Is Coal Ash the New “Green” Material

Design of slurry transportation pipeline for the flow of muti-particulate coal ash suspension

Coal Bottom Ash as a Geomaterial: Influence of Particle Morphology on the Behavior of Granular Materials

BACKGROUND AND AIM: When coal is burned for energy, coal ash, a hazardous waste product, is generated. Throughout the world, over 1 billion tons of coal ash is produced yearly. In the United States, over 78 million tons of coal ash was produced in 2019. Fly ash, the main component of coal ash contains neurotoxic metal(loid)s that may affect children's neurodevelopment and mental health. The objective of this study was to investigate the association between fly ash and depressive problems in children aged 6-14 years old. METHODS: Children and their parents/guardians were recruited from 2015-2020. Tobit regression and Poisson regression were used to assess the association between coal fly ash and depressive problems. To determine fly ash presence, Scanning Electron Microscopy was conducted on polycarbonate filters containing PM10 from the homes of the study participants. Depressive problems in children were measured using the Depressive Problems DSM and withdrawn/depressed syndromic problem scales of the Child Behavior Checklist. RESULTS: In covariate-adjusted Tobit regression models, children with fly ash on the filter had higher scores on the DSM Depressive Problems (3.14 points; 95% CI=0.40, 5.89) and the syndromic withdrawn depression (2.63 points; 95% CI = -0.20, 5.46) scales compared with children who did not have fly ash on the filter. Poisson regression supported these findings. CONCLUSIONS: Coal ash is one of the largest waste streams in the U.S., but it is not classified as a hazardous waste by the Environmental Protection Agency. To our knowledge, no studies have assessed the impact of coal ash on children's mental health. This study highlights the need for further research into the effects of coal ash exposure on children's mental health, and improved regulations on release and storage of coal ash. KEYWORDS: coal ash; fly ash; children's mental health; depression; children's environmental health

Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction

Coal-fired power plants and industrial waste (IW) incinerators increasingly dispose large amounts of fly ash that cause environmental contamination by toxic heavy metals. This study aimed to investigate the concentration of heavy metals and measure the specific activity of naturally occurring radioactive materials (NORM) that remain in the fly ash of coal power plants and industrial incinerators. Ash samples were collected from the Kapar and Jana Manjung coal-fired power plants and the Kualiti Alam industrial incinerator in Malaysia. The concentrations of As, Ba, Co, Cr, Fe, Sb, Zn, Th and U were determined via neutron activation analysis (NAA). Results indicated that the highest concentrations of heavy metals in Kapar and Jana Manjung coal fly ash were 27 012 and 57 500 mg/kg for Fe and 494 and 1,119 mg/kg for Ba, respectively, and the lowest concentrations for Sb were at 3.67 and 2.23 mg/kg, respectively. The concentrations of Fe, Zn, Ba and Cr in industrial fly ash were 31 0007, 7 675, 2 760 and 1,029 mg/kg, respectively. The concentrations of As, Ba, Cr, Fe and Zn were higher in industrial fly ash than in coal fly ash. The specific activity concentrations of NORM, namely, 40K, 226Ra, 232Th and 238U determined by gamma spectrometry in Kapar coal fly ash were 321.65, 27.42, 134.41 and 152.71 Bq/kg, respectively. Elemental concentration results indicated that the amounts of heavy metals depended on feed sources and combustion temperatures. Most heavy metal contents and radionuclides in power plant and incinerator fly ash were significantly lower or within the global ranges.

