Abstract:

The leaching pattern of Pb, Zn, Cu, Cd, Cr, and Ni from three typical solidified/stabilized fly ash samples under variable leaching scenarios (landfill leachate invasion + acid rain corrosion, carbonation + acid rain corrosion) was investigated using multiple extraction procedure (MEP) leaching tests. The results showed that solidified fly ash with Portland cement and stabilized fly ash with chelating agent or phosphoric acid showed different degree of resistance in short-term leaching in the face of different leaching scenarios. However, from a long-term perspective, they also failed to avoid the risk of increasing the leaching level of toxic metals due to the extension of leaching time or the change of leaching scenario, especially in the face of alternative leaching scenarios. In particular, the early leaching stage with landfill leachate or CO₂-saturated water and the replacement of simulated acid rain were all unfavorable factors for increasing the leaching level of toxic metals. Moreover, the prolongation of cumulative extraction time re-increased the leaching level of most toxic metals, but the trend varied with different fly ash samples. Pb and Cd were the two toxic metals with the most frequent over their corresponding standard limits. For example, when cement solidified FA was exposed to acid rain corrosion scenarios after landfill leachate invasion and carbonation, the maximum leaching concentrations of Pb and Cd were as high as 0.36 (>0.25)mg/L and 0.28 (>0.15)mg/L, respectively. Therefore, assessing the leaching level of heavy metals according to the actual disposal scenario of fly ash is of great practical significance for characterizing the actual disposal risk of fly ash in the landfill.

Key words: MSW incineration fly ash, heavy metal leaching, landfill leachate, carbonation, acid rain corrosion, multiple extraction procedure (MEP)

摘要：

采用多级浸提实验（MEP）探究了3种典型固化/稳定飞灰样品在不同浸沥场景（垃圾渗滤液侵入+酸雨侵蚀、碳酸化作用+酸雨侵蚀）下Pb、Zn、Cu、Cd、Cr和Ni的浸出规律。结果表明：短期浸沥时，水泥固化飞灰和螯合剂、磷酸稳定化飞灰均对不同的浸沥场景表现出不同程度的抵御能力。然而，从长期视角看，它们也难以避免因浸沥时间延长或浸沥场景改变而增加重金属浸出水平的风险，特别是在面对浸沥场景更替时。垃圾渗滤液或饱和CO₂水浸沥的早期阶段和模拟酸雨浸沥的更替都是增加重金属浸出水平的不利因素。累积浸沥时间的延长使多数重金属的浸出水平再次升高，但浸出规律变化因飞灰类型而异。Pb和Cd是两种超标频率较高的重金属。以水泥固化飞灰为例，在垃圾渗滤液侵入、碳酸化作用更替为酸雨侵蚀场景后，Pb（标准限值为0.25mg/L）和Cd（标准限值为0.15mg/L）的最大浸出浓度分别高达0.36mg/L和0.28mg/L。可见，根据飞灰的实际处置场景评估其重金属的浸出水平对于表征填埋场飞灰的实际处置风险具有重要的现实意义。

关键词: 垃圾焚烧飞灰, 重金属浸出, 垃圾渗滤液, 碳酸化作用, 酸雨侵蚀, 多级浸提程序