Search

Hazardous waste disposal is a serious environmental concern in China. Therefore, in this study, industrial trials were conducted in a low-temperature thermal degradation facility, a tunnel kiln, and a shaft kiln to effectively treat dioxins in municipal solid waste incineration (MSWI) fly ash. The results indicated that the low-temperature thermal degradation facility efficiently decomposed polychlorinated dibenzo-p-dioxins and dibenzofurans in the MSWI fly ash. Additionally, the concentrations of dioxins in the treated fly ash and exhaust gas were lower than the suggested standard limits and the degradation ratio of dioxins was ∼99%. Therefore, treated fly ash characterized by acceptable dioxin risks could be utilized for the production of non-fired building materials. The results from the tunnel kiln indicated complete decomposition of the dioxins in the firing and insulating sections. However, the addition of fly ash in the tunnel kiln increased the concentration of dioxins in the flue gas. This can be primarily attributed to the heterogeneous catalytic synthesis reaction in the low-temperature section of the tunnel kiln. The results from the shaft kiln indicated degradation of at least 22% of the dioxins in the ash. The dioxin concentration in the flue gas was lower than the national standard while that in the clinker was within a reasonable limit. Furthermore, the environmental risks were significantly reduced at fly ash addition ratios lower than 3%., Competing Interests: Declaration of competing interest None., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A disposal method for fly ash from a municipal solid waste incinerator (MSWI-FA) that involved a water washing pretreatment and co-processing in a cement kiln was tested. The mass flows of toxic heavy metals (HMs), including volatile HM (Hg), semi-volatile HMs (Pb, Cd, Tl, and As), and low-volatility HMs, and polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran (PCDD/Fs) in the input, intermediate, and output materials were characterized. The flue gas Hg concentrations from tests 0, 1, and 2, fed with 0, 3.1, and 1.7 t/h of dried-washed FA (DWFA), were 28.60, 61.95, and 35.40 μg N m -3 , respectively. Co-processing of DWFA did not significantly affect the metal concentration in clinker as most of the major input metals, with the exception of Cd, Pb, and Sb (which came from DWFA), were from raw materials and coal. Co-processing of DWFA did not influence on the release of PCDD/Fs; baseline and co-processing values ranged from 0.022 to 0.039 ng-TEQ/N m 3 , and from 0.01 to 0.031 ng-TEQ/N m 3 , respectively. The total destruction efficiency for PCDD/Fs in MSWI fly was 82.6%. This technology seems to be an environmentally sound option for the disposal of MSWI-FA., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Degradation of polychlorinated dibenzo- p-dioxins and dibenzofurans in municipal solid waste incinerator fly ash is beneficial to its risk control. Fly ash was treated in a full-scale thermal degradation system (capacity 1 t d -1 ) to remove polychlorinated dibenzo- p-dioxins and dibenzofurans. Apart from the confirmation of the polychlorinated dibenzo- p-dioxin and dibenzofuran decomposition efficiency, we focused on two major issues that are the major obstacles for commercialising this decomposition technology in China, desorption and regeneration of dioxins and control of secondary air pollution. The toxic equivalent quantity values of polychlorinated dibenzo- p-dioxins and dibenzofurans decreased to <6 ng kg -1 and the detoxification rate was ⩾97% after treatment for 1 h at 400 °C under oxygen-deficient conditions. About 8.49% of the polychlorinated dibenzo- p-dioxins and dibenzofurans in toxic equivalent quantity (TEQ) of the original fly ash were desorbed or regenerated. The extreme high polychlorinated dibenzo- p-dioxin and dibenzofuran levels and dibenzo- p-dioxin and dibenzofuran congener profiles in the dust of the flue gas showed that desorption was the main reason, rather than de novo synthesis of polychlorinated dibenzo- p-dioxins and dibenzofurans in the exhaust pipe. Degradation furnace flue gas was introduced to the municipal solid waste incinerator economiser, and then co-processed in the air pollution control system. The degradation furnace released relatively large amounts of cadmium, lead and polychlorinated dibenzo- p-dioxins and dibenzofurans compared with the municipal solid waste incinerator, but the amounts emitted to the atmosphere did not exceed the Chinese national emission limits. Thermal degradation can therefore be used as a polychlorinated dibenzo- p-dioxin and dibenzofuran abatement method for municipal solid waste incinerator source in China.

