Metals In Fly Ash Research Articles

Coal beneficiation technology to reduce hazardous heavy metals in fly ash

Fly ash emitted from the coal-fired power plant is the major contributor of the outdoor airborne particulate matters (PMs). Coal beneficiation, an industrial process to improve the quality of raw coal by removing ash-bearing components, can be a cost-effective sustainable and clean technology to reduce the emission of hazardous trace metals. As the removal efficiency of mineral matters and heavy metals within the coal is depend highly on the raw coal and the employed beneficiation process, a wide range of case studies at laboratory- and industrial-scale, published in the last 20 years, are reviewed in this study. Our review indicates that the coal beneficiation processes can effectively reduce content of heavy metals of fly ash, encouraging the use of clean coal to reduce pollutants emission.

Experimental study on the stabilization of heavy metals in fly ash from municipal solid waste incineration by N-30 alkaline silica sol

The disposal of municipal solid waste incineration fly ash is a key environmental issue in China. The high content of heavy metals in fly ash makes ash disposal extremely difficult. A new method which binds N-30 alkaline silica sol and temperature was proposed for the first time in this study. The crystal composition and the patterns of heavy metal leaching concentration and speciation in fly ash were obtained via experiments. The results showed that adsorption of the self-made curing agent and the formation of metal silicate and phosphate promotes the migration of heavy metals from an unstable acid state to a stable residue state, thus improves the stability of heavy metals. The optimum temperature of self-made N-30 alkaline silica sol during treating process is about 700℃. Moreover, the risk assessment of heavy metal emission has proved that, the leaching amount of heavy metals after treatment reaches a risk-free level.

Residual and ecological risk assessment of heavy metals in fly ash from co-combustion of excess sludge and coal

Co-combustion of municipal excess sludge (ES) and coal provides an alternative method for disposing ES. The present study aims to investigate the residual and ecological risk of heavy metals in fly ash from co-combustion of ES and coal. The total concentration and speciation distribution of heavy metals, characterization of SEM, EDX, XRD and leaching test were carried out to assess the fly ash in this study. The results showed that the total concentrations of Cu, Zn and Mn were higher than others in fly ash, and most heavy metals were concentrated in fine particles. For Cd, Cr and Pb, the percentages of speciation of F4 and F5 were all over 90%, suggesting the relatively lower leaching toxicity. The leaching percent of all heavy metals was lower than 5% by two diluted HNO3 solutions for fly ash. The potential ecological risks increased with the decrease of particle size of fly ash, and Cd accounted for the main fraction for ecological risk despite of lower concentration in comparison to other measured heavy metals.

Assessment of heavy metals mobility and correlative recovery and decontamination from MSWI fly ash: Mechanism and hydrometallurgical process evaluation

Fly ash from municipal solid waste incineration (MSWI) enriches many leachable toxic metals which readily migrate into the environment, posing serious risks to the ecosystem and human. In this study, the elements mobility, leaching availability as well as the potential maximum amounts of heavy metals in fly ash were thoroughly evaluated. To decontaminate the toxic elements from resulting fly ash leachates, The aqueous zinc (Zn) was recovered using Cyanex 572, cadmium (Cd) and copper (Cu) were effectively removed through adsorption process by a self-assembled hierarchical hydroxyapatite (HAP) nanostructure. The removal mechanism of Cd, Cu and Zn by leaching, extraction and adsorption was revealed with the results from XRD, ICP-MS and SEM. The results showed that fly ash has a high mobility under maximum availability leaching test (95% of fly ash was dissolved), a recovery rate of 91% for Zn can be obtained using Cyanex 572, and a high adsorption rate (> 95% for both Cu and Cd) was reached using HAP for the pristine fly ash leachate. The outcomes from isothermal and kinetic study revealed that Langmuir isotherm and pseudo-second order model can well describe the Cd and Cu adsorption behavior. Economic assessment suggested that the application of HAP for the removal of Cd and Cu is a technically sound and economically feasible approach. The findings of this study demonstrated that this comprehensive process integrated leaching, solvent extraction and consequential decontamination can be a practical strategy for MSWI fly ash treatment.

