Eggshell-supported Nanoscale Zero-valent Iron For Removal Of Phosphate From Aqueous Solution: Kinetics And Mechanism

It is found that phosphorus is one of the controlling factors of eutrophication,When the concentration of total phosphorus in water is greater than 0.02mg/L,it will lead to eutrophication.it is generally believed that the direct contribution of phosphorus in eutrophication is orthophosphate.Nanosclae zero-valent iron?nZVI?was widely used in the removal of contaminant in aqueous solution because of its high specific surface area,high reactivity and strong reducibility,however,the disadvantages of easy agglomeration and easy oxidation affect the popularization of practical engineering application.In this paper,the kitchen wastes –eggshell?ES?were choosed as a supporter,preparation of eggshell supported nanosclae zero-valent iron?ES-nZVI?,in order to increase the dispersibility and oxidation resistance of nZVI,at the same time,the adsorption properties of eggshell to phosphate were studied,and removal of orthophosphate in water,the purpose of phosphorus removal and waste reuse.In this study,the parameters of eggshell pretreatment,eggshell size,the amount of eggshell and the ethanol content of the system were optimized,the effects of dosage,initial concentration,temperature,pH and coexisting anions on phosphorus removal efficiency of ES-nZVI were investigated,the adsorption mechanism and kinetics of ES-nZVI to orthophosphate were preliminarily investigated.The main conclusions were as follows:?1?ES-nZVI preparation parameters: The pretreatment of 0.5mol/L acid activated eggshell,the particle size of 200,the ratio of eggshell to nano iron was 2.5:1,the ethanol volume in the system was good.?2?Batch experiments show,dissolved oxygen content in water had little effect on the final ES-nZVI removal efficiency.Increasing ES-nZVI can shorten the time required for the reaction to reach equilibrium.The adsorption capacity of ES-nZVI can be increased by increasing initial concentration.Increasing the reaction temperature can accelerate the reaction rate,but when the Fe:P ratio is too low,heating will accelerate the analysis of phosphorus in Fe-P.The coexisting anions show that they have some influence on the removal of orthophosphate.The order of influence degree from large to small,SO₄^2->F->HCO₃^->Cl->NO₃^-,among them,SO₄^2-and F-had greater effect on ES-nZVI removal.?3?Both the Langmuir and Freundich isothermal adsorption models can describe the adsorption process better,the results show that the removal of orthophosphate by ES-nZVI is the result of homogeneous and heterogeneous adsorption;Dynamic process analysis showed that primary and secondary dynamics model can better describe the removal process,indicating that the removal of orthophosphate by ES-nZVI is mainly based on chemical adsorption;?4?The Eggshell and ES-nZVI SEM results showed that the nano dispersed granular iron supported on eggshell pore size and internal surface,TEM and XRD characterization of spherical particles is further verified material surface of the shell for zero valent iron;?5?SEM characterization before and after ES-nZVI reaction shows that the surface morphology of ES-nZVI changes obviously after reaction,which indicates that complex chemical reaction occurs after the contact of the material with orthophosphate;The results of FT-IR showed that after the reaction of ES-nZVI surface Fe-O bond disappeared,the increase of-OH,suggesting that iron oxide in the phosphorus removal process;XPS results showed that the ES-nZVI reaction after Fe mainly exist in the form of Fe?II?,the phosphorus removal process does not occur P redox reaction,phosphorus removal mechanism may be a dissolution-precipitation,adsorption and chemical co precipitation;XRD results further verify the reaction product Fe₃?PO₄?₂·8H₂O and Ca₅?PO₄?₃OH.