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Basic properties, characteristic heavy metals leaching and migration of coal incineration fly ash-based mortar
... The tailings' surface contains active heavy metal ions. In addition to being used for particle refinement, the mechanical energy applied by crushing is also stored in the particle to "weak solidification", and the research on the solidification ability of the low strength of CTB has not been carried out [28,29]. ...
The high consumption and high cost of cement are the bottleneck problems that limit the development of cemented tailings backfilling technology. The low-consumption cement backfill is immersed in a weak acid/alkaline groundwater environment for a long time. Reducing the consumption of cement can easily lead to problems such as a sudden decrease in strength and the leakage of heavy metals. Through the monolithic leaching test in static and uniaxial compressive tests, the heavy metals’ leaching concentration and the compressive strength of low-consumption cement backfills in different pH soaking solutions were measured at different soaking times. Results show that a lower cement concentration will result in a lower CTB compressive strength and a higher rate of heavy metal leaching. Long-term exposure to an acidic/alkaline environment will lead to the instability and destruction of the CTB structure. A microscopic examination reveals that the creation of hydration products can improve the structure’s compactness while also lowering the internal porosity of CTB but can also solidify heavy metal ions in various ways. A first-order reaction/diffusion model (FRDM) can better evaluate the leaching behavior of CTB. This study helps to improve backfilling technology, thereby contributing to the creation of sustainable mining geotechnologies.
... However, reports related to CFA point to up to 0.17 mg/kg to 41.6 mg/kg Pb and 6.2 mg/kg to 88.6 mg/kg Cr [9]. Similar work on ash toxicity reports leaching trends in the order Cr > Pb > Ni > As > Hg [27]. The total leaching in CFAs depends on the carbon source. ...
The study aimed to characterize the physicochemical properties of carbon fly ash (CFA) from a thermoelectric plant in Mexico. The ultimate goal was to find a responsible way to dispose of the CFA and reduce pollution. The CFA were spherical particles ranging from 0.4 to 100 µm in size, with an average size of 22.7 µm. XRF analysis revealed the primary chemical constituents to be 59% SiO2, 26% Al2O3, 7% Fe2O3, and 3% CaO. The XRD analysis showed mullite and quartz crystalline phases. The study also evaluated the leaching of CFA using the Toxicity Characteristic Leaching Procedure. The results showed that the metals As, Cd, Zn, Cu, Ni, and Co were present in decreasing order of concentration. To reduce the mobility of heavy metals traces, the study explores the consolidation of ashes through a geopolymerization reaction in an alkaline medium, achieving an efficient reaction for precipitation hydrated amorphous alkaline aluminosilicate.
... The agglomerates formed by the combination of CaCO 3 and other components can provide a skeleton effect. The chemical composition of the FA was mainly composed of oxides, such as Al 2 O 3 , SiO 2 , and Fe 2 O 3 , with a certain activity [28]. The clay used was Lianyungang coastal clay. ...
To effectively utilize the effectively the solid waste-soda residue (SR) and fly ash (FA), a mixture of 70% SR, 20% FA, and 10% clay was formed to produce soda residue soil (SRS). By adding cement and/or lime, four different SRS proportions were prepared. The compaction properties, mechanical properties, and dry–wet stability. Furthermore, the mechanical mechanisms of SRS were explored, and the improvement effect and efficiency of cement and/or lime on the mechanical performance of SRS were analyzed. The results show that the SRS is lightweight and easy to compact and shape, which is conducive to construction. Compared to cement, lime has a greater impat on the compaction properties of SRS. The mechanical properties of SRS are enhanced after adding cement and/or lime; the unconfined compressive strength (UCS), California Bearing Ratio (CBR), and resilient modulus all increase significantly. The UCS, CBR, and resilient modulus of SRS with different proportions all increase with the increase of compaction degree; the CBR and resilient modulus can meet the requirements of the subgrade, and the UCS can meet the requirements of the base and sub-base. The contribution rate of cement per unit amount is better than that of lime to the mechanical performance of SRS. As dry–wet cycles increase, the dry–wet stability of SRS with different proportions first increases and then decreases, which is affected by hydration and dry–wet deterioration together, with a critical cycle number for the strength transition. The excellent mechanical performance of SRS benefits from the gradation and chemical action. The particles of SR, FA, and clay can complement each other and perform an interlocking action. Therefore, SRS has a good gradation and forms a dense and stable structure. Also, the chemical reactions between materials are very important. The cement and/or lime have a hydration and gelling effect, FA and clay participate in pozzolanic reactions, and SR and FA have certain alkali-activated effects.
The purpose of the article was to conduct an in-depth literature review on the possibilities of managing combustion by-products (mainly fly ash) in the context of a closed-loop economy. First, information on the chemical composition of fly ash in Poland was collected and compared with the composition of fly ash in other European countries. The authors concentrated on describing methods for synthesizing geopolymers and zeolites using fly ash as a substrate. By-products of zeolite synthesis, which are strongly alkaline solutions, can be used as a substrate in the synthesis of geopolymers. A concept has been proposed to combine the synthesis of zeolites and geopolymers into a single process to close the material loop. The search for comprehensive technological solutions that take into account the ideas of a closed-loop economy is essential in an era of resource depletion, and this literature review encapsulates this topic area.
