Preparation Of Fe₃ O₄ Nanoparticles And Mechanism For The Removal Of Cr（Ⅵ） And Mn（Ⅱ） In Aqueous Solution

The superparamagnetic Fe₃O₄ nanoparticles showed a wide application future in wastewater treatment due to its unique physical properties and biocapability. In this study, the process of Fe₃O₄ nanoparticles and mechanism of adsorption of Cr（Ⅵ） and Mn（Ⅱ） on Fe₃O₄ nanoparticles in aqueous solution were investigated.Even size and good dispersion Fe₃O₄ nanoparticles were prepared by the modified hydrolysis method. The morphology and physical properties were measured by XRD, TEM, SEM, FTIR and VSM. There was no any surfactant added in the process, 10nm size of Fe₃O₄ nanoparticles was synthesized just by changing the stirring speed and temperature controlled. During the preparation process, the static magnetic field with 0.30T intensity was employed and one dimension rod like Fe₃O₄ nanoparticles were obtained successfully. The measurement results showed that the length of superparamagnetic Fe₃O₄ nanoparticles was 100 nm¹50 nm and the diameter was about 10 nm.Cr（Ⅵ）-containing wastewater was treated by Fe₃O₄ nanoparticles as absorbent, the factors such as absorption time, initial Cr（Ⅵ） concentration, pH value, ion strength and different anions were investigated during the adsorption process, as well as the two different kinetic mechanism for the adsorption reaction system. The results showed that lower pH value could benefit the removal of Cr（Ⅵ）, ion strength could not influence the process, the anion with more charge could not benefit the removal of Cr（Ⅵ）, the simulation of adsorption kinetic data showed that the“adsorption-reaction mechanism”invented in the study was better than the classical reaction mechanism, the analysis of FTIR and XPS spectra indicated that there was a redox process in the adsorption of Cr（Ⅵ） with Fe₃O₄ nanoparticles.Mn（Ⅱ）-containing wastewater was treated by Fe₃O₄ nanoparticles as absorbent, the factors such as absorption time, initial Mn（Ⅱ） concentration, pH value, ion strength were investigated during the adsorption process. The results showed that higher pH value could benefit the removal of Mn（Ⅱ）, ion strength could not influence the process. The adsorption model of Mn（Ⅱ） treated by Fe₃O₄ nanoparticles was studied by compared Langmuir and Freundlich model with Surface Complexation Model, the simulation results indicated that Surface Complexation Model was more suitable for the process of Mn（Ⅱ） adsorption on Fe₃O₄ nanoparticles. Cr（Ⅵ） and Mn（Ⅱ） containing wastewater was treated by Fe₃O₄ nanoparticles as absorbent, the adsorption process was investigated with pre-treated method and simultaneous method, the factors such as adsorption ways, adsorption time, ratio between Cr（Ⅵ） and Mn（Ⅱ） concentration, pH value were also studied. The results showed that when Cr（Ⅵ） and Mn（Ⅱ） coexist in the solution, the mechanism of Cr（Ⅵ） removal by Fe₃O₄ nanoparticles was very complicated, it was related with the adsorption method and also the pH value of the solution. All influenced factors to be considered, the“selective adsorption-reaction mechanism”was firstly invented in the study to describe the synergistic effect of Cr（Ⅵ） and Mn（Ⅱ） adsorption by Fe₃O₄ nanoparticles in aqueous solution.