Treated Fly Ash Research Articles

Mineral phase evolution and heavy metals migration during the hydrothermal treatment of municipal solid waste incineration fly ash

The solidification of heavy metals in the municipal solid waste incineration fly ash was realized by the hydrothermal treatment with mineral additives added. The experimental results showed that the addition of SiO2 at 200 °C with the NaOH concentration was 0.5 mol/L attributed to the formation of fibrous tobermorite and effectively reduced the heavy metals toxicity of hydrothermal products, especially Pb and Cu. When SiO2 and Al2O3 were both introduced, the generated katoite and sodalite showed a better curing effect on Zn at lower NaOH concentrations. Further, the dynamic correlation between the tobermorite formation and heavy metals solidification was explored. It was found that the heavy metals in fly ash were first dissolved into the alkaline liquid phase and then transferred into the solid phase as the treatment proceed. The solidification of Pb which finished before 8 h was mainly due to the encapsulation of the tobermorite precursor before crystallization, while that of Cu which lasted over 48 h mainly relied on the adsorption and cation exchange effect caused by the formed tobermorite. Therefore, selecting the appropriate mineral addition scheme and hydrothermal time according to the fly ash components and heavy metals categories can effectively improve the curing cost performance.

Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash

The proper treatment and utilization of oily sludge (OS) and incineration fly ash (IFA) remains a significant challenge due to their hazardous nature. To attain effective recovery of petroleum hydrocarbons and synergistic disposal, this study investigated the co-pyrolysis of OS and IFA, resulting in successful energy recovery, CO2 mitigation, and heavy metal immobilization. Results revealed that the peak ratio of light oil to heavy oil fractions reached 179.42% with 20 wt% IFA addition, accompanied by the highest aromatic hydrocarbons selectivity of 30.72% and the lowest coke yield of 106.13 mg/g OS under the optimal temperature of 600 °C. In-depth analysis indicated that IFA inhibited the poly-condensation of macromolecular PAHs and promoted their cracking into light aromatic hydrocarbons. The addition of 50 wt% IFA significantly increased H2 yield (21.02 L/kg OS to 60.95 L/kg OS) and facilitated CO2 sequestration due to its higher content of Ca-bearing minerals. Moreover, high IFA ratios promoted the reduction of Fe species in OS to a low-valence state. Heavy metals in co-pyrolysis char were well immobilized into stable fractions with lower environmental risks. This work highlights the potential of co-pyrolysis as a viable approach for simultaneous disposal of multiple hazardous wastes and offers new insights for their utilization.

Characteristics of Fly Ash and its Influence on the Germination of Amaranthus Seeds

The physical and chemical properties of fly ash collected from three different thermal power stations were studied and the fly ash with neutral to alkaline pH was utilized as a medium for the germination of amaranthus seeds. The germination test was carried out using a completely randomized design with two replications at Agricultural College and Research Institute, Madurai. The various fly ash was analyzed for its physical and chemical properties with standard methods. The fly ash with a slightly alkaline pH was selected and media was prepared with soil, vermicompost and farm yard manure. The seeds of an amaranthus crop were sown and the germination percentage, days to germination, shoot length, root length and vigour index were recorded. The collected fly ashes were recorded with low bulk density, alkaline pH with quantities of micro and macronutrients. The fly ash of Tuticorin has a slightly alkaline pH (8.03) and was utilized for media preparation. Among the different media, the media with treatment Fly ash + Soil + Vermicompost (1:1:4) + Bio Fertilizer has recorded higher germination percentage, shoot length, root length, vigour index, lower days to germination with 94.6%, 18.3 cm, 4.8 cm,16.17 and 2.8 respectively. The vermicompost is best for the enrichment of fly ash compared to farm yard manure as it is completely decomposed organic manure.

Density functional theory study on the formation mechanism of CaClOH in municipal solid waste incineration fly ash.

