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Rare earth elements (REEs) have been identified as valuable and critical raw materials, vital for numerous technologies and applications. With the increasing demand for and supply gap in REEs, many research studies have focused on alternative sources of REEs. This study involved an elemental and mineralogical characterisation of discarded coal from a coal plant and coal fly ash (CFA) from a power station in South Africa for REE presence. XRD results revealed that the discard coal sample consisted mainly of kaolinite, pyrite, siderite, quartz, calcite, gypsum, and muscovite, whereas CFA contained abundant glassy amorphous phases, alumina silicates, quartz, gypsum, calcite, and minute levels of muscovite and hematite. SEM-EDAX showed REE-carrying grains containing phosphorus in both discard coal and CFA samples. This was followed by investigating the leaching potential of REEs using hydrochloric acid from discard coal and CFA. This research's potential impact is possibly providing a new and sustainable source of REEs. For that purpose, multiple batch leaching tests were performed to investigate the effects of temperature and acid concentration on the leaching efficiencies of REEs from discard coal and CFA. The experimental results indicated that temperature strongly influences REE leaching efficiency, while acid concentration has a lesser impact. This study identifies the best leaching conditions for the total REE recovery as 1 M HCl and 80 °C for discard coal and CFA. [ABSTRACT FROM AUTHOR]

Zeolites have been increasingly applied in various fields such as energy conversion, environmental remediation, chemical production, and so on, being used as membranes, catalysts, and supports due to their large specific areas and strong gas adsorption. And, developing low-cost strategies for the preparation of zeolites has attracted the extensive attention of researchers. Coal fly ash, waste glass, discard zeolites, and slags are typical industrial wastes and rich in Si and Al, indicating that these industrial wastes can be utilized as alternative raw materials of zeolite synthesis. Firstly, the chemical composition and properties of these industrial wastes are summarized. Then, the strategies involved in synthesizing different zeolites from various industrial wastes are discussed. In addition, the applications of these zeolites are comprehensively reviewed. [ABSTRACT FROM AUTHOR]

Utilizing calcium-based adsorbents for CO2 adsorption through cyclic calcination/carbonization is one of the most cost-effective methods for carbon emission reduction. In order to improve the cycle stability of the adsorbents and the capture efficiency of CO2, this study used industrial solid waste coal fly ash for the hydration treatment of calcium-based adsorbent to explore the variations in the cyclic adsorption performance of the adsorbent under different doping ratios and hydration conditions. By means of various characterization techniques, the microscopic mechanism for improving the performance of the modified adsorbent was analyzed from the perspectives of chemical composition, physical structure, and surface functional groups of the adsorbents. The results demonstrated that the modification of coal fly ash could significantly enhance the carbonation performance and cycle stability of the adsorbent in multiple CO2 capture processes. The modified material doped with 5% coal fly ash had the highest total CO2 adsorption capacity, which increased by 13.7% compared to before modification. Additionally, the modified material doped with 10% coal fly ash exhibited the strongest cyclic adsorption capacity, which was 14.0% higher than that before modification, and the adsorption attenuation rate decreased by 32.2%. The characterization results showed that the reaction between calcium oxide and coal fly ash formed CaSiO3 and Ca12Al14O33 during the modification process, which was the primary reason for the improvement in the CO2 capture performance of the modified materials. This study provided a new perspective on the resource utilization of solid waste fly ash and efficient CO2 capture. [ABSTRACT FROM AUTHOR]

The compound p-Nitrophenol (p-NP) is widely recognized as a highly toxic nitro-aromatic substance that urgently requires emission control. Reducing p-NP to p-aminophenol (p-AP) not only decreases its toxicity and mineralization properties in nature but also provides a key raw material for the chemical and pharmaceutical industries. The study used coal fly ash (CFA) as a catalyst carrier for synthesizing the p-NP reduction catalyst. Using CFA as an alternative option not only reduces costs but also achieves the objective of treating waste with waste compared to utilizing commercial solid materials for synthesizing catalysts. By employing hydrochloric acid and sodium hydroxide pretreatment methods, the physicochemical properties of CFA are significantly improved, enhancing the dispersion of palladium (Pd) nanoparticles. The structural features of the prepared samples were characterized using various surface analysis techniques, and both intermittent and continuous modes were experimentally tested for the model catalytic reaction involving the sodium borohydride (NaBH4)-mediated reduction of p-NP. The results demonstrate that CFA has potential in wastewater treatment. [ABSTRACT FROM AUTHOR]

Lithium, a critical material for the global development of green energy sources, is anomalously enriched in some coal deposits and coal by-products to levels that may be considered economically viable. Recovering lithium from coal, particularly from coal gangue or coal ashes, offers a promising alternative for extracting this element. This process could potentially lead to economic gains and positive environmental impacts by more efficiently utilizing coal-based waste materials. This review focuses on lithium concentrations in coal and coal by-products, modes of lithium occurrence, methods used to identify lithium-enriched phases, and currently available hydrometallurgical recovery methods, correlated with pretreatment procedures that enable lithium release from inert aluminosilicate minerals. Leaching of raw coal appears inefficient, whereas coal gangue and fly ash are more feasible due to their simpler composition and higher lithium contents. Lithium extraction can achieve recovery rates of over 90%, but low lithium concentrations and high impurity levels in the leachates require advanced selective separation techniques. Bottom ash has not yet been evaluated for lithium recovery, despite its higher lithium content compared to feed coal. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA), a by-product of coal combustion, is a valuable raw material for various applications. However, the heterogeneous nature of the composition and properties of CFA provides challenges to its effective usage and utilisation. This study investigates the thermal behaviour of the fly ashes of lignite (FA1) and brown coal (FA2) and their fractions obtained by dry aerodynamic separation. Thermal analysis techniques, including thermogravimetry (TG), differential scanning calorimetry (DSC), and evolved gas analysis (EGA), were used to characterise the behaviour of the fly ash fractions while heating up to 1250 °C. The results reveal distinct differences in the thermal behaviour between ash types and among their different size fractions. For the FA1 ashes, the concentration of calcium-rich compounds and the level of recrystallisation at 950 °C increased with the decrease in particle size. The most abundant detected newly formed minerals were anhydrite, gehlenite, and anorthite, while coarser fractions were rich in quartz and mullite. For the FA2 ashes, the temperature of the onset of melting and agglomeration decreased with decreasing particle size and was already observed at 995 °C. Coarser fractions mostly remain unchanged, with a slight increase in quartz, mullite, and hematite content. Recrystallisation takes place in less extension compared to the FA1 ashes. The findings demonstrate that the aerodynamic separation of fly ashes into different size fractions can produce materials with varied thermal properties and reactivity, which can be used for specific applications. This study highlights the importance of thermal analysis in characterising fly ash properties and understanding their potential for utilisation in various applications involving thermal treatment or exposure to high-temperature conditions. Further research on advanced separation techniques and the in-depth characterisation of fly ash fractions is necessary to obtain materials with desired thermal properties and identify their most beneficial applications. [ABSTRACT FROM AUTHOR]

