Oxidation of Biogenic U(IV) in the Presence of Bioreduced Clay Minerals and Organic Ligands

Abstract

Bioreduction of soluble U(VI) to sparingly soluble U(IV) is proposed as an effective approach to remediating uranium contamination. However, the stability of biogenic U(IV) in natural environments remains unclear. We conducted U(IV) reoxidation experiments following U(VI) bioreduction in the presence of ubiquitous clay minerals and organic ligands. Bioreduced Fe-rich nontronite (rNAu-2) and Fe-poor montmorillonite (rSWy-2) enhanced U(IV) oxidation through shuttling electrons between oxygen and U(IV). Ethylenediaminetetraacetic acid (EDTA), citrate, and siderophore desferrioxamine B (DFOB) promoted U(IV) oxidation via complexation with U(IV). In the presence of both rNAu-2 and EDTA, the rate of U(IV) oxidation was between those in the presence of rNAu-2 and EDTA, due to a clay/ligand-induced change of U(IV) speciation. However, the rate of U(IV) oxidation in other combinations of reduced clay and ligands was higher than their individual ones because both promoted U(IV) oxidation. Unexpectedly, the copresence of rNAu-2/rSWy-2 and DFOB inhibited U(IV) oxidation, possibly due to (1) blockage of the electron transport pathway by DFOB, (2) inability of DFOB-complexed Fe(III) to oxidize U(IV), and (3) stability of the U(IV)-DFOB complex in the clay interlayers. These findings provide novel insights into the stability of U(IV) in the environment and have important implications for the remediation of uranium contamination.

Interaction between Uranyl Cations and Layered Double Hydroxide Nanoparticles: Implications for Nuclear Wastewater Management

“…Uranium (U) present in wastewaters produced via its mining, processing, and use in the nuclear fuel cycle is a significant environmental concern , with a range of potential ecotoxicological effects identified. , This includes the presence of U in the remediation of contaminated solutes produced during various processes associated with the nuclear fuel cycle, including U-mining, effluents from spent nuclear fuel reprocessing, nuclear fuel storage facilities, , U enrichment sites that are subject to decommissioning, , or cleanup procedures following the nuclear accidents. , To address these challenges, and especially when other radionuclides including transuranics such as plutonium and americium isotopes, and fission products including 90 Sr and 137 Cs may also be present, several studies have investigated U capture using various materials − including layered double hydroxides (LDHs) formed in situ − or prefabricated LDHs as adsorbents. ,− …”