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Towards the sustainable development goals in the built environment, the use of waste and recycled sources has been attaining great interest among researchers and policy-makers, especially in concrete as the most used construction material. Excess use of natural aggregates, as one of the main components of concrete, causes the depletion of natural resources and the associated environmental problems, thus, the use of artificial and recycled aggregates is of great importance. In this regard, the production of lightweight artificial aggregates from industrial and hazardous wastes may be a promising solution that not only mitigates the depletion of natural resources but also stabilize those kinds of wastes. This study aimed to investigate the production of concrete with recycled aggregates from industrial wastes, mainly municipal solid waste incineration fly ash (MSWI-FA). To this end, different kinds of mix designs to manufacture the aggregates were developed based on MSWI-FA, ground granulated blast furnace slag (GGBFS), marble sludge (MS), and cement. The concrete samples containing different artificial aggregates, as well as recycled polyethylene terephthalate (PET) in the sand form, were produced and the properties, including compressive strength and thermal insulation, were evaluated. The obtained results of the lightweight concrete demonstrated enhanced thermal property (up to 30%), but at least 30% lower resistance with respect to the normal concrete produced from the natural aggregate.

Municipal solid waste incinerator (MSWI) fly ash is a residue of municipal solid waste incineration whose recycling is currently a worldwide problem. Therefore, considerable efforts are being made to establish effective recovery techniques so MSWI can be used as a substitute for natural resources in construction, as in masonry blocks, roads and so on, or in the manufacture of new materials. MSWI fly ashes contain elements such as Ca, Si and Al, which make it possible for them to be used as raw material to manufacture cements. This paper presents the results obtained from the physicochemical characterization of two MSWI fly ashes from two Spanish cities. The research aims to explore the feasibility of using MSWI fly ash as raw material for sintering belite cements. The results show that MSWI fly ashes have a suitable composition. However, appropriate pre-treatment will be required to eliminate chloride and possible traces of heavy metals and to improve pozzolanic activity. Furthermore, the addition of vitreous silica in the proper proportions is required. The phases generated after calcination of the blend at 800 °C are not those corresponding to pure belite cements. Nevertheless, the possibility of using these ashes as supplementary cementitious material in the manufacture of eco-cements should be contemplated., The authors would like to thank the Diputación Foral de Gipuz- koa (82/17) and the University of the Basque Country, UPV/EHU (PPG17/22), for financially supporting this work.

This study aimed to investigate the recycling opportunities for industrial byproducts and their contribution to innovative concrete manufacturing processes. The attention was mainly focused on municipal solid waste incineration fly ash (MSWI-FA) and its employment, after a washing pre-treatment, as the main component in artificially manufactured aggregates containing cement and ground granulated blast furnace slag (GGBFS) in different percentages. The produced aggregates were used to produce lightweight concrete (LWC) containing both artificial aggregates only and artificial aggregates mixed with a relatively small percentage of recycled polyethylene terephthalate (PET) in the sand form. Thereby, the possibility of producing concrete with good mechanical properties and enhanced thermal properties was investigated through effective PET reuse with beneficial impacts on the thermal insulation of structures. Based on the obtained results, the samples containing artificial aggregates had lower compressive strength (up to 30%) but better thermal performance (up to 25%) with respect to the reference sample made from natural aggregates. Moreover, substituting 10% of recycled aggregates with PET led to a greater reduction in resistance while improving the thermal conductivity. This type of concrete could improve the economic and environmental aspects by incorporating industrial wastes—mainly fly ash—thereby lowering the use of cement, which would lead to a reduction in CO2 emissions.

