Metals In Fly Ash Research Articles

Development of a Novel Aluminium Based Metal Matrix Composite using Insitu Ternary Mixture (Al2O3-SiC-C) Prepared by Thermal Treatment of Fly-ash

In the present investigation a new ternary ceramic matrix composite is developed from Indian fly ash by thermal treatment under reducing atmosphere. The ternary mixture, comprising of Al2O3-SiC-C, is formed by insitu conversion of SiO2 to SiC in the fly ash under reducing atmosphere. Analyses of the treated product by XRD, SEM, and EDAX have ensured formation of SiC from SiO2. Converted SiC are rod shaped whiskers with the aspect ratio ranging between 40 to 50. The ternary mixture is added to aluminum melt in a bottom pouring pit type resistance furnace for the preparation of novel aluminum fly ash metal matrix composite (ALFMMC). Physical and mechanical properties of the novel ALFMMC (treated fly ash) composite are evaluated. For comparison purpose, aluminum fly ash composite is prepared with (untreated flyash) under identical condition of melting and casting. Wear resistance is found to be superior for the novel composite.

English

Metal matrix composites [MMC] are most important materials used for recent works in the industry and engineering applications. Fly ash particles are used in metal matrix composites are low cost, low density and available in large quantities of waste byproduct in power plants. The adding of fly ash with aluminium reinforcement by using stir casting process it can reduces the cost and density of aluminium material. Metal composites pocesses are improved thermal properties like thermal expansion, thermal cracking, thermal resistance compared to other metals. In study an aluminium and fly ash chemical analysis. Hence, to study the composites in fly ash with aluminium reinforcement in physical and thermal properties of aluminium-fly ash metal matrix composite. In this aluminium fly ash metal matrix composites are widely used in the aerospace craft and automotive application.

Elastic Plastic Fracture Toughness Of Aluminium Alloy AA6061 Fly Ash Composites

Aluminium fly ash metal matrix composites (MMCs) find important applications in aerospace and automobiles where specific stiffness is important. Low cost fly ash and silicon carbide reinforcement are widely used in aluminium metal and matrix composite due to its low density, high young modulus and strength apart from good mechanical and chemical compatibility & thermal stability. However the MMCs often suffer from low ductility, toughness and fatigue crack growth resistance relative to the matrix alloy. Linear elastic fracture mechanics (LEFM) has been used to characterize the plane strain fracture toughness using various specimen geometries and notches but very few studies using EPFM are reported in literature. In the present paper the influences of weight fraction of particulate reinforcement on tensile, fracture toughness have been evaluated. The tensile strength of aluminium fly ash composites increases with the addition of fly ash reinforcement. However the fracture toughness (KIC) of the aluminium fly ash composite decreases that of base alloy. The fracture toughness KQ of AA6061 ALFA composites varied between 13-14 MPa/m as compared to 18 MPa/m for the re-melted base alloy. Similarly the Elastic plastic fracture toughness JQ for the base alloy AA6061 lies is the range of 20-23 kJ/m 2 and that of composites in the range 6-16 kJ/m 2 . The fracture behavior and micro-mechanism of failure in base alloy and composites have been observed under SEM and optical microscopy.

Heavy metal speciation in various types of fly ash from municipal solid waste incinerator

Fly ash (FA) from municipal solid waste incinerators has been known as hazardous waste, which is mostly because of the high content of heavy metal and dioxins. Besides the content, the form of the heavy metals in fly ash is also very important, because it is tightly related with the leaching behavior of fly ash in diverse circumstances. To evaluate the environment potential risk of fly ash, the Tessier chemical extraction method was adopted. In this study, four kinds of fly ash were examined, one sample from China (CFA) and the other three from Japan (RFA, CaFA and NaFA). Five metal elements were detected and they were Ni, Cr, Cd, Pb, and Cu. The result of total heavy metals’ concentration showed CFA has the lowest content. As to the Tessier chemical extraction experiments, the results show that Cd, Pb, and Cu have higher leaching risk in the environment than other heavy metals. The result of leaching test experiment showed that the more exchangeable speciation of Cd, Cr and Pb in FA, the more it could leach out in natural environment.

