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In this study, we report the co-treatment of municipal solid waste incineration fly ash and high arsenic-containing wastewater. The appropriate liquid-solid ratio for co-treatment and the feasibility of co-treatment with 5000 mg/L arsenic in wastewater were investigated, as well as the risk of heavy metals leaching from the co-treated products in the actual leachate. Further, a new index for assessing the risk of heavy metals releasing into the environment was proposed. The results demonstrated that the optimal liquid-solid ratio was 10 mL/ 20 g, considering that it allowed the maximum co-treatment amount of wastewater and would not affect the subsequent disposal of co-treated products in landfills. In the presence of 5000 mg/L arsenic in wastewater, the chemical speciation distribution and leaching toxicity of As, Cr, Cu, and Pb in the co-treated products would not change significantly. The leaching results of co-treated products in actual leachate indicated that the co-treated products can favor the stabilization of As, Cr, and Pb in leachate. The migration and transformation index value of Cu suggested the risk of Cu releasing in a leachate scenario. Through co-treatment, wastewater can be completely absorbed into the fly ash without the need for further treatment, featuring significant economic and environmental benefits. [ABSTRACT FROM AUTHOR]

To completely replace Portland cement for mine backfilling, MSWI fly ash (FA) and solid metallurgical wastes (ground granulated blast furnace slag, steel slag and flue gas desulphurisation gypsum) were used to prepare fly ash-slag-based binder (FBB). The effect of FA content on the hydration and Pb stabilization mechanisms of the FBB was investigated. When a small amount (15%) of FA was added to FBB, hydration product formation and compressive strength were inhibited during early curing (7 d). However, the additional Ca2+, SO42− and OH− carried by FA could partially promote the formation of ettringite, so that the compressive strength of 28 d was comparable to that of the treatment without FA addition (32.5 MPa). When a high amount of FA (30%) was added, the hydration process was strongly inhibited throughout the entire curing period, and the leaching concentration of Zn (1052 μg/L) exceeded the limits of the GB/T 30760–2014 standard (1000 μg/L). Pb2+ was also found to replace Ca2+ in ettringite to form insoluble Pb-ettringite and Pb2(SO4)O precipitates, resulting in remarkable Pb stabilisation in system. Therefore, if the amount of FA incorporated is appropriate, the use of FA as an additional cementitious material for mine backfilling is an ideal method for recycling FA.Highlights: FA as a cementitious material can meet backfilling strength requirements. FBM containing 15% FA met the CS and metal leaching limits for mine backfilling. FBM retains high Pb stabilization efficiency in acidic environment. Pb stabilization in FBM is achieved by the formation of Pb-ettringite and Pb2(SO4)O. The use of FA as a backfilling material is an ideal method to recover resources. [ABSTRACT FROM AUTHOR]

Expansive clays feature high compressibility and large swelling-shrinkage potential, which may cause significant damage to the infrastructures, including pavements. This study investigates the potential use of industrial waste ash generated from municipal solid waste incineration (MSWI) as a more sustainable treatment method to treat expansive soils compared to the use of conventional coal fly ash. A series of tests was conducted to study the mechanical, durability, and environmental performance of the MSWI fly ash in comparison with the coal fly ash. The study reveals that the compressive strength and resilient modulus of 20% MSWI fly ash treated sample increased to 0.86 MPa and 213 MPa respectively, depicting an increase of 150% and 240% of the control clay specimen. Results also indicate that MSWI treated expansive clay shows better performance during the soaked California bearing ratio (CBR) testings, moisture susceptibility and cyclic wetting–drying tests compared to coal fly ash treated samples. Microlevel investigations reveal that the influence of cation exchange is more decisive in the MSWI-treated clays due to the presence of higher Ca2+ ions, during the early stages, and the influence of hydration is stronger at the later stage of stabilisation. X-ray diffraction (XRD) results show that gismondine, albite, calcite, portlandite, andradite, and ettringite are the main crystalline phases formed during the stabilization. Heavy metal concentrations after the stabilisation are within the allowable limit defined by state regulations. Applying MSWI fly ash as a ground treatment for expansive clays can reduce the consumption of natural resources, promoting a "zero landfill" policy. [ABSTRACT FROM AUTHOR]