Dietary arsenic (As) contamination is a major public health issue. In the Middle East, the food supply relies primarily on the import of food commodities. Among different age groups the main source of As exposure is grains and grain-based food products, particularly rice and rice-based dietary products. Rice and rice products are a rich source of core macronutrients and act as a chief energy source across the world. The rate of rice consumption ranges from 250 to 650 g per day per person in South East Asian countries. The source of carbohydrates through rice is one of the leading causes of human As exposure. The Gulf population consumes primarily rice and ready-to-eat cereals as a large proportion of their meals. Exposure to arsenic leads to an increased risk of non-communicable diseases such as dysbiosis, obesity, metabolic syndrome, diabetes, chronic kidney disease, chronic heart disease, cancer, and maternal and fetal complications. The impact of arsenic-containing food items and their exposure on health outcomes are different among different age groups. In the Middle East countries, neurological deficit disorder (NDD) and autism spectrum disorder (ASD) cases are alarming issues. Arsenic exposure might be a causative factor that should be assessed by screening the population and regulatory bodies rechecking the limits of As among all age groups. Our goals for this review are to outline the source and distribution of arsenic in various foods and water and summarize the health complications linked with arsenic toxicity along with identified modifiers that add heterogeneity in biological responses and suggest improvements for multi-disciplinary interventions to minimize the global influence of arsenic. The development and validation of diverse analytical techniques to evaluate the toxic levels of different As contaminants in our food products is the need of the hour. Furthermore, standard parameters and guidelines for As-containing foods should be developed and implemented.
Municipal solid waste incineration (MSWI) fly ash contains highly toxic heavy metals and polychlorinated dibenzo dioxins/furans (PCDD/Fs), which are a type of hazardous waste. The pollution characteristics of fly ash have changed with the development of stoker grate incinerators and the fly ash treatment technology; however, no research has been focused on this in recent years. In this study, 12 fly ash samples were collected from 9 grate power plants in southeastern China, and their PCDD/Fs and heavy metal concentrations were determined and compared to previous fly ash data. The PCDD/Fs concentration in fly ash was in the range of 0.002–0.051 ngI-TEQ/g, with an average of 0.027 ngI-TEQ/g. Furthermore, 1,2,3,4,6,7,8-HpCDD and OCDD made the most significant contributions to PCDDs. The distribution of 10 dioxins exhibited bimodal, unimodal, and normal characteristics. Linear fitting demonstrated a strong correlation between toxicity and 1,2,3,7,8-PentaCDD, 1,2,3,7,8-PentaCDF, and 2,3,4,7,8-PentaCDF. Concerning heavy metals, Pb poses a significant environmental risk. This is the first time that fly ash treated with a chelating agent has been thoroughly analyzed, which is vital for understanding the pollution level and treatment of fly ash derived from current power plants.
Citation: Khan, M.I.; Ahmad, M.F.; Ahmad, I.; Ashfaq, F.; Wahab, S.; Alsayegh, A.A.; Kumar, S.; Hakeem, K.R. Arsenic Exposure through
Industrial effluents/wastewater are the main sources of hexavalent chromium (Cr (VI)) pollutants in the environment. Cr (VI) pollution has become one of the world’s most serious environmental concerns due to its long persistence in the environment and highly deadly nature in living organisms. To its widespread use in industries Cr (VI) is highly toxic and one of the most common environmental contaminants. Cr (VI) is frequently non-biodegradable in nature, which means it stays in the environment for a long time, pollutes the soil and water, and poses substantial health risks to humans and wildlife. In living things, the hexavalent form of Cr is carcinogenic, genotoxic, and mutagenic. Physico-chemical techniques currently used for Cr (VI) removal are not environmentally friendly and use a large number of chemicals. Microbes have many natural or acquired mechanisms to combat chromium toxicity, such as biosorption, reduction, subsequent efflux, or bioaccumulation. This review focuses on microbial responses to chromium toxicity and the potential for their use in environmental remediation. Moreover, the research problem and prospects for the future are discussed in order to fill these gaps and overcome the problem associated with bacterial bioremediation’s real-time applicability.
The level of heavy metals of the sludge in the landfills has attracted the environmental researchers due to their non‐biodegradability, persistence, toxicity and biomagnification. Heavy metals contamination and ecological risk assessment in the sludge landfills were assessed. In this work, the enrichment factor (EF) and geo‐accumulation index were used to analyze heavy metal pollution degree in the sludge landfills. Meanwhile, the potential ecological risk index was used to assess heavy metals potential ecological risk in the sludge landfills. Results indicated that heavy metal concentrations order was Cr > Cd > Ni > Zn > As>Cu = Pb > Hg. Cr, Cd and Ni coefficient variation were 57%, 53% and 38%, respectively, which indicated that Cr, Cd and Ni content have a large range variation. EF and geo‐accumulation index analyze heavy metal pollution degree in the sludge landfills. Results demonstrated that Hg, Cd, Cu and Zn obtained a high pollution degree. However, Cr, Ni, As and Pb have a low pollution in the sludge landfills. Potential ecological risk index indicated that Hg obtained the highest pollution degree, which demonstrated that the potential ecological risk level is the highest value (Erⁱ ≥ 3500, RI ≥ 4163). Whereas, other heavy metals have a low pollution degree in the sludge landfills. Therefore, Hg, Cd and Cu content of sludge should be strictly restricted in agricultural use. Meanwhile, it should be strictly restricted Hg, Cd and Cu content of wastewater discharge, and reduced heavy metal content of sludge.
