Phosphate adsorption characteristics of tidal flat surface sediments and its environmental effect from the Yangtze estuary

Adsorption of phosphate (PO₄-P) on sediments taken from the Yangtze estuarine and coastal tidal flats were determined in laboratory. The results indicate that the process of phosphorus adsorption onto sediments mainly occurs within 0-10 h, and then attends to a dynamic equilibrium. Maximum adsorption rates occurred within 0-0.5 h, ranging from 10.40 to 56.40 mg/kgh. The adsorption rates were obviously influenced by the concentration levels of fine particles. Adsorption isotherm curves were fitted to modified Langmuir's equation. Adsorption capacities varied from 26.32 to 204.08 mg/kg, showing good affinities for Fe³⁺ and total organic carbon (TOC) concentrations. The adsorption efficiency of phosphate on sediments ranged from 21.55 to 248.30 L/kg, showing close correlation with TOC concentrations. Furthermore, the correlation between environmental factors and phosphate adsorption was presented in this experiment, indicating that temperature, pH and salinity have obvious effects on phosphate adsorption.