Remediation Of Hexachloro-cyclohexane Contaminated Soil With Nano Zero-valent And Calcium Peroxide

At present,the remediation of contaminated sites by organochlorine pesticides has been the one of research hotpots,HCH has got a lot of attention due to its high toxicity,accumulated and refractory,Remaining contaminated sites have serious damage for environment.Therefore,researches of measures which to remediate contaminated sites and analyze the mechanism have scientific and practical significance.In this study,?-HCH polluted soil was used as object of study,a Fenton-like system wth modified nanoscale zero valent iron?nZVI?by chemical liquid phase reduction method and calcium peroxide?CaO₂?was used to degrade?-HCH in soil.The effect of degradation and soil quality by single nZVI or CaO₂ to degrade?-HCH was compared with nZVI and CaO₂ combined.Study the best condition of washing?-HCH in soil by TX-100,then disposal?-HCH in soil leaching solution nZVI and CaO₂.Analyze the best condition to degrade,process of dynamics and detection of ion and pH,then study and reveal the mechanism and pathway of degradation.Receiving under main conclusions:?1?Modified nZVI were prepared by chemical liquid phase reduction method.These nZVI were characterized by XRD and then detected these nZVI by TEM.The TEM images revealed particle of PVP-nZVI was more dispersive and smaller,and degradation effect was better.Sequential extraction procedure was used for analyzing speciation of?-HCH in soil,results indicated that mass?-HCH existing in the forms of adsorption state and dissolving state.The study revealed that?-HCH was degraded by nZVI+CaO₂ was the best system in 3 kinds systems.Disposal on soil by nZVI,CaO₂,nZVI+CaO₂ had some negative effect.Results indicated that the highest degree of influence was identified as CaO₂ individually,nZVI+CaO_2,nZVI alone.When the dosage of CaO₂ was 5%,Content of TOC be decgraded 0.206%and available nutrient was degraded 20.75%.?2?Compared the washing rate of?-HCH by SDS,Tween80 and TX-100,results revealed that TX-100 was the best eluting agent.Studying the effect of dosage of TX-100 for the washing rate,results indicated that washing rate of?-HCH was increasing with dosage of TX-100 increasing.The washing rate of?-HCH was up to86.98%,as the dosage was 40g/L,which could be for separation.Exploring the degradation technologic parameters of so il leaching solution,The best degradation technologic parameters was dosage of nZVI and CaO₂ was 1g/L,time was 6h,initial pH was 5,then the degradation rate of?-HCH over 90%.Design the response surface experiment to study degree of 3 factors on?-HCH?COD,results indicated that CaO₂ has high influence on degradation of?-HCH,at the same time,nZVI and CaO₂had high influence on degradation of COD and had interaction on it.As the dosage of CaO₂ was 0.75g/L,dosage of nZVI was 0.42g/L and initial pH was 5.66,the degradation rate was 98.12%,the degradation of COD was 42.01%.?3?In free radical quenching experiments,Explored major free radicals in these processes,then speculated the reaction mechanism.Results indicated that superoxide free radicals had greater contributions than hydroxyl radical.)In the study,intermediate products were detected by GC-MS,and detected change of concentration of ion and pH.The results indicated that main intermediate products were trichlorobenzene and chlorobenzene.The pathway of degradation by nZVI and CaO ₂was speculated that?-HCH reduction for three chlorobenzene firstly,then oxidized and completed mineralization of organic finally.