Carbonation-induced reconstruction of the gel/interfacial framework and its impact on Pb 2+ /Cd 2+ immobilization in a chelator-modified GGBFS–MSWI-FA–SS alkali-activated binder

Municipal solid waste incineration fly ash (MSWI-FA)-containing alkali-activated binders are promising matrices for waste valorization and hazardous-metal stabilization, but their long-term reliability may be compromised by carbonation. This study investigated a ternary GGBFS–MSWI-FA–SS alkali-activated binder to clarify how precursor composition and carbonation affect gel/interfacial structure and Pb2+/Cd2+ immobilization. Tributyl phosphate (TBP) and sixthio guanidine acid (SGA) were introduced to evaluate chelation-assisted stabilization. Higher GGBFS contents favored a more continuous C-(A)-S-H-dominated matrix, whereas increasing SS content produced a more heterogeneous structure. Carbonation was associated with C–(A)–S–H decalcification and structural evolution, together with the development of a compositionally distinct interfacial rim around GGBFS particles. These changes may influence Pb2+/Cd2+ retention. TBP and SGA reduced heavy-metal leaching in several systems, suggesting a possible chelation-assisted stabilization contribution. Overall, the results support a proposed carbonation–chelation interaction framework linking gel/interfacial evolution with heavy-metal immobilization behavior.