| Water resources are the physical infrastructure for human survival and development. However, at the same time, water pollution problem has become increasingly serious, which poses a serious threat to human healthand exacerbated the shortage of water resources.Dye wastewater emissions have serious impact on the environment. It not only has high toxicity, but also hasa certain degree carcinogenic. Its presence will seriously affect the growth of aquatic organisms and then affect human health. Therefore, development of efficient water treatment technology for ease water crisis and improvementof the living environment are of great significance.Advanced oxidation technologies have been widely used in the treatment of refractory organic compounds in water. The heterogeneous Fenton is developed on the basis of Fenton advanced oxidation technology. There are obvious flaws in the Fenton system with extensive research on homogeneous Fenton oxidation technology. For example, a large number of iron sludge produced after the reaction was terminatedunder acidic reaction conditions, which increases the difficulty of sludge treatment,Apart from that, the presence of Fe3+ increases the wastewater effluent color and then forms a secondary pollutio.A lot of researchers have prepared a solid catalyst through fixed iron source involved ona particular carrier in the reaction, which not only retains the efficiency of homogeneous Fenton oxidation method, but also overcomes the shortcomings of homogeneous Fenton oxidation.Therefore, the selection of carrier materialswhich canwithstand hydroxyl radicals and improve the catalytic activity in the heterogeneous Fenton catalytic oxidation systemcould be an important research direction in non-homogeneous catalytic materials Fenton.In this thesis, aiming at the existing technology problemsof homogeneous Fenton oxidation, diatomite with the characteristicsof light, porous, strong adsorption capacity and high specific surface area was chosen as a carrier of heterogeneous Fenton catalytic material. After the diatomite was activated by acid and thermal treatment, two kinds of the diatomite-based heterogeneous Fenton catalysts had been synthesized through precipitation method.The structural characterization of products wereanalyzedby using XRD, FESEM, FT-IR, XPS, BET and exploredthe best preparation conditions of diatomite composites, while testedthe catalytic properties of the catalyst through discoloring Rhodamine B dye from waste water. The effects of pH, catalyst dosage, H2O2 dosage, initial dye concentration and reaction temperature on the catalytic oxidation rates of dye wastewater were discussed.The innovations of this paper were as follows:(1) Diatomite with the characteristicsof light, porous, strong adsorption capacity and high specific surface area was chosen as a carrier.A novel heterogeneous Fenton catalytic materials had been diatomaceous successfully prepared using the precipitation method which loading the Fe2O3 particles onto the surface of diatomite. It had opened up a new direction of using diatomite as heterogeneous Fenton catalyst carrierin the field of dye wastewater treatment.(2) A novel two-component heterogeneous Fenton catalytic material had been developed with the induction of Fe2O3 and MnO2 on the basis ofthe preparation of diatomite supported Fe2O3 catalyst material.Synergistic catalytic effect can play a more efficient, rapid and stable catalytic performance. According to the propertiesof material structure and the experimental results of catalytic degradation, the synergistic catalytic mechanism was explored, which provides new ideas for the heterogeneous Fenton technology in the treatment of dye wastewater.The conclusions about this thesis were as follows:(1) This paper studies the mineralogy of natural diatomite. The selected diatomite was camefrom Changbaiin Jilin province. The composition of diatomite (SiO2 83.70% wt.%, Al2O3 7.97 wt.%, Fe2O3 2.22% wt.%). And the main impurities were muscovite, hematite and organic matter. FESEM was used to observe the morphology of diatomite. The diatom algae of diatomite contained based housing for the disc and a small amount of Melosira. The diatom shell were intact substantially and there were a large number of pores which size were 0.1-0.5 μm on the shell surface. However, a large number of mineral impurities adhered around diatom shell and a little of impurities clogged the surface of the shell channel.(2) In the light of the impurities and structure defects of natural diatomite. The natural diatomitewas calcined and acid leached for the purification and surface activation. The content of SiO2 was 92.06% after purification and Muscovite, hematite minerals and other impurities had been successfully separated. The surface of diatom shell wasclean and pore structure was much clearer, which showed a large number of channels neatly arranged. The channels of diatomite were dredged through purification and surface activation, which increased the number of internal pore size and activity of adsorption sites, hence enhancedthe surfactant diatom shell. It was more favorableto the adsorption properties of dye molecules. Effects of calcination temperature and acid concentration on the structure, morphology and surface properties of natural diatomitewere studied.It was obtained that the majority of organic matter in diatomite was burned when the calcination temperature reached 450 ℃. While the diatom shell was basically intact disc morphology after burning and its structure did not be destroyed. The mineral impurities covering the pores and surface of the diatom shells were removed and parts of the larger pore orifices were dissolved. The pore volume of diatomite reached 0.135 mL/g. The diatomite was treated with different concentrations of HCl solution and the remove effects of Al2O3 and Fe2O3were obvious. The dissolution rate of Al2O3 was 69.26% as well as Fe2O3 was 27.07% when the HCl solution concentration was 20%. The impurities on diatom shell surface could be thoroughly removed, pore structure had been significantly improved, the pore size was increased to 0.3～0.5μm, surface area of diatomite reached 36.56 m2/g.