Formation Characteristics of PCDD/Fs in the Co-combustion and Pyrolysis Process of Coal and Sewage Sludge

ABSTRACT Co-combustion technology of coal and sewage sludge (SS) was encouraged and recommended in China. Previous studies most focused on its influence on combustion characteristics, migration characteristics of heavy metals in fly ash, and emission of conventional pollutants, etc., but less reported the formation characteristics of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs). To well reveal it, this study carried out five parallel experiments, including the pyrolysis of SS, the combustion of SS, the co-combustion of coal and SS with the proportion of 0%, 2.5% and 5%, respectively. The emission concentration of PCDD/Fs respectively increased from 0.42 ng g–1 (0.0022 ng I-TEQ g–1) to 0.54 ng g–1 (0.0030 ng I-TEQ g–1) and 1.70 ng g–1 (0.0305 ng I-TEQ g–1) with increasing blending proportion of SS. The dominant part was also changed from PCDF (0.32 ng g–1 in M-0%, 0.38 ng g–1 in M-2.5%) to PCDD (1.11 ng g–1 in M-5%). The formation concentration of PCDD/Fs in the combustion process of SS was about 0.34 ng g–1 (0.0019 ng I-TEQ g–1). In the pyrolysis process of SS, the concentration of PCDD/Fs was 0.59 ng g–1 (0.0037 ng I-TEQ g–1). The de novo synthesis should be the major formation pathway of PCDD/Fs in the co-combustion process of coal and SS. On the basis of sufficient carbon sources, the PCA analysis revealed the chlorine source (Cl) and metal catalyst (Fe) should contribute a lot on the formation of PCDD/Fs. The results paved the way for further optimization on the operation of co-combustion of coal and SS and assist in controlling the PCDD/F emission from co-combustion process.

Efficiency of burning sediments of waste water in a boiling layer

It has been experimentally shown that the Metso HYBEX steam boiler installed at CHP-1 of JSC APPM and designed to burn a mixture of bark and wood waste and sewage sludge ensures their efficient utilization without highlighting fuel oil. At boiler loads close to the nominal efficiency, the gross value was 85.22–85.24%. The environmental indicators of the boiler unit fully and even with a margin meet the requirements established by directive 2010/75 / EC and GOST R 50831-95. The operation of the boiler ensured the complete utilization of sewage sludge generated at the sewage treatment plant. The annual savings of fossil fuels amounted to more than 80 thousand tons of fuel equivalent. The total content of heavy metals in fly ash emitted into the atmospheric air by a recycling and energy boiler with a bubbling fluidized bed when burning high-moisture biofuels is many times lower than when burning coal, even in low-emission furnaces.

Optimization of wear behaviour of AA6061 – SiC – B4C – Fly ash metal matrix composite using response surface methodology

The usage of Aluminium metal matrix composite (AMMC) is found in all engineering applications but now particularly it is used as an replacements of traditional metals in the field of defence, automobile, aerospace and under-water applications for socio-economical betterments. To enable this AMMC should have a wide range of mechanical properties which may require to have mutually exclusive properties at an optimal level. This paper discusses about the study of AA6061-SiC-B4C-Fly ash composite made by using stir casting process. The casted samples are then prepared for wear tests and the tests are performed by using pin-on-disc apparatus without any lubrication. Two samples are made with different compositions of Silicon carbide and Boron Carbide along with a constant amount of fly ash. The combination sequence in which the levels of each process parameters like load, sliding speed and sliding distance are to be kept for each experiment are sequenced and designed by using Response Surface Methodology (RSM). The observation is that the reinforcement of Al 6061 alloy with SiC, B4C and fly ash is having an influential impact on the wear loss of the AMMC. The incremental raise of SiC and B4C from 5 g each to 10 g each reduces the wear loss of casted composite about 28.03% at optimum operating conditions and at the same time the specific wear rate of the casted samples falls over 10%. This indicates that the addition of SiC and B4C results in improved wear resistance of AMMC.

