Phosphorus sorption behavior on sediments in Sanggou Bay related with their compositions by sequential fractionation

The surficial sediment samples collected from the Sanggou Bay in China were treated by a sequential extraction procedure. After removal of calcite, organic matter and Fe/Mn oxides, P adsorption onto the sediment residues was then evaluated through kinetic and thermodynamic characteristics. The sorption kinetic curves could be described by a two-compartment first order equation. The sorption isotherms fit well with the Langmuir and Freundlich equations. The HCl-treated sediments with calcite removed showed a rising fraction of the rapid step and a higher P adsorption potential compared with the un-extracted samples. For the clay minerals and silicate residue after NH₂OH·HCl treatment, the rapid step fraction was dominant, the sorption capability was prohibited, and the process was much more reversible than the original and previously-generated samples. An increase of temperature was favorable for the sorption. Estimation of thermodynamic parameters showed that the process was spontaneous and endothermic, with an increased randomness at the solid-liquid interface. Compared with the un-extracted sediment, the thermodynamic parameters in our case changed slightly after HCl treatment and NH₂OH·HCl treatment.