Study On Remediation Of Polycyclic Aromatic Contaminated Soil Using Fe And Its Enhancement Technology

Soil organic pollutants represented by polycyclic aromatic hydrocarbons（PAHs）are highly toxic to humans and other organisms,soil is its main sink.PAHs can be firmly adsorbed on the surface and interstices of soil particles and are difficult to be degraded naturally.Nano-zero-valent iron（n ZVI）and its strengthening technology,as an emerging PAHs remediation technology in soil,has the characteristics of simple operation,short remediation time,and low cost,so it has attracted wide attention.In this paper,phenanthrene（PHE）is used as a representative of PAHs pollutants,and zero-valent iron,which can undergo adsorption and oxidation-reduction reactions,is used as a remediation material to remediate organic contaminated soil.The removal of PHE from soil under the optimum experimental parameters was studied,In order to enhance the remediation effect,activated carbon loaded with n ZVI was used as the remediation material for PHE contaminated soil.At the same time,the characterization and enhancement experiments of the materials were carried out,and the possible degradation pathways of pollutants were proposed.Finally,the optimal modified materials were applied to the field removal experiments of PAHs contaminated soil,and a feasible application scheme was proposed.The main research conclusions are as follows:（1）Zero-valent iron technology could repair PHE contaminated soil,and its removal rate of PHE increased with the increase of reaction time.In the experiment,the optimal reaction time was 4.5 h,and the optimal dosage of ZVI was 0.06 g/g.p H affected the extraction rate of PHE.The extraction rate decreased with the increase of p H.Acidic conditions promoted the dissolution of metal ions in the soil,and the soil skeleton structure was destroyed,making the PHE in the soil easy to be extracted,resulting in a higher extraction rate.p H had a significant effect on the removal rate of PHE.Under acidic conditions,the removal effect of PHE was better than alkaline conditions.When the initial p H is 2 and 4,the removal rate was equal to33.8%and 30.6%.（2）n ZVI particles were obtained by reducing Fe SO₄·7H₂O with Na BH₄solution,activated carbon supported n ZVI（AC-n ZVI）and alkali-modified activated carbon supported n ZVI（MA-n ZVI）were obtained by means of loading.The results of BET showed that AC-n ZVI and MA-n ZVI contain a certain amount of macropores.The results of SEM showed that the n ZVI particles were spherical with particle size between 120-180 nm and had a certain dispersivity.Most of them were dispersed on the surface of activated carbon（AC）and alkali-modified activated carbon（MA）.The carrier effect of activated carbon and the dispersion effect of PEG effectively reduced the agglomeration degree of n ZVI.The results of XRD,FT-IR and AFM further confirmed that the nanoparticles were successfully loaded on AC-n ZVI and MA-n ZVI,and the loaded nanoparticles had good oxidation resistance and could be stored stably in absolute ethanol.The two kinds of loading materials fitted well with the second-order kinetic model and Freundlich adsorption isotherm model.（3）MA-n ZVI could achieve 78.84%removal rate compared with the initial concentration after 1h reaction.Compared with blank MA,MA-NZVI could also achieve 71.78%removal rate of PHE,which showed a better time advantage in the removal process of PHE in the soil.The residual concentration of PHE in the soil decreased gradually and the removal rate increased with the increase of the dosage of the two modified n ZVI.When the dosage of AC-NZVI and MA-NZVI were 45 mg/g and 60 mg/g,respectively,the removal rate of PHE reached to 76.13%and 70.03%.The removal of PHE from soil by MA-n ZVI showed a wide range of p H application,and it could achieve a relatively stable removal effect on PHE under both low and high ionic strength conditions.（4）The formation of anthracene due to the complex soil environment,and the PHE added to the soil has been transformed over time.The product was qualitatively analyzed by GC-MS and the degradation products mainly included 1-Butoxy-1-isobutoxy-butane,2,4-Di-tert-butylphenol,2,6-Diisopropylnaphthalene and Phenol,2,2’-methylenebis[6-（1,1-dimethylethyl）-4-methyl].（5）The technical design and cost evaluation of the remediation of PAHs contaminated soil in coking plant with MA-n ZVI loaded material were carried out.The technical design mainly included the transfer and pretreatment of contaminated soil,and the preservation and transportation of load materials should also be considered.The residual concentration of high-ring PAHs was almost reduced to 0,and the remediation cost of 1000 square meters of contaminated soil was 87,704 yuan.