Wang Yegui, Chen Weifang, Zhao Na, Chen Yifan, Deng Baoqing
School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai, China.
PLoS One. 2025 May 14;20(5):e0323729. doi: 10.1371/journal.pone.0323729. eCollection 2025.
This study attempted to investigate the thermal behavior and reaction mechanisms of municipal solid waste incineration fly ash under air and N2. Mass loss patterns at temperatures from 30ºC to 1100ºC were obtained through thermogravimetric analysis. Based on mass loss patterns, the behavior of fly ash under high temperature was divided into three stages. Mass loss in Stage I (30ºC-500ºC) amounted to 3.0%-6.2%. The majority of mass loss concentrated in Stage II (500ºC-800ºC) and Stage III (800ºC-1100ºC). Kinetic parameters of fly ash in Stage II and Stage III were evaluated using Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman methods. By comparison, the iso-conversional FWO method exhibited the highest correlation coefficient with R2 > 0.99. Activation energy (E) values in Stage II calculated via the FWO method indicate that reaction in air showed considerably higher hurdle (E = 171.11 kJ/mol) than reaction in N2 (E = 124.52 kJ/mol). This difference was partly attributed to the presence of carbonation process in air. In contrast, E values in Stage III were similar with E of 373.38 kJ/mol in air and 382.25 kJ/mol in N2. Mechanistic analysis via the Coats-Redfern (CR) model, employing 15 kinetic functions, identified dominant mechanisms of one-dimensional diffusion and contracting sphere for Stage II in air and N2 respectively. At the same time, three-dimensional diffusion could best explain the reaction mechanism in Stage III in both air and N2. Moreover, calculations of thermodynamic parameters (ΔH, ΔG, and ΔS) revealed that major reactions of fly ash during thermal treatment were endothermic and non-spontaneous, with Stage III exhibiting heightened complexity. This multi-stage characterization elucidates the degradation mechanisms of fly ash under varying thermal conditions and provides useful insight into the fly ash thermal treatment processes.
本研究试图探究城市固体废弃物焚烧飞灰在空气和氮气环境下的热行为及反应机理。通过热重分析获得了飞灰在30℃至1100℃温度范围内的质量损失模式。基于质量损失模式，将飞灰在高温下的行为分为三个阶段。第一阶段（30℃ - 500℃）的质量损失为3.0% - 6.2%。大部分质量损失集中在第二阶段（500℃ - 800℃）和第三阶段（800℃ - 1100℃）。使用弗林 - 沃尔 - 小泽（FWO）法、基辛格 - 赤平 - ose（KAS）法和弗里德曼法评估了飞灰在第二阶段和第三阶段的动力学参数。相比之下，等转化率FWO法的相关系数最高，R2 > 0.99。通过FWO法计算得出的第二阶段空气中飞灰的活化能（E）值表明，空气中的反应障碍（E = 171.11 kJ/mol）比氮气中的反应障碍（E = 124.52 kJ/mol）高得多。这种差异部分归因于空气中存在碳酸化过程。相比之下，第三阶段的E值相似，空气中为373.38 kJ/mol，氮气中为382.25 kJ/mol。通过采用15种动力学函数的科茨 - 雷德芬（CR）模型进行机理分析，确定了第二阶段在空气和氮气中分别以一维扩散和收缩球体为主要反应机理。同时，三维扩散最能解释空气和氮气中第三阶段的反应机理。此外，热力学参数（ΔH、ΔG和ΔS）的计算表明，飞灰在热处理过程中的主要反应是吸热且非自发的，第三阶段表现出更高的复杂性。这种多阶段特征阐明了飞灰在不同热条件下降解机理，为飞灰热处理过程提供了有用的见解。