The present study focuses on the synthesis of a manganese dioxide lithium ion sieve and its application for the extraction of lithium from coal fly ash. The preparation and adsorption experiments of the manganese dioxide lithium ion sieve were carried out using the orthogonal method, while the HCl elution experiment was carried out using the single factor method. The results showed that the optimum preparation conditions under which the average lithium adsorption efficiency reached 99.98% were a 10:1 mass ratio of manganese dioxide to lithium hydroxide, calcination at 800 °C for 60 min, 1.5 mol/L HCl, soaking for 24 h and stirring for 18 h. Additionally, the optimum adsorption efficiency was observed with an adsorption time of 30 min, KOH pH of 8 and KOH scrubbing time of 10 min, resulting in 100% lithium adsorption efficiency. The optimum elution conditions for lithium were determined to be an HCl concentration of 0.01 mol/L and an elution time of 40 min, giving 100% lithium elution efficiency. [ABSTRACT FROM AUTHOR]

Lithium belongs to the critical elements and is used in a variety of high-tech applications. In the context of the circular economy, demand has arisen for technologies that are able to recover high-tech metals from wastes and byproducts. To achieve efficient recovery, apart from assessing metal enrichment, extensive knowledge of metal binding and leaching characteristics is required. The aim of the present study is to investigate the Li contents and mode of occurrence in Greek coal fly ashes. Eight coal fly ashes from different power plants in Greece were collected, and their major constituents were analyzed by X-ray fluorescence spectroscopy (XRF); their mineralogy was studied by X-ray powder diffraction (XRD), and their Li content was determined by ICP–MS. To identify Li binding and leaching characteristics, two sequential extraction methods (Tessier and BCR) were employed. The results showed that the Li content in the samples studied was between 95 and 256 μg/g and could be mainly attributed to the amorphous material encountered in the samples. The sequential extraction experiments revealed that 70–90% of Li is included in the residual fraction, indicating that it is strongly bound to the fly ash matrix. [ABSTRACT FROM AUTHOR]

Coal remains an important fuel for use in thermal power plants. However, coal-burning power plants produce large amounts of CFA, which contains TEs such as B, F, and Se, which are leached upon contact with water and act as potential polluters of aquifer systems and soil. To study the transformation of TEs, a thermodynamic calculation (FactSage 7.2) was used. Paper sludge ash was used as a calcium compound additive. The influence of blending a high-calcium additive on the environmental safety of TEs was investigated based on the effect of the mass addition ratio of PS ash. This study's results confirmed that the leaching processes of TEs, namely (CaO)2(Al2O3), CaF2, Ca10(PO4)F2, and CaSeO4(H2O)2, were caused by the formation of B, F, and Se compounds during the leaching process. Thus, it is clear that calcium has the greatest influence on the transformation of TEs due to their reaction, which, in turn, minimizes the effects of the TEs' release into the environment. The concentrations of TEs from the sample and addition of PS ash decreased slightly, indicating that the inhibition of TEs was enabled through the addition of PS ash. Although the PS ash YB had the highest calcium content, the PS ash YC gave the best results during the B and Se inhibition processes. The experimental observation was also evaluated for comparison. For the analysis of TEs' leaching ratios using the thermodynamic calculation and experiment, the experimental results were lower than those initially predicted. These results will help us to choose the best available control technology to minimize the effects of TEs released into the environment. [ABSTRACT FROM AUTHOR]

Despite numerous studies focused on the hydrothermal (HT) synthesis of fly ash zeolites (FAZs), this method still has many limitations, the main of which is the low yield of zeolites. Hydrothermally synthesized zeolites are typically multiphase and exhibit low purity, which limits their applicability. Pure-phase zeolites have been primarily prepared from filtrates after alkaline mineralization of fly ashes, not directly in suspension. In addition, the published methodologies have not been tested in a wider set of samples, and thus their reproducibility is not confirmed. The aim of the study is to propose a reproducible methodology that overcomes the mentioned limitations. The influence of the Si/Al ratio (1.3:1–1:2), the type and concentration of the activator (2/4 M NaOH/KOH/LiOH), the reagent (30% LiCl), the duration (24–168 h), and the temperature (50–180 °C) of the synthesis phases were studied. The sequence of the synthesis phases was also optimized, depending on the type of heat transfer. The fly ashes were analyzed by wavelength-dispersive X-ray fluorescence (WD XRF), flame atomic absorption spectrometry (F-AAS), and X-ray diffraction (XRD). The energy intensity of the synthesis was reduced through the application of unique microwave digestion technology. Both microwave and combined (microwave and convection) syntheses were conducted. FAZs were identified and quantified by XRD analysis. This study presents a three-stage (TS) hydrothermal synthesis of pure-phase sodalite in suspension. Sodalite (>99 wt.%) was prepared from nine fly ashes under the following conditions: I. microwave phase: 120 °C, 150 min, solid-to-liquid ratio (S/L) 1:5, Si/Al ratio 1:1.5, and 4 M NaOH; II. convection phase: 120 °C, 24 h, S/L 1:40, and the addition of 30 mL of 30% LiCl; and III. crystallization: 70 °C for 24 h. The formation of rhombododecahedral sodalite crystals was confirmed by scanning electron microscope (SEM) images. [ABSTRACT FROM AUTHOR]

A large quantity of coal fly ash is generated worldwide from thermal power plants, causing a serious environmental threat owing to disposal and storage problems. In this work, for the first time, coal fly ash is converted into advanced and novel aerogel fibers and high-purity α-Al2O3. Silica–bacterial cellulose composite aerogel fibers (CAFs) were synthesized using an in situ sol-gel process under ambient pressure drying. Due to the unique "nanoscale interpenetrating network" (IPN) structure, the CAFs showed wonderful mechanical properties with an optimum tensile strength of 5.0 MPa at an ultimate elongation of 5.8%. Furthermore, CAFs with a high porosity (91.8%) and high specific surface area (588.75 m2/g) can inherit advanced features, including excellent thermal insulation, stability over a wide temperature range, and hydrophobicity (contact angle of approximately 144°). Additionally, Al2O3 was simultaneously extracted from the coal fly ash to ensure that the coal fly ash was fully exploited. Overall, low-cost woven CAFs fabrics are suitable for wearable applications and offer a great approach to comprehensively use coal fly ash to address environmental threats. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) is the primary solid waste generated by the coal-fired industry, and the predominant treatment methods include accumulation, landfill, and the production of cement-based building materials. However, the availability of these methods is relatively limited, and there is a need for technological upgrades. The extensive accumulation not only leads to environmental pollution but also has detrimental effects on human health. With its loose structure and main chemical components of Al2O3 and SiO2, CFA is conducive to the synthesis of promising nanoporous materials for applications in adsorption. The use of CFA as a raw material can significantly reduce preparation costs, improve comprehensive utilization efficiency, and manufacture more valuable products, aligning with the current strategy of sustainable development. Currently, the most widely used synthesis method is hydrothermal synthesis. This review focuses on the principles, methods, and influencing factors of synthesis, with particular emphasis on CFA-based mesoporous silica, zeolites, and metal–organic frameworks (MOFs), which have not been systematically reviewed previously. The quality of these synthesized nanoporous materials can be finely adjusted through the synthesis process. A comparison of the advantages and disadvantages of each process will be made, and the impact of the synthesis conditions on the synthetic products will be analyzed. Additionally, a brief discussion on the latest research advances in their applications in adsorption will be provided. Finally, relevant challenges and issues have been proposed. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) is a waste that forms via coal combustion in thermal power stations. CFA consists of numerous components, whose recovery can address environmental and resource concerns associated with sustainable development. Most of the alumina (Al2O3) and rare-earth elements (REEs) in CFA are contained in the amorphous glassy mass and in the refractory mullite phase (3Al2O3·SiO2), which can be dissolved only using high-pressure acid leaching (HPAL). In this paper, the method of preactivation of CFA by treatment with a highly concentrated NaOH solution is used to increase the efficiency of Al and Sc extraction during HPAL. This method allows for the elimination of an inert aluminosilicate layer from the surface of mullite, transferring the REEs into an acid-soluble form. The Al and Sc extraction can reach 80% after HCl HPAL at T = 170 °C and a 90 min duration. According to the kinetic data, the dissolution of Al follows the surface chemical reaction and intraparticle diffusion shrinking core models in the initial and later stages of leaching, respectively. A high activation energy of 52.78 kJ mol−1 was observed at low temperatures, and a change in the mechanism occurred after 170 °C when the activation energy decreased to 26.34 kJ mol–1. The obtained activation energy value of 33.51 kJ mol−1 for Sc leaching indicates that diffusion has a strong influence at all studied temperatures. The residue was analysed by SEM-EDX, XRF, BET, and XRD methods in order to understand the mechanism of DCFA HPAL process. [ABSTRACT FROM AUTHOR]

