Study On The Effect Of Concrete Application On The Adsorption And Desorption Characteristics Of Phosphorus In The Sediments

In order to explore the purification performance of natural riparian zone sediments to non-point source pollutant phosphorus,this study is based on the study of the adsorption and desorption performance of natural riparian zone sediments on phosphorus,and analyzes different environmental factors（temperature,time,pH,hydraulic disturbance,overburden）Concentration stress)on phosphorus adsorption and desorption.Through exploring its adsorption kinetics and thermodynamic experiments,we can reveal the adsorption mechanism and law of riparian sediments to phosphate(PO₄^3--P),and explore the prevention and control measures of riparian sediments on phosphorus pollutants.Taking industrial waste concrete slag as the research object,exploring its adsorption law and adsorption mechanism for phosphorus pollutants,adding it as a phosphorus fixation agent to riparian sediments to improve the adsorption and removal of phosphorus pollutants by riparian sediments.And comparatively analyze the adsorption removal effect under different environmental factors,and analyze the analysis of the removal and promotion effect of phosphorus pollutants after concrete is added.It provides a scientific basis for the purification ability of phosphorus pollutants in natural riparian sediments in the northwestern region,and also provides reference value for phosphorus-fixing agent materials.The experimental conclusions are as follows:（1）The adsorption kinetic equilibrium time of the adsorption of PO₄^3--P on natural riparian sediments under different overlying concentration intervals and different hydraulic disturbance conditions is 720 min.Both the Langmuir fitting model and the Fruendlich fitting model can better fit the adsorption thermodynamic adsorption curve of the sediment to PO₄^3--P,and the R²is above 0.95.In comparison,the Langmuir linear fitting is better than the Fruendlich linear Fitting.The enthalpy change value of the adsorption of the sediment on PO₄^3--PΔH^θ>0,the Gibbs free energy changeΔG^θ<0,and the entropy change valueΔS^θ>0,indicating that the sediment absorbs heat in the adsorption process of PO₄^3--P and the enthalpy promotes,Is a spontaneous process.And as the temperature increases,the smaller theΔG^θ,the stronger the spontaneous reaction process.According to the Expassoc model,the time required for the desorption of PO₄^3--P by the sediment is basically the same in the fast adsorption stage and the slow adsorption stage.（2）The influence of different environmental factors:The frequency of disturbance has a positive correlation with the adsorption of phosphorus by sediments.During the desorption process,there is a negative correlation between the disturbance and the amount of desorption;Both temperature and the adsorption and desorption of phosphorus by sediments There is a positive correlation;Under the condition of pH 5,6,7,8,9,10,the removal effect is the best when the interval is 7～8,the sediment dosage is low,and the pH removal rate of phosphorus is the lowest,But the influence of pH is the most obvious.The dosage of sediment increases and the removal rate increases.At this time,the influence of pH begins to gradually decrease.In the desorption stage,the desorption effect is more obvious when the pH is 7～8.The removal rate decreases with the increase of the sediment dosage,and the removal rate decreases with the increase of the concentration of the overlying solution,but the effect of the dosage change is greater than that of the concentration change,and the effect is more obvious under static conditions.（3）The adsorption equilibrium time of concrete to PO₄^3--P is 720 min,and the simulated fitting R²of the pseudo-second-order kinetic equation,EIovich equation and Expassoc equation can reach more than 0.95.This shows that the adsorption process of PO₄^3--P by concrete slag is not a single uniform adsorption process,but includes multiple adsorption processes such as surface adsorption,particle internal diffusion and external liquid film diffusion.It is obtained by fitting the model equation that as the mesh size increases,the particle size of the concrete slag becomes smaller,and the adsorption changes from the stage of multiple adsorption processes to the uniform adsorption process where the surface adsorption is more single.（4）The addition of concrete slag significantly improves the removal rate of the overlying solution PO₄^3--P,and with the increase of the concentration of the overlying solution PO₄^3--P,the improvement effect of the removal rate is more obvious.With the increase of concrete dosage,the removal rate of PO₄^3--P in the solution also increased,basically showing that the higher the concentration of PO₄^3--P in the overlying solution,the faster the increase rate.In the adsorption stage,when the hydraulic disturbance time increases,the adsorption of the sediment on PO₄^3--P increases rapidly.In the desorption stage,the amount of desorption after adding concrete is less than the amount of desorption without adding concrete,and the desorption of phosphoric acid The role of root ion"secondary adsorption"is more obvious.When the disturbance starts,the increasing trend of the removal rate slows down.When the frequency is 100 r/min,the change of the removal rate basically stabilizes,basically maintaining around 89%.The change of pH has a greater impact on its removal rate,but with the increase of concentration,the adsorption effect of pH on phosphorus becomes smaller and smaller.