Characteristics of Melting Incinerator Ashes Using a Direct Current Plasma Torch

Fly ashes both from municipal solid waste incinerator (MSWI) and medical waste incinerator (MWI) are classified as hazardous materials because they contain high amounts of heavy metals. In present these contaminant ashes have become a major environmental problem. In this study, we determine the ability of these contaminating heavy metals to be incorporated into a glass-matrix and in various mineral phases after a high temperature melting process using a direct current plasma torch. After the melting process, the leaching characteristics of heavy metals in fly ash and vitrified slag were investigated using the toxicity characteristic leaching procedure (TCLP), and the products also were characterized by X-ray diffractometry (XRD) for crystal structure determination, and scanning electron microscopy (SEM) for microstructure/morphology observation. After vitrification, there were prominent changes in microstructures and crystalline phases between produced slags and raw ashes. TCLP results indicate the leaching level of heavy metals in slags decreases obviously and additives such as silica and liquid ceramic (LC) contribute to high effect on immobilization of heavy metals in a host glass matrix.

Organic Complex Chelators for Stabilization of Heavy Metals in Fly Ash

The organic complex chelators (OCC) were synthesized and applied to stabilization of heavy metals in fly ash according to the municipal solid waste landfill pollution control standard. The influences of different chelators, amount of chelator, pH value of leaching, solidification time were investigated and optimized. Comparing to the traditional inorganic chelator, this OCC has more powerful performance of stabilization. Under the optimized conditions, the leaching concentrations for typical heavy metals Pb and Cd were less than 0.19 and 0.11 mg/L, respectively, which could meet the demand of landfill. The organic complex chelators could react with heavy metals to form stable complexes, which would be embedded in fly ash particles and have the strong ability to prohibit leaching from acidic environment.

Detoxifying PCDD/Fs and heavy metals in fly ash from medical waste incinerators with a DC double arc plasma torch

Medical waste incinerator (MWI) fly ash is regarded as a highly toxic waste because it contains high concentrations of heavy metals and dioxins, including polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Therefore fly ash from MWI must be appropriately treated before being discharged into the environment. A melting process based on a direct current thermal plasma torch has been developed to convert MWI fly ash into harmless slag. The leaching characteristics of heavy metals in fly ash and vitrified slag were investigated using the toxicity characteristic leaching procedure, while the content of PCDD/Fs in the fly ashes and slags was measured using method 1613 of the US EPA. The experimental results show that the decomposition rate of PCDD/Fs is over 99% in toxic equivalent quantity value and the leaching of heavy metals in the slag significantly decreases after the plasma melting process. The produced slag has a compact and homogeneous microstructure with density of up to 2.8 g/cm3.

Thermal and hydrometallurgical recovery methods of heavy metals from municipal solid waste fly ash

Heavy metals in fly ash from municipal solid waste incinerators are present in high concentrations. Therefore fly ash must be treated as a hazardous material. On the other hand, it may be a potential source of heavy metals. Zinc, lead, cadmium, and copper can be relatively easily removed during the thermal treatment of fly ash, e.g. in the form of chlorides. In return, wet extraction methods could provide promising results for these elements including chromium and nickel. The aim of this study was to investigate and compare thermal and hydrometallurgical treatment of municipal solid waste fly ash. Thermal treatment of fly ash was performed in a rotary reactor at temperatures between 950 and 1050°C and in a muffle oven at temperatures from 500 to 1200°C. The removal more than 90% was reached by easy volatile heavy metals such as cadmium and lead and also by copper, however at higher temperature in the muffle oven. The alkaline (sodium hydroxide) and acid (sulphuric acid) leaching of the fly ash was carried out while the influence of temperature, time, concentration, and liquid/solid ratio were investigated. The combination of alkaline-acidic leaching enhanced the removal of, namely, zinc, chromium and nickel.

Stabilization treatment of the heavy metals in fly ash from municipal solid waste incineration using diisopropyl dithiophosphate potassium

A stabilization treatment was developed for heavy metals in fly ash from municipal solid waste incineration using the heavy metal chelator diisopropyl dithiophosphate potassium (DDP). The mechanism and effect of the DDP chelator treatment on heavy metals in the fly ash was also studied, along with the form transformation rules of the heavy metals after DDP chelator treatment. The results show that 1% DDP achieves a stabilization rate of over 95% for Pb, Zn, and Cd. The effect of DDP was better than that of inorganic stabilizers such as sodium sulphide and lime. The heavy metal concentrations in the leachate after the treatment were lower than those required by the Pollution Control Standards for Hazardous Waste Landfill (GB18598-2001). At pH 1–13, the heavy metal concentrations in the fly ash leachate were far lower than those using the inorganic stabilizers sodium sulphide and lime. DDP retains its stabilizing effect under a broader pH range. After stabilization treatment, the heavy metals in the exchangeable fraction and those bound to carbonates were mainly transformed into those bound to organic matter. This process decreases the unstable content and reduces the risk of secondary pollution of the stabilized products in the environment.

