Effect of temperature on the sorption and desorption of perfluorooctane sulfonate on humic acid

Sorption and desorption of perfluorooctane sulfonate (PFOS) on humic acid at different temperatures were studied. It was found that the sorption process could be modeled with power kinetic equation very well, suggesting that diffusion predominated the sorption of PFOS on the humic acid. The sorption capacity was doubled when the temperature increased from 5 to 35℃, and thermodynamics parameters △G~0 was calculated to be -7.11 to -5.04 kJ/mol, △H~0 was 14.2 kJ/mol, and △S~0 was 69.5 J/(mol·K), indicating that the sorption was a spontaneous, endothermic, and entropy driven process. Desorption hysteresis occurred at all studied temperatures which suggested that humic acid may be an important sink of PFOS in the environment.