Coal Fly Ash Samples Research Articles

ICP-AES determination of rare earth elements in coal fly ash samples of thermal power stations : assessment of possible recovery and environmental impact of rare earth elements

ICP-AES determination of rare earth elements in coal fly ash samples of thermal power stations : assessment of possible recovery and environmental impact of rare earth elements

Microwave assisted aqua regia extraction of thallium from sediment and coal fly ash samples and interference free determination by continuum source ETAAS after cloud point extraction

A simple cloud point extraction method is described for the separation and pre-concentration of thallium from the microwave assisted aqua regia extracts of sediment and coal fly ash samples. The method is based on the formation of extractable species of thallium and its interaction with hydrophobic solubilizing sites of Triton X-114 micelles in the presence of aqua regia and electrolyte NaCl. These interactions of micelles are used for extraction of thallium from a bulk aqueous phase into a small micelles-rich phase. The potential chloride interferences are eliminated effectively, which enabled interference free determination of thallium from aqua regia extracts using continuum source ETAAS. The parameters affecting the extraction process are optimized. Under the optimized conditions, pre-concentration factor and limit of detection are 40 and 0.2ngg−1, respectively. The recoveries are in the range of 95–102%. A characteristic mass, 13pg was obtained. The accuracy of the method is verified by analyzing certified reference materials such as NIST 1633b coal fly ash, NIST 1944 marine sediment and GBW 07312 stream sediments. The results obtained are in good agreement with the certified values and method is also applied to real samples.

Time-Dependent Deposition Characteristics of Fine Coal Fly Ash in a Laboratory Gas Turbine Environment

Time-dependent deposition characteristics of fine coal fly ash were measured in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Two samples of subbituminous coal fly ash, with mass mean diameters of 3 μm and 13 μm, were entrained in a hot gas flow with a gas temperature of 1288 °C and Mach number of 0.25. A nickel-based, superalloy metal coupon approximately 0.3 cm thick was held in a hot particle-laden gas stream to simulate deposition in a gas turbine. Tests were conducted with deposition times of 20, 40, and 60 min. Capture efficiencies and surface roughness characteristics (e.g., Ra) were obtained at different times. Capture efficiency increased exponentially with time, while Ra increased linearly with time. The increased deposition with time caused the surface temperature of the deposit to increase. The increased surface temperature caused more softening, increasing the propensity for impacting particles to stick to the surface. These data are important for improving models of deposition in turbines from syngas flows.

A bacterial bioreporter panel to assay the cytotoxicity of atmospheric particulate matter

Numerous studies have demonstrated that elevated concentrations of suspended atmospheric particulate matter (PM) are associated with adverse health effects. In order to minimize the adverse public health effects of atmospheric PM by exposure management, there is a need for a greater understanding of the toxic mechanisms and the components that are responsible for the toxic effects. The aim of this study was to utilize bioassay techniques to investigate these aspects. For this purpose a reporter panel of 9 genetically engineered bacterial (Escherichia coli) strains was composed. Each panel member was designed to report on a different stress condition with a measurable light signal produced by the luciferase enzyme.Toxic mechanisms and components were studied using six anthropogenic PM source samples, including two vehicle combustion particles, three coal fly ash (CFA) samples and an urban dust sample. The most prominent outcome of the panel exposure results were broad panel responses observed for two of the CFA samples, indicating oxidative stress, respiration inhibition and iron deficiency. These responses were relieved when the samples were treated with EDTA, a non-specific metal chelator, suggesting the involvement of metals in the observed effects. Bioavailability analysis of the samples suggests that chromium was related to the toxic responses induced by two of the CFA samples. Oxidative stress was also observed in several samples of ambient atmospheric aerosols and excess metal toxicity in an urban dust sample collected in a parking lot.The reporter panel approach, as demonstrated in this study, has the potential of providing novel insights as to the mechanisms of atmospheric PM toxicity. Furthermore, combining the panel's results with bioavailability data can enlighten about the role of different PM components in the observed toxicity.

A Meticulous Study on the Adsorption of Mercury as Tetrachloromercurate(II) Anion with Trioctylamine Modified Sodium Montmorillonite and Its Application to a Coal Fly Ash Sample

Clay materials have hogged the limelight for their effectiveness in environmental remediation. In this paper, we report an effective solid phase extraction method for mercury based on the adsorption of tetrachloromercurate(II) anion with trioctylamine intercalated onto sodium montmorillonite. The adsorption is facile in acidic medium, and the adsorbent was well characterized by diverse physicochemical and spectroscopic techniques. Various isotherm models were employed to correlate the experimental adsorption data. The electrostatic interaction between HgCl42- and the protonated amine is well supported by a Langmuir isotherm model with a maximum adsorption capacity of 140.84 mg g–1. The ordered transition state that arises due to the proximity of the HgCl42- and the positively charged amine is accompanied by a decrease in the translational entropy of the system. The N2 adsorption–desorption isotherm study revealed the mesoporous nature of the adsorbent, and the thermodynamically favorable adsorption proces...

