Municipal Solid Waste Incineration Fly Ash Research Articles

Reuse of waste sulfur from biogas desulfurization for potentially toxic metals stabilization in MSWI fly ash towards zero-waste in venous industry park

Waste recycling in venous industrial park is considered to be an effective way for circular economy. However, the reuse of waste sulfur from biogas desulfurization in the park is difficult, and this problem has attracted little attention, leading to waste of resources and pollution. In this study, a stabilizer based on waste sulfur from biogas desulfurization (SBD) was prepared for stabilization of potentially toxic metals in municipal solid waste incineration (MSWI) fly ash (FA) using a simple hot alkali synthesis method. Results showed that the stabilization effect of SBD on the four commercial agents (Na2S, Amm-DTC, PBD-A and PBD-B) were significantly improved. Using 3% SBD+ 3% PBD-A, the excess Pb, Cd and Ni in the original fly ash could reach the landfill standard, and the stabilization efficiency reached 100%, 100%, and 93%, respectively, with treatment cost of 34–50 USD/t (246–366 RMB/t); compared with the single commercial agent (5% PBD-A), the stabilization efficiency of Pb was improved by 13% and the treatment cost was saved by 39%. These results provide an economical and environmentally friendly way to realize the co-disposal of MSWI FA and waste sulfur from biogas desulfurization in the park.

Co-treating MSWI fly ash in iron ore sintering process: Influence of water-washing and roll forming pretreatment on dioxins emission

Co-treating municipal solid waste incineration fly ash (MSWI-FA) in high-temperature iron ore sintering process is winning great concern. Most of the previous studies were about the co-treatment of raw MSWI-FA (without water washing) in sintering process. Although the content of dioxins in MSWI-FA was reduced, the high chlorine content promoted the secondary synthesis of dioxins and had a negative impact on the quality of sinter. This investigation focused on the emission characteristics and regulation approach of dioxins as co-treating MSWI-FA. The results showed that when MSWI-FA was added without pretreatment, the emission concentration of dioxins in sintering flue gas reached 4.28 ng I-TEQ/Nm³ . After water-washing pretreatment, the chlorine in MSWI-FA was significantly reduced, which inhibited the synthesis of dioxins via de novo reaction. The dioxins decreased significantly to 1.44 ng I-TEQ/Nm³ . Based on the washing pretreatment, the MSWI-FA was further prepared into lumps, which inhibited the dispersion of Cl-containing MSWI-FA particles in mixtures and reduced the active sites of dioxins synthesis, thereby hindering the dioxin synthesis path. The emission concentration of dioxins in sintering flue gas was further reduced from 1.44 ng I-TEQ/Nm³ to 1.15 ng I-TEQ/Nm³ . Adding 0.5% water-washed fly ash lumps had little effect on sintering indexes and dioxins concentration in flue gas. The research results laid a certain foundation for the large-scaly recycling of MSWI-FA.

Preparation and characterization of mortar specimens based on municipal solid waste incineration fly ash-activated slag

Municipal solid waste incineration fly ash (MSWIFA) contains a large amount of heavy metals, inhibiting resource utilization. This study used MSWIFA as an alkali activator and ground-granulated blast-furnace slag (GGBS) as a precursor to prepare the MSWIFA GGBS binder. Based on this, used the iron tailing sand instead of natural river sand as fine aggregate prepared mortar specimens by cooperative compression molding. Compressive strength, bulk density, water absorption, and heavy metal leaching tests were conducted and combined with micro XRD, FTIR, and SEM examinations to characterize the mortar specimens. The results show that the optimal MSWIFA: GGBS was 2:8. It was also found that increasing the molding pressure was beneficial to strength development. Compared to the specimens without the application of molding pressure, the 3 d and 28 d strength values increased by 148.6 and 122.2%, respectively, after the application of 35 MPa molding pressure. The reason is that the pressure effect can increase the cohesion of the particles, promote the hydration reaction to proceed, and the hydration products increase to fill the pores, increase the structural compactness and promote strength development. The resource utilization of MSWIFA must be guaranteed not to produce environmental pollution simultaneously. For this reason, the heavy metal leaching test was conducted on 28 d mortar specimens, and the results showed that the leaching rates of Zn, Pb, Cu, Cr, and Ni met the requirements of the Chinese Standard (GB16889-2008). The research results can provide a theoretical basis for the large-scale recycling of MSWIFA.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS2 nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS2 nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS2 in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

Footprints in compositions, PCDD/Fs and heavy metals in medical waste fly ash: Large-scale evidence from 17 medical waste thermochemical disposal facilities across China.