Backfill mining can effectively alleviate the problems of surface collapse and ecological water pollution, in which the mechanical properties of backfill materials, including coal gangue and coal fly ash, have a decisive role in the effect of filling mining. In this study, we analyze the permeability characteristics of coal gangue filler through a set of homemade percolation test systems and introduce fractal characteristics to investigate the key factors affecting percolation in complex pores of broken coal gangue. The results indicate that the fractal dimensions of crushed coal gangue particles show an increasing trend with increasing axial loading and that the variation range is from 2.15647 to 2.58933. The coal fly ash concentration has a positive relationship with the acceleration factor. The permeability of crushed coal gangue follows a hierarchical distribution law and the permeability changes in the magnitude range of 10-11 ~ 10-9 m2. The fractal dimension is inversely related to the permeability of crushed coal gangue. The experimental results show that the coal gangue will be further crushed and that adding a certain concentration of coal fly ash can achieve a better water barrier, which provides theoretical support and engineering significance for the stability analysis of geological engineering and backfill mining technology.

A review of physical, chemical, and biological properties of fly ash and effects on agricultural ecosystems

Characterization comparison of bottom ash and fly ash during gasification of agricultural residues at an industrial-scale gasification plant – Experiments and analysis

Decreased phosphorus (P) losses and improved environmental quality are crucial to consider while recycling farm wastes and adding various soil amendments. This study investigated the impact of coal and wood ash on the extractability of P from soils (sandy loam and loamy sand) amended with organic and inorganic phosphorus fertilizers. These soils were further amended coal and wood ash, and analyses were carried out to quantify the water-, Olsen-, and Mehlich 1-extractable P. Ratio of the ashes applied to soils were 5% to sandy loam soil while 10% to loamy sand soil. Water-extractable P was observed to be mainly dependent on the ash type as well as the extraction method. Ash amendment reduced the solubilization of P across soils up to 9% and 23% and 7% to 17% upon 5% and 10% ash amendment in loamy sand and sandy loam soils, respectively. However, the water-extractable P was found to be low in wood ash-amended soil as compared to coal ash. Interestingly, this extractability was greater in soils treated with inorganic P. Phosphorus extraction from soil followed the trend as Mehlich 1 > Olsen > water. P leachability was found to be mainly dependent on ash amendment but values were high for the soil treated with inorganic P. The study inferred that using ash materials such as coal ash and wood ash can be a practical measure for moderating P losses from soils important for economic and environmental perspectives.

As the coal industry faces increasing demands for resource efficiency and environmental protection, the accurate prediction of coal sample ash content has become crucial for optimizing flotation processes and improving coal washing efficiency. However, traditional ash analysis methods are often constrained by sample heterogeneity, measurement errors, and limited computational precision, making it difficult to meet the fast and accurate detection requirements in industrial applications. Therefore, employing advanced machine learning algorithms for precise prediction of coal sample ash content has emerged as a critical area of research.In this study, coal samples from a coal preparation plant were used as the experimental material. A distribution release experiment was conducted to extend the ash content range from 3% to 13%, and X-ray fluorescence (XRF) spectroscopy was applied to detect the major elements in the coal samples. Four machine learning algorithms – Support Vector Machine (SVM), eXtreme Gradient Boosting (XGBoost), BP neural network(BPNN), and Random Forest(RF) – were employed to explore the correlation between the main components of coal ash and the ash content of flotation cleaning coal. The performance of these models in predicting ash content was evaluated using SHAP value plots, R2, and RMSE metrics.The experimental results demonstrated that the use of secondary calibration samples significantly improved the accuracy of XRF detection. A strong linear correlation was observed between the main components of coal ash and the ash content. Further analysis showed that the SVM model outperformed the other three algorithms in terms of prediction accuracy and robustness.In conclusion, this study provides effective machine learning methods for the precise prediction of coal sample ash content and offers valuable theoretical and methodological support for the intelligent control of flotation processes. The findings have significant implications for industrial applications and further research in coal processing.

