Mechanistic insights into effect of in-situ microplastics on heavy metals leaching behavior from its dyeing sludge incineration bottom ash

Whether the presence of microplastics (MPs) affects the clean incineration of dyeing sludge (DS), especially focusing on the leaching behavior of Cu and Zn from their incineration bottom ashes (BAs), has become an emerging issue. This study tries to explore the effects of typical polyethylene terephthalate (PET) and polyvinyl chloride (PVC) MPs on leaching behavior of Cu and Zn in BAs, and reveal its inner mechanism. Results showed the presence of MPs raised the leaching rate, namely, both MPs accelerated the leaching of Cu and Zn, which eliminated the risk to human health and to the environment. The regulating mechanism to the Cu and Zn leaching behavior in DS-MPs BAs could be attributed to their amorphous structure. It included: (1) Under low MPs content, Cl and polarity actions derived from MPs destroyed the amorphous structure and promoted Cu and Zn leaching. (2) Under high MPs content, the generation of the amorphous Si/Al structure relieved the Cu and Zn leaching, where Cu and Zn were tightly bonded to [SiO4] or [AlO4] and existed stably in BAs. Despite 30% MPs could relief the release of HMs to a certain extent, the existence of MPs still aggravated the HMs threat of DS BA in actual scene.