| Electroplating wastewater generated from the electroplating process, a kind of industrial hazardous materials, laden with various metal and heavy metal ions, such as iron(Fe), zinc(Zn), nickel(Ni) and chromium(Cr) etc., was also a potential valuable resource. It was an effective approach to synthesize ferrite for the reduction of electroplating wastewater as the heavy metal ions were trapped by the ferrite lattice and were more stable against leaching conditions.Firstly, to realize the aim of reuse, reduce and resource of co-treatement, the microwave hydrothermal synthesis of compound ferrite with electroplating wastewater, obtained from Shanghai Hazardous Waste Management Centre, and pickling waste liquor, obtained from Shanghai Second Steel Co., Ltd., was investigated. Response surface method(RSM) was used to investigate the effects of the three reaction conditions, including wastewater volume ratio, pH value and retention time, on the response functions and to determine the optimal conditions. The ferrite synthesized by microwave hydrothermal treatment had high saturation magnetization and was stable in pH range of TCLP, which not only detoxified the electroplating wastewater and pickling waste liquor, but also provided an available approach to the reuse of these two hazardous wastes.Secondly, factors on magnetic properties of ferrite were researched. The impacts of external factors on the grain growth and grain size on the magnetic properties were investigated by changing the temperature and retention time in the control of grain growth. The impact of temperature on grain growth was greater than that of retention time. The reason for the flash reaction velocity of microwave hydrothermal process could be owing to its flash rising temperature. On the other hand, elements Ni, Zn and Cr in electroplating wastewater played an important role in saturation magnetization. The location of Ni could be substituted by Zn, promoting the crystallization of ferrite. To some extent, Cr doping helped the distribution of trivalent ions to divalent ions. As molar ratio of Ni to Zn maintained from 1.5 to 4 and Cr to Me(Ⅲ) from 0.15 to 0.2, the metals in ferrite played a role in regulating ion ratio and prepared ferrite kept a high value of saturation magnetization.Finally, decolorization of malachite green by ferrite was investigated. The effects of ferrite types (Ni-Zn ferrite and Ni-Zn-Cr ferrite), ferrite dosage, initial concentration of malachite green and decolorization time on the decolorization rate were discussed. In the research of Ni-Zn ferrite and Ni-Zn-Cr ferrite prepared by simulating wastewater, it was found that Zn doping was in favour of the decolorization of malachite green. Cr doping was not conducive to the decolorization and Cr could be easily leached. Ferrite dosage, decolorization time and initial concentration of malachite green had an effect on the decolorization. Decolorization rate increased with ferrite dosage rising, decolorization time prolonging and initial concentration of malachite green rising. However, it was not applicable to malachite green wastewater with high initial concentration for the ferrite capacity of adsorption and catalysis. Ferrite synthesized from actual electroplating wastewater and pickling waste liquor also showed a decolorization effect on the malachite green.Summary, it was a feasible method to synthesize ferrite by microwave hydrothermal process from electroplating wastewater and pickling waste liquor with respect to the re-use and self-purification of wastewater. Synthesized ferrite could be used as a material in decolorization of malachite green. |
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