순환유동층 연소로에서 하수슬러지/목질계 바이오매스 혼합펠릿의 연소: 오염물질 저감을 위한 산화제 변화 영향

Combustion experiment for pellets of sewage sludge and woody biomass blend was conducted in a pilot-scale circulating fluidized bed combustor (CFBC) consisting of the riser, two hot cyclones and a loop-seal to reduce pollutant emission in exhausted flue gas. To achieve them, the effect of the oxidant variations, such as superficial velocity, equivalence ratio(ER: 1.2, 1.3, 1.4) and combustion atmosphere (air-fired and oxy-fired) was evaluated. As pollutant emissions in flue gas, SO₂, NO, CO, CO₂, HCl, odor contaminants and leaching behavior of heavy metals were analyzed. As a result, to stably operate combustion of pellet mixed with sewage sludge and woody biomass as alternative renewable fuel in a CFBC system, the superficial velocity in the riser had to be kept under 6 m/s and the equivalence ratio was proper around 1.3-1.4. All odor contaminants formed at these operating conditions met the domestic air pollutant standards. Heavy metals in fly ash met the environment ministry’s standard. Additionally, compared to air-firing, SO₂, NO and CO as precursors of fine particles during oxy-firing were reduced by 70.8, 77.1 and 38.2%, respectively.

The poisoning mechanisms of different zinc species on a ceria-based NH3-SCR catalyst and the co-effects of zinc and gas-phase sulfur/chlorine species

Low-medium temperature NH3-SCR technology has been applied for years in municipal solid wastes incineration (MSWI) to control the emissions of nitrogen oxides. Unlike coal-fired flue gases, the tail gas from MSWI contains high levels of heavy metals in fly ash, especially the zinc species, which may harm SCR catalysts. As such, in this paper, the deactivation mechanism of different zinc species (ZnO, ZnSO4 and ZnCl2) on the Sb-CeZr2Ox catalysts and the co-effects of zinc species and gas-phase pollutants (including SO2 and HCl) were investigated. The experimental results indicated that the deactivation rate of various poisoning zinc species was in the order of ZnCl2 > ZnSO4 > ZnO. Moreover, the interactions between zinc and antimony species would disrupt the structure of the Sb-Ce mixed oxides to decrease the redox ability, consequently suppressing the ammonia activation and NO adsorption. Furthermore, such damaging effects on catalyst structures would promote the formation of bulk-like sulfate species in the presence of SO2, resulting in a decreased mobility of surface oxygen species, which significantly decrease the sulfur resistance. However, the presence of HCl did not show an evident co-effect on the Zn poisoned sample owing to the limited coverage of the chlorine deposition.

Phytoextraction of heavy metals from coal fly ash for restoration of fly ash dumpsites

This study reports the efficiency of Saccharum spontaneum and Saccharum munja for phytoextraction and phytostabilization of metal-contaminated coal fly ash (FA) dumpsites. Pot experiments with FA and garden soil (GS) as control were conducted for a period of one year. Heavy metals in FA and their relative translocation to root and shoot tissues were analyzed. The accumulation of heavy metals in the roots was higher than the shoots. A considerable amount of heavy metals was sequestered and accumulated by the roots but the amount of contaminants was not translocated to the shoot system. This could be supported by the translocation factor (TF) values. Values of bioaccumulation factor (BAF) greater than unity indicated that Saccharum is a potential heavy metal accumulator. The BAF values for roots in S. spontaneum plants grown on FA were higher (8.01, 1.40, 3.02, 0.92, 1.66 and 1.47 for Zn, Pb, Cu, Ni, Cd and As, respectively) than those of S. munja (Zn – 8.54, Pb – 1.66, Cu – 3.24, Ni – 0.76, Cd – 1.63 and As – 1.41). The BAF of the metals was less than unity in shoots. This is congruent with the results on DNA damage that increased significantly in the root cells and remained unaffected in the shoot. Results suggest that the plants are suitable for extracting Zn, Cu, Cd, Pb and As from FA and stabilize them in the underground plant parts. Therefore, for long-term management and restoration of FA, use of Saccharum plants for phytoremediation will be an effective strategy.

Physical and Chemical Properties, Pretreatment, and Recycling of Municipal Solid Waste Incineration Fly Ash and Bottom Ash for Highway Engineering: A Literature Review

Municipal solid waste incineration (MSWI) has been widely used due to its benefits in reducing waste and recovering energy. However, MSWI fly ash and bottom ash are increasing rapidly, causing harm to human health and the environment. This paper discussed the production process, physical and chemical properties, leaching properties, pretreatment methods, and applications of fly ash and bottom ash. By summarizing the previous literature, it is found that MSWI fly ash and bottom ash have mechanical properties similar to natural aggregate. Many beneficial attempts have been made in cement concrete aggregates, ceramic raw materials, and highway engineering materials. Due to concerns about the leaching of heavy metals in fly ash, its application in highway engineering is limited. The application of bottom ash in asphalt pavement is rare because of the side effect on the performance of asphalt mixture. Considering the solidification effect of cement on heavy metals and the low cost of fly ash and bottom ash, the application in cement‐stabilized macadam base has broad application prospects. This is beneficial to reduce the construction cost and promote the process of waste incineration, especially in developing countries.

