介稳态熔渣析晶诱导垃圾焚烧飞灰微晶玻璃化及重金属固化机理研究

It is a promising way to prepare value-added glass-ceramics from municipal solid waste incineration fly ash. However, a large quantity of ingredients should be added to adjust the chemical compositions of fly ash using conventional methods, due to the lack of silicon, aluminum, and iron, etc. The high concentrations of chlorides in municipal solid waste incineration fly ash can inhibit the densification of sintered samples and reduce the properties of glass-ceramics. In addition, the high melting temperature can lead to high energy consumption and high volatilization rate of heavy metals. In this study, therefore, the chlorides in municipal solid waste incineration fly ash were removed firstly. Then the method of preparing glass-ceramics via metastable slag inducing crystallization at low-medium temperature is proposed, due to greater ability of crystallization and sintering activity of metastable slag. The effect of chemical composition, temperature, forming pressure, and sintering atmosphere on crystallization mechanism, mechanical-chemical properties, microstructures, and risk assessment of heavy metals were systematically studied. The rules of polycrystalline transformation and heavy metal transformation in co-sintering process were analyzed. The interfacial reaction mechanism about the nucleation, co-crystallization, and densification of glass-ceramics from dechlorinated incineration fly ash and metastable slag was given. In addition, the models of heavy metals-doped crystals were built and optimized, and the binding energy of the optimum models was calculated by Materials Studio software. The solidification mechanism of heavy metals in the polycrystalline phase of glass-ceramics was finally given. The obtained results will provide a new strategy and theoretical basis for the high value-added utilization of municipal solid waste incineration fly ash as glass-ceramics.

垃圾焚烧飞灰制备微晶玻璃是实现其高附加值利用的途径之一。然而，由于其化学组分中硅、铝和铁等元素含量低、氯元素含量高，采用常规方法合成微晶玻璃存在配料掺杂量高、烧结致密化受氯化物抑制严重、以及灰熔融点高导致的能耗高和重金属挥发率高等问题。本项目在研究焚烧飞灰水热脱氯机制基础上，利用介稳态熔渣较强的析晶能力和烧结活性，提出介稳态熔渣析晶诱导脱氯焚烧飞灰低中温合成微晶玻璃的方法。系统考察混合态配料化学组成、热处理温度、成型压力和烧结气氛等对其析晶机理、机械化学性能、微观结构以及重金属风险评估的影响，重点解析混合态配料在共烧结过程中的多晶演变和重金属迁移规律，揭示介稳态熔渣析晶诱导脱氯焚烧飞灰微晶玻璃化过程中成核、共析晶和致密化的界面反应机制。并通过对掺杂晶体结构模型的构建、优化和结合能计算，从能量角度阐明重金属在多晶共存体系中的固化机理，为生活垃圾焚烧飞灰制备微晶玻璃提供新的策略和理论依据。

垃圾焚烧飞灰制备微晶玻璃是实现其高附加值利用的途径之一。然而，由于其化学组分中硅、铝和铁等元素含量低、氯元素含量高，采用常规方法直接合成微晶玻璃存在配料掺杂量高、烧结致密化受氯化物抑制严重、以及灰熔融点高导致的能耗高和重金属挥发率高等问题。本项目在研究焚烧飞灰水热脱氯机制基础上，提出脱氯焚烧飞灰低中温制备全废物基微晶玻璃的方法，并对重金属在微晶玻璃化过程的固定机理展开研究。结果表明，水洗-水热两步法可有效去除垃圾焚烧飞灰中96.56-97.98%的氯离子，>91.59%重金属被稳定固定于水热固相残渣中。通过调控水热过程关键参数和粉煤灰添加量，飞灰中重金属赋存形态向稳定的残留态转化，使得重金属的浸出浓度和潜在生态风险都显著降低；在微晶玻璃的制备过程中，随着烧结温度的升高，脱氯焚烧飞灰基微晶玻璃的抗压强度逐渐升高，显微硬度呈下降趋势，不同烧结温度下微晶玻璃的耐碱腐蚀性能均大于97%，产品中典型重金属Cr、Cu、Ni、Pb和Zn的浸出浓度均远低于美国EPA TCLP和中国GB 5085.3-2007规定的浸出阈值。此外种子萌发实验表明所制备微晶玻璃产品具有很高的生态安全性；通过介稳态熔渣与Cr和Zn的共微晶玻璃化研究，发现Zn离子会通过形成新晶体被固定在微晶玻璃表面，而大多数Cr离子则以Cr2O3晶体的形式嵌入玻璃基体中，两种重金属呈现不同的固化机理。结合敏感性分析可知重金属的不同固化效率还受重金属初始含量和原子半径的影响。量子化学模拟结果表明重金属原子取代钙长石晶体中原子的难易程度为：Cr>Pb>Ni>Cu>Zn>Cd。本项目从垃圾焚烧飞灰的水热脱氯、衍生微晶玻璃的制备以及重金属固化机理等方面展开研究，所得结果为垃圾焚烧飞灰的微晶玻璃资源化利用提供新的技术和理论支撑。