Chemical speciation and risk assessment of cadmium in soils around atypical coal mining area of China

The distribution characteristics of Cadmium (Cd) fractions in soils around a coal mining area of Huaibei coalfield were investigated, with the aim to assess its ecological risk. The total Cd concentrations in soils ranged from 0.05 to 0.87 mg/kg. The high percentage of phyto-available Cd (58%) when redox or base-acid equilibria changed. Soil pH was found to be a crucial factor affecting soil Cd fraction, and carbonate-bound Cd can be significantly affected by both organic matter and pH of soils. The static ecological evaluation models, including potential ecological risk index (PERI), geo-accumulation index (Igeo) and risk assessment code (RAC), revealed a moderate soil Cd contamination and prensented high Cd exposure risk in studied soils. However, the dynamic evaluation of Cd risk, determined using a delayed geochemical hazard (DGH), suggested that our studied soils can be classified as median-risk with a mean probability of 24.79% for Cd DGH. These results provide a better assessment for the risk development of Cd contamination in coal mining areas

Geochemical characteristics of n-alkanes and isoprenoids in coal seams from Zhuji coal mine, Huainan coalfield, China, and their relationship with coal-forming environment

Ten coal seams in Upper Shihezi Formation, Lower Shihezi Formation, and Shanxi Formation from the Zhuji mine, Huainan coalfield, China, were analyzed for n-alkanes and isoprenoids (pristine and phytane) using gas chromatography-mass spectrometry (GC-MS), with an aim of reconstructing the coal-forming plants and depositional environments along with organic carbon isotope analyses. The total n-alkane concentrations ranged from 34.1 to 481 mg/kg. Values of organic carbon isotope (delta C-13(org)) ranged from -24.6 to -23.7 parts per thousand. The calorific value (Q(b,d)), maximum vitrinite reflectance (Ro(max)), proximate, and ultimate analysis were also determined but showed no correlation with n-alkane concentrations. Carbon Preference Index (CPI) values ranged from 0.945 to 1.30, suggesting no obvious odd/even predominance of n-alkane. The predominance of C-11 and C-17 n-alkanes implied that the coal may be deposited in the fresh and mildly brackish environment. According to the contrary changing trend of pristine/phytane (Pr/Ph) ratio and boron concentrations, Pr/Ph can be used as an indicator to reconstruct the marine transgression-regression in sedimentary environment of coal formation. The influence of marine transgression may lead to the enrichment of pyrite sulfur in the coal seam 4-2. C3 plants (-32 to -21 parts per thousand) and marine algae (-23 to -16 parts per thousand) were probably the main coal-forming plants in the studied coal seams. No correlation of the n-alkane concentration and redox condition of the depositional environment with organic carbon isotope composition were found

n-Alkanes in sediments from the Yellow River Estuary, China: Occurrence, sources and historical sedimentary record

A total of 21 surface sediments from the Yellow River Estuary (YRE) and a sediment core from the abandoned Old Yellow River Estuary (GYRE) were analyzed for n-alkanes using gas chromatography-mass spectrometry (GC-MS). n-Alkanes in the range C-12-C-33 and C-13-C-34 were identified in the surface sediments and the core, respectively. The homologous series were mainly bimodal distribution pattern without odd/even predominance in the YRE and GYRE. The total n-alkanes concentrations in the surface sediments ranged from 0.356 to 0.572 mg/kg, with a mean of 0.434 mg/kg on dry wt. basis. Evaluation of n-alkanes proxies indicated that the aliphatic hydrocarbons in the surface sediments were derived mainly from a petrogenic source with a relatively low contribution of submerged/floating macrophytes, terrestrial and emergent plants. The dated core covered the time period 1925-2012 and the mean sedimentation rate was ca. 0.5 cm/yr. The total n-alkanes concentrations in the core ranged from 0.0394 to 0.941 mg/kg, with a mean of 0.180 mg/kg. The temporal evolution of n-alkanes reflected the historical input of aliphatic hydrocarbons and was consistent with local and regional anthropogenic activity. In general, the investigation on the sediment core revealed a trend of regional environmental change and the role of anthropogenic activity in environmental change

Characteristics of the coal quality and elemental geochemistry in Permian coals from the Xinjier mine in the Huainan Coalfield, north China: Influence of terrigenous inputs

