Preparation of highly dispersive and antioxidative nano zero-valent iron for the removal of hexavalent chromium

Abstract

In this study, carboxymethyl cellulose (CMC) was employed to stabilize zero-valent iron nanoparticles (CMC-nFe⁰) to improve their dispersity and antioxidation for enhanced hexavalent chromium (Cr(VI)) removal. Scanning electron microscope (SEM) observation revealed that the nFe⁰ agglomerated in clusters, while the CMC-nFe⁰ connected as chains and presented higher dispersity. Therefore, compared with 54% of the nFe⁰, the Cr(VI) removal rate of the CMC-nFe⁰ increased by 0.8 time, reaching 97%. Besides, the nFe⁰ precipitated in 1 d and was obviously oxidized within 7 d under anoxic condition, leading to a rapid decease of Cr(VI) removal efficiency from 54% to 3% in 56 d. In contrast, the CMC-nFe⁰ showed no obvious subsidence and oxidized phenomenon within 14 d, which retained a relatively high Cr(VI) removal efficiency of 63% in 56 d, contributing to effective blockage of dissolved oxygen infiltrating from solution to nFe⁰ particles in presence of CMC. After reaction, the valence state distribution of Cr between solution and material surface indicated that Cr(VI) reduction was dominant comparing to physical adsorption to particles in the remediation process conducted by CMC-nFe⁰. In addition, lower initial pH and higher iron dosage facilitated Cr(VI) removal. Those results indicated that the dispersive and antioxidative characteristics of CMC-nFe⁰ were significantly superior to those of nFe⁰, and CMC stabilization thereafter can be a promising method to promote Cr(VI) elimination by nFe⁰.

Keywords: Antioxidation; Carboxymethyl cellulose; Chromium; Dispersity; Zero-valent iron.