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Mercury (Hg) is commonly present at trace levels in coal deposits. Geological processes, particularly magmatic intrusion and hydrothermal cycling in coal-bearing strata can significantly increase Hg levels in coals. However, the effects of thermal stress, magmatic components, magmatic-hydrothermal fluids, low-temperature hydrothermal fluids on Hg enrichment are confounded in a magmatic-affected coal basin. Here, we demonstrate the use of stable Hg isotopes to understand the controlling factors on Hg enrichment in two well-known Chinese coal deposits affected by magmatic activities: Wulantuga low-temperature hydrothermal-altered coal deposit and Wolonghu magmatic-intruded coal deposit. The Wulantuga No. 6 coal seam is extremely enriched in Hg, varying from 0.37 μg/g in middle coal benches to 40–90 μg/g in the upper most and lowest coal benches. Approximately 2.5‰ variation in mass dependent fractionation (MDF, − 3.07‰ to − 0.58‰ in δ 202 Hg) is observed. δ 202 Hg vs. 1/[Hg] diagram suggests a mixture of three Hg end-members: original hydrothermal fluids, fractionated hydrothermal fluids and native coal-forming materials. In addition, Wulantuga coals all show positive mass independent fractionation (MIF) of odd isotopes, up to 0.87‰ in Δ 199 Hg and 0.66‰ in Δ 201 Hg. The Δ 199 Hg/Δ 201 Hg ratios range from 1.3 to 3.3, suggesting that a large fraction of photodegraded methylmercury was likely incorporated into the coal deposit. The magmatic-intruded Wolonghu No. 8 coal seam is only slightly to intermediately enriched in Hg, varying from 0.10 μg/g to 0.40 μg/g. The coals near the contact sill (≤ 5 cm, − 1.81‰ to − 1.52‰) have similar δ 202 Hg as the magmatic sill rocks (− 2.05‰ to − 1.80‰), both with insignificant MIF values. Coals far from the contact sill (≥ 15 cm) have δ 202 Hg values varying from − 3.40‰ to − 1.61‰ and Δ 199 Hg varying from 0.26‰ to 0.58‰, which are significantly enriched in light and odd Hg isotopes compared to coals near the contact sill. Δ 199 Hg and Δ 201 Hg in Wolonghu coals far from the contact sill resemble those of meteoritic waters and seawater in both magnitude and Δ 199 Hg/Δ 201 Hg ratio. Our two case studies show significant MDF and MIF of Hg isotopes, which inform on Hg migration and sequestration in the magmatic rocks and coal deposits, and on the roles of meteoric water and hydrothermal fluid circulation. [ABSTRACT FROM AUTHOR]

The organic matter in coal contains polycyclic aromatic compounds (PACs) of varying quantities in diverse soluble and insoluble forms. PACs in coal are of special interest for organic geochemical studies because they have been successfully used as biological marker compounds (biomarkers) and indicators of thermal maturity. In addition, they could provide critical information to understand the structural and compositional evolution of the coal organic matters during coalification, and to predict PAC releasing characteristics during coal utilization. The main purpose of this paper is to provide a critical review on the current state of knowledge on the potential use of PAC composition to understand the underlying biogeochemical factors that control PAC occurrence and distribution in coal. The published PAC data of world coal are first compiled according to their ranks (natural coke, anthracite, semi-anthracite, bituminous coal, low volatile bituminous coal, medium volatile bituminous coal, high volatile bituminous coal, sub-bituminous coal, lignite), countries (Brazil, Canada, China, France, Germany, Japan, USA), formation periods (Carboniferous, Permian, Jurassic, Cretaceous, Early-Middle Cenozoic). Then, the biogeochemical factors affecting the occurrence and distribution of PACs in coal, including biogenic precursor materials, coal rank, maceral composition, depositional environment, and geological settings, are comprehensively reviewed. The results show that the geochemical parameters of PACs in coal are robust tools to trace the coalification processes from the molecular perspectives, and to understand the corresponding biogeochemical process (e.g. depositional environment, geological settings, igneous intrusion) occurring during coal formation. [ABSTRACT FROM AUTHOR]

