Hydrochemical characteristics of abandoned coal mines derived acid mine drainage in a typical karst basin (Wuma river basin, Guizhou China).

The hydrochemical characteristics of acid mine drainage (AMD) were investigated in Wuma River Basin, China. AMD was sampled from nine closed coal mine (CCM) sites to study the temporal and spatial evolution of pH, dissolved oxygen (DO), electrical conductivity (ED), total hardness (THR), total dissolved salt (TDS), and trace elements. The surface water (river) and groundwater surrounding mine sites were sampled to evaluate the potential pollution derived from AMDs. The TDS content of AMD was higher than that of surface water and groundwater. The dominant factors influencing TDS were the pH, temperature, and wet or dry season (which played a role in controlling microbial activity), HCO3 - balance, and REDOX during the evolutionary process. The hydrochemical type of AMD was dependent on the evolutionary stage. From observations, most AMDs were in the form of the SO4 2--Ca2+•Mg2+ type that was characterized by a low pH, low [HCO3 -], high [SO4 2-], and high [Fe]. In addition, the AMD samples were undergoing stage I and II processes, in which SO4 2- and trace elements were generated. The surface water and groundwater were primarily classified as the HCO3 --Ca2+•Mg2+ type, which accounted for their self-cleaning capacity, as indicated by the high [HCO3 -]. The surface water and groundwater could be affected by the surrounding AMD depending on the geographical location. The surface water and groundwater sites that were located downstream of subsurface and surface runoff were obviously affected by AMD. After being polluted by AMD, surface water and groundwater contained higher levels of trace elements and emerged as the HCO3 -•SO4 2--Ca2+•Mg2+ type.

Remediation of Acid Mine Drainage (AMD) Using Steel Slag: Mechanism of the Alkalinity Decayed Process.

Steel slag has been proven to be an effective environment remediation media for acid neutralization, and a potential aid to mitigate acid mine drainage (AMD). Yet its acid neutralization capacity (ANC) is frequently inhibited by precipitate after a period of time, while the characteristics of the precipitate formation process are unclear yet. In this study, ANC for basic oxygen steel slag was conducted by neutralization experiments with dilute sulfuric acid (0.1 M) and real AMD. Some partially neutralized steel slag samples were determined by X-ray diffraction (XRD), scanning electron microscopy combined with an energy dispersive spectrometer (SEM-EDS), and N2 adsorption tests to investigate the potential formation process of the precipitate. The results indicated that Ca-bearing constitutes leaching and sulfate formation were two main reactions throughout the neutralization process. A prominent transition turning point from leaching to precipitate was at about 40% of the neutralization process. Tricalcium silicate (Ca3SiO5) played a dominant role in the alkalinity-releasing stage among Ca-bearing components, while the new-formed well crystalline CaSO4 changed the microstructure of steel slag and further hindered alkaline components releasing. For steel slag of 200 mesh size, the ANC value for the steel slag sample was 8.23 mmol H+/g when dilute sulfate acid was used. Neutralization experiments conducted by real AMD confirmed that the steel slag ANC was also influenced by the high contaminants, such as Fe2+, due to the hydroxides precipitate reactions except for sulfate formation reactions.

Study on the microstructure of the symbiosis of coal-based graphene and coal-based graphene quantum dots: preparation and characterization.

Coal-based graphene sheets (GS) and coal-based graphene quantum dots (GQDs) are usually prepared separately. In this paper, symbiosis of coal-based GS and coal-based GQDs was successfully prepared with our proposed preparation method by using three raw coals with different reflectance (collected from Qinshui coalfield, Shanxi Province) as carbon sources. The results showed that coal-based GS and coal-based GQDs can exist stably in the symbiosis and are distributed in different layers, and the GQDs are freely distributed between layers of GS. The average number of GS (Nave) in the three symbiosis is about 7 and the average interlayer spacing (d002) is about 0.3887 nm. The average diameter of GQDs in the three symbiosis is about 4.255 nm and the averaged002is about 0.230 nm. The averageNaveof the three symbiosis was about 3 and the averaged002is about 0.361 nm. The morphology and crystal parameters of symbiosis is more similar to that of graphene, the elements are only carbon and oxygen. In the prepared symbiosis, the higher the reflectance of raw coal, the smoother the lattice skeleton and the less vortex-layer structure of GS, and the larger the diameter and the denser the six membered ring of GQDs. The C and O functional groups of the prepared symbionts are similar. The higher the reflectance of coal, the higher the content of C-C/C=C. Under ultraviolet light, the prepared products all emit blue, and the higher the reflectance of coal, the higher the ultraviolet absorption, and the stronger the fluorescence intensity.

