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With the growth of the industrial aluminum smelting sector, and the increasing proportion of incineration treatment in the field of waste management and disposal, there has been a corresponding increase in the production of secondary aluminum dross (SAD) and municipal solid waste incineration fly ash (MSWIFA) annually. In this research, ceramsite is prepared using SAD, MSWIFA, and municipal solid waste incineration bottom ash (MSWIBA) as raw materials. This study explores the impact of various factors on the mechanical properties of ceramsite and their mechanisms under different conditions, including sintering temperature, raw material ball particle size, raw material silica-alumina ratio, and sintering time. Single-factor experiments demonstrate that the compressive strength of ceramsite initially follows a non-linear ascending trend with increasing sintering temperatures. Additionally, the strength is enhanced with reductions in particle size of the raw material balls, prolongation of the sintering time, and a reduction in the silica-to-alumina ratio of the raw materials. Orthogonal experiments reveal the ideal preparation conditions for ceramsite as follows: a preheating temperature of 400 °C, a preheating duration of 20 min, a sintering temperature of 1270 °C, and a duration of 30 min. Under these conditions, the optimal composition ratio of ceramsite is Si:Al = 3, and the ideal particle size is 0.5 cm. Analysis through X-ray diffraction and scanning electron microscopy revealed the formation of new mineral phases such as sodium feldspar and potassium feldspar in the ceramsite, which display a dense structure under microscopic observation. These contribute positively to the mechanical properties of the ceramsite. Fourier-transform infrared spectroscopy analysis indicates that at a sintering temperature of 1260 °C or when the raw material ball size is 2 cm, the [SiO 4 ] tetrahedral bands shift to higher wavenumbers, enhancing the degree of polymerization of the glass network in the ceramsite, thereby strengthening its compressive strength. As the silica-alumina ratio of the raw materials decreases and the sintering duration extends, the [SiO 4 ] tetrahedral bands continue to shift to higher wavenumbers, further enhancing the compressive strength of the ceramsite.

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.

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.

Municipal solid waste incineration fly ash, containing heavy metals and dioxins with strong toxicity and carcinogenicity, would pose severe harm to human health and the environment. This review details the chemical composition of MSWI fly ash, summarizes the sources and pollution characteristics of heavy metals and dioxins. In this paper, various solidification/stabilization (S/S) methods and the resource utilization of MSWI fly ash with S/S, such as cement solidification, geopolymer solidification, chemical stabilization and hydrothermal treatment are comprehensively discussed. Besides, the principle of heavy metals stabilization and the mechanism of dioxins degradation are analyzed in detail. Moreover, an overall comparison of these approaches for the harmless treatment of MSWI fly ash, including pollutants solidification/decomposition, advantages, disadvantages and resource utilization approach, is carried out. The risk assessment methods of solidified and stabilized products for heavy metals were discussed. Finally, studying on degradation of dioxin and enrichment of heavy metals in MSWI fly ash by multi-synergistic treatment, inhibiting the leaching of pollutants into aqueous solution during solidification are proposed. This paper is expected to provide some reasonable development directions for the environmentally safer treatment and resource utilization of MSWI fly ash. Graphical Abstract

Municipal solid waste incineration (MSWI) for power generation can reuse waste effectively, but it generates a large amount of fly ash enriched with heavy metals. If this fly ash cannot be treated properly, it can cause ecological damage and human health risk. According to the production of ceramsites from MSWI fly ash, an evaluation methodology is established, in which the influence of heavy metal stability on the environment is considered for the first time, and the health risks of heavy metals via different exposure pathways are distinguished. The results show that heavy metals in MSWI fly ash have moderate potential environmental risks to environment and have strong non-carcinogenic and carcinogenic risks both to children and adults. By contrast, heavy metals in ceramsites pose little risk to environment and human health. This paper explains some reasons of heavy metal content and leaching ratio change in ceramsite and also illustrates why stability is a concern through comparing the potential risk index method and the improved evaluation method. This evaluation system can be applied to different production processes of building materials using solid hazardous waste and provides a quantitative evaluation method for reducing environment and human health risks of heavy metals.

Incineration is an integral part of the waste management process to reduce the enormous volumes of municipal solid waste generated daily. Of the various incineration products, bottom ash makes up a major portion, which subsequently needs to be disposed or reused. Unavoidably, trace amounts of heavy metal content present in incineration bottom ash (IBA) can be leached out over time, ending up in water bodies and eventually entering the food chain. This can lead to toxic bioaccumulation of heavy metals in animals and humans. To minimize leaching, it is essential for heavy metals in IBA to be effectively immobilized. In this review, we critically evaluate the effectiveness of various heavy metal immobilization strategies to treat IBA in terms of their suppression of heavy metal leaching based on past research examples. Furthermore, these strategies are assessed for their medium to long term stabilities, potential impact on the environment, as well as challenges that may be faced in their successful implementation. Finally, some future directions in heavy metal immobilization efforts are proposed in light of the present climate crisis.

