| At present, Several studies have reported that there are numerously commercially available dyes with an estimated annual production of over 7× 105 tons of dye-stuff. The pollutants in these effluents include high concentrations of organic matter, salts and color. What’s worse, dye effluents contain chemicals that are refractory, toxic, carcinogenic, mutagenic or teratogenic, which makes it result in being one of the most difficult to treating industrial wastewaters in our country. Traditional physico-chemical treatments applied to the purification of dyeing wastewaters cannot lead to ideally effective degradation. On the other hand, the attribute of coloring matter with high toxicity and salinity discourages the application of biological methods. So study on removing dyes from water by environmentally friendly electrochemical oxidation method that can use the high salt content of dye-stuff has become a important subject. It plays an important role in theoretical and practical dyeing wastewater treatment to exploring the products of electrochemical oxidation degradation and course of dye molecules.The study focuses on the the problems of the degradation efficiency existing in the electrochemical oxidation treatment for azo dyes and anthraquinone dyes wastewater containing chlorine salt. In this case, electrochemical oxidation degradation of single or mixed dyes was studied by utilizing Ti/RuO2-IrO2-SnO2 anode, which tested methyl orange, acid red 3R, direct dark brown and reactive brilliant blue X-BR as experimental subjects. Among those control parameters, current density, pH, plate spacing on the effects of the electrochemical oxidation degradation had received great attention. On the other hand, characteristics of the surface of the plate electrode and the behaviors of electrochemical oxidation had also been characterized. The qualitative analysis to the products of electrochemical oxidation degradation had be carried on by ultraviolet-visible spectrophotometry, fourier infrared Spectrophotometric method, three dimensional fluorescence spectrometry, and liquid chromatography-mass spectrometry technology. Hence, the conclusion is as follows.Current density has a greater influence on the electrochemical oxidation degradation of dyes. The difference of current density may lead to the different intermediates produced by electrolysis, and the optimum current condition of methyl orange and acid red 3R are confirmed of 50mA/cm2 and 25mA/cm2. In contrast, the effect of the initial solution pH value and the plate spacing on electrochemical oxidation degradation is relatively small, and best electrode spacing is 2cm. The special DSA electrode with flat surface and firm crystal, has good load performance, stability, as well as special feature of choosing chlorine. DSA electrode in the four kinds of dyes wastewater with is given priority to taking place anode chlorine evolution reaction. In addition, DSA anode in Methyl orange solution is existing both directly oxidation and indirect oxidation.The dates of pH value, chroma removal rate, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) of single dye by electrochemical oxidation degradation were measured for discovering the reaction mechanism and changing rule after determining the optimal process parameters. In the early stage of the reaction, the pH value change of the three kinds of azo dye is big, and in the last the pH value tends to pH of 8. Whereas the pH of anthraquinone dye reactive brilliant blue X-BR is continuously around 3. What’s more, pH value will affect the existence state of active chlorine, and the reaction reveal that the catalytic activity of "HClO" and "ClO-" is higher than that of "Cl2". As a result, the former got higher removal rate of COD and TOC. The decoloration of dyes by electrochemical oxidation is obvious. The dye structures are more simple, and dye color groups are more easily destroyed. Anthraquinones structure is more stable than conjugate system structure of benzene ring. The addition of low molecular organic acids to refractory organic compounds forms synergies, promoting the removal of refractory component, which proves that the reason of electrochemical oxidation reaction termination has excluded the degradation products such as oxalic acid.Finally, the paper analyzes the reaction mechanism and degradation products of azo dyes with different structures and anthraquinone dye, and then summarizes the degradation rule. The UV-Vis spectrum can infer that the biggest characteristic absorption peaks of dyes gradually reduce until disappear, then the appearance of a new characteristic peak, suggesting that a new degradation product generated. IR spectrum,3DEEM spectrum and quality spectrum figures further prove that unsaturated bond of dye molecular changes, so as to achieve the purpose of the decolorization. There are no fluorescence characteristic peaks at the beginning of the reaction of three kinds of azo dyes, because azo bond absorbed electron energy during fluorescence measurement. However, fluorescent positions (EX/EM:320-340nm/380-430nm) of degradation products remained unchanged in the reaction after 180min. The common fluorescence peak position of three kinds of azo dyes belongs to the visible fulvic acid area, showing high stabilization of degradation products, but reactive brilliant blue X-BR didn’t appear the fluorescent peak in the reaction. Electrochemical oxidation destroys the -N=N-bond of azo dyes and -C=N-C= bond of anthraquinone dyes easily. At the same time, the existence of the chloride ion inhibits the benzene ring opening. What’s more, naphthalene rings and anthraquinone structure are not easy to be broken by electrochemical oxidation. In addition, degradation products with stable structure are detected no chlorinated byproducts. In brief, Confirming intermediates and the reason of inhibition of chloride ion are still challenge. |
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