Study on the sorption behaviors of Tween-80 on marine sediments

Batch experiment was carried out to study the sorption behavior of polysorbate 80 (Tween-80) on marine sediments collected from three different sites in Bohai Sea, China. The sorption of Tween-80 reached equilibrium within 3 h and the sorption kinetic curve could be divided into two sections: the rapid sorption part and the slow sorption part. The initial sorption rate increased with the organic carbon (OC) content of the sediment. For the sediments treated by HCl and H2O, sorption behaviors of Tween-80 fit the linear model very well (R2: 0.9516–0.9862) at 298 K. The sorption occurred primarily due to partition function of the hydrophobic chains of Tween-80 into the organic carbon of the sediments. Sorption of Tween-80 on H2O2-treated sediments followed the Freundlich model (R2: 0.9565–0.9732), which indicated that the surface function of clay minerals and other inorganic solids in the sediment played a key role. Moreover, the dependence of sorption on salinity and temperature was examined and the thermodynamic parameters were evaluated. It was found that the sorption was favorably influenced by the increasing salinity and decreasing temperature of seawater. The changes of Gibbs free energy (ΔGθ = −15.33 ∼ −17.54 kJ mol−1), enthalpy (ΔHθ = −62.23 kJ mol−1) and entropy (ΔSθ = −151.68 J mol−1 K−1) of the sorption were also determined. The negative ΔGθ and ΔHθ values indicated that the sorption process was spontaneous and exothermic. The negative ΔSθ value suggested that the degree of freedom decreased during the sorption process.