Solid Waste Incineration Fly Ash Research Articles

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 Properties of Municipal Solid Waste Incineration Fly Ash (IFA) And Cement Used in The Manufacturing of New Inventive Blended Cement

Municipal solid waste incinerator fly (IFA) ash is prone to accumulate high concentration heavy metals. Due to the increasing costs to treat remaining fly ash at the landfill, a lot of research has been done to recycle IFA. This studywas focusing on the properties of IFA and cement as main raw materials in new inventive blended cement. The properties of blended cement were also being investigated. Properties of IFA and cement were examined through several test which includes density, specific gravity, X-Ray Fluorescence (XRF), Loss of Ignition (LOI) and through Toxicity Characteristic Leaching Procedure (TCLP) test. The density test and LOI test were also being done for the blended cement. From the tests for IFA and cement, it can be found that density the density of fly ash and cementthat has been used for this study were found to be 0.76 g/cm3and 3.67 g/cm3respectively. Then, the specific gravity of fly ash and cementwere 1.69 and 2.98, accordingly. XRF results shows that both materialshave highest content of aluminium, silicaand iron, as expected. LOI of fly ash and cementwere found to be 17.33 % and 12.33 %, respectively.In terms of the leaching rates of heavy metals (Mn, Ni, Cd, Cr, Cu), only Cd leached at rate 2.39 mg/L, which is above the USEPA's regulatorylevel, 1.0 mg/L. 5 %, 10 % and 15 % of IFA was mixed with cement to produced blended cement. As the density of blended cement, it was found to be 1.12 g/cm3, 1.08 g/cm3and 1.09 g/cm3for each of 5 %, 10 % and 15 % of fly ash in blendedcement.

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.

Preparation of architectural 3D printing material with a solid waste-derived sulfoaluminate matrix: A high-value conversion of solid waste

The preparation and development of eco-friendly building materials have emerged as feasible options for large-scale solid waste management. This research prepared a high-performance three-dimensional (3D) printing material and printed building components using the two-stage conversion of solid waste. In the first transition process, a sulphoaluminate cementitious material was produced by calcination at 1270 ℃ using industrial solid waste, including municipal solid waste incineration fly ash, flue-gas desulfurization gypsum, and aluminum ash. Then, four admixtures, namely, water-reducing agent, sodium gluconate, dispersible latex powder, and hydroxypropyl methylcellulose, were selected to improve its performance and achieve a further transition of solid waste. The effect of admixtures, standard sand, and fiber on the properties of cementitious materials was studied. It was found that the addition of appropriate proportion admixtures increased the fluidity, extended the initial setting time, and controlled the decrease of compressive strength of the materials. A 1:1 ratio of cementitious material to standard sand with a fiber length of 12 mm, generated a high-performance sulfoaluminate-based cementitious material suitable for the preparation of 3D building components. The material has a fluidity of 188 mm, an initial setting time of 53 min, one-day compressive strength of 37.8 MPa, and one-day flexural strength of 7.6 MPa. Therefore, utilizing solid waste through this two-stage transition to prepare 3D printing materials has significant economic benefits, providing valuable ideas for large-scale solid waste treatment.

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.

Utilization of mechanochemically pretreated municipal solid waste incineration fly ash for supplementary cementitious material

With the rapid development of municipal solid waste (MSW) incineration, the effective disposal and recycling utilization of fly ash is attracting increasing attention. The mechanochemical (MC) treatment as a non-thermal method shows good stabilization of heavy metals and degradation of dioxins in fly ash. The inhibition effect and long-term safety of CaSO4, Ca3(PO4)2, NaH2PO4, and composite additives (50 %NaH2PO4 +50 %CaO) as additives for heavy metals stabilization were investigated. The composite additive showed the best inhibitory effect on heavy metals, and the leaching concentration of Cd, Cr, Cu, Ni, Pb, and Zn were decreased by 95.21 %, 46.84 %, 99.42 %, 49.91 %, 99.83 %, and 99.55 %, respectively. In addition, the modification by MC treatment reduced the particle size and increased the specific surface area of fly ash and improved the activity for resource utilization. Therefore, MC treated fly ash is used as supplementary cementitious material (SCM), which will produce a filling effect and pozzolanic effect improving the performance of fly ash concrete blocks. The compressive strength of the MC-treated fly ash concrete blocks curing for 28 days increased by 35.5 % and exceeded 40 MPa, close to OPC’s strength. The concrete block also had a secondary inhibition on potentially toxic elements, making the resource utilization of fly ash more stable and safer. In general, the MC treatment and the utilization of MC-treated fly ash as SCM effectively inhibit the leaching of heavy metals in fly ash, delivering a promising method for green fly ash disposal.

