Solid Waste Incineration Fly Ash Research Articles

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.

Modification of phases evolution and heavy metal immobilization in alkali-activated MSWI FA by the incorporation of converter steel slag

Municipal solid waste incineration fly ash (MSWI FA) poses serious environmental concerns due to its high content of hazardous organics, heavy metals, and soluble salts. This study aimed to solidify the harmful components in MSWI FA by alkali activation and explore the influence of converter steel slag on the phase evolution. With the increase of curing time, the amount of C-(A)-S-H gel increased and its microstructure shifted to a high crystalline and crosslinked state, accompanied by the increase of Ca/Si ratio. The addition of steel slag was beneficial to the formation of C-(A)-S-H gel and enhanced its crystallinity and crosslinking degree. Compared with alkali-activated MSWI FA, NaCl and KCl content decreased more significantly with curing time and Friedel ’salts were found in the matrix modified by steel slag. The leaching toxicity of heavy metals in alkali-activated matrix was reduced as curing time increased. The increase of C-(A)-S-H gel content and changes of its microstructure were conducive to the stabilization of heavy metals and chlorides. The refinement of pore size and improvement of compressive strength contributed to the physical encapsulation of heavy metals and chlorides.

The Influence of Liquid/Solid Ratio and Pressure on the Natural and Accelerated Carbonation of Alkaline Wastes

The purpose of this research is to assess the yield and reaction rate potential of carbon dioxide (CO2) sequestration through mineralisation using readily available and inexpensive resources by exploiting waste materials. In this case, a blend of four different kinds of ashes and combustion by-products were used, namely, coal fly ash (CFA), flue gas desulphurization (FGD) residues, municipal solid waste incineration fly ashes (MSWI FA) and bottom ash (MSWI BA), produced at the same location. To highlight the impact of these materials on the carbonation process, various factors were analysed, including particle size distribution, immediately soluble contents, mineralogy, particles’ detailed structure, and chemical composition. After preparing the samples, two carbonation processes were tested: natural carbonation and accelerated carbonation. To evaluate the impact of the water content on the reaction rate and yield of the mineral carbonation, various liquid-to-solid (L/S) ratios were used. The results demonstrate that the water content and pressure play a significant role in the CO2 sequestration during the accelerated carbonation, the higher the L/S, the greater the yields, which can reach up to 152 g CO2/kg with MSWI FA, while no substantial difference seems to emerge in the case of the natural carbonation.

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.

Study on Mechanism of MSWI Fly Ash Solidified by Multiple Solid Waste-Based Cementitious Material Using the Rietveld Method

A novel multiple solid waste-based cementitious material (MSWCM) was developed to immobilize municipal solid waste incineration (MSWI) fly ash. The compressive strength of MSWCM with different ratios of MSWI fly ash reached the standard requirements after curing for 28 days. X-ray powder diffraction (XRD) in combination with the Rietveld method was employed to investigate the content and phase transformation of hydration products. The main hydration products of pure MSWCM paste were C-S-H, hydroxyapatite, ettringite and C-A-S-H. With increases in curing time, the content of ettringite and C-A-S-H increased significantly. The main hydration products of MSWCM paste with MSWI fly ash were C-S-H and Friedel’s salt. The contents increased markedly with increased curing time from 21.8% to 28.0% and from 8.53% to 16.7%, respectively. Additionally, a small amount of PbHPO4 (0.51–0.96%) and lead phosphate Pb3(PO4)2 (0.14–0.51%) were detected, indicating that phosphate had an effective curing effect on lead ions. The results showed that most of the hydration reactions had started at the initial stage of curing and reacted quickly to form a large number of hydration products. The quantitative analyses of hydration products provide essential information for understanding the immobilization mechanism of MSWI fly ash in MSWCM paste.