Gaseous Emissions Monitoring and Ash Analysis of an Industrial Incinerator in Pakistan

A study was conducted on an industrial incinerator located at Kala Shah Kaku, Punjab, Pakistan to monitor and evaluate stack emissions (NOX, SOX, CO, VOCS) and determination of heavy metals in bottom and fly ash of an industrial incinerator burning tobacco dust. Incinerated bottom and fly ash samples were collected. For the purpose of ambient air monitoring three different sides of incinerator were selected. The air emissions monitoring included emissions from right side of the incinerator (A1), emissions from left side of the incinerator (A2) and emissions from the main gate of the incinerator (A3). To determine heavy metals in bottom and fly ash, HACH and Merck procedure via spectrophotometer were used. Respirable Dust Sampler and Flue Gas Analyzer were used to monitor ambient air quality and stack emissions respectively. The results of ambient quality (SOx, NOx, CO, CO2, PM& O2) revealed that the emissions from A2 were comparatively higher than emissions from A1 and A3. With the help of Flue Gas Analyzer it was found that carbon monoxide (CO) emissions were higher than SOX, NOX and VOCS. Bottom ash analysis by spectrophotometer showed that the heavy metals were below the detectable limits. The analysis conducted for heavy metals in fly ash by spectrometry as well confirmed that lead (Pb) and cadmium (Cd) were below the detectable limits and chromium was 1.96 mg/kg of the ash.

An immobilisation mechanism for lead in fly ash subjected to mechanochemical treatment

Mechanochemical (MC) processes immobilise heavy metals in fly ash, a desirable outcome because recycled fly ash is commonly used in the synthesis of inorganic materials. We investigate the extent of immobilisation and the mechanism of lead (Pb) leaching during MC treatment of fly ash, using lead oxide (PbO) and lead dichloride (PbCl2) as model compounds. MC treatment of the fly ash inhibited Pb leaching by about 97% after a 12 h treatment. PbO was reduced to elemental Pb in a redox reaction by abraded iron (Fe) produced from the stainless steel ball mill used for MC treatment, and a phase transition of the PbO crystal structure from orthorhombic to tetragonal was confirmed. Production of Pb species with sparing solubility in water resulted in immobilisation of the Pb within the fly ash. Other insoluble intermediates detected in the milled samples, such as Pb2O3, potentially contribute to the inhibition of Pb leaching.

Effects of Hydrothermal Treatment on the Major Heavy Metals in Fly Ash from Municipal Solid Waste Incineration

Circulating fluidized bed (CFB) and stoker grate are the two major municipal solid waste incineration (MSWI) technologies currently being used in China. In this work, the hydrothermal stabilization...

Study on Asphalt Solidification of Hospital Waste Incineraten Fly Ash

Asphalt solidification of hospital waste Incineraten fly ash was studied based on that asphalt can immobilize the heavy metals in fly ash. In the nature hospital waste incineraten fly ash, the leachate concentration of Zn (279.2 mg/L) and Pb (19.88 mg/L)) were significantly higher than the regulatory limit by TCLP test while the leachate concentration of Cu (1.51 mg/L), Cd(0.97 mg/L) and Ni (0.49 mg/L) were respectively beyond the regulatory limit of TCLP. In the asphalt solidified hospital waste incineraten fly ash, the leachate concentration of the heavy metals increased with the increase of fly ash rate in solidified fly ash from 10% to 40%, and the leachate concentration of 5 studied heavy metals were under the limit of the standard.