The availability of fly ash for concrete has decreased due to the shutdowns of coal-fired power plants. Alternatives to conventional fly ash are needed to ensure sustainable and durable concrete. In this study, the impacts of numerous unconventional fly ashes – reclaimed, beneficiated off-spec, and marginal fly ashes on early and later-age properties of cementitious paste were assessed. Heat release characteristics, bulk resistivity, compressive strength, calcium hydroxide content and bound water content were studied. “Unconventional” fly ash performance was compared to conventional fly ashes, inert materials and a cement control. Substantial differences between Class C and Class F fly ashes were observed, even for unconventional fly ashes. The fly ash CaO content is positively correlated with several early-age paste properties, however, certain other properties did not show significant early-age differences based on fly ash type. Class F fly ashes showed significantly higher bulk resistivity at 91-days, while Class C fly ashes showed higher bound water contents. All tested unconventional fly ashes were reactive, contributed to strength development, and did not negatively affect cement hydration. Some fly ashes result in properties that vary significantly from those expected for conventional fly ashes, but there does not appear to be a simple correlation between a fly ash being either off-spec, marginal, reclaimed, or beneficiated and its performance being different from what is expected from similar class fly ashes. The results suggest that fly ash specifications need to be broadened to include unconventional fly ashes.
This paper simulates sediment motion under different hydrodynamic conditions, aiming to investigate the release flux of heavy metals in river sediments. During the lab experiments, carried out in a circular rectangular flume device, water velocity in the flume was altered by controlling the gate switch, and the flow rate was controlled from 0 to 1 m/s. Sediment from the Le'an River and chlorine-removed tap water were used as experimental sediment and water, respectively. Through analyses of Cu, Zn, Cd, and Pb concentration in water at different flow rates, the relationship between the release flux (y) of Cu, Zn, Cd, and Pb and the flow rate (x) was established with a fitting error of less than 15%. In order to judge the reliability of the conclusions, experimental results were verified outdoors. The results showed when the sediment particle size is between 0 and 250 μm, within 1 hour, a quadratic polynomial correlation between the release flux of Cu, Cd, and Pb from river sediments and water velocity when the water pH is 5–9 and the flow rate is 0–65 cm/s; when the water pH is 5–9, the flow rate is 0–35 cm/s, the release flux of Zn from river sediments was shown to have a quadratic polynomial relationship with water velocity. The error between the calculated and measured values of heavy metals released from sediment in the Le'an River were within 5–30%. Our results can provide a theoretical reference for the control and treatment of heavy metal pollution in rivers and further improve corresponding water quality models. HIGHLIGHTS
The heavy metal release flux from sediments in river follows a quadratic polynomial relationship with the flow rate.;
The release of heavy metals in the river sediments at different flow rates within 1 h is greater than the adsorption.;
Flow rate and water pH are two important factors affecting the release of heavy metals from sediments.;
This paper attempts to assess the suitability of fly ashes from the combustion of solid fuels for agricultural development. The analyzed area of ash collection for research was the commune of Choroszcz in northeastern Poland. The purpose of the study was to assess the pH and electrolytic conductivity of fly ashes from the combustion of solid fuels and to determine the amount of heavy metals leaching from water extracts of the ashes tested. Based on the results obtained, it was found that the content of heavy metals in aqueous fly ash extracts was affected by the combustion method and the type of fuel used. Distribution of heavy metals in the tested samples varied; the highest content was found in water extracts from ashes derived from combustible material, which is coal. It was found that fly ash has the highest leaching ability in the case of heavy metal-zinc. In addition, their alkaline nature has a significant impact on the possibility of agricultural use of fly ash.
Heavy metals’ contamination in cosmetic products is a serious threat. Present study was conducted to evaluate the concentrations of heavy metals (HMs) in various brands of cosmetic products with special emphasis on their health risk assessment. Five heavy metals including Cd, Cr, Fe, Ni and Pb were quantified in different brands of lotions, foundations, whitening creams, lipsticks, hair dyes and sunblock creams using atomic absorption spectrometry. Risk to the consumer’s health was determined using systemic exposure dosage (SED), margin of safety (MoS), hazard quotient (HQ), hazard index (HI) and lifetime cancer risk (LCR).
On comparative basis, different brands of sunblock creams depicted highest concentration of Ni, Pb and Cr (7.99±0.36, 6.37±0.05 and 0.43±0.01 mg/kg, respectively), whereas lipsticks had elevated levels of Fe at 12.0±1.8 mg/kg, and Cd was maximum in lotions (0.26±0.02 mg/kg). Multivariate analysis revealed strong associations among Cr, Ni and Pb, while Cd and Fe showed disparity in distribution and sources of contamination. MoS, HQ and HI values were within the permissible limit apart from for lotions and sunblock creams, while LCR value was higher than the permissible limit in all cosmetic products except lipsticks. Regular use of these products can cause serious threat to human health, particularly skin cancer on long time exposure. Therefore, continuous monitoring of cosmetic products, particularly with reference to HMs adulteration should be adopted to ensure the human safety and security.
This paper presents the results of tests of physical-mechanical, durability
and microscopic properties of geopolymer mortar mixtures based on fly ash
and ladle slag. The mixtures are alkali-activated using sodium silicate and
sodium hydroxide solution. Firstly, the effects of different fly ash (class
„F“) particle sizes on the characteristics of the mortar mixtures were
examined when binder and alkali activator were cured at 95ºC for 24 h, also
pozzolanic activity and strength activity index were investigated. After
that, fly ash ground of optimal particle sizes (0,09 mm) was replaced with
ladle slag, 0 to 20% of the mass, the replacement steps being 5%. The
specimens having dimensions 4x4x16 cm were then cured in ambient conditions,
and the effects of replacement of a part of fly ash with ladle slag were
determined by testing water absorption, flexural and compressive strength,
freeze-thaw resistance, sulfate attack, ultrasound velocity, FT-IR
spectroscopy and leaching of heavy metals. According to the test results of
compressive strength resistance of geopolymer mortars exposed to sulfate
solution, the mortar made with fly ash and ladle slag showed better
resistance to sulfate attack than the mortar made with fly ash only.