This study aims to propose a novel backpropagation neural network (BPNN) featured with sequential forward selection (SFS), named the BPNN_s model, to master the leaching characteristics of toxic elements (TEs) in coal fly ash (CFA). A total of 400 datasets and 54 features are involved to predict the fractions of TEs. The determination coefficient (R2), root mean square error (RMSE) and variance accounted for (VAF) and Willmott's index (WI) are used to validate the BPNN_s, and its predictive performance is compared with the other three models, including the unified BPNN (BPNN_u), the adaptive boosting (AdaBoost) and the random forest (RF) models. The results indicate that the BPNN_s outperforms others in predicting the fractions of TEs, and feature selection is an imperative step for developing a model. Moreover, the features selected with SFS suggest that the influence of the element properties is more significant than that of the chemical properties as well as the concentration on predicting the fractions of TEs. Atomic weight is found to be the most critical feature in the prediction through a shapely additive explanations (SHAP) analysis. This study helps to assess the TEs' mobility rapidly and accurately and provides a foundation for obtaining insights into the relationship between the features and the fractions of TEs. [ABSTRACT FROM AUTHOR]

Membrane technology is a promising method for gas separation. Due to its low energy consumption, environmental safety, and ease of operation, membrane separation has a distinct advantage over the cryogenic distillation conventionally used to capture light inert gases. For efficient gas recovery and purification, membrane materials should be highly selective, highly permeable, thermally stable, and low-cost. Currently, many studies are focused on the development of high-tech materials with specific properties using industrial waste. One of the promising waste products that can be recycled into membrane materials with improved microstructure is cenospheres—hollow aluminosilicate spherical particles that are formed in fly ash from coal combustion during power generation. For this purpose, based on narrow fractions of fly ash cenospheres containing single-ring and network structure globules, silicate glass/mullite composites were prepared, characterized, and tested for helium–neon mixture separation. The results indicate that the fragmented structure of the cenosphere shells with areas enriched in SiO2 without modifier oxides, formed due to the crystallization of defective phases of mullite, quartz, cristobalite, and anorthite, significantly facilitates the gas transport process. The permeability coefficients He and Ne exceed similar values for silicate glasses; the selectivity corresponds to a high level even at a high temperature: αHe/Ne—22 and 174 at 280 °C. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) is a technogenic waste formed during coal combustion in thermal power plants (TPPs). The extraction of valuable components from CFA is complicated by the presence of a large amount of amorphous glassy mass and iron. Herein, a novel method of CFA desilication with complete extraction of the amorphous glassy mass without desilication product (DSP) precipitation and simultaneous magnetic fraction recovery in one stage is presented. The Fe recovery in the magnetic fraction using the proposed method was significantly improved from 52% to 68%. After conventional wet magnetic separation, followed by the proposed method for desilication and magnetic fraction separation, the Fe recovery was increased to 73.8%. Because of the absence of DSP precipitation, the Na2O content in the solid residue after desilication was lower than 1 wt.%. The simultaneous desilication and magnetic separation of magnetite was achieved by installing a belt of permanent magnets on the outer surface of the reactor, where the CFA was leached by the highly concentrated NaOH solution. The effects of different parameters on the extraction of Si, Al, and Fe from the raw CFA were elucidated by varying the liquid-to-solid ratio (L:S ratio) from 5 to 10, the temperature from 100 to 120 °C, the leaching time from 10 to 30 min, and the particle size from −50 µm to −73 µm. The optimal leaching parameters were determined to be temperature = 110 °C, L:S ratio = 7.5, and leaching time = 20 min. The extraction of Si and Fe under these conditions was higher than 66 and 73%, respectively. The Al extraction was lower than 10%. The solid residue of NaOH leaching and the magnetic fraction were examined by X-ray diffraction, X-ray fluorescence spectrometry, vibrating sample magnetometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller, and laser diffraction analyses. [ABSTRACT FROM AUTHOR]

Coal fly ashes (COFA) are readily available and reactive materials suitable for CO2 sequestration due to their substantial alkali components. Therefore, the onsite collaborative technology of COFA disposal and CO2 sequestration in coal-fired power plants appears to have potential. This work provides an overview of the state-of-the-art research studies in the literature on CO2 sequestration via the mineralization of COFA. The various CO2 sequestration routes of COFA are summarized, mainly including direct and indirect wet carbonation, the synthesis of porous CO2 adsorbents derived from COFA, and the development of COFA-derived inert supports for gas-solid adsorbents. The direct and indirect wet carbonation of COFA is the most concerned research technology route, which can obtain valued Ca-based by-products while achieving CO2 sequestration. Moreover, the Al and Si components rich in fly ash can be adapted to produce zeolite, hierarchical porous nano-silica, and nano-silicon/aluminum aerogels for producing highly efficient CO2 adsorbents. The prospects of CO2 sequestration technologies using COFA are also discussed. The objective of this work is to help researchers from academia and industry keep abreast of the latest progress in the study of CO2 sequestration by COFA. [ABSTRACT FROM AUTHOR]