Fabrication and performance analysis of sustainable municipal solid waste incineration fly ash alkali-activated acoustic barriers

Abstract The recycling of hazardous municipal solid waste incineration fly ash (MSWIFA) is drawing more attention, in which the alkali-activation technique may provide great potential to make full use of it as sustainable acoustic materials. The present work evaluated the applicability of alkali-activated MSWIFA-based materials (AAFMs) as porous acoustic barriers. The chemical composition and microtomography of the as-prepared AAFMs were characterized by X-ray diffraction. Fourier-transform infrared spectroscopy, and scanning electron microscopy. With the incorporation of MSWIFA and foaming agents, the dry bulk density and porosity of AAFMs were subsequently examined. Moreover, the compressibility and leachability of AAFMs were also investigated to evaluate their mechanical performance and environmental safety as construction materials. A sound absorption test was eventually conducted to explore the sound absorption performance of AAFMs, considering the main factors such as aluminum addition, MSWIFA dosage, and sample thickness. The results verified the good chemical stability, leachability, and sound absorption performance of porous AAFMs. Specifically, it indicated that the aforementioned factors have a boosting effect on forming highly porous structures that improve sound absorption performance, namely sound absorption coefficient and noise reduction coefficient.

Valorization of solid waste incinerator fly ash by geopolymer production for removal of anionic bromocresol green dye from water: Kinetics, isotherms and thermodynamics studies

In this study, solid waste incinerator fly ash (SWI-FA) based geopolymer adsorbents were prepared by alkalination of hazardous SWI-FA and cured at different temperatures of 30 0C (GP30), 50 0C (GP50), 70 0C (GP70), and 90 0C (GP90). The geopolymers were applied as low-cost adsorbents for the removal of anionic bromocresol green (BCG) dye from water under varying conditions. The precursor and geopolymers were characterized by XRD, SEM-EDS, FT-IR, and point of zero charge (PZC). The geopolymers were morphologically different with varying chemical compositions. The kinetic data were best described by the pseudo second order model. The experimental equilibrium adsorption data were fitted to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich-Kaganer adsorption isotherm models. The Langmuir monolayer maximum adsorption capacities increased consistently with curing temperature, from 41.70 mg/g to 515.5 mg/g for GP30 and GP90, respectively, a new benchmark for these materials for anionic dyes. The thermodynamic parameters, namely enthalpy (ΔH<0), Gibbs free energy (ΔG<0), entropy (ΔS >0) and activation energy (Ea) indicated that the processes are spontaneous, exothermic, physical (Ea<5kJ/mol and ΔH<40kJ/mol) and enthalpy-driven. The adsorption mechanisms included strong electrostatic interactions and hydrogen bonding. The production of these geopolymers provides dual advantage of waste valorization with applications in depollution of water.

Novel insight of the thermal degradation kinetics, environmental impact and transformation behavior of heavy metals and chlorine of municipal solid waste incineration fly ash in nitrogen

Thermal treatment is an effective method to dispose of municipal solid waste incineration (MSWI) fly ash (FA), however, present research mainly focuses on the thermal behavior of FA in air, neglecting the investigation of FA pyrolysis characteristic in inert gases. The weight loss, phase transition, environmental impact, and conversion behavior of heavy metals and chlorine during the FA pyrolysis in N2 were measured using TG-FTIR-XRD-ICP-IC to increase understanding of the transformation process and decomposition features of FA in inert gas. The results demonstrated that CO2, NO, C-O(H), HCl, SO2, and H2O are emitted during FA pyrolysis due to the decomposition of inorganic salts and organic compounds. After being roasted at 1200 °C, the volatilization rates of As, Cr, Cd, Cu, Pb, and Zn were 56.71%, 34.75%, 99.56%, 83.41%, 96.22%, and 97.19%, respectively. However, the removal rate of Cl was only 51.43%, owing mostly to the formation of Ca2SiO4CaCl2 at high temperatures, which hampered chlorine volatilization. The kinetic of FA pyrolysis was investigated using FWO, KAS, and CR methods at heating rates of 10, 20, 30, and 40 °C/min, which suited the experimental data of each stage well. Chemical reaction (No. 2), assumed random nucleation and its subsequent growth (No. 11), and three-dimensional diffusion and spherical symmetry (No. 21) were the reaction control procedures of stages I, III and IV, with activation energies of 54.04, 213.03 and 280.85 kJ/mol, respectively. The degradation kinetics, environmental emissions, and reaction mechanisms of FA pyrolysis in the N2 atmosphere can provide a novel insight for pollution reduction and process optimization.