Lead (Pb) toxicity has been a subject of interest for environmental scientists due to its toxic effect on plants, animals, and humans. An increase in several Pb related industrial activities and use of Pb containing products such as agrochemicals, oil and paint, mining, etc. can lead to Pb contamination in the environment and thereby, can enter the food chain. Being one of the most toxic heavy metals, Pb ingestion via the food chain has proven to be a potential health hazard for plants and humans. The current review aims to summarize the research updates on Pb toxicity and its effects on plants, soil, and human health. Relevant literature from the past 20 years encompassing comprehensive details on Pb toxicity has been considered with key issues such as i) Pb bioavailability in soil, ii) Pb biomagnification, and iii) Pb-remediation, which has been addressed in detail through physical, chemical, and biological lenses. In the review, among different Pb-remediation approaches, we have highlighted certain advanced approaches such as microbial assisted phytoremediation which could possibly minimize the Pb load from the resources in a sustainable manner and would be a viable option to ensure a safe food production system.
In this research, a fly ash/epoxy composite was fabricated using fly ash filler classified as industrial waste. The behavior of its mechanical properties was investigated by changing the volume of fly ash to 10, 30 and 50 vol.%. To determine the influence of particle size on the mechanical properties, we used two different sizes of the fly ash, which were separated by sieving to less than 90 μm and 53 μm. To optimize fabrication conditions, the viscosity of the fly ash/epoxy slurry was measured at various temperatures with different fly ash volume fractions. In terms of mechanical properties, tensile strength increased as the amount of fly ash increased, up to a critical point. On the other hand, the compression strength of the composite increased continuously as the amount of fly ash increased. Finally, the fracture surfaces were characterized and correlated with the mechanical properties.
The continuous urbanization and industrialization in many parts of the world and Iran has led to high levels of heavy metal contamination in the soil and then on the surface and groundwater. In this study, the concentrations of 8 heavy metals were determined in forty water samples along distribution drinking water of Khorramabad, Iran. The ranges of heavy metals in this study were lower than EPA and WHO drinking water recommendations and guidelines and so were acceptable. The mean values of CDItotal of heavy metals concentrations in adults were found in the order of Zn > Ba > Pb > Ni > Cr > Cu > Cd > Mo. The health-risk estimation indicated that total hazard quotient (HQing + HQderm) and hazard index values were below the acceptable limit, representing no non-carcinogenic risk to the residents via oral intake and dermal adsorption of water. Moreover, the results of total risk via ingestion and dermal contact showed that the ingestion was the predominant pathway. This study also presents that the carcinogenic risk for Pb, Cr, Cd and Ni were observed higher than the acceptable limit (1 × 10-6). The present study will be quite helpful for both inhabitants in taking protective measures and government officials in reducing heavy metals contamination of urban drinking water. •The data analyzed in this study show a clear situation regarding the quality of drinking water in Khorramabad.•The results of this study can be used to improve and develop the quality of drinking water that directly affects the health of consumers.•The present study will be quite helpful for both inhabitants in taking protective measures and government officials in reducing heavy metals contamination of urban drinking water.
Different types of infant foods categorized as formulas, cereals, and purees imported from seven different countries and available on the Kuwaiti retail market were collected for arsenic analysis. The samples were analyzed both for total arsenic concentration using ICP-MS and for arsenic speciation using HPLC-ICP-MS. Speciation is essential for food analysis because of the toxicity and carcinogenicity of inorganic arsenic species. There was a strong positive linear correlation between the total and inorganic arsenic levels in the tested infant foods at the 95% confidence level. Arsenic concentrations detected in this study were implemented to calculate the total daily intake of arsenic, where the calculated daily intake values were utilized to assess the potential health risks to infants incurred by consuming different infant foods by calculating three different assessment indices namely, hazard quotient (HQ), cancer risk (CR), and margin of exposure (MOE). Both the total arsenic content and the safety of the investigated infant foods were compared to the ones associated with 406 different infant food types from seven different countries reported in the literature. This study confirms that infants are exposed to arsenic via diet since rice-based infant food products contained elevated levels of arsenic; consequently, warranting careful attention to diet choices both to limit this exposure and to avert potentially hazardous adverse health effects to the infants.
The extensive usage of cement in almost all infrastructure projects will affect the health of construction industry around the world. At present, the entire globe is marching towards sustainable, eco-friendly and energy efficient infrastructure development with economic viabilities. The research elucidates the effect of grinding of Fly Ash (FA) and Ground Fly Ash (GFA) was studied. The fly ash particles are ground from 727 cm ² /g to 3526 cm ² /g specific surface area Ground fly ash were analyzed from the Blaine's fineness test and particle size and optimized with 120 min of grinding to achieve the ultra-fine particle size. The Cement replacement by 15% FA and 30% GFA were determined from the mechanical strength of blended mortar specimens. The investigation is aimed to increase the consumption of fly ash and enable to reduce the usage of natural resources for the cement production with ultrafine fly ash as an efficient replacement material.
Tail water from wastewater treatment plants (WWTP) serves as a major supplementary water source for scenic water bodies, whose water quality is one of the major focuses of public and scientific inquiries. This study investigated the temporal and spatial variations in water quality of Tangxihe River, a eutrophic urban river receiving tail water from a nearby WWTP in Hefei City, using the single-factor index (SFI) and principal component analysis (PCA). The results of SFI indicated that the most important parameters responsible for low water quality were total nitrogen (TN) and ammonia (NH4þ-N). PCA showed that tail water from the WWTP greatly reduced water quality, as demonstrated by the significantly increased SFIs and integrated principal component values (F values) of the sampling points around the drain outlet of the WWTP (T3, T4 and T5). The sampling points located at the upstream of the river (T1) and up the water-gate of Chaohu Lake (T6) had negative F values, indicating relatively higher water quality. In addition, the season had a significant effect on the water quality of the river. Moreover, we discuss measures to improve the water quality of urban rivers in order to maintain their ecological functions.