Radiological assessment of wastewater treatment processes based on the use of coal ashes as a filters

Coal combustion products (CCP) include fly ash and bottom ash and are generated nationally at rates of 108 Mg per year. Fly ashes (FA) comprise the majority of CCP production, and can possess widely-variable physicochemical properties. Current consumption/utilization of FA in the US does not approach production levels, and results in FA stockpiling. Class-C fly ash is generated from combustion of sub-bituminous and lignite coal products. This class of FA often possesses an alkaline pH, resulting from calcium, magnesium, and potassium oxide inclusions. Some Class-C FA have been reported to contain as much as 60% calcium carbonate equivalency (CCE), prompting investigations of FA as a lime substitute in agricultural/horticultural applications. Furthermore, FA often possesses small concentrations of exchangeable micronutrients. Thus, considering availability of Class-C FA, its potential beneficial use as a liming agent, and the expansive area of low-to-medium maintenance turfgrass systems currently afflicted by suboptimal soil pH levels; our objective was to evaluate the acid-neutralizing efficacy of a Class-C FA when substituted for pulverized limestone (PL) in field application. This study was conducted on a severely-acidic bermudagrass (Cynodon spp. L.) rough of a Georgia golf course during 2001 and 2002. Following material characterization, CaCO3 equivalent was applied at a prescribed rate of 3.8 Mg CaCO3 ha−1, using either PL or Georgia-produced FA (CCE = 45.5%). Soil samples collected one year following showed FA to have neutralized significantly greater acidity in the upper 8 cm of soil than the PL. Furthermore, exchangeable P, Mg, and Zn levels in the FA-treated 0–8 cm of soil exceeded levels observed in the PL-treated or control plots. Due to the disparity in CCE, requisite FA application greatly exceeded that of PL, reducing economic advantage of FA-substitution. However, in locations where Class-C FA is plentiful, high-grade PL is costly, and soil pH suboptimal for important crops; results of this study indicate soil liming with Class-C FA to be a beneficial use of this CCP. Comprehensive characterization of CCP and proper application rate (not exceeding agronomic requirements) are essential components of beneficial use.

Aimsnnnnnn n This thesis investigated the use of fly ash in concrete by establishing reliable andnaccurate test data on the properties of concrete incorporating different fly ashncontent. In addition, the study focussed on typical uses by local governmentnauthorities in pathways, such as footpaths and bicycle ways, and also looked atnenvironmental impacts, incorporating durability and construction constraints in thenlife cycle costing issues. The aims of the project were:nnn nnn b To obtain experimental data on mechanical properties and durabilityncharacteristics of fly ash concrete containing 23-50% fly ash with a 28-dayncompressive strength of 25MPa;n b To assess the effect of curing on the properties of concrete incorporatingndifferent percentages of fly ash; andn b To draw conclusions as to the cost effectiveness of concrete incorporatingnlarge amounts of fly ash by comparing life cycle assessments that includendurability, construction and environmental factors.nnnnn n Scopenn n This investigation of the high volume fly ash concrete was for the purpose ofnextending its application in footpaths and bicycle ways. Several concrete mixesnusing fly ash at levels ranging between 23-50% as a partial replacement ofnPortland cement were investigated. All concrete mixes had a 28-day compressivenstrength of 25MPa, and were applicable to the footpaths and bicycle waysnconstruction. The effect of fly ash on the mechanical properties of the concretenmixes was determined under standard moist curing and ambient conditions. Thentested properties included setting time, compressive strength, splitting tensilenstrength, flexural tensile strength, drying shrinkage and abrasion resistance.nnnnnn n The test apparatus, procedures and testing data are described in detail. Testnresults are reported and compared. In addition to the experimental work, a simplenlife cycle assessment (LCA) and life cycle cost analysis (LCCA) were undertaken to evaluatenthe environmental impact and cost effectiveness of using high volume flynash in concrete pavement construction. The energy consumption and CO2nemissions were compared between high volume fly ash concrete and the typicalncommercial concrete in the environmental life cycle assessment. The life cycle costnanalysis included the costs of initial material cost, construction, rehabilitation, andnresidual values in the whole life cycle period of pavement structures.nnnnnn n Conclusionsnn n According to the analysis of the experimental results, it is feasible to producenconcrete with fly ash replacement of up to 50%, without significantly altering thenconcrete properties in the hardened state. However, high volume fly ash concretenwith 50% fly ash replacement retarded the setting time by up to 6.5 hours, whichnshould be considered in LCCA. High-volume fly ash concrete gained highernultimate strength under standard moist curing conditions. In typical pavementnconstruction, it is often difficult for the design engineer to ensure that adequatencuring, as per the construction specification, occurs. Indeed, evidence suggestsnthat in many applications curing of concrete pavements does not occur at all.nHowever, without adequate curing, no strength development was observed after 28ndays for high volume fly ash concrete. The 28-day abrasion resistance is verynsimilar for all mixes with various fly ash percentages, but use of a curing compoundnincreased the wear and tear properties of fly ash concrete to some extent.nnnnnn n Based on the information provided by the local industry and the results of thenenvironmental life cycle assessment and life cycle cost analyses, the followingnconclusions are summarized:nnn nnn b From the environmental life cycle assessment, 50% fly ash concrete is the bestnalternate for pavement design with 20% energy and CO2 savings compared tontypical concrete;n b However, in terms of life cycle cost analysis, when variability is considered innthe inputs (cost, setting time, service life, etc.), the typical 23% fly ash concretenwould be the most cost effective material in footpath and bicycle waysnapplications; andn b The results of LCCA are highly dependent on the setting time of concrete.nWhen using setting accelerator admixture in high volume fly ash concrete, the costneffectiveness is dependent on the efficiency of the admixture to reducensetting time. Without an increase in construction cost, the high volume fly ashnconcrete would have a similar life cycle cost to typical concrete.n

