Metals In Fly Ash Research Articles

Study on electro-kinetic remediation of heavy metals in municipal solid waste incineration fly ash with a three-dimensional electrode

Heavy metals of fly ash from incinerated municipal solid waste were removed by electro-kinetic remediation with three-dimensional electrode.

Chemical associations and mobilization of heavy metals in fly ash from municipal solid waste incineration

This study focusses on chemical and mineralogical characterization of fly ash and leached filter cake and on the determination of parameters influencing metal mobilization by leaching. Three different leaching processes of fly ash from municipal solid waste incineration (MSWI) plants in Switzerland comprise neutral, acidic and optimized acidic (+ oxidizing agent) fly ash leaching have been investigated. Fly ash is characterized by refractory particles (Al-foil, unburnt carbon, quartz, feldspar) and newly formed high-temperature phases (glass, gehlenite, wollastonite) surrounded by characteristic dust rims. Metals are carried along with the flue gas (Fe-oxides, brass) and are enriched in mineral aggregates (quartz, feldspar, wollastonite, glass) or vaporized and condensed as chlorides or sulphates. Parameters controlling the mobilization of neutral and acidic fly ash leaching are pH and redox conditions, liquid to solid ratio, extraction time and temperature. Almost no depletion for Zn, Pb, Cu and Cd is achieved by performing neutral leaching. Acidic fly ash leaching results in depletion factors of 40% for Zn, 53% for Cd, 8% for Pb and 6% for Cu. The extraction of Pb and Cu are mainly limited due to a cementation process and the formation of a PbCu0-alloy-phase and to a minor degree due to secondary precipitation (PbCl2). The addition of hydrogen peroxide during acidic fly ash leaching (optimized acidic leaching) prevents this reduction through oxidation of metallic components and thus significantly higher depletion factors for Pb (57%), Cu (30%) and Cd (92%) are achieved. The elevated metal depletion using acidic leaching in combination with hydrogen peroxide justifies the extra effort not only by reduced metal loads to the environment but also by reduced deposition costs.

Mobility, Ecological risk and change in surface morphology during sequential chemical extraction of heavy metals in fly ash: A case study

Abstract Patratu coal based thermal power plant of Jharkhand, India uses Gondwana coal and generates ≈ 0.259 metric tonnes of fly ash. Only 3% of fly ash produced is utilized and rest is dumped as slurry, in the slurry pond and in the low-lying areas of the nearby villages. This study was aimed to find the mobility of metals in the fly ash samples by sequential extraction as well as to evaluate the ecological risk of the fly ash. The transformation of surface morphology after each step of sequential extraction was also studied by SEM-EDX. The results revealed that 13% of Cd and 1% of Ni was water soluble 48% of Ni, 23% of Mn, and 7% of Cd were in exchangeable fraction. The proportion in carbonate bound fraction was Cd (32%), Cu (15%), Zn (12%), Mn (6%), and Ni (3%) of the total metal content. Whereas, the proportion in Fe–Mn oxide bound fraction was Fe (46%), Mn (14%), Zn (13%) and Ni (3%); in organic bound fraction was Pb (38%), Cu (33%), Zn (16%), Cr (15%), Ni (13%), Mn (7%), Fe (6%), and Cd (2%) and in residual fraction was Cr (85%), Pb (62%), Mn (50%), Zn (59%), Cu (44%), Fe (47%), and Cd (25%). Pollution load index of metals in fly ash was more than one. Ecological risk index was also above 600. These values signify high ecological and pollution risk of the fly ash due to presence of heavy metals. So, implementation of proper remediation techniques is necessary to reduce the ecological risk of the fly ash.

Metals Accumulation During Thermal Processing of Sewage Sludge - Characterization of Fly Ash and Air Pollution Control (APC) Residues

Sewage sludge thermal utilization leads to production of fly ash and APC residues which may contain elevated amounts of some metallic or toxic elements (Fe, Zn, Pb, Sn, Au, Hg, Cd, As). Distribution of these elements in studied fly ash and APC residues was unequal and dependent on their melting temperature. Metals in fly ash are present as Fe-rich grains and rims around Si-glass whereas in APC metallic components are mostly represented by Sn-rich inclusions dispersed in matrix, Ca-phosphates or as separate micro-grains. Elements concentrations were elevated but overall content was low thus disqualifying the material in terms of recovery.

