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In this work, an alkali-activated municipal solid waste incineration (MSWI) fly ash-based filling material was prepared with MSWI fly ash as the raw material and slag as the auxiliary material. The filling body experiences long-term creep, which may have a direct effect on the stability of the overlying strata of the mine goaf. The long-term mechanical properties of the fly ash-based filling materials were tested with a triaxial rheological apparatus. First, uniaxial creep testing was carried out at five levels of axial stress: 50%, 60%, 70%, 80% and 90% of the uniaxial compressive strength (UCS). Then, triaxial creep testing was carried out by considering the geological environment of the goaf. The creep characteristics of fly ash-based filling materials under a three-dimensional stress state were explored. The results indicate that (1) under different stress levels, the creep curves of fly ash-based filling materials can be divided into three types: decelerated creep‒stable creep, decelerated creep‒constant creep, and decelerated creep‒constant creep‒accelerated creep. (2) The total creep deformation of the fly ash-based filling material is 0.46 ~ 0.78%, which is similar to the creep deformation of soft rock. The instantaneous deformation during loading contributes most of the total deformation. (3) The polymerization products generated in the fly ash-based filling material system can effectively cement the raw material particles, and the presence of gel can effectively delay the accelerating creep process of the material. (4) A nonlinear fractional-order model composed of an Abel dashpot can fully describe the complete process of decelerating creep-constant creep-accelerating creep.

The inhibition effect of calcined lime (CaO) and limestone (CaCO3) on the formation of dioxins during iron ore co-sintering with fly ash was investigated in a sinter pot in the present work. Experimental results indicated that international total toxicity equivalent concentration of dioxins decreased from 1.4335 to 0.2922, 0.1048, 0.4562, and 0.3098 ng I-TEQ Nm−3 under four different experimental conditions. It can be concluded that 5 wt.% calcined lime with 3 wt.% limestone is the optimal addition to reduce the concentration of dioxins in flue gas, with 92.70% inhibition efficiency. Effects on dioxin distribution was also analyzed. The distribution proportion of low-chlorinated dioxins was found to increase, while that of high-chlorinated dioxins decreased, except for octachlorianted dibenzo-p-dioxins (OCDD). The reason is that the consumption of HCl not only inhibits the de novo synthesis, but also dramatically promotes the condensation and dechlorination to produce more tetrachlorianted dibenzo-p-dioxins and octachlorianted dibenzo-p-dioxins through precursors. Finally, condensation, dichlorination, and inhibition mechanisms of dioxins during co-sintering with municipal solid waste incineration (MSWI) fly ash are proposed.

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.

Fly ash is a hazardous byproduct of municipal solid wastes incineration (MSWI). An alkali activated blast furnace slag-based cementitious material was used to stabilize/solidify the fly ash at experimental level. The characteristics of the stabilized/solidified fly ash, including metal leachability, mineralogical characteristics and the distributions of metals in matrices, were tested by toxic characteristic leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) respectively. Continuous acid extraction was utilized to extract metal ions and characterize their leaching behavior. The stabilization/ solidification procedure for MSWI fly ash demonstrates a strong fixing capacity for the metals by the formation of CS-H phase, hydrated calcium aluminosilicate and ettringite. The stabilized/solidified fly ash shows a dense and homogeneous microstructure. Cr is mainly solidified in hydrated calcium aluminosilicate, C-S-H and ettringite phase through physical encapsulation, precipitation, adsorption or substitution mechanisms, and Pb is mainly solidified in C-S-H phase and absorbed in the Si-O structure.

Over the past decades, extensive studies on municipal solid waste incineration (MSWI) ashes have been performed to develop more effective recycling and waste management programs. Despite the large amount of research activities and the resulting improvements to MSWI ashes, the recycling programs for MSWI ashes are limited. For instance, although the U.S. generates more MSWI ashes than any other country in the world, its reuse/recycle programs are limited; bottom ash and fly ash are combined and disposed of in landfills. Reuse of MSWI ashes in the construction sectors (i.e., geomaterials, asphalt paving, and concrete products) as replacements for raw materials is one of most promising options because of the large consumption and relatively lenient environmental criteria. The main objective of this study was to comprehensively review MSWI ashes with regard to specific engineering properties and their performance as construction materials. The focus was on (1) the current practices of MSWI ash management (in particular, a comparison between European countries and the U.S.), (2) the engineering properties and performance of ashes when they are used as substitutes of construction materials and for field applications, and (3) the environmental properties and criteria for the use of MSWI ashes. Overall, the asphalt and concrete applications are the most promising, from both the mechanical and leachate viewpoints. However, cons were also observed: high absorption of MSWI ash requires a high asphalt binder content in hot-mix asphalt, and metallic elements in the ash may generate H2 gas in the high-pH environment of the concrete. These side effects can be predicted via material characterization (i.e., chemical and physical), and accordingly, proper treatment and/or modified mix proportioning can be performed prior to use.