Studies were carried out to find a relation between the important physical property, i.e., water absorption and the main mechanical parameter, i.e., compressive strength (fcm), of concretes containing coal fly ash (CFA) in the amounts of 0% (CFA-00), 20% (CFA-20%), and 30% (CFA-30). The methodology of the water absorption tests reflected the conditions prevailing in the case of reinforced concrete structures operating below the water table. The microstructure of all materials was also assessed. Based on the conducted studies, it was found that both the fcm of concretes with the addition of CFA and its water absorption depended on the percentage of waste used, whereas both analyzed parameters were closely related to the structure of the cement matrix and interfacial transition zone area between the coarse aggregates and the paste. It should be stated that at the content of 20% CFA in the binder composition, an increase in the fcm of the material is observed, with a simultaneous increase in its water absorption. On the other hand, the addition of 30% CFA results in a significant decrease in both the strength of the composite and its water absorption. Thus, it was found that in the case of concretes with the addition of CFA, the strength of the material is directly proportional to the level of its water absorption. Moreover, the concrete including 30% CFA may increase the durability of reinforced concrete structures subjected to immersion conditions. From an application point of view, the obtained research results may be helpful in understanding the impact of the CFA additive on the level of water absorption in cement concretes with this waste. [ABSTRACT FROM AUTHOR]

The article presents studies of the influence of parameters of synthesis modes and alkali concentration on the synthesis of zeolite materials from coal fly ash (CFA). The purpose of the study was to synthesise zeolite materials from CFA using the method of alkaline fusion and to determine the susceptibility of selected heavy-metal ions to removal from solutions in an ion exchange process on a selected mesoporous zeolite. It was found that the crystalline phase of sodalite was dominated in all of the samples synthesized. The specific surface area (SBET) of the samples was evaluated using the standard Brunauer–Emmett–Teller (BET) method using N2 sorption. Crystalline zeolite materials have been used to study the efficiency of removing heavy metals from aqueous solutions of Ni2+, Cd2+ and Pb2+. The adsorption data were analyzed using the Langmuir and Freundlich isotherm model. When comparing the estimated coefficient of determination (r2), it was noticed that the sorption data are more accurately described by the Langmuir isotherm and the pseudo-second-order kinetic model. The results of metal adsorption experiments suggest that the synthesized zeolite material has great potential to be used as an inexpensive and alternative source in the production of adsorbents. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) is a highly versatile raw material that has the potential to yield multiple value-added products, including cenospheres, zeolites, carbon nanotubes, and fertiliser substrates. Despite its versatility, a majority of these components are often overlooked, and CFA is primarily used for construction. Conventional processing methods of CFA are known to pose significant environmental challenges, including the leaching of hazardous materials, emission of toxic gases, and the high energy consumption needed to extract the value-added components. Herein, we explore the potential of biometallurgical approaches as an eco-friendly alternative to conventional processing methods for the comprehensive utilisation of CFA. Our focus is on the application of different microorganisms to CFA, the domestication of microorganisms, preprocessing of CFA to facilitate effective biometallurgical processes, the use of bioreactors, and synthesis of nano silica particles. We also propose a novel method for extracting the value-added components from CFA using a preprocessing technique (i.e., washing cycle), combined with multiple interactions with biometallurgical processes. Adopting this approach, we not only enhance environmental stewardship but also improve the circular economic aspects of multi-component utilisation, while providing valuable insights for the development of sustainable techniques for utilising CFA. [ABSTRACT FROM AUTHOR]

Some studies have shown that the heavy metal emissions (HMEs) emitted from diesel engines can seriously threaten human health. HMEs are mainly related to the content of heavy metal ions in diesel fuel. Therefore, in order to reduce HMEs from diesel engines, a nano-fiber membrane filtration technology for diesel fuel was investigated. Herein, coal fly ash (CFA) from coal-fired power plants combined with polyvinyl alcohol (PVA) was successfully fabricated into nano-fibrous membranes using green electrospinning technology. In order to evaluate the adsorption properties, various hybrid membranes with different mixing ratios (PVA/CFA = 10/0, 10/1, 10/3, 10/5, and 10/7 by weight) were fabricated. The results show that eight metal ions with different concentrations are found in the diesel fuel, including Pb, Cu, Zn, Al, Fe, Cr, Ba, and Ni. All PVA/FA membranes have different adsorption capacities for metal ions, following the order: Cu > Fe > Pb > Al > Zn > Cr > Ba > Ni. In addition, the adsorption capacity of CFA3 (PVA/CFA = 10/3) is the largest. The super lipophilicity of the PVA/FA membranes also provide more adsorption sites for the contact of HMs with the membranes. The above research results provide guidance for development of ultra-fine filters in the future. [ABSTRACT FROM AUTHOR]

Membrane distillation is an emerging separation technology with a high separation factor in water desalination. Ceramic membranes are increasingly used in membrane distillation because of high thermal and chemical stabilities. Coal fly ash is a promising ceramic membrane material with low thermal conductivity. In this study, three hydrophobic coal-fly-ash-based ceramic membranes were prepared for saline water desalination. The performances of different membranes in membrane distillation were compared. The effects of membrane pore size on permeate flux and salt rejection were researched. The coal-fly-ash-based membrane showed both a higher permeate flux and a higher salt rejection than the alumina membrane. As a result, using coal fly ash as the material for membrane fabrication can effectively increase the performance when applied to MD. Increasing the membrane pore size improved the permeate flux, but reduced the salt rejection. When the mean pore size increased from 0.15 μm to 1.57 μm, the water flux rose from 5.15 L·m−2·h−1 to 19.72 L·m−2·h−1, but the initial salt rejection was reduced from 99.95% to 99.87%. The hydrophobic coal-fly-ash-based membrane with a mean pore size of 0.18 μm exhibited a water flux of 9.54 L·m−2·h−1 and a salt rejection of higher than 98.36% in membrane distillation. [ABSTRACT FROM AUTHOR]

A feasible approach was developed for the synthesis of ordered mesoporous SBA-15-type materials using coal fly ash (CFA) as raw material. In the proposed approach, CFA was, firstly, activated by subcritical water with the addition of NaOH, which allowed an efficient extraction of silicon species from CFA under strong acidic conditions at near room temperature. Subsequently, in the synthesis system, using silicon extraction solution as the silicon precursor, the introduction of anhydrous ethanol as a co-solvent effectively inhibited the polymerization of silanol species and promoted their collaborative self-assembly with surfactant molecules by enhancing the hydrogen bond interactions. The resultant SBA-15 material had a high purity, high specific surface area (1014 m2/g) and pore volume (1.08 cm3/g), and a highly ordered mesostructure, and, therefore, exhibited an excellent removal efficiency (90.5%) and adsorption capacity (160.8 mg/g) for methylene blue (MB) from simulated wastewater. Additionally, the generation of surface acid sites from the homogenous incorporation of Al atoms onto the mesoporous walls of SBA-15 combined with the perfect retention of the ordered mesostructure endowed the obtained Al-SBA-15 material with a further boost in the removal performance of MB. The MB removal efficiency can reach ~100%, along with a maximum adsorption capacity of 190.1 mg/g. [ABSTRACT FROM AUTHOR]