The new technology development for municipal solid waste incineration fly ash treatment and reuse is urgent due to landfill shortage and environmental effect of leached hazardous substances. Chlorine (Cl) is worth considering due to its high levels in fly ash. In this study, a treatment process of ultrasound combined with organic acid was used to eliminate Cl from fly ash to enhance its properties for reuse. Taguchi methodology was implemented to design the experiments by controlling four impact factors and the contribution of each factor was evaluated by the ANOVA analysis of variance. Following two treatment steps within 5 min with a solid/liquid ratio of 1:10 at 165 kHz, 98.8% of Cl was eliminated. Solid/liquid ratio was the most prominent factor that contributed to the Cl removal with more than 90%, according to the ANOVA analysis of variance. Tert-butyl alcohol (tBuOH), an •OH radical scavenger, was utilized to examine different effects of ultrasonic cavitation on Cl removal efficiency. A 20 kHz ultrasound was used to explore the influence of multi-frequency ultrasound with different mechanical and sonochemical effects on the fly ash dechlorination. This ultrasonic-assisted organic acid treatment was found to be a time and cost-effective pathway for fly ash Cl removal.

Fly ash from municipal solid waste incineration (MSWI-FA) contains leachable heavy metals. In the present study the correlations between heavy metal content, particle size, speciation distribution with respect to water leaching are investigated, using a combination of solid-state bulk analytical techniques, leaching treatments, sequential extractions and thermodynamic geochemical modelling. Among the analyzed heavy metals, Zn and Pb are the most abundant in any grain size class, followed by Cu, Cr, Cd and Ni, with concentration that tends to increase with a decrease of the grain size. The phase composition is constituted of salt (halite, sylvite, anhydrite and syngenite), which provide the main minerals regardless of the particle size class; calcite, quartz and gehlenite occur in comparatively lower amounts, while 50% wt is composed of amorphous fraction. Heavy metal leaching is strongly correlated to speciation distribution, and in particular to the fraction (F1) associated with salt, carbonate and weak surface sorption. Leaching from speciation due to surface complexation on Al/Fe (hydr)oxide becomes relevant at acidic regime. Particle size and heavy metal content, in turn, moderately correlate with leaching. The F1-speciation as a function of particle size does not exhibit a definite trend shared by all heavy metals under investigation. This suggests that i) differences in speciation distribution, rather than bare heavy metal content or particle size, govern leaching from MSWI-FA; ii) F1 can be regarded as a marker of the potential heavy metal leaching; iii) a comparatively modest efficiency in managing MSWI-FA is expected from grain size separation strategies.

The environmental impact during concrete manufacturing can be reduced by using less cement or using types of cement with high amounts of secondary cementitious materials (SCMs) and fillers. Fly ash from municipal solid waste incineration (MSWI) is an unused material, which could potentially be used as an SCM or filler. The applicability of MSWI fly ash samples in cement-based materials was investigated through an indirect determination based on the chemical composition, toxic metal content and particle size distribution of the samples. Furthermore, how the samples compared to each other and how representative the samples were for MSWI fly ash, in general, were investigated by multivariate modelling. MSWI fly ash samples were obtained from Denmark, Sweden and Greenland. Comparing the chemical composition of the MSWI fly ash samples with the chemical requirements for coal fly ash to be used in concrete, specified in EN 450-1 2012, indicated a low potential as SCMs. Additionally, the MSWI fly ash contained and leached more toxic metals than the allowed limits. The particle size distributions were larger than cement and indicated limited potential as filler. A principal component analysis showed that the obtained samples were chemically different materials compared to each other and would have different effects if used in cement-based materials. Additionally, the samples from Denmark were unrepresentative of MSWI fly ash, while the Greenlandic and Swedish samples were comparable to previously studied MSWI fly ash samples.

