Study On The Stability Of Four Types Of Characteristic In-Situ Chemical Oxidants In Site Remediation

In situ chemical oxidation technology is a commonly used site restoration technology.According to the characteristics of the site pollution source,different in-situ chemical oxidants can be selected for in-situ remediation.The selected oxidant needs to be transported to reach specific underground contaminated areas.Therefore,the stability of the oxidant injected underground is very important.This article mainly studies the self-decomposition behavior of four kinds of common in-situ chemical oxidants such as hydrogen peroxide,calcium peroxide,permanganate and persulfate,and explores its stability in the presence of different hydrochemical conditions and different aquifer materials.The effects of solution temperature,pH,common anions,natural organic matter and the presence of seven standard ore layers were explored in the hydrogen peroxide stability experiment.Research indicated:The temperature increased from 4℃to 70℃,and the decomposition rate of H₂O₂ gradually increased.The pH value had a significant effect on the stability of H₂O₂.Alkaline accelerated the self-decomposition reaction,and the decomposition rate was the maximum at pH=11.0-11.5.HCO₃^-,CO₃^2-and PO₄^3-promoted the decomposition of H₂O₂,and with the increase of ion concentration,the decomposition rate further accelerated.Humic acid and fulvic acid slightly enhanced the decomposition rate of H₂O₂ compared with self-decomposition under the same conditions at pH=11.5.The influence of seven standard ore layers on the decomposition of H₂O₂ was more severe.The effects were sorted as follows:manganese（high MnO₂）>manganese（low MnO₂）>copper ore>hematite>ilmenite>magnesite>alumina.The effects of pH,characteristic cations,and four clay minerals were explored in the stability experiments of calcium peroxide.Research indicated:Under slightly acidic（pH=6）and neutral（pH=7）environmental conditions,CaO₂ reacted with H₂O to form H₂O₂ and O₂ simultaneously.After the reaction had progressed to a certain extent,it decomposed into a plateau phase.The production of H₂O₂ and O₂ no longer increased,and the total peroxygen bond concentration in the solution no longer decreased.When the pH value rose from slightly acidic（pH=6）to slightly alkaline（pH=8）,it affected the post-platform change of the CaO₂ decomposition reaction.After slightly alkaline conditions,the H₂O₂ production decreased and the O₂ production increased.The addition of Fe²⁺and Co²⁺affected the decomposition of CaO₂.Adding red clay,calcite,montmorillonite and maifan stone didn’t change the decomposition mode of CaO₂,but had different effects on the formation rate and yield of H₂O₂ and O₂ products.The effects of pH,common anions,seven common soils and seven standard ore layers were explored in permanganate stability experiments.Research indicated:The pH and common anions didn’t affect the stability of KMnO₄.The order of the consumption of KMnO₄ by the seven common soils was Jilin black soil>Yunnan red soil=Shaanxi loess>Shandong farmland soil>Beijing fine sand soil>Inner Mongolia loess>Guangdong red soil,and the NOD value of each soil was different.No decomposition of KMnO₄ had been observed for the seven standard ore layers that had been put in place.The effects of pH,common anions,seven common soils and seven standard ore layers were explored in persulfate stability experiments.Research indicated:pH and common anions did not substantially decompose PS.Except for Jilin black soil,the decomposition of other seven kinds of ordinary soils was not obvious for the time being.The input of seven standard ore layers also had a small impact on the stability of PS.