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.

The effects of washing solvents on the properties of ceramsite and heavy metal immobilization via the cosintering of municipal solid waste incineration fly ash and Cr-containing waste glass

Various washing solvents are being extensively researched to remove chlorides from municipal solid waste incineration fly ash (FA) and they have significant impacts on the recycling and reutilization of FA. The cosintering of FA and waste glass (WG) containing chromium (Cr) was explored in this study, as well as the effects of washing solutions (water [W-FA], phosphoric acid [P-FA], and sodium carbonate [Na-FA]) on the treated FA compositions, ceramsite characteristics, and heavy metals speciation. The findings demonstrated that washing process increased calcium oxide (CaO) content while reducing soluble salt level. The particle strength increased from 290.50 N to 926.78 N at 800–1050 °C, while increased from 228.68 N to 820.23 N when WG increased from 20% to 60%. Raw-FA ceramsite had a lower sintering temperature than treated FA ceramsite due to the higher particle strength and lower water absorption rate. At 1000 °C, the acid-soluble fraction of Cr of Na-FA and P-FA ceramsite was 64.72% and 9.07%, showing a promoted and inhibited effect on Cr leaching, respectively. The ecological risk index for P-FA and Na-FA ceramsite, both of which were produced at 1100 °C, were 30.61 and 46.68, respectively, indicating low environmental risk. Wollastonite was the dominating mineral phase in W-FA and Na-FA ceramsite, whereas chlorapatite and halite predominated in P-FA and Raw-FA ceramsite. Chlorine in P-FA ceramsite was combined with phosphates and calcium to generate stable minerals. Washing pretreatment reduced the environmental risk of ceramsite, and introduction of phosphorus could enhance heavy metal immobilization.

Basic Research on Co-treatment of Municipal Solid Waste Incineration Fly Ash and Municipal Sludge for Energy-Saving Melting.

MSWI fly ash and municipal sludge are solid wastes. Melting vitrification treatment was a resource utilization method. However, the flow temperature of grate furnace MSWI fly ash and municipal sludge was high (>1325 °C), which increased the energy consumption in the melting process. MSWI fly ash contained a large amount of CaO, and municipal sludge contained a large amount of SiO2, Al2O3, and Fe2O3. The temperature of melting vitrification can be reduced using these two kinds of CITY garbage as raw materials to change the proportion of ingredients. The eutectic characteristics of MSWI fly ash and municipal sludge and the phase diagrams of CaO-SiO2-Al2O3 (C-S-A) and CaO-SiO2-Al2O3-Fe2O3 (C-S-A-F) were analyzed in this paper. It established a low melting point mixing system. The results showed that when the amount of municipal sludge was 50-70%, the flow temperature of the mixtures was <1215 °C, which was significantly lower than that of MSWI fly ash (1490 °C) and municipal sludge (1325 °C). The optimal range of low melting point components was 14.1-36.3% CaO, 21.6-40.4% SiO2, 6.7-12.6% Al2O3, and 6.3-11.4% Fe2O3. At 400-1400 °C, the minerals in the mixtures mainly changed as follows: CaCO3 + SiO2 + Al2O3 → Ca2SiO4 + Ca3SiO5 + Ca2Al2SiO7 + Ca3Al2O6 + Ca12Al14O33 → CaAl2Si2O8. In the melting experiment, with the increase in temperature, most of the phases in the mixtures might become amorphous. Therefore, the low melting point phase anorthite (CaAl2Si2O8) only accounted for a small part of the final molten product.

