Heavy Metals In Fly Ash Research Articles

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.

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.

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.

Evaluation of a mixed chelator as heavy metal stabilizer for municipal solid‐waste incineration fly ash: Behaviors and mechanisms

This paper compares the stabilization performances of three dithiocarbamate and three phosphate chemical stabilizing agents, selects the best agents from each group, combines them as a mixed heavy metal stabilizer for municipal solid‐waste incineration (MSWI) fly ash, and investigates the effectiveness of the mixed chelator in stabilizing heavy metals in MSWI fly ash from southwest China. The mechanism of stabilization is also analyzed. Results indicate that piperazine dithiocarbamate can stabilize Cd, Cu, and Ni effectively, while sodium dihydrogen phosphate can stabilize Pb better. With the addition of the mixed chelator (2% sodium dihydrogen phosphate and 1% piperazine dithiocarbamate), all the targeted heavy metal concentrations in the leachate were below the standards for pollution control on municipal solid waste landfill sites in China. The stabilizing agents combined with the heavy metals in fly ash could not generate insoluble crystals; however, the heavy metals could combine with the agents' effective groups, generating flocs in the pores or on the surfaces of the fly ash and offering significant densification. The mixed chelator could transfer heavy metals from unstable fractions to stable fractions, so the leaching of heavy metals from the fly ash was greatly decreased.

Mineralogy Characteristics and Heavy Metal Distribution of MSWI Fly Ash

Fly ash from municipal solid waste incineration (MSWI) plants can be categorized as a highly toxic mineral material due to the potential for leaching heavy metals. The mineralogical properties of MSWI fly ash visually reflect the heavy metals distribution in the ash, and are closely related to the release and migration behaviors of heavy metals in fly ash disposal or utilization scenarios. In order to understand the distribution of heavy metals in MSWI fly ash and provide support for heavy metals control technology, comprehensive tests on the macroscopic and microscopic mineralogical characteristics of the fly ash were conducted using X-ray diffraction (XRD), scanning electron microscope, a mineral liberation analysis system, and other methods. The results showed that MSWI fly ash was a heterogeneous material of closely combined mineral and non-mineral phases. The main mineral phases identified by XRD included chlorides and calcium-bearing minerals, mainly calcite and portlandite. The element distribution analysis, conducted with a mineral liberation analyzer, revealed that heavy metals of MSWI fly ash were mainly present in three forms:uniform distribution in the non-mineral amorphous phase, isomorphism in calcite and other minerals, and adsorption on the surfaces of quartz and hematite. Most content of Cu and Cr were distributed in the non-mineral phase due to their lower volatility, while most of semi-volatile heavy metals (43.92% of Zn and 60.61% of Cd) were present in mineral phases. In particular, Cd, Cr and Zn were mainly present in calcite, hematite and silicates respectively.

Characterization of typical heavy metals in pyrolysis MSWI fly ash

ABSTRACTThermal treatment methods are used extensively in the process of municipal solid waste incineration fly ash. However, the characterization of heavy metals during this process should be understood more clearly in order to control secondary pollution. In this paper, the content, speciation and leaching toxicity of mercury (Hg), plumbum (Pb), cadmium (Cd) and zinc (Zn) in fly ash treated under different temperatures and time were firstly analysed as pre-tests. Later, pilot-scale pyrolysis equipment was used to explore the concentration and speciation changes in the heavy metals of fly ash. Finally, the phase constitution and microstructure changes in fly ash were compared before and after pyrolysis using X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The results showed that (a) The appropriate processing temperature was between 400°C and 450°C, and the processing time should be 1 h. (b) The stability of heavy metals in fly ash increased after pyrolysis. (c) XRD and SEM results indicated that phase constitution changed a little, but the microstructure varied to a porous structure similar to that of a coral reef after pyrolysis. These results suggest that pyrolysis could be an effective method in controlling heavy metal pollution in fly ash.

Influence of graphene oxide in a chemically activated fly ash

To divert fly ash from hazardous waste stream to beneficial uses, this work aims to improve the solidification of fly ash as a geopolymer material by using graphene oxide (GO). The hydration precursors, morphology, elemental composition, mineralogy, chemical structure and ordering of GO-modified fly ash geopolymer were investigated by means of Raman spectroscopy, SEM/BSE, EMPA, XRD/TGA and 29Si/27Al MAS-NMR, respectively, to unravel the role of GO. The experimental results suggest that GO regulated the Ca/Si, Si/Al and Ca/(Si + Al) mole ratios to facilitate the formation of fly ash hydrates with improved mechanical strength, as GO showed the ability to selectively affect the distribution of different hydration precursors. GO also promoted the formation of low quartz and jennite-like hydrates. Overall, the 28-day compressive strength of fly ash geopolymer (w/b = 0.35) in this study was improved by 23% (from 33.6 MPa to 41.4 MPa) with GO admixed at 0.02% by mass of fly ash. The NMR study showed that GO improved the polymerization degree of fly ash geopolymer by increasing the total Q3 and Q4 Si-tetrahedrons, which suggests potential for improving the immobilization of heavy metals in fly ash.

