Original Fly Ash Research Articles

Dioxin distribution characteristics and health risk assessment in different size particles of fly ash from MSWIs in China

During the process of treating and recycling Municipal Solid Waste Incinerators (MSWIs) fly ash, polychlorinated dibenzo-p-dioxins (PCDD/Fs) and polychlorinated dibenzofurans (dl-PCBs) in fly ash may potentially mobilize in the atmosphere and be widely distributed in the environment because of the inevitable re-suspension. Thus, this work presents the distributions of PCDD/Fs and dl-PCBs in inhalable coarse particles (Dp10–2.5 (particle diameter in μm)), fine particles (Dp<2.5) of fly ash and original fly ash from four MSWI plants in China. The results show that PCDD/Fs and dl-PCBs preferentially concentrated in Dp10–2.5 and Dp<2.5. Their mass concentrations and TEQ were significantly higher than those in the original fly ash, but the distribution of PCDD/Fs congeners in Dp10–2.5 and Dp<2.5 was close to that in the original fly ash. The main TEQ contribution included 1,2,3,7,8-PeCDD, 2,3,7,8-TeCDD in PCDDs and 2,3,4,7,8-PeCDF in PCDFs for Dp10–2.5, Dp<2.5 fractions and the original fly ash. Furthermore, the mass and TEQ contribution of dl-PCBs was relatively low. In addition, compared with the fluidized bed, the samples from the grate-type furnaces had significantly lower dioxin concentrations. In terms of potential health risk, the non-carcinogenic risk of PCDD/Fs in Dp10–2.5 and Dp<2.5 were estimated at 9.87×10−1 to 4.81 and 1.19–7.95. For the carcinogenic risk of PCDD/Fs, both accumulation of Hazard Quotients (HQ) in Dp10–2.5 and Dp<2.5 exceeded the threshold limit and should be considered as unacceptable risk for onsite workers. The above findings could provide data to support the risk management of MSWI fly ash during the process of recycle and disposal.

Hydrothermal Synthesis of Sodalite on Alkali-Activated Coal Fly Ash for Removal of Lead Ions

Sodalite was prepared by Alkali fusion-desilication-hydrothermal method using fly ash as raw material and characterized by X ray diffraction and scanning electron microscope. In addition, the adsorption characteristics of Pb2+on the sodalite under different conditions were investigatedand the adsorption mechanism was studied by IRspectrum analysis. The results showed thatthe sodalitewith high crystallinity was prepared at the basicity of 2mol/L,crystallization time of 12 hours, and crystallization temperature of 90°C; The adsorption performance of sodalitehad significantly improved than the original fly ash, andit could effectively remove the Pb2+ with considerably lower dosage.; When initial concentration was 100mg/L and the dosage was 2g/L, the removal rate could exceed 99%; The improvement of the initial concentration were in favor of the increase of theadsorption capacity,but we should regulate the relationship between adsorptioncapacity and adsorption rateby adjusting the ratio of solid to liquid;. The adsorption capacity was increased with the increase of temperature and pH; Increasing ionic strength would inhibit the adsorption behavior.;The maximum adsorption capacity of 157.2mg/g was obtained by the Langmuir equation. Through infrared analysis, it can be inferred that the adsorption ofsyntheticsodalite is a physical adsorption. Now, research shows that thesodalite from fly ash has a remarkable removal effect on Pb2+. So, it can be used as an effective adsorbent for heavy metal disposal.

Chlorides Removal and Control through Water-washing Process on MSWI Fly Ash

Wet pretreatment is widely employed as the most economic method to treat municipal solid waste incineration (MSWI) fly ash. Meanwhile, much wastewater containing high concentration of chlorides generated during the wet process if the liquid-solid weight ratio was not appropriate. So measures were taken to control the dissolving amounts of calcium chlorides which contribute to the further reuse as basis with cement kiln and remove more chlorides like sodium chloride (NaCl), potassium chloride (KCl) and so on which produce negative impact. In laboratory experiments, the water-washing process was applied to study the typical MSWI fly ash and investigate the optimal parameters. First, multi-step water-washing process was carried out and key parameters influencing the removal rate of chlorides were determined. Then, cyclic water-washing process was conducted to overcome defects on the basis of the former. In this experiment, calcium hydroxide as a cheap and easily got chemical was added to affect the ionic equilibrium and solubility equilibrium associated with calcium. When compared with the original fly ash, calcium chlorides remained in the treated fly ash won’t be a huge loss while other chlorides are greatly reduced. Combined with the demand for raw materials of low chlorine in cement production, it's potential for MSWI fly ash after wet treatment to be applied in cement kiln when this ash in the cement kiln is at a lower rate of substitution.

