The metal-leaching and acid-neutralizing capacity of MSW incinerator ash co-disposed with MSW in landfill sites

Municipal solid waste (MSW) incinerator (MSWI) bottom ash and fly ash were used as landfill cover or were co-disposed with MSW to measure their potential metal-releasing and acid-neutralizing capacity (ANC) in landfill sites. Five lysimeters (height 1.2m, diameter 0.2m), simulating landfill conditions, were used in the experiment. Four contained either bottom ash (BA) or fly ash (FA) with BA:MSW ratios of 100 and 200 g L(-1) and FA:MSW ratios of 10 and 20 g L(-1), and the fifth was the control, which contained no ash. The lysimeters were arranged so as to contain four layers, with BA or FA placed on top of MSW within each layer. Each lysimeter was recirculated with 100mL leachate using peristaltic pumps, and 100mL of the leachate was collected weekly to measure the soluble metal concentrations. The results showed that the concentrations of soluble alkali metals measured in the leachate were in the order Ca>K>Na>Mg. In addition, the concentrations of soluble alkali metals of Ca and K collected from the lysimeters containing FA were found to be higher than the concentrations from the lysimeters containing BA. The concentrations of heavy metals (Cd, Cr, Cu, Ni, and Zn) were found to be <1 mg L(-1) except for Pb, which reached 2 mg L(-1). These results suggest that for alkali metals there might be an ANC consistent with the results of an acid titration curve, which would provide suitable conditions for anaerobic digestion of the MSW in the landfill. Furthermore, heavy metals and trace metals were found in concentrations, which were too low to exert inhibitory effects on anaerobic digestion, and thus they could serve as micronutrients to exert beneficial rather than detrimental effects on landfill biostabilization.     

Biotoxicity evaluation of fly ash and bottom ash from different municipal solid waste incinerators

Different types of municipal solid waste incinerator (MSWI) fly and bottom ash were extracted by TCLP and PBET procedures. The biotoxicity of the leachate of fly ash and bottom ash was evaluated by Vibrio fischeri light inhibition test. The results indicate the following: (1) The optimal solid/liquid ratio was 1:100 for PBET extraction because it had the highest Pb and Cu extractable mass from MSWI fly ash. (2) The extractable metal mass from both fly ash and bottom ash by PBET procedure was significantly higher than that by TCLP procedure. (3) The metal concentrations of fly ash leachate from a fluidized bed incinerator was lower than that from mass-burning and mass-burning combined with rotary kiln incinerator. (4) The TCLP and PBET leachate from all MSWI fly ash samples showed biotoxicity. Even though bottom ash is regarded as a non-hazardous material, its TCLP and PBET leachate also showed biotoxicity. The pH significantly influenced the biotoxicity of leachate.     

Application of fly ash on the growth performance and translocation of toxic heavy metals within Cajanus cajan L.: Implication for safe utilization of fly ash for agricultural production

The present study was undertaken to examine the influence of the application of fly ash (FA) into garden soil for Cajanus cajan L. cultivation and on accumulation and translocation of hazardous metals from FA to edible part. Numerous studies have been reported on the growth and yield of agricultural crops under FA stress; however, there is a dearth of studies recommending the safe utilization of fly ash for crop production. Pot experiments were conducted on C. cajan L., a widely cultivating legume in India for its highly nutritious seeds. C. cajan L. were grown in garden soil and amended with varying concentrations of FA in a weight/weight ratio (0%, 25%, 50% and 100%; w/w). Incorporation of fly ash from 25% to 100% in garden soil increases the levels of pH, particle density, porosity and water holding capacity from 3.47% to 26.39%, 3.98% to 26.14%, 37.50% to 147.92% and 163.16% to 318.42%, respectively, than the control while bulk density decrease respectively from 8.94% to 48.89%. Pot experiment found that accumulation and translocation of heavy metals in tested plant depends on the concentration of FA. Addition of FA at lower concentration (25%) had shown positive results in most of the studied parameters of growth and yield (14.23% than control). The experimental results confirmed that lower concentration of FA (25%) is safe for C. cajan cultivation, which not only enhanced the yield of C. cajan L. significantly but also ensured the translocation of heavy metals to edible parts within the critical limits.     

