Characteristics of adsorption and desorption of phosphate by sediments in the Suzhou River,East China.

The characteristics of adsorption and desorption of phosphate by sediments in the Suzhou River, East China are investigated. These include the effect of pH of overlying water on adsorption, adsorption and desorption kinetics, and isothermal adsorption. The results are as follows: (1) With an increase of the pH value of the overlying water, the adsorption capacity of phosphate in sediment decreases. (2) The kinetics of phosphate adsorption and desorption exhibit a complex behaviour, including a fast and a slow adsorption and desorption process. The fast phosphate adsorption process lasts 2 hours, then the slow process lasts about 6 hours before reaching the adsorption equilibrium. The fast phosphate desorption process occurs within 1.5 hours, then the slow phosphate desorption process takes place, and the desorption equilibrium reaches a relatively stable concentration of PO4-P. (3) The sediment has a strong phosphate adsorption ability. With an increase of PO4-P concentration, the PO4-P adsorption capacity on sediment increases. The higher the proportion of water to sediment, the lower the phosphate absorption capacity on sediment would be.