Mechanochemical (MC) treatment has been widely proposed to degrade chlorinated organics in various matrix materials. In this study, fly ash from municipal solid waste incineration was grinded without any addition, using an all-dimensional planetary ball mill. The treated fly ash samples were characterised using X-ray diffraction, Raman spectra, scanning electron microscopy and X-ray energy-dispersive spectroscopy. The residual content of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was monitored, as well as polycyclic aromatic hydrocarbons (PAH), a potential precursor of PCDD/F and amorphous carbon or graphite. Finally, de novo formation experiments were performed to test the chemical reactivity of the treated fly ash. The PCDD/F in milled samples was compared to those resulting from de novo tests on these same samples. The results suggest that both milling as well as de novo tests significantly alter the PCDD/F signature, suggesting substantial differences in the mechanisms of formation and destruction.
To stop global warming at well below 2° C, the bulk of the world’s fossil fuel reserves will have to be left in the ground. Coal is the fossil fuel with the greatest proportion that cannot be used, and various advocacy groups are campaigning for a ban on the opening of new coal mines. Recently, both China and the USA implemented temporary moratoria on the approval of new coal mining leases. This article examines whether these coal mining bans reflect the emergence of a global norm to keep coal under the ground. To that end, we review recent coal mining policies in the four largest coal producers and explain them comparatively with a framework based on interests, ideas and institutions. We find that the norm of keeping coal in the ground remains essentially contested. Even in those countries that have introduced some form of a coal mining moratorium, the ban can easily be, or has already been, reversed. To the extent that the norm of keeping coal in the ground has momentum, it is primarily due to non-climate reasons: the Chinese moratorium was mostly an instance of industrial policy (aiming to protect Chinese coal companies and their workers from the overcapacity and low prices that are hitting the industry), while the USA’s lease restrictions were mainly motivated by concerns over fiscal justice. We do not find evidence of norm internalisation, which means that the emerging norm fails to gain much traction amid relevant national actors and other (large) coal producing states. If proponents of a moratorium succeed in framing the issue in non-climate terms, they should have a greater chance of building domestic political coalitions in favour of the norm.
The potential harm to the environment and human body caused by heavy metal elements such as Cd, Cr, Pb in fly ash cannot be ignored. In this study, microscopic analysis and heavy metal hazard analysis were performed on fly ash samples from four regions in China. XRF, XRD, FTIR and SEM/EDS test results showed that the main components of fly ash are Si, Ca, Al, O and other elements, and the main mineral components are mullite, quartz and amorphous aluminosilicate. The results showed that six heavy metal elements of As, Hg, Cd, Cr, Pb and Ni from the EDS test charts of these four types of fly ash. Based on the detection of the six heavy metal contents in fly ash, the results of the pollution evaluation of these four types of fly ash were consistent according to the single factor index, potential ecological risk index, and index of geo-accumulation. This indicated that Cd/Hg in FA 1, FA 2 and FA 3 has a high risk of environmental pollution. In the meantime, Cr and As in fly ash need to be controlled, because the human health risk assessment showed that they will bring carcinogenic risk to the human body through oral intake. The study on the migration law of characteristic heavy metals by taking FA 4 as an example showed that the leaching rate of Cr, Hg and Cd decreased with the increase of grinding particle size. Among the three characteristic heavy metals, mercury had the highest leaching rate. From the XPS detection results of FA 4, it was found that the valence states of these three heavy metals in FA 4 are Cr³⁺, Cr⁶⁺, Cd²⁺, Hg²⁺ respectively. These harmful heavy metal ions gradually enter the deep soil and groundwater through osmosis. Finally, based on the control model constructed in this study, the contents of these three heavy metals in fly ash in different application scenarios were limited.
The availability of traditional siliceous Class F fly ash, produced when burning bituminous coals, is decreasing around the world as many countries begin to switch to renewable energy sources. Existing coal burning power plants are also starting to convert from bituminous to subbituminous coals, which produce calcareous Class C fly ash, or to a blend of the two to reduce emissions and cost. To prolong the availability of siliceous fly ash, suppliers have started distributing blended coal ashes and have also begun to blend siliceous fly ash with other coal combustion products (CCPs), such as calcareous fly ash or bottom ash, or natural pozzolans. A variety of these blended fly ashes were examined in this study and compared to a traditional siliceous fly ash. Although these fly ashes have similar oxide compositions and physical characteristics to a traditional siliceous fly ash, the crystalline and glassy phases present in the fly ash may differ. This can alter cement hydration and result in failure to mitigate expansion due to sulfate attack. In all other performance and durability tests conducted in this study, all fly ashes performed well in cement-based mixtures.
Living beings have been devastated by environmental pollution, which has reached its peak. The disastrous pollution of the environment is in large part due to industrial wastes containing toxic pollutants. The widespread use of chromium (Cr (III)/Cr (VI)) in industries, especially tanneries, makes it one of the most dangerous environmental pollutants. Chromium pollution is widespread due to ineffective treatment methods. Bioremediation of chromium (Cr) using bacteria is very thoughtful due to its eco-friendly and cost-effective outcome. In order to counter chromium toxicity, bacteria have numerous mechanisms, such as the ability to absorb, reduce, efflux, or accumulate the metal. In this review article, we focused on chromium toxicity on human and environmental health as well as its bioremediation mechanism.