Municipal solid waste incineration (MSWI) fly ash is defined as a kind of hazardous waste because of its high levels of multiple pollutants. The main component of MSWI fly ash is CaClOH, and the characteristics have not achieved consensus. And density functional theory (DFT) was used to calculate the formation process of CaClOH in this study, which mainly included HCl adsorption on CaO (0 0 1) surface and Ca(OH)2 (0 0 1) surface and the surface reaction process. The reaction mechanism was investigated. The results showed that the maximum adsorption energies of HCl on CaO and Ca(OH)2 surfaces reached - 195.17kJ/mol and - 83.48kJ/mol, respectively, representing strong chemisorption. The chemisorption process was shown as the adsorption of H atom on O site, and the adsorption capacity was reflected in the adsorption range of O site. The significant electron density overlap between O site and H atom meant that a new chemical bond formed, which made the adsorption structure stable. The adsorption energy of multi-HCl adsorption on the crystal surfaces was not proportional to the number of HCl molecule, indicating that the adsorption processes were influenced by each other. After surface reaction, the H-Cl bond was broken completely, and the structure of CaO and Ca(OH)2 changed to new structures. According to transition state (TS) search, the formation of CaClOH had a higher priority, easier than that of CaCl2, explaining the presence of CaClOH in fly ash. The study provides helpful information for the solidification treatment of fly ash.

Utilization of municipal solid waste incineration fly ash with coal fly ash/metakaolin for geopolymer composites preparation

The geopolymer technique is a promising method for the solidification/stabilization (S/S) treatment of municipal solid waste incineration fly ash (MSWIFA). To investigate the feasibility of resource utilization in MSWIFA by geopolymerization process, the macroscopic and microscopic properties of the coal fly ash/metakaolin-based geopolymer composites containing MSWIFA were studied. The leaching test was conducted to evaluate the S/S effect of geopolymer. Results showed that CFA/MK-based geopolymer demonstrated effective stabilization of heavy metals in MSWIFA. The flowability of geopolymer composites increased with the MSWIFA content, where 40% replacement ratio of MSWIFA significantly improved the slump and consistency of geopolymer mortar by 86.3% and 80.4%. However, 40% content of MSWIFA reduced the compressive strength and splitting tensile strength of geopolymer composites by 80% and 62%. The strength development rate in early ages of geopolymer composites was accelerated by mixing less than 15% MSWIFA. Whereas, the strength development at 7–28 days was almost unaffected by MSWIFA. The addition of MSWIFA decreased the amount of sodium-(calcium) aluminosilicate hydrate and sodium aluminosilicate hydrate gels. Although the addition of MSWIFA refined the gel pores in geopolymer, the pore volume and porosity increased and the compactness of microstructure decreased with the increment of the MSWIFA content in geopolymer composites. Based on these results, it is feasible to realize resource utilization of MSWIFA using geopolymer composites with low content of MSWIFA (less than 15% was recommended in this study).

Enhancing sustainable valorization: Harmless synergistic melting treatment for high-value vitreous products from MSWI fly ash and electrolytic manganese residue

The waste-to-energy and manganese industries face significant ecological challenges due to two major risk sources: municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue (EMR), especially, the MSWI fly is classified as hazardous waste. High temperature melting is a promising method for harmless disposal of solid wastes. However, it has yet to be industrialized due to the high costs and energy consumption. This study proposes using EMR as an additive to co-melt with MSWI fly ash, aiming to develop a method that minimizes energy consumption while producing high value-added products. To this end, the phase evolution and phase-change cooling characteristics during the co-melting process of MSWI fly ash and EMR were experimentally investigated. XRD and SEM analyses revealed that pure vitreous slag can be obtained when mixtures are heated to 1500 °C for 120 min with ≥40 wt% EMR addition under natural air-cooling conditions. Additionally, to produce vitreous slag by air-cooling and increase MSWI fly ash treatment capacity, the molten mixture with 30 wt% EMR addition was adopted in the directional solidification experiments to establish a predictive model relating the average cooling rate to the glass content. The findings ultimately contribute to the advancement of melting-based industrial applications.