Environmental hazard assessment of coal fly ashes using leaching and ecotoxicity tests

The environmental hazard of six coal fly ash samples collected from various coal incineration plants were examined in the present study, using various leaching tests along with physicochemical and ecotoxicological analyses. Physicochemical analyses indicated that the concentration of Ba, Cr, Mo, Se, sulfates and total dissolved solids (TDS) exceeded the threshold values, according to the European Council decision 2003/33/EC for inert, non-hazardous or hazardous waste. The highest sensitivity, among examined organisms, was presented by Daphnia magna and was ascribed to the lowest tolerance of the organism to Cr. The toxic effect profile of the leachates toward Vibrio fischeri revealed that its bioluminescence was significantly altered by the presence of heavy metals in the leachates (such as Cu, Ni and Zn) in low or sub-lethal doses. Although the toxicity of the leachates toward Pseudokirchneriella subcapitata was relatively high, the correlation between the toxicity and heavy metals concentration was rather poor, indicating the significance of the bioavailability of constituents and the importance of toxicity testing. Based on the classification of the samples resulted by physicochemical analyses of the leachates and the results of ecotoxicity tests, Physicochemical and Ecotoxicological indices were also defined, for an overall evaluation of the environmental impact assessment of fly ashes. The suggested indices showed that ecotoxicity tests were in some cases inconsistent with the outcome of waste classification based on physicochemical analyses. Moreover, the examination of leaching protocols and obtained results showed that one stage leaching test (L/S=10L/kg) underestimated the fly ash classification, when compared with the two stage test EN 12457-3 at the cumulative ratio L/S=10L/kg. In addition, the application of availability test NEN 7341 provided useful results about the ecotoxicity wastes. Thus, NEN 7341 is strongly suggested for the implementation of such studies, since the bioavailability of constituents may not be altered by pH adjustment tactics and pH-originated toxicity effects may be avoided.

Leaching behavior of selected trace elements in coal fly ash samples from Yenikoy coal-fired power plants

Short-term leaching test results of alkaline fly ash from Yenikoy coal-fired power plant were reported in this paper. ASTM D-3987-85 and TCLP-1311 test methods were applied to determine leaching behavior of selected elements namely, Fe, Ca, Cu, Co, Cd, Mn, Ni, Pb Zn, and Cr (VI) at different particle size fractions and test conditions. Chemical, mineralogical and morphological characterizations of ash samples were also performed using chemical, XRD and SEM–EDS analysis methods. The results showed that CaO dominates in the Yenikoy fly ash sample which directly affects the mobility of trace elements by determining the pH of the leaching medium. Higher mobility values of Cd, Co Cu, Pb, Ni and Zn elements were observed for TCLP-1311 procedure. The concentration of these elements in leachates showed a tendency to increase by decreasing particle size. Overall results suggested that the amount of the selected elements in the final leachates of both tests was lower than the limit values of landfill regulations except Cr (VI).

Leachability of elements in alkaline and acidic coal fly ash samples during batch and column leaching tests

Three acidic (HA, HB, and MA) and one alkaline (PD) fly ash samples collected from four different power plants were subjected to batch and column leaching tests to evaluate the leachability of several elements. Jar leaching tests (up to 120h), serial batch leaching tests (35days), and long-term (up to 70weeks) batch leaching tests were performed using doubly deionized (DDI) water, and column leaching tests (131–150 pore volumes) were conducted using a synthetic acid rain (SAR) solution. The results of batch and column leaching tests showed that different proportions of As, Cr, Mo, Sb, Se, and V were leached by DDI water and SAR from the four fly ash samples. The increasing leachate concentrations of As, Cr, Mo, Sb, Se (except PD fly ash), and V with time indicated that the long-term release of these elements was controlled by the dissolution of glassy fly ash particles. Mobilization of As from HA fly ash, Cr from PD fly ash, and Se from both HA and PD fly ash also showed a bimodal leaching pattern during column leaching tests, potentially indicating the association of these elements with different fly ash fractions. In general, Mo, Sb, and Se showed high mobilities, while only small amounts of Cr were released from the fly ash samples. Boron, Ca, K, Mg, Mn, and Na were released very rapidly during the initial phases of both serial and column leaching tests. These elements were likely enriched in surface-bound, highly soluble loose particles. During long-term batch leaching tests, HB and MA fly ash leachate concentrations of Ba, Co, Mn, Ni, and Zn decreased with time, indicating possible adsorption or co-precipitation with secondary minerals. Because many of the older fly ash disposal facilities are unlined, these sites are potential sources of hazardous elements to the environment. Therefore, development of effective and economic methods to contain trace elements within the disposal facility site is desirable to prevent contamination of groundwater and surface water resources.

