[Sorption-desorption behavior of Cd2 + and Pb2+ in rhizosphere and bulk soil]

Sorption-desorption behavior of Cd2+ and Pb2+ in the rhizosphere and bulk soil of wheat was studied by the batch method. The results indicated that the sorption capacity of rhizosphere soil to Cd2+ and Pb2+ was higher than that of bulk soil. Isothermal curves of Cd2+ sorption by rhizosphere and bulk soil fitted Freundlich equation well. Isothermal sorption process of Pb2+ could be well described by Langmuir equation and Freundlich equation. Two-constant equation was the best model to describe the sorption kinetics of Cd2+ and Pb2+ followed by Elovich equation, and the worst model was first-order dynamics equation. There was sorption-desorption hysteresis of Cd2+ and Pb2+. The desorptive rates of Cd2+ and Pb2+ in rhizosphere soil was lower than that of bulk soil. The relationship between desorptive quantity of Cd2+ and Pb2+ in two soils and the initial sorptive quantity coincided with quadratic equation. The desorptive rates of Cd2+ and Pb2+ in two soils increased with the higher initial concentrations of Cd2+ and Pb2+ in the treatments, and decreased with the increasing desorptive time. Two-constant equation was the optimal model to describe the desorptive kinetics of Cd2+ and Pb2+ in the two soils, and followed by Elovich equation, while the first-order dynamics equation fitted not well.