Separation of uranium in nitric acid solution is a key issue in the solvent extraction of spent fuel. However, the structures of uranyl complexes in aqueous conditions containing nitric acid remain unclear. The Raman peak generated by uranyl at 870 cm−1 is considered an important internal standard for detecting uranyl complexes, which can be used for identifying the form of uranium in solution. In this work, first-principles calculations reveal multiple origins for this vibrational feature, attributing it to simultaneous contributions from [UO22+ · 5H2O], [UO2NO3+ · 3H2O], and [UO2NO3+ · 4H2O]. Crucially, all three species share pentacoordinate uranyl centers, with interaction mechanism analysis confirming bidentate nitrate coordination in the dominant [UO2NO3+ · 3H2O] configuration. Moreover, the quantitative agreement between computed spectra and experimental benchmarks validates our solvation-corrected theoretical model and method. These findings provide atomic-level insight into the structure of uranyl complexes in nitric acid solution, establishing a predictive framework for interpreting vibrational spectroscopic signatures in complex nuclear waste streams.

Uranium extraction from seawater is a promising strategy to address terrestrial uranium depletion. However, the complex marine environment induces diverse uranium speciation and coordination structures, creating substantial challenges for uranium detection and extraction. Herein, we establish the quantitative structure–spectrum relationship through correlating the uranyl–oxygen bond lengths and symmetric stretching frequencies in typical uranyl complexes by employing density functional theory calculations. Moreover, the structural evolution of uranyl in sodium carbonate solutions under acidic to weakly alkaline conditions is investigated in combination with Raman spectroscopy experiments, demonstrating a linear correlation between the uranyl–oxygen bond lengths and vibrational frequencies in sodium-containing complexes, which verifies and extends the applicability of Badger’s rule in uranyl systems. Atomic-level analyses further reveal that sodium ions modulate ligand charge distributions via strong electrostatic interaction, resulting in weakened uranium–oxygen bonds and enhanced structural stability of the uranyl complexes. These findings deepen the understanding of the structure–spectrum relationship in complex solutions and provide insights for uranium resource exploration in seawater.

In alkaline in-situ leaching uranium, oxygen is the most common oxidizer with bicarbonate as a complexing agent. For those sandstone uranium deposits with strongly reductive capacity or complicated hydrogeological environment, the oxidation by oxygen is low efficiency. An efficient leaching method, therefore, is needed for these uranium deposits. In this study, a typical sandstone uranium deposit which characterizes with high TDS and high chloride content in groundwater and intractable uranium leach is selected to investigate the effects of synergetic oxidation by a strong oxidant with oxygen. Based on the research on batch leach, pressure leach and field trials, the oxidants such as hydrogen peroxide, potassium permanganate and sodium dichloroisocyanurate (NaDCC) are tested. The results of pressure batch leach indicate that synergetic oxidization is achieved by NaDCC in oxygen leaching process. Leaching tests indicate that a minor oxidizer of NaDCC shows good synergetic oxidization with oxygen and leaching effects on uranium minerals. The results also demonstrate that hydrogen peroxide shows no oxidation effects when it is used as a single oxidant. While potassium permanganate shows good oxidation on uranium when it is used as a single oxidant, however, it leads inhibiting effects on oxygen oxidation on uranium minerals. The further field tests are conducted to study the synergetic effects of oxygen with and without sodium dichloroisocyanurate. The preliminary results indicate that a fast leach is observed by the composite oxidants in early stage while no synergetic leach is found after 200 days. Further studies should be conducted in laboratory experiments and pilot scale tests for its potential applications.

Uranium occurrence and gangue mineralogy govern the choice of leaching process for sandstone-hosted uranium deposits. This study evaluates CO₂ + O₂ leaching of calcite-rich uranium ore from the Bayinqinggeli deposit in the northern Ordos Basin using mineralogical characterization, thin-section and agitated leaching experiments, and PHREEQC modeling. The dominant U–Si-bearing phase is interpreted as coffinite, although its mineralogical identification remains provisional in the absence of phase-specific structural and oxidation-state analyses. Thin-section observations revealed pronounced dissolution of exposed calcite and coffinite grains, but only minor surface corrosion of pyrite. Agitated leaching tests showed that increasing bicarbonate concentration improved uranium recovery, with diminishing gains above approximately 2 g/L. Calcite dissolution supplied bicarbonate, but equilibrium calculations indicated that the amount dissolved within a single pore-water volume was small relative to the calcite inventory. Thus, bicarbonate generation does not necessarily imply extensive liberation of encapsulated uranium minerals or a substantial increase in aquifer permeability. Pyrite oxidation may promote carbonate dissolution through acid generation, while also consuming oxygen and potentially producing pore-clogging precipitates. The results support further evaluation of CO₂ + O₂ recovery for this deposit. A modeled initial CO₂ dosage of 5 g/L produces approximately 2 g/L bicarbonate, and maintaining pressure in the surface processing circuit may limit CO₂ loss and calcite precipitation. These operating suggestions require validation under field flow and recirculation conditions.