Wash water, municipal solid waste incineration (MSWI) fly ash, and propylene (PP) fibers were employed simultaneously to produce self-compacting repair mortar (SCRM). Different SCRM mixtures were utilized, incorporating 35, 70, and 140 kg/m3 of MSWI fly ash, along with 0.1% of PP fibers. The research focused on investigating the workability, mechanical properties, and global warming potential (GWP) of SCRM. The incorporation of MSWI fly ash and wash water in SCRM resulted in reduced workability, necessitating an increase in the use of superplasticizer. Adding MSWI fly ash decreases compressive strength. The minimum compressive strength was observed when employing 140 kg/m3 of MSWI fly ash and wash water instead of tap water simultaneously. By increasing the proportion of MSWI fly ash content and correspondingly reducing the cement content in SCRM samples, there was a decrease in flexural strength. The ultrasonic pulse velocity (UPV) of all SCRM samples falls within acceptable range. Adding MSWI fly ash to SCRM reduces fracture toughness, and the concurrent use of wash water and MSWI fly ash significantly decreases fracture toughness. Incorporating PP fibers into SCRM resulted in increased compressive strength. Utilizing wash water and MSWI fly ash in SCRM significantly reduces GWP. The avoidance of wash water consumption mitigates the environmental impact of SCRM. [ABSTRACT FROM AUTHOR]

Melting is an efficient method to turn municipal solid waste incineration (MSWI) fly ash (FA) into non-hazardous material. Coal fly ash (CFA) was selected as the silica-alumina source to carry out co-melting research with MSWI FA in this work. The effects of the temperature and the CFA content on mineral transformation and the migration characteristics of heavy metals were analyzed. The results showed that the mixtures of MSWI FA and CFA reacted at high temperatures to mainly generate Ca2Al2SiO7, Ca2SiO4, and CaAl2Si2O8 primarily and then melted and formed the amorphous-phase vitreous body when the CFA content was more than 40% and the temperature was higher than 1300 °C. During the melting process, Cd and Pb were almost volatilized, while Cr, Mn, and Ni were almost retained. Besides, the volatilization rates of Cu and Zn fluctuated with the temperature and the CFA content. Suitable treatment temperature and CFA content were conducive to the transformation of the heavy metals in the FA into stable forms, and the melting products were no longer hazardous wastes because the vitreous body could effectively encapsulate heavy metals. This study aims to help reuse the FA and CFA collaboratively and be more environmentally friendly. [ABSTRACT FROM AUTHOR]