Pore Structure of Organic Matter in the Lacustrine Shale from High to Over Mature Stages: An Approach of Artificial Thermal Simulation.

The pore structure of organic matter (OM) is affected by the maturity and type of OM, and these exert an important control on the development of OM pores. However, it is often challenging to distinguish between autochthonous and secondary OM. In this study, different types of OM were distinguished by means of morphology and the form of its occurrence under scanning electron microscopy (SEM) observation. Pyrolyzed samples were used to obtain pore structures of autochthonous and secondary OM from a lacustrine shale from high to over mature stages. The SEM observations indicated that the secondary OM is porous, whereas the autochthonous OM is nonporous. Further, nitrogen adsorption data showed that nanopores in the autochthonous OM are blocked in non-extracted samples and reoccurred after extraction, whereas nanopores in the secondary OM remain open from high to over mature stages. Moreover, the pore structure, i.e., pore type and pore size, differed for autochthonous and secondary OM in the lacustrine shale. For instance, nanopores in the autochthonous OM were micropores (smaller than 1.5 nm); nanopores in the secondary OM were mesopores (ranging from 5 to 20 nm) and micropores. Nanopores in the autochthonous OM were formed at reflectance values (Ro) of 1.50%, but they were slightly destroyed at the over mature stage. Nanopores in the secondary OM were formed at 2.00% Ro and were preserved. Therefore, the development of OM nanopores in the lacustrine shale was synchronously affected by the type of OM and maturity. Furthermore, nanopores in the secondary OM were more developed than those in the autochthonous OM; thus, the OM nanopores at the high mature stage belonged to the autochthonous OM, and those at the over mature stage mainly belonged to the secondary OM. Besides, the nanopores in the autochthonous OM are easily blocked. Therefore, the secondary OM is important to the development of OM nanopores in the lacustrine shale at the over mature stage.

Distribution and Migration of Trace Elements during Flotation in Ge-Rich Low-Rank Coal from Wulantuga Coal Mine, Inner Mongolia, China.

The high-Ge low-rank coal in Wulantuga Coal Mine, Inner Mongolia, China, has a high utilization value due to its enrichment of critical element Ge. However, it is also enriched with toxic elements such as Be, F, As, and Hg; therefore, the coal should be cleaned before use. In this study, the flotation experiment, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) analysis, and the release experiment for the high-Ge low-rank coal from Wulantuga were carried out, and the results are as follows. (1) The total mineral content of the feed coal is higher than that of the cleaned coal and tailing, and the content of the functional group -OH is also increased, indicating that the moisture in the cleaned coal is increased after flotation. (2) Argillation occurred and some minerals (dihydrate gypsum and kaolinite) and elements were released into the water during flotation, so the ash yield and the percentage of TiO2, Al2O3, Fe2O3, MgO, and CaO of the cleaned coal and tailing are lower than those of feed coal. (3) The concentrations of elements Li, Be, F, Mn, Zn, Sr, Hg, Tl, and Pb of the cleaned coal are higher than those of tailing, indicating that these elements are more likely to occur in organic matter or fine-grained mineral embedded in organics, but the concentration of other elements such as Ge, As, Sb, and W in the cleaned coal is lower than that of tailing, suggesting that these elements are weakly associated with organics or occur in minerals. (4) After flotation, trace elements Be, Cs, Ti, Ge, Sb, and W enriched in the feed coal were removed in large quantities, while F, As, and Hg were difficult to remove; therefore, other preparation methods should be tried. (5) The release experiment showed that the release rate of chalcophile and siderophile elements and rare earth elements and yttrium (REY) is relatively higher. In addition to those of Be, Ga, Sr, and Cs, the release rate of most elements is relatively low.

Occurrence of Minerals in Coal and Its Geological Controlling Factors-Significance in Evaluation of Coal Washability.

