Removal Of Cr(Ⅵ) From Water By Iron-based Materials

The rapid development of industry（such as printing and dyeing,leather tanning,textile,etc.）and mining industry is accompanied by the generation and discharge of a great deal of chrome-containing wastewater,which would further pollute the river and farmland ecosystems,and ultimately endangers human health.Therefore,it is urgent to develop technologies to treat the chrome-containing wastewater.Compared with hexavalent chromium（Cr（Ⅵ））,which is characterized by high toxicity and high solubility,trivalent chromium（Cr（III））has low toxicity and weak migration ability.Therefore,reduction of Cr（Ⅵ）to Cr（III）is an effective way to treat chromium pollution.Considering that the ability of adsorption and reduction for iron-based materials,it has been developed as one of the important materials for the treatment of chromium pollution in wastewater.Specifically,the main contents of this paper are as follows:1.Zero-valent iron（ZVI）has shown wide application prospects in the treatment of heavy metal pollution due to its wide sources and environmentally friendly characteristics.But its wider application is limited by its low electron transfer efficiency.In this study,ZVI-EDTA was prepared by adding solid acid（ethylenediaminetetraacetic acid（EDTA））during the ball-milling of ZVI process.The characterization results of X-ray photoelectron spectroscopy revealed that the amount of iron metal（Fe⁰）on the surface of iron powder increased from 7.23%to 30.12%after the ball-milling process in the presence of EDTA,which increased the removal rate of Cr（Ⅵ）from 0.0067 g·m^-2·min^-1 to 0.1 g·m^-2·min^-1.By comparing the results of iron dissolution and Tafel test,it was found that the enhanced Cr（Ⅵ）removal efficiency could be attributed to the promoted ferrous ions dissolution and electron transfer efficiency.2.In this paper,manganese ferrite（Mn Fe₂O₄）magnetic nanoparticles were prepared by hydrothermal method and applied to the removal of hexavalent chromium in water.SEM results revealed that the Mn Fe₂O₄ prepared in this study is a nanosphere with a diameter of about 100-500 nm.Subsequently,the effects of ultrasonic dispersion and reaction atmosphere on the Cr（Ⅵ）removal efficiency were investigated.These results showed that ultrasonic pretreatment of Mn Fe₂O₄ could improve the Cr（Ⅵ）removal percentage from Mn Fe₂O₄ from 43%to 100%.More interestingly,the presence of oxygen could also improve the efficiency of Cr（Ⅵ）removal by Mn Fe₂O₄.By monitoring the dissolution of iron irons and manganese ions during the reaction process in the presence and absence of oxygen,it was found that the presence of oxygen promoted the dissolution of iron irons and manganese ions.Therefore,it was speculated that oxygen improves the Cr（Ⅵ）removal efficiency by promoting the dissolution of iron irons and manganese ions,and thus enhancing the flocculation and precipitation process of Cr（Ⅵ）.