Fifty-six coals along with host rocks of Permian age (including samples from the Shanxi Formation, Lower Shihezi Formation and Upper Shihezi Formation) collected from the active Xinjier mine in the Huainan Coalfield, north China were studied in the present work. The overall object of this study was to characterize the coal quality and elucidate the possible genetic types for trace-element enrichment of Xinjier coals. Based on Chinese National Standards, all the coals can be classified as medium-high-volatile to high-volatile coal and ultra-low sulfur to low sulfur coal. The vitrinite-dominated Xinjier coals show phyiso-chemical properties difference along the coal-bearing strata. Compared to the coals of the Shanxi Formation, vitrinite contents are elevated in the coals of the Lower Shihezi and Upper Shihezi Formations, which indicates that they were probably exposed to a more reducing environment during peat accumulation. Most elements, such as Al2O3, K2O, Y, Se, and Sb, are enriched compared to those of Chinese and World coals. The major-element oxides Al2O3 and K2O as well as trace elements Th and Y increase from the lower to upper seams. Some elements are distinctly concentrated in host rocks (roof, floor, and parting) compared with adjacent coals. These geochemical anomalies and &quot;increasing stratigraphically upward&quot; ash yield trend are attributed to influence from terrigenous inputs. Elements in Xinjier coals were classified into three geochemical groups based on the statistical analysis. In particular, sequential extraction experiments of selected coals found that As, Se, and Sb predominantly occur as organic associations in coal.</p

Response of carbon isotopic compositions of Early-Middle Permian coals in North China to palaeo-climate change

To investigate the magnitude to which the carbon isotopic ratio (delta C-13) 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 parts per thousand variation range of delta C-13 values (-25.15%o to -22.65%o) was observed in Huainan coals, with an average value of -24.06 parts per thousand. As coal diagenesis exerts little influence on carbon isotope fractionation, delta C-13 values in coals were mainly imparted by those of coal -forming flora assemblages which were linked to the contemporary climate. The delta C-13 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 delta C-13 values of coeval atmospheric CO2. Notably, our study provides evidence of the Kamura event in the terrestrial environment for the first time

A comparative study on the mineralogy, chemical speciation, and combustion behavior of toxic elements of coal beneficiation products

The huge demand for high-quality coal in China has resulted in increased generation of preparation plant wastes of various properties. A series of beneficiation products collected from a preparation plant were characterized to understand their petrographic and mineralogical characteristics, as well as thermochemical and trace element behavior during combustion. The minerals in the Luling preparation plant wastes from Huaibei coalfield mainly included kaolinite and quartz, with minor calcite, ankerite, pyrite, illite, chalcopyrite, albite, K-feldspar, anatase/rutile, and iron-oxide minerals. Massive clay lumps of terrigenous origin, cleat-infilling carbonate, and pyrite of epigenetic origin were prone to be enriched in the middlings and coal gangue. Minor or trace heavy minerals also reported to the preparation plant wastes. The contents of low-density density vitrinite and liptinite were enhanced in the clean coal, while inertinite-maceral group were enriched in the middlings. The modes of occurrences of toxic elements differed between raw coal and the waste products; and their transformation behavior during heavy medium separation is largely controlled by clay minerals (V, Cr, Co, Sb, and Pb), carbonate minerals (Co and Pb), sulfide minerals (As, Cu, Ni, Cd, and Zn) and organic matters (V, Cr, Se, and Cu). Three groups were classified based on the volatile ratio (Vr) of toxic elements. Group 1 includes the highly volatile element Se with Vr &gt; 85%; Group 2 contained elements As, Pb, Zn, Cd and Sb, with the Vr in the range of 20&ndash;85% and V, Cr, Co, Ni and Cu with Vr less than 20% were placed into Group 3. Thermal reactivity of coal inferred from the combustion profiles could be significantly improved after coal beneficiation, whereas the increased inorganic components probably inhibited the thermal chemical reaction of wastes.<br style="line-height: normal; text-align: -webkit-auto; text-size-adjust: auto;" /

The simultaneous removal of cadmium (II) and lead (II) from wastewater with the application of green synthesized magnesium silicate hydrate

To the purpose of solving the problems of coal-gangue accumulation in the mine and pollution of cadmium (II) and lead (II) in wastewater, magnesium silicate hydrate (M-S-H) was synthesized from coal-gangue by thermochemical. M-S-H had removed Cd(II) and Pb(II) by adsorption. The characterization of M-S-H and adsorption effects factors, including initial solution pH, initial metal concentration, adsorbent dose, temperature, reaction time, and coexisting ions were explored for adsorption performance. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator with an error of ±0.3. These results from this study revealed that M-S-H surface area increased from 8.12 to 26.15 m2/g with a pore volume of 0.12 cm3/g. The maximum adsorptions of Cd(II) and Pb(II) by M-S-H were 59.52 and 83.33 mg g−1, respectively. The adsorption performance for Cd(II) and Pb(II) reached saturation at pH 5, temperature 25°C, M-S-H 6 g/L, reaction time 90 min, and metal concentration 300 mg/L. Cd(II) and Pb(II) adsorption were spontaneous and endothermic and well fitted with the pseudo-second-order kinetic and Langmuir isotherm adsorption models. The adsorption mechanisms were electrostatic interaction, ion exchange, and surface complexation. This research indicated that the synthesized M-S-H from coal gangue was efficiently eliminated metal ions from water, opening up new possibilities for coal gangue reuse