Characterization of sulfur products on CaO at high temperatures for air and oxy-combustion

Oxy-coal combustion is a novel technology that seeks to reduce carbon dioxide emissions from electricity generating units, but the unique combustion environment could potentially affect the manner in which the flue gas and fly ash interact. Of particular interest is the ability of fly ash to reduce SOx emissions, a source of concern in implementing oxy-coal technology. This study seeks to examine the way SOx interacts with calcium oxide, an important fly ash metal oxide, under a variety of flue gas conditions and temperatures. Using DRIFTS and XRD, the major products under the various reaction conditions were analyzed. The dominant sulfur containing product was found to be calcium sulfate. However, a secondary calcium carbonate product was formed under certain oxy-fuel conditions. Additionally, EDX was employed to examine the temperature dependence for sulfur retention.

Carbonization of heavy metal impregnated sewage sludge oriented towards potential co-disposal

Sewage sludge (SS) is adopted as a stabilizer to immobilize externally impregnated heavy metals through carbonization oriented towards the co-disposal of SS and some hazardous wastes. Firstly Cu and Pb were impregnated into SS to ascertain the impregnating capacity and leaching behaviours of heavy metals in the resulting sewage sludge char (SSC). Meanwhile, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to detect the heavy metal phase in the SSC. The results showed that within 400–800°C and an impregnating concentration ≨0.5wt%, more than 90% of the externally impregnated Cu and Pb were remained in the SSC and immobilized. And higher temperatures helped produce non-hazardous SSC. In addition, SEM and XRD analyses revealed that externally impregnated heavy metals could be converted into stable forms and evenly distributed throughout the SSC. In the second step municipal solid waste incineration fly ash (FA) was kneaded into SS and subjected to carbonization; it has been proved that the heavy metals in FA can be well immobilized in the resulting char when FA: SS mass ratio is 1:5. Those results show that sewage sludge can be co-carbonized with wastes contaminated with heavy metals to achieve co-disposal.

Stabilization of Heavy Metals in Municipal Solid Waste Incineration Fly Ash in Circulating Fluidized Bed by Microwave-Assisted Hydrothermal Treatment with Additives

In this work, a microwave-assisted hydrothermal treatment was investigated to solidify the heavy metals of municipal solid waste incineration fly ash in a circulating fluidized bed. The influences of additive dosage, temperature, liquid/solid (L/S) ratio, and reaction time with addition of NaH2PO4 were investigated. The chemical components, hydrothermal product, and the leaching concentration of fly ash were determined by X-ray fluorescence, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. Also, pH tests were conducted to assess the environmental adaptability of the treated fly ash. In terms of the solidification effect of heavy metals, the effectiveness of additives was in the order Na2HPO4, NaH2PO4, H3PO4, and FeSO4. Experimental results revealed that heavy metals in fly ash were solidified by a microwave-assisted hydrothermal process, under the optimized conditions of 1.5 mol/kg NaH2PO4, 2 mL/g L/S ratio, 10 min reaction time, and 200 °C, and the heavy metal contents met ...

Effects of Microwave-Assisted Hydrothermal Treatment on the Major Heavy Metals of Municipal Solid Waste Incineration Fly Ash in a Circulating Fluidized Bed

In this paper, microwave-assisted hydrothermal treatment was performed to stabilize the heavy metals of municipal solid waste incineration (MSWI) fly ashes in a circulating fluidized bed (CFB). Influences of the types of chemical additives, reagent concentration, liquid/solid ratio, reaction temperature, and reaction time were investigated by single and orthogonal experiments. A solid waste extraction procedure for leaching toxicity-acetic acid buffer solution method (HJ/T 300-2007) was adopted to detect the toxicity of raw fly ash and the hydrothermal products. The effect of pH on the leaching test of raw and treated fly ash was also carried out. Characteristics of fly ash were determined by XRF and XRD, and the leaching concentration was determined by ICP-MS. Experimental results revealed that the stabilization of heavy metals in fly ash was facilitated by a microwave-assisted hydrothermal process and, except for Cd, the regulatory limits were achieved when fly ash was treated with 1 mol/L NaOH and a li...

Study on the species of heavy metals in MSW incineration fly ash and their leaching behavior

This study aims to identify the chemical species and leaching behavior of Cd, Zn, Pb, Cu and Cr in a fly ash with high content of calcium collected from the incineration of municipal solid waste (MWS), based on the sequential leaching procedure. A thermodynamic pseudo-equilibrium model was also developed to evaluate the possible chemical compounds of these heavy metals in the fly ash. The results indicate that, approximate 30% of Cu was distributed in the organic bound fraction and very likely combined with some organic ligands. Pb exhibited the highest fraction among these five metals in water soluble fraction, accounting for about 7.5%. It thus potentially causes a menace to the surroundings. In terms of model calculation, the metallic chlorides in the fly ash were responsible for the leaching of Pb, Zn, Cd and Cu even under a rigorous environmental condition (pH=2) where the oxides and/or metallic ferrites were rarely mobile. The leaching of Cr and Cd in the fly ash was controlled by a dissolution mechanism whereas the fate of Pb, Zn and Cu was controlled by the precipitation/sorption. Cu and Zn in fly ash have been proven to associate with Ca-bearing compounds through precipitation/sorption during leaching test while Pb mainly exists as sulfate and phosphate.

