Solidification/stabilization of composite heavy metals using red mud-blast furnace slag based geopolymer

Geopolymers derived from solid waste can effectively remediate heavy metal polluted sites, achieving the ideal fusion of solid waste utilization and environmental remediation. Red mud and blast furnace slag were used to develop a geopolymer for the remediation of composite heavy metal-contaminated soils, focusing on Cd(II)-, Pb(II)-, Cu(II)-, and Zn(II)-contaminated soils. Uniaxial compressive strength tests, toxicity characteristic leaching procedures, pH change characteristics, and pH gradient tests were performed on the solidified/stabilized soil. The results showed that increasing the red mud-blast furnace slag content and curing age significantly enhanced the unconfined compressive strength. Furthermore, it suppressed the leaching of heavy metals in the solidified/stabilized soil. Notably, the treatment effectiveness of Cu(II) and Zn(II) was superior to that of Cd(II) and Pb(II). The leaching concentrations of Cd(II), Pb(II), and Zn(II) decreased in acidic to weakly alkaline environments but increased in strongly alkaline environments. However, the impact of curing age and initial heavy metal content on the pH of the solidified/stabilized soil was the opposite. In conclusion, red mud and blast furnace slag exhibited superior solidification/stabilization effects compared to cement. As environmental protection awareness grows and technology continues to evolve, geopolymers derived from red mud and blast furnace slag will play a greater role in pollution control and remediation, showcasing broad application prospects.