Study On Treatment Of Nitrobenzene Wastewater With Ti-based PbO₂ Electrode

Electro-catalytic oxidation technology is one kind of the advanced oxidation technology (AOP), it depredates the organic matter through the anodic reaction directly, or produces hydroxyl radicals, oxidants such as ozone to depredates the organic matter through the anodic reaction. The technology enables to decompose the organic matter more thoroughly and it is hard to produce the toxic intermediate. Therefore, it fixes the requirements of environmental protection. Especially, it can transform non-biodegradability of organic matter into biochemical degradation of organic matter, or it can transform harmful and toxic organic compounds into harmless and low toxicity ones. The technology has a good prospect of application in the pretreatment of depredating organic compounds in biological methods. It also has incomparable superiority such as simple operation, mild reaction conditions, ease of automation and without secondary pollution, thus, it has drawn great attention in the water sector in recent years. The key of the electro-catalytic oxidation technology is in finding and developing the anode material which has characteristics of high catalytic activity, good conductivity, corrosion resistance and long service life. Besides, reducing the cost of processing is also important, both of them are the research focus at home and abroad.The material of electrodes is one of the most important parts in electrochemical oxidation technology. The feasibility, velocity and the reaction degree of subsidiary reaction of organic substances that are oxidized or deoxidize on different electrode materials and catalyzed materials are different. Therefore, it is an important question for discussion to advance and improve performance of electrode material. Lead dioxide electrodes on Ti substrates were prepared by thermal-deposition and electro-deposition in this paper. Electro-catalytic characteristics of the electrodes prepared by two methods above were investigated through the degradation experiments of phenolic wastewater and the amount of hydroxyl radicals, and so the electrodes mingled with Bi or La prepared by electro-deposition were, and the effects of additives to electrode structure and catalytic characteristics were discussed through SEM and XRD. The experimental results showed that the surface of electrodes prepared by electro-deposition wasβ-PbO2.The additives can improve the micro-structure of electrode surface, reduce inner stress of plating layer, enhance catalytic activity, and make the crystals of the plating layer fine and symmetrical. The four electrodes all have good electro-catalytic characteristics, can reduce the voltage, and the electrochemical degradation of phenol follows one-step reaction dynamics. Electro-catalytic of electrodes prepared by electro-deposition were better than the electrodes prepared by thermal-deposition, and the electrode mingled with La was better than the electrode mingled nothing or with Bi. Electrochemical oxidation can be divided to direct electrochemical oxidation and indirect electrochemical oxidation according to the mechanism of degradation of phenol are different when the electrodes are prepared by different methods or with different additives. The improvement of electro-catalytic activity of electrodes makes the ability of direct electrochemical oxidation and indirect electrochemical oxidation strengthened and the degradation of phenol optimized. The theory on this need to be consummated more. For better use of PbO2-doped lanthanum electrodes in industrial wastewater treatment, the study further improved PbO2-doped lanthanum electrodes, increasing the surface area of the plate, and uses the improved electrode nitrobenzene wastewater treatment. By changing concentrations like the current intensity, nitrobenzene wastewater pH, electrode spacing and Concentration in water, the practicality of doped lanthanum electrodes wastewater treatment nitrobenzene can be tested by measuring the concentration of nitrobenzene in the electrolytic process of and the change of COD, then it can draw conclusions. From the wastewater treatment costs and the life of electrodes, the current experiment used the intensity of 7 A; it can not formats OH efficiently in acidic conditions, the reduction products such as nitrobenzene have been restrained under alkaline conditions ,therefore, the electrolysis efficiency of nitrobenzene has highest efficiency under neutral conditions. Appropriate plate spacing is favorable for nitrobenzene electrolysis, the efficiency of the degradation of nitrobenzene will be affected by too small or too much plate spacing. Under certain circumstance of current intensity, the produce of OH ? is certain in the unit time. When the entering water concentration is lower, the processing is inefficient because there is OH surplus. When the entering water concentration is higher, the processing is also inefficient because there is not enough OH for Organic oxidation treatment. Therefore, only when the concentration of water is moderate, electrode can play the greatest effectiveness.There is strong connection between the water warming and the current intensity. The stronger the intensity of current , the sooner the warm of the water electrolysis, and the higher the water temperature. And pH, electrode spacing and concentration of entering water do not impact deeply on the water temperature increasing. Electrode coating is connected with the strength of electric current and pH, and the strength of electric current has larger influence. When the current intensity is stronger, the loss of electrode coating is performed earlier, and the shedding area of coating is larger. Under alkaline and neutral conditions, the loss of electrode coating are performed later than that in acidic condition, but the shedding area of coating are basically the same under the conditions. The plate spacing and the entering water concentration has little impact on the performing time of loss phenomenon of electrode coating and shedding area of coating.