Development of a loose powder sintering method for the preparation of porous ceramic from municipal solid waste incineration fly ash

Loose powder sintering was used to prepare porous ceramic from municipal solid waste incineration fly ash (MSWI FA) and waste glass (WG). Sintering experiments at various temperatures, holding times, Al2O3 and SiC were conducted to investigate their effect on the ceramic properties and volatile heavy metal removal efficiency. The results show that increasing temperature from 1100 °C to 1250 °C promoted the transition of the mixtures from loose powder to a densified sintered matrix, with a bulk density increase of 31.10% and an open porosity decrease of 70.41%. The bulk density of the ceramic increased to 2.44 g/cm3 with 3% Al2O3 addition. The removal rates of Pb, Zn, Cu and Cd were higher than 90% at 1200 °C for 90 min, and promoted by the increasing temperature and holding time. Notably, 3% Al2O3 addition inhibited the volatilisation of Zn, Cu and Cd, particularly for Zn, the removal rate of which reduced to 61.66% at 1200 °C. The bulk density of the ceramic decreased to a minimum value of 1.48 g/cm3 with 4% SiC. The ratio of MSWI FA:WG:Al2O3:borax of 28.3:56.7:10:5 was proposed to obtain ceramic with a bulk density of 1.54 g/cm3 and a water absorption rate of 8.59% at 1150 °C. The leaching concentration of the porous ceramic met the Chinese regulatory standard (GB 8978-1996). Preparation of MSWI FA-based porous ceramics using the powder sintering method is a promising route for the harmless utilisation of MSWI FA. The porous ceramic is potentially applicable as a thermal-insulation building material.

A novel method for solidification/stabilization of MSWI fly ash by graphene nanoplatelets synergistic alkali-activated technology

Municipal solid waste incineration (MSWI) fly ash with considerable heavy metals needs to be safely disposed of before landfill. In this study, graphene nanoplatelets (GNPs)/MSWI fly ash solidified body was prepared by alkali-activated technology, in order to improve the solidification ability of heavy metals and maximize the utilization of MSWI fly ash to cope with the scarcity of landfill. This paper studied the effect and mechanism of GNPs on heavy metal leaching characteristics. Results showed that solidified body with adding 0.05 wt% GNPs exhibited the highest compressive strength and the lowest heavy metals leaching concentration. Adding GNPs promoted heavy metals in solidified body to be converted into the residual state. Meanwhile, the microstructure and morphology characteristic analysis results indicated that GNPs promoted C-(A)-S-H gels formation. There were various kinds of solidification/stabilization (S/S) mechanisms including physical adsorption, physical encapsulation and chemical bonding in GNPs/MSWI fly ash solidified bodies. This study paves a potential new way for the application of nanomaterials in S/S MSWI fly ash through alkali-activated technology, and graphene is a more promising additive.

Resource utilization of ultrasonic carbonated MSWI fly ash as cement aggregates: Compressive strength, heavy metal immobilization, and environmental-economic analysis

Ultrasonic carbonation technology is effective for municipal solid waste incineration fly ash (MSWI FA) pretreatment. However, the subsequent disposal route is unclear. In this study, the mechanical strength and heavy metal immobilization effects of raw FA (RFA), washed FA (WFA), conventional carbonated FA (CFA), and ultrasonic carbonated FA (UFA) as cement aggregates in the preparation of concrete were investigated in comparison. The reaction kinetic analysis showed that ultrasonic excitation promoted the internal diffusion phase of the carbonation reaction. The compressive strength of the 28-day solidified bodies was in the order of UFA (32.2 MPa) > CFA (22.8 MPa) > WFA (16.4 MPa) > RFA (12.6 MPa). The 3-day UFA solidified body showed the highest degree of hydration and polymerization through 29Si solid-nuclear-magnetic analysis. The nano-CaCO3 in the UFA provided more nucleation sites and hydration reaction sites for the hydration reaction. In addition, the fine UFA particles filled the pores between cement particles, enhancing the strength of the product. Heavy metal leaching tests described that CFA and UFA met the criteria for resource utilization (HJ/T 1134–2020), and the immobilization efficiency of Cu, Pb, and Zn in the UFA solidified body was above 95.6%, 99.3%, and 99.2%, respectively, mainly by the dual immobilization of carbonate chemical precipitation and cement hydration. Considering 11 environmental impact factors and economic benefits, life-cycle-assessment and cost-benefit analysis were selected. The integrated environmental-economic results show that cement usage is the main influencing factor. UFA scenario was recommended as engineering applications with low global warming potential.