Coal deposits were important natural Hg sinks in the Late Paleozoic and Middle-Late Mesozoic. Coal combustion since the industrial revolution has emitted more than 35,000 t of Hg into the atmosphere. Environmental geochemistry research on Hg in coal is essential to understand the natural Hg cycle throughout Earth history and the present-day Hg cycle under human perturbation. In this review, we summarize the methods of Hg isotope measurement in coals, and compile recently published Hg isotope data of > 200 world coal samples according to their locations, formation periods (Carboniferous, Permian, Jurassic, Cretaceous, Early-Middle Cenozoic) and ranks (anthracite, bituminous coal, subbituminous coal, lignite), and illustrate the controls of sources and biogeochemical processes on Hg isotope compositions in coal deposits. Up to 4.7‰ variation (− 3.90 to 0.77‰) in mass dependent fractionation (MDF, represented by δ 202 Hg) and 1.0‰ variation (− 0.63 to 0.34‰) in mass independent fractionation (MIF, represented by Δ 199 Hg) are observed in world coal deposit, with an average value of − 1.16 ± 0.79‰ (1SD) and − 0.11 ± 0.18‰ (1SD) for δ 202 Hg and Δ 199 Hg, respectively. We find that coal δ 202 Hg and Δ 199 Hg are broadly controlled by two source materials: terrestrial plants (biogenic Hg) and crustal rocks (geogenic Hg), accounting for 37–46% and 54–63% of Hg in coals. No clear trends are seen in neither δ 202 Hg vs. coal-forming periods nor δ 202 Hg vs. coal ranks, which we attribute to important overlapping of δ 202 Hg in the source materials of different coal-forming periods and the multidirectional Hg MDF during coalification. Interestingly, a step-wise increase in total Hg and a disappearance of Δ 199 Hg are observed along with increasing coal rank, suggesting the addition of hydrothermal Hg into high-rank coals. The hydrothermal fluids not only upgraded the coal ranks, but also increased the Hg concentrations and Δ 199 Hg of coals. In addition, the addition of hydrothermal Hg into coal deposits was also partly responsible for the comparatively higher total Hg and Δ 199 Hg in the Late Paleozoic coals relative to the Mesozoic and Cenozoic coals. The co-variation of atmospheric oxygen levels and Δ 199 Hg of coals at different coal-forming time widows suggests that the removal of biogenic Hg in response to widespread swamp fires may have increased the Δ 199 Hg in Late Paleozoic coals as well. Our study indicates that coal Hg isotopes provide new insights into the biogeochemical cycle of Hg in coal deposits, and that Δ 199 Hg is a robust indicator to trace Hg addition/removal in coal deposits and biogeochemical processes (magmatic intrusion, hydrothermal fluids penetration, burning of coal swamp) occurring during coal deposition. [ABSTRACT FROM AUTHOR]

Mercury (Hg) stable isotope variations provide a potential tool to better understand the provenance and geochemical processes that control Hg occurrences in coal deposits. In this study, we explore the variations in Hg isotope compositions in coal benches of a single coal seam (No. 3-1 coal seam, Daizhuang Coal Mine, Jining Coalfield, Shandong Province), and in successive coals seams of a coal-bearing sequence (No. 1 to No. 11-2 coal seams, Zhuji Coal Mine, Huainan Coalfield, Anhui Province) to assess Hg isotopes as a Hg biogeochemical tracer in coal deposits. Large variations in mass dependent Hg isotope fractionation (MDF) were observed in both Daizhuang and Zhuji coal deposits, with δ 202 Hg values ranging from − 2.34 to − 0.25 ± 0.12‰ (2 SD, n = 8), and from − 1.62 to 0.44 ± 0.12‰ (2 SD, n = 18), respectively. Daizhuang coals showed insignificant mass independent Hg isotope fractionation (MIF) in most samples (− 0.04 to 0.12 ± 0.08‰ for Δ 199 Hg, 2 SD, n = 8), whereas MIF in the younger Nos. 7-11 coal seams of Zhuji coals (0.06 to 0.22 ± 0.08‰ for Δ 199 Hg, 2 SD, n = 7) were positive and significant. Increased trends in both Hg concentrations and δ 202 Hg values going from older to younger Zhuji coal seams were observed, and were possibly related to variations in coal-forming environment of different coal seams. The significant negative correlations of δ 202 Hg vs. 1/Hg in the Zhuji coals, and of δ 202 Hg vs. Δ 199 Hg in the Daizhuang coals suggest that Hg isotopes can potentially be used to trace organic and inorganic Hg end-members in coal deposits. Natural coke, a metamorphosed form of coal, is on average two-fold enriched in Hg compared to coal, indicating that hydrothermal fluids derived from magmatic intrusions bring Hg into coal deposits. In addition, coke has either distinctly higher (0.70 to 0.91 ± 0.12‰, 2 SD, n = 2) or lower δ 202 Hg (− 4.00 to − 3.47 ± 0.12‰, 2 SD, n = 3) than corresponding coals, demonstrating that significant Hg MDF occurred when coals were thermally contacted by intruded magmas. [ABSTRACT FROM AUTHOR]