Sonochemical treatment of fly ash for dye removal from wastewater

Fly ash samples modified by NaOH solution and sonochemical treatment were tested for a basic dye (methylene blue) adsorption in aqueous solution. It is found that sonochemical treatment of fly ash can significantly increase the adsorption capacity depending on the concentration of NaOH and treatment time. The untreated FA and the sonochemically treated sample exhibits adsorption capacity at 6 x 10(-6)mol/g and 1.2 x 10(-5)mol/g at 30 degrees C, respectively. The adsorption tests show that solution pH and adsorption temperature also influence the adsorption behaviour. The adsorption isotherms can be fitted by Langmuir and Freudlich models, while the two-site Langmuir heterogeneous model will present the best result.     

Cement-stabilized fly ash base courses

Various demonstration projects have been carried out in The Netherlands with cement-stabilized fly ash as a base course. Usually these courses were made of 100 parts by mass of fly ash; 10 parts by mass of cement; 20 to 30 parts by mass of water. However, the projects were not quite successful since delamination was observed, and long-term strength, after a period of six years of performance, appears to be much smaller than expected on the basis of preliminary laboratory research. A model for pozzolanic reaction of fly ash recently developed by Fraay and Bijen pointed out that the reactivity of fly ash is influenced greatly by the pH value of the pore water. A pH of at least 13 is required to initiate fly ash pozzolanic reaction in a Portland cement environment. Pore water extraction measurements showed that the pH of cement-stabilized fly ash often has a substantially lower value. In this high-volume fly ash application the effect of the acidity of fly ash is much greater than in ordinary concrete with cement replaced by fly ash up to 30%. By addition of NaOH and/or sodium silicate to the mixing water, the pH value can be increased above the ‘threshold’ value.

Tests were carried out with different types of class-F fly ashes and with different NaOH concentrations in the mixing water. The results show an increase in compressive strength of up to 300% depending on the type of fly ash, and a substantial decrease in the rate of water absorption.     

Oxidation of arsenic bearing fly ash as pretreatment before solidification.

When a waste fly ash, containing large amounts of As(2)O(3), is solidified using cement and lime, the arsenic concentration in the leachate (extraction test DIN 38 414 S4) is determined by the solubility of CaHAsO(3) and can be lowered to a value of ca. 5 mg/l, in a saturated solution of Ca(OH)(2). One of the criteria for landfilling of hazardous waste is, however, that the arsenic concentration in the leachate must be lower than 1 mg/l. In this paper, it is shown that oxidation of the waste before solidification, whereby As(III) is oxidised to As(V) using H(2)O(2), lowers the leaching of arsenic, and other contaminants, from the solidified product. With the speciation program MINTEQA2, it is calculated that the solubility of As(V) in the presence of a pure Ca(3)(AsO(4))(2) precipitate is lower than the solubility of As(III) in the presence of a pure CaHAsO(3) precipitate. The arsenic concentration in the presence of both a Ca(OH)(2) and a Ca(3)(AsO(4))(2) precipitate can even be lowered to 0.47 mg/l (pH 12.5). The As concentration in the leachate of the extraction test on an oxidised S/S sample was indeed lowered to ca. 0.5 mg/l, which is a reduction by a factor of 10 compared to the concentration of ca. 5 mg/l, obtained in the leachate of the extraction test on a non-oxidised S/S sample. This is in very good agreement with the calculated value of 0.47 mg/l. Also, the pretreatment decreased the cumulative fraction of arsenic released over the entire test period of a semi-dynamic leach test by a factor of 7. At all times during the test, the As concentration did not exceed the norm of 1 mg/l.     

Solid-state conversion of fly ash to effective adsorbents for Cu removal from wastewater

Solid-state conversion of fly ash to an amorphous aluminosilicate adsorbent (geopolymer) has been investigated under different conditions and the synthesised material has been tested for Cu2+ removal from aqueous solution. It has been found that higher reaction temperature and Na:FA ratio will make the adsorbents achieving higher removal efficiency. The adsorbent loading and Cu2+ initial concentration will also affect the removal efficiency while the adsorption capacity exhibits similarly at 30-40 degrees C. The adsorption capacity of the synthesised adsorbent shows much higher value than fly ash and natural zeolite. The capacity is 0.1, 3.5 and 92 mg/g, for fly ash, natural zeolite, and FA derived adsorbent, respectively. The kinetic studies indicate that the adsorption can be fitted by the second-order kinetic model. Langmuir and Freundlich isotherms also can fit to the adsorption isotherm.     

