The adsorption of phosphate on different trophic lake sediments

The difference of phosphate adsorption on the different trophic lake sediments was investigated, including adsorption isotherms, adsorption kinetics, effect of temperature on adsorption, effect of pH on adsorption, thermodynamic parameters of adsorption and adsorption–desorption equilibrium concentration. Three isotherm models were used to characterize the adsorption behavior. The results indicate that the Linear model was the best to describe the adsorption behavior of phosphate on the heavily contaminated sediment with high phosphorus concentration, while for the slightly contaminated sediments the Freundlich model was the best. The adsorption kinetic data were fitted with three kinetic models, while the power function equation was the best kinetic equation, and there was no obvious difference between the different trophic sediments. The phosphate adsorption–desorption equilibrium concentration had a positive correlation with the nutrient level. The slightly contaminated sediment was the sink for phosphate. However, the heavily eutrophic sediment was the source for phosphate, and had the trend to release phosphate to the overlying water. The pH values were different for the various trophic sediments when the phosphate adsorption rates were in maximum and minimum, which may be attributed to the phosphate release. The adsorption process of phosphate on sediments was the endothermic reaction. The phosphate adsorption ability of the heavily contaminated sediments was stronger, and was less affected by temperature than that of the slightly contaminated sediments.