[Sorption and desorption of phenanthrene on sediments].

Batch experiments were employed to investigate the influences of salinity on the sorption of phenanthrene. Influences of initial phenanthrene concentration, sediment properties and salinity on desorption of phenanthrene were also studied and the mechanism for desorption hysteresis was deeply discussed. Salinity enhanced the sorption of phenanthrene on sediments, and the enhancement extent was related to sediment organic matter (SOM). A salting constant of 0.125 L x mol(-1) was derived from the PHE solubility in fresh water and salt water, and in the presence of sediment, salting constant was enhanced to 0.299 L x mol(-1). Desorption of phenanthrene all exhibited hysteresis to some extents and desorption hysteresis were described by a thermodynamic index TII. With the initial phenanthrene concentration increasing from 0.5 mg x L(-1) to 2.5 mg x L(-1), the value of TII first decreased from 0.80 to 0.38 and then increased to 0.55, suggesting the desorption hysteresis of phenanthrene first decreased and then increased. Sediment treated by NaOH showed a reduced sequestration ability on phenanthrene than the original sediment did, with the value of TII decreased from 0.55 to 0.33. Desorption of phenanthrene in fresh water was found for the first time to have a greater hysteresis than in salt water, indicated by the greater TII value of 0.55 in fresh water than that of 0.42 in salt water. Desorption hysteresis could be explained by the sorption of phenanthrene to sorption sites of different energies and sequestration inside the micropores of the sediments.