Removal Of Phenylarsonic Acid By Adsorption And Activated Persulfate Of Iron Based Materials

With the continuous development of rural urbanization construction in our country,groundwater pollution and hazardous health problems emerge in the area containing diphenylcyanoarsine and diphenylchlorarsine chemical agents leaked during the war.However,there is little research on the remediation technology of water contaminated by organoarsenic agent at present.In this study,environmental friendly iron-based materials were selected to explore the removal capacity of phenylarsonic acid from water by adsorption of iron minerals and activated peroxymonosulfate oxidation by ferrate.Three kinds of iron minerals,including ferrihydrite,goethite and hematite,were prepared by simple coprecipitation method,and their adsorption properties and adsorption mechanism for phenylarsonic acid were investigated.A permeable reactive barriers was designed to explore its dynamic adsorption performance for phenylarsonic acid.On this basis,using the technology of adsorption by advanced oxidation in-situ prepared iron oxide,oxidizing phenylarsonic into arsenate,then using in-situ formed iron oxide to adsorb dagradation products.Oxidation and adsorption mechanism of phenylarsonic acid in Fe（VI）/PMS reaction system were investigated.The results show that:（1）Among the three prepared mineral materials,ferrihydrite has the best adsorption performance for phenylarsonic acid,followed by hematite and goethite.The adsorption kinetics and adsorption isotherm fitting results showed that the adsorption processes of the three iron minerals all conform to the pseudo-second-order kinetic model and Langmuir model.The maximum adsorption capacities of phenylarsonic acid at 50 mg L^-1concentration at 298 K were 63.44 mg g^-1,26.27 mg g^-1 and 19.03 mg g^-1,respectively.The experimental results showed that the adsorption properties of the three kinds of iron minerals increased with the increase of environmental temperature.Acidic and neutral environment was favorable for the adsorption of iron minerals,while alkaline environment,carbonate,silicate,phosphate and other acidic ions would exert obvious inhibition on the adsorption properties.The results of infrared spectroscopy,X-ray photoelectron spectroscopy showed that the adsorption of phenylarsonic acid by iron minerals was mainly achieved through electrostatic attraction and ligand exchange between the surface hydroxyl group and the arsenate group of phenylarsonic acid to produce Fe-O-As bond.In the permeable reactive barriers experiment simulating groundwater restoration,it was found that the influent flow rate had a significant impact on the adsorption effect.When the flow rate was 1 m L min^-1,the adsorption effect of the fixed bed of ferrihydrite was the best,and the fixed bed penetrated after315 min.（2）When the molar ration of Fe（VI）/PMS is 1:2,the degradation effect of phenylarsonic acid achieved 80%.When the molar ratio of Fe（VI）and PMS is fixed and the initial p H of the reaction is controlled at4,the degradation effect of phenylarsonic acid will be improved.In the presence of phosphate or carbonate,the degradation rate of phenylarsonic acid will be improved because it promotes the activation of PMS to produce active species.Through free radical quenching experiment,electron paramagnetic resonance experiment,molecular probe experiment,PMS and Fe（VI）decomposition experiment,it is found that Fe（VI）and PMS have synergistic interaction.Through interaction,the active species produced in the reaction system mainly include Fe（IV）and singlet oxygen.By analyzing the concentration of arsenic species in the reaction system and in-situ iron oxides,it is inferred that the adsorption process is that Fe（VI）/PMS rapidly degrades phenylarsonic acid to arsenate,and then iron oxides formed by Fe（VI）in-situ adsorb arsenate to achieve the removal of pollutants.The mechanism of in-situ adsorption of arsenate acid by iron oxide is also through the formation of Fe-O-As bond through ligand exchange to realize the adsorption of arsenic.