Participation influence of silicate on the temporal and spatial distribution of chloride electromigration in the electrokinetics of municipal solid waste incineration fly ashes

The chloride (Cl) content in cement production and the other derivate products has been strictly restricted to avoid the corrosion of steels in building construction, which significantly narrows the possible utilization choices of Cl-abundant municipal solid waste incineration (MSWI) fly ashes. The reduction of soluble Cl from the source materials becomes an important prerequisite for efficient resource utilization of MSWI fly ashes. In this study, an electrochemical platform was constructed to investigate the potential pathways of the migration and transformation of Cl species in silicate-participated MSWI fly ashes during electrokinetic (EK) treatment. The factors including the operating time, voltage, and mass ratio of silicate to fly ashes were adjusted to evaluate the changes in pH, current, and Cl distribution. Each treated fly ash in the sampling area was evenly cut into 3 layers and 72 parts to accurately determine the distribution of Cl in the electrolyzer. More Cl- ions in the surface layer were electromigrated to the anode than those in the middle and bottom layers. The addition of silicate enhanced electromigration and improved the distribution uniformity of Cl species in the sampling area. The reduction in Ca2+ electromigration with the formation of C-S-H caused by the silicate guaranteed the continuous transfer and reactions of Cl- anions in the EK treatment.

Development of a selective nanoporous Na-zeolite X from Moroccan coal fly ash for anionic dye adsorption and removal

ABSTRACT The hydrothermal treatment of Moroccan coal fly ash (CFA) in a basic medium leads to the selective formation of Na-X zeolite. By fusion with sodium hydroxide in the presence of CFA, the particles are transformed into sodium silicate and sodium aluminate, from which hydrothermal reaction favourably results in the production of a pure Na-X zeolite. A good crystallinity of Na-X zeolite was attained at NaOH:fly ash ratio of 1.2. Their high surface area and pore characteristics make the Na-X zeolite useful for the removal of the model anionic dye RY145 from water. The adsorption efficiency of the synthesised Na-X zeolite was evaluated and compared to raw CFA. Dye adsorption is more significant at acid pH, suggesting that the zeolite surface is positively charged. Kinetic and isotherm models applied to fit the experimental data reveal that the adsorption process is physisorption. It results that zeolite X is an efficient adsorbent for the extraction of dyes.

Environmental investigation on the use of a phosphogypsum-based road material: Radiological and leaching assessment

The transformation of phosphate ore into phosphoric acid results in the generation of high volumes of phosphogypsum (PG), an industrial by-product largely stockpiled worldwide. This solution, considered as the least damaging to the environment, constitutes a risk for the receiving environment due to the presence of harmful impurities such as heavy metals and radionuclides which hinder its large-scale valorization. This paper presents an environmental characterization of Moroccan phosphogypsum and an investigation on the environmental performance of a new lime (L) - fly ash (FA) treated phosphogypsum based road material. The concentration of metallic trace elements (Cr, Pb, Ni, Zn, Cu) in raw phosphogypsum ranged between 0.2 and 243 ppm, while its radioactivity reached 970 Bq/kg for Ra-226. The environmental performance of the proposed new road material (40% PG, 42% FA, 18% L) was evaluated using radiological risk indices besides static and dynamic leaching tests. The results showed a radioactivity reduction up to 82%, and an immobilization of metallic trace elements ranging from 25 to 100%. The stabilization/solidification mechanisms involved in the lime - fly ash treatment would be responsible for the fixation of these contaminants within the newly formed matrix.

The migration and transformation mechanisms of heavy metals during molten salt cyclic thermal treatment of MSWI fly ash

Molten salt thermal treatment has been demonstrated to be effective in dissolving heavy metals in municipal solid waste incineration (MSWI) fly ash. However, the complex thermochemical reactions of various heavy metals during the process remain unclear. This study investigated the migration and transformation mechanisms of typical heavy metals during molten salt (NaCl-CaCl2) cyclic thermal treatment of fly ash at 600–750 °C, as well as the leaching characteristics and recovery methods of heavy metals in the reacted products. Molten chlorides could be recycled to extract heavy metals from fly ash, which reduced the leaching toxicity of heavy metals in the reacted slags. Over 64.3% of Cd, Cu and Pb in fly ash were transferred to molten salt while the migration rate of Zn was restrained to only 32.3% during the cyclic process at 750 °C. Regarding Cd, Cu, and Pb in molten salt, the chlorination and dissolution of their oxides were significant, while the combination of their chlorides with free O2– to form oxides precipitation was weak. However, the above reaction characteristics of Zn were the opposite. Furthermore, Zn2+ could be stabilized into hardystonite (Ca2ZnSi2O7) in molten salt by reacting with Si2O76- generated from the combination of O2– and SiO2. Besides, increasing the reaction temperature facilitated the chlorination and dissolution of heavy metals. For recovery, heavy metals could be concentrated on the insoluble matters of molten salt, with a maximum concentration of approximately 5 times that in fly ash.