Preparation of Fly ash Based Adsorbents for Removal Active Red X-3B from Dying Wastewater

Fly ash with a large number of active sites can occur with the adsorbent chemical and physical adsorption, and therefore have a strong adsorption capacity. The original fly ash and raw fly ash compared to the physical and chemical properties to a significant change. On the fly ash in industrial water treatment application were outlined. The purpose is to focus on the modification methods of fly ash and comparison of raw fly ash and fly ash in the effect of dyeing wastewater. Single factor test method; select the appropriate modifier to study the dosage, pH, stirring time on the modification of adsorption properties of fly ash before and after. The results showed that the modified fly ash was better than the adsorption. Greatly improves on active red X-3B dye wastewater removal capacity, pH = 5, 6, dosage is 5g / L, the mixing time is 30min, COD removal rate reached 73.07%. This modified material can be used as adsorbent for pre-treating dying wastewater.

Comparative study on the characteristics of ball-milled coal fly ash

High-energy mill (HEM) has a wide application in material preparation, activation and synthesis. In the present study, fly ash was selected to be milled by HEM under the speed of 700 rpm and the ball-to-powder ratio of 10:1 by weight, but varied periods of milling time. The changes in physical and morphology properties of the milled fly ash were determined using BET analysis and scanning electron microscope, those of chemical properties were determined using X-ray diffraction, mercury intrusion porosimetry and Fourier transform infrared, and their thermal properties were determined using thermogravimetric analysis (TG). The obtained data implied that the ball-milling treatment leads to reductions in both particle size and crystallite size of the milled fly ash, and also changes of their microstructural and functional groups, and loss of crystallinity. The milling time was found an important factor to impact extent of those changes. The large particles of the original fly ash regularly in an average of 5 μm were significantly broken down to much smaller particles (average diameter 300 nm), and the pore size distribution was also greatly changed by the ball-milling treatment and shown a close relevant to the milling time. Both patterns from FTIR and TG indicated the decrease in intensity of –OH stretching vibration peak and increase in peak widths of the ball-milled fly ash with the increase in the ball-milling time, implying along ball-milling time leading the ball-milled fly ash toward more amorphousness and likely the higher reactivity.

STUDY ON PROPERTIES OF FLY ASH REMOVED UNBURNED CARBON BY FLOTATION METHOD

When we use the fly FA-As a concrete admixture, it is known that the properties of the concrete improve. But when we made concrete with fly FA-Fresh property of concrete is adversely affected by unburnt carbon in the fly ash. If there are much quantities of unburnt carbon in the fly ash, they inhibit air entraining performance and fluidity of flesh concrete. So we developed the device removing unburnt carbon from the fly FA-By flotation method in previous studies. It was succeeded remove of unburnt carbon in the fly FA-And to clean the surface of the fly FA-By used the developed device removing unburnt carbon in the fly FA-By flotation method. In this study, it was purpose to confirm the change in the composition and physical properties between the original fly FA-And the reformed fly FA-By flotation method, and to grasp the effects that the physical properties of fly FA-Gave to the unburnt carbon removal when using flotation method. As a result, the specific surface area of reformed fly ash is larger than original fly ash. However, the change of chemical composition for reformed fly FA-By flotation method was as small as 4% at the maximum. It was considered that the addition rate of kerosene and pine oil and the pre-treatment time were changed by difference in sizes and shapes of unburnt carbon in the fly ash. Percent flow and activity index were influenced by the different of physical properties of original fly ash.

