Enhanced remediation of Cr(VI)-contaminated groundwater by coupling electrokinetics with ZVI/Fe3O4/AC-based permeable reactive barrier

Although widely used in permeation reaction barrier (PRB) for strengthening the removal of various heavy metals, zero-valent iron (ZVI) is limited by various inherent drawbacks, such as easy passivation and poor electron transfer. As a solution, a synergistic system with PRB and electrokinetics (PRB-EK) was established and applied for the efficient removal of Cr(VI)-contaminated groundwater. As the filling material of PRB, ZVI/Fe3O4/activated carbon (ZVI/Fe3O4/AC) composites were synthesized by ball milling and thermal treatment. A series of continuous flow column experiments and batch tests was conducted to evaluate the removal efficiency of Cr(VI). Results showed that the removal efficiency of Cr(VI) remained above 93% even when the bed volume (BV) reached 2000 under the operational parameters (iron/AC mass ratio, 2:1; current, 5 mA). The mechanism of Cr(VI) removal by the PRB-EK system was revealed through field emission scanning electron microscopy images, X-ray diffraction, X-ray photoelectron spectroscopy, Fe2+ concentration, and redox potential (E-h) values. The key in Cr(VI) reduction was the Fe-2(+)/Fe3+ cycle driven by the surface microelectrolysis of the composites. The application of an externally supplied weak direct current maintained the redox process by enhancing the electron transfer capability of the system, thereby prolonging the column lifetime. Cr(VI) chemical speciation was determined through sequential extraction, verifying the stability and safety of the system. These findings provide a scientific basis for PRB design and the in-situ remediation of Cr(VI)-contaminated groundwater. (C) 2021 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Automated summary

The study demonstrated that the ZVI/Fe3O4/activated carbon composites as filling materials for PRB combined with the PRB-EK system could efficiently remove Cr(VI)-contaminated groundwater with a continuous removal efficiency above 93% under specific operational parameters. The externally supplied weak direct current helped maintain the redox process, enhancing the electron transfer capability of the system and prolonging the column lifetime. These findings provide a scientific basis for the design of PRB and in-situ remediation of Cr(VI)-contaminated groundwater.