Characterization Of Coal Fly Ash Research Articles

Optimization of synthesis parameters and characterization of coal fly ash derived microporous zeolite X

The present work focused on synthesis of microporous zeolite X (mZX) from Indian coal fly ash (CFA) by modified hydrothermal method. Response surface methodology, namely Box-Behnken design were accounted to optimize the synthesis parameters - NaOH/CFA ratio, crystallization temperature, and crystallization time to maximize crystallinity percentage and yield percentage for mZX. Both CFA and mZX were characterized by various techniques such as XRD, FESEM, TEM, XRF, BET, FTIR and TGA-DTA. XRD patterns of synthesized zeolite are matching with commercial zeolite X at the optimum conditions of NaOH/CFA weight ratio of 1.25, crystallization temperature of 100 °C and crystallization time of 10 h. FESEM of mZX showed the formation of microporous zeolite. The maximum crystallinity of 76% was achieved along with 88% mZX yield. A total surface area of 648.42 m2/g, micropore area of 578.64 m2/g, micropore volume of 0.218 cm3/g and average pore size 9.048 Å were obtained. The optimized average crystal size was calculated as 22.55 nm from XRD and crystal size was observed in the range of 17.43–35.07 nm from TEM. A maximum adsorption for Crystal Violet (CV) were found as 99.62% for mZX in comparison to 82.42% for CFA and 96.23% for commercial zeolite X.

Characterization of coal fly ash and use of plants growing in ash pond for phytoremediation of metals from contaminated agricultural land

ABSTRACTMobilization of heavy metals around coal power plants due to improper disposal of fly ash (FA) and wastewater have led to release of pollutants into the environment. For protection of inimitable natural resources, application of economical and effective technologies is needed such as phytoremediation is cost-effective, ecofriendly and a better option for elimination of metal from contaminated sites. Twelve plant species were sampled from ash dyke of Singrauli and screened for accumulation of metals for this study. Mobilization ratio of metals from soil to plant was evaluated to determine translocation factor. CILLAS analyzer, Raman spectroscopy and SEM-EDX were used for characterization of particle size, functional groups and morphology of fly ash. Results showed mean metal concentrations in contaminated soil for Fe, Mn, Cr, Zn, Ni, Cu, Cd and Pb were 909.4, 60.6, 9.5, 134.8, 13.6, 26.7, 2.9 and 25.4 µg g−1 respectively. Enrichment factors for soil, root and shoot for a contaminated site were 1.9, 3.8 & 4.3 for Zn and 2.7, 3.5 & 3.8 for Cd. Six hyper-accumulators with absorption efficiency >1 viz. I. carnea, S. nigrum, S. munja, T. angustifolia, C. dactylon and P. hysterophorus were identified which may be cultivated successively to reclaim and restore damaged agricultural land.

Application of mine water leaching protocol on coal fly ash to assess leaching characteristics for suitability as a mine backfill material

ABSTRACTOver the years, coal mining in the Mpumalanga Province of South Africa has negatively affected the environment by causing pollution of water resources, land subsidence and spontaneous coal combustion. Previous studies show that in-situ treatment of acid mine drainage (AMD) using coal fly ash (CFA) from local power stations was possible and sludge recovered out of such treatment can be used to backfill mines. In this article, the authors have attempted to understand the leaching characteristics of CFA when placed underground as a backfill material using the mine water leaching protocol (MWLP). The results show that the migration of contaminants between the coal fly ash and the AMD in the mine voids depends on the pH and quality of the mine water. While backfilling mine voids with CFA can neutralize and scavenge between 50% and 95% of certain environmentally sensitive elements from AMD such as Fe, Al, Zn, Cu, Ni, Co and Mn. At this moment, it is also important to point out that certain scavenged/removed contaminants from the AMD during initial phases of backfilling can be remobilized by the influx of acidic water into the mine voids. It has therefore been concluded that, while CFA can be used to backfill mine voids, the influx of fresh acidic mine water should be avoided to minimize the remobilization of trapped contaminants such as Fe, Al, Mn and As. However, the pozzolanic material resulting from the CFA-AMD interaction could prevent such influx.

Comparison of multiple regression analysis using dummy variables and a NARX network model: an example of a heavy metal adsorption process

AbstractIn the present study, the adsorption characteristics of coal fly ash obtained from the Kangal Power Plant, Turkey and activated fly ash in the planetary ball mill were investigated to remove the heavy metal ions from aqueous solutions. The adsorption capacity was compared for the first time using a multiple regression analysis with dummy variables and a non‐linear auto regressive exogenous (NARX) network model. An equation was obtained for all types of adsorbents or heavy metals using the regression of qe on the dummy variables. The predictive ability of NARX was found to be better than that of multiple regression using dummy variables. These models can also be successfully implemented on the experimental data to evaluate the adsorption process. In addition, fly ash is a low cost alternative since it is a more economical and environmentally friendly adsorbent and it is abundant in both nature and from waste material from industry.