Comparative study of adsorption properties of Turkish fly ashes. II. The case of chromium (VI) and cadmium (II)

The purpose of the study described in this paper was to compare the removal of Cr(VI) and Cd(II) from an aqueous solution using two different Turkish fly ashes; Afsin-Elbistan and Seyitomer as adsorbents. The influence of four parameters (contact time, solution pH, initial metal concentration in solution and ash quality) on the removal at 20+/-2 degrees C was studied. Fly ashes were found to have a higher adsorption capacity for the adsorption of Cd(II) as compared to Cr(VI) and both Cr(VI) and Cd(II) required an equilibrium time of 2h. The adsorption of Cr(VI) was higher at pH 4.0 for Afsin-Elbistan fly ash (25.46%) and pH 3.0 for Seyitomer fly ash (30.91%) while Cd(II) was adsorbed to a greater extent (98.43% for Afsin-Elbistan fly ash and 65.24% for Seyitomer fly ash) at pH 7.0. The adsorption of Cd(II) increased with an increase in the concentrations of these metals in solution while Cr(VI) adsorption decreased by both fly ashes. The lime (crystalline CaO) content in fly ash seemed to be a significant factor in influencing Cr(VI) and Cd(II) ions removal. The linear forms of the Langmuir and Freundlich equations were utilised for experiments with metal concentrations of 55+/-2mg/l for Cr(VI) and 6+/-0.2mg/l for Cd(II) as functions of solution pH (3.0-8.0). The adsorption of Cr(VI) on both fly ashes was not described by both the Langmuir and Freundlich isotherms while Cd(II) adsorption on both fly ashes satisfied only the Langmuir isotherm model. The adsorption capacities of both fly ashes were nearly three times less than that of activated carbon for the removal of Cr(VI) while Afsin-Elbistan fly ash with high-calcium content was as effective as activated carbon for the removal of Cd(II). Therefore, there are possibilities for use the adsorption of Cd(II) ions onto fly ash with high-calcium content in practical applications in Turkey.     

Cr(VI) concentration from batch contact/tank leaching and column percolation test using fly ash with additives

Batch contact, tank leaching and column percolation tests were conducted to investigate the Cr(VI) concentration in the solution/leachate from two fly ashes (fly ash A and B) with additives. The additives used were cement, low alkalinity additive and Ariake clay. There are several factors influencing Cr(VI) concentration in solution/leachate, namely (1) properties of solid/liquid mixture (chemical composition, pH value, etc.), (2) cementation effect, (3) amount of water in contact with the solid mass (solid/liquid ratio in case of batch contact test), and (4) adsorption characteristics of the solid particles to Cr ions. The test results indicate that fly ash A has less cementation component (CaO of 1.92%) and the amount of water in contact with the fly ash played an important role. As a result, Cr(VI) concentration from the column percolation test was much higher than that of the batch contact test. Adding Ariake clay had more effect on reducing Cr(VI) concentration for fly ash A than B because the pH value of the solution from fly ash A was lower, which provided a favorable condition for Cr(VI) ions to be reduced to Cr(III) and possibly to be adsorbed by clay particles. Fly ash B has more cementation component (7.15%) and for column percolation test, curing the sample for 1 week reduced Cr(VI) concentration significantly. The test results indicate that in engineering practice, a method which closely simulates the field condition should be selected to assess possible environmental effects and corresponding countermeasure methods.     

Solidification/stabilization of electric arc furnace dust using coal fly ash. Analysis of the stabilization process

In this paper, the stabilization of electric arc furnace (EAF) dust containing hazardous metals such as Pb, Cd, Cr or Zn is described. The treatment involves a waste solidification/stabilization (S/S) process, using coal fly ash as the fundamental raw material and main binder. The article also contains a brief review of the most important recent publications related to the use of fly ash as S/S agents.The efficacy of the process has been evaluated mainly through leaching tests on the solidified products and compliance with some imposed leachate limits. The concentration of metals leaching from the S/S products was strongly leachate pH dependent; thus, the final pH of the leachate is the most important variable in reaching the limits and, therefore, in meeting the stabilization goals.In this study, the dependence relationship between the leachate pH and the concentrations of metals in the leachate are analyzed; in some cases, this allows us to estimate the speciation of contaminants in the S/S solids and to understand the mechanism responsible for reduced leachability of heavy metals from solidified wastes.     

