Solid Waste Incineration Fly Ash Research Articles

A novel binder prepared from municipal solid waste incineration fly ash and phosphogypsum

At present, the recycling technology for municipal solid waste incineration fly ash (MSWIFA) and phosphogypsum (PG) is not yet mature, and they are mostly disposed of in open piles or in situ landfills, taking up a lot of land resources and harmful to the environment. A novel binder was developed from MSWIFA and PG in this study. Firstly, the feasibility of using MSWIFA to activate slag (GGBS) and fly ash (FA) for a ternary binder MGF was investigated. Subsequently, based on the optimal mix proportions of MGF, 5%–15% PG was used to substitute GGBS for a quaternary binder MGFP. The results revealed that without PG, the alkali environment provided by MSWIFA can effectively activate GGBS and FA, achieving a compressive strength of 14.0 MPa at 3 d and 25.7 MPa at 28 d when MSWIFA: GGBS: FA = 3: 6: 1. The strength of the ternary binder MGF was further improved by the addition of 5% PG due to the fact that the SO42− from PG reacts with the intermediate product [Al(OH)6]3- generated during MSWIFA activation of GGBS-FA to form ettringite which optimizes the microstructure of the hardened matrix. However, excessive PG over 5% was found to cause reduction in compressive strength, attributed to the dilution of the hydration products and the formation of cracks induced by excessive ettringite. The developed binders presented excellent ability in stabilization and solidification of heavy metals and the heavy metal leaching results meet the Chinese Standard GB18598-2019. The results obtained in this study provide technical support for the application of MSWIFA and PG in construction and building materials.

Phosphate-based geopolymer: Influence of municipal solid waste fly ash introduction on structure and compressive strength

Materials resulting from incorporation of solid waste incineration fly ash into phosphate-based geopolymers, to partially replace metakaolin (up to 50% wt), were studied. X-ray diffraction, scanning electron microscopy, solid-state nuclear magnetic resonance spectroscopy and infrared spectroscopy were adopted to describe the mineralogical changes and the structural modifications of the geopolymer networks which impacted on the mechanical performance (compressive strength) of the materials. The results indicated that fly ash displays a different reactivity compared with metakaolin, behaving preferentially as a source of alkali that compete with the aluminosilicate metakaolin fraction by precipitating crystalline and amorphous phosphates. At 10 wt% of metakaolin substitution with fly ash, the extent and reticulation of the amorphous geopolymer matrix is preserved, and the mechanical properties are retained. At higher waste content (30–50% wt), the fast kinetics of the acid-base reactions involving the fly ash reactive phases prevail over the metakaolin dealumination, and the nature of the material shifts to an alkali-phosphate cement/phosphate-geopolymer composite. This behaviour, together with the development of porosity and presence of low-strength phases in the ash, led to a decline in the mechanical performance with increasing amount of substitution. All in all, this work provides fundamental information in the direction of a sustainable employment of phosphate-based geopolymers, which is limited by the relatively high cost of both metakaolin and phosphoric acid. Moreover, it indicates a recycling opportunity for this type of fly ash.

Regional CO2 accounting and market layout of incinerator fly ash management in China

The reduction of greenhouse gas (GHG) emissions from solid waste incinerator fly ash (IFA) management attracts growing interests since China's zero-waste plan and carbon peak/neutral goals. Herein, provincial GHG emissions from four demonstrated IFA reutilization technologies in China were estimated after analyzing IFA spatial-temporal distribution. Results indicate that technologies transition (landfilling-to-reutilization) could reduce GHG except for glassy slag production. IFA to cement option could potentially realize negative GHG emissions. Spatial GHG variation drivers in IFA management were recognized as provincial-different IFA composition and power emission factors. IFA management options were recommended provincially after weighting local development goals related to GHG reduction and economic benefits. Baseline scenario analysis shows that China's IFA industry would reach carbon peak in 2025 (5.02 Mt). 2030's GHG reduction potential (6.12 Mt) is equivalent to that of absorbed CO2 by 340 million trees annually. Overall, this research could contribute to illustrating future market layout complying with carbon peaking.