Study on Three-Stage Counter-Current Water Washing Desalination Characteristics and Mechanism of High Chlorine Waste Incineration Fly Ash

The high chloride content of municipal solid waste incineration (MSWI) fly ash and hazardous waste incineration (HWI) fly ash has considerably affected their disposal. This study focused on investigating the three-stage counter-current (TSC) water-washing process to reduce the chlorine content efficiently under the premise of low water consumption. The liquid–solid ratio (LSR) and washing time were investigated, a chloride migration model was established, and the characteristics of the water-washing solution (WWS) and washed fly ash were investigated. The results showed that the dechlorination effect of TSC washing could reach more than 99% in a low liquid–solid ratio (LSR) of 2–4 kg/L. The most appropriate LSR and washing time were found to be around 3:1 L/kg and 15 min per stage, respectively. The concentration of Cl− in WWS reached over 90 g/L, which is very high among industrial saline wastewater. Some heavy metals were also contained in the WWS, and lead was the main heavy metal, followed by zinc, copper, and arsenic. The concentration of WWS of different stages was calculated by a model, and the transfer characteristic of chloride was strongly related to the mass balance between the liquid contained in the solid–liquid separation residue (SR) and the separated liquid. After washing, due to the dissolution of soluble salt, the specific surface area of fly ash increased, and thus the absorption ability of the washed fly ash was greater than the raw one. This study provides a washing condition reference for highly chlorinated fly ash, the basic data of WWS, and the chloride migration model that is a preliminary calculation method to improve the water-washing process.

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.

3D-printed polymeric lattice-enhanced sustainable municipal solid waste incineration fly ash alkali-activated cementitious composites

The disposal of municipal solid waste incineration fly ash (MSWIFA) has become a prominent issue due to high environmental risks. In this study, as a potential aluminosilicate precursor, MSWIFA was further alkali-activated as a sustainable construction material in the form of an alkali-activated MSWIFA-based material (AAFM), with a low leaching level of heavy metals. Various 3D-printed polymeric lattices were designed and inserted into the AAFM to promote its inherent brittleness. A special coating was also considered to enhance the alkali resistance of the PEGT lattices. Through a flexural tension test with a 3D digital image correlation (3D-DIC) technique, the failure patterns and strain distributions of the 3D-printed polymeric lattice-enhanced MSWIFA-based composites were tracked. These polymeric lattice-containing composites indicated the promotion of mechanical performance, i.e., higher flexural strengths and good ductility. The 3D polymeric lattice-enhanced MSWIFA-based composites showed application prospects as sustainable construction materials, gaining both environmental benefits and good mechanical performance.

Submicron tourmaline enhanced the solidification of municipal solid waste incineration fly ash by chemical structure reorganization and stabilized heavy metals

Municipal solid waste incineration fly ash (MSWIFA) exsits in large quantitities and contains pollutants such as heavy metal. While solidification is one of the most effective methods for treating MSWIFA, this application is limited by cost, subsequent treatment, and simultaneous immobilization of anions and cations. This research demonstrated that under a certain initial pressure (20 MPa), a gelation reaction involving ball milling-modified tourmaline powder, a small amount of cement clinker, and MSWIFA forms a stable consolidated body and significantly reduces the risk of heavy metal dissolution. The consolidated MSWIFA can easily be formed into unfired bricks in large-scale pilot production, and a response surface model was used to optimize the experimental parameters. When the mass ratio of tourmaline: cement clinker: MSWIFA was 15:15:200 (mixed with a moisture content of 13 to 15 %), the compressive strength of the consolidated body reached 13 MPa, and the amounts of Cr and Pb leached decreased from 12 mg/L to 0.1 mg/L and 25 mg/L to 0.3 mg/L, respectively. The consolidated form contained a new mineral phase (Ca3Si2O7·3H2O, Ca10Mg0.8(SiO4)0.6O2Cl, and CaCl2∙Ca(OH)2·H2O) with a high compressive strength. Notably, the soluble PbSO4 in the MSWIFA was converted into relatively stable PbSiO3, and Cr(VI) was lattice-wrapped. This study was the first to demonstrate that tourmaline synchronously passivates Pb(II) and Cr(VI) in fly ash in the solid phase, with a low cost and requires no subsequent treatment. This study provided a novel technical path for recycling MSWIFA. Eventually, leaching of the heavy metals Pb, Cr, Cu, Cd, and Zn from the solids achieved concentrations less than 0.25, 1.5, 0.5, 0.15, and 100 mg/L.

