Study On Removal Mechanism Of Polycyclic Aromatic Hydrocarbons In Water By Zero-valent Iron

China is a big agricultural country.The agricultural issue is one of the most important issues for national survival.With the rapid development of the national economy,in the process of agricultural production,we are paying more attention to the improvement of quality while pursuing quantity.The state of agricultural water security has become a quality improvement of agricultural production.One of the important guarantees.The problem of water pollution in China is becoming increasingly serious,especially with organic pollution.According to the results of relevant environmental toxicology studies,organic pollutants in contaminated water can migrate to the plants to enrich and enlarge,thus harming human health.In this study,four kinds of polycyclic aromatic hydrocarbons?PAHs?were degraded and removed by ordinary reducing zero-valent iron,and the zero-valent iron?ZVI?was measured before and after the reaction by means of scanning electron microscope?SEM?and X-ray diffraction?XRD?.Characterization of physical and chemical properties;Influencing factors of zero-valent iron on the removal of four PAHs were discussed:such as additional auxiliary means,dosage of ZVI material,system conditions?initial pH of system,H₂O₂/zero-valent iron Synergy,H₂O₂/pH ZVI synergy,removal kinetics?Fenton system,repeated use properties of ZVI materials etc;mechanism of removal of four PAHs by ZVI under different system conditions And its dynamic adsorption properties.research shows:?1?From the SEM and XRD results,it can be seen that the zero-valent iron material selected for this experiment has a bulky appearance with a particle size of10-100?m and exists in the form of?-Fe⁰.Better,a high degree of crystals.A layer of dense layered material was attached to the surface of the ZVI after adsorption saturation,and the XRD diffraction peak was weakened.However,after the acidic system containing H₂O₂ eluted with eluent,the surface dense layered material disappeared and the diffraction peaks of the ZVI three sites significantly increased.?2?The research results of zero-valent iron on the removal performance of four PAHs in water and the influencing factors have shown that zero-valent iron has excellent removal capacity for all four PAHs,and the average removal treatment is above 90%.The removal efficiency and material of PAHs The dose is proportional to the initial concentration of the system PAHs inversely proportional.Neutral and alkaline conditions are more conducive to the removal of four PAHs.The Fenton-like system constructed by adjusting the pH value of the system and H₂O₂ content has a certain ability to remove the four PAHs,and the low-ring PAHs can be easily removed.Zero-valent iron has excellent reusability in the acid system containing H₂O₂,and the removal rate of PAHs is maintained at about 100%.With the increase in the number of repeated use,the removal efficiency also increases.?3?The removal of PAHs in water by zero-valent iron includes surface adsorption removal and open-loop degradation.Under different system conditions,the ratio of surface adsorption to open-loop degradation of zero-valent iron is different.Using Phe as a probe and GC-MS to determine the intermediate products in different reaction systems,it can be seen that there are differences in the reaction mechanism followed in the removal of different systems.The acid system containing H₂O₂ is more conducive to the ring-opening degradation of Phe.The ultrasonic effect is better than the constant temperature oscillation aid.?4?The zero-valence iron-packed column designed in this study has excellent adsorption and removal performance for all four PAHs in water.The adsorption of PAHs by packed columns is superior to acidic systems under neutral or alkaline conditions.After multiple PAHs were mixed with each other or mixed together,the competitive adsorption between low-concentration PAHs was not obvious,while there was obvious competitive adsorption between high-concentration PAHs and the adsorption rate of high-ring PAHs on zero-valent iron-packed columns.higher.The saturated adsorption capacity of zero-valent iron material to thorium PAHs can reach0.015 g·g^-1,and when the PAHs dosage is 25?g,the penetrating column can reach4 L.