Geopolymer, a sustainable alternative to ordinary Portland cement (OPC), offers reduced embodied energy, lower carbon emissions, enhanced durability, eco-compatibility, and waste valorization potential. In confining structural members, geopolymer still has limitations with respect to its brittleness and other properties. Enhancing the properties of geopolymer by adding banana fibers (BF) and fly ash (FA) to form banana geotextile-reinforced geopolymer mortar (BGT-RGM) as confining material, is investigated in this experimental study. BGT-RGM is a textile-reinforced mortar with varying thickness of BF-reinforced geopolymer mortar (BFRGM) through NaOH-treated 10 mm BFs and 2 mm banana geotextile (BGT) having varied grid spacings. To develop BGT-RGM, the physical, mechanical, and chemical properties of the BFs were determined, while BFRGMs were evaluated for compressive and dog-bone tensile strengths, workability, scanning electron microscopy (SEM) imaging, and thermogravimetric analysis (TGA). The BGT-RGM-confined and unconfined concrete were evaluated, and the strength variations were imparted by the confinement as reflected on the stress-strain curves. The local crack formation mode of failure was also determined through crack patterns during an axial load test. The BGT-RGM with 20 mm thickness of BFRGM with 15 mm and 20 mm geotextile grid spacings, exhibited 33.3% and 33.1% increases in strength, respectively. Future investigations towards the development and application of BGT-RGM are also discussed. [ABSTRACT FROM AUTHOR]

The huge annual output of coal fly ash is harmful to the environment, but it is widely used because of its good adsorption potential. In this study, using coal fly ash as a raw material and sodium hydroxide as an activator, a novel adsorbent was synthesized at 300 °C and used to adsorb low concentrations of ammonia nitrogen from water. In this study, scanning electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and a surface area and porosity analyzer were used to analyze the adsorbent's physicochemical properties. The results showed that after alkali modification, the activity of the adsorbent had greatly enhanced. The impacts of solution pH, adsorbent dosage, adsorption time, and initial concentration of ammonia nitrogen on the adsorption capacity and removal efficiency were evaluated through a series of adsorption experiments. Moreover, the adsorption data were better fitted to the pseudo-second-order kinetic model and Langmuir model, indicating that the adsorption process was mainly chemical adsorption and monolayer uniform adsorption. As a result, the new adsorbent is inexpensive and effective, and it could be used to remove low-concentration ammonia nitrogen from water with a maximum removal efficiency of approximately 89%. [ABSTRACT FROM AUTHOR]

The rational utilization of solid waste has always been a worldwide concern. In this study, coal fly ash (CFA) and red mud (RM) were used in combination to synthesize efficient heavy metal adsorbents. A new way of resource recycling was provided with the collaborative reuse of CFA and RM. To obtain the modified composite materials, CFA and RM were mixed and melted in three ratios. After modification, these materials were then utilized to adsorb Pb, Cu, and Cd in water in both single and ternary systems. The physicochemical properties of CFA, RM, and three modified composite materials were measured by X-ray diffraction analysis, energy dispersive X-ray spectroscopy, scanning electron microscope, Fourier transform infrared spectroscopy, vibrating sample magnetometer, surface area analyzer, and porosity analyzer. In the single and ternary systems, the effects of the modified composite material dosage, solution pH, initial concentration of heavy metals, and adsorption time were discussed, and the results were better fitted with the Langmuir isotherm and the pseudo-second-order kinetic. It was discovered that the modified composite materials had a greater specific surface area (63.83 m2/g) than CFA and RM alone, as well as superior adsorption capacity and magnetic characteristics. The adsorption capacities of C1R4 for Pb, Cu, and Cd were 149.81 mg/g, 135.96 mg/g, and 127.82 mg/g in the single system, while those of Cu and Cd decreased slightly in the ternary system, and the preferential adsorption order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. Among the three modified composite materials, C1R4 had the best adsorption capacity. [ABSTRACT FROM AUTHOR]

Coal fly ash (FA) dust negatively impacts human health and the environment. This study aimed to prevent wind erosion through the technology of enzyme-induced carbonate precipitation (EICP) to improve the surface stability of FA. In order to investigate the influence of urease activity, salt solution ratio, and polyacrylamide (PAM) concentration on the EICP process, unconfined compressive strength (UCS) test, sieving test, and wind tunnel test was carried out in the laboratory. Scanning electron microscopy (SEM) was also used to analyze the microscopic crystal morphology characteristics of mineralized products. The results showed that the wind erosion rate of the samples treated with EICP reduced significantly (the minimum wind erosion rate is 1.986 mg/(m2·min)) due to the crystal bridge function of CaCO3, while the UCS of these samples increased clearly. Appropriately increasing urease activity in the treatment solution contributed to the increased CaCO3 content and microscopic size. Excess urea concentration had a certain inhibitory effect on urease activity. The addition of PAM provided more nucleation sites for the EICP process and improved the strength of the cementation. These findings suggested that the EICP-PAM was a promising technique for the protection of FA sites from wind erosion. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH4)2SO4 helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70–80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90–110 °C), liquid-to-solid ratio (5–10), and leaching time (15–120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate. [ABSTRACT FROM AUTHOR]

Incessant generation and mismanagement of industrial waste, resource scarcity, and environmental degradation have created non-sustainability in human life. Though industrial wastes are hazardous or non-hazardous in nature based on their source, open dumping disposal is commonly done for both types of waste. The adversity associated with waste enhances the environmental and health impacts. However, this waste has the potential to recycle and minimize resource scarcity. The circular economy works on the concept of reuse, recycling, and recovery to convert waste into a resource. Thus, industrial waste can benefit the environment and economic growth to build industrial ecology. However, the opportunities and challenges associated with industrial ecology for the reuse and recycling of waste have to be identified and preserved. Therefore, this study has identified challenges associated with waste, analyzed their impact, and industrial regulations, prioritized their criticality, and developed solution strategies to alleviate them. Two case studies on industrial byproducts, i.e., fly ash and red mud, based on different income groups are discussed in this study. It highlights the circular economy has minimized waste generation and enhanced the recovery of secondary resource materials. In addition, this study supports achieving the sustainable development goals (SDGs) 11 and 12 to build a sustainable industrial ecosystem. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA) is a type of solid waste produced in the process of coal combustion, which is rich in silicon oxide, aluminum oxide and a small number of heavy metals and radioactive elements. Therefore, CFA is considered a secondary resource with high recovery value. Currently, CFA is mainly reused in the fields of building materials, mine backfilling, soil conditioners and fertilizers, among which the production of building materials is one of the most important ways to realize large-scale utilization of CFA. This paper introduces the physical and chemical properties, classification and environmental impact of CFA and summarizes the utilization status of CFA in building materials such as cement, concrete, ceramics and geopolymers, as well as the management policy of CFA. In addition, the existing problems in the utilization of CFA as a building material are analyzed, and their development prospects are discussed. [ABSTRACT FROM AUTHOR]

Ternary Portland cement usage with a high amount of cement constituents different from clinker can afford great climate change advantages by lowering the Portland cement clinker content in the final product. This will contribute to cutting greenhouse gas emissions to close to zero by 2050. Such ternary Portland cements can be composed of different amounts of ground granulated blast-furnace slag (GBFS), coal fly ash (CFA), and clinker (K). Cements made with GGBFS, or CFA boast pozzolanic characteristics. Therefore, they would improve both the concrete compressive strength at later ages and durability. The 28- and 90-days mechanical strength test, non-steady state chloride migration test, described in NT BUILD 492, and natural chloride diffusion test (NT BUILD 443) were performed in concrete. Ternary cements made with GBFS and/or CFA presented better chloride diffusion resistance than concrete made with plain Portland cements. Furthermore, the development of compressive strength was delayed. The service life study was developed for concretes made with ternary cements with regard to the chloride penetration case. [ABSTRACT FROM AUTHOR]