(3) A novel heterogeneous Fenton compositethat Fe2O3 loaded on the surface was prepared through precipitation method. The result of XRD demonstrated that the load of Fe2O3 did not change the skeleton structure of diatomite and Fe2O3 intensive grown in diatomite wall as the form of amorphous. The results of FESEM were as following:The pore structure of diatomiteloaded with Fe2O3 was not changed. The Fe2O3 particles were tandem grown on the surface ofthe diatom shell, which pointed mainly around the channels and was not found to be clogged pores. The pore size could still maintain 400 nm.The interface of Fe2O3 particle was clear with only a small amount of reunion. The particle size is about 50 nm. The analysis results of FI-IR and XPS showed the valence of Fe in Fe2O3 loaded on the surface was +3 and Fe2O3 particles on the surface of diatomite were held together by Si-O-Fe bond rather than by adsorption on the surface of diatomite.(4) The effects of diatomite loaded Fe2O3 composite material were discussed. The microscopic changes in the structure of the diatomite with loading Fe2O3 composites through changing prepare conditions. The degrade performance in Rhodamine B dye wastewater of diatomite with loading Fe2O3 composites were detected under different preparation conditions. The best preparation condition was molar concentration of Fe3+ was 0.02 mol/L, the additional molar concentration of NaOH was 0.06 mol/L, calcination temperature was 450℃.(5) The degradation performance of Rhodamine B dye by diatomite load Fe2O3 composites was detected. The results showed that the decolorization rate of Rhodamine B had reached 98.33% and TOC removal rate reached 74.91% after the reaction 120 min when diatomite loaded Fe2O3 catalyst and H2O2 were added with the light. The decolorization rate of Rhodamine B by using natural diatomite was 37.22% and TOC removal rate was less than 5% at the same experimental conditions. It was described that Fe2O3 loaded on diatomite surface played an important catalytic role indegradation of Rhodamine B. The best degradation of Rhodamine B solution optimal reaction conditions had been got by changing the reaction conditions of heterogeneous Fenton reaction system. The decolorization rate of diatomite loaded Fe2O3 composite was 98.33% when the initial concentration of Rhodamine B solution was 50.0 mg/L, solution pH was not adjusted, dosage of catalyst was 0.10 g/L, dosage of H2O2 was 5.0 mmol/L and the reaction temperature was 25 ℃.(6) It was a disadvantage that degradation of Rhodamine B by diatomite loaded Fe2O3 compositeshad taken a long time. A new heterogeneous Fenton composite had been prepared by co-precipitation method on the basis of the preparation of diatomite loaded Fe2O3 composites. and MnO2 particles were existed in the form of amorphous in diatomite loaded composites. Fe2O3 particles are more dispersed growth on diatom shell surface without agglomeration. The pores of diatom shell surface were not blocked and the aperture could still maintain about 400 nm. MnO2 particles were spherical and grain boundaries and their diameter were about 300 nm, which scattered primarily in the form of adsorption at the surface of the diatom shell. The results of FI-IR and XPS showed that the valence of Mn was +4 in diatomite loaded Fe2O3/MnO2 composites, MnO2 particles were held together by adsorption with diatomite. There was no chemical bonding with diatomite.(7) The microscopic changes in the structure of diatomite loaded Fe2O3/MnO2 compositesby changing the diatomite loaded Fe2O3/MnO2 composites preparation conditions. The Rhodamine B dye degradation in wastewater properties of the diatomite loaded Fe2O3/MnO2 composites was detected with different preparation conditions. The optimum conditions for the preparation of diatomite loaded Fe2O3/MnO2 composites were determined ultimately. The addition ofFe3+ molar concentration was 0.02 mol/L and the molar concentration of Mn2+was 0.01 mol/L, the calcination temperature was 450℃.(8) The degradation performance of Rhodamine B dye by diatomite loaded Fe2O3/MnO2 composites was observed. By comparing the degradation of Rhodamine By using two diatomite-based heterogeneous Fenton compositematerials, diatomite supported Fe2O3/MnO2 catalyst and H2O2 were added in the light of conditions. The decolorizing rate of Rhodamine B by using diatomite loaded Fe2O3/MnO2 composites was faster than using diatomite loaded Fe2O3composites under addition diatomite load Fe2O3/MnO2 catalyst and H2O2 in the light.The reaction time required only 80 min and the decolorization rate had reached 99.23%, which illustrated that diatomite loaded Fe2O3/MnO2 composite materialswere highly heterogeneous Fenton catalysts. The best degradation of Rhodamine B conditions by using diatomite loaded Fe2O3/MnO2 catalyst with changing the heterogeneous Fenton reaction conditions were as following:the decolorization rate of Rhodamine B by using diatomite load Fe2O3/MnO2 composite was 99.23% when the initial concentration of Rhodamine B solution was 50.0 mg/L, solution pH was not adjusted, dosage of catalyst was 0.10 g/L, dosage of H2O3 was 5.0 mmol/L and the reaction temperature was 25℃.The research results indicated that diatomite as a heterogeneous Fenton carrier of catalytic materials not only give full play to the excellent performance of natural mineral materials, but also combining with the senior Fenton oxidation technology. It plays a positive role to promote water pollution governance and has good prospects for development. In addition, it’s one of the effective ways to solve the problem of water pollution of the environment, which have the value for further research. |
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