Individual Fly Ash Research Articles

Real-time dynamic measurement of scattering characteristics of optically-levitated fly ash interacting with water-soluble ammonium sulfate aerosol

This paper proposes a coupled laser levitation and scattering measuring system to realize real-time dynamic measurement of scattering characteristics of individual fly ash particles interacting with water-soluble ammonium sulfate aerosols of different concentrations. The scattering coefficients, absorption coefficients, and phase functions of aerosols were calculated. The disparities in scattering characteristics interacting fly ash with ammonium sulfate, and the impact of typical influencing parameters on the scattering characteristics were discussed in detail. The findings highlighted that the scattering characteristics of aerosols followed with those of Mie particles, with an increase in the particle size leading to an enhancement in the forward scattering intensity. Notably, dynamic measurement demonstrated that the scattering intensity with high ammonium sulfate concentrations (≥1 mol/L) showed an upward trend, exerting a more pronounced impact than low-concentration counterparts. Furthermore, the particle size has a stronger effect on the scattering characteristics than the complex refractive index induced by varying concentrations.

Fouling Simulations of a Passive Part of the Testing Combustion Facility

Results from the previous work of Strouhal et al. (2020) suggest that the used CFD fouling model together with user-implemented subroutines is not sufficient for obtaining satisfactory agreement with deposits observed in a described experimental device. The objective of this work is to create a basis for qualitative improvements of the simulation results. This includes using more detailed geometry and testing an influence of variation of parameters of two implemented fouling models. An accurate estimation of these parameters requires either empirical evidence from device operation or detailed information about fly ash composition and properties, which is usually accessible only for individual fly ash constituents. The goal of the sensitivity analysis was to show influence of these parameters on deposition rates, identify insignificant parameters for the tested range of particle properties and diameters and the most significant parameters for each of the six tested fly ash size fractions. To the authors’ knowledge, such an analysis is not present in available literature. The first tested model shown that one parameter to be significantly higher compared to other, except for the smallest particles. For the second model, all parameters were found to be significant at least for one examined particle diameter. Elastic deformation, plastic deformation and adhesion are thus considered important across the tested range of particle properties and sizes, at least for the fouling model used.

Using the Particle Model to predict electrical resistivity performance of fly ash in concrete

The electrical resistivity performance of fly ash in concrete is not easy to predict due to the diverse sources of fly ash and their varying reactivity. Electrical resistivity gives direct evidence of the rate of corrosion within the concrete and provides indirect clues into the fluid transport into the material. This paper aims to develop predictive models for the electrical resistivity of fly ash concrete by applying the Particle Model. The Particle Model rapidly examines individual fly ash particles without human intervention and is used to derive predictive models for 20% and 40% fly ash replacement levels in concrete at seven different periods of hydration. The R-squared values of predictive models in the Particle Model show significant improvement over using the classification method based on Class C and F for both fly ash replacement at all investigated time periods. The derived predictive models are able to accurately estimate the electrical resistivity within +/- 10% for 80% of all measurements at 20% fly ash replacement and within +/− 10% for 75% of all measurements at 40% fly ash replacement. These investigations provide important insights into how the Particle Model can help predict the electrical resistivity of fly ash concrete even at different mixtures and hydration times.

Application of micro-scale correlation analysis to estimate metal speciation and the matrix in municipal solid waste incineration fly ash

Micro-scale correlation analysis was applied to estimate metal speciation and the matrix in municipal solid waste incineration (MSWI) fly ash in this study. The results showed that dominant metal speciation and the bonding states with fly ash matrix are different in individual fly ash particle. Micro-scale correlation analysis also suggests metal behaviors in fly ash formation processes. Metal oxides likely react with and/or are trapped in Al/Ca/Si-based matrix such as aluminosilicate in the gas phase and then followed by KCl/NaCl adsorption on the surface. Zinc can possibly form other speciation depending on combustion condition. Zinc chlorides (ZnCl2 and/or K2ZnCl4) and Zn spinels (ZnAl2O4 and ZnFe2O4) are not trapped in Al/Ca/Si-based matrix, however, adsorbed on the surface together with KCl/NaCl-based aggregates. Because metal oxides basically combine with and/or are trapped in Al/Ca/Si-based matrix, metal leachability might be controlled by not only metal oxide leachability but also leachability of Al/Ca/Si-based matrix around metal oxides.

Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO3, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO3 concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a between-plant basis. Variations in fly ash quality will occur in larger-scale operations, so on-going attention to the fly ash quality and the response of the fly ash to beneficiation is necessary. Changes in the Plant D fly ash with time imply that both the freshness of the original ash and the length and conditions of its storage at the site of beneficiation could be factors in the quality and consistency of the processed fly ash.

Chemical Property of the Fly Ash Collected at an Incinerator and its Effects on Near Ambient Particles

It is crucial for understanding the characteristics of fly ash, emitted from the incinerator of municipal solid waste, to properly diagnose its impact on air quality and human health. In this study, to precisely describe the chemical property of the fly ash and its effects on near ambient particles, an intensive measurement was conducted. Fly ash was collected in dry condition from the downstream of a bag filter dust collector which is installed at an incinerator located in Iksan City, Korea. Sampling of ambient particles was carried out at both near and far away sites from an incinerator. Elemental analyses of the pretreated samples were subsequently performed by a Particle Induced X-ray Emission (PIXE) and a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-ray Detector (EDX). Moreover, in order to estimate the residents’ exposure to the fly ash and the effect of fly ash on the near ambient particles, Gaussian plume model was carried out. The high content of soluble S, Cl, K, and Ca in fly ash were detected. Small quantities of heavy elements including Zn, Br, and Pb were also detected in the water-soluble fraction. The scattering plots drawn by the ratios of Z/Zn (i.e., the ratio of mass concentration of each element (Z) to that of zinc) of ambient PM2.5 and that of fly ash reveal a good relationship regardless of the distance from an incinerator. A ternary plot drawn by the wt% concentrations of Na, K, and Cl in the individual ambient particles and fly ash powders indicates that a small portion of the fine and coarse ambient particles was directly influenced by the fly ashes. Modeling evaluation of fly ash diffusion suggests that the air quality at the incinerator nearby areas, especially 1.5 km points, was strongly influenced by the air pollution materials emitted from an incinerator.

Intra- and inter-particle heterogeneity of municipal solid waste incineration fly ash particles

This study firstly investigated elemental heterogeneity of municipal solid waste incineration (MSWI) fly ash particles. Two types of heterogeneities were measured quantitatively focusing on three structural components of fly ash particles. They are internal heterogeneity of individual fly ash particles (intra-particle heterogeneity) and inter-particle heterogeneities among fly ash particles. On the surface of fly ash particles, Cl, K, and Na have 0–82% larger intra-particle heterogeneities than Al, Ca, and Si owing to KCl/NaCl-based aggregates. Smaller intra-particle heterogeneity of Ca in semi-soluble component than those of Al and Si suggest that semi-soluble Al/Ca/Si-based matrices around insoluble cores are Ca-based materials including aluminosilicate domains. Inter-particle heterogeneities of Al, Ca, and Si in semi-soluble and insoluble components are 9–40% and 49–352% higher than those of fly ash particle surface, respectively. Inter-particle heterogeneity analysis also suggests that insoluble components mainly consists of Si-, Al-, or Ca-rich cores. MSWI fly ash particles have both internal heterogeneities inside their bodies and also are heterogeneous in inter-particle level. When MSWI fly ash becomes wet during chelate treatment, it changed intra-particle heterogeneity as well as inter-particle heterogeneity. Their variations were contrast depending on element and site (fly ash particle component).