Mineralogical, Microstructural and Thermal Characterization of Coal Fly Ash Produced from Kazakhstani Power Plants

Coal fly ash (CFA) is a waste by-product of coal combustion. Kazakhstan has vast coal deposits and is major consumer of coal and hence produces huge amounts of CFA annually. The government aims to recycle and effectively utilize this waste by-product. Thus, a detailed study of the physical and chemical properties of material is required as the data available in literature is either outdated or not applicable for recently produced CFA samples. The full mineralogical, microstructural and thermal characterization of three types of coal fly ash (CFA) produced in two large Kazakhstani power plants is reported in this work. The properties of CFAs were compared between samples as well as with published values.

Experimental study on the magnetic characteristics of coal fly ash at different combustion temperatures

ABSTRACTTwo different coals containing iron minerals were combusted in a drop tube furnace at different temperatures. The ash samples collected were analyzed in detail to investigate the transformation behaviors of iron-bearing minerals and the magnetic characteristics of coal fly ash (FA). The vibrating sample magnetometer (VSM) was used to analyze the magnetic characteristics of the ash samples and Mössbauer spectroscopy was used to analyze the iron-bearing components in FA. The results indicate that combustion temperature does not significantly affect the crystals phases formed in FA, but does change the relative content of crystals. With an increase in temperature, the relative content of maghemite (γ-Fe2O3) and magnetite (Fe3O4) decreases, while the relative content of hematite (α-Fe2O3) increases. The rising combustion temperature also results in a decreasing trend on saturation magnetization of FA. Furthermore, there is a significant positive correlation between the equivalent content of iron-bearing minerals and the saturation magnetization of FA, which can be applied to remove the particulates from flue gas more efficiently.

Characterization of Coal Fly Ash by the Absolute Foam Index

Long foam index test times and the inability to characterize different loss on ignition (LOI) in cementitious materials using the same solution concentrations prompted an examination of different test solution concentrations for various fly ash samples. A 15-minute duration forced the test into a number of cycles where air-entraining admixture (AEA) drops with sensitivity compatible to the fly ash allowed diffusion and reaction consistency throughout all the tests, allowing both low- and high-carbon fly ash to be characterized uniquely. The absolute foam index, defined as the amount of undiluted volume of AEA solution added to obtain a 15-minute endpoint (limits 12 to 18 minutes) signified by 15-second metastable foam, uniquely characterized 15 fly ash samples with LOI values that ranged from 0.17 to 23.3%. The absolute foam index strongly correlated to LOI values for fly ash samples greater than 5% LOI but variability was observed in samples less than 5% LOI.

Characterization of Coal Fly Ash by the Absolute Foam Index

Characterization of Coal Fly Ash by the Absolute Foam Index

Fractional Characteristics of Coal Fly Ash for Beneficial Use

As a primary by-product of coal combustion produced in large quantities, coal fly ash is a material receiving considerable interest for potential large-scale engineering applications. However, the beneficial use of coal fly ash in concrete production and contaminant removal, which have divergent constraints to sorption capacity, requires a more complete understanding of the surface and sorptive characteristics offly ash. A systematic analysis of fly ash particle size fractions established linkages between particle size, particle morphology, unburned carbon content, surface area, and sorption capacity. Unburned carbon was enriched in fly ash fractions of the largest particle sizes and associated with irregularly shaped particles. Further, most of the surface area and sorption capacity of fly ash could be attributed to unburned carbon. More importantly, unburned carbon content, specific surface area, and methylene blue sorption capacity were shown to strongly correlate to one another, providing a potentially quantitative basis for understanding the surface properties of fly ash and developing more effective process options to enhance the fly ash sorption behavior desirable for specific engineering applications. DOI: 10.1061/(ASCE)MT.1943-5533 .0000550. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Coal; Surface properties; Sorption; Particle size distribution. Author keywords: Fly ash; Surface properties; Sorption; Particle size distribution.