Degradation of PCDD/Fs by mechanochemical treatment of fly ash from medical waste incineration

The potential of mechanochemical treatment (MC) to degrade PCDD/Fs contained in fly ash was tested via grounding with and without calcium oxide (CaO) under atmospheric pressure. Three types of fly ash collected from medical waste incineration were compared, originating either from rotary kiln fluidized bed multi-stage incinerator using activated carbon spray (FA1, FA2), or a simple stoker incinerator without activated carbon spray (FA3). In test I: CaO to FA1 mixed at ratio of 6-60% was milled at rotational speed of 350 rpm; in test II: FA2 and FA3 without CaO were milled at rotational speed of 400 rpm. The duration of the tests was 2h. The results from the present study indicate that (1) under two test conditions of with and without CaO, PCDD/Fs contained in real fly ash both can be degraded by mechanochemical treatment, (2) under condition of blending with CaO, the degradation efficiency of PCDD/Fs increased with increasing ratio of CaO, (3) the degradation efficiency of PCDD/Fs may increase with rotational speed increasing and (4) the destruction and dechlorination are major mechanism for PCDD/Fs degradation. These results show that mechanochemical treatment is a high potential technology for PCDD/Fs degradation in fly ash.     

Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials

Polish bituminous (PB) and South African (SA) coal fly ash (FA) samples, derived from pilot-scale circulated fluidized bed (CFB) combustion facilities, were utilized as raw materials for the synthesis of zeolitic products. The two FAs underwent a hydrothermal activation with 1 M NaOH solution. Two different FA/NaOH solution/ratios (50, 100 g/L) were applied for each sample and several zeolitic materials were formed. The experimental products were characterized by means of X-ray diffraction (XRD) and energy dispersive X-ray coupled–scanning electron microscope (EDX/SEM), while X-ray fluorescence (XRF) was applied for the determination of their chemical composition. The zeolitic products were also evaluated in terms of their cation exchange capacity (CEC), specific surface area (SSA), specific gravity (SG), particle size distribution (PSD), pH and the range of their micro- and macroporosity. Afterwards the hybrid materials were tested for their ability of adsorbing Cr, Pb, Ni, Cu, Cd and Zn from contaminated liquids. Main parameters for the precipitation of the heavy metals, as it was concluded from the experimental results, are the mineralogical composition of the initial fly ashes, as well as the type and the amount of the produced zeolite and specifically the mechanism by which the metals ions are hold on the substrate.     

Supercritical fluid extraction and accelerated solvent extraction of dioxins from high- and low-carbon fly ash

This study investigates the replacement of Soxhlet extraction by supercritical fluid extraction (SFE) or accelerated solvent extraction (ASE) for the removal of dioxins from municipal waste incinerator fly ash. SFE is very matrix dependent; higher percent recoveries versus Soxhlet extraction can be obtained for low-carbon-level fly ash, but only a few percent of dioxins can be extracted from high-carbon-level fly ash. The addition of large quantities of toluene in the extraction cell prior to extraction of high-carbon fly ash improves the recovery of the lowest chlorinated dioxins (approximately 90%), but a maximum of 20% of the octachlorodibenzo-p-dioxins can be extracted. Since large quantities of toluene are needed to improve the recoveries, ASE with toluene was tested. Recoveries similar to Soxhlet extraction can be obtained in 2 h at 80 degrees C. Increasing the temperature to 150 degrees C increases the extraction rate and yields recoveries of approximately 110-160% compared to 48-h Soxhlet extraction for all congeners for both low- and high-carbon fly ashes. These results question the choice of Soxhlet extraction as a reference method for dioxin determination.     