This study focuses on the health risks caused by potentially toxic metal (Cd, Cr, Hg, Ni, and Pb) contamination in soil. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to identify the source of heavy metal. While non-carcinogenic and carcinogenic risks were determined using deterministic (USEPA’s human health risk assessment methods) and probabilistic methods (Monte Carlo Simulation model), respectively. The mean concentration of heavy metal increased in the order of Cd < Ni < Pb < Hg < Cr. PCA, HCA, and spatial distribution demonstrated that Pb and Ni may be derived from anthropogenic activities, whereas Cr and Hg were mostly derived from natural sources. Adults and children were relatively safe from non-carcinogenic risk except for children living near mining and cement factories (THI > 1). The total average cancer risk of adults and children was 2E-03 and 7E-04, respectively. This indicates that both adults and children were at high risk of developing cancer in the future (TCR > 1E-04). Based on the sensitivity analysis, Cr concentration, exposure frequency, and exposure duration were the most influential factors to cancer risk. Therefore, we must implement integrated risk management, which includes reducing Cr concentration in soil, and educating people to avoid soil contact, and implementing good personal hygiene. The recommended concentration of Cr in the soil was 20 mg/kg.
An innovative hybrid cement, based on type F fly ash (FA), iron and steel slag (ISS) and Portland cement (OPC), is proposed in the present paper. The precursors were activated by powder-form elements – sodium sulphate or sodium chloride – forming what is known as a ‘one part geopolymer’ cement, which was then evaluated considering both mechanical and microstructural perspectives. Results showed that, in these conditions, the reactivity of the ISS is lower than that of the FA, with or without the presence of the activators. In the ternary pastes formed by 50%ISS +25%FA + 25%OPC and 25%ISS +25%FA + 50%OPC, with no activator included, both the ISS and the FA reacted due to its inherent pozzolanic activity. The presence of the powder-form activators increased the mechanical strength of the pastes (which are known as “hybrid cements”, since an activator and OPC are simultaneously present), relatively to the no-activator pastes. Furthermore, the inclusion of Na2SO4 or NaCl increased and decreased the activation rate, respectively, relatively to the equivalent binder hydrated with water (i.e. without the presence of an activator). Regardless, in both cases, strength values above 40 MPa and 35 MPa, after 28 days curing, were obtained. In the hybrid cements, the activators first reacted with the OPC phases; with the activator anions originating products such as calcium sulphate, ettringite or Friedel's salt (depending on the activator type), which increase the density of the matrix and, therefore, the resulting mechanical strength. Furthermore, in the presence of the Na⁺ cation, local NaOH is generated, increasing the alkalinity of the medium and, consequently, accelerating the reaction of the ISS and FA, which further improves the mechanical strength. Behind every combination, a C-(A)-S-H gel is the main reaction product.
In this study, systematic macroscopic and microscopic analyses on the mechanical performance of metakaolin (MK)/fly ash (FA) based geopolymer mortar were carried out through compression tests, bending tests, and phase analysis, to illustrate the mechanisms of the interaction between fiber and nano additives and mortar leading to the improvement of mechanical properties of matrix. The detailed analyses on the microscopic mechanisms of mechanical performance enhancement due to the nano-SiO2 (NS) and polyvinyl alcohol (PVA) fibers were made based on the microscopic tests using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffractometer (XRD). The microscopic morphology and phase analyses demonstrated that an appropriate amount of NS promoted the geopolymerization and improved the mechanical properties of the mortar; however, after a certain value, the continued increase of the proportion of NS negatively affected mechanical properties of geopolymer mortar. Microstructural analyses and crystal identification indicated that in addition to its filling effect, NS formed more structurally stable (N, C)-A-S-H crystals that enhanced the adhesion between the matrix and PVA fiber surfaces. However, excessive NS negatively impacted the hydration of the FA and MK, thus inhibiting the formation of aluminosilicate, which resulted in a reduction in the strength of the geopolymer mortar. Through the above experiments, the microscopic mechanism of the macroscopic mechanical behavior changing caused by NS and PVA was revealed, aiming to provide reference for future improvement on mix proportion of MK/FA based geopolymers and in-depth research.
The study of the relationships between freshwater organisms, pollution and public awareness has been little researched. The public’s perception of risk from pollution is a fundamental component in determining consumer behavior and promoting healthy habits. For instance, understanding how consumers perceive the risks associated
with pollution can help with adoption of safe behaviors to reduce the health hazard associated with pollutant exposure. This study focused on the southeastern United States, a region predicted to be exposed to high mercury stress by increasing mercury deposition and methylation. First, we placed our study region in the world map of regions more prone to suffer from increasing mercury stress in a climate change scenario. Second, mercury levels in fish tissues was quantified by direct mercury analyzer (DMA). Third, we explored human fish consumption habits and risk social perception, including willingness to adapt fish consumption based on two future hypothetical scenarios of mercury stress. From a global perspective, our analysis demonstrates that the southern US is one of five world areas of greatest conservation concern for mercury stress. In this region, the average monomethyl
mercury concentration in fish tissues exceeded the limits considered safe for human consumption. Even though many in the local population were aware of the health hazards associated with fish consumption, only women of reproductive age were willing to adopt safe consumption habits. Altogether, these results show how bringing together field data, social perceptions, and consumption habits can help in designing an adaptive strategy to confront mercury pollution. Although our results are for the United States, other world regions prone to suffer increasing mercury stress have been identified and should be the focus of future studies and prescriptions.