Comprehensive study of recycling municipal solid waste incineration fly ash in lightweight aggregate with bloating agent: Effects of water washing and bloating mechanism

Recycling into lightweight aggregate (LWA) by sintering is a promising technology for disposal of municipal solid waste incineration fly ash (FA). In this study, FA and washed FA (WFA) were combined with bentonite and SiC (bloating agent) to make LWA. The performance was comprehensively studied by hot-stage microscopy and laboratory preparation experiments. Water washing and increased FA/WFA improved LWA bloating extent, while shorten the bloating temperature range. Water washing also increased the 1 h-water absorption rate of LWA, making it harder to meet the standard. Excessive FA /WFA usage (70 wt%) will prevent LWA from bloating. For the goal of recycling more FA, mixture with 50 wt% WFA could prepare LWA that meet standard GB/T 17431 at 1140–1160 °C. After water washing, the ratio of Pb, Cd, Zn, and Cu stabilized in LWA increased by 279 %, 410 %, 458 %, and 109 % for 30 wt% FA/WFA addition, and 364 %, 554 %, 717 %, and 697 % for 50 wt% FA/WFA addition, respectively. The change of liquid phase content and viscosity at high temperature were determined using the thermodynamic calculations and chemical compositions. The bloating mechanism was further investigated by integrating these two properties. To obtain accurate results of the bloat viscosity range (2.75–4.44 log Pa·s) for high CaO systems, the composition of the liquid phase should be taken into account. The liquid phase viscosity required for bloating start was proportional to the liquid phase content. With temperature increasing, bloating would end when viscosity drops to 2.75 log Pa·s or liquid phase content reach 95 %. These findings provided further understanding of the heavy metal stabilization during LWA production and the bloating mechanism of high CaO content systems, and could contribute to the feasibility and sustainability of recycling FA and other CaO-rich solid wastes into LWA.

Physicochemical and pozzolanic properties of municipal solid waste incineration fly ash with different pretreatments.

Swelling caused by gas generated from municipal solid waste incineration fly ash (MSWIFA) when it is mixed with alkali limits its uses. Besides, the leaching of anion salts and heavy metals contained in MSWIFA poses a high risk to environment. This study presents the feasibility of a one-step alkaline washing, one-step thermal quenching and two-step combination of alkaline washing and thermal quenching pretreatment methods in altering the key properties of MSWIFA for promoting its reusability. It was found that apart from H2(gas), NH3(gas) was also generated during the alkaline washing of the MSWIFA. Besides, pretreatments led to the reduction in particle size, the increase in pore volume and specific surface area of the MSWIFA, as well as the removal of chloride and sulfate anions. All the pretreatment methods were effective in reducing leaching of heavy metals to below levels of nonhazardous waste except Cd and Pb with alkaline washing. Furthermore, both the chemical Frattini test and the mechanical activity index test showed improvement in pozzolanic activities of the MSWIFA after the pretreatments. Overall, the combined pretreatment method was most effective in eliminating gas emission, and reducing leaching of metal ions and anions from the ash, while enhancing the pozzolanic activity of the ash.

Effect and mechanism of nano-alumina on early hydration properties and heavy metals solidification/stabilization of alkali-activated MSWI fly ash solidified body

Municipal solid waste incineration (MSWI) fly ash has serious pollution. It needs to be solidification/stabilization (S/S) to sanitary landfill as quickly as possible. In order to achieve the objective, the early hydration properties of alkali-activated MSWI fly ash solidified body were investigated in this paper. Meanwhile, nano-alumina was utilized as an agent to optimize the early performance. Therefore, the mechanical properties, environmental safety, hydration process and mechanisms of heavy metals S/S were explored. The results showed that after adding nano-alumina, the leaching concentration of Pb and Zn in solidified bodies after 3 d curing was significantly reduced by 49.7–63% and 65.8–76.1%, respectively, and the compressive strength was enhanced by 10.2–55.9%. Nano-alumina improved the hydration process, and the predominant hydration products in solidified bodies were C-S-H gels and C-A-S-H gels. Meanwhile, nano-alumina could obviously increase the most stable chemical speciation (residual state) ratio of heavy metals in solidified bodies. Pore structure data showed that, due to the filling effect and pozzolanic effect of nano-alumina, the porosity has been reduced and the ratio of harmless pore structure has been increased. Therefore, it can be concluded that solidified bodies mainly solidify MSWI fly ash by physical adsorption, physical encapsulation and chemical bonding.