Fly ash particle characterization for predicting concrete compressive strength

A new classification approach is presented that uses individual fly ash particle measurements to provide improved and more in-depth information about the properties of the concrete. The technique uses machine guided X-ray microanalysis to measure the compositions of 2000 randomly selected particles from 20 different fly ashes. This paper details the methods used to acquire the particle composition data and the derivation of the representative groups of the fly ash particles or classification groups. This method is named the Particle Model. To investigate the utility of these groups, 12 fly ashes were used at a 20% mass replacement of the cement in a series of concrete mixtures, which were tested for compressive strength at various times over 180 d of curing. Seven of the nine particle compositions identified were found to influence the compressive strength of the concrete with a linear model R-squared value of 0.99. The Particle Model showed a statistically significant improvement over the Class C or F classification from ASTM C618 and EN450. This work aims to establish the Particle Model and show that the classification shows promise to be used as a method to predict the physical properties of concretes that contain fly ash.

Investigation on the Rheological Behavior of Fly Ash Cement Composites at Paste and Concrete Level

Towards developing sustainable concrete, nowadays, high volume replacement of cement with fly ash (FA) is more common. Though the replacement of fly ash at 20–30% is widely accepted due to its advantages at both fresh and hardened states, applicability and acceptability of high volume fly ash (HVFA) is not so popular due to some adverse effects on concrete properties. Nowadays to suit various applications, flowing concretes such as self compacting concrete is often used. In such cases, implications of usage of HVFA on fresh properties are required to be investigated. Further, when FA replacement is beyond 40% in cement, it results in the reduction of strength and in order to overcome this drawback, additions such as nano calcium carbonate (CC), lime sludge (LS), carbon nano tubes (CNT) etc. are often incorporated to HVFA concrete. Hence, in this study, firstly, the influence of replacement level of 20–80% FA on rheological property is studied for both cement and concrete. Secondly, the influence of additions such as LS, CC and CNT on rheological parameters are discussed. It is found that the increased FA content improved the flowability in paste as well as in concrete. In paste, the physical properties such as size and shape of fly ash is the reason for increased flowability whereas in concrete, the paste volume contributes dominantly for the flowability rather than the effect due to individual FA particle. Reduced density of FA increases the paste volume in FA concrete thus reducing the interparticle friction by completely coating the coarse aggregate.

Surface and bulk characterization of an ultrafine South African coal fly ash with reference to polymer applications

South African coal-fired power stations produce about 25 million tons of fly ash per annum, of which only approximately 5% is currently reused. A growing concern about pollution and increasing landfill costs stimulates research into new ways to utilize coal fly ash for economically beneficial applications. Fly ash particles may be used as inorganic filler in polymers, an application which generally requires the modification of their surface properties. In order to design experiments that will result in controlled changes in surface chemistry and morphology, a detailed knowledge of the bulk chemical and mineralogical compositions of untreated fly ash particles, as well as their morphology and surface properties, is needed. In this paper, a combination of complementary bulk and surface techniques was explored to assess the physicochemical properties of a classified, ultrafine coal fly ash sample, and the findings were discussed in the context of polymer application as fillers. The sample was categorized as a Class F fly ash (XRF). Sixty-two percent of the sample was an amorphous glass phase, with mullite and quartz being the main identified crystalline phases (XRD, FTIR). Quantitative carbon and sulfur analysis reported a total bulk carbon and sulfur content of 0.37% and 0.16% respectively. The spatial distribution of the phases was determined by 2D mapping of Raman spectra, while TGA showed a very low weight loss for temperatures ranging between 25 and 1000°C. Individual fly ash particles were characterized by a monomodal size distribution (PSD) of spherical particles with smooth surfaces (SEM, TEM, AFM), and a mean particle size of 4.6μm (PSD). The BET active surface area of this sample was 1.52m2/g and the chemical composition of the fly ash surface (AES, XPS) was significantly different from the bulk composition and varied considerably between spheres. Many properties of the sample (e.g. spherical morphology, small particle size, thermal stability) appeared to be suitable for its applicability as filler in polymers, although the wide variation in surface composition between individual particles may challenge the development of a suitable surface modification technique. The observation that the bulk and surface compositions of the particles were so intrinsically different, strongly suggested that surface characterization is important when considering compatibility between matrices when applying fly ash as filler in polymers.

