Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface

Pieter Bots, Arjen van Veelen, J. Frederick W. Mosselmans, Christopher Muryn, Roy A. Wogelius, Katherine Morris

Research output: Contribution to journalArticle

Abstract

Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.
LanguageEnglish
Article number81
Number of pages15
JournalGeosciences
Volume9
Issue number2
DOIs
Publication statusPublished - 8 Feb 2019

Fingerprint

Neptunium
neptunium
Ferrosoferric Oxide
Uranium
magnetite
uranium
Bicarbonates
bicarbonate
Ultraviolet spectroscopy
Carbonates
spectroscopy
Radioisotopes
X-ray spectroscopy
radionuclide
X ray photoelectron spectroscopy
Actinoid Series Elements
Radioactive Waste
carbonate
actinide
Nuclear fuels

Keywords

  • uranium
  • neptunium
  • magnetite
  • surface
  • synchrotron
  • geodisposal

Cite this

Bots, P., van Veelen, A., Mosselmans, J. F. W., Muryn, C., Wogelius, R. A., & Morris, K. (2019). Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface. Geosciences, 9(2), [81]. https://doi.org/10.3390/geosciences9020081
Bots, Pieter ; van Veelen, Arjen ; Mosselmans, J. Frederick W. ; Muryn, Christopher ; Wogelius, Roy A. ; Morris, Katherine. / Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface. In: Geosciences. 2019 ; Vol. 9, No. 2.
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Bots, P, van Veelen, A, Mosselmans, JFW, Muryn, C, Wogelius, RA & Morris, K 2019, 'Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface' Geosciences, vol. 9, no. 2, 81. https://doi.org/10.3390/geosciences9020081

Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface. / Bots, Pieter; van Veelen, Arjen; Mosselmans, J. Frederick W.; Muryn, Christopher; Wogelius, Roy A.; Morris, Katherine.

In: Geosciences, Vol. 9, No. 2, 81, 08.02.2019.

Research output: Contribution to journalArticle

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T1 - Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface

AU - Bots, Pieter

AU - van Veelen, Arjen

AU - Mosselmans, J. Frederick W.

AU - Muryn, Christopher

AU - Wogelius, Roy A.

AU - Morris, Katherine

PY - 2019/2/8

Y1 - 2019/2/8

N2 - Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.

AB - Neptunium and uranium are important radionuclides in many aspects of the nuclear fuel cycle and are often present in radioactive wastes which require long term management. Understanding the environmental behaviour and mobility of these actinides is essential in underpinning remediation strategies and safety assessments for wastes containing these radionuclides. By combining state-of-the-art X-ray techniques (synchrotron based Grazing Incidence XAS, and XPS) with wet chemistry techniques (ICP-MS, liquid scintillation counting and UV-Vis spectroscopy), we determined that contrary to uranium(VI), neptunium(V) interaction with magnetite is not significantly affected by the presence of bicarbonate. Uranium interactions with a magnetite surface resulted in XAS and XPS signals dominated by surface complexes of U(VI), while neptunium on the surface of magnetite was dominated by Np(IV) species. UV-Vis spectroscopy on the aqueous Np(V) species before and after interaction with magnetite showed different speciation due to the presence of carbonate. Interestingly, in the presence of bicarbonate after equilibration with magnetite, an unknown aqueous NpO2+ species was detected using UV-Vis spectroscopy, which we postulate is a ternary complex of Np(V) with carbonate and (likely) an iron species. Regardless, the Np speciation in the aqueous phase (Np(V)) and on the magnetite (111) surfaces (Np(IV)) indicate that with and without bicarbonate the interaction of Np(V) with magnetite proceeds via a surface mediated reduction mechanism. Overall, the results presented highlight the differences between uranium and neptunium interaction with magnetite, and reaffirm the potential importance of bicarbonate present in the aqueous phase.

KW - uranium

KW - neptunium

KW - magnetite

KW - surface

KW - synchrotron

KW - geodisposal

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Bots P, van Veelen A, Mosselmans JFW, Muryn C, Wogelius RA, Morris K. Neptunium(V) and uranium(VI) reactions at the magnetite (111) surface. Geosciences. 2019 Feb 8;9(2). 81. https://doi.org/10.3390/geosciences9020081