Solidification/stabilization (S/S) is a typical technique to immobilize toxic heavy metals in Municipal solid waste incineration fly ash (MSWI FA). This study utilized blast furnace slag, steel slag, desulfurization gypsum, and phosphoric acid sludge to develop a novel metallurgical slag based cementing material (MSCM). Its S/S effects of MSWI FA and long-term S/S effectiveness under dry–wet circulations (DWC) were evaluated and compared with ordinary Portland cement (OPC). The MSCM-FA block with 25 wt.% MSCM content achieved 28-day compressive strength of 9.38 MPa, indicating its high hydration reactivity. The leaching concentrations of Pb, Zn and Cd were just 51.4, 1895.8 and 36.1 μg/L, respectively, well below the limit standard of Municipal solid wastes in China (GB 16889–2008). After 30 times' DWC, leaching concentrations of Pb, Zn and Cd for MSCM-FA blocks increased up to 130.7, 9107.4 and 156.8 μg/L, respectively, but considerably lower than those for OPC-FA blocks (689, 11,870.6 and 185.2 μg/L, respectively). The XRD and chemical speciation analysis revealed the desorption of Pb, Zn and Cd attached to surface of C-S–H crystalline structure during the DWC. The XPS and SEM–EDS analysis confirmed the formation of Pb–O-Si and Zn–O-Si bonds via isomorphous replacement of C-A-S–H in binder-FA blocks. Ettringite crystalline structure in OPC-FA block was severely destructed during the DWC, resulting in the reduced contents of PbSO4 and CaZn2Si2O7·H2O and the higher leachability of Pb2+ and Zn2+. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash is a collection of aggregates with different particle sizes, and the size distribution played an important role in its physicochemical and pollution characteristics. In this work, MSWI fly ash was divided into four size distributions (> 100 mesh, 100–200 mesh, 200–400 mesh, and < 400 mesh) with the negative pressure screen analyzer. The composition, structure, and morphology of MSWI fly ash, the total amounts, leaching toxicity, and chemical speciation distribution of heavy metals in MSWI fly ash varied with size distribution and was investigated. The results uncover that the phase composition of MSWI fly ash is almost the same regardless of size distribution, but the content varied. As the particle size decreases, the spherical particles of MSWI fly ash increase and its surface shape tends to be regular. There is no significant mathematical correlation between the leaching concentration or total amounts of heavy metals and size distribution of MSWI fly ash, but most heavy metals tend to deposit on fine particles. The residual and carbonate fractions form the main chemical speciation of heavy metals in MSWI fly ash, and carbonate states of high proportion facilitate the migration and leaching of heavy metals. This study highlights the importance of size distribution on enrichment of heavy metals on MSWI fly ash. And it also proposes that the influence of the incineration process, municipal wastes composition, and other factors on performances of MSWI fly ash remains to be clarified further. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash treated with toxicity metals holds enormous potential for constructure use to economize on resources and protect environment. To reach the goal, this study investigated the effects of sintering conditions on leaching characteristic of heavy metals for MSWI fly ash, especially Cr, Cr6+, Ag, and Ba, with the orthogonal and Box-Benhnken design experiment, which considered grain size (D50 = 30, 45, and 60 μm), fluxing agent (CaO = 0, 2.5, and 5%), setting temperature (1000, 1050, and 1100 °C), and setting time (120, 180, and 240 min). The mechanism of immobilization for heavy metals was also discussed through the analyses of morphological characterizations, mineral phases, chemical composition, and leaching values of metals. The results indicated that changing grain size and adding fluxing agent of CaO have positive influence on reducing the leaching of heavy metals compared with direct sintering. The leaching values of As, Pb, Cd, Cu, Ni, Zn, Mn, Hg, Be, Se, and fluoride are not detected after sintering. Ideal sintering condition with desirability of 1.00 was predicted and optimized by the Box-Benhnken response method in grain size of D50 = 30 μm, fluxing agent of CaO = 5%, setting temperature = 1050 °C, and setting time = 180 min, which immobilized Cr, Cr6+, Ag, and Ba lower than the limitation of standards. Actual experiment was consistent with numerical optimization. Furthermore, the model of leaching characteristic for heavy metals in MSWI fly ash was established with the discussion on species distribution of heavy metals to better explain the mechanism during sintering. [ABSTRACT FROM AUTHOR]

In this study, the long-term leaching behaviors of Cd, Cr, Cu, Ni, Pb, and Zn in municipal solid waste incineration (MSWI) fly ash samples from grate-type (GT) and circulating fluidized bed (CFB) incinerators were investigated and compared under the simulated landfill leachate corrosion scenario, which was determined to be more severe than the acid rain corrosion scenario. The total heavy metal contents showed increasing hierarchies of Ni

