Performance and mechanism of chromium removal using flow electrode capacitive deionization (FCDI): Validation and optimization

The contamination of wastewater with hexavalent chromium (Cr (VI) poses significant health and environmental risks. To alleviate this challenge, our research explores the potential of flow electrodes capacitive deionization (FCDI) technique, an energy-efficient and environmentally friendly approach, for Cr (VI) removal and detoxification. We incorporated varying weight loadings of carbon nanotubes (CNTs) into activated carbon (AC) flowable electrodes, and assessed the system's performance under different operational conditions. Our findings revealed that by adding just 1.5 wt% CNT to AC and applying a voltage of 0.9 V, the current response increased 3.4 times compared to that of pure AC flowable electrode, resulting in a remarkable Cr (VI) removal efficiency of 99.5 %. This study also revealed that the presence of high concentrations of co-existed chloride ions (Cl-) did not significantly influence the efficiency of Cr (VI) removal. Incorporation of CNT in AC flow electrodes reduced the inter-tube aggregation and enhanced the contact efficiency between the AC particles, forming a connecting percolation network and enhancing the conductivity of the slurry electrodes for Cr (VI) removal. In addition to Cr (VI) removal, FCDI technique transformed extremely dangerous Cr (VI) to less toxic Cr (III) from 5.4 to 49.8 % during multiple cycles. In summary, we presented an innovative, efficient, eco-friendly approach for Cr (VI) removal and detoxicity by using CNTs incorporated electrodes, underscoring the potential FCDI technology in heavy metal disposal.