Proximate analysis and XRF results of fly ash.

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.本研究旨在探究空气与氮气（N₂）氛围下城市生活垃圾焚烧飞灰的热行为与反应机理。通过热重分析（Thermogravimetric Analysis）获取了30℃至1100℃温度区间内的质量损失规律。基于质量损失特征，将飞灰的高温热行为划分为三个阶段：第一阶段（30℃~500℃）的质量损失率为3.0%~6.2%；大部分质量损失集中于第二阶段（500℃~800℃）与第三阶段（800℃~1100℃）。采用Flynn-Wall-Ozawa（FWO）、Kissinger-Akahira-Sunose（KAS）以及Friedman三种方法对第二、三阶段的飞灰动力学参数进行了求解。对比结果显示，等转化率FWO法的相关系数最高，决定系数R²>0.99。通过FWO法计算得到的第二阶段活化能（Activation Energy）表明，空气氛围下的反应能垒（E=171.11 kJ/mol）显著高于氮气氛围（E=124.52 kJ/mol），该差异部分源于空气氛围中存在碳酸化过程。与之相反，第三阶段的活化能数值较为接近：空气氛围下为373.38 kJ/mol，氮气氛围下为382.25 kJ/mol。通过Coats-Redfern（CR）模型结合15种动力学函数进行机理分析，分别确定了空气与氮气氛围下第二阶段的主导反应机理为一维扩散与收缩球模型；同时，三维扩散可最优解释两氛围下第三阶段的反应机理。此外，热力学参数（焓变ΔH、吉布斯自由能变ΔG以及熵变ΔS）的计算结果表明，飞灰热处置过程中的主要反应为吸热且非自发的，且第三阶段的反应复杂性更高。本研究通过多阶段表征阐明了飞灰在不同热环境下的降解机理，可为飞灰热处置工艺提供有益的理论参考。