Study of dynamic sorption and desorption of polycyclic aromatic hydrocarbons in silty-clay soil.

This study reported a well controlled laboratory experiment of high concentration PAHs solute, containing fluorene, phenanthrene, fluoranthene and pyrene, through a nearly homogeneous soil column to reveal sorption and desorption behavior of these four PAHs in soil. The duration of the experiment was 64 days and the flow rate through the soil column was a constant which equals to 2000 mL d(-1). The result showed that the mechanism of isothermal sorption and desorption of fluorene can be perfectly described by the Langmuir model, and the correlation coefficients were greater than 0.997. The first-order Lagergren and the Bangham equation can precisely describe the rate of sorption of PAHs, while the rate of desorption can be represented by the second-order kinetics model. The results of the desorption experiment indicated that the desorption hysteresis of fluorene was evident. Few phenanthrene, fluoranthene and pyrene were desorpted to the aqueous phase for the chemical bond with the clay minerals. The most important process determining the behavior of PAHs in soils and their availability to further transformations was the sorption to soil solids with further sequestration and desorption to the aqueous phase.