Electroreductive removal of uranium from uranium-organic wastewater using TiO₂ nanotube arrays electrodes

Direct electrochemical reduction of soluble U(VI) to relatively insoluble U(IV) presents a simple yet highly efficient approach for treating uranium-containing wastewater. However, the remediation of radioactive wastewater co-contaminated with uranium and organic compounds remains a significant challenge. In this work, both anatase and rutile phases TiO₂ nanotube arrays (A/R-TiO₂ NTAs) electrodes were fabricated through anodizing and annealing of a Ti plate, enabling efficient electroreductive removal of U(VI) from both simulated and real uranium-organic co-existing wastewater. Compared to the Ti electrode, the TiO₂ NTAs electrodes exhibited a lower U(VI) reduction potential, a larger electrochemical active surface area (ECSA), and a smaller charge transfer resistance (R_ct). Consequently, the TiO₂ NTAs electrode demonstrated exceptional U(VI) removal performance, achieving reduction efficiencies of 96.05 ± 1.24% (A-TiO₂ NTAs) and 93.07 ± 1.45% (R-TiO₂ NTAs) after 10 h of electrochemical treatment. The TiO₂ NTAs electrodes demonstrated exceptional stability, maintaining average U(VI) removal and recovery efficiencies above 90% over eight consecutive removal-recovery cycles. Moreover, the electrodes exhibited strong anti-interference capability against co-existing organic compounds, except for urea. Even in real uranium-laden wastewater containing high concentrations of organic contaminants-such as tetrahydrofurfuryl alcohol (THFA), polyvinyl alcohol (PVA), and urea-the TiO₂ NTAs electrodes achieved remarkable U(VI) removal efficiencies of 96.38 ± 1.43% (A-TiO₂ NTAs) and 94.56 ± 0.97% (R-TiO₂ NTAs) after only 2 h. Systematic mechanistic investigation revealed that the electroreductive removal of U(VI) is a multi-step process, primarily involving three key stages: adsorption, reduction and transformation, ultimately immobilizing uranium as UO₂ on the electrode surface. This work conclusively demonstrates that direct electrochemical reduction is a highly efficient strategy for treating complex uranium-organic co-existing wastewater.