The heavy metal leaching property and cementitious material preparation by treating municipal solid waste incineration fly ash through the molten salt process.

This research investigated the heavy metal leaching property and cementitious material preparation by treating municipal solid waste incineration fly ash through the molten salt process. The results indicated that the heavy metal thermal evaporation of fly ash in the molten salt was related to molten salt composition, heat treatment temperature and atmosphere. After treatment with sodium chloride molten salts (contains 10-50 wt% calcium chloride) from 900°C to 1000°C for 2 h, the leaching concentrations of lead, cadmium, copper, zinc and other heavy metals in fly ash were decreased more than 90% and they could fully meet with the landfill standard. Moreover, after molten salt treatment, the weight fraction of fly ash was reduced by 50 wt% than the original one, and the fly ash has been changed as a kind of cementitious material, which has excellent cementitious property. The X-ray diffraction result indicated that the main crystal mineral composition of cementitious materials obtained was alite, belite, alinite and calcium sulphate.

Mineralogy Characteristic Study and Exploration on the Valuable Metals Enrichment of Coal Fly Ash

The separation and enrichment can be targeted to enrich in fly ash and reduce the cost of leaching and recovering of fly ash. Regarding their different properties, the single-component separation was used to obtain uncompleted burned carbon, glass microbeads, minerals, and other characteristic components from the ash. Also, the mineral composition of each component was analyzed by electron microscopy. The metal minerals were mainly concentrated in the mineral components. Besides, the electron probe microanalysis shows that the Pt content in the minerals of fly ash was significantly correlated with the metal contents of Ni and Cu. After the obtainment of the characteristics of fly ash metal enrichment, the heavy minerals with Cu, Ni, Pt, Pd, and other target metal elements were enriched by gravity separation and flotation. The enrichment coefficients of Cu, Ni, Pt, and Pd were 1.45, 1.33, 1.90, and 1.60, respectively, and the recovery rates were 77%, 81%, 97%, and 88%, respectively. Since the yield of heavy minerals obtained by separation was 62.24%, it indicated the physical separation method could significantly reduce the cost of leaching and recovering of fly ash metal resources.

Characteristics of geopolymer hybrid concrete in peat water

Geopolymer hybrid is a combination of geopolymer and Ordinary Portland Cement (OPC) or other binders to produce an alternative binder. This type of binder could be used to transform low-quality fly ash into multi-purpose concrete. Ordinary Portland Cement (OPC) concrete subjected to an acidic organic environment such as peatland, is more prone to deterioration in long-term than concrete using the supplementary cementitious material. In this research, the geopolymer was made by activating low-quality fly ash (contains more than 5% carbon) with the alkaline activator. The inclusion of OPC and Portland Cement Composite (PCC) as a fly ash replacement material is intended to promote curing at ambient temperature and immobilization of heavy metals in fly ash. The specimens were cast and cured at ambient temperature up to 28 days. OPC was used as a control mix. Subsequently, the concrete was immersed in fresh peat water in the laboratory up to 28 days. Characteristics of the geopolymer hybrid such as compressive strength, porosity, and leaching were determined. Microstructure analysis, such as SEM-EDX and FTIR, were conducted. Results show that the geopolymer hybrid has a good strength development at early days. At 28 days, there was a reduction of strength and increase of porosity, probably due to the attack of calcium from the OPC concrete. There was a transformation of aluminosilicate gel into C/N-A-S-H that is advantageous for the strength development at the early days. However, a weaker material has formed in the long term that cannot resist further acid attack. It can be concluded that the geopolymer hybrid is a promising binder, but it is essential to design the material appropriately to have better strength, durability and environmental properties in the long term.

Investigation of controlling factors on toxic metal leaching behavior in municipal solid wastes incineration fly ash.