Safe and sustainable treatment of municipal solid waste incineration fly ash (MSWI FA) is urgently needed worldwide because of its high heavy metals, dioxin, and chlorine (Cl) contents. Thermal treatment is widely considered as a promising method for treating MSWI FA owing to its high toxic content removal efficiency and resource recovery; however, residual Cl is a concurrent critical problem faced during reutilisation of thermal treatment products. This review summarises the innovative thermal treatment methods of MSWI FA, such as those employed in production of cement, lightweight aggregates, glass slag, and metal alloys. The characteristics of Cl in MSWI FA, removal rate, transformation of water-soluble Cl into water-insoluble Cl, and the effect of different influencing factors such as temperature, composition, superheated steam, and mechanical pressure were analysed. The volatilization and decomposition of NaCl, KCl and CaClOH dominates Cl removal; however, the degradation of organic Cl and heavy metal chlorination volatilization process that generate HCl and heavy metal chlorides, respectively, also contributed to Cl removal. To promote the reutilisation of MSWI FA-based products, the leaching behaviour of residual Cl in products obtained by different thermal treatments was investigated.

With urbanization, municipal solid waste (MSW) generation is increasing. Traditional landfill methods face land shortages and environmental pollution. Waste incineration, which reduces waste and recovers resources, has become a key management method. However, nitrogen oxides (NO x ) produced during incineration severely impact the environment, requiring improved control technologies. This study optimized three denitrification technologies—air staging, flue gas recirculation (FGR), and selective non-catalytic reduction (SNCR)—using numerical simulations. The research provides support for improving waste incinerator efficiency and stability while reducing NOx emissions, aiding the sustainable development of waste incineration technology. By optimizing the primary and secondary air distribution ratios, the initial NOx generation was reduced by 8.39%. When 20% of the recirculated flue gas was introduced as secondary air, NOx generation was reduced by 23.54%, and boiler efficiency increased to 83.78%. The study examined the impact of different sludge mixing ratios on the temperature and NOx emissions within the context of municipal solid waste (MSW) incineration. Initially, the study aimed to address the environmental concerns of NOx emissions during the incineration process by exploring how the introduction of sludge at various mixing ratios would affect combustion parameters. The results showed that a sludge mixing ratio between 3 and 13% optimized the combustion process with 7% being the most effective in balancing temperature control and NOx emissions. Specifically, the best value of the sludge mixing ratio refers to achieving an optimal reduction in NOx emissions while maintaining stable incinerator operation. The chemical compositions of the sludge included key elements such as carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O), with approximate proportions of C: 31.2%, H: 4.7%, N: 2.5%, S: 0.6%, and O: 31.8%.

Municipal solid waste incinerator (MSWI) bottom ash (BA) is the main product of municipal solid waste after being burned. MSWI bottom ash aggregate (BAA) which is made from processed BA can be used in road engineering due to its strength and gradation. And it can be provide more choices for road engineering aggregates and relieve the demands for natural aggregates in road engineering construction. In order to verify the difference between BA asphalt pavement and ordinary asphalt pavement in engineering practice, the Mechanistic-Empirical Pavement Design Guide (MEPDG) was used to analyze and predict the road performance of BA asphalt pavement, such as rutting, fatigue cracking, temperature cracking, and pavement smoothness. The results showed that the incorporation of MSWI BA had a great impact on the rutting depth of the pavement, but was less affected by temperature changes and had little effect on the fatigue cracking and smoothness of the pavement. Overall, MSWI BA did not degrade the long-term performance of asphalt pavements and is suitable for replacing part of the natural aggregates for road construction.

The growing demand for metals such as aluminum, copper, iron, and zinc has driven the search for alternative sources. Waste-to-Energy markets enable energy generation and recovery of valuable materials from municipal incinerator bottom ash. This study addresses the occurrence of seasonal variability in metal concentrations, its potential impact on recovery efficiency, and the comparability of incineration residues with natural deposits. Unlike previous research, our approach focused on identifying possible seasonal drivers, interpreting correlations between metals, and comparing bottom ash composition with residues from other plants and natural ores, thereby supporting the concept of sustainable resource management. We analyzed samples collected over 52 weeks to identify seasonal variations in metal concentrations. Seasonal analysis and correlation matrices revealed variability and weak dependencies between metal concentrations. A comparative analysis was performed across European and Asian waste-to-energy facilities. The mean value of aluminum in Poland is 32,481 ppm, while in other cities it ranges from 17,000 to 85,000 ppm. Copper concentrations range from 597 to 25,100 ppm (4567 ppm in Poland). Our results show that the concentrations of analyzed metals vary throughout the year, with colder seasons exhibiting higher levels than warmer periods of the year, highlighting the need for effective recycling strategies.