Research On Preparation Of Ferrate (VI) And Its Properties In Decolorization Of Dyes Wastewater

Ferrate (Ⅵ) is an advanced oxidant, which with high selectivity, good flocculability, outstanding adsorbability and effective disinfection property. In recent years, there has been an increasing interest in ferrate (Ⅵ), due to its high potential in green organic synthesis, battery anode material and water treatment. So far, mass production of ferrate (Ⅵ) industrially is not available. Ferrate (Ⅵ) is still not widely used in various fields. Therefore, it's of great significance to study the preparation of ferrate (Ⅵ).In this dissertation, we reviewed the preparation, physicochemical properties, and quantitative analysis methods of ferrate (Ⅵ) as well as its application in organic oxidation, water treatment and anode material. Then, the purpose and significance of the presented work were introduced.In the second chapter of this dissertation, potassium ferrate was prepared through hypochlorite oxidation method. The influence of oxidation reaction time, model of sand-core funnel and purification times was investigated in detail. The results showed that reaction time has great effect on the yield of product. With too short time, ferric nitrate can not be completely oxidized by potassium hypochlorite. While with an extreme long reaction time, the generated ferrate (Ⅵ) will decompose. The optimum reaction time is 90 min. As for the model of sand-core funnel, funnel with big pore size can't completely remove the by-products, which mainly in the form of Fe (Ⅲ) compounds. However, a funnel with small pore size will lead to the decomposition of ferrate (Ⅵ) because of too slowly filtration process. The optimum funnel for filtration is G3 sand core funnel. High purity of potassium ferrate (Ⅵ) can be obtained through three times of purification. After the reaction, by-products, organic lotion, and liquid waste should be recycled. Analytical conditions of chromite titration were also investigated in this chapter. Better results can be obtained with chromite titration rather than arsenate titration, and the toxicity of chromite titration is much lower, too. To reduce the titration error, the test samples should be pre-treated with a grinder firstly to make them fully dissolved before titration. During the titration process, alkaline chromite solution should be prepared with saturated alkaline solution to ensure the accuracy of test results. Mixture of sulfuric phosphoric acid is essential because it can reduce the redox potential of Fe3+/Fe2+and prevent the interference of Fe3+ions. The volume of sulfuric acid will affect the reaction during titration process. For example, the concentration of sulfuric is 10 mol/L, the required volume of sulfuric will be more than 63.6 mL.In the third chapter of this dissertation, sodium peroxide and iron oxide were used as raw materials to produce ferrate (VI) by thermo-chemical oxidation method. The influence of reactor material, shielding gas, reaction temperature, Na/Fe molar ratio, reaction time and heating rate on the yield of potassium ferrate were investigated. The optimum reaction conditions are as flow: reactor is stainless steel tube; shielding gas is O2; Na/Fe molar ratio is 6.0; calcination temperature is 700℃; reaction time is 1 h; heating rate is 6℃/min. Under these optimum conditions, the purity of sodium ferrate was 39.78%. In this chapter, potassium ferrate prepared by thermochemical oxidation method were characterized and analyzed by chromite titration, ICP, XPS, XRD, FT-IR, UV/VIS, TG-DTG and SEM. The results showed that the composition of the product potassium ferrate was K2FeO4, which had a orthorhombic unit cell structure with the same space group Pnma and its cell parameters were calculated as a= 0.7722 nm, b= 1.0363 nm and c= 0.5885 nm. The purity of the synthesized K2FeO4 was determined as high as 98.7% after purification. The K2FeO4 crystals are plump, columnar and have obvious cone-shape growth surface at the two ends of the crystalline grains.In the forth chapter, potassium ferrate was used as a water treatment agent to decolor seven kinds of simulated azo-dye effluent. The decoloration rate of dye effluent and the structure change reflected by UV/VIS spectra were used to evaluate the effect of various conditions on the decoloration of azo-dye by potassium ferrrate. The results indicated that initial pH value, the amount of potassium ferrate, reaction time, dye concentration and the molecular structure of azo-dye had great effect on the decoloration.In the fifth chapter, potassium ferrate was used to decolor Direct Fast Turquoise Blue GL. a typical metal-complex dye. A series of experiments were performed to study the effects of pH value, oxidant dose, reaction time, initial concentration of dye and temperature on the decoloration efficiency. The results showed that the optimum pH range for the decoloration was 4.0-6.0 because of the high redox potential and low decomposition rate of ferrate (Ⅵ) under this condition. The decoloration efficiency could be improved by increasing the loaded amount of potassium ferrate, which could increase the collision frequency between oxidants and dye. The oxidizability of potassium ferrate was so strong that the decoloration efficiency was obvious in the beginning of the reaction. Although the decoloration efficiency decreased with the increase of initial dye concentration, the actual decolored amount of the dye increased. The temperature had little effect on the decoloration, and a higher temperature was more favorable. From the UV-vis absorption spectrum during the decoloration process, we found that the residual absorbtion at visible light region declined dramatically, while the absorption at near ultraviolet region increased. It indicated that Cu-phthalocyanine macrocycle of Direct Fast Turquoise Blue GL is easily destroyed by potassium ferrate, and aromatic intermediates generate at the same time. In the decoloration process, it could also be found that the decoloration of the dyes undergoes a faster reaction than the mineralization. Thus, complete mineralization of Direct Fast Turquoise Blue GL can not be achieved under the oxidation by potassium ferrate.In the sixth chapter, preliminary study on the preparation of potassium ferrate by hydrogen peroxide method was conducted. By analyzing and comparing the UV/VIS spectra, we investigated various factors. The results showed that the iron sources, type of alkaline solution, charging sequence, preparation way of colloid, amount of colloid, amount of EDTA and concentration of alkaline solution had effect on the decolorization. The UV/VIS spectrum of ferrate (Ⅵ) obtained by hydrogen peroxide method was similar to the ferrate (Ⅵ) with high purity, which had maximum absorption at 500 nm and minimum absorption at 415 nm. In the preparation process, Fe(OH)3 colloid was chosen as the iron material and without dialysis. The volume of Fe(OH)3 colloid was 10～15 mL. To ensure the generation of ferrate (Ⅵ), EDTA must be added during the preparation. The concentration of NaOH solution should be less than 6 mol/L.