Carboxymethyl cellulose enhanced Cr(VI) removal of zero-valent iron via the coating anti-passivation mechanism

Abstract

Competition for electrons from dissolved oxygen and secondary passivation resulting from the deposition of FeCr hydroxide are two challenges that impede the removal of hexavalent chromium (Cr(VI)) with zero-valent iron (ZVI). In this study, we fabricated micron-sized zero-valent iron modified with carboxymethyl cellulose (CMC-ZVI) via a mechanical ball milling process and demonstrated its improved performance up to eight times for Cr(VI) removal. Owing to the CMC protective film, the inhibition of dissolved oxygen for Cr(VI) removal, aging of ZVI in air, and secondary passivation of ZVI by the deposition of FeCr hydroxides were all inhibited. Even after a week of continuous aging, the CMC-ZVI maintained a stable Cr(VI) removal efficiency of over 50 %. The excellent hydrophilicity of CMC enhanced the interaction of CMC-ZVI with water and Cr(VI), thus improving its capacity for Cr(VI) removal. Furthermore, CMC-ZVI not only proficiently reduced and completely removed the high-mobility Cr(VI) from actual electroplating effluent, but also effectively alleviated the inhibition of Cr(VI) removal via CMC-ZVI by aeration and air aging. The efficiency of CMC-ZVI in removing Cr(VI) from actual electroplating effluent was improved by over 41 times compared to pristine ZVI. This advantage has the potential to make the storage and transportation of ZVI more affordable and convenient and increases its potential for practical applications. This study provides an efficient Cr(VI) removal strategy using ZVI for environmental remediation and a strategy for the production of highly reactive, aging-resistant, easily stored, and transported zero-valent iron with the potential for practical applications.