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Sources, toxicity, and remediation of mercury: an essence review
Mercury (Hg) is a pollutant that poses a global threat, and it was listed as one of the ten leading ‘chemicals of concern’ by the World Health Organization in 2017. The review aims to summarize the sources of Hg, its combined effects on the ecosystem, and its remediation in the environment. The flow of Hg from coal to fly ash (FA), soil, and plants has become a serious concern. Hg chemically binds to sulphur-containing components in coal during coal formation. Coal combustion in thermal power plants is the major anthropogenic source of Hg in the environment. Hg is taken up by plant roots from contaminated soil and transferred to the stem and aerial parts. Through bioaccumulation in the plant system, Hg moves into the food chain, resulting in potential health and ecological risks. The world average Hg concentrations reported in coal and FA are 0.01–1 and 0.62 mg/kg, respectively. The mass of Hg accumulated globally in the soil is estimated to be 250–1000 Gg. Several techniques have been applied to remove or minimize elevated levels of Hg from FA, soil, and water (soil washing, selective catalytic reduction, wet flue gas desulphurization, stabilization, adsorption, thermal treatment, electro-remediation, and phytoremediation). Adsorbents such as activated carbon and carbon nanotubes have been used for Hg removal. The application of phytoremediation techniques has been proven as a promising approach in the removal of Hg from contaminated soil. Plant species such as
Brassica juncea
are potential candidates for Hg removal from soil.
Journal Article
Utilization of coal fly ash in China: a mini-review on challenges and future directions
The rapid economic development in China places a large demand for energy, and as a result, thermal power plants in China are producing an enormous amount of coal fly ash (CFA) which causes severe environmental pollution. This paper briefly describes the current production and utilization status of CFA in China and identifies the challenges confronting sustainable CFA utilization as the Chinese economy is being transformed. These issues include a regional imbalance in supply and demand, reducing demand in the real estate industry as well as stricter laws for environmental protection. Viable directions for future CFA utilization are proposed, for example, production of CFA-based ceramic tiles, recovery of elemental resources, agricultural melioration, treatment of wastewater and flue gas, and production of high-volume CFA concretes. This paper has some guiding significance for sustainable and cleaner utilization of CFA in China and even worldwide.
Graphical abstract
Journal Article
The multiple value characteristics of fly ash from Indian coal thermal power plants: a review
Coal-powered thermal plants are the primary source of energy production around the globe. More than half (56.89%) of the Indian power plants use coal for power production. Coal burning in power plants results in coal combustion residuals, which contain coal fly ash (CFA) that is recognized as principle by-product. CFA is difficult to characterize due to its broad compositional variation. Hence, the present article summarizes the various physical, chemical, mineralogical, and petrological characterizations of CFA to its use in different applications. Indian coal thermal power plants are found to release two types of CFA: F (fine) and C (coarse). CFA particles are identified as unburned carbon particles with a large fraction of silica oxides, alumina oxides, and iron oxides with a small fraction of calcium oxide (CaO). Morphologically, CFA particles are spherical, with large carbon molecules and a smooth texture surface. In terms of mineralogy; quartz, mullite, magnetite, and hematite are the dominant mineral phases of CFA and tend to be non-plastic, with permeability levels ranging from 8 × 10
−6
to 1.87 × 10
−4
cms
−1
. Petrographically, CFA is enriched in inertinite and liptinites as well as collotelinite, collodetrinite, and vitrodetrinite particles. Moreover, CFA is found to be composed of various organic and inorganic particles. By virtue of multiple characterizations, it has been utilized in several applications for decades, which is still quite limited. Therefore, current study aim to provide helpful insights into the potential use of CFA-derived products in different ways to increase sustainability.
Journal Article
Cytotoxicity and genotoxicity induced by coal and coal fly ash particles samples in V79 cells
Exposure to coal and coal ashes can cause harmful effects in in vitro and in vivo systems, mainly by the induction of oxidative damage. The aim of this work was to assess cytotoxic and genotoxic effects using the V79 cell line treated with coal and coal fly ash particles derived from a coal power plant located in Santa Catarina, Brazil. Two coal samples (COAL11 and COAL16) and two coal fly ash samples (CFA11 and CFA16) were included in this study. COAL16 was co-firing with a mixture of fuel oil and diesel oil. The comet assay data showed that exposure of V79 cells to coal and coal fly ash particles induced primary DNA lesions. Application of lesion-specific endonucleases (FPG and ENDO III) demonstrated increased DNA effects indicating the presence of high amounts of oxidative DNA lesions. The cytokinesis-block micronucleus cytome assay analysis showed that exposure of V79 cells to high concentrations of coal and coal fly ash particles induced cytotoxic effects (apoptosis and necrosis) and chromosomal instability (nucleoplasmic bridges, nuclear buds, and micronucleus (MN) formation). These results may be associated with compounds contained in the surface of the particles as hazardous elements, ultrafine/nanoparticles, and polycyclic aromatic hydrocarbons (PAHs) which were detected in the samples.
