Fenton-like Reaction For Remediation Of Polycyclic Aromatic Hydrocarbon Contaminated Soil And Mechanism Of Calcium Peroxide Based Fenton-like Reactions

Significant difference between calcium peroxide and hydrogen peroxide based Fenton-like systems was revealed.Although many of studies and applications of CaO₂ in Fenton-like reaction have been done,the basic understanding on the intrinsic difference between CaO₂ and H₂O₂ based Fenton-like reaction should be improved.In the firse part of this study,the notable differences between the two systems were understood by ROS identification,intermediate track,electrochemical and kinetic analyses;and the endogenous reducibility of CaO₂ to facilitate Fenton-like reaction was finally revealed.High dosages of hydrogen peroxide were used as oxidant in traditional Fenton-like reactions leading to low utilization efficiency.Moreover,transition metal was applied as catalyst,limiting the pH range to 2-4,and the leaching of iron causes the acidification of soil.In response to the above two problems,in the second part of this study,calcium peroxide was combined with hydrogen peroxide as oxidant and natural clay was modified as catalyst to promote the degradation of polycyclic aromatic hydrocarbons in soil and reduce H₂O₂ loss.Meanwhile,this technology can adjust the appropriate pH to neutral,and avoid soil acidification.The main conclusions are as follows:?1?Phenol degradation in the H₂O₂ system displayed an initial latent time of 60 min,while phenol can be degraded immediately in the CaO₂system.The contribution of ¹O₂ in CaO₂ system was excluded by the poor selectivity in phenol conversion and the comparable ¹O₂-TEMP EPR signals in both CaO₂ and H₂O₂ systems.?2?Kinetic analyses using chloroform as the probe of superoxide radical suggested the high production rate of superoxide radicals,which is four orders of magnitude higher than that in H₂O₂ system.The mechanism of the accelerated CaO₂ based Fenton-like reactions was featured by that two electrons coming from CaO₂ can be utilized to promote reduction of Fe^III:an inner sphere electron transfer takes place to reduce Fe^III-EDTA and produce superoxide radicals,and subsequently superoxide radical provides an electron to reduce another Fe^III-EDTA.?3?Modified HT-H500 catalyst and hydrogen peroxide or calcium peroxide were used to remediate the PAHs contaminated soil in Shanghai?worksite?and Nanjing?farmland?.After 24 hours,the total PAHs content in worksite soil and farmland soil decreased from 6.977 mg/kg and 1.2083mg/kg to 2.585 mg/kg and 0.3511 mg/kg,respectively.Meanwhile,the soil fertility was improved,and the change of pH is negligible.After two weeks,the plants such as water spinach,fungus and leek were in good condition.?4?Compared with H₂O₂ system,the degradation of PAHs was better in CaO₂,especially for high molecular weight PAHs,but the economic benefit was lower.Three strengthening sets of the hydrogen peroxide system significantly promoted the degradation of low molecular weight PAHs.Significant promotion of high ionization potential PAHs was detected in the natural promoters set.Linear relationship between the degradation effect and the ionization potential was found in other two sets.Considering the degradation effect and economic benefits,the optimal scheme for soil polycyclic aromatics degradation was:0.01 g/g HT-H500 catalyst,0.001 g/g calcium peroxide,0.015 mmol/g hydrogen peroxide.