Chemical compositions, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) profiles and heavy metals (HMs) leachability of medical waste fly ash (MWFA) from 17 thermochemical treatment facilities in eight Chinese provinces were first investigated. Large-scale and extended monitoring revealed high chloride and Zn contents and similar PCDD/Fs congener profiles in MWFA. Particularly, the PCDD/Fs and HMs concentrations implied greater toxicity than that observed for municipal solid waste incinerator fly ash (MSWIFA). The maximum international toxic equivalent value of PCDD/Fs in MWFA was 40 times that of MSWIFA, and the leaching concentrations of Zn and Hg were 15 and 4 times those of MSWIFA, respectively. Notably, MWFA characteristics suggest the possibility of recycling and sustainable disposal solutions owing to the high Cl and Zn content with good recovery instead of landfill disposal. Similarities in chemical composition, PCDD/Fs homolog distribution, and water-solubility of chloride salts allows co-processing of MWFA and MSWIFA via water-washing detoxification and thermal treatment, such as that used in cement kilns. This study supplements existing literature on the characteristics and risk management of MWFA.

Influence of leaching agents on the melting behavior of MSWI fly ash and its variation mechanism

In this paper, a new technology was proposed to substantially decrease the high cost of plasma melting of municipal solid waste incineration (MSWI) fly ash(FA) and the mechanism was studied. MSWI FA was leached with water, ammonium chloride (NH4Cl) solution and hydrochloric acid (HCl) solution. X-ray diffraction(XRD) and X-ray fluorescence(XRF) results indicate that soluble chloride, soluble chloride plus Ca (OH)2, and soluble chloride, Ca (OH)2 plus CaCO3 from the ash, were removed, respectively. Their flowing temperatures (FT) were decreased from 1545 °C to 1529 °C,1380 °C and 1197 °C, which is well related to their slag contents calculated with FactSage 7.3. Through FactSage simulation of mineral composition during heating process and the ternary phase diagram of SiO2–CaO–Al2O3, the influence of leaching agents can be attributed to the content of CaO. With the decrease of CaO content, the chemical compositions of the ash move from high liquidus temperature area to low liquidus temperature area. Acid-leaching technology can substantially decrease the cost of plasma melting of MSWI FA by both greatly decreasing the melting temperature and the amount of ash to be molten.

Study on preparation of glass-ceramics from municipal solid waste incineration (MSWI) fly ash and chromium slag

In order to realize the harmless treatment of municipal solid waste incineration (MSWI) fly ash and chromium slag, the CaO–SiO2–Al2O3 glass-ceramics were successfully prepared by the one-step method using a mixture of lead-zinc tailings and coal gangue as a flux. The results showed that the mixture successfully reduced the melting temperature of MSWI fly ash with a maximum blending ratio of 70% at 1450 °C, and realized the co-sintering of chromium slag and the base glass of MSWI fly ash. In addition, according to the analysis results of XRD, SEM, and EDS, combined with heavy metal leaching data measured by the TCLP method, diopside ferrous crystals exerted a better solidification effect on Zn and Cd than did gehlenite crystals. Uvarovite crystals exhibited an effective solidification effect on Cr owing to the participation of Cr in its formation, and the toxicity assessment of heavy metals in all samples satisfied the demand of the EPA and the CN GB 5058.3. This work provides a consult for the low-cost, green and efficient treatment of chromium slag, MSWI fly ash, coal gangue, and lead-zinc tailings.

Solidification and stabilization of Pb–Zn mine tailing with municipal solid waste incineration fly ash and ground granulated blast-furnace slag for unfired brick fabrication

