The unique and diverse features of uranyl peroxide nanoclusters may contribute to the enhanced mobility of uranium in the environment. This study examines the sorption of the uranyl peroxide nanocluster [UO2(O2)(OH)]6060‑ (U60) to Na-montmorillonite (SWy-2), plagioclase (anorthite), and quartz (SiO2) as a function of time, U60 concentration, and mineral concentration. SWy-2 was studied in both its untreated form as well as after two diﬀerent pretreatments, denoted as partially treated SWy-2 and fully treated SWy-2. U60 was removed (∼99%) from solution in the presence of untreated and partially treated SWy-2. However, U60 was not removed from suspensions containing anorthite, quartz, or fully treated SWy-2, even after several months. The removal of U60 from suspensions containing untreated SWy-2 is promoted in part by the exchange of Li+ counter-ions, normally weakly associated with U60 in solution, for Ca2+ ions naturally present in the clay. In solution, Ca2+ ions induce the aggregation of nanoclusters, which precipitate on the surface of SWy-2. Ca-rich U60 aggregates associated with SWy-2 were identiﬁed and characterized by scanning electron microscopy with energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. This research enhances our understanding of the molecular-scale processes controlling U60 behavior at the mineral−water interface.
Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U60 in the Presence of Na-MontmorilloniteArticle
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