Influence of flue gas SO2 on the toxicity of heavy metals in municipal solid waste incinerator fly ash after accelerated carbonation stabilization

The influence of CO₂ content and SO₂ presence on the leaching toxicity of heavy metals in municipal solid waste incinerator (MSWI) fly ash was studied by examining the carbonation reaction of MSWI fly ash with different combinations of simulated incineration flue gases. Compared with raw ash, the leaching solution pH of carbonated ash decreased by almost 1 unit and the leaching concentrations of heavy metals were generally lower, with that of Pb decreasing from 19.45 mg/L (raw ash) to 4.08 mg/L (1# carbonated ash). The presence of SO₂ in the incineration flue gas increased the leaching concentrations of heavy metals from the fly ash to different extents after the carbonation stabilization reaction. The pH of the leaching solution was the main factor influencing the leaching concentrations of heavy metals. The increase in buffer capacity with the pH of carbonated ash caused an increase in heavy metal stability after the carbonation reaction. Accelerated carbonation stabilization of MSWI fly ash could reduce its long-term leaching concentrations (toxicity) of Cu, Pb, Se, and Zn. The leaching concentrations of heavy metals from carbonated ash also likely had better long-term stability than those from raw ash. The presence of SO₂ in the incineration flue gas increased the proportion of exchangeable state species of heavy metals; slightly increased the long-term leaching toxicity of Cu, Pb, Se, and Zn; and reduced the long-term stability of these metals in the fly ash after the carbonation reaction.     

Coal ash conversion into effective adsorbents for removal of heavy metals and dyes from wastewater

Fly ash was modified by hydrothermal treatment using NaOH solutions under various conditions for zeolite synthesis. The XRD patterns are presented. The results indicated that the samples obtained after treatment are much different. The XRD profiles revealed a number of new reflexes, suggesting a phase transformation probably occurred. Both heat treatment and chemical treatment increased the surface area and pore volume. It was found that zeolite P would be formed at the conditions of higher NaOH concentration and temperature. The treated fly ash was tested for adsorption of heavy metal ions and dyes in aqueous solution. It was shown that fly ash and the modified forms could effectively absorb heavy metals and methylene blue but not effectively adsorb rhodamine B. Modifying fly ash with NaOH solution would significantly enhance the adsorption capacity depending on the treatment temperature, time, and base concentration. The adsorption capacity of methylene blue would increases with pH of the dye solution and the sorption capacity of FA-NaOH could reach 5 x 10(-5) mol/g. The adsorption isotherm could be described by the Langmuir and Freundlich isotherm equations. Removal of copper and nickel ions could also be achieved on those treated fly ash. The removal efficiency for copper and nickel ions could be from 30% to 90% depending on the initial concentrations. The increase in adsorption temperature will enhance the adsorption efficiency for both heavy metals. The pseudo second-order kinetics would be better for fitting the dynamic adsorption of Cu and Ni ions.     

Phosphate removal from aqueous solutions using raw and activated red mud and fly ash

The effect of acidification and heat treatment of raw red mud (RM) and fly ash (FA) on the sorption of phosphate was studied in parallel experiments. The result shows that a higher efficiency of phosphate removal was acquired by the activated samples than by the raw ones. The sample prepared by using the RM stirred with 0.25 M HCl for 2h (RM0.25), as well as another sample prepared by heating the RM at 700 degrees C for 2h (RM700), registered the maximum removal of phosphate (99% removal of phosphate). This occurred when they were used in the phosphate sorption studies conducted at pH 7.0 and 25 degrees C with the initial PO(4)(3-) concentration of 155 mg P/l. The FA samples treated in the same way described above can achieve 7.0 and 8.2 mg P/l phosphate removal for FA0.25 and FA700 respectively, corresponding to 45.2% and 52.9% removal. The activated materials performed higher phosphate removal over broader pH range compared with the raw ones. The influences of various factors, such as initial pH and initial phosphate concentration on the sorption capacity were also studied in batch equilibration technique. Solution pH significantly influenced the sorption. Each sample achieved the maximal removal of phosphate at pH 7.0. The amount of phosphate removal increased with the solute concentration. The Freundlich and Langmuir models were used to simulate the sorption equilibrium. The results indicate that the Langmuir model has a better correlation with the experimental data than the Freundlich model.     