Graphical abstract
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Journal Article
Study on mechanical properties of coal gangue and fly ash mixture as backfill material based on fractal characteristics
Backfill mining can effectively alleviate the problems of surface collapse and ecological water pollution, in which the mechanical properties of backfill materials, including coal gangue and coal fly ash, have a decisive role in the effect of filling mining. In this study, we analyze the permeability characteristics of coal gangue filler through a set of homemade percolation test systems and introduce fractal characteristics to investigate the key factors affecting percolation in complex pores of broken coal gangue. The results indicate that the fractal dimensions of crushed coal gangue particles show an increasing trend with increasing axial loading and that the variation range is from 2.15647 to 2.58933. The coal fly ash concentration has a positive relationship with the acceleration factor. The permeability of crushed coal gangue follows a hierarchical distribution law and the permeability changes in the magnitude range of 10
–11
~ 10
–9
m
2
. The fractal dimension is inversely related to the permeability of crushed coal gangue. The experimental results show that the coal gangue will be further crushed and that adding a certain concentration of coal fly ash can achieve a better water barrier, which provides theoretical support and engineering significance for the stability analysis of geological engineering and backfill mining technology.
Journal Article
Anthropogenic arsenic menace in contaminated water near thermal power plants and coal mining areas of India
Coal mining and coal combustion in thermal power plants (TPPs) are the major anthropogenic sources of arsenic (As) contamination in many different industrial regions. In this study of industrial regions of West Bengal and Singrauli, it is observed that there is an anthropogenic contribution to the contamination from As-bearing coal. Up to 14.53 mg/kg of As is obtained in coal of West Bengal which also has very high average Fe concentration (16,095 mg/kg) along with high concentration of Cu, Mn and Hg. Similar observations are also found in Singrauli Industrial Region where 3.14 mg/kg of As with very high concentration of Fe 43,867 mg/kg along with high Cu, Mn and Hg concentration is found in coal samples. This low-grade bituminous coal contains arsenopyrite as observed by SEM–EDX. Arsenopyrite is converted to arsenolite upon combustion in these TPPs as observed in XRD. The fly ash has average As concentration of 1.53 mg/kg for West Bengal and 2.38 mg/kg for Singrauli Industrial Region and high concentration of toxic elements. The soil near these TPPs and mining areas is enriched in As, Fe, Hg, Cu and Mn. Not only As but high concentrations of Fe, Hg, Mn are also observed from analysis of water which relates to the anthropogenic inputs. The dissolution of arsenolite in reducing environments caused by periodic flooding releases As into water. Hence, the As contamination in the study area also has anthropogenic origin from coal consumption in TPPs.
Journal Article
Handbook of coal analysis
Provides users with everything they need to know about testing and analysis of coal
* Includes new coverage on environmental issues and regulations as related to coal
* Provides the reader with the necessary information about testing and analyzing coal and relays the advantages and limitations in understanding the quality and performance of coal
* Explains the meaning of test results and how these results can predict coal behavior and its corresponding environmental impact during use
* Includes a comprehensive Glossary which defines items in straightforward language that enable readers to better understand the terminology related to coal
* Treats issues related to sampling, and accuracy and precision of analysis
eBook
Leaching of Polycyclic Aromatic Hydrocarbons from the Coal Tar in Sewage Wastewater, Acidic and Alkaline Mine Drainage
Polycyclic aromatic hydrocarbons (PAHs) have been a problem in the environment for an extended period. They are mostly derived from petroleum, coal tar and oil spills that travel and are immobilized in wastewater/water sources. Their presence in the environment causes a hazard to humans due to their toxicity and carcinogenic properties. In the study, coal tar was analyzed using Gas Chromatography–Mass Spectrometry (GC–MS) and a concentration of 787.97 mg/L of naphthalene, followed by 632.15 mg/L of phenanthrene were found to be in the highest concentrations in the various water sources such as sewage, alkaline and acid mine drainage. A design column was used to investigate the leaching process and assessments were conducted on 300 mL of the various water sources mentioned, with 5 g of coal tar added and with monitoring for 4 weeks. The influence of the physiochemical properties of the receiving water sources, such as sewage, and acid and alkaline mine drainage, on the release of PAHs from the coal tar was assessed. The acidic media was proven to have the highest release of PAHs, with a total concentration of 7.1 mg/L of released PAHs, followed by 1.2 mg/L for the sewage, and lastly, 0.32 mg/L for the alkaline mine drainage at room temperature.
Journal Article
Chromium in Chinese coals: geochemistry and environmental impacts associated with coal-fired power plants
Chromium (Cr), one of the prime hazardous trace elements in coals, may engender adverse effects on eco-environment and threaten human health during utilization of coal. Based on the samples obtained in our laboratory and published literature, the abundance and modes of occurrence of Cr in Chinese coals, and the environmental impacts associated with coal-fired power plants (CFPPs) were elucidated in this study. With a total of 1397 sets of data, the mean concentration of Cr in Chinese coals was calculated as 21.33 μg/g by the “reserve-concentration” weighted calculation method. Spatially, the average Cr contents increased gradually from North China to South China. Temporally, coals from T3, E–N and P2 were relatively enriched in Cr compared to the other geological time. The Cr concentration in coal varied with different coal ranks. The geological factors accounted for Cr enrichment in coals could be divided into the primary, secondary and epigenetic processes. Higher percentages of organically Cr occurred in low-rank coals, while inorganically associated Cr was mainly found in clay minerals. After coal combustion, most of Cr was enriched in solid wastes (e.g., fly ash and bottom ash). The leaching of Cr from solid wastes in the rainy season (especially acid rain) needs to be a concern for CFPPs. It was estimated that the atmospheric emission of Cr from CFPPs increased annually from 2015 to 2019 and reached approximately 159 tons in 2019.
Journal Article