Preparation and characterization of porous fly ash/NiFe2O4 composite: Promising adsorbent for the removal of Congo red dye from aqueous solution

A series of fly ash/NiFe2O4 composites were prepared using fly ash and aqueous solutions of Ni, Fe nitrate salts and NaOH by co-precipitation followed by calcination method. The % mass ratio of fly ash: NiFe2O4 was varied in the range of 0:100 to 100:0. Samples were characterized by powder XRD, SEM, FTIR and N2 adsorption–desorption measurements. These samples were further evaluated for their adsorptive performance in removal of Congo red (CR) dye from an aqueous solution. In all the composites, spinel nickel ferrite phase was found to be capable to get anchored with the fly ash surface and exhibited more crystalline nature as compared to pure NiFe2O4 phase. The BET surface area and porous character of the composite were found to increase with the decrease in the contribution of the fly ash, reach to maximum and then decreases on further decrease in fly ash. The composite having % mass ratio of fly ash: NiFe2O4 = 50:50 exhibited maximum CR adsorption from the aqueous solution on account of the higher BET surface area, more porous character, favorable condition for diffusion of dye molecules and combined effect of chemisorption and physisorption. Under optimum conditions, it has shown the recyclability with adsorption capacity of the magnitude 23.33 mg g−1, which is much higher than individual fly ash, NiFe2O4 and other composites. The sorption data provided good fit with pseudo-second order kinetic model. The analyses of the adsorption data indicated that, the Langmuir model provides better correlation with the experimental data.

Co-combustion and its impact on fly ash quality; full-scale experiments

As second part of an extensive study on the relation of co-combustion of biomass and fly ash quality, co-combustion fly ashes were investigated from full-scale co-combustion experiments in the Netherlands using agricultural biomass, meat and bone meal, paper sludge and municipal sewage sludge as secondary fuel. The fly ash was investigated in relation to its performance for use in concrete. It was shown that the quality of co-combustion fly ash can be explained from the characteristics of the fuel and the combustion process. Further, it was shown that also fly ash obtained from high co-combustion percentages is able to meet the basic requirements of the European standard for fly ash in concrete (EN 450). Whether an individual co-combustion fly ash does so, depends on the nature of the co-fired fuel and especially on the amount and nature of its inorganic matter.

Study of Influence of Fly Ash Character on its Behaviour during Clinkering Process

Fly ash is currently secondary raw material, which is produced in huge quantities and its applicability is still not optimal. Even though it is used in cement, concrete, mortars, aerated concrete, ceramics, etc., it is still used, more than 80 % of it, for the reclamation of industrial areas and open cast mines. The production of artificial aggregate by clinkering fly ash utilizes at least 90 % of fly ash in the mixture and it is, together with aerated concrete, one of the ways to make the most of the potential of this raw material. This article deals with the description of the nature of individual fly ash types produced in the Czech Republic and the study of its influence on the behaviour during the thermal process. Chemical composition is the decisive parameter; it indicates the ratio of silicon, iron and aluminium oxides, and thus affects the melting point of the entire complex. This article points out the differences among the various fly ash types and it directly shows, using a picture-analysis, the changes in a sample cross-section during annealing.

Co-combustion and its impact on fly ash quality; pilot-scale experiments

As first part of extensive study on the relation of co-combustion and fly ash quality, co-combustion fly ash was generated from Paso Diablo coal and one secondary fuel, namely poultry dung, demolition wood or solid recovered fuels. The co-combustion experiments were performed in a 1MWth test boiler (dry bottom). The fly ash was investigated in relation to its performance for use in concrete. It was shown that the properties of co-combustion fly ash can be explained by the characteristics of the fuel and the combustion process. Further it was shown that also fly ash obtained from very high co-combustion percentages (up to 33% e/e) is able to meet the basic requirements of the European standard (NEN-EN 450). Whether an individual co-combustion fly ash does so, depends on the nature of the co-fired fuel and especially on the amount and nature of its inorganic matter.