From the year 2021 on, heavy metals from Swiss municipal solid waste incineration (MSWI) fly ash (FA) must be recovered before landfilling. This is predominantly performed by acid leaching. As a basis for the development of defined recovery rates and for the implementation of the recovery process, the authorities and plant operators need information on the geochemical properties of FA. This study provides extended chemical and mineralogical characterization of all FA produced in 29 MSWI plants in Switzerland. Acid neutralizing capacity (ANC) and metallic aluminum (Al0) were additionally analyzed to estimate the effort for acid leaching. Results show that all FA samples are composed of similar constituents, but their content varies due to differences in waste input and incineration conditions. Based on their geochemical properties, the ashes could be divided into four types describing the leachability: very good (6 FA), good (10 FA), moderate (5 FA), and poor leaching potential (8 FA). Due to the large differences it is suggested that the required recovery rates are adjusted to the leaching potential. The quantity of heavy metals recoverable by acid leaching was estimated to be 2420 t/y Zn, 530 t/y Pb, 66 t/y Cu and 22 t/y Cd.

We developed a phenomenological approach to explain the kinetic experimental data of PCDD/F formation/destruction based on a reaction mechanism model at the congener group level. In the present work, we investigated the formation and destruction of PCDD/F on fly ash as a function of time at 280 °C, chlorine mass balance, evolution of the total equivalent toxicity and kinetic modelling. We determined that the volatilization process is negligible and that the reactive processes at short reaction times only become important above 300 °C. The results provide a substantial improvement on existing studies. We experimentally demonstrated, for the first time, that there is a correlation between the oxidative breakdown of native carbon and PCDD/F de novo synthesis. Data processing by our kinetic model showed that the formation of oxygen complexes C(O) was the determining step for de novo synthesis of PCDD/F. Indeed, the calculated reaction time at which the PCDD/F concentration was at a maximum (850 min) was greater than that calculated for the oxygen complexes C(O) (435 min). Moreover, the experimental carbon conversion efficiency for PCDD/F production (0.0032% at 600 min maximum) was in a very good agreement with the theoretical conversion (0.0041%).

Cement kiln collaborative disposal of municipal solid waste incineration (MSWI) fly ash (referred to as fly ash) can achieve harmless recycling of fly ash. However, because of high chlorine (Cl) content in fly ash, the practical application of this technology is seriously restricted. In order to find a suitable leaching solvent for dechlorination of fly ash, this study compared the effect of lactic acid fermentation liquid (FL) and sludge FL of food waste on dechlorination. Results show that 90% of water-insoluble Cl in fly ash can be removed by a three-step leaching process with lactic acid FL and sludge FL, and the Cl content in leached fly ash residue is 0.44% and 0.39%, respectively. According to calculation, permissible fraction of the residue after three-step leaching with addition of lactic acid FL and sludge FL in kiln is 4.28% and 4.99% higher than that of the residue after three-step leaching with pure water, respectively. Furthermore, the properties of leaching solvents after leaching experiments indicate that organic acids with low pH value and high concentration are more conducive for removal of water-insoluble Cl. Therefore, it is feasible to use two kinds of FL as leaching solvent for fly ash dechlorination.

Fishbone, a common waste generated in coastal areas, especially from the fish processing industry, is known as the natural resource of hydroxyapatite (HAP). Researchers have investigated the removal of heavy metals from the contaminated environments based on the exchange capacity of Ca in HAP with heavy metal ions, while there are limited numbers of researches on the effect of natural HAP on municipal solid waste incineration (MSWI) residues. This work is an attempt to ascertain the feasibility of fishbone used for stabilizing Pb in lime-treated MSWI fly ash via leaching process. Lime-treated MSWI fly ash and ground fishbone of Japanese horse mackerel (aji in Japanese) were used during the whole experiment. The result from X-ray fluorescence on fly ash indicated that Ca and Cl are the two main elements, and Zn and Pb take the first two places among heavy metals. Based on X-ray diffractometry analysis, HAP is the only mineral phase in aji fishbone. The effects of fishbone on Pb immobilization of fly ash under different fishbone doses and various contact times were investigated by batch leaching test at room temperature, and Pb concentration in leachates was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Different fishbone/fly ash ratios were examined; 0 (control group), 5%, 10%, 15%, and 20% (test groups) by weight, and the tests were run for different periods; 3, 6, 24, and 72 h. The results indicated that higher dosage of fishbone and longer contact time were more effective for Pb sequestration from the leachate and the highest removal efficiency of Pb in leachate under the given conditions reached to 24.76% after 72 h leaching process at fishbone dosage of 20%. Although the effectivity of fishbone on Pb removal was not as expected, the preliminary experiments provided promising results regarding the possibility of using low-cost waste fishbone as an environmental-friendly alternate for the stabilization of Pb in MSWI fly ash.

