Study On The Removal Of Cr(â…¥) Using ZVI Catalyzed By POM And Removal Of As(â…¢) By CMC Stabilized NZVI

Recently, zero-valent iron (Fe0, ZVI) as a reducing agent to treat heavy metal pollution has drawn extensive attention. However, iron tended to be oxidized in the process of removing heavy metal contamination. Meanwhile, iron surface would produce corrosion products in contact with the surrounding media such as dissolved oxygen and water, which diminished reaction activity on iron surface. Therefore, the removal of Cr(â…¥) and As(â…¢) was discussed in this article based on ZVI technology and in combination with other technologies. This article consists of two parts. In the first part of the article, the removal of Cr(â…¥) from wastewater using acid-washed ZVI catalyzed by polyoxometalate (POM) under acid conditions was discussed. With the aid of POM, the removal of Cr(VI) increased significantly by acid-washed ZVI under acid conditions in air environment. The effects of iron loadings, POM concentrations, and initial pH values on the removal of Cr(â…¥) in ZVI/POM/air system were investigated and reaction mechanism was studied. In the second study of the article, carboxymethyl cellulose (CMC) was chosen as a dispersant to prepare stable and highly reactive CMC-nZVI. The influence of CMC-nZVI loading, initial concentration of As(â…¢), initial pH as well as cation (Na+ and Ca2+) on arsenic removal by CMC-nZVI were investigated. Moreover, X-ray diffraction (XRD) analysis was performed in order to characterize CMC-nZVI. The main conclusions of this study are as follows:(1) Batch experiments showed that the removal of Cr(â…¥) from wastewater using acid-washed ZVI catalyzed by polyoxometalate under acid conditions was rapid and effective. Some factors including the initial pH, ZVI addition and POM concentration caused greater effects on the removal of Cr(â…¥). Results showed that the removal efficiency of Cr(â…¥) increased with increasing of the dosage of ZVI and POM, and decreased with increasing pH values within a certain range. There was a 98% drop in Cr(â…¥) concentration using 1.0 g/L acid-washed ZVI catalyzed by 1.5 mM polyoxometalate in 2 h at pH 3.0 under the optimal conditions. POM was employed to catalyze acid-washed ZVI in the removal of Cr(â…¥) under acid conditions. POM can serve as an electron shuttle for accelerating transferring electrons from the ZVI to the dissolved O2 accompanied with producing H2O2. In addition, in the presence of air, the oxidation of ZVI by O2 would generate H2O2 which was favorable for Cr(â…¥) removal.(2) CMC was used as a stabilizer in the synthesis of the nanoscale zero-valent iron considering its advantage such as non-toxic, cheaper and widely application after optimizing the condition for preparation of CMC-nZVI. The presence of CMC contributes to reducing agglomeration of nano-particles through electrostatic repulsion and steric hindrance. In addition, it is conducive to preventing nano-particles from reacting with surrounding media (including dissolved oxygen and water) and to weakening the physical interactions. According to the experimental results, the treatment process of As(â…¢) was affected by CMC-nZVI addition, initial As(â…¢) concentration, pH value, the cations concentration (Na+ and Ca2+). The removal efficiency of As(â…¢) increased with the increasing of CMC-nZVI dosage, but decreased with the increasing initial pH values and initial concentration of As(â…¢). Moreover, the presence of Na+ and Ca2+ has an inhibitory effect towards the removal efficiency of As(â…¢).