The characteristics of the underlying soil greatly influence the stability of building foundations. Clay and sandy soils are commonly used in civil construction, each with drawbacks. This study aims to enhance the shear strength of clay and sandy soils by adding Type C fly ash. Clay soil samples were taken from Cengkareng, West Jakarta, fly ash from steam power plant Paiton, Central Java, and sandy soil from Garut, West Java. Testing included index properties, atterberg limits, grain size analysis, compaction, triaxial, and direct shear. The results indicate that adding Type C fly ash can significantly increase sandy soil's shear angle and cohesion. In contrast, adding fly ash in clay soil tends to reduce the shear angle but increase cohesion. Assuming an everyday stress of 10 kg/cm², the shear strength of sandy soil increased by 11,91 % with a 20% Type C fly ash mixture, whereas the shear strength of clay soil decreased by 43,00 % with a 20% Type C fly ash mixture. The conclusion from this study indicates that Type C fly ash is more effective when used in sandy soil to enhance shear strength, and further research is needed to determine the optimal fly ash content for various soil conditions. Abstrak Stabilitas pondasi bangunan sangat dipengaruhi oleh karakteristik tanah di bawahnya. Dalam konstruksi sipil, tanah lempung dan pasir sering digunakan, namun keduanya memiliki kelemahan masing-masing. Penelitian ini bertujuan untuk meningkatkan kuat geser tanah lempung dan pasir melalui penambahan fly ash tipe C. Sampel tanah lempung diambil dari Cengkareng, Jakarta Barat, fly ash dari pembangkit listrik tenaga uap (PLTU) Paiton, Jawa Tengah, dan tanah pasir dari Garut, Jawa Barat. Pengujian meliputi index properties, atterberg limit, grain size analysis, kompaksi, triaxial, dan direct shear. Hasil menunjukkan bahwa penambahan fly ash tipe C dapat meningkatkan sudut geser dan kohesi tanah pasir secara signifikan, sedangkan pada tanah lempung, penambahan fly ash cenderung mengurangi sudut geser namun meningkatkan kohesi. Dengan asumsi tegangan normal 10 kg/cm², kuat geser tanah pasir meningkat sebesar 11,91 % pada campuran fly ash tipe C 20%, sedangkan kuat geser tanah lempung menurun sebanyak 43,00 % pada campuran fly ash tipe C 20%. Kesimpulan dari penelitian ini menunjukkan bahwa fly ash tipe C lebih efektif digunakan pada tanah pasir untuk meningkatkan kuat geser, dan penelitian lebih lanjut diperlukan untuk menentukan kadar fly ash yang optimal pada berbagai kondisi tanah.

