Cement kiln dust is commonly recycled back into the production process. This results in elevated concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the flue gases of cement plants. The present study investigated the effects the reaction temperature, oxygen content, and origin of kiln dust had on the thermal reaction characteristics of PCDD/Fs. The concentration of 2,3,7,8-PCDD/Fs that were desorbed from the kiln dust decreased as the reaction temperature was increased and the higher temperature facilitated the degradation of PCDD/Fs. However, the oxygen content, which ranged from 6-21%, had only a minor impact on the thermal reaction characteristics of PCDD/Fs. Finally, the thermal reaction characteristics of PCDD/Fs were largely affected by the origin of the kiln dust; 1.2 pg I-TEQ g À1 was desorbed from kiln dust originating from a cement plant that co-processed refusederived fuel (RDF) and 47.5 pg I-TEQ g À1 was desorbed from kiln dust originating from a cement plant that co-processed hazardous waste. The study also found that PCDD/F formation pathways were dependent on the origin of the kiln dust; precursor synthesis dominated PCDD/F formation on the kiln dust collected from a cement plant that co-processed RDF, while de novo synthesis dominated the formation of PCDD/Fs on the remaining samples of kiln dust.
Municipal solid waste incineration (MSWI) fly ash has been classified as hazardous waste in China because of the leachable toxic heavy metals and high concentrations of chlorides and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Currently, the main treatment method is still landfilling after chemical treatment or cement solidification, and an effective approach to realize fly ash utilization is still lacking. In the present work, the fly ash was firstly water-washed to remove the soluble chlorine salts, which can improve the performance of the produced cement mortar in later work. Mechanochemical pre-treatment was adopted to destroy the PCDD/Fs and improve the heavy metals’ stabilization. The results show that 75% of PCDD/Fs can be degraded and that most of the heavy metals are stabilized. After the mechanochemical pre-treatment, the average particle size of the fly ash decreases to 2–5 μm, which is beneficial for promoting the activation energy and accelerating the hydration process in cement mortar production. The compressive and flexural strengths of the fly ash cement mortar improve to 6.2 MPa and 32.4 MPa, respectively, when 35% of the OPC is replaced by treated fly ash. The similarity in the 3-day and 28-day strength with or without the addition of the treated ash shows the light influence of the fly ash addition. Thus, the mechanochemical process can stabilize the heavy metals and activate the fly ash, allowing it to partly substitute ordinary Portland cement in building materials, such as cement raw materials and concrete.
2021 will be the first year of China's 14 th Five-year period, and all cities have been working on making new local environmental protection plans. To further improve air quality, reduce smog, and control ozone pollution, many cities intend to set more stringent local air quality targets than the national requirements. However, how to set a reasonable and attainable air quality targets is very important because the targets have impacts not only on the welfare of local residents, but also on the local economy. This work presents a comprehensive approach to set reasonable local air quality targets. This approach has been applied to determine PM 2.5 and O 3 ambient concentration targets for Lishui city in its 14th Five-year Environmental Protection Plan. In this study, five years monitoring data of PM 2.5 and O 3 from year 2014 to 2018 in Lishui was collected and analyzed to assess the status quo and trends of its air quality. Then the concentration distribution of PM 2.5 and O 3 in Lishui surrounding cities and counties in Zhejiang Province were also analyzed and the possible impacts on Lishui city were evaluated. Moreover, PM 2.5 and O 3 air quality standards in other developed countries were reviewed and compared with Chinese current standards to assist the setting of appropriate ambient air quality targets. Based on the analysis, three-year sliding average concentration of PM 2.5 and O 3 are included in Lishui's annual air quality targets for the first time, and different air quality targets are set for both the whole city and each specific area of Lishui city.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.