Fate of Metals in Fly Ash During Aging in Laboratory-Scale Ash Impoundments

Abstract Release of metals from fly ash stored in ash impoundments can pose environmental risks. Laboratory-scale impoundments loaded with Class C and Class F fly ashes were studied to investigate the release of metals during aging, changes in the mineralogy of the ash, and associated changes in the leachability of the metals. The water column above the settled ash was sampled over 9–12 months, and cores of ash were regularly collected from one of the Class C ash impoundments and subjected to a sequential extraction procedure that targeted metals bound by specific mechanisms. The long-term nature of experiments and integration of aqueous- and solid-phase analyses are unique aspects of the study that yielded insights into the fate of metals during fly ash storage and disposal. For Class C ashes, high concentration of alkaline solids led to pH values as high as 11.6 that gradually declined as the impoundment took up carbon dioxide from the atmosphere. A considerable fraction of the selenium in the ash (∼50%...

Analysis of Heavy Metal Leaching in Fly Ash from One Shanghai Municipal Solid Waste Incineration (MSWI) Plant

The characteristics and leaching behavior of heavy metals in fly ash, sampled from one MSWI (municipal solid waste incineration) plant in Shanghai China, were investigated. The results indicated that the main elements of fly ash were Fe, K, Na, Cl, Si, Ca, Al, and the total fraction of heavy metals was in the range of 0.8 % - 2.0%. Hence, MSWI fly ash was considered to be one kind of hazardous waste due to its potential environmental risk. Leaching toxicity was performed on fly ash samples from the MSWI plant in Shanghai China. Leaching toxicity of the heavy metals by the ALT (available leaching toxicity) procedure exceeded that by the HVEP (horizontal vibration extraction procedure) standard. Leaching concentrations of Ni, Zn, Cd and Pb exceeded the limit of hazardous waste identification standard. Hence, fly ash is a hazardous waste.

Effect of Flue Gas Treatment on the Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Studies were conducted to examine the effect of flue gas carbon dioxide (CO2) on solubility and availability of different metals in fly ash of Powder River Basin (PRB) coal, Wyoming, USA. Initial fly ash (control) was alkaline and contains large amounts of water-soluble and exchangeable metals. Reaction of flue gas CO2 with alkaline fly ash resulted in the formation of carbonates which minimized the solubility of metals. Results for metal fractionation studies also supported this fact. The present study also suggested that most of the water-soluble and exchangeable metals present in the control (untreated) fly ash samples decreased in the flue gas-treated samples. This may be due to the transfer of the above two forms to more resistant forms like carbonate bound (CBD), oxide bound (OXD), and residual (RS). Geochemical modeling (Visual MINTEQ) of water solubility data suggested that the saturation index (SI) values of dolomite (CaMg(CO3)2) and calcite (CaCO3) were oversaturated, which has potential to mineralize atmospheric CO2 and thereby reduce leaching of toxic metals from fly ash. Results from this study also showed that the reaction of flue gas CO2 with alkaline fly ash not only control the solubility of toxic metals but also form carbonate minerals which have the potential to fix CO2.

Valvulopathies

In this study we have examined the distribution of the chemical forms of Cd, Cu, Fe, Mn, Pb and Zn in the coal and coal + biomass fly ash (FA) collected in a three stage electrostatic precipitator (ESP) of a pulverized fuel fired boiler system. The concentrations of environmentally available volatile metals (Cd, Cu, Pb and Zn) increased towards finer grained ESP fractions, whereas the concentrations of hardly volatile metals (Fe and Mn) underwent a slight reduction. The concentration of Cd in all ESP fractions of FA was very low (< 1.5 mg/kg).We have proposed a new approach to determining the occurrence mode of trace metals in FAs by the modified Tessier scheme. A relatively uniform pattern of chemical fractionation was obtained for metals having various properties. The effect of co-combustion of biomass was observed for Cu and Mn distribution. Cu present in coal + biomass FA exhibits a clearly higher mobility than Cu in coal FA. The behavior of Mn is just the opposite and a difference in mobility is smaller. The characteristic feature of metal occurrence in the fly ash is a large share of the environmentally persistent fraction (40–90%) and a very low proportion of the water leaching fraction (< LOD). This has a large environmental significance, as it can be predicted that the pulverized coal combustion (PCC) FAs, even if found in extremely unfavorable environmental conditions, will not become an effective source of heavy metals.The sequential extraction results made it possible to propose an outline of the mechanism of formation of individual chemical fractions of the investigated metals.