Radioactive cesium found in municipal solid waste incineration (MSWI) fly ash can be easily eluted through contact with environmentally sourced water, such as rainwater. Dissolution suppression treatment of radioactive cesium, such as through cement solidification or geopolymer solidification, has been previously studied. Treatment through solidification requires the addition of a fixation agent, which results in an increase in the volume of fly ash following solidification. It is likely that the level of security at the landfill site will be high. In an attempt to simply suppress the elution of water-soluble radioactive cesium from MSWI fly ash without an increase in volume, we examined a water-repellent treatment method using four types of water repellents. Our results indicate that when the incinerated fly ash is impregnated and mixed with a commercially available water repellent, such as a silane-based oligomer, an alkyl alkoxysilane compound, or a fatty acid, it is possible to suppress the elution of radioactive cesium without a corresponding increase in fly ash volume. [ABSTRACT FROM AUTHOR]

Fusion pretreatment is introduced to the microwave-assisted hydrothermal process to improve the zeolite fabrication from municipal solid waste incineration (MSWI) fly ash. The fusion-pretreated microwave-assisted hydrothermal method (FMHM) and microwave-assisted hydrothermal method are conducted and systematically compared. With fusion pretreatment, the quartz is transformed into amorphous form, which is easier to dissolve into a hydrothermal solution and thus accelerates the zeolite fabrication process. The scanning electron microscope, X-ray diffraction, Fourier transform infrared measurement and thermal gravimetric analysis are performed, whose results suggest the formation of zeolite materials in the FMHM product, such as needle-like tobermorite and rose-like sodalite. The thermal gravimetric analysis indicates water adsorption of the FMHM product is improved. The cation exchange capacity of the FMHM product is 1.172 meq g−1, more than twofold larger than that of the MHM product. Additionally, the toxicity test indicates that the leakage of heavy metal ions from the FMHM product is dramatically reduced. The improved safety makes the zeolitic product synthesized from MSWI fly ash promising for further applications. FMHM significantly facilitates the disposal and reuse of the MSWI fly ash. [ABSTRACT FROM AUTHOR]

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100 °C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900 °C) and MSWI BA (1100 °C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900 °C). The water permeability ranged between 0.106 and 0.391 cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability. [ABSTRACT FROM AUTHOR]

The strength of cement substituted mortar decreases with the increase in fly ash amount, whereas the strength increases when the fly ash is blended as sand substitute. A mortar with highest strength (compressive strength = 30.2 Mpa; flexural strength = 7.0 Mpa) was obtained when the sand replacement ratio was 0.75%. The k value (cementing efficiency) of fly ash varied between 0.36 and 0.15 for the fly ash fraction in binder between 5% and 25%. The k values of fly ash used for sand replacement were all significantly above that used for cement substitution. The macropores assigned to the gaps between particles decreased when the fly ash was used as sand replacement, providing an explanation for the strength enhancement. The waste-extraction procedure (toxicity-sulphuric acid and nitric acid method (HJ/T 299-2007)) was used to evaluate metal leaching, indicating the reuse possibility of fly ash blended mortar. For the mortar with the mass ratio of fly ash to binder of 0.5%, the carcinogenic risks (CR) and non-carcinogenic hazard quotient (HQ) in sensitive scenario for blended mortar utilization were 9.66 × 10−7 and 0.06, respectively; these results were both lower than the threshold values, showing an acceptable health risk. The CR (9.89 × 10−5) and HQ (3.89) of the non-sensitive scenario for fly ash treatment exceeded the acceptable threshold values, indicating health risks to onsite workers. The main contributor to the carcinogenic and non-carcinogenic risk is Cr and Cd, respectively. The CR and HQ from inhalation was the main route of heavy metal exposure. [ABSTRACT FROM AUTHOR]

