Removal Of Chromium (Ⅵ) From Wastewater By Mg-aminoclay Coated Nanoscale Zero Valent Iron

Heavy metals are widely used in industrial processes,and their release has become a serious threat to the aquatic environment and public health.Chromium is a common heavy metal contamination,and it is extensively used in leather,textileproduction,pigments,printing and dyeing,chromium plating and other industries.In recent years,nano zero-valent iron（nZVI）has great potential for the remediation of wasterwater due to its huge specific surface area,fast reaction and high reactivity with heavy metals.However,nZVI is prone to aggregation via Van der Waals and magnetic attraction forces,which is responsible for reducing the reactivity and restricts the direct use of it on a large scale.The main contents are as follows:The preparation conditions of MgAC-nZVI were optimized and the removal of Cr（Ⅵ）by MgAC-nZVI was investigated.Batch experiments showed that the removal efficiency of Cr（Ⅵ）was the highest when the mass ratio of MgAC and nZVI was0.15:1,with the material dosge of 0.2 g·L-1,T=30 ℃,pH=5 and the initial Cr（Ⅵ）concentration of 20 mg·L-1.The MgAC-nZVI was characterized by XRD,FTIR,TEM,UV-VIS and Zeta potential.It was found that the MgAC was capable of inhibiting the aggregation of nZVI particles,and the Zeta potential of MgAC-nZVI was higher than that of nZVI at the same pH,which significantly improved the dispersibility and stability of nZVI in the aqueous solution.The MgAC-nZVI material was used to remove Cr（Ⅵ）from wastewater.During the experiment,the effects of MgAC-nZVI dosage,initial pH,temperature and initial concentration of Cr（Ⅵ）on Cr（Ⅵ）removal were analyzed.As a result,the maximum efficiency of removal of Cr（Ⅵ）reached 100% after 3 min under the optimum conditions（MgAC-nZVI dosage: 0.125 g·L-1,T=30 ℃,pH=5,initial concentration of Cr（Ⅵ）: 20 mg L-1）.The effects of different cations,anions and organics matter on the removal of Cr（Ⅵ）by MgAC-nZVI were also investigated.The results show that Cu²⁺,Ni²⁺and Zn²⁺ could promote the removal of Cr（Ⅵ）by MgAC-nZVI.Although SO₄^2-,NO₃^-,C₂O₄^2-and CH₃COO^-were competitive with Cr（Ⅵ）in adsorption,they could promote the corrosion of nZVI and then slightly improve the removal rate of Cr（Ⅵ）.In addition,PO₄^3-and HA occupied the active sites on the MgAC-nZVI surface by competitive adsorption,thereby inhibiting the removal of Cr（Ⅵ）.Moreover,the MgAC-nZVI particles have a better performance of reusability.The removal of Cr（Ⅵ）by MgAC-nZVI and nZVI was proved to be in accordance with the pseudo-second-order adsorption kinetics model.Compared with uncoated nZVI,the adsorption rate constant of MgAC-nZVI and the removal ability of Cr（Ⅵ）were significantly improved.The adsorption rate constant of Cr（Ⅵ）removal by MgAC-nZVI increased with the increase in MgAC-nZVI dosage,temperature and initial pH,and decreased with the initial concentration of Cr（Ⅵ）increased.Based on the indentifying of reduction products,,the mechanism of Cr（Ⅵ）removal by MgAC-nZVI was divided into three parts: the rapid adsorption of Cr（Ⅵ）onto MgAC-nZVI,the chemical reduction of Cr（Ⅵ）t℃r（Ⅲ）and the formation of Cr_xFe_1-x（OH）₃ coprecipitate.