Fenton-like Process Of Sponge Iron/O₂ System And Degradation Of Refractory Organic Compounds （A Case Study Of Aniline）

The first field application of Zero-valent iron ZVI in permeable reactive barrier（PRB） technology for in situ-remediation of groundwater contaminated. Due to the success of the Fe⁰-based PRB, ZVI technology gained considerable attention on water treatment. Zero valent iron own strong ability of reduction so that ZVI has been extensively applied for the remediation or treatment of groundwater and wastewater contaminated with halogenated organics, nitroaromatics, heavy metals and various oxyanions including arsenate, nitrate, chromate, bromates. With the rapid development of industry and agriculture, the contamination that is emitted during the production process leaded to water pollution increased. Groundwater and surface water receive toxic and harmful organic pollution is becoming more and more complex. Single zero valent iron system due to its own constraints is not sufficient to repair polluted surface water and groundwater. Therefore, it is necessary to improve and strengthen the treatment ability of zero valent iron system.In recent years, many countries have been studying further on ZVI system. Several studies reported that the presence of oxygen in certain concentration could enhance the contaminants sequestration by ZVI remarkably while the presence of excessive oxygen definitely would inhibit the removal of contaminants by ZVI. That is under acidic conditions, Fe⁰（s） reacts with oxygen to produce hydrogen peroxide and ferrous iron, H₂O₂ ultimately reacts with ferrous iron via the Fenton reaction to produce an oxidizing intermediate, such as hydroxyl radical and other reactive oxygen species, which then reacts with the contaminant of interest. This process based on the theory of Fenton, and it was considered that Fenton like reaction. In addition, add metal materials or chemicals（such as aluminum, nickel; Organic ligands-Oxalate, EDTA, etc.） to the Fe⁰/O₂ system can further strengthen the system ability of produces reactive oxygen species and increase the reaction rate.This experiment uses a new type water treatment materials-sponge iron, by constructing sponge iron/O₂ system, and adding acid-sodium acetate buffer solution as organic ligands, and pH control agent at the same time. Studying the factors influencing the ability of the sponge iron/O₂ system Fenton-like reaction, through Single factor analysis, orthogonal test variance analysis, master the influence degree of each factor, and the optimization of response surface can find the optimum factor combination of sponge iron/O₂ system produce maximum yield of reactive oxidative species. Degradation of Aniline Wastewater from the optimum combination. At the same time, studying the transformation of different forms of nitrogen in the sponge iron/O₂ system is made to further explain the law of the redox of the system, and put forward a new solution for the restoration of nitrogen pollution in the water environment. In addition, research on the Fenton like reaction occurred in the Oxygen and different metal materials and the comparison of the degradation of aniline with iron. All the studies provide a theoretical support for future research. The main results of the study are showed as follows:（1）When the initial was pH=4, the yield of reactive oxidative species that were produced by sponge iron/O₂ system reach at maximum, while the yield of Fe²⁺ was the largest when pH=3. At initial pH < 7, the amount of generation of reactive oxygen species in Sponge iron/ O₂ system indicated that acidic conditions were more conducive to the occurrence of Fenton like reaction of Fe⁰/O₂ system; dosage was bigger, larger yield of Fe²⁺, H₂O₂ and ·OH in sponge iron/O₂ system, when the dosage was 120g/L, the yield of Fe2, H₂O₂ and ·OH reached the maximum; with the increase of the grain size, the yield of reactive oxygen species（H₂O₂ and ·OH） and the amount of Fe²⁺ decreased. Small size sponge iron particle own larger specific surface area, with oxygen and H+ contact area larger, more conducive to the reaction; when reaction at 120 min, the concentration of H₂O₂ and Fe²⁺ in the oxygen aeration system reached maximum value, whereas the yield of H₂O₂ and Fe²⁺ at 60 minutes in stirring aeration system reach the maximum. The yield of H₂O₂ and Fe²⁺: aeration > mixing aeration; yield of ·OH: aeration stirring > aeration; the yield of H₂O₂ and ·OH fluctuated with the increase of stirring speed, but in the speed R=110r/min reached a maximum value. The yield of Fe²⁺ increased with the increased of the stirring speed;（2）The variance analysis of orthogonal test shows that the initial pH is the most influential factors among the four factors（initial pH value, particle size, dosage and rotational speed） for the yields of Fe²⁺, H₂O₂ and ·OH produced by the sponge iron/O₂ system.（3） Response Surface Methodology adopted BBD model. Initial pH, dosage, stirring speed as factor, yields of H₂O₂ and ·OH as response value, to obtain the response surface quadratic equation model significant. Model is accurate and reliable. The order of the 3 factors on the system of the impact of the yield of H₂O₂: pH > Dosage > Stirring speed; the system generated and the amount of ·OH is significantly affected by the order: Dosage > Stirring speed > pH. The response surface fitting was obtained by the sponge iron /O₂ system to produce the reactive oxygen species（H₂O₂, ·OH） to achieve the best combination of factors: pH=3.92, sponge iron dosage（g/L） =118.76, Stirring speed（r/min） =113.55.（4） The ability of sponge iron and Oxygen system has a stronger degradation of aniline. The system is the use of zero valent iron strong reduction, and use of the zero valent iron O₂ system of Fenton like reaction of oxidizing substances at the same time of the target pollutants degradation; in the high concentration aniline group, the concentration of aniline and sponge iron O₂ system degradation ability showed positive correlation, the higher the concentration of aniline, the faster the degradation rate of the system; in the low concentration aniline group, the lower the concentration of aniline, the degradation rate of the system faster.（5） The capacity of the sponge iron/O₂ system degraded the pollutant is stronger than the cast iron /O₂ system, reflect the superiority of the sponge iron materials; system of Fe⁰ /O₂ will depend on the nature of the pollutant, system to adjust itself to the oxidation reduction, to removal of pollutants better. Both oxidizing and reducing the Fe⁰/O₂ system had; nitrate as electron acceptor its ability is stronger than O₂ to compete for electronic;（6）Sponge iron, copper, high carbon steel, cast iron, manganese steel, aluminum, titanium reacted with O₂ under the condition of aeration experiment, in addition to copper, several other metals can be reacted with O₂ and then occurred Fenton reaction; the yield of H₂O₂ by metal/O₂ system from big to small order: C sponge iron>Chigh carbon steel > C manganese steel > CFe/C > C cast iron > Caluminum >Ctitanium >Ccopper; the yield of ·OH in descending order: A sponge iron >A cast iron =A aluminum>A high carbon steel >A manganese steel > AFe/C > A titanium > Acopper. Sponge iron, cast iron, Fe/C, high carbon steel, manganese steel, under the condition of aeration, degradation of aniline wastewater, the removal rate of reactor to aniline in descending order: ρsponge iron=ρFe/C>ρcast iron >ρhigh carbon steel>ρmanganese steel;Sponge iron /O₂ system in acid-sodium acetate as organic ligands and pH regulator, can occur Fenton-like reaction, this system in acidic conditions has good removal effect on aniline. The system possesses strong oxidation and reduction properties and has a broad prospect in the repair of hard degradation organic pollution of surface water or groundwater.