The Degradation Of Pahs In Soil By Solvent Pretreatment In Collaboration With Fenton-like

Polycyclic aromatic hydrocarbons（PAHs）are a class of organic compounds containing two or more benzene rings in their molecular structure.It is the largest group of carcinogens in the environment and has been widely concerned at home and abroad.Some PAHs can affect the nervous,immune,digestive and reproductive systems and induce cancer in humans and animals.Because of the advantages of higher repair efficiency,lower drug cost,less influence on soil p H and fewer harmful byproducts,Fenton-like oxidation has become a hotspot technique for remediation of organic contaminated soil.The difficulty of soil remediation lies in the fact that PAHs and other organic matter are closely adsorbed in the pores of the soil,resulting in their inability to contact with oxidants.In this paper,on the basis of optimizing the Fenton-like oxidation conditions,the soil is pretreated with organic solvents,which aims to remove the strong adsorption of PAHs on contaminated soil and make PAHs dissociate to the soil surface,so as to effectively participate in the oxidation reaction.Subsequently,deep degradation provided a new idea for improving the remediation efficiency of PAHs contaminated soil and reducing the remediation cost.The specific conclusions are as follows:（1）By studying the effects of activator types and oxidation conditions on H₂O₂oxidation of PAHs,it is found that among Fe₃O₄,Fe S₂,Fe S and Fe SO₄,Fe SO₄has the strongest activation performance.The PAHs removal rate was 35%when the activator was Fe SO₄,the total amount of H₂O₂was 4mmol/g,and the water/soil ratio was 1:1.At the same time,the removal rate of PAHs in soil increased with the increase of H₂O₂addition times.（2）By changing the type and dose of complexing agents used in Fenton-like oxidation,it is found that among four complexing agents,disodium EDTA-2Na,citric acid monohydrate（CAM）,sodium pyrophosphate（SP）and ammonia triacetic acid（NTA）,when the EDTA-2Na/Fe SO₄molar ratio is 1:10,the oxidation effect of Fenton-like oxidation is most significantly improved.（3）The degradation effect of organic solvent pretreatment combined with Fenton on PAHs in soil was investigated.It was found that n-hexane was the best pretreatment solvent among all single solvents and mixed solvents.When the n-hexane/soil（m L:g）≥1:2 was used to pretreat the soil for 4 h,the total removal rate of PAHs reached 84%,which was significantly higher than that of Fenton oxidation alone.In addition,solvent pretreatment is effective for different types of soil.EDTA-2Na is still the best complex agent in solvent pretreatment and Fenton-like oxidation process.When the EDTA-2Na/Fe SO₄molar ratio was 1:10,PAHs were reduced by 92%.Adding too much complexing agent will have a negative effect on the degradation of PAHs.（4）FTIR and BET tests were conducted on the soil before and after solvent pretreatment.It was found that after soil pretreatment,the content of organic matter such as PAHs and humic acid on the soil surface increased significantly,and the average pore diameter of soil particles became larger,while the specific surface area became smaller.The results showed that PAHs which desorbed in soil pores for a long time were adsorbed to the soil surface by solvent pretreatment.（5）The deep degradation experiment of PAHs found that after the secondary treatment of soil by solvent pretreatment and Fenton oxidation,the removal rate of PAHs can be further improved,which is conducive to reducing the cost of using solvents and H₂O₂in industrial applications.The degradation effects of PAHs in soil were not significantly different between oscillating and ultrasonic solvent pretreatment.