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.

Synthesis of metakaolin-based geopolymer foamed materials using municipal solid waste incineration fly ash as a foaming agent

The existence of metallic aluminum in municipal solid waste incineration fly ash (MSWIFA) makes it challenging to recycle MSWIFA into cement materials because expansion occurs in the resultant matrices. Geopolymer-foamed materials (GFMs) are gaining attention in the field of porous materials due to their high-temperature stability, low thermal conductivity and low CO2 emission. This work aimed to utilize MSWIFA as a foaming agent to synthesize GFMs. The physical properties, pore structure, compressive strength and thermal conductivity were analyzed to assess different GFMs which were synthesized with various MSWIFA and stabilizing agent dosages. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis were conducted to characterize the phase transformation of the GFMs. Results showed that when MSWIFA content was increased from 20 to 50%, the porosity of GFMs increased from 63.5 to 73.7%, and bulk density decreased from 890 to 690 kg/m3. The addition of stabilizing agent could trap the foam, refine the cell size, and homogenize the cell size range. With the stabilizing agent increase from 0 to 4%, the porosity increased from 69.9 to 76.8%, and the bulk density decreased from 800 to 620 kg/m3. The thermal conductivity decreased with increasing MSWIFA from 20 to 50%, and stabilizing agent dosage from 0 to 4%. Compared with the collected data from references, a higher compressive strength can be obtained at the same level of thermal conductivity for GFMs synthesized with MSWIFA as a foaming agent. Additionally, the foaming effect of MSWIFA results from the H2 release. The addition of MSWIFA changed both the crystal phase and gel composition, whereas the stabilizing agent dosage had little impact on the phase composition.

Life-Cycle Assessment of Municipal Solid Waste Incineration Fly Ash Recycling as a Feedstock for Brick Manufacturing

The recovery of municipal solid waste incineration (MSWI) fly ash is currently considered to be the most viable solution for its management. However, in developing resource recovery technologies, it is crucial to consider the overall environmental impact. This study employed a life-cycle assessment (LCA) to compare environmentally friendly red bricks partially utilizing MSWI fly ash as a raw material with conventional red bricks. The results demonstrate that the use of phosphoric acid during the resource recovery process imposes the most significant environmental burden, followed by electricity consumption. To address this issue, in this study, we simulated the replacement of phosphoric acid with phosphoric acid monohydrate recovered from discarded fire extinguishers, resulting in the production of second-generation environmentally friendly red bricks. The analysis revealed that the environmentally friendly red bricks exhibited a mere 5.52% increase in total environmental impact compared with traditional red bricks. Moreover, by stabilizing heavy metals using recovered phosphoric acid monohydrate, the second-generation environmentally friendly red bricks achieved an 8.75% reduction in total environmental impact relative to traditional red bricks. These findings highlight the environmental benefits of fly ash reuse in red brick production, and the incorporation of other industrial waste or byproducts could further enhance its efficacy. The application of the LCA facilitated the identification of key areas for improvement and enabled precise evaluation of the environmental benefits associated with waste reuse.

Ceramic Aggregate Material Formulated with MSWI Fly Ash and Fuel Ash for Use as Filter Media

This study aimed to develop a novel filtering medium ceramic aggregate prepared using municipal solid waste incineration (MSWI) fly ash and the fuel ash from coal power plants, together with small amounts of silicon carbide foaming agent and magnesia flux as additives. For the manufacturing process, the dosage of MSWI fly ash and the sintering temperature were optimized to maximize the performance of the resulting materials. Leaching test results indicated that the heavy metal concentrations in the ceramic aggregate were significantly below the limits proposed by GB5085.3-2007, demonstrating its safety for wastewater treatment. The ammonia nitrogen removal efficiency was assessed, and the removal rate of the developed ceramic aggregate was found to be 16.4% higher than that of zeolite, making it comparable to commercial ceramic aggregate. Scanning electron microscopy and X-ray diffractometer analyses were conducted on the ceramic aggregates. The ammonia-nitrogen-removing mechanism, attributed to adsorption and ion exchange, is discussed based on the microstructural analysis results.

