Electrochemical Remediation of Uranium(VI) From Aqueous Media Using the Boron-Doped Diamond Electrodes: Mechanisms, Products and Applications

Abstract

The proliferation of nuclear science and technology has led to a pressing challenge: the accumulation of radioactive waste and subsequent contamination, raising significant concerns about its impact on human health and the environment. Uranium (U), a primary contributor to nuclear contamination, warrants attention due to its extensive use in various applications. This study proposes the application of electrochemical processes to reduce uranium (VI) [U(VI)] to uranium (IV) [U(IV)], thereby mitigating the presence of this radionuclide in aqueous environments. Initially, electrochemical bioremediation of uranium (VI) was investigated using Geobacter sulfurreducens immobilized on a boron-doped diamond electrode (BDD). The G. sulfurreducens/BDD system effectively removed U(VI) ions, reducing them to U(IV) from a solution containing 2.0 mM uranyl acetate in the bacterium growth media, employing a potential of -0600V vs. Ag/AgCl (3M NaCl). This process was validated through analytical techniques including cyclic voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray fluorescence spectroscopy (EDS), and Raman spectroscopy. Subsequently, electrochemical remediation of the uranyl ion was pursued using a BDD electrode modified with nano zero-valent iron particles (nZVIs). This approach facilitated the removal of U(VI) from a solution containing 2 mM uranyl acetate in 0.1M KClO4, employing a potential of -0.800V vs. the reversible hydrogen electrode (RHE). Characterization of the BDD electrode surface revealed the presence of various uranium oxides, including UO2, UO3, and U3O8, as confirmed by cyclic voltammetry, SEM/EDS, and Raman spectroscopy. Furthermore, the tendency for uranium electrodeposition on the BDD electrode surface was explored across a range of reduction potentials (from -0.600V to -2.00V vs. RHE). In addition to the previously mentioned techniques, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the BDD surface after the electrodeposition processes. Analysis revealed the electrodeposition of uranium oxides, predominantly U3O8, at specific applied potentials. Notably, an optimal potential of -1.75 V vs. RHE was identified for achieving uniform electrodeposition without crystal growth.These investigations contribute to the development of cost-effective and eco-friendly methods for addressing radionuclide contamination in aqueous phases, with potential implications for future nuclear technologies.