| Environment pollution caused by dye wastewater is becoming progressively serious in recent years. In China, the total discharge of dye wastewaters per day exceeds 4×106 m3. Generally speaking, dye wastewaters are characterized of high concentration of organic matter, high chroma, high salinity, complex compounds, low biodegradability, and contain many organic compounds which are toxic to microbes. Mn (hydro)oxides, which have large surface area, low pHzpc, high surface activity and high reducing potential, are distributed widely in natural environments, such as soils and sediments. It may play a key role in degradation and mineralization of a lot of organic contaminants such as phenol, aniline, aliphatic amine, aromatic amine and heterocyclic N-organism. Therefore, Mn (hydro)oxides significantly affect the concentration and species of organic matters in soil and aquatic systems.The thesis consists of two parts:(1) The presence of Mn (hydro)oxides is mainly in two forms in the nature. In areas rich in iron and manganese, Mn (hydro)oxides exist as granule. In most sediments and soils, Mn (hydro)oxides exist as coating on clay minerals, because, under anoxic conditions, Mn(II) is readily adsorbed on negatively charged surfaces such as clay particles (especially montmorillonite), then is oxidized to Mn (hydro)oxides coating on clay minerals. The coating may cause significant variation in surface properties of clay particles. Also the surface chemistry of Mn (hydro) oxide coating differs greatly from those of pure Mn (hydro)oxides. To date, investigations on Mn (hydro)oxide coating are rare. In this thesis, the method proposed by Boonfueng (2005) is used for synthesis ofδ-MnO2 andδ-MnO2- montmorillonite complexes (FHT). In simulated acidic conditions (pH = 4.0~5.5), contributions of absorption and oxidation ofδ-MnO2 in the form of granule and coating to MB decolorization are evaluated, respectively; effects of Mn content in the FHT, the solution pH and the presence of humic acid on MB decolorization are investigated. The results show that heterogeneous oxidations on the surfaces ofδ-MnO2 are the main mechanism for MB decolorization, and surface absorption is an important process for following oxidation degradation. As for decolorization ratios of MB, the capacities of two forms ofδ-MnO2-granule and coating-to degrade MB are similar, and the former is slightly lower than the latter. The MB decolorization ratio increases with increasing Mn amount and decreasing pH. As for the total MB decolorization, the contribution from absorption mechanism increases with an increase in pH. However, the contribution from oxidation mechanism decreases with an increase in pH. When pH is at the range between 4.0 and 5.5, HA coats FHT in a form of organic film, which can improve the decolorization ratio of MB through both absorption and partitioning mechanisms.(2) The content of Mn (hydro)oxides in Fe-Mn nodules is high. Fe-Mn nodules and their residues after extraction of valuable metals are found to be good adsorbents for a number of pollutants such as Zn2+, Pb2+, Ni2+, phosphate and selenite, and thus can be used in wastewater treatment. But few researches on application of Fe-Mn nodules as an effective oxidant for degradation of organic contaminants in water treatment are arried out. Manganese oxides are powerful oxidizers as well as scavengers for many inorganic and organic compounds. Fe-Mn nodules collected from the East Pacific Ocean are used for decolorization of MB in a batch system. Factors influencing MB decolorization are also evaluated. The results show that heterogeneous oxidations on the surfaces of Fe-Mn nodules are the main mechanism for MB decolorization. In typical concentration range of dye wastewaters (10~50 mg·L-1), Fe-Mn nodules can be used as an effective material for MB wastewater treatments. The percentage of MB decolorization is enhanced rapidly with increasing loading and decreasing particle size of Fe-Mn nodules, as well as decreasing MB concentration. A high degree of MB mineralization can be obtained at an optimal condition, but usually lower than that of MB decolorization. pH exerted effects on MB decolorization by influencing both the formation of surface precursor complex and redox potential of the system. At pH <4.0, MB decolorization increases with a decrease in pH, while pH at the range between 4.0 and 10.0 exerts only limited effect on MB decolorization. In a consecutive reuse system, Mn2+ accumulation due to reductive dissolution of Mn oxides, and pH increase due to H+ consumption are probably two important factors causing a decrease in MB decolorization with time.The results of the thesis showed that there is good development foreground for the application of Mn (hydro)oxides on the dye wastewater treatments.
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