The Research Of Modified Clay Minerals In The Application Of In Situ Coagulation And Sedimentation Technology

Eutrophication is one of the major pollution of freshwater and coastal waters. Phosphorus is the main limiting factor to eutrophication. Since exogenous phosphorus has been controlled effectively, more attention should be put on the research of restoration method of sediment phosphorus. La-modified bentonite(Phoslock) is a relatively new phosphorus deactivation/sedimentation drug. Phosphorus could be effectively absorbed by the active ingredient lanthanide and settle to the sediment, forming a inert cover. Phoslock have proved to be ideal due to its high P adsorption capability, low solubility, nontoxicity, and environment-friendly property, and made its mark on eutrophic water purification during the applications in Australia, England, Netherland, China, Mexico, South Africa and so on.Like other adsorbents, environmental factors would cause a significant effect on its performance on P adsorption. Thus, batch experiments were performed in this work to investigate the influence of various experimental factors, e.g. p H, coexisting anions(Cl- and HCO3-) and three typical LMWOAs(formic acid, acetic acid, lactic acid) on the performance of Phoslock by the single-factor method. We analyzed its main mechanisms of the adsorption of phosphorus by studying the change of the phosphorus adsorption amount per unit under different p H conditions. The experiment included three parts. The first one was the preparation and characterization of Phoslock. The second was dynamic experiment with shaking table. The third was stastic test, using a self-made reator to stimulate the reation in actual waterbody. The technoly purification-soaking with acid solution-soaking with La3+ solution-microwave heating. The XRD patterns of Phoslock showed a success in modification. The adsorption isotherm and kinetic curve results suggest that a monolayer adsorption and a high absorption rate, which enables the instant removal of phosphorus. A 7-step sequential extraction procedure was used to analyze sediment P fraction changes. The results showed that optimum p H value for the removal of P was between 5.0 and 8.0. Excess H+ or OH- would weaken the performance of Phoslock. The performance of Phoslock was significantly affected in the presence of HCO3- and all three LMWOAs. Phoslock could effectively immobilize P to the sediment without the presence of any experimental factors. However, the presence of HCO3- and all three LMWOAs inhibited P adsorption onto Phoslock and activated relatively stable P fractions(Ca-P + De-P) into exchangeable P fraction.These findings would be of great importance when Phoslock was supposed to restore a specific water body with various environmental factors. Appropriate dosage or united restoration method should be considered to achieve a better result.