Sorption kinetics, isotherms and mechanisms of PFOS on soils with different physicochemical properties

Perfluorooctane sulfonate (PFOS), an emerging contaminant, is environmentally persistent, bioaccumulative and toxic to human health and ecosystems. It has been widely detected in groundwater, surface water, soil and sediment. So far, very few research has reported on the PFOS sorption behaviors onto soils, one of the primary processes that influence its fate and transport in the subsurface. In this study, the sorption and desorption of PFOS onto six soils with different physicochemical properties were investigated. Kinetic and equilibrium studies of PFOS sorption onto six soils were carried out in batch experiment. The sorption kinetics of PFOS on the six soils demonstrated that PFOS sorption reached equilibrium within 48h, and the well-fitted pseudo-second-order kinetic model to experimental data suggested that chemisorption was involved in PFOS sorption on soils. The intraparticle diffusion model results indicated that both film diffusion and intraparticle diffusion were the rate-limiting steps for five of the six soil samples, while the intraparticle diffusion was the only limiting step in the PFOS sorption on the sixth soil. PFOS sorption isotherms can be described by the Freundlich model well for all six soils (R²=0.979-0.999). The correlation analysis between K_F of PFOS and the physicochemical properties of the soils showed that a positive correlation between K_F and Al₂O₃, SOC and Fe₂O₃. The FTIR data demonstrated hydrophobic interaction, ion exchange, surface complexing and hydrogen bonding might all play a role in the PFOS sorption onto soil samples. PFOS sorption onto soil minerals, especially iron oxide minerals, needs to be further explored in future.