Study On The Efficiency Of Fluorine Removal By Coagulation And Sedimentation Enhanced By Modified Magnetic Mediu

At present,the problem of excessive fluoride concentration exists in many places in China,which poses a great threat to the environment and water safety.The deep defluoridation process commonly used in sewage treatment plants is mostly the coagulation sedimentation method.However,when the concentration of fluoride in the water is high,it is necessary to add an excessive amount of coagulant to achieve the defluoridation effect.This will lead to the risk of excessive coagulant residual concentration in the water body,and will increase costs and sludge production.Compared with traditional coagulation,magnetic media coagulation has the advantages of small footprint,good flocculation effect,fast sedimentation speed,and low sludge moisture content,and is widely used in upgrading and upgrading projects of sewage plants.However,magnetic media The defluoridation effect of coagulation and sedimentation is not ideal,and the effluent still cannot be directly discharged up to the standard.Rare earth metals have the characteristics of high efficiency,selectivity and reusability,and have great application potential in the field of defluoridation of water bodies,which provides new ideas and methods for further improving the defluoridation effect of sewage treatment plant sewage.In this study,lanthanum（La）,cerium（Ce）,and calcium（Ca）were used to modify the magnetic media respectively,and the optimal modified magnetic media was screened out by comparing the fluorine removal effects.Through experiments,the fluoride removal performance of modified magnetic medium enhanced coagulation precipitation technology was studied under different environmental conditions,the optimal reaction conditions were determined,and the enhanced coagulation mechanism of modified magnetic medium for fluoride was discussed.Characterization of the modified magnetic media by using SEM,BET,XRD,and EDS four test methods shows that the prepared lanthanum-loaded magnetic media（La@Magnetite）has a rough core-shell structure.The main elements on the surface are iron（Fe）,oxygen（O）and La,and the mass percentages of the elements are 3.7 wt%,17.8 wt%and 78.5 wt%,respectively,among which La element accounts for a large proportion.Its main components are ferric oxide（Fe₃O₄）,lanthanum hydroxide（La（OH）₃）and lanthanum oxide（La₂O₃）.Compared with the magnetic medium（Magnetite）,the modification greatly increases the specific surface area,pore volume and average pore size,providing more contact area for the adsorption of fluoride,and its defluorination performance is greatly improved,and to a certain extent The addition of coagulants and coagulants is reduced,effectively avoiding secondary pollution that may be caused by chemicals.By investigating the stirring speed,stirring time,dosage of magnetic medium,dosage of polyaluminum chloride（PAC）,dosage of polyacrylamide（PAM）,precipitation time,pH value and coexisting anions,the effects of modified magnetic media on strengthening mixing were studied.Based on the influence of coagulation and sedimentation technology on the performance of fluorine removal,the optimal process parameters for magnetic media coagulation and sedimentation defluorination are determined as follows:the time of the first stage of fast stirring and the second stage of fast stirring is 5 minutes,the time of slow stirring is 4 minutes,and the speed of fast stirring is 250 rpm,the slow stirring speed is 80rpm,the dosage of magnetic medium is 1.2 g/L,the dosage of PAC is 60 mg/L,the dosage of PAM is 1.2 mg/L,and the precipitation time is 30 min.Under this working condition,the fluorine removal efficiency reaches 78.38%,which is 47.25%higher than that of unmodified magnetic media.The fluoride concentration in the effluent can be stably controlled below 1mg/L,meeting the Environmental Quality Standard for Surface Water（GB 3838-2002）Class I standards.In addition,the optimum pH range of raw water for defluoridation by this process is below 9;chlorine ions in water have little effect on its defluoridation effect,while phosphate ions slightly inhibit its defluoridation effect.Finally,under the above optimal operating parameters,through SEM,XRD,EDS,and XPS characterization analysis of La@Magnetite before and after the reaction,it was found that the surface elements of the modified magnetic medium did not change in valence state after the reaction;The order of defluoridation effect from strong to weak is:La（OH）₃>La₂O₃>La;in the flocculation process,the flocs generated by coagulation and precipitation with unmodified magnetic media are larger and more compact,and the sedimentation speed is faster,Higher sludge compression rate.It is speculated that the fluorine removal mechanism of modified magnetic media enhanced coagulation precipitation includes ion exchange and surface adsorption in addition to electric double layer compression,electrical neutralization,bridging,net capture and sweeping,and magnetic interaction between magnetic media.