Preparation Of Fe₃O₄/FeC From NdFeB Waste By Mechanochemical Method And Treatment Of Wastewater Containing Chromium

With the development of industry,the pollution problem of Cr（Ⅵ）in wastewater is becoming more and more serious.At present,the materials used to treat wastewater containing chromium have problems such as high cost and easy to cause secondary pollution.Therefore,it is imperative to develop new materials to treat wastewater containing chromium.In this thesis,Nd Fe B waste is used as raw material,and Fe₃O₄/FeC material is prepared by mechanical mechanochemical modification of Nd Fe B waste and applied to the treatment of chrome-containing wastewater.Then,the physicochemical adsorption mechanism is discussed through thermodynamic and dynamic tests.The research results are as follows:The optimal process of mechanical and chemical materials preparation:the primary and secondary relationship of influencing factors was determined by orthogonal test,and then the optimal process conditions of preparing materials were determined by single factor test.The optimal process was as follows:the grinding time of 3 h,the rotating speed of 400 r/min,the ratio of pellet to material 10:1.The main and secondary factors affecting the performance of materials treating chrome-containing wastewater were as follows:Pellet ratio>ball grinding speed>ball grinding time>ball size.Material characterization analysis:The characterization analysis method was used to analyze the properties of the prepared materials.The X-ray diffractometer（XRD）characterization analysis showed that the intensity of the diffraction peak of FeC was reduced,the crystallinity was reduced,and the mechanical and chemical ball milling resulted in the destruction of structural crystals and chemical bond breakage,which improved the material activity and enhanced the physical and chemical properties of the materials.According to the scanning electron microscope（SEM）and the specific surface area tester（BET）,it was found that the material morphology changed,the porosity increased,the internal specific surface area and the overall specific surface area increased,the adsorption sites increased,and the adsorption capacity also increased.Fourier infrared spectroscopy analysis showed that after Cr（Ⅵ）was adsorbed,the area of the peak at 3423.028 cm^-1 increased,and hexavalent chromium was successfully adsorbed on the material.The optimum conditions for the treatment of chrome-containing wastewater are as follows:The optimal conditions for the treatment of simulated chrome-containing wastewater with Fe₃O₄/FeC material are 25℃at room temperature,pH=7,0.08g of material,and 90 min of reaction time.Coexisting ions have a great effect on Cr（Ⅵ）removal by Fe₃O₄/FeC materials.Sulfate ions have the greatest effect on Cr（Ⅵ）adsorption,followed by chloride ions.Bicarbonate ions have no effect on Cr（Ⅵ）adsorption.Study on reaction mechanism:The linear fitting of pseudo-second-order kinetic model is the best.According to the intercept and slope of the Arrhenius equation,Ea=25.304 k J/mol can be calculated.The adsorption process of Cr（Ⅵ）by Fe₃O₄/FeC material was mainly physical adsorption accompanied by chemical adsorption.The adsorption thermodynamic results show that the adsorption process of Cr（Ⅵ）by Fe₃O₄/FeC material is more consistent with Langmuir adsorption isotherm equation.According to the calculation results of the equation,ΔG⁰<0,the adsorption reaction of Cr（Ⅵ）by Fe₃O₄/FeC material is spontaneous,andΔS⁰ is stable around 0.5,the value ratio is small,and the reaction is less affected by temperature.ΔH⁰ greater than zero indicates that the adsorption of Cr（Ⅵ）by Fe₃O₄/FeC is an endothermic reaction,whileΔH⁰=22.9625 k J/mol is larger than the range of 4～10 k J/mol of van der Waals force.The adsorption process of Fe₃O₄/FeC includes physical adsorption and chemical adsorption.Physical adsorption is the main method.Analysis of results of desorption test and repeated regeneration test:low concentration of Na OH solution can desorption of materials,desorption rate of 74%.The analysis of repeated regeneration test found that recycling would lead to the decrease of Cr（Ⅵ）removal rate,and the main reason for the decrease was the loss in the desorption and desorption process.The overall Cr（Ⅵ）removal rate always maintained above 80%,with the ability of recycling and regeneration.There are 44 figures,16 tables and 90 references in this thesis.