This paper presents a route for the treatment of MSWI fly (FA) and bottom ashes (BA) using microorganisms to critically assess whether bioleaching is within reach of effective industrial application. The leaching of metals from BA and FA was investigated in a controlled laboratory environment using a culture isolated from a natural system where the dominant strains are acidophilic bacteria, mainly Acidothiobacillus thiooxidans and Acidothiobacillus ferrooxidans. The community of microorganisms (mostly acidophilic, S- and Fe-oxidizing bacteria) was collected directly from overflows and ponds at the sediment–water interface of a natural system near a post-mining site. Pre-cultivation was done in 250 mL flasks followed by the adaptation to the different substrates (both FA and BA). The effect of different material pre-treatment and elemental sulphur concentrations were evaluated for both BA and FA, at a starting pH of 4. The bioleaching of BA and FA substrates experienced good yields of metal extraction with an optimum duration of two weeks. The results showed that more than 90% Zn, Cu, and 10% Pb are removed from FA; while 100% Cu, 80% Zn and 20% Pb are removed from BA samples. Batch experiments with regenerating ion-exchange resins did not perform well for metal recovery, but could serve as a valuable decontamination step. The techniques used here with FA and BA can be used for urban mining purposes (e.g. ashes and other meal-rich anthropogenic wastes), but also low-grade ores in the mining industry, contributing to resource recovery or decontamination agendas. [ABSTRACT FROM AUTHOR]

The proper disposal of municipal solid waste incineration fly ash (MSWI FA) is necessary due to the presence of hazardous metals (Cu2+, Zn2+, Pb2+ and Cd2+). 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, SiO2/Na2O 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 Cu2+, Zn2+, Pb2+ and Cd2+ 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. [ABSTRACT FROM AUTHOR]

In this study, a microwave-assisted hydrothermal process (MAHP) is used to modify municipal solid waste incineration (MSWI) fly ash. The influences of the dosage, additives, liquid-to-solid ratio (L/S), temperature, and reaction time are investigated in detail, and it is found that the modified fly ash (MFA) exhibits the highest adsorption capacity of Cu2+ (32.05 mg/g) when modified under the conditions of 1 mol/L Na2HPO4, an L/S ratio of 3 mL/g, a reaction temperature of 200 °C and a reaction time of 30 min. The cation exchange capacity (CEC) of the fly ash remarkably increases from 0.022 to 0.498 meq/g after treatment, which is an increase of approximately 22 times. X-ray diffraction results reveal the formation of zeolitic crystals in the MFA. To study the adsorption mechanism, the Cu2+ adsorption isotherms and kinetics are measured. The adsorption behaviors are well described by the Freundlich isotherm equation with a correlation coefficient of 0.986 and by a pseudo-second-order kinetic equation with a correlation coefficient of 0.998. Overall, utilizing MSWI fly ash as adsorbents should receive more attention, and the MAHP is considered to be a promising technology. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash is a by-product from municipal waste incineration. According to incomplete statistics, each year more than one million tons MSWI fly ash was produced in China. Owing to high heavy elements content, widely used disposal methods of landfill are not suitable for MSWI fly ash treatment. In this study, by using MSWI fly ash as raw materials, glass-ceramics was synthesized for the solidification of heavy metals and waste recycle. Process parameters, including composition, heat treatment temperature and time, were studied and optimized. Under optimizing conditions, the product has good properties of density of 3.42 g·cm−3 and Vickers hardness of 6.91 GPa. Moreover, the leaching concentration of heavy metal elements meets allowable values of toxicity characteristic leaching procedure (TCLP). This study offers an alternative for MSWI fly ash recycle. [ABSTRACT FROM AUTHOR]

Cement solidification is an important pre-treatment technology for municipal solid waste incineration (MSWI) fly ash into landfill. The physicochemical properties and leaching characteristics are the foundation for assessing the long-term stability of the fly ash solidified with benchmark cement in landfills. The leaching performances of bulk components (Na, K, Ca, Cl, CO32−, and SO42−) and heavy metals (Cu, Zn, Cr, Pb, and Zn) were analyzed based on the percolation column test and pH dependent test respectively. The research showed that in the cement-solidified fly ash, Na and K were mainly in the form of soluble chloride salts and would be washed out severely at the initial leaching stage due to the weak fixation effect of cement. Moreover, a considerable amount of Ca was washed out simultaneously with Na and K, causing a temporary increase in pH value, and then Ca leaching was controlled by the solubility of minerals, mainly calcium carbonate, ettringite formed with CO32− and SO42−. Cement solidification reduced the cumulative release of mobile Cu, Zn, Cr, Pb, and Cd contained in MSWI fly ash. In the cement-solidified fly ash, the leaching of Cu and Zn was controlled by mineral solubility under alkaline conditions, Cr was dependent on the redox conditions, and Pb was related to the complex structures formed with Si-O bonds of silicates. A further research on the long-term stability of the cement-solidified fly ash in landfills was needed. [ABSTRACT FROM AUTHOR]

