Degradiation Of Phthalates Contaminated Soil By Chemical Oxidation Technology

With the rapidly development of modern society and human living standards are improving,global environmental pollution has gradually become a serious problem that affecting the sustainability development of human society.Phthalates?PAEs?are often used in plastics as a plasticizer and have been widely distributed in nature,researchers have found the existence of PAEs in various environmental media such as in the atmosphere,soil and water.With a large number of PAEs inters into the natural environment,the soil has become the main destination.Therefore,the effective prevention and remove of PAEs in soil has become a key problem that we need to solve,but also a central issue of common concern to the people all of the world.The advanced oxidation processes used for remediation PAEs contaminated soil,have the advantages of low cost,without secondary pollution and short remediation period,it has been an application techniques that having a lot of development.In this thesis,DEHP contaminated soil collected from a chemical plant relocation was used,studied the remediation effect of contaminated soil and explored the feasibility of DEHP or other plasticizers contaminated soil by advanced oxidation technology,the main results were as follows:?1?Four kinds of oxidants has been used to remediate DEHP contaminated soil,the study found that Fe²⁺/Na₂S₂O₈ had the highest DEHP degradation rate for four kinds of oxidizing agents,the order of the degradation of DEHP was Fe²⁺/Na₂S₂O₈>Fenton>KMnO₄>H₂O₂.The degradation kinetics of DEHP for four oxidants has been investigated and the results has been fitted at the concentration of 3 mmol·g-1,the pH was 8.06,the liquid-to-soil ratio was 2 and the temperature was 25 ?.Compared the three fitting equations of zero-order kinetics?first-order kinetics and second-order kinetics,the correlation coefficients?R2?has better for second-order kinetics of four oxidants,indicated the degradation of DEHP in line with second-order reaction.At the same time,before and after remediation,soil properties have been analyzed and found that after adding oxidizing agents,all of the soil pH were decreased,in which the pH by Fe²⁺/Na₂S₂O₈ oxidized decreased most significantly;added four oxidants the soil TOC have decreased,especially Fe²⁺/Na₂S₂O₈ system;Eh and EC increased significantly;CEC was weakly declined;the whole soil N,P,K have declined.Using an oxidizing agent remediated DEHP contaminated soil had little effect on soil properties,while it did not cause loss of the soil functions.?2?Researched the DEHP degradation effect in ?Fe⁰/Na₂S₂O₈,H₂O₂/Na₂S₂O₈,OH/Na₂S₂O₈ three systems.Experiments have performed for selection of suitable catalyst iron-containing compound??Fe⁰,nFe⁰,ferric chloride,ferrous sulfate,ferric nitrate?,we found the degradation rate of DEHP was highest in.Fe⁰ conditions.A comparative study of the three systems??Fe⁰/Na₂S₂O₈,H₂O₂/Na₂S₂O₈,OH-/Na₂S₂O₈?has conducted,and the order of the degradation of DEHP was OH-/Na₂S₂O₈>?Fe⁰/Na₂S₂O₈>H₂O₂/Na₂S₂O₈.SO4-·has produced Under three different ways of catalytic conditions,while the reaction also generated other radicals such as O₂^·- and OH^-,but SO₄^-· was still dominant role in the reaction.The results showed that the oxidation technology in three different activation ways could be used to remediate DEHP or other PAEs contaminated soil,in which the best way was an alkali activation method.?3?We studied the surface morphology of Fe⁰ and the DEHP degradation mechanism in OH^-/Na₂S₂O₈ oxidation process.By the scanning electron microscopy characterization for nFe⁰ and ?Fe⁰,it has found that boh the nFe⁰ and ?Fe⁰ surfaces were corroded severely,with the reaction,the corrosion increased obviously.While snow-like substances were produced on the surface of Fe⁰,speculated that the mainly substance was FeOOH.Detected the degradation trends and intermediates of DEHP in different times By LC/MS,it has found that the DEHP concentration gradually decreased with the reaction,while the concentration of four intermediate products increased slowly.DEHP and four intermediate products spectrum has been analyzed,intermediates identified in this study include 2-?3-pentene-O-acyl?benzoate isoheptaldehyde?2-?3-pentene-O-acyl?benzoate hexadiene?2-?3-pentene-O-acyl?benzoate pentadiene and 5-?2-hydroxy ethyl?-6-hydroxyl hexanal,respectively.A series of new compounds were formed by the oxidation of SO₄^-· to DEHP,then,several compounds further oxidation with radicals,some of DEHP has been mineralized into CO₂ and H₂O at last.