Characteristics of heavy metals during heat-treatment municipal solid waste incinerator (MSWI) fly ash were investigated in this paper. The experiment was performed using a pilot-scale oil furnace in the range 800-1350 °C.In this work we investigated the effect of temperature on solidification efficiency, evaporation of heavy metals and on composition change, X-ray diffractometer (XRD), the leach toxicity of molten slag. The results showed that the main contents, solidification efficiency and evaporation of heavy metals had a tremendous change between 1150-1260 °C. With temperature increasing, the percentage of CaO, SiO2 and Al2O3 increased, and SO3, K2O, Na2O and Cl decreased. Especially in 1260 °C, the four compositions decreased sharply from 43.72% to 0.71%. Finally, the leaching concentrations of all heavy metals in molten slag were far lower than the standard values of TCLP.

Municipal solid waste incineration fly ash (MSWI FA) and granulated lead smelting slag (GLSS) are toxic industrial wastes. In the present study, granulated lead smelting slag (GLSS) was pretreated as a geopolymer precursor through the high-energy ball milling activation process, which could be used as a geopolymeric solidification/stabilization (S/S) reagent for MSWI FA. The S/S process has been estimated through the physical properties and heavy metals leachability of the S/S matrices. The results show that the compressive strength of the geopolymer matrix reaches 15.32 MPa after curing for 28 days under the best parameters, and the physical properties meet the requirement of MU10 grade fly ash brick. In addition, the toxicity characteristic leaching procedure (TCLP) test results show that arsenic and heavy metals are immobilized effectively in the geopolymer matrix, and their concentrations in the leachate are far below the US EPA TCLP limits. The hydration products of the geopolymer binder are characterized by X-ray diffraction and Fourier transform infrared methods. The results show that the geopolymer gel and Friedel&rsquo, s salt are the main hydration products. The S/S mechanism of the arsenic and heavy metals in the geopolymer matrix mainly involves physical encapsulation of the geopolymer gel, geopolymer adsorption and ion exchange of Friedel&rsquo, s salt.

The effects of a washing pre-treatment of municipal solid waste incineration (MSWI) fly ash with deionised water on both the physico-chemical characteristics of this material and the hydration behaviour and physical properties of ash—Portland cement mixtures rich in MSWI fly ash (55 wt% of total solids) were investigated in view of a possible reuse of such solidified products as concrete aggregates in the building industry. A four-stage washing pre-treatment was found to be able to convert the raw MSWI fly ash into a material with improved chemical characteristics for its incorporation into cementitious matrices (reduced concentrations of alkali chlorides and sulphates, transformation of metallic species in less reactive forms). As a result, the cementitious mixtures incorporating washed fly ash in place of raw fly ash were found to exhibit better performance characteristics in terms of setting, dimensional stability, compressive strength and environmental quality.

The present work discusses a new method, based on the use of silica fume, for heavy metal stabilization. The inertization procedure is reported and compared with other technologies, involving the employ of amorphous silica as stabilizing agent for municipal solid waste incinerator fly ash treatment (i.e. colloidal silica and rice husk ash). The obtained final materials are characterized in terms of chemical composition and phase analysis. The reported method, realized at room temperature, employs all waste or by-product materials. As a consequence it appears to be economically and environmentally sustainable.