The destruction of DDT formulations and DDT contaminated soil was conducted by feeding wastes into the flue gas chamber at the kiln inlet of two different preheater/precalciner cement kilns in China. The concentration of DDT, PCDD/PCDFs and HCB were measured in the flue gas of the main stack, in the solid material under baseline conditions and when feeding DDT-wastes. The destruction efficiency and the destruction and removal efficiency for DDT were in the range of 99.9335%-99.9998% and 99.9984%-99.9999%, respectively. The emissions of PCDD/PCDFs and HCB in the flue gas varied in the range of 0.0019-0.0171 ng I-TEQ/Nm(3) and 0.0064-0.0404 μg/Nm(3), respectively. The emission factor for PCDD/PCDF and HCB varied from 0.0137 to 0.0281 μg/ton and from 17.32 to 109.34 μg/ton of clinker, respectively. The concentration of PCDD/PCDFs and HCB in solid samples decreased as follows: cement kiln dust, 4.1-5 ng I-TEQ/kg and 0.70-0.71 μg/kg, respectively; >raw meal, 0.82-0.97 ng I-TEQ/kg and 0.18 μg/kg, respectively; >cement clinker, 0.09-0.22 ng I-TEQ/kg and 0.14-0.18 μg/kg, respectively. This study indicates that the feeding of DDT and POPs-wastes to the lower temperature part of a cement kiln system possibly to create a buildup of trace not-destroyed compounds in the system and might cause emissions; the technical feasibility and the environmental acceptability of this practice need to be investigated thoroughly., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The multi-source hazardous waste co-disposal system, a recent innovation in the industry, offers an efficient approach for hazardous waste disposal. The incineration fly ash (HFA) produced by this system exhibits characteristics distinct from those of typical incineration fly ash, necessitating the use of adjusted disposal methods. This study examined the physicochemical properties, heavy metal content, heavy metal leaching concentration, and dioxin content of HFA generated by the new co-disposal system and compared them with those of conventional municipal waste incineration fly ash. This study investigated the solidification and stabilization of HFA disposal using the organic agent sodium diethyl dithiocarbamate combined with cement on a field scale. The findings revealed significant differences in the structure, composition, and dioxin content of HFA and FA; HFA contained substantially lower levels of dioxins than FA did. Concerning the heavy metal content and leaching; HFA exhibited an unusually high concentration of zinc, surpassing the permitted emission limits, making zinc content a critical consideration in HFA disposal. After stabilization and disposal, the heavy metal leaching and dioxin content of HFA can meet landfill disposal emission standards when a 1% concentration of 10% sodium diethyldithiocarbamate (DDTC) and 150% silicate cement were employed. These results offer valuable insights into the disposal of fly ash resulting from incineration of mixed hazardous waste. [ABSTRACT FROM AUTHOR]

Arsenic (As) and antimony (Sb) are heavy metals that have a toxic effect on human and environmental biology. Industrial tests were conducted on cement kiln co-processing of industrial sludge containing arsenic and waste resin containing antimony. The migration and distributions of arsenic and antimony in the cement kiln were studied. For antimony, the time required to establish a new mass balance and reach the steady state was significantly shorter than that for arsenic. Under the assumption that the input rates of arsenic and antimony in the co-processing test were 100%, almost all of the antimony and 70·52% of the arsenic were removed from the kiln as clinker. Minimal amounts of arsenic and antimony were emitted to the atmosphere via flue gas. 0·96% of arsenic and 4·37% of antimony formed external circulation with the cement kiln dust. 105·43% of arsenic and 123·56% of antimony were introduced by waste incineration residues and led to internal circulation with the hot meal in the kiln. Some arsenic (28·51%) accumulated in the kiln and was not discharged. The antimony inputs and outputs agreed with the mass balance. The mass distribution ratios in the clinker, flue gas and kiln dust varied with changing inputs of arsenic and antimony. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low-temperature thermal treatment is highly efficient and low energy consumption. • The degradation and ash discharge phases of dioxins are comprehensively considered. • Temperature is the main factor for the degradation and ash discharge stages. • The increase in oxygen content promotes the desorption of dioxins to the gas phase. • Below 200℃, the oxygen content has little effect on the ash discharge stage. Dioxins in municipal solid waste incineration fly ash (MSWIFA) can cause significant risks to the environment and human health. In this study, the low-temperature thermal treatment of MSWIFA under industrial conditions was simulated in the laboratory to investigate the process parameters for dioxin degradation and ash discharge stages. Correlation analysis and dioxin fingerprint characterization were used to analyze the degradation and ash discharge processes. The degradation efficiency of low-temperature thermal treatment was influenced by multiple factors. At 400℃ for 90 min and 1% O 2 , the dioxin removal rate was 95.80%, the detoxification rate was 91.73%, and the residual dioxin toxicity in MSWIFA was 22.7 ± 17.8 ng I-TEQ/kg, which was in line with the limit value of 50 ng I-TEQ/kg in the "Technical specification for pollution control of fly-ash from municipal solid waste incineration" (HJ1134-2020). The increase in dioxins during ash discharge did not follow a linear relationship with the process parameters. This was assumed to be related to the MSWIFA composition, as some components containing P, Si, and Al at 150 °C may inhibit dioxin formation. The dioxin increased only by 0.79 ± 2.65 ng/kg, an increase in toxicity of 0.42 ± 0.10 ng I-TEQ/kg, when treated at 150 °C for 30 min and 10% O 2. [ABSTRACT FROM AUTHOR]

• The behaviour of Cd and Pb are closely related to the presence of Cl−1. • The concentrations of Cd and Pb increased sharply after recycling of kiln dust. • Thermodynamic software can effectively simulate the fixation of heavy metals. • Using model can optimize kiln control strategy and ash recirculation ratio. Fly ash produced from incineration of municipal solid wastes (MSW) contains heavy metals, such as Cd and Pb, that make this material difficult to manage and dispose of safely. Because the composition of fly ash is similar to cement raw meal, partial replacement of raw meal with fly ash may be a feasible way to reduce the health and environmental hazards of the ash, provided that the heavy metals can be effectively stabilized in the solid phase. This research employs proprietary thermochemical software to simulate the thermodynamic behavior and single-step fixation of Cd and Pb in industrial cement kilns. The effect of Cd, Pb and Cl loadings on the fixation and/or evaporation of Cd and Pb during the sintering process is analyzed using data from industrial cement kilns. A simplified model is created based on elemental mass balance to evaluate multi-step fixation of Cd and Pb with cement kiln dust recycle.The results indicate that Cd forms Cd(OH) 2 (g) in a highly alkaline environment, while nearly 90% Pb is volatilized as PbCl 2 (g). In the clinker, increased Cl−1 decreased the proportion of Pb and Cd, moreover, Pb and Cd increased in kiln dust with Cl−1 increased; Calculations using a kiln dust recycle model showed that, the concentrations of Pb and Cd in both kiln dust and clinker increased sharply after recycling of kiln dust in steady state. Under unstable conditions, the concentrations of Pb and Cd in kiln dust increased, as well as the heavy metals re-entering the cement kiln. [ABSTRACT FROM AUTHOR]

There is a limited body of research on the recovery of soluble salts from municipal solid waste incineration fly ash (MSWI-FA), with challenges stemming from the effective management of residual heavy metals and dioxins. In this investigation, we propose using water-washing treatment for fly ash dechlorination and using CO 2 aeration carbonation combined with ceramic membrane filtration to recover soluble salt resources from fly ash. This study investigated the impact of combined processes on fly ash soluble salt recovery, carbon dioxide capture and sequestration, heavy metal removal, and dioxin diffusion reduction. The findings revealed that the combined process can significantly enhance the rate of carbonation and the removal of heavy metals. Specifically, the removal rates of Pb and Zn reach 100%. The resulting CaCO 3 precipitation particle size is smaller, averaging only approximately 4 μm, with greater surface porosity, higher heavy metal and dioxin content, and dioxin toxic equivalents as high as 8.11 ng TEQ/kg. Moreover, the dioxin content in the recovered mixed salt decreased, and its dioxin toxic equivalent was only 3.228.11 ng TEQ/kg. Consequently, the combined process of CO 2 aeration combined with ceramic membrane filtration was used in conjunction to significantly reduce pollutants (heavy metals and dioxins) in the MSWI-FA recovered salt. This approach enhances the recyclable resource utilization of MSWI-FA and reduces the risk of pollution dispersal during MSWI-FA disposal and resource utilization. [Display omitted] • Removal of heavy metals from MSWI-FA water washing solution by CO 2 carbonation. • Ceramic membrane interception to control the diffusion of dioxin pollution. • The combined process improves the efficiency of pollutant removal. • Recovering low pollutant soluble salts from MSWI-FA. • Sustainable development through the technology of treating waste with waste. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molten chlorides can be recycled to extract heavy metals from fly ash effectively. • The migration and reaction of Cd, Cu, Pb in molten salt differ from those of Zn. • Heavy metal oxide and chloride in molten salt can be converted into each other. • Zn2+ can react with Si 2 O 7 6- formed by O2– and SiO 2 , to be stabilized as Ca 2 ZnSi 2 O 7. • For recovery, heavy metals can be enriched in the slags of molten salt. Molten salt thermal treatment has been demonstrated to be effective in dissolving heavy metals in municipal solid waste incineration (MSWI) fly ash. However, the complex thermochemical reactions of various heavy metals during the process remain unclear. This study investigated the migration and transformation mechanisms of typical heavy metals during molten salt (NaCl-CaCl 2) cyclic thermal treatment of fly ash at 600–750 °C, as well as the leaching characteristics and recovery methods of heavy metals in the reacted products. Molten chlorides could be recycled to extract heavy metals from fly ash, which reduced the leaching toxicity of heavy metals in the reacted slags. Over 64.3% of Cd, Cu and Pb in fly ash were transferred to molten salt while the migration rate of Zn was restrained to only 32.3% during the cyclic process at 750 °C. Regarding Cd, Cu, and Pb in molten salt, the chlorination and dissolution of their oxides were significant, while the combination of their chlorides with free O2– to form oxides precipitation was weak. However, the above reaction characteristics of Zn were the opposite. Furthermore, Zn2+ could be stabilized into hardystonite (Ca 2 ZnSi 2 O 7) in molten salt by reacting with Si 2 O 7 6- generated from the combination of O2– and SiO 2. Besides, increasing the reaction temperature facilitated the chlorination and dissolution of heavy metals. For recovery, heavy metals could be concentrated on the insoluble matters of molten salt, with a maximum concentration of approximately 5 times that in fly ash. [ABSTRACT FROM AUTHOR]

CaCr 2 O 4 (Cr (III)), mainly generated through the decomposition of CaCrO 4 (Cr (VI)), is a significant intermediate for toxic Cr (VI) formation during solid fuel combustion. In this study, the formation, oxidation and sulfation kinetics of CaCr 2 O 4 were analyzed to forecast the potential of CaCr 2 O 4 oxidation during co-firing of coal and solid waste in a circulating fluidized bed boiler. The results indicated that the formation and oxidation of CaCr 2 O 4 were fitted to a single step nucleation and growth model while CaCr 2 O 4 sulfation was fitted to a shrinking core model. CaCr 2 O 4 formation through CaCrO 4 decomposition was favored in oxygen-lean atmosphere and considerably suppressed in the presence of oxygen. In contrast, CaCr 2 O 4 oxidation was mainly determined by the contacts between CaCr 2 O 4 and CaSO 4 /CaO, which influenced not only oxidation rates but also the product species. Moreover, the oxidation reactivity of CaCr 2 O 4 was higher in the presence of CaO than that of CaSO 4. On the other hand, CaCr 2 O 4 sulfation can occur more easily than CaCr 2 O 4 oxidation, the reaction rate of which was deeply affected by sulfate product layer. Findings in this study suggested that spraying calcium in furnace for desulphurization may increase the risk of CaCr 2 O 4 oxidation. Measures including the adjustment of Ca/S ratio in blended fuel (with added limestone) and operating conditions (such as temperature and local atmosphere) in co-firing system could be taken to control CaCr 2 O 4 formation and oxidation. • Cr oxidation was determined by the formation, oxidation and sulfation of CaCr 2 O 4. • Nucleation and growth model was fitted to the formation and oxidation of CaCr 2 O 4. • CaCr 2 O 4 sulfation could be described by shrinking core model. • Available calcium content affected not only oxidation rate but also product species. • CaCr 2 O 4 sulfation was easier to occur than CaCr 2 O 4 oxidation. [ABSTRACT FROM AUTHOR]