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1-20 ng/g) by wet chemistry is challenging. Combustion-trapping techniques have been shown to be an appropriate alternative []. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into HO, CO, SO, etc. The O carrier gas, including combustion products and elemental Hg, is then purged into a 40 % ( v/ v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO/1HCl ( v/ v), 25 mL/min O flow rate, and a dynamic temperature ramp rate (15 °C/min for 25-150 and 600-900 °C; 2.5 °C/min for 150-600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81-102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80-120 %. This protocol has the advantages of a short sample processing time (∼3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis. [ABSTRACT FROM AUTHOR]

Abstract: Coal-fired utility boiler (CFUB) emissions of mercury (Hg) represent the largest anthropogenic Hg source to the atmosphere. Hg stable isotope signatures in coal have been shown to vary among coal deposits and coal basins. There is therefore a substantial interest in tracing CFUB Hg emissions at local, regional and global scales. However, CFUB operating conditions, Hg capture technologies and post-emission Hg transformations may potentially alter the original feed coal Hg isotope signatures. Here we investigate Hg isotopic fractionation between feed coal and coal combustion products in six utility boilers of two large power plants in Huainan City, Anhui Province, China. We observe identical trends in all six boilers: relative to feed coal with δ202Hg ranging from −0.67 to −0.18‰, oxidized Hg species in bottom ash and fly ash are enriched in the lighter isotopes with δ202Hg from −1.96 to −0.82‰. Flue gas desulphurization by-product gypsum shows δ202Hg from −0.99 to −0.47‰. No mass independent fractionation was observed during the transport and transformation of Hg inside the boilers. An isotope mass balance suggests that gaseous stack Hg emissions are enriched by up to 0.3‰ in the heavier Hg isotopes relative to feed coal and that the enrichment depends on the Hg capture technology. The observation that oxidized Hg species are enriched in the lighter isotopes suggests that oxidized and reduced forms of Hg in stack emission carry different isotope signatures. This has implications for near-field and far-field Hg emission tracing. [Copyright &y& Elsevier]

Abstract: The comprehensive information of coal quality and its relationship with coal-forming environment in Zhuji exploration area, Huainan coalfield Anhui, China, have been studied. The data of coal quality including proximate and ultimate analysis, calorific values, sulfur forms, petrography and selected trace elements (Ga, Ge, V, U, Th, Cl and As) are based on 614 samples of 13 minable coal seams from 88 drilling holes collected during exploration periods. These data were designed to provide information on the technological performance of coal. Characteristics of coal quality deposited in three different sedimentary environments, namely in coal-bearing strata of the Shanxi Formation, Lower Shihezi Formation and Upper Shihezi Formation, were analyzed. Results show that moisture, volatile matter, and ash yield all increase stratigraphically upward, which is opposite to the variation of calorific values. The correlation between ash yield and calorific value shows negatively higher relevance that than of moisture and ash yield. The coal quality parameters of the boreholes along the divided faults were rarely controlled by geological setting. It was suggested that other factors such as magmatic activity and underground water cycling may modify the parameters of coal quality to some extent and cause their redistribution. [Copyright &y& Elsevier]

