Study On The Removal Of Phenanthrene From Contaminated Soil And Groundwater By Iron Carboxylate

Polycyclic aromatic hydrocarbons（PAHs） are a type of persistent organic pollutants that have carcinogenic,teratogenic,and mutagenic effects and pose a serious threat to human health.Soil is the storage and transfer station of PAHs in the environment.PAHs accumulated in the soil are carried by the pore water of the soil and migrate to the groundwater,causing pollution to the groundwater.Therefore,there is an urgent need to develop a remediation method that can effectively remove PAHs in soil and groundwater and reduce the toxicity of contaminated soil and groundwater.This thesis mainly carried out a photochemical reaction using iron carboxylate complexes to repair PAHs contaminated soil and groundwater.Taking phenanthrene（PHE）as the representative pollutant of PAHs,simulating phenanthrene-contaminated soil and groundwater as the remediation object,the degradation effect of the remediation agent on soil remediation and groundwater treatment is optimized,and the reaction mechanism of the remediation agent under visible light is explained to evaluate the phytotoxicity of the soil after restoration.The main findings are as follows:（1）Using ferrous oxalate as a remediation agent and phenanthrene-contaminated soil as the object of remediation,ferrous oxalate and phenanthrene contaminated soil are mixed into a thin soil layer,and the thin soil layer can be irradiated with visible light to efficiently remove phenanthrene in the contaminated soil.When the addition amount of ferrous oxalate is 1 wt%,the degradation rate of phenanthrene in the contaminated soil can reach 82.7%after being irradiated with visible light for 2 hours.The addition of ferrous oxalate,soil thickness and water content,and the mixing method of ferrous oxalate and soil all directly affect the removal of phenanthrene in contaminated soil.Ferrous oxalate can generate Fe²⁺and H₂O₂ in situ under visible light irradiation,and the reaction releases strong oxidizing·OH,which can degrade phenanthrene in contaminated soil.The lettuce cultivation experiment is used to evaluate the toxicity of contaminated soil after restoration.According to the data of lettuce root length,leaf length and fresh weight,it is shown that the toxicity of the restored soil is greatly reduced.（2）Ferric citrate is used as a remediation agent,and phenanthrene-contaminated soil is the remediation object.Ferric citrate and phenanthrene-contaminated soil are mixed with water to form a suspension.By irradiating the suspension with visible light,the phenanthrene in the contaminated soil can be efficiently removed at a near neutral p H.When the addition amount of ferric citrate is 1.5 wt%and visible light is irradiated for 6 hours,the degradation rate of phenanthrene in the contaminated soil can reach85.5%.The light time,the initial p H of the suspension,the addition of ferric citrate,and the ratio of water to soil all directly affect the effect of phenanthrene in contaminated soil.Under visible light irradiation,ferric citrate can produce Fe²⁺and H₂O₂ in situation,which is Fenton reagent,to achieve the oxidative degradation of phenanthrene in contaminated soil.The toxicity of the contaminated soil after remediation was evaluated through the cultivation experiment of the salsola and lettuce.According to the growth index data of the cultivated salsola and lettuce,it was found that the toxicity of the soil after the restoration was significantly reduced.（3）Ferric citrate is used as the treatment agent,and the phenanthrene in the simulated groundwater is used as the treatment object.At near neutral p H,it has a strong oxidative degradation effect on the phenanthrene in the simulated groundwater.When the addition amount of ferric citrate is 300 mg/L and exposed to visible light for 6 hours,the degradation rate of phenanthrene in the solution can reach 87.4%.The addition amount of ferric citrate,the initial p H value of the mixture and the full aeration of the mixture directly affect the degradation effect of phenanthrene in the aqueous solution.Anions and cations have a certain inhibitory effect on the photodegradation of phenanthrene in aqueous solution.The inhibitory effect of Cl^-in the anion is more significant,and the inhibitory strength of the cation is Ca²⁺>Mg²⁺>K⁺.