Facile treatment of municipal solid waste incineration fly ash by one-step microwave hydrothermal method: Hazards detoxification and tobermorite synthesis

A one-step microwave hydrothermal method is proposed here for the harmless treatment and resource recycling of water-washed municipal solid waste incineration fly ash (WMSWI-FA). Dioxins and heavy metals in WMSWI-FA can be detoxified, tobermorite can be synthesized by adjusting the parameters of NaOH dosage, reaction temperature and time. We conclude that NaOH is essential to synthesize tobermorite from WMSWI-FA, and higher temperatures and longer times are beneficial for degrading dioxins. However, excessive NaOH has a negative effect on the degradation of dioxins. Experiments showed that adding 20 wt% NaOH to WMSWI-FA and reacting at 260 °C for 3 h, the tobermorite was successfully synthesized, the residual dioxins (42.80 ng-TEQ/kg) and the leaching concentrations of heavy metals were lower than the limited value of the HJ 1134–2020 standard. The hydrothermal treated WMSWI-FA contains tobermorite, which supports it to be recycled as construction material and adsorbent. The one-step microwave hydrothermal treatment demonstrates favorable industrialization prospects, as it performs well in harmless treatment and resource utilization of WMSWI-FA.

Municipal Solid Waste Incineration Fly Ash: From Waste to Cement Manufacturing Resource.

This study investigates the possibility of using municipal solid waste incineration fly ash as a supplementary cementitious material to replace part of the clinker in cement. Life cycle assessment has shown that the partial replacement of clinker with blast furnace slag (CEM III) reduces cement's global warming potential by ~30%, while replacing clinker with fly ash reduces it by up to 55%. When using CEM III as the control binder in cement in which 55 wt% of the clinker was replaced with hydrothermally treated fly ash, the flexural strength decreased by ~60% and the compressive strength by ~65%. When the fly ash was mixed with calcined and vitrified demolition materials, flexural strength decreased by ~30% and compressive strength by ~50%. The hardening of the hydraulic binders fixed the heavy metals in the municipal solid waste incineration fly ash.

Migration, solidification/stabilization mechanism of heavy metal in lightweight ceramisite from co-sintering fly ash and electrolytic manganese residue

Municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue, as hazardous waste, were roasted into lightweight ceramisite with coal fly ash. The migration, transformation and stabilization/solidification mechanism of heavy metals during ceramisite formation process was explored. Heavy metals in ceramisite pellet were concentrated and experienced the transportation among solids below 710 ℃, then heavy metals were prone to flue gas in the form of chlorides above 710 ℃, in particular for Pb, Cd and Cu. Heavy metal chlorides depended on the generation of HCl and Cl2, which needs co-existence of silicon oxide and aluminum oxide. Note that gibbs free energy change of copper chlorides generation reaction decreased with temperature, resulting in higher volatilization rate compared with Mn, Zn and Cr. Remained heavy metals in the solid phase like Cu, Zn and Cr were prone to ion-exchange, balance-charge and specific-adsorb with calcium-bearing minerals (Ca(Mg,Al)(Si,Al)2O6 and (Ca,Fe)SiO3) in ceramisite based on mineral analysis and principle component analysis at 1160 ℃.

A novel method of calcium dissolution-crystallization-polymerization for stabilization/solidification of MSWI fly ash

Municipal solid waste incineration fly ash (MSWI FA) stabilization/solidification using calcium carbonate (CaCO3) oligomer is an efficient, low-carbon disposal method. The insoluble Ca in FA was converted to free-Ca, utilizing for CaCO3 oligomer preparation, which was crystallized and polymerized by thermal induction to develop continuous cross-link or bulk structures for stabilization/solidification of potentially toxic elements (PTEs, e.g., lead (Pb) and zinc (Zn)). Experimental results showed that the weakly alkaline acid-leaching suspension provided an excellent condition for the generation of CaCO3 oligomers, with Pb and Zn immobilization reaching over 99.4%. With the acid strengthening of the suspension, H+ took the lead in protonating with TEA and limiting the capping action of TEA, which was harmful to the synthesis of CaCO3 oligomers. Ethanol with a low dielectric constant was considered an ideal solvent for oligomer production, and triethylamine (TEA) as a capping agent established hydrogen bonds (N⋯H) with protonated CaCO3. H2O molecules competed with the protonated CaCO3 molecules for TEA with ethanol concentration decreasing, resulting in erratic precipitation of CaCO3 molecules and significantly elevated leaching risk of Pb and Zn. The sequential extraction procedure, pH-dependent leaching, and geochemical analysis results revealed that the dissolution/precipitation of Ca, Pb, and Zn in treated FA was mostly controlled by the carbonate mineral phases. Moreover, the low boiling points of ethanol and TEA can be recovered for recycling. The gel-like, flexible combination of CaCO3 oligomers and FA particles formed by FA offers great resource utilization potential via a controlled crystallization polymerization process.

