天然土壤中菲的解吸行为特征研究

Desorption Behavior Characteristics of Phenanthrene in Natural Soils

选取天然土壤样品,以菲作为代表性污染物,利用批量吸附-解吸实验考察不同初始浓度、不同吸附时间条件下菲解吸行为的滞后性特征.实验数据采用Freundlich方程式拟合,并由基于热力学的TII指数表征.结果表明,天然土壤吸持菲的比例随其初始浓度的增加而减少.在土壤多次解吸过程中,每次释放菲的比例随其初始浓度的升高而增加,随解吸次数的增加而减少.吸附过程的拟合指数n大于解吸过程的对应值,并随初始固相浓度的加大而增加.天然土壤吸附-解吸过程的滞后性特征表现为初始固相浓度越高,TII值越接近0,滞后性越弱;反之,则TII值越接近1,滞后性越强.另外,吸附平衡时间30 d对应的n值小于5 d的,而两者的TII值随初始浓度增高则呈现降低趋势.就同一浓度而言,吸附平衡30 d所对应的TII值高于5 d的.

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 soll solids and the TII values closer to 0, and vlce-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.