Adsorption characteristics of loess-modified natural silt towards Pb(II): equilibrium and kinetic tests

Vertical wall is one of the barriers used to prevent contamination of subsurface soil and groundwater. Natural soil is the main resource of the barrier materials. Loess is added to a natural silt to enhance its adsorption capability. Lead is chosen to represent the contaminants. Equilibrium and kinetic adsorption tests are carried out to investigate the effects of loess on the adsorption characteristics of the mixed soils. The effects of loess proportion, initial solute pH value, shaking time and initial solute on the adsorption capability of mixed soils are considered. The maximum adsorption capacity of the mixed soils increases linearly with the increase of the amount of the loess. The adsorption capacity of the mixed soils amended with 20% loess can be two times greater than that of the natural soil. Compared with that of the natural silt, the adsorption time of Pb(Ⅱ) can also be reduced for the loess-modified soil. Using the electron spectroscope and X-ray diffraction, it is illustrated that the high adsorption capability of loess is due to the surface precipitation of calcite with lead. The adsorption of lead on silty soil is ascribed to cation exchanging process. It is indicated that loess can be used as an additive to increase the adsorption ability of the natural soil and then to reduce the risk to the environment pollution regarding heavy metals due to high content of calcite and high adsorption capability of lead.