Perhydrous coal (PHC) had been widely investigated; however, a systematic research on the relationship between the structure of PHC and its thermal reactivity was rarely reported in the previous studies. The PHC was widely developed in the Carboniferous-Permian coal-bearing strata in the northern and eastern regions of the Huainan coalfield. In this study, we chose No. 13-1 PHC as the research object. Based on the macroscopic observation of No. 13-1 PHC of the borehole #9-3 and its logging response, a typical PHC sample was selected and pyrolyzed using a thermogravimetric analyzer (TGA) to acquire a set of coal samples after pyrolysis with wide range of random vitrinite reflectance (% VRo) from 0.86 to 7.79%. The thermal evolution process of PHC before and after pyrolysis was investigated by atomic force microscopy (AFM) and Raman spectroscopy. Research results show that: 1) in the experimental temperature range, the reflectance (VRo) range of PHC varied greatly; 2) with the increase of pyrolysis temperature, the Raman spectra of PHC changed significantly in the D band of disordered structure and the G band of ordered structure and the orderliness of its macromolecule particle arrangement was increasing gradually; 3) the relationship between the thermal reactivity of PHC and its Raman structure parameters was established, the FWHM of G-band can be used as indicators of the degree of thermal evolution of PHC; 4) compared with the G FWHM of normal coal with different rank, the thermal reaction temperature of PHC was advanced. Under the premise of comparable reaction temperature, the thermal maturity of PHC was gradually higher than that of bituminous coal, and slightly lower than anthracite, indicating that the actual PHC thermal maturity was suppressed by a higher amount of hydrogen. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hg concentrations in coal and surface water samples were determined. [•] Hg is enriched in the Huaibei coals. [•] Magmatic activities imparted influences on Hg content and distribution. [•] Hg contents in surface waters are relative low at the present status. [ABSTRACT FROM AUTHOR]

Abstract: Rare earth element (REE) concentrations in coals are a source of information relevant to the evolution of source rocks, depositional environment, and epigenetic tectonic activity as well as the effects of igneous intrusions. In this study, 186 coal samples, 11 intrusion-affected coal samples, 4 samples representative of the intrusive rocks, one coal roof and one parting samples were collected from 29 boreholes at the Zhuji coal mine, Huainan Coalfield, Anhui Province, China. The main objective is to characterize the intrusive rocks in the coal-bearing sequence and to investigate the correlation of REE parameters in the coals with the source rocks, depositional environment, localized faults, igneous intrusions, and thickness of the coal beds. A sequence (from base to top) of acidic to basic intrusive rocks through the coal-bearing strata was identified, which possibly corresponds to different intrusive episodes of granite, diorite/monzonite and gabbro. Both the REE contents and degree of fractionation of light rare earth elements (LREE) and heavy rare earth elements (HREE) increase from acidic to basic rocks. Most rocks are slightly depleted in Ce but highly depleted in Eu. The REE concentrations in coals from the Zhuiji mine (average of 118μg/g) are nearly identical to recently-updated average Chinese values, but significantly higher than global values. The REE content of the intrusion-affected coals is not distinctively different from that of the other coals (P=0.2), and REE concentrations of the igneous rocks appear to have no clear relationship to those of the intrusion-affected coals. The depositional environment and source rocks are presumably the main REE contributors to the coal-accumulation basin. The REE content in coals from fault-affected boreholes is higher than that in other boreholes and this trend is stronger in the coal seams of the upper strata. The HREE tend to be incorporated into thinner coal seams and the degree of fractionation between LREE and HREE of the coal-forming materials increases with coal thickness. [Copyright &y& Elsevier]

To investigate the magnitude to which the carbon isotopic ratio (δ 13 C) varies in coals in response to their contemporary terrestrial environment, the Early-Middle Permian Huainan coals (including coals from the Shanxi Formation, Lower Shihezi Formation and Upper Shihezi Formation) in North China were systematically sampled. A 2.5‰ variation range of δ 13 C values (−25.15‰ to −22.65‰) was observed in Huainan coals, with an average value of −24.06‰. As coal diagenesis exerts little influence on carbon isotope fractionation, δ 13 C values in coals were mainly imparted by those of coal-forming flora assemblages which were linked to the contemporary climate. The δ 13 C values in coals from the Shanxi and Lower Shihezi Formations are variable, reflecting unstable climatic oscillations. Heavy carbon isotope is enriched in coals of the Capitanian Upper Shihezi Formation, implying a shift to high positive δ 13 C values of coeval atmospheric CO 2 . Notably, our study provides evidence of the Kamura event in the terrestrial environment for the first time. [ABSTRACT FROM AUTHOR]

