| Batch sorption and desorption experiments were employed to investigate the desorption hysteresis of phenanthrene as a model compound at different initial concentrations and different sorption time using natural soils. The experimental data were fitted by the Freundlich empirical isotherms and described by a thermodynamic index TII ranged between 0 and 1. The results demonstrated that, the higher the initial concentration of phenanthrene, the greater the retention rate of the soil samples. The releasing rate of phenanthrene in each step of the multi-step desorption procedure increased with the initial concentration, and decreased with the desorption steps. The fitted n values in the Freundlich equations corresponding to the sorption stage were larger than those corresponding to the subsequent desorption stage, and rose with the increase in the initial soil particle concentration. The sorption-desorption hysteresis reduced with the higher initial concentration of soil solids and the TII values closer to 0, and vice-versa. Moreover, the n value corresponding to the sorption balance time of 30 days was less than that of 5 days, while TII values for both 5 days and 30 days showed a similar decreasing trend with the increase of initial concentrations. As to the same concentration, the TII value for 30 days was higher than that of 5 days. |