Decomposition of asbestos by a supernatant used for immobilization of heavy metals in fly ash

A supernatant solution, obtained after immobilization of heavy metals involved in fly ashes by a solution of sulfur and calcium hydroxide, was re-used for immobilization of heavy metals and decomposition of asbestos in construction materials. Asbestos was decomposed to more than 99.9 % by mixing it with the supernatant in a ball mill at room temperature. The decomposition of asbestos was confirmed by X-ray diffraction (XRD), a phase contrast microscope after staining the asbestos with solutions of different diffractive indexes and a scanning electron microscope. XRD indicated complete disappearance of specific main peaks of asbestos: chrysotile, crocidolite, amosite and tremolite. Heavy metals such as chromium(VI) and lead(II) in fly ashes were completely immobilized by the supernatant. It is the first time that a solution obtained after the treatment of wasted fly ash is recycled for decomposition of hazardous waste materials such as asbestos.

Management of Fly Ash Through Vermicomposting: A Rational Approach

Fly ash is a by-product of coal combustion in thermal power plants. Its generation poses several environmental problems, the most important ones being its capacity for causing pollution and the need for large storage areas to keep it out of the environment. Fly ash management remains a major concern in the 21st century; however, despite these challenges, the material has great potential for beneficial use in agriculture due to its efficacy in modifying and improving soil health and improving crop performance. Vermicomposting is an excellent technique for reducing the toxic heavy metals in fly ash through the introduction of earthworms. The activities of several earthworm species minimize the solubility of heavy metals and increase the bioavailability of major nutrient elements such as phosphorous (P) and nitrogen (N). This article provides a comprehensive review of the scope and benefits of vermiremediating fly ash, demonstrating the abilities of different species of earthworms to accumulate heavy metals and increase the availability of plant nutrients. On the basis of a literature survey, the authors have concluded that adopting vermicomposting technology promises increased, effective fly ash utilization for agricultural benefits.

Heavy Metal Migration and Potential Environmental Risk Assessment During the Washing Process of MSW Incineration Fly Ash and Molten Slag

Based on the simulated moderate acid rainfall condition, MSW fly ash and molten slags were washed to investigate the effect of alkalinity on the migration and the speciation transformation of heavy metals in the approaching natural environment. All the samples were washed 150min at 25̊C with the 100ul/min flow speed, then the after-washing samples were placed at air atmosphere for 60 days to get dried after-washing fly ash and molten slag samples. The total concentration of heavy metals in raw fly ash was followed by Zn>Pb>Cu>Cr>Cd>As>Ni, After washing process, the order is still the same, and the content of heavy metals in fly ash were significantly increased due to soluble salt leaching, especially Cr, Cu, Ni, Zn. The potential ecological risk (PEI) analysis, using STI toxicity model, indicated that PEI index of fly ash after washing was 2.3 times than that before washing. Therefore, it will cause greater ecological risk for the open storage of fly ash. When the fly ash was converted into molten slag, the alkalinity in the range between 0.8 and 1.2 was benefical for reducing PEI index of molten slags. The ash molten slag can be directly used as roadbed material due to the good solidification effect of heavy metals.

Risk assessment of heavy metals from combustion of pelletized municipal sewage sludge.

Fly ash and slag are important by-products obtained from combustion of municipal sewage sludge (MSS) after pelletization. The quantitative environmental impact assessment of heavy metals in fly ash and slag, compared to MSS, were performed in accordance with bioavailability and eco-toxicity, geo-accumulation index (GAI), risk assessment code (RAC), and potential ecological risk index (PERI). The results demonstrated that not only direct but also long-term bioavailability and eco-toxicity of heavy metals in fly ash and slag decreased except direct bioavailability and eco-toxicity of Pb in fly ash. The GAI demonstrated that combustion significantly weakened (P < 0.05) the pollution levels of heavy metals. PERI indicated that all risks attributed to heavy metals were significantly lowered (P < 0.05) from 777.07 (very high risk) in MSS to 288.72 (moderate risk) and 64.55 (low risk) in fly ash and slag, respectively. In terms of the RAC, seven heavy metals had low even no risk to the environments after combustion besides As in slag. The environmental risk of heavy metals in fly ash and slag was decreased compared with MSS. However, the results of PERI showed that fly ash had a moderate risk.

