Solidification/stabilization of landfill leachate concentrate contaminants using solid alkali-activated geopolymers with a high liquid solid ratio and fixing rate

Landfill leachate concentrate (LLC) is a highly toxic wastewater that contains many refractory contaminants. One of the technical and economic treatment methods is solidification/stabilization (S/S), where the contaminants of LLC can be sealed in one step to achieve zero wastewater discharge. This study presents the S/S of LLC contaminants using solid alkali-activated geopolymers prepared from blast furnace slag (BFS) and powdery sodium silicate. The stability of the formed geopolymer was studied through unconfined compressive strength (UCS) and leaching tests. The strongest UCS was obtained when the modulus of the activator was 1.16 with a high liquid/solid ratio of 0.64. BFS-based geopolymers presented excellent LLC S/S efficiency. The S/S rates of TOC, CODCr, NH3–N, Cl−, and SO42− were 81%, 89%, 97%, 97%, and 78%, respectively. The S/S rates of heavy metals, i.e., Cd and Pb, were all more than 99%. The results of microstructure characterization showed that the S/S mechanism of LLC pollutants was the dual effect of physical closure and chemical stability. Cl− and SO42− were respectively stabilized in the crystal lattice by Friedel's salt and calcium sulfate, respectively, while organic matter and NH3–N were physically encapsulated in the dense structure of the geopolymer. Overall, BFS based geopolymers demonstrated high treatment capacity and excellent S/S efficiency, and have a potential application prospects in LLC treatment. [Display omitted] •Landfill leachate concentrate contaminants can be immobilized in geopolymers.•Landfill leachate concentrate promotes the geological polymerization of geopolymers.•The toxicity of landfill leachate concentrate is reduced after geopolymerization.•The critical method for stabilizing Cl− is the formation of Friedel's salt.