The precombustion washing and washability of coal are increasingly gaining attention as a clean coal technology in China. In this study, the raw coal was collected from different coal seams in the south of Qinshui Coalfield, and flotation experiments were carried out in the laboratory after simple crushing. X-ray diffraction was used for qualitative analysis of the minerals in coal, and mineral morphology and disseminated particle size were measured with the help of an optical microscope. The samples were characterized to determine the original mineral content, combination type, occurrence characteristics, and dissemination type in coals of different lithotypes to establish a relationship with the coal-forming environment and to evaluate coal selectivity from a geological perspective. The results were obtained from the float-sink experiment by which the coal washability of different lithotypes is evaluated, combined with the information resulting from investigating the change law of the mineral occurrence and dissemination characteristics of the raw coal and the clean coal before and after the flotation experiment. The content of minerals with the particle size larger than 200 µm accounts for 35-50% of the easy-to-wash coal. The particles were mostly concentrated in the 50-100 µm size range in moderate difficulty washability coal, and the mineral occurrence forms are diverse. The disseminated particle size distribution of 10-20 µm in the refractory washability coal is between 35 and 45%, and the massive and fracture filling minerals are rarely found in the coal. The proportion of minerals smaller than 2 µm in the extremely difficult washability coal is more than 60%, and cell filling, dispersed, and banding forms are plentiful in this type of coal. The removal rates of ash and sulfur obtained through elution match well with the mineral form and distribution characteristics. The reason for the difference was the influence of the coal-forming environment on the occurrence of minerals in coal, which led to the removal of minerals in the coal washing procedure. The process is controlled by the occurrence and dissemination characteristics of minerals.

Proposed Cleaning Potential Gradient Based on a Study of Coals from Three Exploration Areas in Shanxi Province, China.

The cleaning potential of selected Chinese bituminous coals during coal preparation was evaluated in terms of coal quality, cleaning grade, and cleanability. The cleaning potentials were determined for coals sampled from a total of six seams, two each in three different general exploration areas in southern Shanxi, China. Distribution maps of resources with different cleaning potential characteristics were prepared using mapping and geographical information software. In each case, the area and calculated reserves for coals having different classifications of cleaning potentials were determined. The total areal extent of the six coals studied is about 410 million m2, and the total reserves of these coals amount to about 1460 million tonnes, which include coals of poor, fair, good, and proficient cleanabilities. The proportion of high-quality coals is about 28.9%. Coals that can be processed into high-quality coals account for about 69.2%. A cleaning potential gradient is proposed for indicating the cleaning potential level, and an equation for calculating it is established. The necessity of processing raw coal of good quality is also to be considered in terms of economics. It does not make economic sense to process coal with an organic sulfur content more than 1.5%, even though it may have a good cleanability.

Measurements of the leachability of potentially hazardous trace elements from solid coal gasification wastes in China.

Solid wastes from commercial coal gasification plants are a significant environmental issue in China because of the large quantities produced. In recent years, with the rapid development of coal gasification technologies in China, more and more coal gasification residues are being disposed of in landfills because of the low utilization of the residues. In the present study, the column leaching procedure M1314 developed by the U.S. Environmental Protection Agency was used to evaluate the potential for environmental pollution by potentially hazardous trace elements (Be, V, Mn, Cr, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Sb, Cs, Ba, Tl, Pb, Hg, Th, and U) in the coarse and fine gasification residues from two plants using General Electric (GE) and Gaskombinat Schwarze Pumpe (GSP) coal gasification technologies in northwest China. The potentially hazardous trace elements in the residues show different release patterns with the liquid-solid ratio increasing. The cumulative leached concentrations of the potentially hazardous trace elements from the coal gasification residues were generally low, and only Mo in the leachate of GSP fine residue was moderately soluble. V in the GSP coal gasification residues showed an increasing leachability in the leaching procedure. As, Se, Mo, Sb, and Tl in some leachates exceeded their thresholds in Level III of the Chinese Quality Standard for Groundwater and/or the Maximum Contaminant Levels of the U.S. National Primary Drinking Water Regulations. According to the risk assessment code, Se in the GE fine residue and Mo in the GE and GSP fine residues had medium risk to the ecosystem. Those data indicated that the potential for environmental pollution by those elements from coal gasification plants should be given consideration.

Evaluation of carbon forms and elements composition in coal gasification solid residues and their potential utilization from a view of coal geology.