Serial batch leaching procedure for characterization of coal fly ash

Although many leaching methods have been used for various purposes by research groups, industries, and regulators, there is still a need for a simple but comprehensive approach to leaching coal utilization by-products and other granular materials in order to estimate potential release of heavy metals when these materials are exposed to natural fluids. A serial batch characterization method has been developed at the National Energy Technology Laboratory that can be completed in 2-3 days to serve as a screening tool. The procedure provides an estimate of cumulative metals release under varying pH conditions, and leaching the sample at increasing liquid/solid ratios can indicate the rate at which this process will occur. This method was applied to eight fly ashes, adapted to the acidic or alkaline nature of the ash. The leachates were analyzed for 30 elements. The test was run in quadruplicate, and the relative standard deviation (RSD) was used as a measure of method reproducibility. RSD values are between 0.02 and 0.70, with the majority of the RSD values less than 0.3. The serial batch leaching procedure was developed as a simple, relatively quick, yet comprehensive method of estimating the risk of heavy metal release from fly ash when it is exposed to natural fluids, such as acid rain or groundwater. Tests on a random selection of coal fly ashes have shown it to be a reasonably precise method for estimating the availability and long-term release of cations from fly ash.

Valorization of coal fly ash by mechano-chemical activationPart I. Enhancing adsorption capacity

The adsorption characteristics of coal fly ash have been enhanced by mechano-chemical activation with a high energy mono-planetary ball mill. The best performing sample for the adsorption of phenol from aqueous solution (i.e., fly ash with the higher carbon content and mechano-chemically activated for 4 h in N 2 atmosphere) was compared with powdered activated carbon, yielding quite encouraging results such as favorable adsorption isotherms, improved specific adsorption capacity and very fast adsorption rate. This provides new opportunities for utilizing fly ash in environmental protection applications like the stabilization/solidification treatment of hazardous waste and contaminated soil.

Valorization of coal fly ash by mechano-chemical activationPart II. Enhancing pozzolanic reactivity

The pozzolanic and adsorptive characteristics of coal fly ash have been enhanced by mechano-chemical activation in order to evaluate their potential utilization in the stabilization/solidification treatment of hazardous wastes. To that aim a soil artificially contaminated by large amounts of Phenol and Pb underwent that treatment, wherein increasing amounts of powder activated carbon and Portland cement were substituted by mechano-chemically activated fly ash. Under the experimental conditions investigated, very encouraging results, in terms of contaminants leaching and mechanical properties of the stabilized/solidified matrix, were obtained when up to 100% of the powder activated carbon and up to 50% of the Portland cement were substituted by mechano-chemically activated fly ash, thus opening improved possibilities for using this latter in environmental applications.

Characteristics of coal fly ash and adsorption application

Several fly ash samples were collected and their physico-chemical properties were characterised using N 2 adsorption, XRD, SEM, and pH titration. These fly ash samples were applied as low-cost adsorbents for removal of methylene blue and humic acid from aqueous solution. It is found that the adsorption has a close relationship with surface area and pore volume. Higher surface area and pore volume of fly ash will result in higher adsorption of methylene blue (MB) and humic acid (HA). The adsorption of MB and HA on various fly ash samples can reach 7 and 10 mg/g, respectively. Solution pH will also influence humic acid adsorption on fly ash and higher pH will result in lower adsorption. Ionic strength will also influence HA adsorption.

Resource recovery from coal fly ash waste: an overview study

Coal fly ash (CFA) is a useful byproduct of the combustion of coal. It is composed primarily of almost perfectly spherical aluminosilicate glass particles. This spherical characteristic and other characteristics of CFA should be exploited, rather than simply using CFA as inert filler for construction. Unfortunately, the presence of carbon residues and high levels of heavy metals has so far limited the uses of CFA. Forced leaching methods have been used to improve the technical and environmentally friendly qualities of CFA, but these processes do not seem to be economically viable. Actually, CFA is a major source of Si and Al for the synthesis of industrial minerals. Potential novel uses of CFA, e.g., for the synthesis of ceramic materials, ceramic membrane filters, zeolites, and geopolymers, are reviewed in this article with the intention of exploring new areas that will expand the positive reuse of fly ash, thereby helping to reduce the environmental and economic impacts of CFA disposal.

Characterization of coal fly ash for possible utilization in glass production

The recycling of three different fly ashes obtained from the coal fired thermal power plants has been studied. Coal fly ashes were vitrified by melting them at 1773 K for 5 h without any additives. After the glass production, glass samples were subjected to a heat treatment process to be able to see whether or not the glasses could be transformed into a microcrystalline structured materials. Produced glass samples were heated to 1423 K and held at this temperature for 2 h to determine the effect of heat treatment process on the properties of glasses. The properties of glass and the heat treated glass samples produced from coal fly ash were investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. DTA study indicated that there were only inflection points of the endothermic peaks in the DTA curves of the glass samples. XRD analysis showed the amorphous state of the glass samples and also the presence of only the diopside phase in the heat-treated glass samples. SEM investigations revealed that small amount of crystallites occurred in the microstructure of the heat treated glass samples in contrast to the amorphous structure of the glass samples. The mechanical, physical and chemical properties of the heat-treated glass samples are found better than those of the glass samples. Toxicity characteristic leaching procedure (TCLP) results showed that the heavy metals of fly ashes were successfully immobilized into both glass and heat treated glass samples. It can be said that glass and heat treated glass samples obtained by the recycling of coal fly ash can be taken as a non-hazardous material. Overall, results indicated that the vitrification technique is an effective way for the stabilization and recycling of coal fly ash.