Desilication of high-silica Indian coal fly ash by alkali leaching with KOH and NaOH: A comparative study

ABSTRACT Indian coal fly ash generally comprises 50–60% Si O 2 , and 25–35% A l 2 O 3 can potentially replace bauxite as an aluminum resource. Aluminum recovery from coal fly ash is highly dependent on removing amorphous silica, activating the inactive mullite phase, and increasing the Al / Si ratio. This work thoroughly investigated and compared the alkali-desilication operation by two widely used alkalis, KOH and NaOH , based on four operational parameters: liquid-to-solid ratio, KOH or NaOH concentration, leaching time and temperature. Using SEM, EDX, and XRD, the morphology and phase of fly ash and solid byproducts were analyzed. NaOH was more effective than KOH in Si O 2 dissolution at all operational parameters. A 20 wt% concentration, 5:1 liquid-to-solid ratio, 2hrs leaching time, and 100°C temperature were the optimum removal conditions for silica from fly ash using NaOH . With KOH , the ideal desilication conditions were obtained at 28 wt% concentration, 3hrs leaching time, and 150°C temperature. The highest Al / Si ratios were obtained under the same optimal desilication conditions. Using KOH and NaOH , the Al / Si ratio was enhanced from 0.58 to 1.26 and 1.45, respectively. The main zeolitic products obtained were Hydroxysodalite in NaOH -treated fly ash and Linde F zeolite and Kalsilite in KOH -treated fly ash.

Utilization of municipal solid waste incineration fly ash as construction materials based on geopolymerization

Incineration has been widely used to dispose municipal solid wastes (MSWs) with heat recovery. The generation of fly ash (FA, around 3∼5 wt% of the fed amount) that is normally defined as hazardous wastes remains a serious problem. It is ideal to work out a way to reutilize FA for valuable use instead of landfilling. As a novel utilization technology for municipal solid waste incineration (MSWI) fly ash, geopolymerization can produce geopolymer as construction materials with the advantages of low energy consumption, low pollution and high utilization rate. In this paper, metakaolin (MK) and washed fly ash (WFA) were used to prepare MSWI fly ash-based geopolymer (FAG) with alkali activator. Besides, the strength, heavy metals immobilization and acid resistance of FAG were in detail studied. Under the proper formulation, all the prepared FAGs exhibited strength higher than MU15 level (≥15 MPa) and the maximized one reached MU30 (≥30 MPa). Heavy metals including Cr, Mn, Cu, As, Pb, Zn and Cd had a immobilization rate of more than 92%, and others like As, Pb and Zn were nearly fully immobilized. As for the simulated testing for acid rain scenario, FAG could still fix up the heavy metals well indicating a controllable risk for the environment, which could be ascribed be its high acid neutralization capacity. In a word, this work reports a feasible method for treatment and resource reutilization of MSWI fly ash.

The reaction pathway and mechanism of 2,4-dichlorophenol removal by modified fly ash-loaded nZVI/Ni particles.

Nanoscale zero-valent iron (nZVI) is more valuable in environmental restoration than other materials. Chemical treatment of fly ash (CFA) was employed as a support material to disperse iron nickel bimetal nanoparticles (CFA-nZVI/Ni) to remove 2,4-dichlorophenol (2,4-DCP). Batch experiments showed that 2,4-DCP was completely removed by CFA-nZVI/Ni, and an optimal loading ratio was 8:1. The degradation of 2,4-DCP by CFA-nZVI/Ni was a chemical control reaction with an activation energy of 95.6 kJ mol-1 and followed pseudo-first-order kinetics. The addition of Cl- increased the removal rate of 2,4-DCP by 4%, while the addition of CO32- and SO42- decreased the removal rate of 2,4-DCP by 32% and 72.3%, respectively. The removal process of 2,4-DCP by CFA-nZVI/Ni included adsorption and reduction. The 2-CP (7.1 mg/L) and 4-CP (11.6 mg/L) could be converted to phenol using the CFA-nZVI/Ni system. Cl on the para-position of 2,4-DCP was simpler to remove than on the ortho-position. The following steps were taken in the electrophilic substitution reaction between substituted phenols and hydrogen radicals: 2,4-DCP > 2-CP > 4-CP > phenol. This research provides a novel concept to effectively remove 2,4-DCP and mechanism analysis.

