and can be identified easily under an oil immersion lens. The pyrite present filled the plant tissue pores (Figure 3c) and subhedral areas on the surface of the coal matrix (Figure 3d). The filled pyrite was formed by the deposition of the ore-bearing solution during the late diagenetic stage. The sizes of the subhedral pyrite are more than 200 μm. These pyrites mainly formed at the early diagenetic stage. Due to the long geological period, the favorable growth direction is horizontal, and due to the overlying pressure from the strata, the pyrite presents as flat lenticel in the coal. The SEM-EDS results show that the surface of the coal matrix is a favorable place for the enrichment of arsenic (Figure 3e), and that some silicate minerals are also distributed on the surface of the organic matter (Figure 3f).

5. Discussion

5.1. Enrichment Characteristics of As in the Coal

There are at least five different modes of occurrence for elements in coal: a water-soluble state, an exchangeable state, an adsorption state, a mineral state, and an organic state [1,3,6]. The adsorption-state arsenic can be adsorbed on the surface of the mineral and the coal matrix, and it can even adsorb into the pores and fractures. The mineral state means that arsenic is an independent mineral, which occurs in the mineral lattice and inclusion. The organic-state arsenic means that the arsenic is combined into the coal molecule [27,28].
There are many studies on the enrichment characteristics of arsenic in coal [27,28,29,30]. Arsenic content in coal has relativity with the coalification [29,30]. Arsenic can be easily combined with the organic matter in low-rank coal, while, with the increased coalification of the coal, polymerization of the aromatic hydrocarbon in the bituminous coal decreases the binding ability with the trace elements, at which point arsenic tends to concentrate in the low-rank coal (Table 1). In addition, the distribution of arsenic in Chinese coal is related to the coal accumulation period to some extent. The arsenic content decreases successively from the Triassic period, Tertiary, Jurassic, and Carboniferous to the Permian period (Table 1) [21]. The various coal-forming plants and the different organs of the same plant also contribute to the variety of adsorption capacities of the trace elements [17,21]. The inferior organisms, algae, and herbs contribute a higher arsenic content than the advanced plants (Spermatophyta, Pteridophyta, and Bryophyta), and arsenic is easily enriched in coal formed in marine sedimentary environments [31,32,33].
The coal formed in the Jurassic period from the Xishanyao Formation in the Santanghu Coalfield is of the continental sedimentation with a low coalification degree, and the coal is long-flame coal which belongs to the low rank of sub-bituminous coal. The average arsenic contents in world coal and Chinese coal are 8.30 μg/g and 3.79 μg/g, respectively [5,34]. Based on the enrichment coefficient (CC) proposed by Dai (2012) [5], the enrichment characteristics of the various elements in the coal from the Hanshuiquan mine show that the enrichment of arsenic presents characteristics of significant enrichment. The average arsenic content in coal from the Hanshuiquan mine, compared with the average values of Chinese coal and the world’s coal, the CC values are 10.87 and 4.97, respectively (Table 2). Arsenic in the 9# coal seam presents an extremely high content of 108.37 μg/g, which is approximately 13 times that of world hard coal and 28 times that of Chinese coal [35] (Table 2). The average arsenic content ranges from 0 μg/g to 5 μg/g for the raw coal in Santanghu Basin, which is classified as first- and second-grade arsenic coal. In addition, the arsenic content in some individual mines is very high and can even be classified as be third- or fourth-grade arsenic coal [36]. The arsenic content of the raw coal in the 9# coal seam in the Hanshuiquan reconnaissance and survey area ranges from 0 μg/g to 54 μg/g [37]. Although an abnormal enrichment of arsenic has been found, there has seldom been any research carried out on it.