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

The present work aims to provide a comprehensive review of the experimental studies focusing on municipal solid waste incineration fly-ash (FA) treatments that are required before the application of advanced processes aimed at their final reuse or safe disposal. The investigated pre-treatments are divided into three categories: (1) water washing/chemical leaching; (2) electrodialysis; and (3) thermal separation. Analysed aspects include: (1) process efficiency; (2) effect on FA physical–chemical characteristics; and (3) process applicability as a function of secondary FA treatment steps which are generally required for final disposal or reuse of the remediated waste. Investigations related to these elements allows a determination of the efficacy and the operational convenience of a specific pre-treatment to achieve a proper FA remediation level. A comparison of studies in the literature provides a thorough source and a useful basis for correctly addressing future experimental activities and research efforts. The discussion of the results provides the basis for the development of a suitable methodology to optimize the environmentally sustainable reuse or safer disposal of treated FA.

The proper disposal of municipal solid waste incineration fly ash (MSWI FA) is necessary due to the presence of hazardous metals (Cu 2+ , Zn 2+ , Pb 2+ and Cd 2+ ). The solidification/stabilization through alkali-activated cementitious materials (having aluminosilicates) is regarded as one of the best methods for its disposal. In this paper, an uncalcined coal gangue–based alkali-activated cementitious material was used to solidify the MSWI FA. The compressive strength of these cementitious materials was evaluated through different contents of alkali activators, SiO 2 /Na 2 O molar ratios, liquid/solid ratios and curing temperatures by utilizing a single-factor experiment. The specimens with the highest compressive strength (31.37 MPa) were used for solidification of MSWI FA. The results indicated that compressive strength decreased with the addition of MSWI FA which caused the higher leaching of heavy metals. The solidification efficiencies of Cu 2+ , Zn 2+ , Pb 2+ and Cd 2+ were more than 95%. In addition, leaching concentrations had not surpassed the critical limit up to 20% addition of MSWI FA in solidified samples and representing the potential application of these samples for construction and landfill purposes. Heavy metals in MSWI FA were solidified through physical encapsulation and chemical bonding which was verified by speciation analysis, X-ray diffraction, Fourier transform infrared spectrometry and scanning electron microscopy with energy dispersive spectrometry analyses.

Leachate sludge is generated from the biochemical treatment sludge tank for disposing the leachate from landfill municipal solid waste (MSW). It has the characteristics of high water content and high organic matter content. Sulfoaluminate cement (SAC) is used as the main curing agent, and municipal solid waste incineration (MSWI) by-products are used as auxiliary curing agents to solidify/stabilize the leachate sludge. The influences of SAC content and MSWI by-products content on the strength and solidification mechanism of the leachate sludge are investigated by unconfined compressive strength (UCS) test and micro-observation tests. Moreover, the leaching concentration of heavy metals of the solidified samples is analyzed by leaching toxicity test. The results show that the UCS of the solidified samples increases with an increase in cement content. When the cement content is larger than 20%, the UCS of the solidified samples satisfies the strength requirement of landfill. The enhancing effect of bottom ash on the cement-solidified samples is slight. The fly ash is a good auxiliary curing agent for improving the UCS of cement-solidified samples, and the optimal dosage of fly ash is 5% and 15% for the solidified samples with 10 ~ 30% and 40 ~ 50% cement content, respectively. Ten percent fly ash can replace 10% cement to achieve better solidification effect for the solidified samples. The leaching concentration of heavy metals in the solidified sample with 30%/40% cement and 15% fly ash/bottom ash can satisfy the strength and leaching toxicity requirements of landfill. The immobilization of heavy metal of the cement and MSWI by-products solidified samples is mainly achieved through physical adsorption, physical encapsulation, ion exchange, and chemical precipitation.

Municipal solid waste incinerator (MSWI) fly ash poses intricate compositional challenges and potential environmental hazards. Effective management of such hazardous waste is imperative to mitigate the release of toxic compounds into the environment. Solidification/stabilization (S/S) processes have emerged as a viable strategy to transform MSWI fly ash from incineration waste into a safer and more environmentally benign material. This study aims to comprehensively investigate the potential of utilizing cow bone waste to stabilize heavy metals, focusing on Pb, within municipal solid waste incineration fly ash. Experimental investigations encompassed cow bone-to-fly ash weight ratios ranging from 0.0 (control group) to 7:3, a settling time of 2 h, and a liquid-to-solid (L/S) ratio of 1.0 mL/g. Cow bone waste exhibited pronounced efficacy, particularly within the short settling time, yielding a remarkable Pb removal efficiency of up to 99% at a cow bone waste dose of merely 2% and an L/S ratio of 1.0 mL/g. Concurrently, other heavy metals such as Cd, Cu, and Zn were effectively stabilized with a cow bone waste dose of 1.5% during the same 2-h settling period. The results underscore the pivotal roles of ash/bone ratio and settling time in augmenting Pb stabilization in MSWI fly ash. The application of cow bone waste is anticipated to offer a cost-effective and environmentally sound approach, aligning with sustainable waste management principles. Graphical Abstract