The Study On Decolorization Of Crystal Violet By Green Rust

At present the method of Fenton oxidation and the method of Fenton-like oxidation have many advantages and have made significant progresses in many methods of disposing the dye wastewater, but they are generally carried out at low pH and use visible light little, even H₂O₂ should be put into the system in some methods, so they have some limitations in the practical application.Therefore,seeking low-cost and efficient methods of disposing the dye wastewater is concerned.The thesis simulate the Fenton-like reaction, make the Fe (â…¡) -EDTA system as the basic system at near neutral pH, use the visible light during the reaction, because of the generation of the high active intermediate material during the reaction ,we can use them to degrade some organic dyes, find the optimal conditions of the degradation by changing the temperature,the light intensity,the initial pH of the system, and make a preliminary study of the reaction mechanism, it will be momentous current significance in dealing with the dye wastewater.The main researches of the thesis are as follows:1. Study the impact factors of the decolorization of crystal violet, study the influence of crystal violet's decolorization rate by the concentration of EDTA, the initial pH, the light and other factors. Experiments show that reducing the concentration of EDTA system or the temperature of the system, reducing the light intensity, increasing the concentration of crystal violet or the initial pH can increase the decolorization rate of crystal violet, but reduce the reaction rate of the system. The system of adding the crystal violet after the pH adjustment and the system of adding the crystal violet before the pH adjustment, the former has smaller rate and bigger decolorization rate. The efficiencies of the oxidation of Fe (OH)₂ by air are different with monochromatic light of different wavelength, in a certain range of wavelength, the longer the wavelength the better catalytic efficiency, but it is bad to the decolorization of crystal violet. Different wavelength of monochromatic light can affect the phase and the pattern of the final products.2. Study the final products in different factors. Experiments show that in a certain range of temperature , the oxidative products of Fe (OH) 2 is the mixture ofα-FeOOH andγ-FeOOH without EDTA at pH=8;if the concentration of EDTA reaches a certain value, the oxidative products isγ-FeOOH.The oxidative products are the mixture ofα-FeOOH and Fe₃O₄ at pH=9.3.Adding a little inorganic complex NaH₂PO₄ to the system, study the influence of the sequence of adding NaH₂PO₄,the light intensity and the air flow to the reaction rate of the system and the decolorization rate of crystal violet. Experiments show that after adding NaH₂PO₄ ,it prolongs the existence time of Green Rust obviously , inhibites the formation of FeOOH, and increases the decolorization rate of the crystal violet. The system without NaH₂PO₄, the system of adding NaH₂PO₄ after adjusting pH , the system of adding NaH₂PO₄ before adjusting pH, the reaction time increases in turn, and the decolorization rate of the crystal violet also increases.After adding NaH₂PO₄ to the system,γ-FeOOH has low crystalline.If increase the the light intensity or the air flow,the rate accelerates, but the decolorization rate of the crystal violet reduces.4. Make a preliminary study on the mechanisms about the decolorization of crystal violet. The results show that Green rust plays a decisive role in the process of crystal violet's decolorization,the longer the existent time of Green rust,the better the crystal violet's decolorization.The adsorption of Green rust to crystal violet is effect, only the crystal violet adsorbed by Green rust may be degraded, the electron transfer between Green rust and crystal violet occurs and make the conjugated system of crystal violet destroyed then crystal violet can be decolorized. The decolorization of the crystal violet experiences the adsorption,the degradation and the desorption. The strong oxidizing free radicals mainly accelerate the oxidation of Green rust, but degradate crystal violet little.γ-FeOOH of pure phase almost cannot adsorb and degradate crystal violet.