Utilization of cement and other additives for solidification/stabilization of soil contaminated simultaneously with Cd2+ and Pb2+ ions

Various additives, including cement, quicklime, fly ash, montmorillonite, sepiolite and their proportions were employed to stabilize/solidify artificially prepared soils contaminated simultaneously with two kinds of ions such as Cd²⁺ and Pb²⁺. The unconfined compressive strength of the stabilized soils was measured to estimate the possibility of recycling. The efficiency of Cd²⁺ and Pb²⁺ immobilization in contaminated soils was also evaluated using the US EPA TCLP toxicity test. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to elucidate the mechanisms responsible for the immobilization of heavy metals. The experimental results demonstrate that in terms of soils simultaneously polluted with Cd²⁺ and Pb²⁺ ions, the curing effect of fly ash is better than that of montmorillonite and sepiolite. When Cd²⁺ and Pb²⁺ coexist in soil specimens, the curing is more difficult than for Cd2+ or Pb2+ alone, which is antagonistic mechanism. Also, the leaching concentration of Cd²⁺ and Pb²⁺ gradually decreases upon increasing pH when pH < 8. For pH ≥ 8, the leaching concentration of Cd²⁺ and Pb²⁺ reached a minimum. Besides, the results of XRD and SEM are in agreement with those of the strength and leaching tests.