Molecular dynamics simulations of the structure and thermodynamics of carrier-assisted uranyl ion extraction

Manori Jayasinghe; Thomas L. Beck

doi:10.1021/jp903470n

Molecular dynamics simulations of the structure and thermodynamics of carrier-assisted uranyl ion extraction

Manori Jayasinghe, Thomas L. Beck

Research output: Contribution to journal › Article › peer-review

34 Scopus citations

Abstract

We present molecular dynamics simulations of interfaces relevant to the selective chemical extraction of uranyl ions from aqueous solution. These molecular-level simulations model ion transfer in the PUREX process and in synthetic, selective membranes. We first present simulations of water/oil interfaces modified by incorporation of tributyl phosphate (TBP) into the oil phase (hexane). A range of concentrations is examined, from a single TBP molecule to values close to those utilized in the PUREX process. The TBP molecules exhibit strong interfacial activity, and the interface broadens relative to the water/oil case with increasing TBP concentrations. Additional structural features, including radial distribution functions and orientational distributions, are examined to elucidate the molecular ordering at the interface; the interface structure changes substantially with increasing TBP concentration. Finally, free-energy profiles are computed for (1) a single TBP molecule and a single uranyl nitrate complex [UO₂(NO ₃)₂] across the water/oil interface and (2) a UO ₂(NO₃)₂·TBP₂ complex across both water/oil and water/(oil+TBP) interfaces. The UO₂(NO ₃)₂ complex is strongly repelled from the water/oil interface, while the UO₂(NO₃)₂·TBP ₂ complex exhibits interfacial activity that decreases with increasing TBP concentration. The UO₂(NO₃) ₂·TBP₂ complex displays a net free-energy driving force for partitioning into the oil phase that increases with increasing TBP concentration.

Original language	English
Pages (from-to)	11662-11671
Number of pages	10
Journal	Journal of Physical Chemistry B
Volume	113
Issue number	34
DOIs	https://doi.org/10.1021/jp903470n
State	Published - 2009
Externally published	Yes

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title = "Molecular dynamics simulations of the structure and thermodynamics of carrier-assisted uranyl ion extraction",

abstract = "We present molecular dynamics simulations of interfaces relevant to the selective chemical extraction of uranyl ions from aqueous solution. These molecular-level simulations model ion transfer in the PUREX process and in synthetic, selective membranes. We first present simulations of water/oil interfaces modified by incorporation of tributyl phosphate (TBP) into the oil phase (hexane). A range of concentrations is examined, from a single TBP molecule to values close to those utilized in the PUREX process. The TBP molecules exhibit strong interfacial activity, and the interface broadens relative to the water/oil case with increasing TBP concentrations. Additional structural features, including radial distribution functions and orientational distributions, are examined to elucidate the molecular ordering at the interface; the interface structure changes substantially with increasing TBP concentration. Finally, free-energy profiles are computed for (1) a single TBP molecule and a single uranyl nitrate complex [UO2(NO 3)2] across the water/oil interface and (2) a UO 2(NO3)2·TBP2 complex across both water/oil and water/(oil+TBP) interfaces. The UO2(NO 3)2 complex is strongly repelled from the water/oil interface, while the UO2(NO3)2·TBP 2 complex exhibits interfacial activity that decreases with increasing TBP concentration. The UO2(NO3) 2·TBP2 complex displays a net free-energy driving force for partitioning into the oil phase that increases with increasing TBP concentration.",

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AB - We present molecular dynamics simulations of interfaces relevant to the selective chemical extraction of uranyl ions from aqueous solution. These molecular-level simulations model ion transfer in the PUREX process and in synthetic, selective membranes. We first present simulations of water/oil interfaces modified by incorporation of tributyl phosphate (TBP) into the oil phase (hexane). A range of concentrations is examined, from a single TBP molecule to values close to those utilized in the PUREX process. The TBP molecules exhibit strong interfacial activity, and the interface broadens relative to the water/oil case with increasing TBP concentrations. Additional structural features, including radial distribution functions and orientational distributions, are examined to elucidate the molecular ordering at the interface; the interface structure changes substantially with increasing TBP concentration. Finally, free-energy profiles are computed for (1) a single TBP molecule and a single uranyl nitrate complex [UO2(NO 3)2] across the water/oil interface and (2) a UO 2(NO3)2·TBP2 complex across both water/oil and water/(oil+TBP) interfaces. The UO2(NO 3)2 complex is strongly repelled from the water/oil interface, while the UO2(NO3)2·TBP 2 complex exhibits interfacial activity that decreases with increasing TBP concentration. The UO2(NO3) 2·TBP2 complex displays a net free-energy driving force for partitioning into the oil phase that increases with increasing TBP concentration.

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Molecular dynamics simulations of the structure and thermodynamics of carrier-assisted uranyl ion extraction

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