The physiochemical properties and heavy metal pollution of fly ash from municipal solid waste incineration

Fly ash originating from municipal solid waste incineration (MSWI) is potentially hazardous waste and is harmful to the surrounding area once it enters the environment. In this study, we measured the physiochemical properties of fly ash derived from domestic waste incineration as well as the leaching toxicity of heavy metals in fly ash was contained. The results suggested that the porosity of fly ash is relatively high, and the leaching concentration of heavy metals can be greatly reduced through densification strategies in which fly ash is stabilized by chemical agents. The adsorption–desorption curve of fly ash had an obvious hysteresis loop that belongs to the H2-type hysteresis loop. Fly ash was typically mesoporous, and the silicate in fly ash was relatively stable. Its glass phase contents were higher—this allowed it to be used in ceramic tile decoration. In addition, Pb and Cd were the major heavy metals in fly ash. These heavy metals were mainly distributed in the residue. Heavy metals were easily leached out under strong acid or alkaline conditions.

Chemical speciation, mobility and phyto-accessibility of heavy metals in fly ash and slag from combustion of pelletized municipal sewage sludge

Combustion of pelletized municipal sewage sludge (MSS) can generate pestilent byproducts: fly ash and slag. Comparisons of heavy metal sequential extraction results among MSS, fly ash and slag showed that after combustion, the bioavailable heavy metal fractions (acid soluble/exchangeable, reducible and oxidizable fractions) were mostly transformed into the very stable heavy metal fractions (residual fractions). On the other hand, the results of toxicity characteristic leaching procedure (TCLP), diethylenetriamine pentaacetic acid and HCl extraction (phyto-accessibility assessment) demonstrated that the mobility and toxicity of heavy metals were greatly reduced. The direct and long-term bioavailability and eco-toxicity of heavy metals in fly ash and slag were relieved, which implied that combustion of pelletized MSS could be a promising and completely safe disposal technology for MSS treatment.

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

This study was conducted to examine the synthesis and application of novel nano-size calcium/iron-based composite material as an immobilizing and separation treatment of the heavy metals in fly ash from municipal solid waste incineration. After grinding with nano-Fe/Ca/CaO and with nano-Fe/Ca/CaO/[PO4], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash). Heavy metals in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized, respectively. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) observations indicate that the main fraction of enclosed/bound materials on treated fly ash includes Ca/PO4-associated crystalline complexes. After nano-Fe/Ca/CaO/[PO4] treatment, the heavy metal concentrations in the fly ash leachate were much lower than the Japan standard regulatory limit for hazardous waste landfills. These results appear to be extremely promising. The addition of a nano-Fe/Ca/CaO/PO4 mixture with simple grinding technique is potentially applicable for the remediation and volume reduction of fly ash contaminated by heavy metals.Implications: After grinding with nano-Fe/Ca/CaO and nano-Fe/Ca/CaO/[PO4], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash), whereas heavy metals either in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized. These results appear to be very promising, and the addition of nano-Fe/Ca/CaO/PO4 mixture with simple grinding technique may be considered potentially applicable for the remediation and volume reduction of contaminated fly ash by heavy metals.

A comparative study on the heavy metal solidification/stabilization performance of four chemical solidifying agents in municipal solid waste incineration fly ash

Investigated in this paper were the content, specification distribution, and risk assessment code (RAC) determination of six targeted heavy metals and potentially toxic metals in fly ashes from a municipal solid waste incinerator in China. Contained in it is a comparison of the solidification/stabilization performance of two novel solidifying agents of sixthio guanidine acid (SGA) and tetrathio bicarbamic acid (TBA) with sodium dimethyldithiocarbamate (SDD) and Na2S, and analysis of their leachability in accordance with TCLP 1311 of the US EPA and the extraction procedures of China (HJ/T 299-2007 and HJ/T300-2007). The total concentration of Zn, Cu, Ni, Pb, Cr, Cd is 37383.47, 3080.77, 1583.92, 1356.43, 566.15, and 77.83mg/kg, respectively. Cr (3.7%) and Pb (7.50%) pose low risk; and Ni (12.93%) and Zn (15.45%) have a medium risk; while Cu (69.84%) and Cd (82.5%) have a very high risk according to their RAC score. Compared with SDD and Na2S, SGA and TBA show an excellent overall solidifying performance due to their multiply hydrosulfide groups that bind with heavy metals very efficiently. The obtained results indicate that the leaching content of Cd, Ni, Pb and Zn is higher than the thresholds prescribed in GB5085.3-2007, and the excessive acetic acid makes its binding capacity stronger in HJ/T 300-2007 than in TCLP 1311.