Reuse of waste sulfur from biogas desulfurization for potentially toxic metals stabilization in MSWI fly ash towards zero-waste in venous industry park

Waste recycling in venous industrial park is considered to be an effective way for circular economy. However, the reuse of waste sulfur from biogas desulfurization in the park is difficult, and this problem has attracted little attention, leading to waste of resources and pollution. In this study, a stabilizer based on waste sulfur from biogas desulfurization (SBD) was prepared for stabilization of potentially toxic metals in municipal solid waste incineration (MSWI) fly ash (FA) using a simple hot alkali synthesis method. Results showed that the stabilization effect of SBD on the four commercial agents (Na2S, Amm-DTC, PBD-A and PBD-B) were significantly improved. Using 3% SBD+ 3% PBD-A, the excess Pb, Cd and Ni in the original fly ash could reach the landfill standard, and the stabilization efficiency reached 100%, 100%, and 93%, respectively, with treatment cost of 34–50 USD/t (246–366 RMB/t); compared with the single commercial agent (5% PBD-A), the stabilization efficiency of Pb was improved by 13% and the treatment cost was saved by 39%. These results provide an economical and environmentally friendly way to realize the co-disposal of MSWI FA and waste sulfur from biogas desulfurization in the park.

Self-alkali-activated self-cementation achievement and mechanism exploration for the synergistic treatment of the municipal solid waste incineration fly ashes and the arsenic-contaminated soils

The feasibility and potential mechanisms of the self-alkali activation brought by municipal solid waste incineration (MSWI) fly ashes to the self-cementation of arsenic-contaminated soils were quantitatively evaluated and comprehensively analyzed to avoid the additional application of the alkali activators and binder materials traditionally. The employment of the two kinds of precursor materials achieved the self-alkali-activated self-cementation (‘double self’) under ambient conditions. The largest compressive strength (MPa) of 25.64 and lowest leaching toxicities (mg/L) of 21.05, 2.86, 0.08, 0.02, 2.05, and 0.34 for Zn, Cu, Cr, Cd, Pb, and As were obtained in the solidified matrix. Geopolymerization kinetics of the ‘double self’ cementation can be mathematically fitted by the Johnson-Mehl-Avrami–Kolmogorov model. CaClOH and halite in the MSWI fly ashes set up the self-alkali activation by reacting with the kaolinite and quartz in soils contaminated with arsenic by forming layered hydration and three-dimensional geopolymerization products to push for self-cementation.

Co-treating MSWI fly ash in iron ore sintering process: Influence of water-washing and roll forming pretreatment on dioxins emission

Co-treating municipal solid waste incineration fly ash (MSWI-FA) in high-temperature iron ore sintering process is winning great concern. Most of the previous studies were about the co-treatment of raw MSWI-FA (without water washing) in sintering process. Although the content of dioxins in MSWI-FA was reduced, the high chlorine content promoted the secondary synthesis of dioxins and had a negative impact on the quality of sinter. This investigation focused on the emission characteristics and regulation approach of dioxins as co-treating MSWI-FA. The results showed that when MSWI-FA was added without pretreatment, the emission concentration of dioxins in sintering flue gas reached 4.28 ng I-TEQ/Nm³ . After water-washing pretreatment, the chlorine in MSWI-FA was significantly reduced, which inhibited the synthesis of dioxins via de novo reaction. The dioxins decreased significantly to 1.44 ng I-TEQ/Nm³ . Based on the washing pretreatment, the MSWI-FA was further prepared into lumps, which inhibited the dispersion of Cl-containing MSWI-FA particles in mixtures and reduced the active sites of dioxins synthesis, thereby hindering the dioxin synthesis path. The emission concentration of dioxins in sintering flue gas was further reduced from 1.44 ng I-TEQ/Nm³ to 1.15 ng I-TEQ/Nm³ . Adding 0.5% water-washed fly ash lumps had little effect on sintering indexes and dioxins concentration in flue gas. The research results laid a certain foundation for the large-scaly recycling of MSWI-FA.

