| 低温热处理生活垃圾焚烧飞灰中二噁英的降解机理 |
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| 引用本文： | 李唯实,李丽,文卓钰,闫大海,刘美佳,黄启飞,朱占恒.低温热处理生活垃圾焚烧飞灰中二噁英的降解机理[J].环境科学研究,2023,36(6):1227-1235. |
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| 作者姓名： | 李唯实 李丽 文卓钰 闫大海 刘美佳 黄启飞 朱占恒 |
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| 作者单位： | 1.中国环境科学研究院固体废物污染控制技术研究所，北京 100012 |
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| 基金项目： | 国家重点研发计划项目(No.2019YFC1906902) |
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| 摘 要： | 生活垃圾焚烧飞灰中二噁英类污染物会对人体健康和环境造成严重的危害，有必要了解固相中二噁英的降解机理从而帮助其降解至环境可接受的水平. 本研究将理论和试验相结合探究低温热处理法降解飞灰中二噁英的机理. 以八氯代二苯并对二噁英（OCDD）作为目标污染物附着在模拟飞灰〔mCaO∶mCa(OH)2=3∶1〕上，利用密度泛函理论（DFT）对固相中OCDD的低温热处理降解机理进行分析，并进行模拟飞灰降解试验. 首先对降解前的模拟飞灰进行热重（TG）分析，然后采用红外光谱（FTIR）和透射电子显微镜（TEM）测试对固体产物进行表征，并对反应气相进行收集和检测从而验证反应机理. 结果表明:①从室温到400 ℃模拟飞灰共有三段失重过程，失重率为9.61%. ②—OH是低温热处理降解OCDD的关键官能团. ③结合FTIR和TEM分析结果可知，当多个—OH取代OCDD上的Cl后会氧化OCDD生成大量CO32?，这是OCDD转化的主要路径. OCDD转化的次要路径是在降解过程中会形成小部分C—O—结构，该结构可能与其他降解后的OCDD分子相结合形成大分子有机物. ④结合气相检测可知，Cl转化的主要路径是整个—OH完全取代Cl，取代后的Cl会脱离出反应体系形成Cl2. 次要路径是仅—OH上的—O—会取代Cl形成C—O—，该结构由于自由基未完全配对而不稳定，Cl和H相结合生成HCl脱离反应体系. CO2平均含量仅有0.008 5%，说明几乎没有碳酸盐分解或与HCl发生反应. 研究显示，低温热处理降解生活垃圾焚烧飞灰中二噁英的关键基团为—OH，二噁英的主要物质归趋为碳酸盐，Cl的主要物质归趋为Cl2.
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| 关 键 词： | 低温热处理 生活垃圾焚烧飞灰 二噁英 OCDD 反应机理 |
| 收稿时间： | 2023-02-06 |
Degradation Mechanism of Dioxins in Municipal Solid Waste Incineration Fly Ash by Low-Temperature Thermal Treatment |
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| Affiliation: | 1.Research Institute of Solid Waste, Chinese Research Academy of Environmental Sciences, Beijing 100012, China2.College of Water Science, Beijing Normal University, Beijing 100085, China3.Zhejiang Jinglan Environmental Technology Co., Ltd., Hangzhou 311215, China |
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| Abstract: | Dioxin-like pollutants in municipal solid waste incineration fly ash (MSWIFA) can pose serious health and environmental risks, and it is necessary to understand the degradation mechanism of dioxins in the solid phase to help them degrade to environmentally acceptable levels. This study combined theoretical and experimental approaches to investigate the degradation mechanism of dioxins in MSWIFA with a low-temperature thermal treatment. Octachlorodibenzo-p-dioxin (OCDD) was used as a target contaminant that was attached to simulated fly ash (FA, mCaO:mCa(OH)2=3:1), and the low-temperature thermal treatment degradation mechanism of OCDD in the solid phase was analyzed with density functional theory (DFT) and to conduct simulated FA degradation experiments. The simulated FA prior to degradation was initially analyzed by thermogravimetric (TG) analysis, and then the solid products were characterized by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The reaction gas was collected and tested to verify the reaction mechanism. The results showed that: (1) There were three stages of weight loss in the simulated FA from room temperature to 400 °C, and the weight loss rate was 9.61%. (2) -OH was the key functional group for the degradation of OCDD by low-temperature thermal treatment. (3) Combining the FTIR and TEM analysis results, it can be seen that when multiple -OH groups replace the Cl on OCDD, they oxidize OCDD to generate a large amount of CO32?, and this is the primary pathway for OCDD conversion. A sub-pathway of OCDD conversion is the formation of a small fraction of C-O- structures during degradation, which may combine with other degraded OCDD molecules to form macromolecular organics. (4) Combined with the gas-phase test results, it is clear that the primary pathway of Cl conversion is the complete substitution of Cl by the whole -OH group and the substituted Cl will leave the reaction system to form Cl2. The sub-pathway is that only -O- on -OH replaces the Cl to form C-O-, a structure that is unstable because of the incomplete pairing of radicals, and the Cl and H combine to form HCl to leave the reaction system. The average CO2 content was only 0.0085%, thus indicating that almost no carbonate decomposition or reaction with HCl took place. The study reveals the key groups of dioxins degradation in MSWIFA by low-temperature thermal treatment is -OH, the main substance of dioxins tends to be carbonate, and the main substance of Cl tends to be Cl2. |
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