SREL Reprint #3545

Sequestration of U(VI) from acidic, alkaline, and high ionic-strength aqueous media by functionalized magnetic mesoporous silica nanoparticles: capacity and binding mechanisms

Dien Li1, Shani Egodawatte2, Daniel I. Kaplan1, Sarah C. Larsen2, Steven M. Serkiz1, John C. Seaman3,
Kirk G. Scheckel4, Jinru Lin5, and Yuanming Pan5

1Savannah River National Laboratory, Aiken, South Carolina 29808, United States
2Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
3Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802, United States
4National Risk Management Research Laboratory, U.S. Environmental Protection Agency,
Cincinnati, Ohio 45224, United States
5Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatoon S7N 5E2, Canada

Abstract: Uranium(VI) exhibits little adsorption onto sediment minerals in acidic, alkaline or high ionic-strength aqueous media that often occur in U mining or contaminated sites, which makes U(VI) very mobile and difficult to sequester. In this work, magnetic mesoporous silica nanoparticles (MMSNs) were functionalized with several organic ligands. The functionalized MMSNs were highly effective and had large binding capacity for U sequestration from high salt water (HSW) simulant (54 mg U/g sorbent). The functionalized MMSNs, after U exposure in HSW simulant, pH 3.5 and 9.6 artificial groundwater (AGW), were characterized by a host of spectroscopic methods. Among the key novel findings in this work was that in the HSW simulant or high pH AGW, the dominant U species bound to the functionalized MMSNs were uranyl or uranyl hydroxide, rather than uranyl carbonates as expected. The surface functional groups appear to be out-competing the carbonate ligands associated with the aqueous U species. The uranyl-like species were bound with N ligand as η2 bound motifs or phosphonate ligand as a monodentate, as well as on tetrahedral Si sites as an edge-sharing bidentate. The N and phosphonate ligand-functionalized MMSNs hold promise as effective sorbents for sequestering U from acidic, alkaline or high ionic-strength contaminated aqueous media.

SREL Reprint #3545

Li, D., S. Egodawatte, D. I. Kaplan, S. C. Larsen, S. M. Serkiz, J. C. Seaman, K. G. Scheckel, J. Lin, and Y. Pan. 2017. Sequestration of U(VI) from acidic, alkaline, and high ionic-strength aqueous media by functionalized magnetic mesoporous silica nanoparticles: capacity and binding mechanisms. Environmental Science and Technology 51(24): 14330-14341.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).