[Sorption-desorption behaviors of Cd2+ and Pb2+ in different pollution load soils]

With batch method, this paper studied the sorption-desorption behaviors of Cd and Pb in soils with heavy, medium, and slight pollution loads. The results showed that the soil with slight pollution load had a high sorption capacity of Cd2+ and Pb2+ than the other two. For the three test soils, the isothermal curve of Cd2+ sorption fitted Freundlich equation better, while that of Pb2+ sorption could be well described with Langmuir equation and Freundlich equation. Two-constant equation was the best model to describe the sorption kinetics of Cd2+ and Pb2+, Elovich equation was the second, and the worst was first-order dynamics equation. The desorption lag of Pb2+ was more obvious than that of Cd2+, and the desorption rates of adsorbed Cd2+ and Pb2+ were higher in the soil with heavy pollution load. The relationships between the desorbed and the initial absorbed amounts of Cd2+ and Pb2+ fitted quadratic equation. In test soils, the desorption rates of Cd2+ and Pb2+ increased with increasing initial concentrations of Cd2+ and Pb2+, but decreased with increasing duration of desorpion.