5.2. Occurrence Modes of As in the Coal

The determination of the occurrence mode of arsenic in the coal from the Santanghu Coalfield is the main research target in this study. The occurrence modes of arsenic in coal from the Hanshuiquan mine measured by the sequential chemical extraction experiment (SCEE) and two-orbit atomic fluorescence (AFS) methods indicate that the occurrence modes of arsenic were divided into sulfide form state, residual form state, organic state, and adsorption state [25] (Table 3). The average proportion of arsenic in coal in a sulfide form state was 73.09% [25]. The electron probe micro analysis (EPMA) results show that arsenic exists in the pyrite, but the maximum content in pyrite is less than 0.5% (wt. %) (Figure 4) [26]. Although there are content differences among the various areas [38,39], the extremely low arsenic content in pyrite from the Hanshuiquan mining area indicates that there are differences in enrichment states compared to the coal from Wulantuga in China [40,41] and Sarawak in Malaysia [42]. The pyrite form state and arsenopytire form state are not the main states for arsenic in the inorganic state; there is another inorganic state for arsenic in the coal of the Hanshuiquan mine. Even though there are differences in the occurrence modes, arsenic in coal from several regions (Santanghu, Ningwu, Wulantuga, and Guizhou) mainly occurs in pyrite (Table 3).
An arsenate form state has been reported. The arsenate form state is partly found in Guizhou, China [28,44], and arsenic can become enriched in the arsenate form state from the high content of arsenic in the coal of western Guizhou [31,45]. It is speculated whether arsenic can also exist in the form of arsenate. The SEM-EDS can directly observe the combination state and distribution of the arsenic in the coal [46,47]. The element distribution density identified via SEM-EDS shows that the surface of the organic matter, where a large amount of silicate minerals are enriched, also contains a certain amount of arsenic (Figure 5a). Arsenic is also present in the kaolinite, showing that the arsenic occurs in the residual state in line with previous results (Figure 5b). Figure 5c also shows that there is a certain relationship between the silicate minerals and arsenic contents (Figure 5c).
The XRD results show that there is little ojuelaite and scorodit in the coal, while it is not possible to observe the relationship between Fe and the As via SEM-EDS. The distribution of the Fe is unordered, which relates to one of the properties of the element. As an active element, in fact, the modes of occurrence for Fe in coal are various. Fe can not only become enriched in the iron-rich minerals, but also occur in various components. XRD can help to identify the compounds of the materials accurately, and is a reliable way to be sure of the compounds in the coal [1,2,3,4,5,6]. There is a better relationship between the As and Zn, which secure the ojuelaite in the coal. Except for the silicate minerals, there is also a good relationship between the As and Zn content in the organic matter (Figure 5a). It can be predicted that the form of Zn-arsenate is a mode of occurrence for arsenic in the coal, and that Zn-arsenate is distributed in the organic matter [24,48].

5.3. Origin of As in the Coal

The Santanghu Basin is a medium-scale composite basin formed by the superimposition of the residual basin from various sedimentary periods. During the late Permian period, the basin formed a northeast thrust uplift zone, a central depression zone, and a southwest thrust nappe zone from the north to south with a tectonic pattern of “two salients with one sag” influenced by the north–east trend extrusion stress [44,49]. The source rocks of Xishanyao Formation mainly came from the northeast thrust uplift zone, and the southwest thrust nappe zone was the sub-provenance [50,51]. These provenances form two metallogenic provinces (Figure 6), the porphyre Cu-Au mineral deposit in the northern Qiongheba ore-concentrated area and the epithermal Au mineral deposit in the southern Kalameili metallogenic belt [52,53]. Pyrite and arsenopytire are the dominant carriers for Au in these two ore-concentrated areas, and the pyrite that carries the Au also contains a certain amount of arsenic with an average content of 0.099% (wt. %), and the average arsenic content in the arsenopyrite can even reach 40.68% (wt. %). The pyrite and arsenopytire with arsenic can be weathered to become scorodite. According to the measurement data from the EPMA and XRD, the scorodite in the coal seams of the Hanshuiquan coal mine may originate from this provenance. Therefore, it can be reasonably speculated that the arsenic in the study area, at least to some extent, may come from the pyrite and arsenopytire in the provenance [25,54].