In the vulnerable Arctic environment, the impact of especially hazardous wastes can have severe consequences and the reduction and safe handling of these waste types are therefore an important issue. In this study, two groups of heavy metal containing particulate waste materials, municipal solid waste incineration (MSWI) fly and bottom ashes and mine tailings (i.e., residues from the mineral resource industry) from Greenland were screened in order to determine their suitability as secondary resources in clay-based brick production. Small clay discs, containing 20 or 40% of the different particulate waste materials, were fired and material properties and heavy metal leaching tests were conducted before and after firing. Remediation techniques (washing in distilled water and electrodialytical treatment) applied to the fly ash reduced leaching before firing. The mine tailings and bottom ash brick discs obtained satisfactory densities (1669-2007 kg/m3) and open porosities (27.9-39.9%). In contrast, the fly ash brick discs had low densities (1313-1578 kg/m3) and high open porosities (42.1-51. %). However, leaching tests on crushed brick discs revealed that heavy metals generally became more available after firing for all the investigated materials and that further optimisation is therefore necessary prior to incorporation in bricks. [ABSTRACT FROM AUTHOR]

Municipal solid waste incinerator (MSWI) fly ash contains large amounts of arsenic and antimony. This study focuses on the incorporation and evaporation of arsenic and antimony when MSWI fly ash added to clinker raw meal. Thermal analysis was used to simulate the “single incorporation” of arsenic and antimony into clinker with HSC. Statistical analysis was acquired by cement industrial monitoring data to determine the effect of total chloride, arsenic and antimony input on the incorporation or evaporation of arsenic or antimony. A simplified mass balance model was used to evaluate the effect of cement kiln dust (CKD) recirculation on the “multiple incorporation” of arsenic and antimony in clinker and the evaporation of arsenic and antimony in waste CKD. The results indicated that arsenic and antimony was largely incorporated into the clinker as Ca2(AsO4)2(s), even in the presence of chlorides. Moreover, CKD recirculation promoted arsenic and antimony incorporation into clinker. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration (MSWI) fly ash is by-product and hazardous waste produced from MSWI plant. In the MSWI fly ash there are high contents heavy metals, among which cadmium (Cd) is more active and toxic. Although inorganic acid leaching is an effective way to remove heavy metals out from the MSWI fly ash and nitric acid has great efficiency for Cd removal, little literature reported the redistribution of remaining Cd in the MSWI fly ash. This investigation focused on the change of different factions (exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual) of Cd in treated (i.e. washed with nitric acid) MSWI fly ash. Sequence extraction procedures (SEP) have been used to derive different fractions of Cd, results indicated that fractions of Cd have changed significantly after nitric acid washing procedures. Due to the changes of main compounds and microstructures stable Cd (bound to organic matter and residual) had opportunity to leach out, which resulted in a higher potential risk (or higher bioavailability index) for living creatures, although the total amount of Cd decreased. X-ray diffraction (XRD) and images of scanning electron microscope (SEM) proved these changes in washed MSWI fly ash. [ABSTRACT FROM AUTHOR]

