Utilization of cement and other additives for solidification/stabilization of soil contaminated by dual ionic Cd2+ and Pb2+

CONTAMINATED SIMULATANEOUSLY WITH Cd 2+ and Pb 2+ 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 Cd 2+ and Pb 2+ .The unconfined compressive strength of the stabilized soils was measured to estimate the possibility of recycling.The efficiency of Cd 2+ and Pb 2+ 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 Cd 2+ and Pb 2+ ions, the curing effect of fly ash is better than that of montmorillonite and sepiolite.When Cd 2+ and Pb 2+ coexist in soil specimens, the curing is more difficult than for Cd 2+ or Pb 2+ alone, which is antagonistic mechanism.Also, the leaching concentration of Cd 2+ and Pb 2+ gradually decreases upon increasing pH when pH < 8.For pH ≥ 8, the leaching concentration of Cd 2+ and Pb 2+ reached a minimum.Besides, the results of XRD and SEM are in agreement with those of the strength and leaching tests.