Studtite (UO2O2∙4H2O), a uranyl peroxide mineral, has been found in nuclear waste storage tanks alongside complexing agents such as EDTA, HEDTA, and NTA. The influence of these ligands on the fate and transport of uranium, a risk driving contaminant, is critical for understanding the consequences of nuclear waste leakages. This study investigated the stability of studtite in the presence of these ligands under varying pH conditions (3, 7, 9, and 11), ligand concentrations (0.15 mM, 1.5 mM, and 15 mM), and ionic strengths. Batch kinetic experiments were conducted with 1 mg of studtite in 50 mL suspensions (12.7 mg/L total U), and the uranium concentration in the aqueous phase was monitored over time. Results showed uranium release from studtite even in the absence of ligands at pH 3 and 11, while at pH 7 and 9 uranium was only released in the presence of ligands. The presence of EDTA and NTA increased aqueous uranium at pH 7 and 9 by forming soluble U-ligand complexes, as confirmed by NMR and speciation diagrams. HEDTA enhanced studtite dissolution at all tested pH values. Increased ionic strength reduced electrostatic repulsion between ligands and the mineral surface, further promoting dissolution. In simulated nuclear waste, uranium predominantly favored the aqueous phase regardless of ligand presence. These findings indicate that EDTA, HEDTA or NTA presence in waste can provide a pathway for studtite dissolution, increasing the amount of aqueous uranium in waste while also changing aqueous uranium speciation. This impacts the mobility of contaminated waste in the occurrence of waste leakage, complicating uranium fate and transport in the environment. These findings have implications for uranium fate and transport modeling and the development of nuclear waste treatment strategies.
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