Fractal Characteristics of Geopolymer Mortar Containing Municipal Solid Waste Incineration Fly Ash and Its Correlations to Pore Structure and Strength

Compression and mercury intrusion porosimetry (MIP) tests were conducted to analyze the effect of municipal solid waste incineration fly ash (MSWIFA) content on the mechanical performance and pore structure of geopolymer mortar. The MSWIFA weight contents were 0%, 5%, 15%, 25%, and 35% and the pore diameter distribution, specific surface area, and pore volume were considered to assess the pore structure of the geopolymer mortars. The popular fractal model was used to investigate the fractal features of the geopolymer mortars. Additionally, mathematical models of fractal dimension with pore structural parameters and compressive strength were established. The results showed that the compressive strength of geopolymer mortars decreased while the total pore volume and total specific surface area of mortars increased with the increase in MSWIFA content. As the MSWIFA content increased, the harmless pores (pore diameter &lt; 20 nm) were refined. Specifically, the pores with a diameter of 5–10 nm increased in number but the pores with a diameter of 10–20 nm decreased in number with the increase in MSWIFA content. The pore structure in the mortars showed scale-dependent fractal characteristics. All fractal curves were divided into four segments according to the pore diameter, namely, Region I (&lt;20 nm), Region II (20–50 nm), Region III (50–200 nm), and Region IV (&gt;200 nm). The surface fractal dimension (DS) in Region I and Region IV was between 2 and 3. However, the DS in Region II and Region III was greater than 3, indicating the pores in Region II and Region III were non-physical according to the surface geometry because of the presence of ink bottle pores which distorted the result of the MIP. The complexity of pores in Region I and Region IV was reduced by the addition of MSWIFA. The DS is a comprehensive parameter that well describes the spatial and morphological distribution of pores in geopolymer mortars and exhibited a good correlation with the specific surface area, pore volume, and compressive strength. A mathematical model based on the DS was established to predict the compressive strength of the geopolymer mortar containing MSWIFA.

Accelerated and natural carbonation of a municipal solid waste incineration (MSWI) fly ash mixture: Basic strategies for higher carbon dioxide sequestration and reliable mass quantification

The carbonation of alkaline wastes is an interesting research field that may offer opportunities for CO2 reduction. However, the literature is mainly devoted to studying different waste sequestration capabilities, with lame attention to the reliability of the data about CO2 reduction, or to the possibilities to increase the amount of absorbed CO2.In this work, for the first time, the limitation of some methods used in literature to quantify the amount of sequestered CO2 is presented, and the advantages of using suitable XRD strategies to evaluate the crystalline calcium carbonate phases are demonstrated. In addition, a zero-waste approach, aiming to stabilize the waste by coupling the use of by-products and the possibility to obtain CO2 sequestration, was considered. In particular, for the first time, the paper investigates the differences in natural and accelerated carbonation (NC and AC) mechanisms, occurring when municipal solid waste incineration (MSWI) fly ash is stabilized by using the bottom ash with the same origin, and other by-products. The stabilization mechanism was attributed to pozzolanic reactions with the formation of calcium silicate hydrates or calcium aluminate hydrate phases that can react with CO2 to produce calcium carbonate phases. The work shows that during the AC, crystalline calcium carbonate was quickly formed by the reaction of Ca(OH)2 and CaClOH with CO2. On the contrary, in NC, carbonation occurred due to reactions also with the amorphous Ca. The sequestration capability of this technology, involving the mixing of waste and by-products, is up to 165 gCO2/Kg MSWI FA, which is higher than the literature data.

