Degradation Of Polycyclic Aromatic Hydrocarbons In Coking Site Soil By Mn_xFe_yO Activated Persulfate

Polycyclic aromatic hydrocarbons（PAHs）are carcinogenic,teratogenic and mutagenic to human body.Due to improper industrial emissions,a large number of polycyclic aromatic hydrocarbons（PAHs）are deposited in the soil,resulting in a large number of coking sites left.How to effectively degrade PAHs in coking site soil is one of the hot issues at present.Persulfate oxidation technology has been widely concerned in recent years,with the advantages of high efficiency and low cost.Firstly,a series of Mn_xFe_yO were prepared,and the best Mn_xFe_yO was selected by structure characterization and performance comparison.Secondly,the effects of reaction conditions on the degradation of PAHs by Mn_xFe_yO activated persulfate were investigated to obtain the optimal reaction conditions.Finally,the degradation effect and reaction mechanism of organic solvent extraction and Mn_xFe_yO activated persulfate on PAHs in soil were explored.The study provides a new idea for the remediation of contaminated sites.（1）Mn_xFe_yO activators with different Mn/Fe ratios were prepared and characterized by SEM,XRD,XPS and BET.The results show that spinel Mn_xFe_yO was successfully synthesized.By comparing the activation performance of different Mn/Fe molar ratio,it was found that the activation performance was the best when Mn:Fe was 4:1.（2）The effects of oxidant dosage,the ratio of activator to oxidant dosage,and the ratio of water to soil on the degradation of PAHs in soil by Mn_xFe_yO activated persulfate were investigated.The results showed that when the dosage of persulfate was 1 mmol/g,the molar ratio of Mn_xFe_yO/PDS was1:10,the ratio of water to soil was 2:1,the initial p H was 6.7,and the reaction time was 4 h,the best degradation rate of PAHs in soil was 73.60%.（3）To investigate the synergistic effect of different organic solvents extraction and Mn_xFe_yO activation on the degradation of PAHs in soil.The results showed that n-hexane was better than other single or mixed organic solvent systems.When the solid-liquid ratio of soil to n-hexane was 1:2,oxidation after ultrasonic extraction for 30 min,the final degradation rate of PAHs in soil could reach 92.21%.The best activator was added in the oxidation stage.（4）By analyzing the change of soil surface organic matter before and after extraction and the formation of free radicals in the reaction system,the mechanism of n-hexane extraction and Mn_xFe_yO activated persulfate degradation of PAHs in soil was explored.FTIR analysis showed that n-hexane extraction made PAHs in soil particles migrate to the soil surface,which was easy to contact with activators and oxidants,and improved the degradation rate of PAHs.The analysis of soil properties before and after the reaction showed that the content of soil organic matter decreased,and organic matter such as PAHs was mineralized during the oxidation process.EPR analysis showed that Mn_xFe_yO activated persulfate to produce SO₄^·-,^·OH and O₂^·-radicals,SO₄^·-and^·OH played a major role in the reaction.