Study On Fenton Oxidation Mechanism And Degradation Characteristics Of Methyl Orange With Fenton Processes

The existence and the formation law of complex formed in Fenton oxidation reaction were investigated individually by UV-Visible spectrophotometer exclude the impact of substrate and ultraviolet in this paper,. The degradation characters of methyl orange were investigated in a self-designed cylindrical reactor with Fenton reagent.Firstly, Fenton oxidation mechanism was investigated in non-substrate homogeneous Fenton system. Absorbance of different concentrations of Fe2+, Fe3+and H2O2were investigated individually using UV-Visible spectrophotometer without separation of the substances. With the changes of UV-Vis spectra of the mixture of these three substances throughout the whole reaction, the law of complex formation was studied. The result showed that in addition to Fe3+, iron-based complex was found in Fenton reaction which exhibited a great absorbance across the range300～500nm, besides this complex concentration increased with the increase of Fenton’s reagents. Also, the relationship between the iron complex intermediate and Fe was equimolar. Furthermore, in addition to the iron-based complex mechanism, the hydroxyl radical mechanism also existed.Secondly, we select the azo dye methyl orange as our target compound, and its degradation in homogeneous Fenton system and the effects of pH value, H2O2dosage, the concentration of Fe2+were discussed. The results showed that at pH=3.0and the room temperature the high level97.74%of250mL20mg/L methyl orange decoloration was achieved only after2minutes when the dosage of H2O2was5.4846mmol/L, Fe2+was0.3mmol/L and H2O2/Fe2+molar ratio=18:1, while TOC removal rate was50.18%after120minutes. According to the kinetic analysis of methyl orange decoloration by different Fe2+and H2O2dosage, fist stage oxidation mechanism was mainly ferric complex oxidation, the final stage was mainly hydroxyl radical reaction, whereas the middle stage is a transitional one.In addition, natural light Fenton, UV/Fenton, dark Fenton and Fenton-like oxidation systems were studied in our self-designed cylindrical reactor by changing the light source and Fenton reagents. The results showed that Ultraviolet light is the effective light source to mineralize the substrate. Fenton-like reaction needed a delay period, and the occurrence of Fenton-like reaction mainly relied on the reduction of Fe3+by intermediates formed during the substrate degradation rather than simply relied on H2O2. Fenton reaction can only destroyed the azo chromophore quickly; however the pollutants had not been completely mineralized.