5.4. Occurrence Modes for Arsenic in Coal and Its Influence on the Environment

5.4.1. Occurrence Modes for Arsenic in Coal

Arsenic is one of the common trace elements in coal and has attracted much attention due to its great harm to the environment. The arsenic content in coal varies depending on the type of coal, the coal-forming environment, and the geological background [3]. The average arsenic concentrations in the worldwide low-rank coals and hard coals are 7.6 ppm and 9 ppm, respectively [34], while the average arsenic concentrations in coals for China and Australia are 3.79 ppm and 3 ppm, respectively [3]. In addition, the arsenic concentration in coal and its combustion products can reach up to 35,000 ppm [3].
The occurrence modes of arsenic in coal are diverse (Section 5.1 and Section 5.2, [3,10,13,43]). At present, the common understanding in academia is that the majority of arsenic in most coals occurs in pyrite as an isomorphic substitute for sulfur, or solid solutions (this work [3,55]). Arsenic may be enriched in pyrite, and its genesis can be either a syngenetic or epigenetic origin [3,56]. However, this does not mean that the arsenic content in coal rich in pyrite will be high. For example, studies show that framboidal pyrite in the Pennsylvania coal of the Appalachian Basin is usually deficient in arsenic [3,57]. Meanwhile, arsenic in coal is also related to clay minerals, phosphates, and arsenates (this work, [3,8]). Arsenic in coal occurs not only in minerals but may also be associated with organic matter in some cases (this work, [3]). However, it is mainly found in low-rank coal. Whether it is definitely present in high-rank coal requires further evidence [3].
Based on previous studies and this work, we believe that (1) arsenic in coal is predominantly in the form of pyrite, and (2) arsenic in coal is associated with organic matter in low-rank coal and to a lesser extent in high-rank coal.

5.4.2. The Impact of Arsenic in Coal on the Environment

Understanding the occurrence modes of arsenic in coal is of great significance because it has significant impacts on coal mining, preparation, combustion, and utilization, and has adverse effects on the environment and human health.
During the mining process, the dust produced by coal mining may contain arsenic. Long-term inhalation of arsenic-containing dust by people engaged in mining operations may lead to chronic arsenic poisoning [8,9]; in addition, untreated mine water containing arsenic may also affect groundwater and even surface water.
During the preparation stage, if the coal-washing wastewater generated from coal washing and selection is not properly treated, it will also cause water pollution. Arsenic that cannot be completely removed by washing (such as in organic form or in the form of fine mineral particles) will affect the subsequent combustion process [41].
During the coal combustion process, arsenic has a relatively high volatility. Most of it enters the atmosphere along with the flue gas, while a small portion remains in the ash and slag. The release form of arsenic (for example, gaseous As2O3, As2O5, or a granular adsorbed state) directly affects its environmental migration ability [8,9,41].
During the utilization stage, the ash produced by coal combustion is widely used in the construction industry, but the arsenic in coal limits its safe and clean utilization. In the industry of coal chemical utilization, arsenic in coal can inhibit the activity of catalysts, thereby affecting production efficiency.
In summary, arsenic in coal has the following impacts on the environment. (1) Air pollution: Coal-fired power plants, industrial boilers, and the burning of loose coal by residents are the main sources of arsenic emissions. Arsenic is oxidized to gaseous oxides at high temperatures and then adsorbed on fine particulate matter (PM2.5) through condensation, forming pollutants that can be transported over long distances. In addition, arsenic enters the surface through dry and wet deposition. Especially in areas with dense coal burning (China, India), atmospheric arsenic deposition can significantly increase the arsenic load of the surrounding soil and water bodies. (2) Water and soil pollution: When coal ash is stored in the open air or landfilled, rainwater leaching leads to arsenic leaching, polluting groundwater and surface water. (3) Human health risks: Residents in coal-burning areas may suffer from chronic arsenic poisoning by breathing arsenic-containing particulate matter, drinking contaminated groundwater, or consuming high-arsenic crops [5].

6. Conclusions

  • Analysis of coal samples from the Hanshuiquan mine in the Santanghu Coalfield shows that the main minerals are quartz, kaolinite, and dolomite, with a certain amount of secondary minerals such as brookite and anatase; there is also a small amount of pyrite. Some samples (from 9# coal seam) were also found to contain arsenate minerals. The kaolinite filled the plant tissue pores in the fusinite, indicating an early diagenesis. The subhedral and filled plant tissue pores of the pyrite denotes an early diagenesis.
  • The occurrence mode of the arsenic in the coal from the Hanshuiquan mine in the Santanghu Coalfield is dominated by the arsenate form state. The results of XRD and SEM-EDS show the existence of ojuelaite, and the presence of scorodite may come from the provenance.
  • The pyrite and arsenopyrite, as the dominant gold-bearing minerals, provide the most abundant originate of arsenic for the coal of the Xishanyao Formation in the Santanghu Coalfield, and these gold-bearing minerals are formed to be produced from the epithermal Au mineral deposit at both the Qiongheba and the Kelameili ore-concentrated areas.

