Effective inspissation of uranium(VI) from radioactive wastewater using flow electrode capacitive deionization

• Flow electrode capacitive deionization was utilized for effective inspissation of U(VI) from wastewater. • Removal ratio of U(VI) maintained 99% even after 48th operation cycles. • The excellent adsorption capacity of U(VI) is credited to electrosorption and electroreduction. • The original concentration of 60 mg L −1 was effectively concentrated to 2843 mg L −1 by FCDI process. The treatment for large amounts of low concentration radioactive wastewater has always been a worldwide problem, just like the Fukushima nuclear power plant is facing the problem of insufficient storage space. In this work, we have assessed the effectiveness of flow electrode capacitive deionization (FCDI) as a recently developed electrochemical technology to concentrate the radioactive wastewater for the first time. Continuous batch experiments demonstrated that uranium (U) can accumulate into the electrolyte and on activated carbon at the same time in the flow electrode, and the removal efficiency of U remained over 99% during each cycle. Combined with XPS analysis, the migration route and valence change of U in the flow electrode were revealed, which helped to understand the high adsorption capacity of U in FCDI. Long-term batch experiments exhibited that the low concentration of feed water (60 mg L −1 U) could be concentrated by 47 times after 48th continuous cycles, achieving a final concentration of 2843 mg L −1 U in the electrolyte, and 40 mL reduced volume of uranium-containing water from 2,400 mL. Under optimized conditions, a charge efficiency of 86% and a low energy consumption of 2.03 mg J −1 were achieved in 360 mg L −1 initial concentration of UO 2 2+ . Overall, high removal rate, excellent concentration effect and low energy consumption make FCDI to be a promising way for radioactive wastewater treatment.