Adsorption and Release Behaviors of Phosphate on Sediments in the Upper and Middle Reaches of Yellow River

A total of 8 sediment samples collected from the upper and middle reaches of the Yellow River were studied for adsorption and release kinetics,adsorption isotherms,adsorption-desorption equilibrium phosphate concentration,differences among the sediments in adsorption and influences of P forms on P adsorption characteristics in sediments.Results show that both the processes of adsorption and release of phosphate in the sediments completed mainly within the initial 8 h,and the highest adsorption and desorption rates were observed within the first 0.5 h and the reactions basically reached equilibrium in 24 h;P adsorption isotherms accorded with both the linear equation and the Freundlich equation as well as the Langmuir equation(4).Calculation using the Langmuir equation(4),indicate that the maximum P adsorption capacity of the sediments varied from 0.095 to 0.272 mg·g^-1,showing significant positive correlations of the capacity with total P(TP),exchangeable loosely-bound phosphorus(Ex-P),and organic matter in the sediments;the sediments have a P adsorption-desorption equilibrium point during adsorbing P in the overlying water,and its corresponding adsorption-desorption equilibrium mass concentration was in the range of 0.009-0.031 mg·L^-1,higher than the P concentration in the overlying water,indicating a trend of sediments releasing P to the overlying water.