Comprehensive assessment of thermal characteristics, kinetics and environmental impacts of municipal solid waste incineration fly ash during thermal treatment

The volatilization of heavy metals and the release of harmful gases during the thermal treatment of municipal solid waste incineration (MSWI) fly ash (FA) can cause secondary pollution. Understanding the thermal characteristics, heavy metal behaviors and environmental emissions in FA roasting is significant for pollution control and heavy metal elimination. In this work, the thermodynamics, kinetics, environmental impacts, carbon emission, phase transition, leaching toxicity, transition behavior of chlorine and heavy metals in FA thermal treatment were investigated comprehensively for the first time through TG-FTIR, XRD, ICP-OES and IC. The apparent activation energy and thermodynamic parameters were obtained according to the kinetic modeling method. The average apparent activation energy values of the first, second, third, and fourth stages were 60.21, 114.91, 190.23, and 226.67 kJ/mol, respectively, and the reaction control models were chemical reaction model (No.3), assumed random nucleation and subsequent growth model (No.21), assumed random nucleation and subsequent growth model (No.14), and nucleation model (No.10). The environmental impacts illustrate that large amounts of gaseous products, including CO2, H2O, NO and SO2, are released during the thermal treatment of FA, and the emission of CO2 sharply increases as the temperature exceeds 550 °C. When treating 1 kg of FA at 1000 °C, the release of CO2 in stages I, II, III and IV is 0.18, 7.06, 116.34 and 177.21 g, respectively, and the total carbon emission is approximately 300 g. The leaching toxicity of heavy metals in FA is higher below 800 °C, and it is mainly caused by Pb. In addition, the volatilization rate of heavy metals and chlorine increased significantly as the calcination temperature exceeded 800 °C, among which, the volatilization rates of Pb, Cu, and Cl can reach 99.87%, 90.25% and 73.85%, respectively. At high temperatures, heavy metals in FA exist primarily in oxidizable and residual states. The obtained findings can provide theoretical guidance for pollution control and process optimization of FA thermal treatment.

Low Temperature Thermal Treatment of Incineration Fly Ash under Different Atmospheres and Its Recovery as Cement Admixture.

Municipal solid waste incineration fly ash is classified as hazardous waste because it contains dioxins and a variety of heavy metals. It is not allowed to be directly landfilled without curing pretreatment, but the increasing production of fly ash and scarce land resources has triggered consideration of the rational disposal of fly ash. In this study, solidification treatment and resource utilization were combined, and the detoxified fly ash was used as cement admixture. The effects of thermal treatment in different atmospheres on the physical and chemical properties of fly ash and the effects of fly ash as admixture on cement properties were investigated. The results indicated that the mass of fly ash increased due to the capture of CO2 after thermal treatment in CO2 atmosphere. When the temperature was 500 °C, the weight gain reached the maximum. After thermal treatment (500 °C + 1 h) in air, CO2, and N2 atmospheres, the toxic equivalent quantities of dioxins in fly ash decreased to 17.12 ng TEQ/kg, 0.25 ng TEQ/kg, and 0.14 ng TEQ/kg, and the degradation rates were 69.95%, 99.56%, and 99.75%, respectively. The direct use of fly ash as admixture would increase the water consumption of standard consistency of cement and reduce the fluidity and 28 d strength of mortar. Thermal treatment in three atmospheres could inhibit the negative effect of fly ash, and the inhibition effect of thermal treatment in CO2 atmosphere was the best. The fly ash after thermal treatment in CO2 atmosphere had the possibility of being used as admixture for resource utilization. Because the dioxins in the fly ash were effectively degraded, the prepared cement did not have the risk of heavy metal leaching, and the performance of the cement also met the requirements.

