Iron Oxyhydroxide Nanoparticle-Coated Carbon Cloth Electrode for Remediation of Cr(VI)-Contaminated Wastewater

: Among in situ and ex situ groundwater technologies, electrochemical treatment has been successfully employed to remediate water heavily contaminated with metals. Electrochemical treatment of Cr(VI)-contaminated wastewater has been attempted using various factors such as electrode materials, surfactants, and electrolytes. In this study, inexpensive carbon cloth was selected and coated with iron oxyhydroxide nanoparticles to enhance electrochemical remediation of Cr(VI)-contaminated wastewater. Iron oxyhydroxide nanoparticles (INP) synthesized by chemical precipitation were coated on carbon cloth electrodes by immersion to examine Cr(VI) removal. The efficiency of Cr(VI) reduction/immobilization was compared between carbon cloth (CC) and carbon cloth coated with iron oxyhydroxide nanoparticles (INP-CC) with/without DC application at a constant potential of 5.0 V to treat water contaminated with 100 mg/L Cr(VI) for 48 h. The removal rate of Cr(VI) was as follows: 10% for CC electrodes and 32% for INP-CC electrodes, compared to >90% for both CC and INP-CC electrodes with DC application for 48 h. In the INP-CC + EC group the pH-Eh condition tended to acidic oxidizing condition due to oxidative substances, O2(g) and hydrogen ions generated on anodic reaction during 12~24 h when Cr(VI) removal reached at 80%, but the CC + EC group remained with minor change for 36 h resulting less reduction efficiency of Cr(VI), despite a successful removal efficiency after 48 h which is similar to the INP-CC + EC group. These results indicated that multiple interactions (C/Cr6+–Cr3+/Fe3+–Fe2+/H+–OH−) on the surface of CC and INP-CC enhanced by EC might contribute to reduction of Cr(VI) and adsorption/precipitation of chromate ions. In particular, INP-CC+ EC might perform dual roles as an electron donor for Fe2+ and/or as an absorbent with DC application in Cr(VI) immobilization. INP-CC enhanced-EC technology could be an economic and efficient approach to remediation of wastewater heavily contaminated with Cr(VI).