Petrochemical industries are widely distributed in China. As a negative consequence, heavy metals in petrochemical area can result in soil contamination. However, the relevant research of heavy metals contamination in petrochemical area was few. In this study, a total of 103 topsoil samples (<20 cm) and 25 profile soil samples were collected and examined in a retired petrochemical industrial area, South China. The results showed the mean contents of Hg, Cd, As, Pb, Ni and Cu were 0.18, 0.69, 16.22, 47.24, 31.62 and 93.06 mg·kg⁻¹, respectively. The spatial distribution of six metals in topsoil was largely attributed to the industrial activities during the petroleum refining and transshipment process. Ni was the main pollutant in the petroleum refining process. While, the contamination of other metals mainly were caused by the leakage of the oil during transshipment. The migration of six metals to subsoil layers was also observable. In accordance, Hg, Cd, As, Pb, Cu, and Ni dropped by 95.02, 71.91, 89.45, 90.88, 99.22, and 65.07%, respectively, compared to their contents in topsoil. The contamination of the heavy metals was mainly caused during the process of petroleum refining and transshipment. The distribution of heavy metals in the factory was mainly affected by the industrial activities or the lateral infiltration of Lianhuashan River. Soil ingestion was the primary pathway for children and adults exposure to heavy metals. The total non-cancer human health risk induced by heavy metals was within the limit of USEPA (10⁻⁶ a⁻¹). While the cancer risks alone induced by As through soil ingestion to children was 1.14×10⁻⁶ a⁻¹, which exceeded the limit of USEPA. This study indicated that not only petroleum hydrocarbon but also heavy metals can cause soil contamination in a retired petrochemical industrial area, which provides a novel cognition. Altogether, measures should be taken in practice to substantially improve the soil quality in petrochemical industrial area.
In this study, the concept of “full-volume fly ash (FVFA) geopolymer mortar” is proposed using FA geopolymer as a binder and sintered fly ash aggregates (FAAs) to fully replace the conventional river sand (by volume), aiming to conserve natural sand resources through further utilizing of FA. The influences of the FAAs, the alkali concentration, and curing regime on the physical, mechanical, microstructure, and mineralogy properties of the FVFA geopolymer mortars were experimentally evaluated. The properties of the conventional river sand control mortars were used as a benchmark reference. The results indicated that both compressive strength and density of the FVFA geopolymer mortars were relatively lower compared to that of the control mortars. The change of alkali concentration and steam-curing duration could generate a wide variant range of the compressive strength and density. Further, the FVFA geopolymer mortars were found to have much higher total porosity relative to the control mortars. The drying shrinkage of the FVFA geopolymer mortars was much lower than that of control mortars due to the internal curing effect of the FAAs. It was challenging to identify the interfacial transition zone (ITZ) between the sintered FAAs and the FA geopolymer binder relative to that between sand and paste in control mortars. It was found that the external layer of the FAAs has reacted with the alkaline solution while the internal core remains relatively stable during the 28 days.
Municipal SolidWaste (MSW) management in China has been transitioning from a mixed collection and treatment system to a separated collection and treatment system. The continuous rise of MSW treatment capacity and the optimization of technology structure provided basic facility support for China to promote MSW separation at source. China preferred a four-type separation system. Regulated recycling should be enhanced to improve the efficiency and sustainability of recycling industry. As food waste is the main composition of MSW in China, 20%–30% of the food waste diversion and land application could maximize the comprehensive environmental performance. Incineration is to be the pillar technology in MSW separated treatment system in China.
Calcium-silicate-hydrate (C-S-H) gel is the most important product of cement hydration and the only phase with the evolving microstructure in cement-based materials. Previously, extensive researches have adopted nanoindentation to investigate the mechanical properties of various C-S-H gels at mature ages, revealing two packing morphologies of C-S-H gels (i.e. loose-packed C-S-H and dense-packed C-S-H). However, the study on the early-age formed C-S-H gel is rare, resulting in the poor understanding on the evolution of the mechanical properties of C-S-H gel. The study adopts nanoindentation and dynamic modulus mapping to investigate the C-S-H gel formed by C3S hydration and give an insight into the evolution of the elastic properties of C-S-H gel.
Recently, surface soils of remote or protected areas, that receive pollutants from the surroundings or in situ activities through dry and wet deposition, exceed the baseline content of heavy metals. In the last decades, the use of single and integrated indices is a powerful tool to process, analyze and convey information about metal accumulation degree for decision makers to better manage protected areas. Single indices provide information about only one metal, whereas the integrated ones give a holistic evaluation. The aim of the research was to assess the temporal trends of three single (Contamination Factor, Enrichment Factor and Geo-accumulation Index) and two integrated (Pollution Load Index, Nemerow index) indices in order to evaluate if the touristic impact caused soil metal (Cr, Cu, Ni and Pb) accumulation. In autumn 2016 and in spring 2016 and 2017, the surface soils (0–10 cm) were collected at eight sites inside the Vesuvius National Park (Southern Italy), characterized by intense tourism from spring to autumn. The metal concentrations were measured in the soils and used to calculate the indices. In addition, the Ecological Risk Factor was calculated and the phytotoxicological assays were performed. The findings showed that the surface soils of the Vesuvius National Park were polluted by Cr, Cu, Ni and Pb, according to both single and integrated indices. The touristic impact would seem to be the main cause of soil metal accumulation, as the highest values of the calculated indices were detected for samples collected at the end of the touristic season and the lowest at the beginning of the touristic season. Anyway, Cu and Pb would seem also to derive by ex situ anthropogenic sources, whereas Cr and Ni also by natural sources, such as spontaneous fires and substrate weathering. Finally, the soils showed phytotoxic effects and low ecological risks.