Municipal solid wastes incineration (MSWI) fly ash has drawn worldwide attention for its substantial annual generation capacity and high toxic metals leachability. Although many factors have been shown to affect the leachability of metals in fly ash, the controlling factors, which guide the selection of appropriate risk reduction method, remain unclear. The purpose of this study was to evaluate the effects of the two most important factors, total metal content, and remaining alkaline substances of MSWI fly ash, on the leaching behavior of toxic metals. In this work, a series of leaching tests and sequential extraction procedures were performed for seven fly ash samples collected from one MSWI plant. Results show that particulate size distribution, morphology, and mineralogy of all samples are similar, indicating the effects of these properties on metal leaching behavior can be ignored. In leaching tests, although the leaching behavior in terms of metal species and concentration levels vary as expected, only the leachate Pb concentration in four samples (up to 17.32 mg/L) exceeds the threshold in Chinese regulation (0.25 mg/L). The variation of the leachate Pb concentration is not consistent with the change of the total Pb concentration in fly ash. Further correlation analysis evidences that the acid-soluble Pb, which is highly correlated to the calcium content of fly ash, dominates the concentration of leachate Pb. Notably, when the addition of lime is about 1.5 times over the theoretical value, the concentration of leachate Pb would exceed the threshold regardless of the total Pb concentration in fly ash. Overall, this study demonstrates that the remaining alkaline substances (mainly calcium-bearing compounds), rather than the total content of metals, are the controlling factor of metal leaching behavior in fly ash. Thus, strategies to delicately optimize the quantity of lime addition in acid gas purification process should be considered to minimize MSWI fly ash environmental risks in the future.

Mechanochemical stabilization of heavy metals in fly ash with additives

Mechanochemistry, as a non-thermal method showing remarkable degradation for persistent organic pollutants, is extended to stabilize the heavy metals in municipal solid waste incineration (MSWI) fly ash in the present study. The leaching suppression of heavy metals (i.e., Zn, Pb, Cu, Cr, Cd, and Ni) facilitated by five additives during mechanochemical (MC) treatment is systematically investigated, identifying that almost all heavy metals are effectively suppressed with the assistance of either CaO or Ca3(PO4)2. The pH-dependent leaching test further reveals the superiority of Ca3(PO4)2 over CaO for heavy metals stabilization. Moreover, the evolution of heavy metal speciations analysed via an optimized sequential extraction procedure shows that MC treatment with Ca3(PO4)2 significantly reduces the water- and acid-soluble fraction with high mobility from 56.8, 1.39, 12.3, 8.46, 1.13, and 29.5% to 4.96, 0.17, 0.14, 7.36, 0.12, and 0.22%, respectively for Cd, Cr, Cu, Ni, Pb, and Zn. The risk assessment indicates remarkable detoxification of fly ash in terms of heavy metals after MC treatment: the Nemerow pollution index is dramatically decreased from 9.35 (far above 3.0- the threshold of seriously polluted domain) to 0.71 (slightly over 0.7- the threshold of safety domain). Finally, a hypothetical mechanism according with results in this study for MC stabilization of heavy metals in fly ash is proposed as: the conversion of heavy metal compounds from mobile to immobile form through reaction with additives after activated by mechanical energy.

Research on a closed-loop method that enhances the electrokinetic removal of heavy metals from municipal solid waste incineration fly ashes

The high leachability of heavy metals and toxic organic components has severely discouraged the broader resource recycling of municipal solid waste incineration fly ashes. In this study, a recycling system combining water washing treatment, cationic buffer solution recovery, and electrokinetic remediation was designed based on pH controls and comprehensively explored in terms of strengthening the removal of heavy metals from samples and reducing the risk of environmental leaching of heavy metals in fly ashes. The water washing pretreatment removed a considerable amount of soluble minerals from the fly ash and lowered the initial pH of the electrochemical system to below 10. The dosing of buffer cations decreased the thickness of the diffuse double layer and ameliorated the mobility of the heavy metal species in the pore fluid. Cu was most sensitive to the changes in the operating factors during electrokinetics. The effects of the remediation times and voltage gradients were more significant on heavy metal removal than those of the nitric acid concentration in the electrokinetic optimization system. The leaching toxicities of zinc, lead, copper, and cadmium were reduced by 82.59%, 73.64%, 67.07%, and 93.13%, respectively. Generally, the recovery of the water washing leachate not only enhanced the performance of the electrokinetic remediation for the municipal solid waste incineration fly ash but also avoided downstream disposal of the effluent.