The environmental concerns of carbon emissions by the energy industry have led to a change in the way energy is generated as the UK moves to a low carbon future. While biomass combustion is gaining attraction as the most available renewable energy source, the resulting ash is most often landfilled and is still not accepted in the concrete industry as in the case of coal fly ash. This is mainly because of the limited knowledge of the in-service life of concrete made with this fly ash. This research investigates the use of two types of wood biomass fly ash, obtained from two power plants in the UK, in cement and concrete production to provide a performance-based database for evaluating its utilization in the concrete industry. The study comprises of three parts, the first part deals with determining the chemical, mineralogical and physical properties of these two fly ashes enhanced biomass ash (EBA) and virgin wood biomass ash (WBA). The results show that EBA has a chemical composition more similar to coal fly ash (CFA) than WBA and EBA satisfies the BS EN 450-1 requirements for the main oxides and other chemical components. The mineralogical structure of both ashes is mainly amorphous; EBA particles are mainly spherical whereas the morphology of WBA particles is fibrous irregular in shape and size. WBA has a higher surface area than both EBA and CFA while its pozzolanic reactivity is less. The mechanical and durability properties investigated in parts 2 and 3 are related to these characteristics (e.g., chemical compositions, pozzolanic reactivity and particle size) and also to pore properties investigated in part 2. Part 2 of this study is concerned with the effect of both ashes on the fresh and hardened properties of concrete compared to coal fly ash. Blended fly ash pastes and mortars substituting the cement at 10, 20 and 30% were produced and numerous tests were performed. The results show that the incorporation of EBA reduces the water demand and improves the workability similar to the effect of coal fly ash while the behavior of WBA is the opposite. The coarse and high surface area of WBA particles contributes to its higher water demand. The early age hydration behavior of EBA is quite similar to CFA. The CFA and EBA mixes release considerably higher heat than WBA mixes, indicating a higher rate of hydration. The compressive and flexural strength decreases gradually as the percentage of both EBA and WBA in the mix increases. The compressive strength of CFA mixes is higher than EBA mixes while WBA mixes give the lowest strength. The incorporation of EBA and WBA increases the total porosity of cement pastes. Part 3 investigates the durability properties of enhanced biomass fly ash concrete by exposing it to long-term sulphate, chloride and carbon dioxide environments which are substances that cause deterioration and damage to concrete structures. Durability properties were tested under laboratory conditions over a period of one year and control samples of ordinary OPC concrete and coal fly ash concrete were produced for comparison. Generally, enhanced biomass fly ash concrete shows better durability properties than OPC concrete except for the carbonation resistance. The depth of carbonation of enhanced biomass fly ash concrete is higher than OPC concrete but less than coal fly ash concrete which shows the highest carbonation depth. The results also show that the incorporation of enhanced biomass fly ash improves the sulphate resistance compared to control OPC, however, it is still less effective than coal fly ash in resisting sulphate attack. The chemically and physically bound chloride of enhanced biomass fly ash concrete is lower than OPC concrete but it is higher than coal fly ash concrete. The efficiency of both enhanced biomass fly ash and virgin wood biomass ash in mitigating alkalisilica reaction was also examined based on the accelerated mortar bar test. The results show that enhanced biomass fly ash reduced the expansion caused by ASR to the low-risk level of deterioration according to ASTM C1260/1576 standards whereas the reduction of expansion in the case of virgin wood biomass ash was not sufficient to reduce the risk from potentially deleterious level to low risk.