Experimental Study of Strength of Leachate Sludge Solidified with Sulfoaluminate Cement and Municipal Solid Waste Incineration Fly Ash

Landfill leachate sludge produced by the immersion combustion process on the leachate has extremely high soluble salt content. The leachate sludge is solidified by sulphoaluminate cement (SAC) combined with municipal solid waste incineration fly ash (MFA). The unconfined compressive strength (UCS) test, microscopic observation test, and leaching toxicity test are carried out on the solidified sample. The UCS of the cement-solidified samples with different curing agents is tested, and the relative solidification mechanism is analyzed. The results show that the 28d UCS of the solidified samples with cement content increases with an increase in cement content and a decrease in water-cement ratio. The solidification effect of MFA on the SAC solidified sludge has an optimal content of 5% (20% and 30% of cement content) and 10% (40% of cement content), respectively. The three-dimensional interlocking structure formed by the hydration products of ettringite and C─ S─ H gels is the main reason for the enhancement of the UCS of the solidified samples blended with MFA. The SAC and MFA binders can effectively immobilize heavy metals in the solidified leachate sludge. The leaching concentration of heavy metals and PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) in the solidified sample with 30% SAC and 5%–15% MFA is much lower than that of the raw MFA and the limit value.