Study On Degradation Of Methyl Orange Solution With Iron Oxide Coated Sand In Fenton-fluidized Bed Process

Azo dyes waste water, which needs to be treated urgently, has characteristics with high chromatic, strong toxity, difficuly degradation and easy discomposion to carcinogenic aromatic amine under deoxidization condition.In recent years, advanced oxidation processes (AOPs) have been widely applied to deal with azo dye wastewater by the generation of highly oxidative hydroxyl radicals (?OH) in the homogeneous or heterogeneous phase. However, ferrous which act as catalysts are dissolved in water in the homogeneous Fenton process, the dosage of ferrous is very high, and produce a lot of chemical sludge. This obviously leads to more cost as well as secondary pollution, thus limiting its industrial application.According to the problems above, this study focused on the treatment of Methyl Orange (MO) wastewater with azo structures, developed the new type of heterogeneous Fenton-Fluidized Bed process. The experimental results indicate that under the following experimental conditions: 400mg/L of MO solution, pH of 3, room temperature, H₂O₂ of 10mM and the molar ratio of H₂O₂ to Fe²⁺ at the range from 10 to 15, 84% decoloration and 51.2% TOC removal could be achieved in 30 min. During the beginning of the reaction in the heterogeneous Fenton-Fluidized Bed process, the decreasing rate of ferrous has reached to 40%, which helps to reduce the cost of iron sludge treatment. The experiments also showed that a better result was obtained though adding the Fe²⁺ into the process separately. While in the FBR- Fenton process, with the alternative iron source instead of Fe²⁺, the operation problems from separate adding procedures can be eliminated. Also, there are other advantages, such as reducing the ferric, ferrous sludge in the end of the reaction. With the increasing of the iron chips dosage, the ferrous will reach to the climax, where the ferrous increases slowly.A new type of catalyzed carrier- iron oxide coated sand was made using in this study. The catalyzed carrier of iron oxide coated sand was characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectra analysis (FTIR) methods. It was found that the pore diameter, and the particle aperture of the iron oxide coated sand were about 100nm, 2～9nm separately. The BET special surface area of the coated sand was 4 times that of uncoated sand. The dominated phase of iron oxide on coated sand was FeOOH. It also showed that hydroxy-Fe with low polymerization degree intercalated into the interlamination of raw quartz sand successfully. The stability of the coated sand was evaluated through repeated test. The results showed that with pH of 3.0⁴.0, H₂O₂ of 10mmol/L, coated sand dosage of 40g/L, and lower Fe²⁺ dosage of 0.2mmol/L, 97.5 % discoloration of MO was achieved under visible irradiation after 100 min treatment. Furthermore, decoloration efficiency was still higher than 70% after the coated sand being used for 5 cycles. Hence, it has demonstrated that the iron oxide coated sand can be successfully used in the Fenton-Fluidized Bed process for AOP wastewater treatment.Comparing the treatment of the MO solution through the different reaction processes, it can be found that the sequence is as following: the iron oxide coated sand Fenton-Fluidized Bed process > the iron chips-Fenton-Fluidized Bed process > the Fenton-Fluidized Bed process > the iron chips -Fenton process > the traditional homogeneous Fenton process. From the experiments this new type of heterogeneous Fenton-Fluidized Bed process is promising in future industrial application.