Investigation of mechanical properties and microstructures of aluminum-fly ash composite processed by friction stirring

An aluminum-fly ash (ALFA) composite comprising aluminum alloy ADC6 and 5wt% fly ash was produced by the stir casting method, and multipath friction stir processing (MP-FSP) was then applied to the composite. The microstructure of the processed area and the fracture surfaces of a tensile test specimen were investigated to determine the distribution of the fly ash in the aluminum matrix, the grain refinement, and the failure mechanisms. The experimental results showed that the grain of the composite was significantly refined by MP-FSP, with the original fly ash particle size of 53–106μm reduced to 10μm or less. Compared to the ALFA composite without stir processing, the tensile strength and elongation parallel to the direction of stirring were respectively increased from 143MPa to 227MPa and from 1.19% to 7.18%; whereas the same properties perpendicular to the stirring direction were respectively increased from 143MPa to 226MPa and from 1.19% to 3.12%. The presence of many rosette patterns and dimples on the fracture surface of the specimen clearly indicated that plastic deformation occurred in the composite after MP-FSP, resulting in recrystallization refinement and hence significant improvement of the mechanical properties.

Selected Properties Of Geopolymers With Different Portions Of Ground Fly-Ash

Abstract Geopolymers are polymeric materials resulting from the polycondensation reaction of alumino-silicate materials in a strongly alkaline environment. In consequence, stable polymeric networks of aluminosilicates are formed. The binding potential of FA (fly ash) amorphous component can also be “activated” by mechanical activation, which unfolds new possibilities of FA utilization. Mechanical activation, such as the method, which can improve FA reactivity, is often applied for different applications for geopolymers based on ground fly ash. This paper presents possibilities of preparation of geopolymer mixtures based on modified (ground) FA (TEKO – produced by the Heating plant Kosice), which was used in varying percentages to unground (original) FA. The particle size of the original unground FA (PVT) was 84.7μm and particle size of the ground FA (T60S1) was 52.8μm. Properties to be evaluated were selected from the expected application point of view – protective coating of concrete. Next properties of geopolymer mixtures after 28 days of hardening were tested and evaluated: dry density, absorptivity, capillarity, compressive and flexural strength.

Treatment of Cr(VI) WasteWater with Modified Coal Fly Ash

In this work, modified fly ash by Na2CO3 was prepared and used to remove the Cr (VI) in simulate wastewater, which was rarely reported in domestic and foreign. In the meantime, every single-factor experiment, which maybe influenced the removal ratio of Cr (VI), was done. The major-minor order of test factors and the optimum combination processing conditions influencing the treatment effects of Cr (VI) were determined according to the orthogonal experiment. The results showed that the major-minor order was initial concentration of Cr (VI), dosage of modified fly ash, adsorption duration, temperature and pH values. And the optimum combination of above discussed factors was 15 mg/L, 5 g, 90 min, 30 oC and 2.5, respectively. Under this optimum condition, the removal rate of Cr (VI) can reach more than 74.86%, approximately 1.35 times compared to that of original fly ash.

Leaching and indirect mineral carbonation performance of coal fly ash-water solution system

The leaching and carbonation performances of indirect mineral carbonation are investigated using coal fly ash (FA) as the raw source and water as the solvent. The reactions were conducted at ambient temperature and pressure with a gas mixture comprised of 15 and 33mol% CO2. The overall CO2 storage and mineral carbonation capacities of FA suspended solution in which alkaline components had been previously leached for 2h (2S33) were 31.06 and 17.36mg CO2/g FA, respectively. The mineral carbonation capacity of FA in 2S33 was 18% of the theoretical value and its mineral carbonation storage capacity ratio was 55.9%. The performance of 2S33 was higher than that of its filtrate because the alkaline components were leached from the suspended FA simultaneously with the mineral carbonation. Submicrometer-sized particles were present in raw FA and their size was reduced by stirring during the leaching, as well as slightly increased, compared to the original raw FA, due to the carbonation. These submicro FA particles strongly affected the performance of the mineral carbonation of the FA-water solution.

Formation and potential mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans on fly ash from a secondary copper smelting process.