Fly ash is a waste material obtained from burning of coal in thermal power plants. Coal consumption is still very high and is expected to remain above 38% globally. Therefore, large volumes of fly ash are produced every year that need to be managed as waste. Improper disposal of fly ash can lead to surface water and ground water pollution and adversely affect human health and environment. The use of fly ash as an agent to stabilize soil has recently become popular in geotechnical engineering due to its many benefits such as being eco-friendly and cost-effective, and improving the geotechnical characteristics of the soil. This paper presents a review of the geotechnical properties of fly ash-stabilized fine-grained soils. Several features of fly ash, including classification, physical, geotechnical, chemical, and mineralogical properties, health concerns, disposal, availability, and cost are analyzed. The effects of fly ash in improving a wide range of mechanical properties of soils including unconfined compressive strength, shear strength, CBR value, consolidation and/or swelling characteristics, and permeability are reviewed in detail. It is shown that fly ash can be a substitute material for use in soil stabilization, leading to substantial economic and environmental benefits. [ABSTRACT FROM AUTHOR]

Chromium (Cr) and vanadium (V) are micronutrients playing a role in carbohydrate and lipid metabolism but can be toxic at high concentrations, especially in specific forms. The study documents the effect of Cr and V concentrations on glucose and lipid metabolism in workers exposed to coal fly ash. We quantified selected metals (Cr, V) in the blood and serum of workers from a thermal power plant in Kosovo and compared them with the reference biological values. We determined fasting serum glucose and lipid profiles using a biochemical analyzer Synchron CX7 (Beckman Coulter). We quantified blood and serum Cr and V by inductively coupled plasma mass spectrometry. We also evaluated the association between carbohydrate and lipid metabolism biomarkers (glucose, cholesterol, and triglycerides) and co-exposure to coal fly ash. Power plant workers had significantly higher blood Cr and V levels (p < 0.0001) and significantly lower serum Cr and V levels (p < 0.0001) than the controls. We also found statistically significant (p < 0.0001) correlations between high blood Cr levels and low glucose/blood Cr ratios as well as between high serum Cr levels and low glucose/serum Cr ratios. Finally, in power plant workers, high blood V levels significantly correlated with low triglycerides/blood V and cholesterol/blood V ratios (p < 0.0001), while high serum V levels correlated with low cholesterol/serum V ratios (p = 0.005). Based on these findings, we concluded that the glucose/Cr, triglycerides/V and cholesterol/V ratios should be considered when evaluating carbohydrate and lipid metabolism disorders in occupationally-exposed workers. [ABSTRACT FROM AUTHOR]

Due to the increasing demand for rare earth elements (REE) resources in the market and the shortage of their direct sources, the research on REE in coal fly ash (CFA) has attracted the increasing attention of scholars because of its high content of rare earth. To extract and separate REE from the leaching solution of CFA, the method of solvent extraction after acid leaching is usually adopted. In this paper, the leaching solution of coal fly ash from Panbei, south China, with an average REE content of 478 μg/g, was taken as the research object. The extracted di-2-Ethylhexyl phosphonic acid (P204) was used to explore the solvent extraction effect and mechanism. When performed with the conditions: pH value of 2.1, oil-water ratio (O/A) of 1, extraction time of 25 min, solvent concentration of 6% and temperature of 30 ℃, the extraction rates of La, Ce, Pr, Nd, and Y were 89.16%, 94.11%, 95.56%, 96.33%, and 99.80%, respectively. It was indicated that the P204 extraction system separated REE well from the aqueous phase. The structure of the extraction complex was deduced by taking yttrium as an object of analysis, and the extraction mechanism equation was determined by using the slope method. In this extraction system, the molecular formula of the complex is YCl2(HA2) and the enthalpy change (△H) is +86.68 kJ/mol, which provides theoretical guidance for the extraction of REE in industrial production. [ABSTRACT FROM AUTHOR]

Increases in biodiesel prices remains a challenge, mainly due to the high cost of conventional oil feedstocks used during biodiesel production and the challenges associated with using homogeneous catalysts in the process. This study investigated the conversion of waste-derived black soldier fly (BSF) maggot oil feedstock over hydroxy sodalite (HS) zeolite synthesized from waste coal fly ash (CFA) in biodiesel production. The zeolite product prepared after fusion of CFA followed by hydrothermal synthesis (F-HS) resulted in a highly crystalline, mesoporous F-HS zeolite with a considerable surface area of 45 m2/g. The impact of post-synthesis modification of the parent HS catalyst (F-HS) by ion exchange with an alkali source (KOH) on its performance in biodiesel production was investigated. The parent F-HS zeolite catalyst resulted in a high biodiesel yield of 84.10%, with a good quality of 65% fatty acid methyl ester (FAME) content and fuel characteristics compliant with standard biodiesel specifications. After ion exchange, the modified HS zeolite catalyst (K/F-HS) decreased in crystallinity, mesoporosity and total surface area. The K/F-HS catalyst resulted in sub-standard biodiesel of 51.50% FAME content. Hence, contrary to various studies, the ion exchange modified zeolite was unfavorable as a catalyst for biodiesel production. Interestingly, the F-HS zeolite derived from waste CFA showed a favorable performance as a heterogeneous catalyst compared to the conventional sodium hydroxide (NaOH) homogeneous catalyst. The zeolite catalyst resulted in a more profitable process using BSF maggot oil and was economically comparable with NaOH for every kilogram of biodiesel produced. Furthermore, this study showed the potential to address the overall biodiesel production cost challenge via the development of waste-derived catalysts and BSF maggot oil as low-cost feedstock alternatives. [ABSTRACT FROM AUTHOR]

The extensive production of coal fly ash by coal combustion is an issue of concern due to its environmental impact. TiO2-zeolite composites were synthesized, at low cost, using recycled coal fly ash from a local thermoelectric power plant to produce the zeolite using the hydrothermal method. TiO2 was loaded by means of the impregnation method using ethanol and titanium isopropoxide between 8.7 and 49.45 wt% TiO2. The samples were characterized by X-ray diffraction, Raman, electron spin resonance, high-resolution transmission electron microscopy, N2 adsorption-desorption, doppler broadening of annihilation radiation, and diffuse reflectance techniques, and the photocatalytic activity of the composites was evaluated according to the degradation of methyl orange under UV light. The results show that TiO2 crystallizes in the anatase phase with a Ti3+ oxidation state, without post-treatment. TiO2 particles were located within the pores of the substrate and on its surface, increasing the surface area of the composites in comparison with that of the substrates. Samples with TiO2 at 8.7 and 25 wt% immobilized on hydroxysodalite show the highest degradation of methyl orange among all studied materials, including the commercial TiO2 Degussa P25 under UV light. [ABSTRACT FROM AUTHOR]

