Adsorption of phosphorus on sediments from the Three-Gorges Reservoir (China) and the relation with sediment compositions

The adsorption of phosphorus (P) on four sediment samples (CunTan, XiaoJiang, DaNing and XiangXi) from the Three-Gorges Reservoir on the Yangtze River in China was studied systematically in batch experiments. A sequential chemical extraction experiment was conducted to clarify the effect of sediment composition on P adsorption. The results showed that P adsorption on four sediment samples mainly occurred within 6 h. P adsorption kinetics can be satisfactorily fitted by both power function and simple Elovich model. A modified Langmuir model may describe well the P adsorption on all the samples in our study. Theoretically, the maximum adsorption amount (Qmax) was 0.402 mg-P/g for XiaoJiang sediment, 0.358 mg-P/g for DaNing sediment, 0.165 mg-P/g for CunTan sediment, and 0.15 mg-P/g for XiangXi sediment. The sediment compositions such as organic matter, metal hydroxides, calcium and clay content showed influences on the P adsorption. Wherein, organic matter and metal hydroxides were the main factors affecting the P adsorption. The maximum P adsorption capacity (Qmax) enhanced with the increase of the content of (Fe + Al + Ca). Compared the zero-equilibrium P concentration (EPC0) values obtained by the modified Langmuir models with actual P concentrations in water, all the sediments studied in this paper except for XiaoJiang showed a trend of releasing P as a source role, which could enhance the risk of eutrophication occurrence in the Three-Gorges Reservoir.