ABSTRACT

To achieve a more sustainable waste-to-energy (WTE) process, the recycling of solid waste incineration (MSWI) bottom ash (BA) has received large attention nowadays. This study investigated how WTE BA form is changed after the hydration and the impacts of WTE BA hydration on its leaching characteristics by using geometrical and leaching tests when incorporated in cement matrix for the recycling. The material composition and characteristics of anhydrous BA, hydrated BA, cement paste, Portland cement concrete (PCC), and BA-combined PCC were evaluated through scanning electron microscopy, X-ray spectroscopy and X-ray diffraction analyses. The results confirmed that the WTE BA newly formed a complex phase of hydration products in a cement matrix. Synthetic precipitation leaching procedure (SPLP) test was also conducted to investigate the leaching behaviors of alkaline components and metals of BA in the crushed BA-PCC samples. Through the leaching study, the leachability of crushed BA-combined concrete was rigorously evaluated when recycled as construction materials (e.g. base, subbase, subdrainage, etc.), which is the worst–case scenario. The results revealed that the release of highly alkaline elements increases with increasing BA content. However, the release of trace metals was reduced by 20-30% significantly when mixed properly with Portland cement concrete (PCC), which is due to both physical and chemical binding in cement hydration products. In addition, the thresholds of water regulations, set by the World Health Organization (WHO) and the Environmental Protection Agency (EPA) of the United States, were assessed as the basis for evaluating the extent of the risk of the leaching of toxic materials.

Implications: This study investigated how waste to energy (WTE) bottom ash (BA) form is changed after the hydration and the impacts of WTE BA hydration on its environmental leaching characteristics by using geometrical and leaching tests when incorporated in cement matrix for the recycling. Incorporating of WTE BA in cement mixture can form new mineralogical phases of hydration products in cement matrices such as Copper Hydrogen Arsenate Hydrate and Jahnsite. A significant reduction of alkaline elements (Si, Al, and K) from crushed PCC mixed with WTE BA due to the hydration. The lowest concentrations of major alkaline elements leached from the crushed PCC containing either 10% or 20% of BA contents. The averaged leaching concentration of detected elements is substantially below the water quality guidelines (provided by U.S. EPA and WHO) except Al.

摘要

为了实现更可持续的废物转化能源 (WTE) 过程，固体废物焚烧 (MSWI) 底灰 (BA) 的回收利用如今受到了广泛关注。本研究通过使用几何学和浸出试验研究了 WTE BA 形式在水化后如何变化以及 WTE BA 水化对其浸出特性的影响，当将其加入水泥基体进行回收时。通过扫描电子显微镜、X 射线光谱和 X 射线衍射分析评估了无水 BA、水化 BA、水泥浆、波特兰水泥混凝土 (PCC) 和 BA 组合 PCC 的材料组成和特性。结果证实，WTE BA 在水泥基体中新形成了复杂的水化产物相。还进行了合成沉淀浸出程序（SPLP）测试，以研究粉碎的 BA-PCC 样品中 BA 的碱性成分和金属的浸出行为。通过浸出研究，当作为建筑材料（例如基层、底基层、排水系统等）回收时，破碎的 BA 组合混凝土的浸出性得到了严格评估，这是最坏的情况。结果表明，随着 BA 含量的增加，高碱性元素的释放增加。然而，当与波特兰水泥混凝土 (PCC) 适当混合时，微量金属的释放显着减少了 20-30%，这是由于水泥水化产物中的物理和化学结合。此外，水法规的门槛，

含义：本研究通过使用几何学和浸出试验研究了水化后废物转化为能源 (WTE) 底灰 (BA) 的形式如何变化以及 WTE BA 水化对其环境浸出特性的影响，当将其加入水泥基体进行回收时。在水泥混合物中加入 WTE BA 可以在水泥基体中形成新的水化产物矿物相，如水合砷酸铜和 Jahnsite。由于水合作用，与 WTE BA 混合的粉碎 PCC 中碱性元素（Si、Al 和 K）显着减少。从含有 10% 或 20% BA 含量的粉碎 PCC 中浸出的主要碱性元素的浓度最低。除铝外，检测元素的平均浸出浓度大大低于水质指南（由美国环保署和世界卫生组织提供）。