Removal of heavy metals from fly ash using electrodialysis driven by a bioelectrochemical system: a case study of Pb, Mn, Cu and Cd

ABSTRACT Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to high leachable heavy metals, and incineration leachate belongs to organic wastewater with high biodegradability. Electrodialysis (ED) has shown potential for the removal of heavy metals from fly ash, and bioelectrochemical system (BES) employs biological and electrochemical reactions to generate electricity and remove contaminants from a wide range of substrates. In this study, the ED-BES coupled system was constructed for the co-treatment of fly ash and incineration leachate, where the ED was driven by BES. The treatment effect of fly ash by varying additional voltage, initial pH and liquid-to-solid (L/S) ratio was evaluated. Results showed that the highest removal rates of Pb, Mn, Cu and Cd were 25.43%, 20.13%, 32.14% and 18.87% after 14 days treatment of the coupled system, respectively. These values were obtained under 300 mV of additional voltage, L/S 20 and initial pH3. After the treatment of the coupled system, the fly ash leaching toxicity was lower than the threshold of GB5085.3-2007. The highest energy saving for removed Pb, Mn, Cu and Cd were 6.72, 15.61, 8.99 and 17.46 kWh/kg, respectively. The ED-BES can be considered a cleanliness approach to treating fly ash and incineration leachate simultaneously.

Preparation and characterization of mortar specimens based on municipal solid waste incineration fly ash-activated slag

Municipal solid waste incineration fly ash (MSWIFA) contains a large amount of heavy metals, inhibiting resource utilization. This study used MSWIFA as an alkali activator and ground-granulated blast-furnace slag (GGBS) as a precursor to prepare the MSWIFA GGBS binder. Based on this, used the iron tailing sand instead of natural river sand as fine aggregate prepared mortar specimens by cooperative compression molding. Compressive strength, bulk density, water absorption, and heavy metal leaching tests were conducted and combined with micro XRD, FTIR, and SEM examinations to characterize the mortar specimens. The results show that the optimal MSWIFA: GGBS was 2:8. It was also found that increasing the molding pressure was beneficial to strength development. Compared to the specimens without the application of molding pressure, the 3 d and 28 d strength values increased by 148.6 and 122.2%, respectively, after the application of 35 MPa molding pressure. The reason is that the pressure effect can increase the cohesion of the particles, promote the hydration reaction to proceed, and the hydration products increase to fill the pores, increase the structural compactness and promote strength development. The resource utilization of MSWIFA must be guaranteed not to produce environmental pollution simultaneously. For this reason, the heavy metal leaching test was conducted on 28 d mortar specimens, and the results showed that the leaching rates of Zn, Pb, Cu, Cr, and Ni met the requirements of the Chinese Standard (GB16889-2008). The research results can provide a theoretical basis for the large-scale recycling of MSWIFA.

Numerical simulation on the deposition characteristics of MSWI fly ash particles in a cyclone furnace

In melting municipal solid waste incineration (MSWI) fly ash by cyclone furnace, the deposition characteristics of particles affect the slag flow and the secondary MSWI fly ash formation. In this study, the composition mechanism based on critical viscosity is selected as the particle deposition model to predict the deposition and rebound of particles on the furnace wall. The Riboud model with an accurate viscosity prediction performance is selected, then the particle deposition model is integrated into a commercial computational fluid dynamics (CFD) solver through the user-defined function (UDF) to realize the coupling of particle motion and deposition process. The results show that under the same case, the deposition rate decreases obviously with the increase of MSWI fly ash particle size. And the escape rate reaches a maximum at particle size 120 μm. Controlling the particle size of fly ash particles within 60 μm can effectively reduce the generation of secondary MSWI fly ash. During the forward movement of the fly ash inlet position, the escape of MSWI fly ash particles with large particle sizes has been significantly weakened. This measure not only lowers the post-treatment cost but also dramatically reduces the pretreatment step of MSWI fly ash before the melting and solidification process. In addition, the deposition rate and quality will reach the maximum values, respectively, along with gradually increasing MSWI fly ash input flow. Overall, this study has the guiding significance for reducing the pretreatment steps and post-treatment costs of MSWI fly ash by melting in the cyclone furnace.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS2 nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS2 nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS2 in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