Coal fly ash (CFA), hazardous to the environment and human health, has been considered to be a potential alternative source for rare earth elements (REEs) in recent years. However, information on how REEs distribute and occur in coal fly ash is still incomplete. In this work, particle size analysis, inductively coupled plasma–mass spectrometry, scanning electron microscopy, and electron probe microanalysis were applied to study the occurrence and distribution of REEs in a fly ash sample from the Qianxi coal-fired power plant in Guizhou province. The results show that the REEs content in the CFA was 630.51 ppm. Wet grinding-enhanced leaching experiments revealed that a part of the rare earth particles was encapsulated within the glass body. These rare earth particles could be liberated and released to a certain extent by wet grinding, which would increase the acid-leaching recovery of REEs from 23.49% to 41.68%. This study classifies the speciation of REEs in coal fly ash as (1) amorphous glassy particles with REE minerals or compounds encapsulated inside; (2) amorphous glassy particles with REEs distributed throughout; and (3) discrete REE minerals or compounds. The results of this study are a basis for developing an economically viable and environmentally sustainable technology for recovering REEs from CFA. [ABSTRACT FROM AUTHOR]

Recently, soil reinforcement using arranged or randomly distributed fibers has attracted increasing attention in geotechnical engineering. In this study, polypropylene (PP) fibers with three lengths (6, 12, and 24 mm) and three mass percentages (0.5%, 1%, and 1.5%) were used to reinforce a coal fly ash soil (FAS) mixture. Unconsolidated, undrained triaxial tests were carried out in order to study the mechanical properties of the polypropylene fiber-reinforced FAS mixture and evaluate the impact of fiber on the shear strength of the FAS mixture. It is found that the fiber length of 12 mm could significantly improve the shear strength of the polypropylene fiber reinforced FAS mixture, and little effect is shown on the shear strength while using a fiber length of 24 mm. Additional fibers enhance the energy absorption capacity of the FAS specimens and therefore the highest energy absorption capacity occurs when the fiber content is 1% and the fiber length is 12 mm. The peak deviator stress enhances impressively with the addition of polypropylene fiber. The impact of fiber on the peak deviator stress is the largest when fiber content is within 1.0%. The fiber length has little effect on the peak deviator stress when it exceeds 12 mm. [ABSTRACT FROM AUTHOR]

After years of decline, coal consumption has risen significantly in the last year (2021), driven mainly by the ever-increasing demand in fast-growing Asian countries and fostered by rising gas prices in Europe and the United States. Coal is both the largest electricity production source and the largest source of carbon dioxide emission. Coal-fired plants produce electricity by generating steam by burning coal in a boiler, but also large amounts of coal fly ash. Coal fly ash contains essential constituents for cement production, such as Ca, Si, Al, and Fe. Application of coal-fired ash to produce clinker at high doses may reduce the limestone content in the raw mix. Furthermore, coal fly ash is one of the industrial source materials utilized in the development of low-carbon cements and concretes on account of its chemical characteristics. The monitoring methodology is based fundamentally on the analysis of a set of variables (Na2Oe, Na2O, K2O, free CaO, and reactive silica content and fineness) over time. Weak relations between Na2O and K2O, and Na2Oe, and reactive silica content were found. This applied research has been done to verify previously done research. The scope of this paper is to assess the alkaline content of coal fly ash over a period of 10 years. The Na2O-equivalent of coal fly ash ranged from 0.35% to 2.53%, with an average value of 0.79%. These values should be taken into account producing concretes made with potentially reactive aggregates in order to mitigate the alkali–silica reaction (ASR). [ABSTRACT FROM AUTHOR]

The incorporation of coal fly ash (CFA) in fired clay bricks (FCBs), as a clay replacement, contributes toward cleaner production practices. CFA disposal is an important issue worldwide due to its huge volume and to its potential negative environmental impacts, and currently does not have a recovery route due to its high concentration in unburned materials. In this study, the impact of the incorporation of two CFA, with different content of unburned carbon, FAA (low LOI) and FAB (high LOI) in FCBs, from a technical and environmental point of view was conducted. Unburned carbon plays an important role on the final properties of FCBs. The thermal decomposition during the firing process promotes an increase of water absorption, decreasing the flexural strength as the porosity increases, although the technical and mechanical properties of samples containing up to 30% FAA and percentages of 20% FAB are acceptable. The leaching behaviour showed an immobilisation of Cr and Se in FCBs while Mo reduced its mobility to values below non-hazardous limits. Acid gas emission values do not exceed the reference emission value, except for SO2 emissions while the level of CO2 emissions must be estimated based on the total annual production of the ceramic factory. [ABSTRACT FROM AUTHOR]

Solidification/stabilization (S/S) of acid waste using Ordinary Portland Cement (OPC) is widely implemented, but, due to the impact on climate change, alternative methods are being investigated. In this work, first, the feasibility of using coal fly-ash/clay-based geopolymers for the S/S of Zn plant residues (ZPR), Cadmium Sponge (CS), and Anode Mud (AM) is proposed as a treatment prior to disposal in landfills. Different variables, such as the type of processing, molding (as-received waste), and pressing (dried waste), and activators, a commercial and an alternative residual sodium carbonate, have been studied. The technical and environmental assessments of the S/S process by means of compressive strength and the leaching of critical pollutants have been monitored. Immobilization efficiencies of Cd and Zn higher than 99% have been obtained by dosing 50% of the acid waste, 6 M NaOH solution (20 min contact time), cured at 75 °C (48 h) and at room temperature (28 days), achieving in the leachates pH values of 7 to 10 and [Cd] and [Zn] < 1 and 2.5 mg/kg, respectively. However, alkaline activation increases As leaching, mainly associated with the clay. Secondly, removing clay from the geopolymer formulation, the optimization of geopolymer parameters, acid waste/geopolymer ratio, liquid/solid ratio, and NaOH molar concentration enables obtaining a significant reduction in the release of As and Cd, and Zn is kept at acceptable values that meet the non-hazardous waste landfill disposal limits for the S/S of both acid wastes. [ABSTRACT FROM AUTHOR]

The environmental benefits of incorporating coal fly ash (CFA) into the concrete manufacturing process as a partial substitute for Portland cement are well known. What is less studied is the potential release of CFA derived nanomineral and amorphous nanoparticles during this process of incorporation. A thorough understanding of this makes it possible to understand the risks of exposure to particulates that are harmful to human health when CFA is mixed into concrete. The general objective of this study is to analyze airborne particulates released when CFA is mixed into concrete at the point of manufacture, focusing on the levels of nanominerals, amorphous nanoparticles and hazardous elements (HEs) contained within that are considered harmful to human health. These airborne particulates can be easily inhaled by plant workers in the absence of personal protective equipment. The authors analyzed samples of ash itself and collected actual airborne particulates using self-made passive samplers installed at the manufacturing plant. Regarding the ash analyzed, iron (Fe) was found in large amounts in relation to calcium (Ca), magnesium (Mg) and silicon (Si). The transport, disposal and application of CFA in civil construction projects can provide an increased efficiency and reduce overall costs associated with the production of concrete. However, CFA poses a threat to human health due to the significant amount of HEs, nanominerals, and amorphous nanoparticles found to be released into the environment at the manufacturing plant. [ABSTRACT FROM AUTHOR]