Abstract: The rapid expansion of coal-fired power plants (CFPPs) in China has produced huge volume of toxic elements associated combustion residues, which pose great threat to local environment. In this study, feed coal, fly ash, bottom ash and FGD gypsum samples were collected from two different CFPPs at Huainan, Anhui, China. Feed coal and combustion residues were morphologically and mineralogically characterized by scanning electron microscopy equipped with energy-dispersive microanalyser and X-ray diffraction. Concentrations of thirteen major and trace elements in these samples were determined by inductively coupled plasma atomic emission spectrometry (B, Ti, Mn, Ni and Zn), inductively coupled plasma mass spectrometry (Cd, Co, Cr, Cu, Pb, Sn and V) and atomic fluorescence spectroscopy (As). The results show that most of the trace elements were concentrated in the fly ash, only Fe and Mn were enriched in the bottom ash. The diameters of ash particles removed by the electrostatic precipitator were in an inverse relationship with the enrichment factors of most trace elements. To address possible exposure of combustion residues in the environment, laboratory controlled leaching tests were carried out on fly ash and gypsum to understand the environmental behaviors of these elements. Both fly ash and gypsum were identified as not-hazardous wastes. [Copyright &y& Elsevier]

The Wuda coalfield, Inner Mongolia, China, has been suffering from serious coal fire disaster for more than half a century. In the past decade, the central and local governments have carried out many fire-fighting projects to put out the coal fires, but coal fires still sporadically occur in the coalfield. Previous studies showed that coal fires could release large amounts of mercury (Hg) into the environment. Meanwhile, the rapid industrial development in recent years in Wuda area has also discharged a certain amount of Hg. Identification and quantification of the Hg emitted from coal fires and industrial sources is critical to formulate appropriate environmental policies. This study determined Hg isotope compositions in different types of coals from Wuda coal fire area and surface soils with different distances to the coal fire area, with an aim of anchoring the potential Hg sources in soils. The results showed that the coals had moderately negative δ202Hg (−2.02∼-1.21‰) and slightly negative Δ199Hg (−0.14–0.00‰), while the soils generally had more positive δ202Hg (−1.97∼-0.26‰) and Δ199Hg (−0.07–0.04‰) with distinct isotope ranges among different sampling sites. According to characteristic Hg isotope compositions of different sources, we concluded that the Hg in Wuda soils mainly sourced from cement plants and coal fires, and coal fires were still an important Hg contamination source in Wuda area. Image 1 • Wuda coals have moderately negative δ202Hg and slightly negative Δ199Hg. • Wuda soils have distinct mercury isotope ranges among sites. • Mercury in Wuda soils mainly sourced from cement plants and coal fires. • Coal fires are still an important mercury contamination source in Wuda area. [ABSTRACT FROM AUTHOR]

Tin (Sn) is a redox-sensitive element and geochemically incompatible that accumulates in evolved magmas and associated hydrothermal fluids. Here, a Sn stable isotope approach is used to characterize sources and geochemical behaviors of Sn in magmatic intruded coal deposits by combining with petrographic and elemental analysis. Sn isotope ratios of twelve coal samples with various magmatic-affected degrees show a δ120/118Sn variation from −0.06 to 0.22‰ (2σ of 0.07‰, relative to NIST 3161a). Basing on Sn isotope data and geochemical characteristics of the samples, we suggest binary source mixing and redox state related isotope shift as two mechanisms accounting for the isotope variations. The first mechanism is an admixture of magmatic-hydrothermal fluids, characterized by high δ120/118Sn, into coal deposits with low δ120/118Sn. A binary mixing model is used to estimate Sn contributions of the two end-members. The second process results in a positive isotope shift caused by an oxidation of sample states when they are affected by magmatic intrusions. In fact, magmatic intrusions could trigger the oxidation of Sn, resulting in heavy Sn isotope enrichment in the magmatic affected samples. The change in coal redox-state is supported by a concomitant change of redox proxies, such as V/(V + Ni), Mn/Cr and V/Cr. The enrichment of heavy Sn isotopes in samples impacted by magmatic hydrothermal fluids compared to normally-deposited coals could be explained by the conversion of dominant Sn species from Sn (II)–S to Sn (IV)–O under the influence of oxidative magma, which favors the enrichment of heavier Sn isotopes in Sn (IV)–O due to its shorter bond length. This study shows that Sn isotope ratios are useful tools for investigating Sn geochemical behavior in different Earth reservoirs and during redox sensitive processes. • The Sn isotope variations of twelve coals with different magma intrusion degrees ranged between −0.06 and 0.22‰ (2σ = 0.07). • A binary mixing model on Sn isotopes was applied to reflect the contributions of magmatic Sn and coal-deposited Sn. • A correlation between Sn isotope shifts and sample redox changes was observed. [ABSTRACT FROM AUTHOR]