The study of the effect of pH on phosphate sorption by different trophic lake sediments

This paper studies the effect of pH on phosphate sorption by the sediments of different trophic lakes, including sorption isotherms with different pH values, their effect on sorption rate, their impact on the kinetics of sorption and desorption. The following conclusions are drawn. (1) The phosphate sorption capacity of lake sediment is correlated with pH, but not with its trophic level; that is, pH at 7.0>5.5>9.0. The three isotherms models cannot well describe phosphate sorption by different trophic sediments with different pH, and its applicability seems irregular. (2) The power function equation is one of the best kinetic models, which can provide satisfactory fitting of the kinetic data of phosphate sorption by different trophic sediments, and there is no obvious difference between them. The quick phosphate sorption by the sediment takes place mainly at 0-0.5 h, the pH value has a remarkable effect on the rate of phosphate sorption by the sediment, and sediments in different trophic states tend to have similar trends of change, with pH 5.5>7.0>9.0. (3) The effect of pH on phosphate sorption shows a similar trend for different trophic sediments; namely, as pH increases phosphate sorption rate tends to increases sharply at first and then drop suddenly. After a while it increases slightly, and finally a slight decrease follows as the pH increases. The maximum and minimum of phosphate sorption capacity may be attributed to the rate of phosphate release. (4) Phosphate sorption by lake sediments is not completely reversible and strong bonding occurs between sediment particles and sorbed phosphate. This makes it difficult for the sorbed phosphate to be desorbed from the sediments. The amounts of desorbed phosphate are almost the same in different trophic sediments with different initial pH values; that is, the effect of pH on phosphate desorption is small.