Secondary copper smelting (SeCu) is widely considered to be an important source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs; PCDD/Fs). Laboratory experiments were performed using SeCu fly ash as a matrix for thermochemical reactions to investigate the effects of fly ash on the formation of PCDD/Fs and the potential mechanisms. Thermochemical reactions on SeCu fly ash over a temperature range of 250-450°C and reaction times of 10-120min caused the PCDD/F concentrations in the fly ash to increase significantly. The PCDD/F concentrations formed in the thermal reactions were about 99-139 times higher than the PCDD/F concentrations in the original fly ash, clearly indicating that fly ash promoted the formation of PCDD/Fs. The PCDFs dominated the PCDDs, and the PCDF/PCDD concentration ratio was about 30-40. Octachlorodibenzofuran (OCDF), octachlorodibenzo-p-dioxin, and the heptachlorodibenzofurans were the most dominant homologs that were formed. A comparison of the PCDD/F patterns produced in the thermochemical reactions and the patterns in the original fly ash suggested that the chlorination of less chlorinated PCDFs might be an important pathway in the formation of higher chlorinated furans. The results of this study indicated that SeCu fly ash has a high PCDD/F formation potential. It is crucial to have the fly ash filter at low temperature and that fly ash in the cooling system should be minimized.

Lead sorption performance on active silica derived from fly ash.

The object of this study was to estimate the sorption property of active silica derived from fly ash after separation of silica and aluminum. The specific surface area of active silica enlarged to 115 m(2)/g was compared with the original fly ash (4 m(2)/g). Field emission scanning electron microscopy displayed the active silica, which looked like a honeycomb or curly layer with many lamellae that formed many mesopores. The uptake kinetics indicated that the residual concentration of Pb(2+) in the aqueous solution decreased rapidly from the initial 1.25 mg/L to less than 10 μg/L within 45 min. The removal efficiency of Pb(2+) on active silica was pH dependent. The increase in pH value promoted Pb(2+) removal because the negative surface provided more electrostatic attraction sites. A stepwise non-linear isotherm was obtained because the lamellae of active silica provided a heterogeneous surface with various kinds of active sites. The maximum sorption amount of Pb on active silica was more than 90 mg/g, which was better than some pristine-activated carbon.

Preparation of high performance mullite ceramics from high-aluminum fly ash by an effective method

High performance mullite ceramics were prepared from high-aluminum fly ash without any extra materials via a series of steps. The original fly ash was pretreated with alkali and acid to adjust the chemical composition. Furthermore, the physical properties and phase transformation of the as-prepared samples at different sintering temperatures were systematically investigated. The results showed that by pretreated process, Al2O3 content can reach up to 65.35wt%, and most of the impurities were removed. The beneficiated sintering sample exhibited a mullite content of 88.33%, an apparent porosity of 1.20%, a bulk density of 2.78g/cm3 and a compressive strength of 169MPa, which was comparable with previous reports. All results indicate that high-aluminum fly ash, pretreated by an effective and feasible method, is suitable to prepare high performance mullite ceramics.

Vitrification of municipal solid waste incineration fly ash using biomass ash as additives

Thermal melting is an energy-costing solution for stabilizing toxic fly ash discharged from the air pollution control system in the municipal solid waste incineration (MSWI) plant. In this paper, two different types of biomass ashes are used as additives to co-melt with the MSWI fly ash for reducing the melting temperature and energy cost. The effects of biomass ashes on the MSWI fly ash melting characteristics are investigated. A new mathematical model has been proposed to estimate the melting heat reduction based on the mass ratios of major ash components and measured melting temperature. Experimental and calculation results show that the melting temperatures for samples mixed with biomass ash are lower than those of the original MSWI fly ash and when the mass ratio of wood ash reaches 50%, the deformation temperature (DT), the softening, hemisphere temperature (HT) and fluid temperature (FT) are, respectively, reduced by 189°C, 207°C, 229°C, and 247°C. The melting heat of mixed ash samples ranges between 1650 and 2650 kJ/kg. When 50% wood ash is mixed, the melting heat is reduced by more than 700 kJ/kg for the samples studied in this paper. Therefore, for the vitrification treatment of the fly ash from MSW or other waste incineration plants, wood ash is a potential fluxing assistant.

Effect of Mechanical Activation on Properties of Alkali Activated Binders

Effect of mechanical activation of fly ashes on strength of alkali activated binders is investigated. Four different kinds of fly ashes are mechanically activated. The aim of mechanical activation is to increase the reactivity of fly ashes. Mechanically activated fly ash is used as an admixture to the untreated original fly ash in proportion of 0, 50, 75 and 100 %. Fly ashes are alkali activated with solutions containing sodium hydroxide and sodium water glass. Compressive and flexural strength is tested on hardened alkali activated binders.