Direct solid sampling electrothermal atomic absorption spectrometric determination of toxic and potentially toxic elements in certified reference materials of brown coal fly ash

This work describes a method for the direct determination of Bi, Cd, Cr, Ni, Pb, Sb, Sn and Zn in reference materials of brown coal fly ash, using solid sampling electrothermal atomic absorption spectrometry. The use of chemical modifiers was found to be necessary for obtaining reproducible and sufficiently sensitive signals for the analytes under study. The mixture of Pd and Mg(NO3)2 was used for the determination of Bi, Cd, Pb, Sb, Sn and Zn, W (permanent modifier) in combination with Mg(NO3)2 (as aqueous modifier) provided well-defined signal profiles for Cr and Ni determination in coal fly ash samples. A systematic study focused on the use of alternative (less sensitive) lines for obtaining sufficient sensitivity. The following analytical lines were used: Bi 306.8nm, Cd 326.1nm, Cr 520.6nm, Ni 305.1nm, Pb 205.3nm, Sb 206.8nm, Sn 300.9nm, Zn 307.6nm. The limits of detection were 0.057μg g−1 for Bi, 0.21μg g−1 for Cd, 1.1μg g−1 for Cr, 1.4μg g−1 for Ni, 4.0μg g−1 for Pb, 0.13μg g−1 for Sb, 0.33μg g−1 for Sn and 16μg g−1 for Zn, respectively.

Determination of Trace Level Lanthanides and Thorium by Inductively Coupled Plasma Atomic Emission Spectrometry in Different Types of Geological, Red Mud, and Coal Fly Ash Samples After Separation as Oxalates Using Calcium as Carrier

Determination of Trace Level Lanthanides and Thorium by Inductively Coupled Plasma Atomic Emission Spectrometry in Different Types of Geological, Red Mud, and Coal Fly Ash Samples After Separation as Oxalates Using Calcium as Carrier

Studies on synthesis and characteristics of zeolite prepared from Indian fly ash

In the present study, samples of coal fly ash were obtained from seven major Indian thermal power plants. These samples were transformed into fly ash zeolite (FAZ) using hydrothermal activation by treatment with NaOH. All experiments were carried out at 100 °C, but with different solid:liquid ratios, different concentrations of alkali and different incubation times. The chemical composition, mineralogy and morphology of the fly ash and FAZ were determined by wet chemical method after Na2CO3 fusion, x-ray diffraction and scanning electron microscopy. The cation exchange capacity of fly ash and FAZ was determined using the ammonium acetate method (IS:2720). The ammonium exchange capacity was determined by the titrimetric method. The experiments demonstrate that zeolite can be synthesized at 100 °C using alkali. The cation exchange capacity and ammonium adsorption capacity of FAZ (up to 250 meq/100 g and 22.93 mg NH4 +/g respectively) indicate that the FAZ may be potentially useful to reduce heavy metals and other pollutants from contaminated environments. Therefore, zeolitization at low temperature potentially allows waste fly ash to be used in an economically advantageous way.

Impact of Trona-Based SO2 Control on the Elemental Leaching Behavior of Fly Ash

Trona (Na3HCO3CO3·2H2O) injection has been used to control SO2 emissions in coal-fired power plants. This study evaluated the impact of trona injection on fly ash physical and chemical characteristics, especially the leaching characteristics. One set of paired coal fly ash samples, collected from a full-scale power plant with and without trona injection for SO2 control, was used. The results showed that trona injection introduced significant amounts of soluble sodium compounds into the fly ash, elevated the fly ash pH, reduced the ash surface area, and changed the fly ash morphology. A comparison of 30 constituents in leachates from both ashes demonstrated that trona ash leached significantly greater amounts of Na, sulfate, chloride, fluoride, total inorganic carbon (TIC), and oxyanions, especially As and Se. Effects of the liquid/solid (L/S) ratio, pH, dry storage time, and leaching time on As and Se leaching and speciation were examined. AsV, SeIV, and SeVI were the As and Se species in trona ash leacha...

