Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U60 in the Presence of Na-Montmorillonite

Luke R. Sadergaski; Meena Said; Amy E. Hixon

doi:10.1021/acs.est.8b06731

Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U₆₀ in the Presence of Na-Montmorillonite

Luke R. Sadergaski, Meena Said, Amy E. Hixon

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Abstract

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)]₆₀^60- (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.

Original language	English
Pages (from-to)	4922-4930
Number of pages	9
Journal	Environmental Science and Technology
Volume	53
Issue number	9
DOIs	https://doi.org/10.1021/acs.est.8b06731
State	Published - May 7 2019
Externally published	Yes

Funding

*Telephone: +1-(574)-631-1872; e-mail address: ahixon@nd. edu. ORCID Amy E. Hixon: 0000-0003-4513-4574 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding This material is based on work supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award no. DESC0001089. Student funding was provided in part by the CEST Bayer Predoctoral Research Fellowship (L.R.S.) and the Arthur J. Schmitt Leadership Fellowship in Science and Engineering (M.S.). Notes The authors declare no competing financial interest.

Funders	Funder number
CEST
Office of Basic Energy Sciences
U.S. Department of Energy
Office of Science

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10.1021/acs.est.8b06731

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title = "Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U60 in the Presence of Na-Montmorillonite",

abstract = "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.",

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Calcium-Facilitated Aggregation and Precipitation of the Uranyl Peroxide Nanocluster U₆₀ in the Presence of Na-Montmorillonite

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