Desorption Kinetics and Difference in Removal Enhancement of PAHs in Aged Soils by Tween 80

The desorption process and desorption rate is an important factor that influence the bioavailability and remediation efficiency. PAH contaminated soils from former Beijing coking plant are remediated by Tween 80 solution. Desorption kinetics and efficiency enhancement of PAHs by Tween 80 are investigated in this paper. Results show that (1) For the relatively water-insoluble PAHs with high molecular weight, the time needed for desorption equilibrium is longer than that of relatively water-soluble PAHs with low molecular weight. The desorption kinetics of PAHs fit better to Elovich equation than to the first-order kinetics equation, especially for the PAHs with 4-6 ring numbers, which means that the desorption of PAHs from soil is an heterogeneous diffusion process; (2) Due to the severe sorption loss of Tween 80, and the difficulty in removing PAHs from aged contaminated soils, Tween 80 solution at a concentration of 5000 mg/L can only remove the PAHs with efficiencies of 11.31-18.23%. The desorption enhancement of PAHs is 7.62-14.04%, with the values of 4-6 ring number bigger than that of 2-3 ring number, which indicated that surfactant is more favorable to the desorption of PAHs with more ring numbers and thus more hydrophobic.