Alkali-activated binders – A sustainable alternative to OPC for stabilization and solidification of fly ash from municipal solid waste incineration

This research aims to evaluate the sustainability of alkali-activated binders for the stabilization/solidification (S/S) of municipal solid waste incineration fly ash (MSWI FA). A detailed environmental assessment of different alkali-activated mixtures was conducted using life cycle assessment (LCA) to identify the factors affecting their environmental burden. Ground granulated blast-furnace slag (GGBS) and metakaolin (MK) were used as the precursors. Results showed that all the alkali-activated blocks fulfilled the requirements for landfill and reuse as fill materials. Adopting alkali activation for S/S of MSWI FA instead of OPC allowed up to 70% reduction of global warming potential. However, in other impact categories such as human toxicity and land use, the alkali mixtures recorded higher values than the mix with OPC (+60–70%), primarily because of the impacts related to the production of chemical activators. The sensitivity analysis demonstrated that alternative production methods for sodium silicate and sodium hydroxide could enormously reduce the impacts related to the alkali solution. When the hydrothermal method for sodium silicate and the ODC method for sodium hydroxide were adopted, a reduction of 71%, 22%, and 24% was recorded in global warming potential, fossil resource scarcity, and human toxicity categories, respectively, compared with the mix with OPC. Therefore, this study sheds light on alkali-activated materials as sustainable S/S alternative to OPC for hazardous waste management to promote carbon neutrality.

Speciation and leaching characteristics of heavy metals from municipal solid waste incineration fly ash

• Characteristics of heavy metals in MSWI fly ash were investigated. • Coarse and fine particles MSWI fly ash can enrich more heavy metals. • Long-term environmental risk was low for As and Cr, but high for Pb and Hg. • CaO can effectively inhibit the leaching of As and Pb from MSWI fly ash. Fly ash from municipal solid waste incineration (MSWI) is classified as hazardous waste because it is rich in heavy metals (HMs), dioxins and other hazardous substances. In this paper, four kinds of MSWI fly ash were selected and tested to understand their physical and chemical properties, HM enrichment pattern, HM fugacity pattern and leaching toxicity. The results show that the main mineral components of MSWI fly ash are chlorine minerals and calcium minerals (NaCl, NaSO 4 , KCl, CaClOH, CaCO 3 , CaSO 4 , etc.), while only NaSO 4 and NaCl exist in MSWI fly ash without CaO injection. The HM contents in MSWI fly ash were As (25.8–922.0 μg/g), Cr (26.9–173.3 μg/g), Pb (988.8–1259.4 μg/g) and Hg (7.29–8.47 μg/g) and showed a trend of an initial decrease and later increase as the MSWI fly ash particle size decreased. The major species of As and Cr in the four MSWI fly ash samples were As(V) and Cr(III); Pb mainly existed as PbCl 2 and PbSO 4 . The injection of CaO could make the fly ash alkaline and promote the formation of Ca 3 (AsO 4 ) 2 , CaCrO 4 and PbCl 2 , which reduced the leaching rate of As and Pb to<10 % and 15 %, respectively. Hg exists mainly in the species of Hg 0 , Hg-OM, HgCl 2 , HgO and HgSO 4 , and its distribution is mainly influenced by the flue gas components. These results can provide a basis for studying the escape mode and leaching toxicity of HMs in MSWI fly ash.

Preparation of Alkali Activated Cementitious Material by Upgraded Fly Ash from MSW Incineration.

Utilization of municipal solid waste incineration fly ash (MSWI-FA) can avoid land occupation and environmental risks of landfill. In this paper, MSWI-FA was used to prepare alkali activated cementitious materials (AACMs) after two-step pretreatment. The ash calcination at 450 °C removed 93% of dioxins. The alkali washing with 0.2 g NaOH/g ash removed 89% of chlorine and retained almost 100% of calcium. The initial setting time of AACMs was too short to detect for 20% of MSWI-FA addition, and the prepared block had extensive cracks and expansion for CaClOH and CaSO4 inside. Alkaline washing pretreatment increased the initial setting time by longer than 3 min with 30% ash addition and eliminated the cracks and expansion. The significance of the factors for compressive strength followed the modulus of alkali activator > silica fume amount > alkaline washing MSWI fly ash (AW-MSWI-FA) amount. When the activator modulus was 1.2, 1.4 and 1.6, the blocks with 30% of AW-MSWI-FA had a compressive strength of up to 36.73, 32.61 and 16.06 MPa, meeting MU15 grade. The leaching test shows that these AACM blocks were not hazardous waste and almost no Zn, Cu, Cd, Pb, Ba, Ni, Be and Ag were released in the leaching solution.