Solidification/Stabilization of Composite Heavy Metal‐Contaminated Soil by Red Mud‐Slag‐Based Geopolymer

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 CO ₃ 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.