The mismanaged and abandoned mine tailings are an important source of heavy metal pollution in the mining regions, and there is a significant need to develop technically, environmentally, and economically feasible and sustainable solutions to manage them. This study explored the solidification and stabilization of the tailing from an abandoned Pb–Zn mine using municipal solid waste incineration fly ash (MSWIFA) blended with ground granulated blast-furnace slag (GGBFS) for fabricating unfired bricks, and systematically characterized the products’ mechanical and environmental performance. Various hydration products, such as ettringite, portlandite, and hydrotalcite, were formed in the unfired bricks in the solidification and stabilization process, which enhance the physical strength of unfired bricks and help immobilize the heavy metals. Slaking treatment of MSWIFA significantly increased the mechanical strength, reduced the water absorption, and improved the durability of unfired bricks, with the product prepared from MSWIFA with 7-day slaking exhibiting the highest unconfined compressive strength (12.3 MPa) after 56 days of curing. The concentrations of As (0.35–1.49 μg/L), Cd (0.35–0.70 μg/L), Cr (1.38–9.40 μg/L), Cu (2.28–5.87 μg/L), Ni (0.16–2.24 μg/L), Pb (0.16–59.80 μg/L), and Zn (1.60–10.80 μg/L) in the leachates of unfired bricks were below the relevant regulatory limits for surface water and groundwater. Converting the mine tailing (with MSWIFA and GGBFS) to different types of unfired bricks could yield economic payback in the range of 283.7–306.5 Yuan per ton. Replacing cement with MSWIFA blended with GGBFS in the solidification and stabilization treatment could save about 0.15 ton of cement per ton of mine tailing disposed, which avoids significant energy use and carbon dioxide emissions. These findings demonstrate that utilization of mine tailings and industrial wastes to fabricate unfired bricks is a promising way of reusing such wastes and controlling the associated pollution, which also brings significant economic benefit and improves environmental sustainability.

Environmental filling materials based on phosphogypsum powder with municipal solid waste incineration ash

A new building filling materials (NBFM) using phosphogypsum and municipal solid waste incineration (MSWI) fly ash is prepared in this paper. The effects of MSWI fly ash dosage and MSWI fly ash water washing pretreatment on mechanical properties, setting time, metal leaching, hydration products and microstructure of NBFM are analyzed by a range of experimental studies. The results indicate that the mechanical properties, setting time and the density of micro interface of NBFM are optimal when the MSWI fly ash dosage is 3%. The mechanical properties of NBFM rise and the condensation time and leaching concentration of heavy metals decline after washing the MSWI fly ash. With the increase of the curing age, the metal element leaching of NBFM decreases, and when the curing age is 7 days, the solidification effect of NBFM on most metal elements meets the standard of Chinese code (GB5085.3-2007). The feasibility of MSWI fly ash and phosphogypsum as filling materials for building engineering is verified, and the change of macroscopic properties of NBFM is explained as well.

CO2 sequestration by direct mineral carbonation of municipal solid waste incinerator fly ash in ammonium salt solution: Performance evaluation and reaction kinetics

In this study, we investigated CO2 mineral sequestration by municipal solid waste incineration fly ash (MSWI-FA) in both pure water and ammonium salt solutions [NH4Cl, (NH4)2SO4 and CH3COONH4]. The introduction of NH4+ significantly promoted the solid–liquid mass transfer of the active calcium on the MSWI-FA particles and the generation of free ammonia in the solution, which enhanced the carbonation kinetics and crystallization of the calcium carbonate product. Changes to the mineralogy, morphology, and surface properties of the MSWI-FA particles before and after carbonation confirmed the reaction mechanism. A novel kinetic model based on the two-film theory was developed to evaluate the mass transfer and chemical reaction of heterogeneous carbonation in both pure water and ammonium salt solutions. To optimize the carbonation rate and efficiency, the complex effects of various operating parameters on the CO2 sequestration characteristics were systematically investigated. Maximum carbonation kinetics was achieved at 60 °C, an ammonium salt concentration of 1.0 mol/L, and a gas flow rate of 1.0 L/min, resulting in a carbonation efficiency and CO2 sequestration capacity of 78.49 % and 0.236 g CO2/g MSWI-FA, respectively. A comparison of the present results with those of other studies suggests that direct aqueous carbonation in ammonium salt solutions is feasible owing to its higher carbonation kinetics and CO2 sequestration capacity.

Lead-chlorine synergistic immobilization mechanism in municipal solid waste incineration fly ash (MSWIFA)-based magnesium potassium phosphate cement.

