Diclofenac Degradation In A Weak Magnetic Field Enhanced Zerovalent Iron/ligand System And The Interfacial Reaction Mechanism Study

As a classic series of PPCPs,nonsteroidal anti-inflammatory drugs?NSAIDs?are difficult to be biodegraded in water.In recent years,it has become one of the new organic pollutants concerned by researchers.In this study,a zero-valent iron/ligand system based on magnetic field?MF/ZVI/ligand?was established for the degradation of diclofenac?DCF?–a typical pollutant of NSAIDs,to investigate the effect of the system on DCF degradation and explored MF-induced heterogeneous interfacial reaction mechanism.The result showed that MF/ZVI/EDTA Fenton-like system could degrade DCF efficiently.In the process of degradation,there existed the initial stagnation?phase??and the rapid degradation period?phase??.MF could improve phase?and phase?degradation rate to a great extent.Studies has shown that MF can accelerate the corrosion of Fe_xO_y@Fe⁰ on the surface of ZVI.Under the combined action of the lorentz force and the gradient magnetic force,Fe²⁺accumulated on the surface of Fe_xO_y.Fe²⁺can expose fresh Fe⁰ sites,promoting the activation of O₂,accelerating homogeneous fenton reaction,and produced more·OH efficient degradation of DCF.When it's neutral in the water environment,the use of inorganic ligand TPP instead of EDTA can increase the degradation rate of DCF in MF/ZVI/ligand system by 3-5 times.The effect of magnetic is slightly different when iron passivation is used instead of ZVI.This difference may be caused by the different effects of magnetic field on the dissolution mode when different iron oxide layers are complexated with TPP.MF may cause pitting corrosion on ZVI in the initial stagnation period,but it has a weak impact on the rapid degradation period,indicating that the pitting corrosion caused by magnetic plays an important starting point of the rapid degradation period.The dissolved TPP in the MF/ZVI/TPP reaction will be adsorbed on the surface of ZVI or be the form of FePO₄bounded with Fe⁰@Fe_xO_y.Different inorganic anions have different effects on the degradation of DCF in the ZVI/TPP system.The reaction will be inhibited when the concentration of HCO₃^?/CO₃^2?and SO₄^2?increase.The concentration of NO₃^?has no effect on the reaction rate.The increase of the concentration of Cl^?appropriately will promote the reaction to degrade DCF,but it will have an inhibitory effect when the concentration outside of setpoint range.Br^?can significantly inhibit the degradation of DCF.The interference mechanism is mainly related to the synergistic or quenching action of different inorganic anions reacting with·OH.MF can effectively avoid the adverse interference of inorganic anions.In addition,an iron-sand column reactor was designed for internal circulating reaction,and it's found that the reactor can degrade DCF effectively.The presence of MF can make the degradation more efficient.This study provids a technical support for the engineering application of MF/ZVI/TPP system to degrade pollutants.