Adsorption and Desorption of Phosphate onto Surface Sediments from the Yellow River

Adsorption isotherms and adsorption-desorption kinetics of phosphate(P) onto surface sediments of Baotou and Lamawan sections taken from the Upper and Middle Reaches of the Yellow River were determined,and the impact of various factors on P adsorption was also researched.The results indicated that:(1) The P adsorption on different sediments was related not only to species and grain size of sediments,but to concentrations of sediments and beginning phosphate.Both the P adsorption and desorption process on different sediments mainly occurred within 0~8 h,the maximum adsorption and desorption rates occurred within 0~0.5 h,and then the interface interaction would gradually tend to the dynamic equilibrium;(2) P adsorption isotherms on different sediments fitted well with linear equation and isotherm curves crossed concentration axis,showing the occurrence of the negative adsorption.Based on the linear equation,P adsorption-desorption equilibrium mass concentrations(EPC0 values) on different sediments were obtained,which was 0.011 mg/L and 0.022 mg/L,respectively.These EPC0 values were higher than the P concentration in the overlying water,indicating a trend of releasing P from sediments.