Effect of curing temperatures on geopolymerization and heavy metal solidification in alkali-activated zeolite/MSWI fly ash specimens

Admixtures of pozzolanic materials or solid wastes with municipal solid waste incineration fly ash (MSWIFA) can improve heavy metal stabilization/solidification (S/S) properties in alkali-activated MSWIFA specimens. In this work, the compressive strength of MSWIFA admixes with zeolite activated by Na2O·1.7SiO2·nH2O (FZNS) specimens with different curing times (3, 7, 14, and 28 d) and temperatures (20, 50, and 80 ℃) is investigated. The results reveal that a 40 wt% zeolite replacement of MSWIFA in FZNS specimens (FZNS40) not only increases the early compressive strength by 129% but also reduces strength loss during continuous high-temperature (50 or 80 ℃) curing. Moreover, zeolite addition promotes the creation of geopolymers at 28.5°–30.5°in X-ray diffraction (XRD) curves. During 50 or 80 ℃ curing, the NaCl peak disappears and a marginal Friedel's salt peak can be detected at 11.4°. The gel contents are more concentrated on C-S-H in FZNS0 and C-(A)-S-H/N-A-S-H in FZNS40, as demonstrated by differential thermogravimetry (DTG) and magic angle spinning nuclear magnetic resonance (MAS NMR) analysis. With zeolite addition, long-time and high-temperature curing can improve the heavy metal solidification ratio in FZNS specimens. After high-temperature curing, the honeycomb or cluster morphologies of the gel products, visible by scanning electron microscopy (SEM) in the FZNS specimens, reveal high heavy metal stabilization properties. It is easier to form the fibrous C-(A)-S-H/N-A-S-H gel near zeolite owing to the high content of SiO2 and Al2O3. Zeolite modifies the compressive strength, high-temperature stability, and heavy-metal S/S efficiency in FZNS specimens, which promotes the utilization of MSWIFA as an ecologicalresource in the future.

Effect of nano silica on solidification/stabilization of heavy metal in alkali-activated MSWI fly ash solidified body

Municipal solid waste incineration fly ash (MSWIFA) containing considerable heavy metals is classified as a hazardous waste. Alkali-activated technology can effectively improve the environmental safety of MSWIFA. Due to the low silica content of MSWIFA, the addition of nano silica (NS) solves the problem to enhance the ability of solidification/stabilization (S/S) and maximize the utilization of MSWIFA. NS/MSWIFA solidified body was prepared by alkali-activated technology in this work. The mechanical and environmental properties of NS/MSWIFA solidified body with various dosages (0–3 wt%). NS were characterized by compressive strength, leaching concentration, and chemical speciation distribution of heavy metals. A comparative study of MSWIFA and solidified bodies for exploring S/S mechanisms was investigated using XRD, FTIR, TG/DTG, NMR, and SEM/EDS tests. The results showed that the leaching concentration of Pb in MSWIFA based on different leaching methods was 23.54 mg/L and 31.7 mg/L, 19.6 times higher than the standard of hazardous waste landfill and 126.8 times higher than the standard of landfill site of municipal solid waste, respectively. The total amount of Zn and Pb was 4739 mg/kg and 2451 mg/kg, respectively, exceeding other heavy metals by 1–2 orders of magnitude. When the addition of NS was 2 wt% and 3 wt%, the compressive strength and the leaching concentration of heavy metals in solidified bodies reached the highest and the lowest, respectively. Comparative analysis indicated that adding NS promoted heavy metals in MSWIFA to be converted into a stable state, and increased hydration product C-(A)-S-H gels formation, making the structure denser. On a broader perspective, NS/MSWIFA solidified body was developed as a low-carbon and environment-friendly binder.