Evaluation of the distribution of heavy metals and their chemical forms in ESP-fractions of fly ash

In this study we have examined the distribution of the chemical forms of Cd, Cu, Fe, Mn, Pb and Zn in the coal and coal+biomass fly ash (FA) collected in a three stage electrostatic precipitator (ESP) of a pulverized fuel fired boiler system. The concentrations of environmentally available volatile metals (Cd, Cu, Pb and Zn) increased towards finer grained ESP fractions, whereas the concentrations of hardly volatile metals (Fe and Mn) underwent a slight reduction. The concentration of Cd in all ESP fractions of FA was very low (<1.5mg/kg).We have proposed a new approach to determining the occurrence mode of trace metals in FAs by the modified Tessier scheme. A relatively uniform pattern of chemical fractionation was obtained for metals having various properties. The effect of co-combustion of biomass was observed for Cu and Mn distribution. Cu present in coal+biomass FA exhibits a clearly higher mobility than Cu in coal FA. The behavior of Mn is just the opposite and a difference in mobility is smaller. The characteristic feature of metal occurrence in the fly ash is a large share of the environmentally persistent fraction (40–90%) and a very low proportion of the water leaching fraction (<LOD). This has a large environmental significance, as it can be predicted that the pulverized coal combustion (PCC) FAs, even if found in extremely unfavorable environmental conditions, will not become an effective source of heavy metals.The sequential extraction results made it possible to propose an outline of the mechanism of formation of individual chemical fractions of the investigated metals.

Occupational Risk Evaluation of Using Bottom Ash and Fly Ash as a Construction Material

As a case study, the potential to use bottom ash and fly ash from a large-sized (120 MW) bubbling fluidized bed boiler (BFB) at the power plant of a fluting board mill were assessed to determine their suitability for use as an earth construction agent. In addition, the extractability of heavy metals in the ashes was determined using artificial sweat and gastric fluids to assess the potential occupational risk from ash handling. Owing to the relatively high total concentration of polycyclic aromatic hydrocarbons (PAHs) [23.0 mg/kg; dry weight (d.w.)], and the extractable concentrations of Mo (3.9 mg/kg; d.w.) and Se (0.2 mg/kg; d.w.) in the fly ash, which exceed the Finnish limit values for materials used in covered earth construction (20 mg/kg; d.w. for PAHs, 0.5 mg/kg; d.w. for Mo, and 0.1 mg/kg; d.w. for Se), the utilization of this ash residue fraction in such structures requires an environmental permit. Because of the high extractability of certain heavy metals in fly ash by using an artificial gastric fluid, e.g., Ba (446 mg/kg; d.w.), V (65.6 mg/kg; d.w.), Zn (100 mg/kg; d.w.), Cu (38.3 mg/kg; d.w.), and As (36.7 mg/kg; d.w.), the careful handling of this ash residue is recommended to prevent the ingestion and penetration of ash particles across the human gastrointestinal tract.

Irradiation effect on leaching behavior and form of heavy metals in fly ash of municipal solid waste incinerator

Fly ash from a municipal solid waste incinerator (MSWI) is commonly classified as hazardous waste. High-energy electron beam irradiation systems have gained popularity recently as a clean and promising technology to remove environmental pollutants. Irradiation effects on leaching behavior and form of heavy metals in MSWI fly ash have not been investigated in any significant detail. An electron beam accelerator was used in this research. Electron beam irradiation on fly ash significantly increased the leaching potential of heavy metals from fly ash. The amount of absorbed dose and the metal species affected leaching behavior. When electron beam irradiation intensity increased gradually up to 210 kGy, concentration of Pb and Zn in the leachate increased linearly as absorbed dose increased, while that of Cu underwent no significant change. Concentration of Pb and Zn in the leachate increased up to 15.5% (10.7 mg/kg), and 35.6% (9.6 mg/kg) respectively. However, only 4.8% (0.3 mg/kg) increase was observed in the case of Cu. The results imply that irradiation has significant effect on the leaching behavior of heavy metals in fly ash, and the effect is quite different among the metal species tested in this study. A commonly used sequential extraction analysis which can classify a metal species into five forms was conducted to examine any change in metal form in the irradiated fly ash. Notable change in metal form in fly ash was observed when fly ash was irradiated. Change in Pb form was much greater than that of Cu form. Change in metal form was related to leaching potential of the metals. Concentration of heavy metal in leachate was positively related to the exchangeable form which is the most mobile. It may be feasible to treat fly ash by electron beam irradiation for selective recovery of valuable metals or for pretreatment prior to conventional processes.