The Study On Adsorption Removal Of Phosphate Using Iron Oxide Nanoparticles And Their Composites

Nowadays,water eutrophication keeps increasing and has long been a global environment problem.Phosphorus(P)is one of the main nutrients that lead to the water eutrophication.Therefore,it is highly necessary to remove the excess phosphorus from wastewater and recover phosphorus resource.A number of methods including chemical precipitation,activated sludge treatment process,and adsorption have been proposed to remove phosphorus from wastewater.However,it is difficult to remove the excess phosphorus from wastewater within the phosphorus discharge standards(below 0.1 mg·L-1).Recently,magnetic iron oxide nanoparticle(Fe3O4 NP)is one of the main promising materials for P removal in laboratory study or full-scale application due to its low-cost,effective performance,good biocompatibility,readily available and easily recovery by using a simple magnet due to their outstanding magnetic properties.However,Fe3O4 is not very stable for the reason that it is easily agglomerate and form large clusters,which will reduce the specific surface area,amounts of surface reaction site,and the stability when dispersed in aqueous solution.The surface modification and immobilization are the attractive potential approaches to stabilize the Fe3O4 NPs.Hence,in this study,the polyethyleneimine(PEI)modified Fe3O4NPs and biochar(BC)immobilized Fe3O4 NPs are synthesized by chemical coprecipitation method.And the adsorbents as synthesized are characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),Zeta potential and Fourier transform infrared spectroscopy(FTIR).Then,the performances of PO43-adsorption and desorption are investigated,and the adsorption conditions are optimized.The thermodynamic and kinetic studies of PO43-adsorption were also investigated.The mechanisms of PO43-adsorption are also explored in the study.The main results of the study are shown as follows:1.The magnetite(Fe3O4)is synthesized by co-precipitation of ferrous and ferric chlorides in aqueous solution.Most of Fe3O4 NPs are spinel structure with the qusi-spherical shape and with an average diameter of 20 nm.The magnetic parameters,such as saturation magnetization(Ms),is determined to be 70 emu·g-1.The isoelectric point(IEP)of Fe3O4 NPs is approximately 7.The Fe3O4 NPs showes good ability in PO43-adsorption.The adsorption efficiency reaches 73.01%under the following conditions:pH=3,50 mg·L-1 of PO43-,200 mg Fe3O4 and reaction temperature of 25 ?.The desorption efficiency of PO43-from Fe3O4 reaches 65%in NaOH solution(2.0 mol·L-1).The adsorption kinetic of Fe3O4 NPs is fit with the pseudo-second-order kinetics,indicating that the adsorption kinetics is mainly controlled by chemical processes rather than diffusion.The bare Fe3O4 NPs shows the poor reusability.2.PEI modified Fe3O4 NPs(Fe3O4/PEI)are synthesized and characterized.And the results indicates that PEI not only improves the dispersity of Fe3O4,but also increases the positive charge of Fe3O4.The PO43-adsorption ability of Fe3O4/PEI is obviously enhanced compared with that of bare Fe3O4 NPs.The PO43-removal efficiency has been enhanced from 73.01%to 91%and the PO43-desorption also has been enhanced(from 65%to 84%).Furthermore,the reusability of the adsorbent is also improved,the PO43-removal efficiency is maintained at 78%even after four successive trials.The adsorption kinetic of Fe3O4/PEI is also fit well with the pseudo-second-order kinetics.The maximum adsorption capacity of Fe3O4/PEI is calculated to be 29.88 mg·g-1.3.Biochar immobilized Fe3O4 NPs(Fe3O4/BC)are synthesized.The stability and dispersity of Fe3O4 NPs are both enhanced with the biochar as the supporter.The spherical Fe3O4 NPs disperses well on the surface of biochar with little aggregation,the BET of Fe3O4/BC is enhanced to 176.83 m2·g-1.As a result,the PO43-removal efficiency of Fe3O4/BC is enhanced to 92.14%.The PO43-desorption of Fe3O4/BC can reach 80%which indicated the better ability in PO43-recovery.Moreover,the Fe3O4/BC also shows a better reusability compared with bare Fe3O4 NPs(75%PO43-removal efficiency after four successive trials).In summary,Fe3O4/PEI and Fe3O4/BC both exhibit better PO43-removal ability compared with bare Fe3O4 NPs.This study demonstrates that Fe3O4 composites are the promising alternative for PO43-removal,and it is potentially applicable in real domestic wastewater treatment...