Extraction of uranyl peroxo clusters from aqueous solution by mesoporous silica SBA-15

Kinetics of Uranyl Peroxide Nanocluster (U60) Sorption to Goethite

The unique properties of uranium-based nanomaterials may significantly impact our current understanding of the fate and transport of U(VI) in environmental systems. Sorption of the uranyl peroxide nanocluster [(UO₂)(O₂)(OH)]₆₀^60- (U₆₀) to goethite (α-FeOOH) was studied using batch sorption experiments as a function of U₆₀ concentration (0.5-2 g·L^-1), mineral concentration (100-500 m²·L^-1), and pH (8-10). The resulting rate law describing U₆₀ interactions with goethite at pH 9 was R = - k_rxn[U₆₀]^0.29±0.02[goethite]^1.2±0.1 where k_rxn = (6.7 ± 2.0) × 10^-4 (g·L^-1)^0.71±0.02(m²·L^-1)^-1.2±0.1(day^-1). The largest fraction of U₆₀ removed from solution was at pH 8, which is below the isoelectric point of the goethite used in this study. Site density calculations suggest that U₆₀ may exist on the goethite surface at a center-to-center distance of 5.4-6.5 nm, depending upon pH, which mirrors the center-to-center distance observed in the aqueous phase near the U₆₀ solubility limit. At pH 10, approximately 20% uranium was desorbed within 3 days. Analysis of the reacted mineral surface using X-ray photoelectron spectroscopy confirmed the presence of a single U(VI) species on the mineral surface, and electrospray ionization mass spectrometry revealed that U₆₀ remains intact during the sorption and desorption processes. These results demonstrate that the behavior of U₆₀ at the goethite-water interface is similar to that of discrete U(VI) but is governed by different sorption mechanisms and reaction kinetics, which has the potential to alter our current understanding of the fate and transport of uranium species in the environment.

Uranyl Peroxide Nanocluster (U60) Persistence and Sorption in the Presence of Hematite

The presence of uranium-based nanomaterials in environmental systems may significantly impact our current understanding of the fate and transport of U(VI). Sorption of the uranyl peroxide nanocluster [(UO₂)(O₂)(OH)]₆₀^60- (U₆₀) to hematite (α-Fe₂O₃) was studied using batch sorption experiments with varying U₆₀, hematite, and alkali electrolyte (i.e., NaCl, KCl, and CsCl) concentrations. Data from electrospray ionization mass spectrometry and centrifugal microfiltration revealed that U₆₀ persisted in the presence of hematite and the background electrolyte for at least 120 days. K⁺ ions were removed from solution with uranium whereas Li⁺ ions remained in solution, indicating that the U₆₀ cluster behaved like an anion and that the Li⁺ ions did not play a significant role in the sorption mechanism. Analysis of the reacted mineral surface using X-ray photoelectron and Raman spectroscopies confirmed the presence of U(VI) and uranyl species with bridged peroxo groups associated with the mineral surface. These results indicate that uranyl peroxide nanoclusters may persist in the aqueous phase under environmentally relevant conditions for reasonably long periods of time, as compared to that of the uranyl cation.