Codisposal of landfill leachate concentrate and antimony mine soils using a one-part geopolymer system for cationic and anionic heavy metals immobilization

Abstract

Geopolymer solidification/stabilization technology has developed rapidly in the remediation field of heavy metal-contaminated soil. However, geopolymers exhibit low anionic heavy metal immobilization efficiency due to their electronegativity and alkali activation characteristics. This study constructed a one-part blast furnace slag-based geopolymer system using landfill leachate concentrate (LLC) as chlorine and humic acid sources and achieved the solidification/stabilization of cations (Cd, Cu, Hg, and Pb) and anions (Sb and As) in the antimony mine soils (AMS). The LLC addition increased the Sb and As fixation rates from 92%∼94% and 82∼86%, respectively, to over 99%, reducing the leaching concentration of all heavy metal ions to the ppb level. LLC improved the chemical stability and physical encapsulation of Sb/As in three ways: inducing a Friedel’s salt (FS) formation, enhancing humic acid complexation/chelation, and promoting geopolymerization. Wet curing was more conducive to FS formation in the geopolymer than dry curing and increased the 28-day compressive strength by 38.5%. Due to the SiO2 skeleton support effect in AMS, a 30 wt% AMS addition was beneficial for geopolymer strength development. Our study provided a harmless method for the codisposal of LLC and AMS and improved the efficiency of geopolymer fixation of complex heavy metal cations and anions.