Influence of magmatic intrusions on organic nitrogen in coal: A case study from the Zhuji mine, the Huainan coalfield, China

Although the influence of magmatic intrusions on coal has been studied extensively at many locations, data on changes of organic nitrogen forms in coal in response to this kind of geological instantaneous heating is still scarce. To fill this information gap, a total of five coal samples, including four coal samples collected along a coal transect approaching a magmatic intrusion and one unaltered coal sample, were collected from the No. 3 coal seam of the Zhuji mine in the Huainan coalfield, China and were analyzed for organic nitrogen forms using X-ray photoelectron spectroscopy (XPS), together with the determination of coal quality parameters and elemental composition. Due to the effect of magmatic intrusion, ash yield and carbon content of the coals increase, whereas moisture, volatile matter, oxygen, nitrogen and total sulfur decrease. The N-5 peak is dominant in unaltered and moderately altered coals, but disappears entirely in the coals adjacent to the magmatic intrusion due to the strong thermal influence. The N-Q peak mainly represents &quot;protonated&quot; quaternary nitrogen in unaltered and moderately altered coals. The N-Q peak can be transformed to the N-6 peak through the deprotonation of &quot;protonated&quot; quaternary nitrogen resulting from the loss of oxygen groups under the thermal influence of the magmatic intrusion. Closer to the magmatic intrusion, the N-Q peak is assigned to &quot;graphitic&quot; quaternary nitrogen, which increases sharply and becomes the predominant form eventually. Magmatic intrusion is responsible for the conversion of less stable nitrogen forms to more stable forms in coal

Spatial distributions, fractionation characteristics, and ecological risk assessment of trace elements in sediments of Chaohu Lake, a large eutrophic freshwater lake in eastern China

The concentrations, spatial distribution, fractionation characteristics, and potential ecological risks of trace elements (Cu, Pb, Zn, Cr, Ni, and Co) in the surface sediment samples collected from 32 sites in Chaohu Lake were investigated. The improved BCR sequential extraction procedure was applied to analyze the chemical forms of trace elements in sediments. The enrichment factor (EF), sediment quality guidelines (SQGs), potential ecological risk index (PERI), and risk assessment code (RAC) were employed to evaluate the pollution levels and the potential ecological risks. The results found that the concentrations of Cu, Pb, Zn, Cr, Ni, and Co in the surface sediments were 78.59, 36.91, 161.84, 98.87, 38.92, and 10.09 mg kg(-1), respectively. The lower concentrations of Cu, Pb, Zn, Cr, and Ni were almost found in the middle part of the lake, while Co increased from the western toward the eastern parts of the lake. Cr, Ni, Co, and Zn predominantly existed in the residual fractions, with the average values of 76.35, 59.22, 45.60, and 44.30%, respectively. Cu and Pb were mainly combined with Fe/Mn oxides in reducible fraction, with the average values of 66.4 and 69.1%, respectively. The pollution levels were different among the selected elements. Cu had the highest potential ecological risk, while Cr had the lowest potential ecological risk

Particle-Associated Polycyclic Aromatic Hydrocarbons (PAHs) in the Atmosphere of Hefei, China: Levels, Characterizations and Health Risks

Airborne PM2.5 and PM10 samples were collected in summertime (August 2015) and wintertime (December 2015-January 2016) in an industrial complex area in Hefei, China. The average concentrations of PM2.5 and PM10 (90.5 and 114.5 mu g/m(3), respectively) were higher than the regulated levels of China National Ambient Air Quality Standard (grade I) and the WHO Ambient (outdoor) Air Quality and Health Guideline Value. Seasonal variations in PM2.5/PM10 indicated that the secondary sources of particulate matters, formed by gas-to-particle conversion, were enhanced in summer due to longer time of solar radiation and higher temperature. The total concentrations of PM2.5- and PM10-associated PAHs were 5.89 and 17.70 ng/m(3) in summer as well as 63.41 and 78.26 ng/m(3) in winter, respectively. Both PM2.5- and PM10-associated PAHs were dominated by 4- to 6-ring PAHs, suggesting that the fossil fuel combustion and vehicle emissions were the primary sources of PAHs in atmospheric particulate matters in Hefei. The total concentration of PAHs had a slightly higher correlation coefficient with PM2.5 (R = 0.499, P &lt; 0.05) than PM10 (R = 0.431, P &gt; 0.05), indicating the higher association tendency of PAHs with PM2.5. The coefficient of divergence analysis showed that the compositions of PAH were quite different between summer and winter. Total BaP equivalent concentration (BaP-TEQ) for particulate-bound PAHs in winter (58.87 ng/m(3)) was higher than that in summer (5.53 ng/m(3)). In addition, particulate-bound PAHs in winter had an inhalation cancer risk (ICR) value of 2.8 x 10(-3), which was higher than the safe range (10(-4)-10(-6))