Degradation Of Chlordane In Triton X-100 Solution By UV/Goethite/H₂O₂

Organochlorine pesticides（ocps）is a kind of synthetic organochlorine pesticides,which are difficult to degradation in the natural environment and belong to the persistent organic pollutants,it has been widely used in pest control and improving the quality of agricultural production.OCPs tends to accumulate in organisms and severely threatened to human health.With the implementation of“Stockholm International Conventionand”and the rapid development of urbanization,many organochlorine pesticide production enterprises have been closed or relocated,leaving a large number of organochlorine-contaminated sites,these contaminated sites are facing the secondary development and needs to be repaired quickly.Among many methods of soil remediation,soil washing has been widely attention because of its advantages of low cost and high efficiency.However,during the process of soil washing,pollutants will remain in the soil washing effluent,it is easy to cause secondary pollution,so the treatment of soil washing effluent is also important.At present,the heterogeneous photo-fenton technology can improve the circulation efficiency between iron ions and increase the utilization efficiency of H₂O₂,which has a good effect on the degradation of organic pollutants.Iron oxides such as goethite have been widely attention and have great development potential because of their abundant in nature and environmentally friendly.In this paper,chlordane was used as the representative of organochlorine pesticide,and Triton X-100 was used as the soil washing solvent,explore the feasibility,the best process parameters and the degradation mechanism of degradation of chlordane in Triton X-100 solution by UV/goethite/H₂O₂.The main contents of the study are as follows:1.Explore the feasibility and the best process parameters of degradation of chlordane by UV/goethite/H₂O₂,including the degradation effects of chlordane by goethite,H₂O₂,and goethite/H₂O₂ under light or no light conditions,and the effects of reaction conditions including the initial pH,loading of goethite and concentration of H₂O₂ on the degradation of chlordane by UV/goethite/H₂O₂.2.Studied the adsorption kinetics and isothermal adsorption of chlordane onto goethite,investigated the influence of pH and concentration of Triton X-100 on the adsorption of chlordane by goethite.3.Investigate the mechanism of chlordane degradation by UV/goethite/H₂O₂ and speculate its possible transformation pathway.4.To explore the feasibility of UV/gothite/H₂O₂ in soil washing remediation.After a series of experimental studies,the results are as follows:1.The minerals synthesized in the laboratory were characterized,the XRD patterns of precipitates suggesting that the minerals prepared by Fe（NO₃）₃ and KOH are pure goethite.It can be observed by scanning electron microscope that goethite is acicular mineral with particle size ranging from0.5μm to 2.5μm and appear the distinct aggregation.The BET analysis revealed that the specific surface area of the goethite was 33.11 m²/g.2.The optimal condition for degradation of chlordan in Triton X-100solution by UV/goethite/H₂O₂ are as follows:when chlordane concentration was 1 mg/L,the concentration of Triton X-100 was 1 CMC,the reaction temperature was 28℃,initial pH was 3,the loading of goethite was 0.1 g/L and the concentration of H₂O₂ was 50 mmol/L,after 24 hours of reaction,the degradation efficiency of chlordan reached 88.57%.3.Goethite has adsorption effect on chlordane and Triton X-100.The adsorption kinetics of chlordane onto goethite could be fitted well with the pseudo-second-order model,the fitting equation was Y=1.6129X+0.1959,R²=0.9996.The isothermal adsorption of chlordane by goethite could be fitted well with the Langmuir model and the Freundlich model,the Langmuir fitting equation is Y=0.1518X+0.0538,R²=0.9249,and the Freundlich fitting equation is Y=0.8563X+0.6652,R²=0.9688.Adsorption capacity of chlordane by goethite decreased gradually as pH increased,and the maximum adsorption capacity was 1.51 mg/g in the range of 3-11.Adsorption capacity increased initially and then decreased as concentration of Triton X-100increased,maximum adsorption amount of chlordan by goethite was reached4.73 mg/g under the concentration of Triton X-100 was 0.5 CMC.4.During the reaction of UV/goethite/H₂O₂ to degrade chlordane in Triton X-100 solution,hydroxyl radicals play a major role,and the reaction mechanism of this system is surface catalytic mechanism,that is,chlordane is first adsorbed on the goethite surface,and then iron ions on the goethite surface react with H₂O₂ to·OH,·OH reacts with chlordane adsorbed on the surface of goethite,causing chlordane to degrade.During the degradation of chlordane by UV/goethite/H₂O₂,chlordane was firstly oxidized,then chlorides are formed,and finally monocyclic ketone compounds are formed.5.When the concentration of chlordan in the soil was 4 mg/kg,5 mmol/L Triton X-100 was used to washing the soil,after 1 hour of reaction,the elution efficiency was up to 48.37%.Then the chlordane in the soil washing effluent was treated with UV/goethite/H₂O₂,the degradation efficiency of chlordane was reached 91.32%after 7 day of reaction under the reaction pH was 3,loading of goethite was 0.1 g/L and concentration of H₂O₂ was 50mmol/L.Meanwhile,the degradation efficiency of Triton X-100 reached99.53%.This article uses UV/goethite/H₂O₂ to degrade chlordane in Triton X-100solution,explores its feasibility and influencing factors,reveals that its degradation mechanism is surface catalytic mechanism,infers the degradation pathway of degradation of chlordane by UV/goethite/H₂O₂ and proved its feasibility in soil washing remediation.Therefore,the soil contaminated with chlordane was first washing by Triton X-100,and then the soil washing effluent was treated by UV/goethite/H₂O₂ technology,which can effectively repair the soil contaminated with chlordane.