Mechanical and microstructural dissimilarities in alkali-activation for six Class F Korean fly ashes

This study presents the preliminary investigation for the microstructural characteristics of the alkali-activated fly ashes, synthesized using six different Korean Class F fly ashes, to address the large mechanical strength differences between the activated ashes using compressive strength testing, XRF, XRD, and SEM/EDS (YAG BSE, SE and elemental mapping). The results show that although the original fly ashes are not much different in XRD and XRF data, the reaction products after activation were dissimilar between the activated ashes. Particularly, the activated sample containing Al-rich chabazite produced much higher compressive strength than the other samples with zeolite A–Na. The SEM/EDS results exhibit that the activated fly ashes tended to have the higher compressive strengths as the reaction products possessed the lower Si/Al ratios down to one.

The experimental study of fly ash decarbonization on a circulating fluidized bed combustor

Fly ash is a by-product of coal-fired power plants, whose production is huge. As the coal resources are in short supply in recent years, most circulating fluidized bed (CFB) boilers in China burn hard coals, thus, the carbon content in the fly ash is much higher than expected. The high carbon content in the fly ash limits the potential utilization as building materials. At present, the decarbonization method of high carbon content CFB fly ash is mainly fly ash recirculation combustion (FARC). Because of the huge difference between original boiler operating conditions and fly ash ideal combustion state, the decarbonization effect is disappointed. Therefore, a series of fly ash decarbonization experiments were carried out on a bench-scale CFB combustor designed on fluidization properties of fly ash, and the decarbonization characteristics were discussed. Results show that fly ash requires a minimum sectional thermal load of 0.42 MW/m2 for continuous and stable combustion in test combustor, corresponding to the critical carbon content in the fly ash is 18%. The maximum decarbonization efficiency of the test CFB combustor is approximately 75%, which is much higher than that of FARC.

Experimental Study on Influence of Fly Ash on Mercury Removal in Flue Gas with UV Light

The original fly ash samples fetched from the power plant and the treated fly ash samples after screening, magnetic separation and mixing were used in the experiment of photocatalytic removal on mercury in flue gas. The fly ash samples and the absorption solution after experiment were tested for mercury content. The results showed that different sizes of the original fly ash had different characteristics of photocatalytic removal of mercury. The adsorption of mercury by fly ash was an important condition for the occurrence of photocatalytic effect. When the mercury adsorption capacity of fly ash was stronger, the capacity of photocatalytic removal mercury was also greater. The presence of iron oxide on the fly ash surface can promote the capability of photocatalytic removal of mercury by fly ash. The presence of ultraviolet light can significantly promote Hg0 oxidize to Hg2+ by fly ash. Thus the oxidized mercury in the flue gas can be easily absorbed by the solution.

Study of Solid Amine CO&lt;sub&gt;2&lt;/sub&gt; Sorbents Based on the Modified Fly Ash

In this paper, coal fly ash was modified by the hydrothermal synthesis method based on sodium hydroxide solution, and then was macerated by ethanol amine. Then we obtained the solid amine adsorbents used to absorb CO2. The modified fly ash was investigated by scanning electron microscope (SEM) and the specific surface area analyzer (BET) for the microstructure and specific surface area. Then, the solid CO2 adsorbent was analyzed by fourier transform infrared spectrometer (FT-IR) and thermal analyzer (TGA) in CO2 atmosphere. Results showed that modified fly ash generated many kinds of zeolite material by the SEM and the BET analysis, greatly increasing the specific surface area, improved the adsorption capacity. FT-IR analysis that the surface of solid amine CO2 adsorbent with amine groups; TGA analysis that compared with the original fly ash, CO2 adsorbent by this paper made has the capability of adsorption of CO2.

High Strength Geopolymers Produced from Coal Combustion Fly Ash

High strength geopolymers were produced from coal combustion fly ashes. These matrices reached compressive strength values over 100 MPa, much stronger and denser than obtained by using Portland Cement binders. Size fractions were obtained by size separation techniques and the relationship between strength and particle size was investigated. The differences in compressive strength measured in the geopolymers made from fine fractions, the original fly ash and a coarse fraction of the same ash, were not significantly higher than the variation found for a reference geopolymer material. Therefore, a direct size-strength relationship could not be proven. Moreover, the chemistry and the pH of the fractions also varied, and this might as well has played a role in the strength development.