The high chlorine (Cl) and lead (Pb) content characteristics of municipal solid waste incineration fly ash (MSWIFA) pose environmental risks and hinder resource utilization. Herein, an MSWIFA-based magnesium potassium phosphate cement (MKPC) preparation strategy was developed, which allowed the MSWIFA recycling and the Pb-Cl synergistic immobilization without the washing pretreatment. The compressive strength of the resulting 10wt% MSWIFA-based MKPC was 28.44MPa, with over 99.2% reduction in leaching toxicity of Pb and Cl. The high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and X-ray absorption spectroscopy (XAS) analyzes showed that Pb, phosphate and Cl- formed Pb5(PO4)3Cl in MKPC. In-situ X-ray diffraction (XRD) tests showed that Pb3(PO4)2 was gradually transformed to Pb5(PO4)3Cl through a dissolution-precipitation process. The formation energy, Bader charge, charge density difference and density of states (DOS) of Pb5(PO4)3Cl were analyzed by first-principles calculations, confirming that Pb5(PO4)3Cl was more thermodynamically stable than Pb3(PO4)2 and PbCl2 and that electronic interactions between Pb-p, O-p, P-p and Cl-p orbits were the origin of Pb-Cl synergistic immobilization. This work provides a new strategy for the resource utilization of MSWIFA without washing pretreatment, and provides an in-depth understanding of the Pb-Cl synergistic immobilization mechanism.

Research and Application of Detoxification and Harm Reduction Technology for Fly Ash from Refuse Incineration

Municipal solid waste incineration fly ash (MSWIFA) is rich in chlorine salt, carbon component, heavy metal and dioxin (PCDD/Fs) with high concentration. It has been listed in the national hazardous waste list. It must be safely and innocuous treated before its resource utilization and landfill. There are few studies on the pollution characteristics and treatment of msi fly ash in Macao. The pollution characteristics of toxic and harmful substances such as heavy metals and dioxins in msi fly ash were introduced in this paper. The research status of many fly ash detoxification and harm reduction technologies such as chemical agent stabilization method, cement solidification technology, heat treatment technology, flotation technology and microwave pyrolysis technology were analyzed. The research progress and existing problems in the treatment of heavy metals and dioxins in msi fly ash by the latter three technologies were elaborated emphatically, and their application prospects were prospected.

Municipal solid waste incineration (MSWI) fly ash could be used as a catalyst for pyrolysis of oil-based drill cuttings from shale gas exploitation industry

Oil-based drill cuttings (OBDC) and MSWI fly ash are both hazardous wastes and are produced in huge amounts every year. OBDC are often treated by pyrolysis for recovering hydrocarbons, while municipal solid waste incineration (MSWI) fly ash is solidified and then landfilled. This study found that MSWI fly ash had the porous structure with catalytic metal element loaded on the solid acid catalyst structure. Moreover, the specific surface area and pore size of MSWI fly ash were suitable for cracking and mass transfer of hydrocarbons in OBDC. Control experiment indicated that MSWI fly ash could promote pyrolysis of OBDC by 14.5% compared with that without any catalyst. Orthogonal experiments further confirmed that the catalytic properties of MSWI fly ash were comparable to some commercial catalysts and laboratory catalysts. Thermogravimetric results showed that the pyrolysis of OBDC was divided into three stages, and the activation energy of each stage increased gradually. Kinetic analysis proved that using MSWI fly ash as catalyst could reduce the activation energy of the third stage which needed the maximum activation energy to react, so promoted the cracking of heavy hydrocarbon and enhanced the recycling rate of hydrocarbons in OBDC.

Strength and Environmental Behaviours of Municipal Solid Waste Incineration Fly Ash for Cement-Stabilised Soil

Many sandy soil foundations need to be solidified during traffic construction in Guangxi, China. Because it has a similar chemical composition as cement, municipal solid waste incineration fly ash (MSWIFA) can strengthen sandy soil. However, the chloride ions and heavy metals in MSWIFA may have a negative influence on the solidification of sandy soil. Thus, FA resource use faces great challenges. This study evaluates the feasibility of using MSWIFA to solidify sandy soil. The acetic acid buffer solution method was used in the leaching test to simulate the weak acid groundwater environment in the Guangxi karst landform. The effects of the treatment methods (washing with ferrous sulphate solution, pre-treatment of organics via chelation, and adding sugarcane ash) on the strength and environmental characteristics of fly ash cement-stabilised soil (FACS) are discussed in detail. The results indicate that the FACS unconfined compressive strength (UCS) decreased by 24.82–46.64% when 5% cement was replaced with FA. Sugarcane ash effectively improved the strength of FACS by more than 10%. The leaching concentrations of Zn and Cu in the FACS meet the concentration limit set by GB 16889-2008. The leaching concentrations of Cr and Pb after washing with 6% ferrous sulphate solution were reduced by more than 30%. Meanwhile, the FACS strength developed faster. Organic chelating agents solidified most heavy metals.