Characterization of individual fly ash particles in surface snow at Urumqi Glacier No. 1, Eastern Tianshan

This research aimed to identify and characterize individual spherical fly ash particles extracted from surface snow at Urumqi Glacier No.1 (UG1), Eastern Tien Shan, central Asia. Characterization of the spherical particles (i.e. morphology, chemical composition and genesis) was obtained by scanning electron microscopy coupled with energy dispersive X-ray spectrometer (SEM-EDX). This method enabled the characterization of submicroscopic spherical particles, which were present in very small quantities. Spherical particles and agglomerates were identified according to their morphology in five snow samples. Prevalent particle types in all samples were granular spherical particles, hollow spherical particles, irregularly shaped carbonaceous particles and agglomerates. The vast majority of spherical particles in our samples had mostly smooth and glossy surfaces, although these particles varied in diameter and elemental composition. The diameter of fly ash particles ranged from 0.76 to 16.7 μm, with an average of 3.79 μm (median: 3.21 μm). Individual particle analyses of elemental composition showed that particles formed in combustion were mainly composed of carbon, silicon, aluminum and trace elements (e.g. Na, K, Ca, Fe). Some spherical fly ash particles contained toxic heavy metals (e.g. Pb, Cr, As, Zn), and indicated that fly ash particles acted as the main possible carriers of toxic heavy metals deposited in snow and ice of glaciers in high altitudes of central Asia. On the basis of chemical information obtained from EDX, the fly ash particles deposited in the snow could be classified into four types. Namely, Si-dominant particles, with average diameters of 3.24 μm were formed by industrial coal combustion via high temperature processes in typical coal-fired heating stations and thermal power plants. Moreover, Fe-dominant particles, with average diameters of 3.82 μm, and Ti-dominant spherical particles formed by lower temperature processes in foundry and iron or steel plants. In addition, C-dominant particles, with average diameters of 8.43 μm, formed from unburned coal. Fe-dominant particles had larger average diameters than Sidominant particles, indicating that the former were easier to form and developed earlier in the furnace because of their differential melting points of compositional oxide. Backward air mass trajectory analysis suggests that the developed urban regions of central Asia contributed the primary fly ash particles from industrial combustion to the study site through the high-level westerlies jet steam.

PIXE ANALYSIS OF INDIVIDUAL PARTICLES IN COAL FLY ASH

Consumption of coal is increasing as an alternative for petroleum. During the process, coal fly ash particles are produced and are disposed as an industrial waste. Coal ash contains toxic heavy metals, which leads to a concern about the possibility of leakage into environment. The spatial distribution and chemical form as well as elemental concentration of the toxic elements in the particles are important factors in assessing the leakage into the environment. In this study, we analyzed individual coal fly ash particles with 1 µm spatial resolution by using the simultaneous micro-PIXE/RBS/off-axis STIM system at Tohoku University. Eighty fly ash particles were analyzed. The particles are mainly composed of O , Si and Al and estimated as dioxide. Hydrogen and carbon are not observed in these particles. V , Zn , Sr , Cu , Ni , Mn , Cr and As are contained in the particles. The content of each element is quite different in each particle. These elements are distributed homogeneously. As an exception, Al , Ca , Fe , Zn , As and Zr are distributed on the surface of the particle which might be related to the combustion process.

Micro-CT characterization of structural features and deformation behavior of fly ash/aluminum syntactic foam

The structure of a fly ash/aluminum syntactic foam was characterized using X-ray microcomputed tomography. Microstructural features, such as size, morphology and distribution of fly ash microballoons, were quantitatively related to the deformation behavior using interrupted compression tests. The syntactic foam was found to exhibit four distinct stages of deformation: (i) elastic; (ii) dispersed collapse of the fly ash microballoons; (iii) unification of the dispersed collapse region forming a band of densification, usually normal to the loading axis, via localized plasticity; and (iv) final densification. The tomographic observations show that deformation is initially controlled by the fragmentation and collapse of dispersed individual fly ash particles. After significant strain, sufficient microballoons have collapsed, localizing the stress and hence damage, and forming densification bands through severe plastic deformation of the aluminum matrix. A peak stress of 73 MPa and an energy absorption capacity of 27 MJ m −3 at 47% strain were obtained.

