Study On Efficient Removal Of Phosphate From Water By Iron-fiber Composite

Phosphorus（P）is an important resource widely used in modern agriculture and chemical industry.Nowadays,with the rapid development of P chemical industry and excessive fertilization,the P in natural water body exceeds the standard,resulting in water eutrophication and other serious resource and environment problems.In addition,P is a non-renewable resource,which is estimated to fully consumed within the next 100-400years due to an annual demand growth rate of 3%.Although P pollution can be reduced by developing new phosphorus fertilizer and improving the efficient use of P fertilizer.However,P from soil can still enter water bodies through runoff,infiltration and drainage from farmland.Therefore,the prevention and treatment of phosphorus pollution in farmland tail water is of great significance to the prevention and control of water environmental pollution and the alleviation of phosphorus resource crisis.In view of the above problems,this paper proposed a new idea of developing new materials for the prevention and control of agricultural non-point source pollution P,and carried out a study on the synthesis and P removal performance of fiber-iron composite materials based on the advantages of fiber carrier and the strong interaction between iron and P.The main research contents and experimental results were as follows:（1）Firstly,hydroxyl oxidize iron（Fe OOH）loaded aminated polyacrylonitrile fiber was synthesized by sol-gel method（PAN_AF-Fe OOH）,which was used for phosphate removal from wastewater.The results showed that PAN_AF-Fe OOH has a wide p H adaptation range（3-9）for phosphate adsorption,and optimal p H is 7.In addition,the adsorption equilibrium can be achieved within 30 min,indicating a rapid adsorption efficiency.The kinetic and isothermal data were better fit the pseudo-second-order kinetic model and Langmuir isothermal model respectively,declaring the process is monomolecular chemisorption.The maximum phosphorus adsorption capacity was estimated to be 9.92 mg P/g.It was worth mentioning that phosphate can still be effectively removed in solutions with Cl^-,NO₃^-,CO₃^2-and other co-anions and can be reused for at least 5 times.（2）The iron ion-loaded aminated polyacrylonitrile fiber（PAN_AF-Fe）was prepared to efficiently purify phosphate from water.The results revealed that PAN_AF-Fe has widely p H adaptability for phosphate adsorption,and the optimum p H is 6.The adsorption process is more consistent with the pseudo-second-order adsorption kinetics model and the equilibrium adsorption can be achieved within 5 min.The maximum adsorption capacity estimated by Langmuir model is 24.14 mg P/g,which is better than many other adsorbents.More importantly,phosphate concentration in actual wastewater decreased to less than0.002 mg P/L,lower than P threshold concentration（0.01 mg P/L）for surface water eutrophication suggested by United States Environmental Protection Agency（USEPA）.The mechanism was studied by XPS,founding the adsorption of phosphate by PAN_AF-Fe mainly relies on chemisorption with supported Fe³⁺on fiber’s surfaceIn this study,two new iron-based fiber adsorbents were prepared to remove phosphate from water.The results showed that PAN_AF-Fe was more excellent as phosphorus removal adsorbent,and its maximum adsorption capacity of phosphate on water was 24.14 mg P/g,and the adsorption equilibrium was reached in 5 min which is far superior than most other P removal adsorbents.In addition,it can be reused for at least 5 times and can reduce phosphate concentration to 0.002 mg P/L,which has great potential for practical application.In summary,PAN_AF-Fe is an excellent phosphorus removal adsorbent with high removal efficiency,low removal lower limit,great practical application potential and good recycling.