Thermodynamic model of MSWI flue gas cooling path: Effect of flue gas composition on heavy metal binding forms.

In the context of circular economy and heavy metal (HM) recovery from municipal solid waste incineration (MSWI) fly ash (FA), detailed knowledge of HM binding forms is required for achieving higher extraction rates. The FA mineralogy is still poorly understood due to its low grain size and low metal concentration. To investigate the HM binding forms, a sophisticated thermodynamic reactive transport model was developed to simulate ash-forming processes. The stability of different binding forms was investigated at different flue gas conditions (varying ratios of HCl, SO2, O2) by simulating the gas cooling path in closed system and dynamic open system, where the gas composition is changing upon cooling due to precipitation of solids. The simulations predict that at flue gas conditions of molar ratio S/Cl < 1, Cu and Zn precipitate as oxides (and Zn silicates) at approximately 650°C. At temperatures <300°C, Zn, Cu, Pb and Cd are predicted to precipitate as easily soluble chlorides. In flue gas with molar ratio S/Cl > 1, the HM precipitate as less soluble sulphates. The results indicate that the less soluble HM fraction in the electrostatic precipitator ash represent oxides and silicates that formed in the boiler section but were transported to the electrostatic precipitator. The model provides insight into the physical-chemical processes controlling the metal accumulation in the flue gas and FA during the cooling of the flue gas. The obtained data serve as valuable basis for improving metal recovery from MSWI FA.

Experimental study on iron ore tailings sand and municipal solid waste incineration fly ash used in semi-rigid base of asphalt pavement

In order to co-dispose and effectively utilize the bulk solid waste of iron ore tailings (IOT) sand and hazardous solid waste of municipal solid waste incineration (MSWI) fly ash, a study on using them in pavement base course is carried out in this paper. In this work, cement and fly ash (with a ratio of 1:3) were used as stabilizing materials. IOT was used as aggregate, while MSWI fly ash was used as a part of the cementitious material or as a partial replacement for the aggregate in the road base. The samples were tested for unconfined compressive strength, indirect tensile strength, drying shrinkage, temperature shrinkage and toxicity leaching. XRD and SEM-EDS were also used to analyze the changes in structure and properties. The results showed that the samples incorporated with washed ash instead of IOT had greater strength development. The unconfined compressive strength of the unconstrained samples decreased after partially replacing cement and fly ash. At the same time, the drying shrinkage rate became larger compared to the group without adding MSWI fly ash. The leaching results of toxic substances showed that most of the lead and zinc contents were easily diffused into the environment. However, after cement hardening, the leaching rate of various heavy metals was significantly reduced, which was far below the threshold of national standards.

Removal of dioxins from municipal solid waste incineration fly ash by low-temperature thermal treatment: Laboratory simulation of degradation and ash discharge stages

Dioxins in municipal solid waste incineration fly ash (MSWIFA) can cause significant risks to the environment and human health. In this study, the low-temperature thermal treatment of MSWIFA under industrial conditions was simulated in the laboratory to investigate the process parameters for dioxin degradation and ash discharge stages. Correlation analysis and dioxin fingerprint characterization were used to analyze the degradation and ash discharge processes. The degradation efficiency of low-temperature thermal treatment was influenced by multiple factors. At 400℃ for 90 min and 1% O2, the dioxin removal rate was 95.80%, the detoxification rate was 91.73%, and the residual dioxin toxicity in MSWIFA was 22.7 ± 17.8 ng I-TEQ/kg, which was in line with the limit value of 50 ng I-TEQ/kg in the “Technical specification for pollution control of fly-ash from municipal solid waste incineration” (HJ1134-2020). The increase in dioxins during ash discharge did not follow a linear relationship with the process parameters. This was assumed to be related to the MSWIFA composition, as some components containing P, Si, and Al at 150 °C may inhibit dioxin formation. The dioxin increased only by 0.79 ± 2.65 ng/kg, an increase in toxicity of 0.42 ± 0.10 ng I-TEQ/kg, when treated at 150 °C for 30 min and 10% O2.