The toxic leaching behavior of MSWI fly ash made green and non-sintered lightweight aggregates

With the rapid development of urbanization and the economy, the amount of municipal solid waste incineration fly ash (MSWI fly ash) dramatically increases and stacks up. Declining the leaching concentration of hazardous heavy metals in municipal solid waste incineration fly ash and enlarging the application range in wastewater and biosorption of non-sintered LWAs have always got more attention from more and more researchers. Green and non-sintered LWAs were prepared by using the waste solids (MSWI fly ash and coal fly ash) as raw materials through autoclave technology. In the meantime, the effect of severe leaching environment (pH = 1, 3, 5 and 7) on the stabilization of heavy metals in the LWAs with MSWI fly ash and extra heavy metals were systematically investigated by means of Inductively Coupled Plasma Optical Emission Spectrometer, X-ray diffraction, Fourier Transform Infrared Spectrometer, X-ray photoelectron spectra and Scanning electron microscope. The results revealed that the heavy metals are well immobilized in the LWA matrix through physical encapsulation and adsorption by hydration products (C-S-H). The leaching rate (LR) and cumulative leaching rate (CLR) of heavy metals, phase compositions and chemical structures in LWAs with heavy metals at pH of 1 are significantly changed, but the cumulative leaching rate of Pb2+ is lower than that of Zn2+ and Cu2+. The structure of hydration products in the matrix will be broken and reformed to gypsum under an acid environment (pH = 1). The leaching rate and cumulative leaching rate of heavy metals in LWAs with heavy metals under various leaching environments are much lower when the pH is above 1, which could meet the leaching requirement. This research could provide theoretical support for the application of non-sintered and municipal solid waste incineration fly ash based LWAs in concrete.

Thermal treatment of municipal solid waste incineration fly ash and nanofiltration membrane concentrate co-processing: Speciation of chromium and its leachability

The thermal treatment of municipal solid waste incineration fly ash (MSWI FA) has raised serious concerns due to the increasing leaching concentration of Cr, and Cl severely limits the reuse and utilization of MSWI FA. A nanofiltration membrane concentrate (NF-MC) is utilized in this study to leach the MSWI FA to remove Cl and the fate of Cr in the leaching MSWI FA by NF-MC (L-MSWI FA) is investigated. The results showed that Cl in the MSWI FA was effectively removed at a removal rate greater than 95%. After the thermal treatment of the proportion of the MSWI FA based on the L-MSWI FA (P-MSWI FA), it was revealed that Cr primarily as Cr2O3 hexagonally shaped flake-like crystallites, was oxidated first to Cr(VI), and the leaching concentration reached the maximum (1.17±0.05 mg/L) at 800°C. Cr(VI) was then reduced, and the chemical valence of Cr between Cr(III) and Cr(VI) confirmed that the leachability of the Cr-containing materials rose after the thermal treatment. In addition, it was believed that Cr(VI) was reduced when the temperature was greater than 1000°C. The results of this study provide theoretical guidance for controlling the enhancement of Cr leachability during the thermal treatment process.

Footprints in compositions, PCDD/Fs and heavy metals in medical waste fly ash: Large-scale evidence from 17 medical waste thermochemical disposal facilities across China.

Chemical compositions, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) profiles and heavy metals (HMs) leachability of medical waste fly ash (MWFA) from 17 thermochemical treatment facilities in eight Chinese provinces were first investigated. Large-scale and extended monitoring revealed high chloride and Zn contents and similar PCDD/Fs congener profiles in MWFA. Particularly, the PCDD/Fs and HMs concentrations implied greater toxicity than that observed for municipal solid waste incinerator fly ash (MSWIFA). The maximum international toxic equivalent value of PCDD/Fs in MWFA was 40 times that of MSWIFA, and the leaching concentrations of Zn and Hg were 15 and 4 times those of MSWIFA, respectively. Notably, MWFA characteristics suggest the possibility of recycling and sustainable disposal solutions owing to the high Cl and Zn content with good recovery instead of landfill disposal. Similarities in chemical composition, PCDD/Fs homolog distribution, and water-solubility of chloride salts allows co-processing of MWFA and MSWIFA via water-washing detoxification and thermal treatment, such as that used in cement kilns. This study supplements existing literature on the characteristics and risk management of MWFA.