RESUMEN
Vertically tiered soil profiles, comprising miscellaneous fill (S1), plain fill (S2), silty clay (S3), and completely weathered slate (S4), were collected from a zinc smelter site in Zhuzhou City, Hunan Province, and their Cd and Pb adsorption characteristics were examined. Static batch experiments were conducted with different initial Cd and Pb solution concentrations, at temperatures of 288-308 K and pH values of 2-6. The results showed that a pseudo first-order model could be fitted to the kinetics of Cd/Pb adsorption in these soils. The soil profiles had a large retention capacity for Cd and Pb. The Cd and Pb adsorption isotherms for these soils conformed to the Freundlich isotherm, with maximum adsorption at 298 K of 2097-4504 mg ·kg-1 for Cd and 4376-10564 mg ·kg-1 for Pb, based on the Langmuir isotherm. The adsorption capacity of Cd and Pb increased with an increase in initial pH and temperature. The Cd and Pb adsorption process were a spontaneous physical and chemical process, and the soil profiles were ranked by their Cd and Pb adsorption capacities in the following order:completely weathered slate (S4)>miscellaneous fill (S1)>silty clay (S3)>plain fill (S2). The variation in adsorption capacities resulted from the differences in physical and chemical properties of the soil, mainly Fe/Al content and cation exchange capacity. Fourier transform infrared and SEM-EDS analysis showed that the main adsorption mechanism is the exchange of Cd and Pb with Fe/Al, while -OH/Cï¼O sites in soils were the predominant adsorption sites for Cd and Pb. In the study area, exogenous Cd and Pb discharged by smelting activity accumulated predominantly in surface soil, and their concentration gradually decreased with depth. These results provide a scientific basis for the prevention and control of heavy metal pollution in the soil and groundwater of a smelting site.