Influence of ignition of waste fishbone on enhancing heavy metal stabilization in municipal solid waste incineration (MSWI) fly ash

Abstract Natural fishbone was found effective for heavy metal stabilization (particularly Pb) in municipal solid waste incineration (MSWI) fly ash in a previous study presented by the authors. Natural fishbone containing hydroxyapatite (HAP) could stabilize Pb and Zn under appropriate conditions; however, undesirable release of Cu and P occurred in the presence of non-HAP fraction. Therefore, ignition of fishbone for optimizing this technique was investigated. Based on thermogravimetry and differential thermal analysis, mass loss test, and X-ray diffractometry, it was found that ignition not only removed the non-HAP fraction, but also increased the crystallinity of HAP in fishbone as a function of temperature. Various ignition temperatures were carefully evaluated based on the performance of candidate fishbones in metal stabilization under designated conditions. Accordingly, fishbone ignited at 430 °C (IGN-430) was selected. Both natural and IGN-430 fishbones were involved in the stabilization of heavy metals in fly ash under various scenarios. IGN-430 provided more efficient metal stabilization than natural fishbone under the same conditions, because it supplied more fishbone HAP at the same dose. The non-HAP fraction in fishbone was the main source of released P in the leachate and presumably facilitated Cu and Zn release from fly ash. This facilitation hindered metal stabilization, the influence of which was greater at higher liquid condition. Consequently, IGN-430 fishbone is preferred to natural fishbone used for metal stabilization in fly ash, as it provided a more efficient metal stabilization without undesirable release of the other elements. A solid-like condition was even more beneficial for heavy metal stabilization in fly ash by fishbone HAP.

Stabilization of heavy metals in fly ashes from municipal solid waste incineration via wet milling

This study reports the stabilization of toxic heavy metals in fly ashes from incineration of municipal solid waste (MSW) in a grate furnace incinerator (GFI) and a fluidized bed incinerator (FBI) using wet milling without water-extraction pretreatment. After wet milling for 24 h, the relative leaching rates (RLRs) were decreased for all the studied heavy metals (Cr, Cu, Zn, Cd and Pb) and met the regulatory leaching concentrations as determined by Toxicity Characteristic Leaching Procedure (TCLP). For the GFI fly ash, the RLRs of Cr, Cu, Zn and Pb decreased from 11.00%, 4.27%, 5.12%, and 72.64% to 0.81%, 0.08%, 0.33%, and 1.12%, respectively. The decreased rate of RLRs for all four heavy metals had exceeded 90%. For the FBI fly ash, the RLRs of Cr, Cu, Zn, Cd and Pb decreased from 6.81%, 0.09%, 1.99%, 8.92%, and 0.10% to 1.51%, 0.05%, 1.14%, 3.05% and 0.02%, respectively. European Community Bureau of Reference (BCR) sequential extraction results demonstrate that, for the GFI fly ash, wet milling led to decreases in the water- and acid-soluble and reducible fractions, but an increase in the more stable residual fraction. For the FBI fly ash, except for Cu, the residual fraction increased while the water- and acid-soluble fraction largely decreased after wet milling.

Utilization of waste natural fishbone for heavy metal stabilization in municipal solid waste incineration fly ash

Waste fishbone that is a rich source of hydroxyapatite (HAP) was investigated for the stabilization of heavy metals (mainly Pb) in municipal solid waste incineration (MSWI) fly ash, which has not been particularly studied to date. In the present study, the original status of fishbone and fly ash was preserved. The stabilization was initially conducted during a leaching process (Scenario A). Greater doses of fishbone and longer contact times benefited the stabilization in this scenario, and the highest Pb stabilization efficiency reached 59.31% after a 72 h-leaching process at fishbone dose of 100% (w/w). The abundant supply of Pb relative to fishbone HAP might affect the efficient stabilization. Therefore, the influence of liquid/solid (L/S) was examined for improving the stabilization under a settling condition (Scenario B). Lower L/S conditions were beneficial to the stabilization, and the highest Pb stabilization efficiency achieved was 66.35% at L/S of 1 mL/g for 24 h of settling when fishbone dose was 50% (w/w). Additionally, as the second most leachable metal, Zn was also considerably stabilized at L/S < 1.5 mL/g (solid-like conditions) in Scenario B. Cu in the leachates of both scenarios increased in the presence of fishbone. The facilitation of Cu release undesirably hindered Pb stabilization; however, this impediment presumably occurred during the leaching process rather than settling period. The solid-like condition was found to be more favorable for using fishbone HAP on the stabilization of heavy metals in fly ash. L/S and settling period were identified as the critical factors for the efficient stabilization of Pb and Zn, respectively. It is suggested that this technique not only helps treat MSWI fly ash in a low-cost and environmental-friendly approach, but also helps reduce the problems associated with waste fishbone disposal.