Municipal solid waste incinerator (MSWI) fly ashes are characterized by high calcium oxide (CaO) content. Carbon dioxide (CO) adsorption by MSWI fly ash was discussed based on thermogravimetry (TG)/differential thermal analysis (DTA), minerology analysis, and adapting the Stenoir equation. TG/DTA analysis showed that the weight gain of the fly ash below 440 °C was as high as 5.70 %. An adapted Stenoir equation for MSWI fly ash was discussed. The chloride in MSWI fly ash has a major impact on CO adsorption by MSWI fly ash or air pollution control (APC) residues. Geochemical modeling of the critical trace elements copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), and antimony (Sb) before and after carbonation was performed using a thermodynamic equilibrium model for solubility and a surface complexation model for metal sorption. Leaching of critical trace elements was generally found to be strongly dependent on the degree of carbonation attained, and their solubility appeared to be controlled by several minerals. Adsorption on ferrum (Fe) and aluminum (Al) colloids was also responsible for removal of the trace elements Cd, Pb, and Sb. We used Hakanson's potential ecological risk index (HPERI) to evaluate the risk of trace element leaching in general. The results demonstrate that the ecological risk showed a V-shaped dependency on pH; the optimum pH of the carbonated fly ash was found to be 10.3-11, resulting from the optimum carbonation (liquid-to-solid ( L/ S) ratio = 0.25, carbonation duration = ∼30-48 h). The dataset and modeling results presented here provide a contribution to assessing the leaching behavior of MSWI fly ash under a wide range of conditions. [ABSTRACT FROM AUTHOR]

Thermal treatment is a promising technology for the fast disposal of hazardous municipal solid waste incineration (MSWI) fly ash in China. However, fly ash produced in grate incinerator (GFA) is rich in CaO and chlorides, which promote the formation of toxic hexavalent chromium [Cr(VI)] and ash agglomeration during the thermal process, inhibiting the thermal disposal of GFA. In this study, sintering characteristics of CaO-rich GFA were improved by adding Si/Al-rich MSWI ash residues. According to the results, ash agglomeration was well suppressed during thermal treatment of the mixed ash. Si/Al/Fe-compounds competed with un-oxidized Cr-compounds to react with CaO and suppressed Cr(VI) formation. Meanwhile, chlorides in GFA facilitated heavy metal volatilization from added ashes to the secondary fly ash, favoring the recovery of these metals. Ca-aluminosilicates was found as the main mineral phase in the thermally treated mixed ash, which has attractive potential for applications. The formation of the aluminosilicates made the heavy metals that remained in the treated mixed ash more stable than the thermally treated single ash. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Washing pre-treatment of municipal solid waste incineration (MSWI) fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets. A formula uniform design was performed to arrange the mixture ratio of the materials. The optimal mixture ratio of the materials was determined by measuring the bulk density, granule strength, and 1 h water absorption of the pellets. It is shown that the optimal mixture ratios of materials, MSWI fly ash, shale, and sludge, are 23.16%, 62.58%, and 14.25% (mass fraction), respectively. The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio: bulk density of 613 kg/m, granule strength of 821N, and 1 h water absorption of 11.6%, meeting 700 grade light-aggregate of GB/T 17431.2-1998 standard. The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values. [ABSTRACT FROM AUTHOR]

Municipal solid waste incinerator (MSWI) fly ash was melted into slag and then pulverized to generate particle sizes of less than 38 mμ in diameter (sieve #400) for experimental studies. Several slag-blended cement concrete (SBCC) specimens 10 cm in diameter and 20 cm in height were molded using 20% cement replacement with slag powder. Then, three water/cementitious (w/c) ratios, namely 0.36, 0.52 and 0.68, were selected to test the specimens for slump, setting time, compressive strength and durability. The compressive strengths of specimens of various ages were compared with those of ordinary Portland cement concrete (OPCC) specimens. The results reveal that the compressive strengths of the SBCC specimens were lower than those of the OPCC specimens at an early stage and became similar to those of the OPCC specimens at the age of 28 days. Moreover, the compressive strengths of the SPCC specimens are 100-113% and 105-118% those of the OPCC specimens after 56 and 90 days, respectively. The slumps (i.e. workability) and setting times for both the SBCC and OPCC specimens were similar. Our test results show that MSWI slag-blended cement concrete is usable for practical applications and can be applied to the concrete pavement. [ABSTRACT FROM AUTHOR]