Author Contributions

Conceptualization, B.Z., W.W. (Wenfeng Wang), S.F. and M.W.; Methodology, B.Z., W.W. (Wenfeng Wang), J.T., W.W. (Wenlong Wang), S.F. and M.W.; Software, B.Z. and J.T.; Formal analysis, B.Z. and W.W. (Wenlong Wang); Investigation, S.F. and M.W.; Writing—original draft, B.Z.; Writing—review & editing, B.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by the Major Science and Technology Special Project of Xinjiang Uygur Autonomous Region (2022A03014), the Natural Science Foundation of China (42162017, 42472236, 42402176), and the Third Xinjiang Scientific Expedition Program (2022xjkk1003).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We give sincere thanks to the editor and anonymous reviewers for their valuable and constructive comments on the paper.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Applsci 15 07092 g001
Figure 1. Location map of study area (modified from Zhang et al., 2018) [25]. The red line represents the fault, and the area within the blue line indicates the location of the study area.
Figure 1. Location map of study area (modified from Zhang et al., 2018) [25]. The red line represents the fault, and the area within the blue line indicates the location of the study area.
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Figure 2. X-ray diffraction (XRD) pattern of coal samples STH9-1 and STH9-6. (a) Detection of scorodite in sample STH9-1; (b) detection of ojuelaite in sample STH9-6 (Zhang et al., 2018) [25].
Figure 2. X-ray diffraction (XRD) pattern of coal samples STH9-1 and STH9-6. (a) Detection of scorodite in sample STH9-1; (b) detection of ojuelaite in sample STH9-6 (Zhang et al., 2018) [25].
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Figure 3. Microscopic images under oil immersion lens and scanning electron microscope. (a) Kaolinite infillings of fusinite (500×); (b) kaolinite and other clay minerals in fusinite (500×); (c) pyrite filled into the plant tissue pores; (d) subidiomorphic pyrite; (e) As distribution map of coal particles under scanning electron microscope; (f) silicate minerals distributed on the surface of the organic matter.
Figure 3. Microscopic images under oil immersion lens and scanning electron microscope. (a) Kaolinite infillings of fusinite (500×); (b) kaolinite and other clay minerals in fusinite (500×); (c) pyrite filled into the plant tissue pores; (d) subidiomorphic pyrite; (e) As distribution map of coal particles under scanning electron microscope; (f) silicate minerals distributed on the surface of the organic matter.
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Figure 4. Images of pyrite in sample STD9-1 (Feng et al., 2018) [26]. (a) Filling status of pyrite; (b) pyrite in fracture. Clay—Clay; Ct—Telocollinite; Cg—Corpocollinite; Sf—Semifusinite; Py—Pyrite; Vd—Vitrodetrinite; Id—Inertodetrinite.
Figure 4. Images of pyrite in sample STD9-1 (Feng et al., 2018) [26]. (a) Filling status of pyrite; (b) pyrite in fracture. Clay—Clay; Ct—Telocollinite; Cg—Corpocollinite; Sf—Semifusinite; Py—Pyrite; Vd—Vitrodetrinite; Id—Inertodetrinite.
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Figure 5. The secondary electron microscope, element distribution density, and EDS images of the mineral compounds from the typical grain samples. (a) is the organic matter covered by the silicate minerals (i) and the element distribution density of As (ii), O (iii), Zn (iv), and Fe (v); (b) is the kaolinite (i) and the element distribution density of As (ii), O (iii), Si (iv), and Al (v); (c) is the organic matter (i), the element distribution density of As (ii), and the area spectrum (iii), spectrum 2 (iv), and spectrum 4 (v) from the EDS.