Fractionation of Heavy Metals in Fly Ash from Wood Biomass Using the BCR Sequential Extraction Procedure.

The aim of this study was to extract the wood biomass fly ash fractions by a three-stage sequential extraction method for acetic acid and ion exchangeable (BCR 1), hydroxylamine hydrochloride reduction (BCR 2), and hydrogen peroxide oxidation (BCR 3) fractions in order to access the leaching behavior of this residue. The fly ash was collected as a by-product from the processing of mixed wood biomass in Udbina combustion facility, Croatia. Concentrations of several elements (As, Cd, Cr, Cu, Ni, Pb and Zn) in all extracts were determined by inductively coupled plasma atomic emission spectrometry. The acidic exchangeable form of the metals was used to evaluate the potential ecological risk of biomass fly ash. According to calculated potential ecological risk index, it is confirmed that mobility of Ni and As has major environmental impact. However the results of potential ecological risk show that biomass fly ash had a low risk.

Municipal solid waste incineration (MSWI) fly ash washing pretreatment by biochemical effluent of landfill leachate: a potential substitute for water

ABSTRACTSulfate-rich biochemical effluent of landfill leachate (BEL) resulting from aged refuse bioreactor was employed to wash municipal solid waste incineration (MSWI) fly ash. The dechlorination ability of BEL was found to be nearly equivalent to redistilled water (RW), and the concentrations of lead (Pb) and zinc (Zn) in the washing solution resulting from the BEL washing process were lower than that of the RW washing process. Fourier transform infrared (FTIR) analysis indicated that the formation of calcium sulfate and hydroxides in fly ash after BEL washing and their entrapping function could significantly inhibit the leaching of Pb and Zn. Besides, toxicity characteristic leaching procedure (TCLP) tests showed that the BEL washing treatment did not increase the risk of heavy metals leaching from fly ash, and the leaching concentrations of Pb, Zn, copper (Cu) and cadmium (Cd) of BEL washed fly ash were lower than that of RW washed fly ash, which suggested BEL washing treatment could slightly immobilize heavy metals in fly ash. For MSWI fly ash dechlorination, our present results indicated that BEL used in this batch experiment could be a potential substitute for water.

A conjugative study of Typha latifolia for expunge of phyto-available heavy metals in fly ash ameliorated soil

With the ever-increasing demand for coal, the drawbacks associated with it also increase. Accelerating accumulation of fly ash, a byproduct in coal combustion processes, is of major environmental concern at present. Fly ash finds its maximum utilization in concrete and cement factory due to its pozzolanic property. However, fly ash is also used in the agricultural division as a “fertilizer” especially in West Bengal. However, there is no upper limit to how much fly ash should be added to agricultural soil. Current study deals with fly ash, that has been mixed with soil in four proportions namely, 0% (FA0), 25% (FA25), 50% (FA50) and 75% (FA75). A wetland emerged plant – Typha latifolia - has also been incorporated in the system. Mobility and metal(loids) relation has been established determining soil-ash physico-chemical properties along with nutritional enrichment to the plant system. Sequential Extraction methods are therefore employed to examine the element speciation. Application of 25 percent Fly ash was found to enhance the N(0.11%), P(0.09%), K(0.051%) and Si(7.7%) availability in soil and also resulted in better plant growth and xylem integrity as justified by electron microscopic observation. At end of final sampling, total arsenic concentration was 50.07±0.25mgKg–1 in Typha associated sample comparing to 59.51±0.19mgKg-1 in without Typha system using 25% ash. This study reflects the utility strategies of fly ash and Typha latifolia in combination for the better expunge of phyto-available metals form agricultural soil during a stop gap, before further crop production particularly another wetland plant, rice.

Stabilization of lead in incineration fly ash by moderate thermal treatment with sodium hydroxide addition.

Municipal solid waste (MSW) incineration fly ash (IFA) can be potentially reused as a substitute for some raw materials, but treatment for detoxification is indispensable owing to high contents of heavy metals in fly ash. In the present work, due to excessive leaching concentration of lead (Pb), a moderate thermal treatment with sodium hydroxide (NaOH) addition was employed to stabilize Pb in IFA. The moderate thermal treatment was performed under relatively low temperature ranging from 300 to 500°C and at retention time from 1 to 3 h with NaOH addition in a range of 1 to 9%. Leaching results showed that leaching concentrations of Pb in IFA leachates decreased below the standard for hazardous waste identification (5 mg/L) in China under all treatment scenarios. With the increase of temperature, retention time and the amount of NaOH, the concentration of Pb were further suppressed in IFA leachates. Especially, at 500°C for 3 h with 9% NaOH addition, the concentration of Pb dropped to 0.18 mg/L, which was below the standard for sanitary landfill (0.25 mg/L) in China. In thermal process, needle-like crystallites melted to form granules and clumps with compacter structure and less pores. After the thermal treatment, water-soluble and exchangeable fractions of Pb significantly decreased. Therefore, the thermal treatment coupled with NaOH could be applied to realize the environmentally sound management of MSW IFA.