Analysis of arsenic and some other elements in coal fly ash by X-ray photoelectron spectroscopy

Surface characterization of coal fly ash (CFA) was carried out by use of X-ray photoelectron spectroscopy (XPS), especially focusing on the occurrence of As. A peak in the XPS spectrum of CFA was assigned to oxide forms of As(3d). The molar ratios of Al, As, Ca, Fe, and S normalized to Si were obtained from XPS analysis (MR-X). Also, the molar ratios of those elements were calculated from bulk analysis (total element concentration in CFA) (MR-B). The MR-X/MR-B ratio of As was much higher than those of other elements, suggesting that As is highly enriched on the surface of CFA. When eight CFA samples were analyzed, there was an approximate relationship between the MR-X values and MR-B values for As. The leaching of elements from CFA was examined by XPS analysis and by bulk analysis. The leaching tests using EDTA and HNO 3 resulted in a great decrease in the As(3d) peak area; the %leaching of As obtained by XPS analysis was almost equal to that by bulk analysis.

Influence of Soaking on Stress-Strain Characteristics of Fly Ash

Abstract A series of confined uniaxial compression (oedometer) tests and triaxial compression tests were conducted to study the influence of soaking on the stress-strain characteristics of coal fly ash widely used in Mainland China. The focus was on the collapsibility of fly ash with porous structure under different conditions, such as different relative density, initial water content, stress state, stress level, consolidation stress ratio, and soaking history. Main results of the test program are presented in this paper. It is determined that soaking collapsibility of fly ash depends on the relative density, initial water content, stress state, stress level, consolidation stress ratio, and soaking history, which the fly ash has experienced. The larger the relative density, the initial water content, and the consolidation stress ratio σ′3/σ′1 are, the smaller the soaking collapsibility is. The soaking collapsibility increases with stress level, which has a strong influence on the stress-strain characteristics of the fly ash.

99/02396 Characterization of coal fly ash from Israel

99/02396 Characterization of coal fly ash from Israel

Characterization of coal fly ash from Israel

The use of coal in electric power plants in Israel is relatively recent (1982). However, already in 1996, the Hadera and Ashqelon power plants had produced about 850 000 tons of fly ash. Most of it was used as an additive to clinker (cement). Nevertheless, because of the increase in electricity production, the amount of ash produced will increase proportionally. It is predicted that 1.2 million tons of coal ash will be produced by the year 2000. Since 800 000 tons of ash is the maximum that can be added to clinker under present legislation, this means that considerable quantities of ash (some 400 000 tons per year) will have to be used (apart from cement production) or disposed off without polluting the environment. As a consequence, a large national program was carried out in Israel to characterize coal ash produced in Israel and study the potential toxic effect of coal ash leachates on groundwater and soils. In particular, two compliance tests were studied: the European CEN/TC192 and the US TCLP 1311 methods. The results show that the TCLP 1311 method is more appropriate for testing the alkaline fly coal ash produced in Israel. The fine particles and particularly the very fine particles (<1 μm) in coal ash play an important role above their weight concentration because of their large active surface area. This is significant both for leaching and physical properties. We used computerized scanning electron microscope feature analysis to characterize these particles and to determine their distribution among the different small grain sizes in two industrial fly coal ashes. While the results are not quantitative, they add considerable knowledge to coal fly ash characterization.

Surface Chemical Characteristics of Coal Fly Ash Particles after Interaction with Seawater under Natural Deep Sea Conditions

The surface (0.2−0.5 nm) chemical characteristics of coal fly ash (CFA) before and after interaction with Mediter ranean deep seawater was studied by X-ray photoelectron spectroscopy (XPS). Significantly lower values of Si, Ca, and S and higher values of Mg and Cl were found in the retrieved CFA as compared to fresh CFA. It is suggested that hydrolysis of the oxide matrixes results in an alkaline environment which rapidly leads to several chemical reactions. The two most important are (a) dissolution of the amorphous silicate and the calcium phases and (b) precipitation of Mg(OH)2−brucite. A depth profile of the retrieved CFA was measured by both line-shape analysis of the XPS spectra and by consecutive cycle of sputtering. The thickness of the brucite layer is estimated to be 1.3 nm.