Mineralogy and Mobility Patterns of Chemical Species in Weathered Coal Fly Ash

Chemical interactions of disposed coal fly ash with O2, CO2, and infiltrating rain-water lead to chemical alteration, flushing/leaching of soluble chemical species locked in different physico-chemical forms as the coal fly ash is aging. This study was carried out to gain insight into the chemical alterations and its effects on the mobility patterns of chemical species in weathered coal fly ash. Weathered coal fly ash samples of ages 1 year and 20 years were sampled at a coal burning power station in the Mpumalanga Province, South Africa. The chemical and mineralogical compositions of the weathered coal fly ash were investigated using X-ray fluorescence spectrometry, inductive coupled plasma-optical emission spectrometry, ion chromatography, X-ray diffraction, and Fourier transform infrared spectroscopy. X-ray fluorescence results showed the presence of major oxides, such as SiO2, Al2 O 3, Fe2 O 3, while CaO, K2O, TiO2, MnO, MgO, P2 O 5, and SO3 occur in minor concentrations. The major elements, such as Fe, Si, Mg, K, and Mn, showed increasing trends down the depth of the core, while Ti and Al show decreasing trends down the depth of the core (20-year-old coal fly ash). Trace metals, such as P and Zn, show increasing trends down the depth, while Ba, Ni, Pb, Sr, V, and Cr increase up the depth of the core (20-year-old ash). The trace metals distribution patterns in 1-year-old ash showed increasing trends down the depth of the core for Cr, Ni, Pb, Y, S, and P, while Ba and Sr decrease down the depth of the core. Major mineral phases as revealed by X-ray diffraction include quartz and mullite. Other minerals identified are hematite, calcite, lime, anorthite, mica, and enstatite. The pH of interstitial pore water for 1-year-old and 20-year-old coal fly ash ranged from 9.0–10.6 and 7.2–9.9, respectively, while in the 2-week-old coal fly ash ranged from 9.9–10.9. Analysis of extracted pore water shows that several toxic metals, such as B, Cr, As, Mo, and Se, are leaching from the weathered ash. The core ash samples in contact with the atmosphere and those at the saturation point record the highest availability of chemical species, such as Mg, Ca, Fe, K, Na, B, Cr, As, Mo, and Se in pore water. The 1-year-old and 20-year-old coal fly ash cores showed a lower pH and greater leaching/flushing of the soluble buffering constituents than the 2-week-old placed ash.

Heavy metal characterization of CFB-derived coal fly ash

The present study investigates the heavy metal content of coal fly ash (FA) samples coming from three different sampling points (secondary cyclone, cooler and filter) of a pilot plant combustion facility. The combustion experiments were carried out in a 0.1MW Circulated Fluidized Bed (CFB) boiler using South African coal, with the addition of limestone for sulfur capture. FA was tested for the presence of selected heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES); batch leaching tests were conducted as well. The samples were also characterized in terms of their microstructure, chemical and mineralogical composition, total surface area and particle size distribution. Most of the studied metals (Cd, Cr, Cu, Ni, Mn, Zn) showed enrichment in the fine, filter FA particles, while Pb was mostly concentrated in the cooler sample. Regarding leaching characteristics of the examined samples, Cr was found to occur in considerable amounts. Although the use of CFB technology for the combustion of solid fuels steadily gets bigger worldwide, only a very limited number of studies have environmentally assessed CFB-coal FAs to date. Thus, the current study aims to contribute toward building a more integrated knowledge on the environmental impact of this abundant power production by-product.

Removal of arsenic in coal fly ash by acid washing process using dilute H 2SO 4 solvent

Coal fly ash emitted from coal thermal power plants generally contains tens ppm of arsenic, one of the hazardous elements in coal, during combustion and their elution to soil or water has become a public concern. In this study, the acid washing process developed by the authors was applied to the removal of arsenic from coal fly ash. Laboratory- and bench-scale investigations on the dissolution behavior of arsenic from various coal fly ash samples into dilute H 2SO 4 were conducted. Arsenic in the coal fly ash samples were dissolved into H 2SO 4 solutions rapidly. However, its concentrations decreased with an increase in the pH of H 2SO 4 solution in some cases. The species of arsenic in the dilute H 2SO 4 was estimated as H 3AsO 4, and its anionic species was considered to adsorb with the elevation of pH under the presence of ash particle. Such adsorption behavior was enhanced under the presence of Fe ion in the solution. The sufficient removal of arsenic was achieved by controlling pH and avoiding the adsorption of arsenic on the surface of coal fly ash particles, and the elution of arsenic from coal fly ash sample was successfully below the regulation limit.

