Polyethyleneimine-derived dithiocarbamates for Pb(II) stabilization in MSWI fly ash leachate: Mechanisms, stability and economic assessment

Municipal solid waste incineration (MSWI) fly ash is hazardous due to its high heavy metal content, particularly Pb, which is highly mobile and poses significant health risks. This study synthesized polyethyleneimine-derived dithiocarbamates (PDTCs) with multiple sulfur-containing functional groups for chelation-based Pb(II) stabilization in MSWI fly ash leachate-related systems. The dissolved Pb(II) removal efficiency exceeded 95% under optimized conditions, indicating effective chelation-based stabilization of mobile Pb(II). X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were employed to characterize the properties of Pb–PDTC precipitates and elucidate the chelation mechanism. The results demonstrate that coordination between -CSS- groups in PDTCs and Pb(II) was the main mechanism for Pb(II) chelation and stabilization. Among the tested PDTCs, PDTC-600 exhibited the best overall Pb(II) stabilization performance due to better accessibility of active -CSS- groups. Under acidic conditions, a lower pH destabilized the chelates. Despite this, PDTCs maintained high dissolved Pb(II) removal efficiency in aqueous batch systems, indicating their potential for chelation-based Pb(II) stabilization in leachate-related systems. This study provides a mild and potentially cost-effective strategy for chelation-based Pb(II) stabilization in MSWI fly ash leachate-related systems. Future research should further verify the performance of PDTCs in real, highly alkaline fly ash leachate and optimize chelator molecular weight to balance Pb(II) stabilization efficiency, precipitate stability, reagent safety, and environmental compatibility.