Lead-chlorine synergistic immobilization mechanism in municipal solid waste incineration fly ash (MSWIFA)-based magnesium potassium phosphate cement
2023
Cao, Xing | Zhang, Qiushi | Yang, Weichen | Fang, Lin | Liu, Shiwei | Ma, Rui | Guo, Kai | Ma, Ning
The high chlorine (Cl) and lead (Pb) content characteristics of municipal solid waste incineration fly ash (MSWIFA) pose environmental risks and hinder resource utilization. Herein, an MSWIFA-based magnesium potassium phosphate cement (MKPC) preparation strategy was developed, which allowed the MSWIFA recycling and the Pb-Cl synergistic immobilization without the washing pretreatment. The compressive strength of the resulting 10 wt% MSWIFA-based MKPC was 28.44 MPa, with over 99.2% reduction in leaching toxicity of Pb and Cl. The high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and X-ray absorption spectroscopy (XAS) analyzes showed that Pb, phosphate and Cl⁻ formed Pb₅(PO₄)₃Cl in MKPC. In-situ X-ray diffraction (XRD) tests showed that Pb₃(PO₄)₂ was gradually transformed to Pb₅(PO₄)₃Cl through a dissolution-precipitation process. The formation energy, Bader charge, charge density difference and density of states (DOS) of Pb₅(PO₄)₃Cl were analyzed by first-principles calculations, confirming that Pb₅(PO₄)₃Cl was more thermodynamically stable than Pb₃(PO₄)₂ and PbCl₂ and that electronic interactions between Pb-p, O-p, P-p and Cl-p orbits were the origin of Pb-Cl synergistic immobilization. This work provides a new strategy for the resource utilization of MSWIFA without washing pretreatment, and provides an in-depth understanding of the Pb-Cl synergistic immobilization mechanism.
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