The MSWI (Municipal Solid Waste Incinerator) fly ash may represent a potential health and environmental hazard for its high heavy metal content. Fly ash is commonly disposed in specific landfills to prevent the leaching of pollutants into underground aquifers. Several technologies (for example, thermal treatment, physical/chemical separation, and stabilization/solidification techniques) have been developed for treatment of fly ash to obtain second-hand inert materials. Moreover, reuse of these materials is strictly dependent on their physical and mechanical features. Possible applications of these materials are clinkering, road pave, and construction works where, specific performances are required. Recently, at the University of Brescia (Italy) a new process has been developed to inertize fly ash, by means of colloidal silica. The new inertization process involves low temperature reactions and produces a final material named COSMOS (Colloidal Silica Medium to Obtain Safe inert) that can be employed as a filler substituting natural materials such as carbon black, sand, etc. The project is supported by LIFE program of the European Community (LIFE + 2008 project ENV/IT/000434). In this study we present results about the reuse of COSMOS in different high quality controlled plaster materials. An appropriate waste management, based on the principles of sustainable development, is based on the principle that waste cannot be considered as something to eliminate but rather a potential resource.

Fly ash from municipal solid waste incineration (MSWI) is classified as hazardous waste. However, the fly ash has showed pozzolanic behavior, and therefore it has been investigated whether MSWI fly ash may partly substitute cement in Portland cement mortar after upgrading the MSWI fly ash by electrodialytical removal of metals and salts. The influence of MSWI fly ash according to workability, strength and heat evolution has been investigated. It was shown that MSWI fly ash has potential for reuse in Portland cement mortar, which could solve a waste problem and reduce CO2 emissions from the cement industry.

In the present paper, the properties of Portland cement mixtures containing fly ashes (FA) collected at four different Italian municipal solid waste incineration (MSWI) plants were investigated. In particular, physical/mechanical characteristics (setting time, unconfined compressive strength (UCS) and shrinkage/expansion), as well as the acid neutralisation behaviour of the solidified products were considered. The FA composition, revealing enrichment in heavy metals, chlorides and sulphates, significantly altered the hydration behaviour of Portland cement. Consequently, for some of the investigated FA the maximum allowable content for the mixtures to achieve appreciable mechanical strength was 20 wt.%. Even at low FA dosages setting of cement was strongly delayed. In order to improve the properties of FA/cement mixtures, the use of additives was tested.Moreover, the acid neutralisation capacity (ANC) of the solidified products was evaluated in order to assess the ability of the matrix to resist acidification, and also to provide information on hydration progression, as well as on heavy metal release under different pH conditions. Comparison of the results from the present work with previous studies carried out on spiked mixtures lead to the conclusion that the mechanical properties of the stabilised FA could not be predicted based on the effect exerted by heavy metals and anions only, even when the dilution effect exerted on cement was taken into account. It was likely that a major role was also played by alkalis, which were present in the FA at much higher concentrations than in cement.

Concrete manufacturing impacts the environment and construction industry sustainability. The impact is reducible by either using less cement or replacing it with secondary cementitious materials (SCMs). Limited potential for further reduction has been identified, due to low SCM availability. Fly ash from municipal solid waste incineration (MSWI) is an unused material, that could be used as an SCM to further reduce the environmental impact. Before implementing MSWI fly ash for use in cement-based materials, its chemical and physical properties should be evaluated. The present study aims to evaluate the potential of using untreated MSWI fly ash in cement-based materials and its quality, by comparing the chemical properties of MSWI fly ash samples with the chemical requirements of coal fly ash specified in EN 450-1 2012, as well as analysing their potential as filler materials. The screened ash in the present study was sourced from different types of combustion units, in different locations, and from the same location at varying times. MSWI fly ash samples were acquired from three different combustion units, located in Denmark, Sweden and Greenland respectively. Two fly ash samples were acquired from both the units in Denmark and Greenland, sourced several months apart and one from the unit in Sweden. The screening showed that the five fly ash samples, based on their chemical properties, were unsuited for use in cement-based materials. The samples potential as filler materials were found to be limited for all but one sample that had a slightly finer particle size distribution than CEM I cement.