Treatment of coal fly ash and its environmentally friendly use in the rubber and plastic industries

Treatment of coal fly ash and its environmentally friendly use in the rubber and plastic industries

Designing low-carbon cement-free binders for stabilization/solidification of MSWI fly ash

Low-carbon and high-efficiency binder is desirable for sustainable treatment of municipal solid waste incineration fly ash (MSWI FA). In this study, CaO or MgO was used to activate ground granulated blast furnace slag (GGBS) to form calcium silicate hydrate and magnesium silica hydrate gel for stabilization/solidification of hazardous MSWI FA. Experimental results showed that potential toxic elements (PTEs), such as Pb and Zn, significantly inhibited the formation of reaction products in CaO-GGBS system due to the complexation between Ca(OH)2 and PTEs, whereas PTEs only had insignificant inhibition on transformation from MgO to Mg(OH)2 in MgO-GGBS system, resulting in lower leachabilities of PTEs and higher mechanical strengths. Stabilization/solidification experiments demonstrated that MSWI FA (70 wt%) could be recycled by MgO-GGBS binder (30 wt%) into blocks with desirable 28-day compressive strengths (3.9 MPa) and PTEs immobilization efficiencies (99.8% for Zn and 99.7% for Pb). This work provides mechanistic insights on the immobilization mechanisms of PTEs in CaO/MgO-GGBS systems and suggests a promising MgO-GGBS binder for low-carbon treatment of MSWI FA.

Amelioration of flexible pavement subbases using fly ash and natural fibres

The use of fly ash as a stabilizing element has already been demonstrated to be successful. Moreover, the CBR values of fly ash do not meet IRC criteria. This study intends to analyze the addition of coir fibre, a natural and environmentally sustainable resource, as a reinforcing material. Fly ash and coconut coir are waste materials that can be locally sourced, making them cost-effective and environmentally friendly materials. The article discusses the benefits of fly ash and coconut coir in flexible pavement subbases, highlighting their potential as a sustainable solution for road construction and maintenance. The laboratory experiments conducted on fly ash subbases reinforced with various percentages of coconut coir ranging from 0.1, 0.2, and 0.3 prove that the addition of natural fibres can enhance the subbase's strength properties, with a maximum improvement observed at a 0.2% reinforcement level. Further, the cyclic plate load tests conducted on the treated fly ash subbase at optimum conditions provide valuable insights into the subbase's performance under repeated loading conditions. The results suggest that the natural fibres performed satisfactorily in improving the subbase's load-carrying capacity and reducing rebound deformations, indicating that this approach can be a viable alternative to conventional pavement subbase materials.

Facile treatment of municipal solid waste incineration fly ash by one-step microwave hydrothermal method: Hazards detoxification and tobermorite synthesis

A one-step microwave hydrothermal method is proposed here for the harmless treatment and resource recycling of water-washed municipal solid waste incineration fly ash (WMSWI-FA). Dioxins and heavy metals in WMSWI-FA can be detoxified, tobermorite can be synthesized by adjusting the parameters of NaOH dosage, reaction temperature and time. We conclude that NaOH is essential to synthesize tobermorite from WMSWI-FA, and higher temperatures and longer times are beneficial for degrading dioxins. However, excessive NaOH has a negative effect on the degradation of dioxins. Experiments showed that adding 20 wt% NaOH to WMSWI-FA and reacting at 260 °C for 3 h, the tobermorite was successfully synthesized, the residual dioxins (42.80 ng-TEQ/kg) and the leaching concentrations of heavy metals were lower than the limited value of the HJ 1134–2020 standard. The hydrothermal treated WMSWI-FA contains tobermorite, which supports it to be recycled as construction material and adsorbent. The one-step microwave hydrothermal treatment demonstrates favorable industrialization prospects, as it performs well in harmless treatment and resource utilization of WMSWI-FA.

Municipal Solid Waste Incineration Fly Ash: From Waste to Cement Manufacturing Resource.

This study investigates the possibility of using municipal solid waste incineration fly ash as a supplementary cementitious material to replace part of the clinker in cement. Life cycle assessment has shown that the partial replacement of clinker with blast furnace slag (CEM III) reduces cement's global warming potential by ~30%, while replacing clinker with fly ash reduces it by up to 55%. When using CEM III as the control binder in cement in which 55 wt% of the clinker was replaced with hydrothermally treated fly ash, the flexural strength decreased by ~60% and the compressive strength by ~65%. When the fly ash was mixed with calcined and vitrified demolition materials, flexural strength decreased by ~30% and compressive strength by ~50%. The hardening of the hydraulic binders fixed the heavy metals in the municipal solid waste incineration fly ash.