Stabilization of Cd and Pb in the contaminated soils by applying modified fly ash

This study investigated the stabilization of heavy metals by adding modified fly ash (FA) to contaminated soils, and two similar materials, NaOH-zeolite (ZE) and natural zeolite (ZO) were introduced into the soils for comparison. Column leaching tests were conducted to analyze the difference of stabilization effects between the three materials. Leaching columns were run for 6 months, and a considerable stabilization of heavy metals in the soils was observed. The concentration of cadmium (Cd) and lead (Pb) in the amended soil substantially decreased (p <0.05). The results indicated that after 11 weeks of column leaching, Cd and Pb concentrations in the soil leachate decreased to below the detection limit due to amendment stabilization. Among the three amendments, the ZE amendment showed the optimum capacity for heavy metal immobilisation in the soils. In addition, after 6 months of leaching, Pb and Cd concentrations in the soils with the three different amendments decreased to various degrees. The amendments of modified FA and ZE were better than those of natural ZO. Coal FA, after modification, is a useful amendment for the remediation of heavy metals in the contaminated soil.