A novel and sustainable technique to immobilize lead and zinc in MSW incineration fly ash by using pozzolanic bottom ash

Fly ash (FA) generated from Municipal Solid Waste (MSW) incineration contains high leaching potential of toxic metals. Calcium silicate hydrate (C–S–H) is the main hydration product of cement and can immobilize the leaching of toxic metals, formed by the reaction of Ca with pozzolanic Si in a highly alkaline environment. Toxic metals can be immobilized by the addition of pozzolan to FA residues (in lieu of cement), which is a source of Ca and provides an alkaline condition. The current study proposed a new approach of reusing the fine-fraction of MSW incineration bottom ash (BA), which contains amorphous silica, known as pozzolan for immobilization of lead (Pb) and zinc (Zn) in FA. The dissolved amorphous silica and alumina emerged from the BA, with available Ca ions and in an extremely alkaline condition owing by FA, stimulate the pozzolanic reaction, resulting the formation of cementitious compounds of C–S–H gel and calcium aluminate hydrates (C-A-H) that can immobilize the heavy metals leaching from FA. The existence of calcium hydroxide promotes the carbonation process, reducing pH, and consequently immobilizing heavy metals. The method involves the simple mixing of BA and FA with water. The mixture was settled for 1, 4, 16, and 30 days at room temperature and annealed (120 °C) conditions. The leaching concentrations of Pb and Zn significantly reduced in the stabilized FA samples followed by standard Japanese leaching test (JLT- 46). Pb stabilization efficiency was reached >99.9% after 16-days of settling periods with 10% dosage of BA at room temperature. The added BA to FA residues reacted with Ca(OH)2 and CaClOH produced the C–S–H gel. pH, XRD, and SEM-EDX analyses evaluated the carbonation and pozzolanic reactions that promoted the immobilization of Pb and Zn. Immobilization of heavy metals by using fine-fraction of BA seems to be very effective and technically feasible. The technology can save original material, produce inert material and avoids landfilling of incineration residues. More advanced and detailed experiments have been designed to promote the optimization of the proposed technology for application in industries.

The Distribution Pattern and Leaching Toxicity of Heavy Metals in Glass Ceramics from MSWI Fly Ash and Andesite Tailings.

The leaching of heavy metals (HMs) is the key factor affecting the resource utilization of municipal solid waste incineration (MSWI) fly ash. A novel fly ash and andesite-tailings-based (FAAT) glass ceramic is prepared with the full-component utilization of MSWI fly ash and andesite tailings. The effects of the content and distribution state of HMs on their leaching toxicity are studied by performing a sequential extraction procedure and leaching toxicity test. The results show that the MSWI fly ash content greatly impacts the HMs' leaching toxicity in glass ceramics. Thus, the addition of MSWI fly ash must be maintained at below 20% so as to meet the class III groundwater standard. Furthermore, the different distribution states of Zn and Cr also affect their leaching toxicity. Zn suits the requirements for leaching toxicity only in a 2080c sample, while Cr fulfills the class III groundwater standard for all the glass ceramics. Since this finding is mismatched with the calculated potential ecological risk index of glass ceramics, the latter can only be used as a reference. Therefore, the results of the present study are of great significance in the vitrification application of MSWI fly ash.

Use of Municipal Solid Waste Incineration Fly Ash in Geopolymer Masonry Mortar Manufacturing

The feasibility of partially replacing pulverized fly ash (PFA) with municipal solid waste incineration fly ash (MSWIFA) to produce ambient-cured geopolymers was investigated. The influence of mixture design parameters on the compressive strength of geopolymer paste was studied. The investigated parameters included MSWIFA dosage, the ratio of sodium silicate to sodium hydroxide (SS/SH), the ratio of liquid to solid (L/S) alkaline activator, and the ratio of SH molar. A water immersion method was selected as a pretreatment process for MSWIFA, leading to effectively maintaining the volume stability of the MSWIFA/PFA geopolymer. The mixture of 30% treated MSWIFA and 70% PFA with 12 M SS, 0.5 L/S ratio, and 3.0 SS/SH ratio produced the highest three-day compressive strength (4.9 MPa). Based on the optimal paste mixture, category four masonry mortars (according to JGJT98-2011) were prepared to replace various ratios of natural sand with fine recycling glasses. Up to a 30% replacement ratio, the properties of the mortars complied with the limits established by JGJT98-2011. The twenty-eight-day leaching rate of mortars containing 30% MSWIFA was lower than the limits proposed by GB5085.3-2007. Microstructural analysis indicated that the main reaction product was a combination of calcium silicate hydrate gel and aluminosilicate gel.