Leaching heavy metals in municipal solid waste incinerator fly ash with chelator/biosurfactant mixed solution

The chelator [S,S]-ethylene diamine disuccinic acid, citric acid, and biosurfactant saponin are selected as leaching agents. In this study, the leaching effect of saponin mixed with either ethylene diamine disuccinic acid or citric acid on the levels of copper, zinc, lead, and cadmium in municipal solid waste incinerator fly ash is investigated. Results indicate that saponin separately mixed with ethylene diamine disuccinic acid and citric acid exhibits a synergistic solubilisation effect on copper, zinc, lead, and cadmium leaching from fly ash. However, saponin and ethylene diamine disuccinic acid mixed solution exhibits a synergistic solubilisation effect that is superior to that of a saponin and citric acid mixed solution. The extraction rate of heavy metal in fly ash leached with a saponin and chelator mixed solution is related to the pH of the leaching solution, and the optimal range of the pH is suggested to be approximately neutral. After leaching with a saponin and chelator mixed solution, copper, zinc, lead, and cadmium contents significantly decreased (p < 0.05) in the extractable or acid-soluble and reducible fractions. By adopting the proposed approach, the leaching concentrations of copper, zinc, lead, and cadmium in treated fly ash are in accordance with Standard for Pollution Control on the Security Landfill Site for Hazardous Wastes GB18598-2001.

An Assessment of Metal in Fly Ash and Their Translocation and Bioaccumulation in Perennial Grasses Growing at the Reclaimed Opencast Mines

Rapid expansion of the industrial sector adds more effluent into the agricultural land and in the vicinity of industry, which possesses the major threat of land contamination and environmental degradation. The present study was conducted to determine toxic metal concentration in fly ash and metal accumulation potential of the Saccharum munja and Cynodon dactylon, the two main grass species growing naturally on fly ash lagoon for Fe, Ni, Zn, Cu, Mn, Pb and Cd. Accumulation of metals were found in the order of Fe > Zn > Mn > Cu > Ni > Pb and Cd. In spite of significant accumulation of Fe in the root and shoot, the BCF and BAC were found very low ( 1 for Zn and Pb) and low bioaccumulation coefficient (<1 for Fe, Mn, Ni, Cu and Cd) suggests its suitability for phytoremediation of fly ash lagoons. Findings of the study suggest that weed species may be used for the stabilization of toxic metals contaminated land and to empower the rural economy.

Fly-ash augmented soil enhances heavy metal accumulation and phytotoxicity in rice (Oryza sativa L.); A concern for fly-ash amendments in agriculture sector

Fly-ash (FA) utilization in the agriculture sector is very common practice due to presence of beneficial elements required for plant growth. However, presence of excessive amount of toxic metals in FA may be serious concern for agriculture. In the present study, the effects of FA on soil health, plant growth, toxic metal accumulation and antioxidant responses were investigated in rice (Oryza sativa L.), grown on soil amended with 50 % FA in natural condition. FA application resulted in reduction in soil enzymatic activities viz., dehydrogenase, acid phosphatase, β-glucosidase and urease than garden soil (GS). FA amendments significantly decreased the root, shoot and panicle length and augmented sterility in rice. Interestingly, ICPMS analysis for metal accumulation revealed that the total accumulation of toxic metals, particularly Cd, Cr, Pb and As were 14–15 fold higher in roots and shoots and 4–20 fold higher in grains for the plants grown on FA amended soil than GS. The levels of nutrient elements viz., Mn, Co, Cu and Se were lesser in grains of FA treated soil than GS. Lipid peroxidation was increased in root and shoot of FA treated plants indicating oxidative stress. Activities of various antioxidant enzymes viz., SOD, APX, GPX, GR and their isozymes were correlated to each other and also increased against heavy metal induced toxicity. Human associated risk analysis revealed that the calculated maximum tolerable daily intake values for toxic metals (µg d−1) viz., Cr, As, Cd, Hg and Pb was beyond the safe limit in the rice grown in FA implicated soil. In conclusion, 50 % FA implication deteriorates the soil quality, rice production and elevates the toxic metals in grains, which may be a concern for safer rice consumption.