Figure 5. The secondary electron microscope, element distribution density, and EDS images of the mineral compounds from the typical grain samples. (a) is the organic matter covered by the silicate minerals (i) and the element distribution density of As (ii), O (iii), Zn (iv), and Fe (v); (b) is the kaolinite (i) and the element distribution density of As (ii), O (iii), Si (iv), and Al (v); (c) is the organic matter (i), the element distribution density of As (ii), and the area spectrum (iii), spectrum 2 (iv), and spectrum 4 (v) from the EDS.
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Figure 6. Distribution of enriched elements and sources of sediments in the Santanghu Basin (modified from Zhang et al., 2018) [25].
Figure 6. Distribution of enriched elements and sources of sediments in the Santanghu Basin (modified from Zhang et al., 2018) [25].
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Table 1. Concentration of As in coal for different rank and coal-forming ages (μg/g) (from Zheng et al., 2006) [21].
Table 1. Concentration of As in coal for different rank and coal-forming ages (μg/g) (from Zheng et al., 2006) [21].
RankPeatLigniteBitumiteAnthraciteBone Coal
As(μg/g)3–32.30.3–6700.5–1760.7–3115–2820
PeriodCarboniferousPermianTriassicJurassicTertiary
As(μg/g)3.74.211.13.510.5
Table 2. Concentrations (μg/g) and concentration coefficients of As from the Hanshuiquan mine (modified from Feng et al., 2018) [26].
Table 2. Concentrations (μg/g) and concentration coefficients of As from the Hanshuiquan mine (modified from Feng et al., 2018) [26].
SampleSTH7-1STH7-2STH7-3STH8-1STH9-1STH9-2
As61.139.6714.3735.34108.379.71
CC17.371.171.734.2613.061.17
CC221.993.485.1712.7138.983.49
SampleSTH9-3STH9-4STH9-5STH9-6STH9-7Average
As34.6324.8426.2556.4572.6541.22
CC14.172.993.166.808.754.97
CC212.468.949.4420.3126.1310.87
Note: CC1 = concentration in investigated coals/world hard coals; CC2 = concentration in investigated coals/Chinese coals.
Table 3. Concentration (μg/g) and occurrence of arsenic in coal from the Hanshuiquan coal mine (modified from Feng et al., 2018) [26].
Table 3. Concentration (μg/g) and occurrence of arsenic in coal from the Hanshuiquan coal mine (modified from Feng et al., 2018) [26].
Sample NumberAdsorption ArsenicOrganic Bound ArsenicResidual Form of ArsenicSulfide Bound ArsenicThe Result of Reductive Difference MethodPercentage of As5+Sum of All FormsThe Total Arsenic Content (by AFS)
P1P2P3P4As(III)As(III) + As(V)As(V)(%)(µg/g)
µg/gµg/gµg/gµg/gug/gug/gug/g
3#0.553.126.4560.548.144637.952.6470.6672
5#02.46.440.815.660.544588.2449.651
6#023354612.540.828.326.20104108
7#01166332.26330.838.028081
NW ++ +
GZ +++
WLTG +
Note: NW, Samples from the Ningwu coalfield, data from reference [40]; GZ, samples from Guizhou Province, China, data from reference [22,31,43]; WLTG, samples from the Wulantuga coalfield, data from reference [41]. “+” means that the occurrence mode of arsenic exists in the sample.
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Zhu, B.; Wang, W.; Tian, J.; Wang, W.; Feng, S.; Wang, M. Occurrence Modes of Arsenic in Coal: A Case Study from the Hanshuiquan Coal Mine, Santanghu Coalfield, Xinjiang Province, China. Appl. Sci. 2025, 15, 7092. https://doi.org/10.3390/app15137092

AMA Style

Zhu B, Wang W, Tian J, Wang W, Feng S, Wang M. Occurrence Modes of Arsenic in Coal: A Case Study from the Hanshuiquan Coal Mine, Santanghu Coalfield, Xinjiang Province, China. Applied Sciences. 2025; 15(13):7092. https://doi.org/10.3390/app15137092

Chicago/Turabian Style

Zhu, Bo, Wenfeng Wang, Jijun Tian, Wenlong Wang, Shuo Feng, and Meng Wang. 2025. "Occurrence Modes of Arsenic in Coal: A Case Study from the Hanshuiquan Coal Mine, Santanghu Coalfield, Xinjiang Province, China" Applied Sciences 15, no. 13: 7092. https://doi.org/10.3390/app15137092

APA Style

Zhu, B., Wang, W., Tian, J., Wang, W., Feng, S., & Wang, M. (2025). Occurrence Modes of Arsenic in Coal: A Case Study from the Hanshuiquan Coal Mine, Santanghu Coalfield, Xinjiang Province, China. Applied Sciences, 15(13), 7092. https://doi.org/10.3390/app15137092

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