Preliminary screening of wood biomass ashes for partial resources replacements in cementitious materials

Worldwide there is a significant increase in amounts of wood biomass ash (WBA), a waste from wood biomass combustion process. In this case study, 21 different sources of wood biomass ash (WBA), namely fly ash, bottom ash, and mixed ash from 10 different power plants in the Republic of Croatia were characterised based on their physical-chemical properties. Compared to the criteria listed for the use of coal fly ash in the concrete industry (EN 450), most WBAs exhibit higher loss of ignition values, high CaO and MgO contents, and higher total alkali and sulfur content. The results show a higher amount of alkalies and heavy metals in fly ash (WBA-F) as compared to bottom ash (WBA-B), but also their potential stabilisation in glassy phases. Based on WBA characterisation results, collected WBAs were benchmarked and categorised for three different resource replacements in production of cement and concrete: 1) partial replacement of a raw material for clinker production; 2) partial cement replacement as a mineral admixture in cementitious composites, and 3) partial replacement of aggregates used for concrete production. For this a new method for WBAs quality-ranking ordering is proposed, based on a normalisation approach relative to some quality criteria. The proposed preliminary screening methodology enables to address an important technological challenge in high variability in quality parameters of WBAs originating from many different sources. It will help engineers in selecting from the huge number of available WBAs types the most suitable ones, on which further valorisation laboratory tests can be better planned.

Characteristics and speciation of heavy metals in fly ash and FGD gypsum from Chinese coal-fired power plants

This research focused on the distribution and chemical speciation of Cr, Pb, Cd, Cu, Zn, and As in fly ash and flue gas desulfurization gypsum (FGD gypsum) from a large-scale pulverized coal-fired (PC) power plants in Anhui Province of eastern China. The partitioning behavior of the heavy metals (HMs) revealed that trace metals were mainly retained in coal combustion ash (88.9–98.7%) and FGD gypsum (1.26–4.33%). Other fly ashes generated from different PC boilers and a circulated fluidized boiler (CFB) were collected to comparatively study the ash mineralogy and chemistry. The PC fly ashes were dominated by glassy materials including cenospheres, pleiospheres, ferrospheres, solid spheres, and Fe-bearing spinel, while irregular glassy particles and unburned carbon were observed in the CFB ashes. The results of SEM-EDS found that PC ash mainly consisted of <100-µm-diameter aluminosilicate spherical particles. In contrast, CFB ash was primarily comprised of fine irregular Al-Si-Ca-O agglomerates. FGD gypsums, occurring as large flaky crystals, were primarily composed of CaSO4·2H2O with minor quartz and calcite. According to the sequential chemical extraction procedure, the amount of HMs occurring as oxidizable associations of fluidized ash was higher than that of PC ash, which might be associated with the lower flame temperature in CFB boiler. The percentage of Cr (43.1–53.2%), Cu (79–87.8%), Zn (67.8–89.6%), and As (64.5–75.6%) as effective fraction was notably higher in FGD gypsums compared with fly ashes. The leaching tests revealed that all combustion residues were non-hazardous materials. The RACs (risk assessment codes) of Cr, Pb, Cd, and As in fly ashes indicated that they posed no risk or low risk to the ecosystem, while the HMs in all FGD gypsums showed a medium risk or high risk to the ecosystem. Therefore, the reuse of FGD gypsums should be carefully evaluated since the environmental stability of HMs in gypsums was weaker compared with fly ashes.

A Study of Ferrospheres in the Coal Fly Ash

Coal fly ash is an industrial by-product, produced from coal combustion in thermal power plants. It is the most complex anthropogenic materials, which consists of combination of minerals originated from different sources. Coal fly ash and its byproduct has become an environmental concern over the World. Therefore, there is a pressing and ongoing need to investigate the structures and some properties of coal fly ash and develop new recycling methods for it. The amount of silica, aluminum, calcium, potassium, magnesium, sodium, titanium and phosphorus oxides contained in power plant fly ash was determined by X-ray flouresecence (XRF) analysis. Concentration of heavy metals in fly ash was in sequence of Pb > Zn > Cu > Cr > Ni. As results of Scanning Electron Microscopy (SEM), except for porous and hollow particles, large and small microspheres were observed. These particles are classified as ferrospheres. X-ray diffraction (XRD) analysis show that fly ash consists of the following crystal phases: quartz, albite, anorthite and hematite.