Effect of curing regime on the immobilization of municipal solid waste incineration fly ash in sustainable cement mortar

Stabilizing/solidificating municipal solid waste incineration fly ash (MIFA) with cement is a common strategy, and it is critical to study the high-value utilization of MIFA in ordinary Portland cement (OPC) components. With this aim, binary-binding-system mortar was produced by partially replacing OPC (∼50%) with MIFA, and the effects of different curing regimes (steam curing and carbonation curing) on the properties of the cement mortar were studied. The results showed that the setting time of the cement paste was shorten with the increase of MIFA content, and steam curing accelerated the hardening of the mixture. Although the incorporation of MIFA reduced the strength of the mortar, compared to conventional curing method, steam curing and carbonation curing increased the 3-d strength of the mortar. For high-volume MIFA mortars, the CO2-cured samples had the highest long-term strength and lowest permeability. The incorporation of MIFA increased the initial porosity of the mortar, thereby significantly increasing the carbonation degree and crystallinity of the reaction product - CaCO3. Steam curing also further narrowed the difference in the hydration degree between MIFA-modified sample and plain paste, which may be due to the enhanced hydraulic reactivity of MIFA at high temperatures. Although the incorporation of MIFA increased the porosity of the mortar, this waste-derived SCM refined the bulk pore structure and decreased the interconnected porosity. Additionally, the heavy metal leaching contents of MIFA-modified mortars were all below 1%, which meet the requirements of Chinese standards. Compared with standard curing, steam curing and carbonation curing made the early-age and long-term performance of MIFA-modified mortar better, which can promote the efficient application of MIFA in OPC products.

Andesite tailings and municipal solid waste incineration fly ash based glass ceramics

To realize the utilization of andesite tailings and solve the environmental problems caused by municipal solid waste incineration (MSWI) fly ash, both of them were selectively used as raw materials to prepare glass ceramics by sintering process. The effects of components on the properties of glass ceramics were analyzed. The results showed that glass-ceramic sample 21 prepared from andesite tailings and MSWI fly ash had the best performance, the bending strength was 94.8Mpa. At the same time, its acid and alkali resistance were the best, while the thermal conductivity was the lowest. The leaching of heavy metal elements in all the samples met the Chinese national standard. These results will provide some reference for the resource utilization of andesite tailings and MSWI fly ash.

Zeolite NaP1 synthesized from municipal solid waste incineration fly ash for photocatalytic degradation of methylene blue

The disposal of hazardous municipal solid waste incineration (MSWI) fly ash is a challenge nowadays. Recently, the re-utilization of MSWI fly ash by converting it to useful zeolite-containing materials has attracted attention. However, the zeolitic products fabricated from MSWI fly ash are usually of low quality and rarely reported to be applied for photocatalysis. In this study, valuable zeolites (e.g., NaP1) are synthesized from MSWI fly ash via a modified microwave-assisted hydrothermal method. The key parameters for the hydrothermal method including temperature, duration, the amount of additive, and water volume, are investigated and optimized. Specifically, increasing the hydrothermal temperature can promote the synthesis of zeolitic materials; a relatively long hydrothermal duration is essential to accomplish the assembly of zeolites; the addition of Na2SiO3 can increase the precursor for the fabrication of zeolites; the water volume makes little influence on the crystal style of products. Eventually, the hydrothermal condition of 180 °C, 1 h, 0.5 g Na2SiO3, and 10 mL water is suggested based on the energy consumption and the quality of zeolites. The product containing zeolite NaP1 from such a condition is further applied to degrade methylene blue by photocatalysis. The removal rate has reached 96% within 12 h, which dramatically surpasses that of the raw fly ash (38%). Such excellent photocatalytic performance is attributed to the 10-fold increased surface area (24.864 m2 g−1) and active metal elements embedding in the zeolite structures.