As the development of coal gasification technology expands in China, the resulting solid by-products can become environmental and economic concerns. Evaluation of carbon forms and elemental composition in coal gasification solid residues from three advanced commercial-scale entrained-flow gasification plants in China related to feedstock coal properties are studied and their potential utilization is discussed in the present study. The properties of the residues of the three entrained-flow gasification processes differed as a result of the type of process applied, even though the properties of their feedstocks are similar. Eight types of carbon forms were identified. The high-inertinite feedstock resulted in a fusinite-like carbon being the primary carbon form of the residues, except for the General Electric fine residue (GE-FR) sample. The carbon contents of the coarse residues (CRs) produced from the Opposed Multi-Burner (OMB) coal-water slurry gasifier and the Gaskombiant Schwarze Pumpe (GSP) pulverized coal gasifier are comparable, lower than 2% (Cd), but a high content of carbon present as "black particles" (79.90%, Cd) was concentrated from the OMB-CR sample. Fourier transform infrared spectroscopy (FTIR) analyses indicate that the main functional group of the fusinite-like material in OMB-CR is methyl (CH3-). From the chemical composition point of view, the high proportions of F2O3 and CaO in the GE residues make them potential sources of high-Fe or high-Ca material. The relatively high concentrations of In, Ga, Sb, Cs, Cr, Ba, and rare earth elements in the residues make them potential raw materials for extracting critical trace elements, especially the OMB-FR and GSP-FR samples for extracting Ga.

Fate of potentially hazardous trace elements during the entrained-flow coal gasification processes in China.

With the rapid and wide application of the coal gasification technology in China, the corresponding environmental issues require increasing attention. In this study, the feed coal, coal gasification wastewater samples at key technical links, and the coal gasification residues were collected from three entrained-flow coal gasification plants in Northwest China and were characterized to understand the migration and partition of 21 potentially hazardous trace elements (PHTEs) in coal gasification process and their potential environmental impacts. Compared with Chinese coal, the concentrations of the PHTEs in the feed coals are mainly at the level of "depleted" and "normal". Undergoing the heating process in the gasifier, purification procedure for the syngas, and the residue-wastewater separation, the PHTEs in the feed coals are transferred into gaseous phase, wastewater, and gasification residues. The PHTEs are easier to be released into the gaseous phase during the GSP gasification process compared with the OMB and GE gasification processes. The chalcophile elements Zn, As, Se, Cd, Sb, Tl, Pb, and Hg tend to be enriched in the fine residues, and the retention capability of Hg by the residues is the lowest. With the grey water circulation and the use of additives, the black water samples have higher PHTEs concentrations than other water samples. Except for Sr, Mo, Sb, and Cs, most of the elements in the original water samples can be reduced effectively by removing the particulate matters. In some cases, Cr6+, Zn, As, Se, Cd, and Pb in the original wastewater samples exceed the limit for industrial use as indicated in the Chinese Environmental Quality Standards for Surface Water and the Emission Standard for Pollutants from Coal Industry. The potential environmental impacts of As and Se in the water cannot be reduced by filtration. The environmental impacts of the coal gasification residues should be further evaluated.

The daily fluorine and arsenic intake for residents with different dietaries and fluorosis risk in coal-burning fluorosis area, Yunnan, Southwest China.

The daily fluorine (F)/arsenic (As) intake (DFI/DAsI) for residents at different ages with different dietaries and dietary changes was investigated to analyze the fluorosis risk in coal-burning fluorosis area in Yunnan, Southwest China. The DFI for residents with a dietary of roasted corn and roasted chili was 5.06, 9.60, and 14.38 mg for age groups 3-7, 8-15, and over 15 years, respectively. Over 90 % of DFI was from roasted foodstuffs. The DFI for residents of the same age group living on rice and roasted chili was 1.94, 3.50, and 4.95 mg, respectively, which were less than that for the former dietary type, and 65 % of DFI was from roasted chili. The main sources for their DFI are roasted foodstuffs. Both were higher than the dietaries with non-roasted foodstuffs and the recommended daily allowances (RDAs) for USA and China at different levels. The DAsI for all residents ranged from 25 to 135 µg, and at this level of DAsI, it would not influence human health. However, As pollution of roasted foodstuffs might have an important influence for the fluorosis. Residents are changing their staple food from roasted corn to rice, and especially, younger people are more focused on quality life. However, even if residents change their staple food, the habit of eating chili will not change, which also may cause them getting fluorosis. Developing economy, changing dietary types, and changing the habit of drying and keeping chili will help to reduce the fluorosis risk in coal-burning fluorosis area of Southwest China.

Calibrating the end-Permian mass extinction.

The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.