The Study Of Groundwater Trichloroethylene Remediation In Siderite Catalyzed Hydrogen Peroxide And Persulfate System

Trichlorethylene （TCE） is a potential carcinogenic, teratogenic, mutagenicvolatile chlorinated organic pollutant. It is widely used as a metals degreasing, fabricsdry cleaning agent, and intermediates in organic synthesis. As a dense non-aqueousphase liquid （DNAPL） with low water solubility, TCE dissolves into the aquifer alongwith the flow of groundwater, and cause secondary pollution.Using catalyzed hydrogen peroxide （H₂O₂） and persulfate process to remediategroundwater contamination is a very potential in situ chemical oxidation technique. Itis a effective means of groundwater remediation, and it can overcome the drawbacksof both the rapidly decomposes of H₂O₂of traditional Fenton-like method and the toostable of persulfate to react with the target contaminants’ problem. Since the reactionmechanism of H₂O₂and persulfate catalyzed by iron minerals systems are poorlyunderstood, so this study is trying to determine some new mechanistic clues aboutsiderite catalyzed hydrogen peroxide and persulfate method. The main research resultsare as follows.The iron ions dissolved from siderite played an important role in the catalyticactivity. And the higher the dissolved iron ions concentration, the better catalyticeffect can obtain. However, iron ions could likely scavenge hydroxyl radicals （HO·）and sulfate radicals （SO₄^-·）, which affected the removal rate of TCE when theconcentration of iron ions was too high.HO· and SO₄^-· were considered to be two effective radicals in the system, andHO· was the main effective radicals for oxidizing TCE. The addition of persulfateslowed the decomposition of H₂O₂. Persulfate has two effects on the system. First ofall, it was lower the pH of the system, and enhance the usage of H₂O₂. Secondly, itcould produce SO₄^-· to participate in the oxidation reaction. A higher temperaturecould enhance the spontaneous degree of the reaction （ΔG could changed frompositive to negative when temperature increased）. The activation energy （Ea） is68.82 kJ/mol.Under catalytic conditions, the stimulation and proliferation of free radicals is thekey factor for the removal of TCE. Using benzoic acid as the radical capturer to detectHO·, the product p-hydroxybenzoic acid could continue react with the system, so it isnecessary to dectect the reaction rate of p-hydroxybenzoic acid with the system. Theformation of HO· followed the zero-order kinetics reaction. Part of the generatedSO₄^-· participated in the TCE removal, and the other part converted into HO·.Dichloroacetic acid and formic acid were generated as the by-product of thereaction. The rate of chlorine balance was about64.75%. The formation rate ofchloride ion followed the first-order kinetics reaction, which slightly less than theremoval rate of TCE. So there were other chlorinated products generated during thereaction.In catalyzed H₂O₂combined persulfate system, the generation of racal is morestable, and the oxidants can abtain a batter migration. The more radical generation, thebatter oxidants utilization, and high contamination removal efficiency maks thesiderite catalyzed hydrogen peroxide and persulfate method becoming a new andeffective remediation method for groundwater contamination.