Sulfidation and Reoxidation of U(VI)-Incorporated Goethite: Implications for U Retention during Sub-Surface Redox Cycling

Abstract

Over 60 years of nuclear activity have resulted in a global legacy of contaminated land and radioactive waste. Uranium (U) is a significant component of this legacy and is present in radioactive wastes and at many contaminated sites. U-incorporated iron (oxyhydr)oxides may provide a long-term barrier to U migration in the environment. However, reductive dissolution of iron (oxyhydr)oxides can occur on reaction with aqueous sulfide (sulfidation), a common environmental species, due to the microbial reduction of sulfate. In this work, U(VI)–goethite was initially reacted with aqueous sulfide, followed by a reoxidation reaction, to further understand the long-term fate of U species under fluctuating environmental conditions. Over the first day of sulfidation, a transient release of aqueous U was observed, likely due to intermediate uranyl(VI)–persulfide species. Despite this, overall U was retained in the solid phase, with the formation of nanocrystalline U(IV)O2 in the sulfidized system along with a persistent U(V) component. On reoxidation, U was associated with an iron (oxyhydr)oxide phase either as an adsorbed uranyl (approximately 65%) or an incorporated U (35%) species. These findings support the overarching concept of iron (oxyhydr)oxides acting as a barrier to U migration in the environment, even under fluctuating redox conditions.

Stabilization of Uranium in Acid Ore Wastewater through Hydrothermal Mineralization-Induced Crystallization

“…Although the uranium removal efficiency was about 60% in the Mg 3 (PO 4 ) 2 system when the pH values were 7.0 and 9.0, the leaching rates were about 45–55%. It resulted from the remobilization of surface-adsorbed UO 2 2+ . The high leaching rate meant the considerable surface physical adsorption of Mg 3 (PO 4 ) 2 to uranyl, being similar to the results of uranium adsorption on hydroxyapatite .…”

“…It resulted from the remobilization of surface-adsorbed UO 2 2+ . 37 The high leaching rate meant the considerable surface physical adsorption of Mg 3 (PO 4 ) 2 to uranyl, being similar to the results of uranium adsorption on hydroxyapatite. 38 It showed the leaching risk.…”

Determination of Uranium Central-Field Covalency with 3d4f Resonant Inelastic X-ray Scattering

“…In recent years, M 4,5 -edge HERFD has matured into an essential method for determining actinide electronic structure, bonding, and speciation. ,, An increasing number of studies demonstrate that the method carries sensitivity to oxidation state, 5 f ligand field splitting, and covalency. − ,,,− It has also been shown that additional insights can be obtained by extending HERFD measurements to include 3 d 4 f RIXS planes, particularly in identified variations in resonant versus nonresonant XES maxima. ,, The present study reports the sensitivity of 3 d 4 f RIXS to U(IV) metal–ligand bonding at both the M 5 -edge and the M 4 -edge. It is identified that the RXES part of the RIXS planes contains fine structures that are not captured via HERFD measurements.…”

Chelating Effect of Siderophore Desferrioxamine-B on Uranyl Biomineralization Mediated by Shewanella putrefaciens

“…The development of nuclear energy is important for the sustainable energy industry. The uranium ore processing, nuclear energy generation, and spent-fuel treatment leads to uranium contamination in underground water and soil environment. , Therefore, the effective disposal of radioactive uranium-containing wastewater and the study of uranium cycling in biogeochemistry are mandatory in environmental science. , Species of two predominant oxidation states, hexavalent U­(VI) in uranyl (UO 2 2+ ) and tetravalent U­(IV) or U 4+ , of environmental uranium species have been studied extensively. − Noncrystalline U­(IV) species have been detected to be markedly more labile than solvable species of uranyl because they tend to be promptly oxidized and mobilized by O 2 , persulfate and bicarbonate. , Uranyl species with high aqueous solubility and mobility have huge effects on the hydrosphere and geosphere. − Under anaerobic conditions, uranyl species are rapidly reduced by organophosphates to crystalline U­(IV)-phosphate minerals, which are more difficult to oxidatively reactivate than products of microbial uranyl reduction . Biological treatments are widely used for the immobilization of uranyl in aqueous solution. , Especially, biomineralization is a process in which organisms coordinated and controlled by living organisms generate inorganic minerals, with virtue of low cost and high stability of the products.…”