Coal Fly Ash (CFA) is a hazardous waste from coal-fired power plants, but has increasingly become a popular supplementary cementitious material for cement in the construction industry. As a secondary resource of REE, its main advantage lies in its fine particle size that eliminates the need for costly and energy-intensive comminution. In this study, the potential of CFA from the Philippines as a secondary REE resource was investigated by direct leaching of REEs with hydrochloric acid (HCl). The CFA sample came from a coal-fired power plant with a circulating fluidized bed combustion (CFBC) technology. For the leaching tests, the effects of HCl concentration, leaching time and leaching temperature on REE extractions were elucidate optimized via Response Surface Methodology (RSM). The RSM results showed that the optimum leaching occurred at 3M HCl, 65 °C and 270 min with extractions of Nd, Er, Eu, Tb and Dy at 70.8%, 76.34%, 88.02%, 90.01% and 73.38%, respectively. According to these results, the CFA from the Philippines is a promising secondary resource of REE and the extraction method employed was effective in achieving a relatively high REE dissolution. Moreover, the empirical model that was established accurately predicted the dissolution of REE with an accuracy of 98.20%, 96.66%, 97.09%, 98.17% and 97.78% for Nd, Er, Eu, Tb and Dy, respectively. [ABSTRACT FROM AUTHOR]

Ground coal bottom ash is considered a novel material when used in common cement production as a blended cement. This new application must be evaluated by means of the study of its pozzolanic properties. Coal bottom ash, in some countries, is being used as a replacement for natural sand, but in some others, it is disposed of in a landfill, leading thus to environmental problems. The pozzolanic properties of ground coal bottom ash and coal fly ash cements were investigated in order to assess their pozzolanic performance. Proportions of coal fly ash and ground coal bottom ash in the mixes were 100:0, 90:10, 80:20, 50:50, 0:100. Next, multicomponent cements were formulated using 10%, 25% or 35% of ashes. In general, the pozzolanic performance of the ground coal bottom ash is quite similar to that of the coal fly ash. As expected, the pozzolanic reaction of both of them proceeds slowly at early ages, but the reaction rate increases over time. Ground coal bottom ash is a promising novel material with pozzolanic properties which are comparable to that of coal fly ashes. Then, coal bottom ash subjected to an adequate mechanical grinding is suitable to be used to produce common coal-ash cements. [ABSTRACT FROM AUTHOR]

Svalbard is an arctic archipelago where coal mining generates all electricity via the local coal-fired power station. Coal combustion produces a waste product in the form of particulate matter (PM) coal fly ash (CFA), derived from incombustible minerals present in the feed coal. PM ≤10 µm (diameter) may be "inhaled" into the human respiratory system, and particles ≤2.5 µm may enter the distal alveoli to disrupt normal pulmonary functions and trigger disease pathways. This study discovered that Svalbard CFA contained unusually high levels of iron-rich magnetic minerals that induced adverse effects upon human lungs cells. Iron is a well-characterised driver of reactive oxygen species (ROS) generation, a driving force for cell death and disease. CFA physicochemical characterisation showed non-uniform particle morphologies indicative of coal burnt at inefficient combustion temperatures. The bioreactivity (ROS generation) of PM2.5/10 fractions was measured using plasmid scission assay (PSA, DNA damage) and haemolysis assays (erythrocyte lysis), with PM2.5 CFA showing significant bioreactivity. CFA leached in mild acid caused a significant increase in toxicity, which could occur in CFA waste-stores. The CFA and leachates were exposed to a surrogate model of human bronchial epithelia that confirmed that CFA induced apoptosis in bronchial cells. This study shows that CFA containing magnetic iron-rich minerals mediated adverse reactions in the human lung, and thus CFA should be considered to be an environmental inhalation hazard. [ABSTRACT FROM AUTHOR]

Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N-A-S-H) and calcium (alumino) silicate hydrate (C(-A)-S-H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead. [ABSTRACT FROM AUTHOR]

There are increasing demands and great potential of coal gasification in China, but there is a lack of studies focused on the disposal and utilization of coal fly ash produced by the gasification process. In this study, a coal fly ash sample derived from a gasifier in Jincheng, China, was utilized as raw material for the synthesis of zeolite by alkali fusion followed by hydrothermal treatments. The effects of operation conditions on the cation exchange capacity (CEC) of synthesized zeolite were investigated. The synthesized zeolite with the highest CEC (270.4 meq/100 g), with abundant zeolite X and small amount of zeolite A, was produced by 1.5 h alkali fusion under 550 °C with NaOH/coal fly ash ratio 1.2 g/g followed by 15 h hydrothermal treatment under 90 °C with liquid/solid ratio 5 mL/g and applied in Ni2+ removal from water. The removal rate and the adsorption capacity of Ni2+ from water by the synthesized zeolite were determined at the different pH, contact time, adsorbent dose and initial Ni2+ concentration. The experimental data of adsorption were interpreted in terms of Freundlich and Langmuir equations. The adsorption of Ni2+ by the synthesized zeolite was found to fit sufficient using the Langmuir isotherm. More than 90% of Ni2+ in water could be removed by synthesized zeolite under the proper conditions. We show that the coal fly ash produced by the gasification process has great potential to be used as an alternative and cheap source in the production of adsorbents. [ABSTRACT FROM AUTHOR]

A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al2O3 and SiO2, and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 °C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium. [ABSTRACT FROM AUTHOR]

The establishment of an inexpensive leaching control method to prevent the leaching of trace elements from fly ash is required for the utilization of large-scale fly ash as an embankment material. This study examined the effects of the additives on suppressing As, B, and Se leaching from coal fly ash using Ca(OH)2, paper sludge ashes (PS Ash 3, PS Ash 4 and PS Ash 5), and filter cake (FC). PS Ash and FC are waste generated in the papermaking and lime industry processes and contain high levels of calcium. The treated fly ash H (FAH) and the resulting mixtures were subjected to a leaching test as per the Environmental Agency of Japan Notifications No. 13. The results indicate that the leaching concentrations of As, B, and Se could be greatly reduced in FAH with the highest effect given by Ca(OH)2, followed by PS Ash 3 and PS Ash 5. Ca(OH)2 greatly reduced both the leaching concentrations of As, B, and Se by about 91-100%, while PS Ash 3 reduced the As and B leaching concentrations by approximately 89-96% and 83-92%, respectively; and PS Ash 5 reduced the Se leaching concentration by about 87-96%. FC did not have any impact on As and B leaching, but reduced Se leaching by about 58-78%. A reason for the decrease in leaching concentrations of As, B, and Se may be the precipitation with calcium or the formation of ettringite. The presence of leached Ca and Na ions are key factors affecting the decrease of As, B, and Se leaching concentrations from fly ash. The utilization of PS Ash 3 and PS Ash 5 as inexpensive additives is a promising method to control the leaching of As, B, and Se into the environment. [ABSTRACT FROM AUTHOR]