Hydrothermal solidification of municipal solid waste incineration (MSWI) fly ash has been conducted under saturated steam pressure at 200 °C for up to 48 h with quartz addition. To enhance the strength of solidified specimens further, the raw fly ash was pre-treated by water-washing and mixed with NaOH solution (2 M) as reaction solvent. Experimental results showed that curing time and temperature had significant effects on strength development. Strength development was found to be mainly due to tobermorite formation, and addition of quartz and NaOH solution promoted tobermorite formation. The raw fly ash could also be used as an additive to solidify MSWI bottom ash, and with raw fly ash addition (10%) the flexural strength of solidified specimens reached more than 21 MPa, suggesting high potential to recycle 100% MSWI ash (e.g. as 10% fly ash + 90% bottom ash). Leaching tests were conducted to determine amounts of heavy metals dissolved from solidified specimens. The results showed that under the hydrothermal conditions of this study, leaching of heavy metals was very low. As such, the hydrothermal processing method might have high potential for recycling/reusing MSWI fly ash on a large scale. [ABSTRACT FROM AUTHOR]

The activities of municipal solid waste incineration (MSWI) fly ash and incineration residues were studied contrastively, through the component analysis and the activity ratio tests. The mechanical properties, hydration mechanism and leaching toxicity of the hardened cement paste mixing with MSWI fly ash and incineration residues were investigated. The experimental results indicated that the active constituents (CaO+Al2O3+Fe2O3) in MSWI fly ash were higher than those in incineration residues. Therefore the activity ratio of MSWI fly ash was 43.58%, twice as much as that of incineration residues. Meanwhile, the hydration of cement was delayed by mixing with MSWI fly ash and incineration residues, which also reduced the cement strength markedly. By adding with exceeding 20% MSWI fly ash, the specimens expanded and microcracks appeared. The leaching toxicities of cement pasted mixed with MSWI fly ash and incineration residues were lower than the Chinese national standard. Accordingly the cement mixed by MSWI fly ash and incineration residues can be considered as the environment-friendly materials. [ABSTRACT FROM AUTHOR]

The possibilities of MSWI fly ash as a major constituent of novel solidification/stabilization matrices for secure landfill were investigated by mixing MSWI fly ash with rich aluminum components, which was added as bauxite cement or metakaolinite instead, to form Friedel and Ettringite phases with high fixing capacities for heavy metals. The physical properties, heavy metals-fixing capacity, mineral phases and its vibration bands in the novel matrices were characterized by compressive strength, TCLP(toxic characteristic leaching procedure), XRD (x-ray diffraction), DTG (derivative thermogravimetry), and FTIR (fourier transform infrared spectroscopy), respectively. The Tessier’s five-step sequential extraction procedure was used to analyze the fractions of chemical speciation for Pb, Cd and Zn ions. The experimental results indicate that Friedel-Ettringite based novel solidification/stabilization matrices can incorporate Pb, Cd and Zn ions effectively by physical encapsulation and chemical fixation, and it exhibits a great potential in co-landfill treatment of MSWI fly ash with some heavy metals-bearing hazardous wastes. [ABSTRACT FROM AUTHOR]

The chemical composition, the content and the leachability of heavy metals in municipal solid waste incineration (MSWI) fly ash were tested and analyzed. It is shown that the leachability of Pb and Cr exceeds the leaching toxicity standard, and so the MSWI fly ash is considered as hazardous waste and must be solidified. The effect of solidifying the MSWI fly ash by cement was studied, and it is indicated that the heavy metals can be well immobilized if the mass fraction of the fly ash is appropriate. The heavy metals were immobilized within cement hydration products through either physical fixation substitution, deposition or adsorption mechanisms. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.