Determination of the Cd-Bearing Phases in Municipal Solid Waste and Biomass Single Fly Ash Particles Using SR-μXRF Spectroscopy

By using an excitation energy of 27.0 keV, synchrotron radiation-induced micro-X-ray fluorescence (SR-microXRF) is employed to extract information regarding the composition and distribution of Cd-bearing phases in municipal solid waste (MSW) and biomass fly ashes. Significance of observation is based on statistics of totally more than 100 individual MSW and biomass fly ash particles from a fluidized bed combustion (FBC) plant. Cd concentrations in the parts-per-million range are determined. In general, although previous leaching studies have indicated Cd to be predominant in the smaller-size ash particles, in the present study Cd is more evenly distributed throughout all the particle sizes. For MSW fly ashes, results indicate the presence of Cd mainly as CdBr2 hot-spots, whereas for biomass fly ashes, which exhibit lower CdX2 concentration, a thin Cd layer on/in the particles is reported. For both ashes, Ca-containing matrixes are found to be the main Cd-bearing phases. Support for this observation is found from independent first-principles periodic density functional theory calculations. The observations are condensed into a schematic mechanism for Cd adsorption on the fly ash particles.

X-ray fluorescence tomography of individual municipal solid waste and biomass fly ash particles.

Information about Cd distribution inside single municipal solid waste and biomass fly ash particles is fundamental since it affects its leachability. The internal 2D distributions of the main and trace elements in such highly inhomogeneous matrixes were successfully determined by means of the combined synchrotron radiation induced micro X-ray fluorescence (micro-SRXRF) and tomography (micro-SRXRFT) techniques. Scanning micro-SRXRF measurements show Cd elemental distribution within single fly ash particles to be inhomogeneous, but no information can be obtained about its internal distribution. During micro-SRXRFT analysis, single fly ash particles are successively measured by a rotational-translational scan in a VH=2 x 5 microm2 microbeam. The 2D internal elemental distribution images, obtained by the modified simultaneous algebraic reconstruction technique algorithm, provide the size and the location of Cd-containing areas together with the location of other measurable elements. Results showed Cd concentration to be higher in the core of the fly ash particles analyzed rather than on the surface of the particles. Moreover, in both ashes, Ca-containing matrixes are found to be the main Cd-bearing phases. A possible mechanism for Cd adsorption on the fly ash particles is proposed based on the obtained results.

Micro- and nanochemistry of fly ash from a coal-fired power plant

Fly ash from a coal-fired power plant was investigated to obtain detailed information on its physical and chemical properties, and to gain an understanding of potential environmental and health impacts associated with itsdisposal in landfills. The studied material was produced through combustion of Illinois Basin coal and trapped within the power plant by an electrostatic precipitator. It is a fine-grained, low-Ca fly ash containing primarily SiO 2 , Al 2 O 3 , and Fe 2 O 3 , and is enriched in many toxic elements (e,g., Be, Zn, As, Cd, Tl, Pb, and U) by a factor of up to 30 relative to coal. The ash consists of mainly hematite, magnetite, mullite, quartz, and amorphous material. These constituents occur mostly as spherical particles with diameters of less than 13 μm. We examined the physical, chemical, and structural characteristics of individual fly ash particles by scanning and transmission electron microscopy and electron probe microanalysis. The results demonstrate that, with the exception of complex plerospheres, individual particles are chemically fairly homogeneous, but a pronounced compositional variation exists among particles with similar physical and structural attributes. Electron microprobe data document that several trace elements, including U, are partitioned into the Fe-rich particles. Transmission electron microscopy revealed that various types of small (<1 μm) crystalline Ca-rich phases, including lime, are attached to the glass spheres, particularly the nonmagnetic glass. These crystals may contain substantial amounts of S. Even though only a few of these crystals were analyzed quantitatively, our data indicate that the Ca-rich and S-rich phases may be important hosts for trace elements such as V and Zn. The observed element partitioning and the existence of surface-attached crystals enriched in certain trace elements suggest that fly ash from coal-fired power plants might have a more deleterious environmental impact than is inferred from bulk analytical data.