This study examines the pozzolanic effect of calcined lime sludge
(CLS), a residual solid waste from the paper industry, and fly
ash (FA), a residue generated from thermal power plants. CLS
is obtained by calcination of lime sludge (LS) at the temperature
750 to 800°C (1382 to 1472°F) for 2 hours. The formation of
calcium silicate hydrate (C-S-H), which is responsible for binding
aggregates in concrete, is observed by hydrothermal method for
three different proportions of CLS and FA in 1:5, 2:5, and 3:5 ratios
at the temperature 220 to 250°C (428 to 482°F) in a hydrothermal
cell. The chemical composition, physical properties, morphology,
and mineralogical characteristics of the precursor materials and
the formed C-S-H are analyzed by using XRF, XRD, SEM/EDS,
TG-DSC, and FT-IR. In addition, the hydration behavior of ternary
blended cementitious paste at a constant temperature of 30°C
(86°F) is evaluated for pozzolanic activity by using ordinary portland
cement (OPC), FA, and CLS in three different proportions. The
result shows that the premature stiffening during early hydration of
ternary blends compared to control. This study leads to potential
use of FA and CLS in large quantities in a promising direction.
Bioleaching of heavy metals (Cu, Zn, Cr and Pb) from coal fly ash by cyanobacterial strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis and Aulosira fertilissimia), that are commonly used as biofertilizers in rice cultivation was studied to assess utilization of fly ash while mitigating its environmental metal toxicity. Cyanobacteria were grown at different concentration of fly ash at 0, 5, 10, and 20% was treated with different blue green algal strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis, and Aulosira fertilissimia) in suitable growth medium (BG-11) and distilled water to observe their growth and metal accumulation. Nostoc muscorum (ARM 442 mg g⁻¹) showed maximum uptake of Cr (3.65 mg g⁻¹), Pb (2.12 mg g⁻¹) at BG 11(-N) medium amended with 10% fly ash, respectively. Anabaena variabilis (ARM 441) showed maximum uptake of Cu (0.313 mg g⁻¹) and Pb (2.01 mg g⁻¹) in BG 11 (–N) medium amended with 5% fly ash whereas Cr uptake (1.21 mg g⁻¹) at 10% fly ash and Zn uptake (0.697 mg g⁻¹) at 20% fly ash grown in BG 11(-N) medium. Increased accumulation of metals in blue green algae biomass grown in BG 11(-N) medium amended fly ash confirms that metal concentration was balanced between the algal strains.
The characterization of the concentration and chemical speciation of heavy metals in surface and vertical profile soils is a necessary for pollution monitoring and the potential risk assessment of the heavy metals (HMs) to animal and human health. Surface soil samples (n = 14) and vertical profile soil samples (n = 36) from selected sites (n = 6) were collected from coal-mine brownfield in the Qingshui River Basin, in which the concentrations and chemical speciation of HMs (Cd, Cr, Cu, Mn, Ni, Pb, Zn) in surface soils and HM concentrations in vertical profile soils were determined by ICP-OES and analyzed using methods of geo-accumulation index (Igeo), Tucker 3 model and health risk assessment. The chemical fractions of HMs were extracted by BCR- sequential extraction procedure. Results show that HMs in surface soils accumulate in descending order of Cd > Pb > Cu > Ni > Mn > Zn > Cr. All HMs are associated with residue fraction to different degrees. Manganese and Ni are closely related to extractable BCR fractions and turn to be the severer pollutants in some sites. The Igeo values of HMs in vertical profile soils indicate ‘uncontaminated’. Whereas coal mining activities with long history increase HM concentrations in subsurface soils at the coal mine former site. The non-carcinogenic risk posed by HM extractable fractions to children and adults fall below the safe level of 1. Lead extractable fraction exhibits the highest risk value in the case of children. The levels of carcinogenic risk posed by Cr and Ni extractable fractions are above that of the United States Environmental Protection Agency (USEPA) acceptable level (1 × 10− 6). Nickel extractable fraction exhibits the highest carcinogenic risk values for children with exceeding that of the maximum USEPA acceptable level (1 × 10− 4).
In this paper fly ash based geopolymer mortars have been prepared and their thermal behavior evaluated in order to assess the suitability of fly ash based alkali-activated binders for thermal energy storage in solar thermal plants. Different parameters, such as binder/aggregate ratio, percentage of fly ash replaced by slag, temperature and curing time, have been changed and optimized using the Design Of Experiments (DOE) approach. In order to estimate the thermal cycling stability of geopolymeric mortars at elevated temperatures, mechanical strength and weight loss of each sample subjected to different thermal cycles in the temperature range 150–550 °C were evaluated. Finally, thermal conductivity of some of the mixtures, selected on basis of the thermal stability test results, have been measured.
Fly ash based geopolymeric mortars remained stable after each thermal treatment and specimens treated at elevated temperatures retained acceptable compressive strength. The thermal stability was preserved also after repeated thermal cycles, proving that fly ash based geopolymers are suitable materials for thermal energy storage concretes.
Research on coal consumption control policies of the power industry during the 14th Five-Year Plan period
- Yuan
Chemical Composition and Physicochemical Properties of Fly Ash and Its Application
- Quan
Analysis and Prediction of Equal Strength Mechanism of Fly Ash Mortar under Low Water-Binder Ratio
- Wen-bo
Effect of particle characteristics of fly ash on hydration properties of recycled concrete
- Xiao-min