The performance and application of fly ash modified by PDMDAAC

Fly ash modification by polydimethydiallylammonium chloride (PDMDAAC) in laboratory scale was explored in this work and the adsorption performance of modified fly ash and its application in dyeing wastewater treatment were also studied. The key factors (concentration and temperature) for PDMDAAC to affect the adsorption properties of fly ash (FA) were revealed using the orthogonal test with four factors. The results indicated that the adsorption magnitude of fly ash to PDMDAAC increased due to its favorable specific surface causing the change of the surface charge nature. Hence, adsorption performance of modified fly ash on organic molecules and its ion exchange capacity are strengthened. The maximum color removal efficiency was obtained as 88.2% by modified fly ash with 2.0 g/100 mL dosage in dyeing wastewater, which is much higher than 12.5% color removal efficiency by raw fly ash with the same dosage. And, the used modified fly ash could be used for cement production as additive agent. The intensity of cement produced with 15% the modified fly ash in weight reached the Chinese Cement Standard (GB/T17671-1999), blazing a promising novel way in fly ash utilization.     

Phosphate removal from water by fly ash: factorial experimental design

The influence of three variables (phophate concentration, initial pH of solution (pH(0)) and the fly ash dosage) on the removal efficiency of phosphate (% E) and equilibrium pH of solution (pH(eq)) by using fly ash was studied by means of 2(3) full factorial experimental designs. The parameters coded as x(1), x(2) and x(3), consecutively(,) were used. The parameters were investigated at two levels (-1 and 1). The effects of these factors on dependent variables, namely, % E and pH(eq) were investigated. To determine the significance of effects, the analysis of variance with 95% confidence limits was used. It was shown that % E and pH(eq) obtained in this study were found to be 99.6% and 11.16, corresponding to the operating condition of 25 mg l(-1), 2 g l(-1) and 5.5 for the phosphate concentration, fly ash dosage and pH(0), respectively.     

Biostabilization assessment of MSW co-disposed with MSWI fly ash in anaerobic bioreactors

Municipal solid waste incinerator (MSWI) fly ash has been examined for possible use as landfill interim cover. For this aim, three anaerobic bioreactors, 1.2m high and 0.2m in diameter, were used to assess the co-digestion or co-disposal performance of MSW and MSWI fly ash. Two bioreactors contained ratios of 10 and 20 g fly ash per liter of MSW (or 0.2 and 0.4 g g(-1) VS, that is, 0.2 and 0.4 g fly ash per gram volatile solids (VS) of MSW). The remaining bioreactor was used as control, without fly ash addition. The results showed that gas production rate was enhanced by the appropriate addition of MSWI fly ash, with a rate of approximately 6.5l day(-1)kg(-1)VS at peak production in the ash-added bioreactors, compared to approximately 4l day(-1)kg(-1)VS in control. Conductivity, alkali metals and VS in leachate were higher in the fly ash-added bioreactors compared to control. The results show that MSW decomposition was maintained throughout at near-neutral pH and might be improved by release of alkali and trace metals from fly ash. Heavy metals exerted no inhibitory effect on MSW digestion in all three bioreactors. These phenomena indicate that proper amounts of MSWI fly ash, co-disposed or co-digested with MSW, could facilitate bacterial activity, digestion efficiency and gas production rates.     

Investigations of sequential leaching behaviour of Cu and Zn from coal fly ash and their mobility in environmental conditions

The quantitative evaluation of chemical fraction of Cu and Zn in the coal fly ash by methods of five-step sequential extraction was carried out in order to characterize metal mobility in environmental conditions. The research involved (i) water-soluble (pH 7), (ii) acid-soluble (pH 5), (iii) oxide, (iv) difficult reducible and (v) residual metal fractions. It was discovered, that the total extraction of the studied metals from coal fly ash to solutions take place in the following quantities Cu-39.0mgkg(-1) and Zn-89.0mgkg(-1). The investigations of chemical fractions proved that the subject metals occur mainly in coal fly ash as: oxide (Cu-12.0mgkg(-1), Zn-37.0mgkg(-1)) and residual (Cu-9.5mgkg(-1), Zn-27.0mgkg(-1)) as well as difficult reducible (Cu-16.5mgkg(-1), Zn-22.0mgkg(-1)). Low concentrations of metals for water-soluble fraction (Cu相似文献