Determination of metals in coal fly ashes using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry

A method for determination of Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn in coal fly ash samples using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) is proposed. The digestion procedure consisted in the sonication of the previously dried sample with hydrofluoric acid and aqua regia at 80 °C for 30 min, elimination of fluorides by heating until dryness for about 1 h and dissolution of the residue with nitric acid solution. A classical digestion method, used as comparative method, consisted in the addition of HCl, HNO 3 and HF to 1 g of sample, and heating on a hot plate until dryness for about 6 h. The proposed method presents several advantages: it requires lower amounts of sample and reagents, and it is faster. It is also advantageous when compared to the published methods, which also use ultrasound-assisted digestion procedure: lower detection limits for Co, Cu, Ni, V and Zn, and it does not require shaking during the digestion. The detection limits (μg g −1) for Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn were 0.06, 0.37, 1.0, 25, 0.93, 0.45, 4.0, 1.7 and 4.3, respectively. The results were in good agreement with those obtained by the classical method and reference values. The exception was Cr, which presented low recoveries in classical and proposed methods (83 and 87%, respectively). Also, the concentration for Cu obtained by the proposed method was significantly different from the reference value, in spite of the good recovery (91 ± 1%).

Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials

Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, were utilized as raw materials for the synthesis of zeolitic products. The two FAs underwent a hydrothermal activation with 1M NaOH solution. Two different FA/NaOH solution/ratios (50, 100g/L) were applied for each sample and several zeolitic materials were formed. The experimental products were characterized by means of X-ray diffraction (XRD) and energy dispersive X-ray coupled-scanning electron microscope (EDX/SEM), while X-ray fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro- and macroporosity. Afterwards the hybrid materials were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids. Main parameters for the precipitation of the heavy metals, as it was concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.

Electricity from Coal and Utilization of Coal Combustion By-products

Most electricity in the world is conventionally generated using coal, oil, natural gas, nuclear energy, or hydropower. Due to environmental concerns, there is a growing interest in alternative energy sources for heat and electricity production. The major by-products obtained from coal combustion are fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) materials. The solid wastes produced in coal-fired power plants create problems for both power-generating industries and environmentalists. The coal fly ash and bottom ash samples may be used as cementitious materials.

Determination of mercury in ash and soil samples by oxygen flask combustion method–Cold vapor atomic fluorescence spectrometry (CVAFS)

A simple method was developed for the determination of mercury (Hg) in coal fly ash (CFA), waste incineration ash (WIA), and soil by use of oxygen flask combustion (OFC) followed by cold vapor atomic fluorescence spectrometry (CVAFS). A KMnO 4 solution was used as an absorbent in the OFC method, and the sample containing a combustion agent and an ash or soil sample was combusted by the OFC method. By use of Hg-free graphite as the combustion agent, the determination of Hg in ash and soil was successfully carried out; the Hg-free graphite was prepared by use of a mild pyrolysis procedure at 500 °C. For six certified reference materials (three CFA samples and three soil samples), the values of Hg obtained by this method were in good agreement with the certified or reference values. In addition, real samples including nine CFAs collected from some coal-fired power plants, five WIAs collected from waste incineration plants, and two soils were analyzed by the present method, and the data were compared to those from microwave-acid digestion (MW-AD) method.

Preparation and characterization of carbon-enriched coal fly ash

Carbon-enriched fractions have been obtained from two coal fly ash (FA) samples. The FA came from two pulverized-coal fired power stations (Lada and Escucha, Spain) and were collected from baghouse filters. Sieving was used to obtain carbon-enriched fractions, which were further subjected to two beneficiation processes: acid demineralization using HCl and HF, and oil agglomeration using soya oil–water. Yield in weight after sieving, unburned carbon content, and several physicochemical characteristics of the obtained fractions were used to compare the performance of the beneficiation methods. Low carbon concentration was obtained by sieving, particularly in the case of Escucha FA. However, after acid demineralization or oil agglomeration, fractions containing unburned carbon in a range of 63% to 68% were obtained. These fractions showed differences in mineral phase composition and distribution depending on the FA and on the beneficiation method used. The textural properties of the obtained fractions varied as a function of their carbon content and the beneficiation method used. However, no significant differences in morphology of the carbonaceous particles were found.