Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE RM–BFS geopolymers effectively stabilize composite heavy metal-contaminated soils. Increasing the concentration of a single heavy metal raises leachability but hardly induces soil acidification, whereas the coexistence of various metal ions substantially accelerates soil acidification. Higher precursor dosages significantly enhance UCS and markedly reduce the toxic leaching concentrations. Mechanistic insights reveal chemical transformation, physical encapsulation, and chemical precipitation.

ABSTRACT
To mitigate composite heavy metal pollution and realize the valorization of industrial solid waste, a geopolymer synthesized from red mud and blast furnace slag was employed for the solidification of composite heavy metals. The solidification effectiveness of the geopolymer under varying conditions of the precursor dosages, heavy metal concentration levels, and curing was evaluated using unconfined compressive strength tests, toxicity leaching assessments, and pH analysis. The stabilization mechanisms were elucidated by means of BCR, SEM-EDS, XRD, TG-DTG, and FTIR. The results show that higher precursor dosages significantly enhance UCS and markedly reduce the toxic leaching concentrations. Higher heavy metal concentrations decrease UCS and impair the advantages of long-term curing, despite the fact that prolonged curing partially offsets the increase in leaching concentrations. Elevated concentration of a single heavy metal increases leachability yet hardly triggers soil acidification; diverse ions substantially accelerate acidification. Mechanistic analysis indicates that increasing precursor dosage facilitates heavy metals conversion from labile into stable fractions. Microstructural analysis further verifies that hydration products can adsorb and encapsulate metal ions. Meanwhile, OH− and CO3
2− released from precursors induce the formation of precipitates. This work provides critical insights for optimizing geopolymer formulations to achieve efficient, regulatory-compliant remediation of composite heavy metal-contaminated soils.