Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface

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 an...

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Main Authors: Pieter Bots, Arjen van Veelen, J. Frederick W. Mosselmans, Christopher Muryn, Roy A. Wogelius, Katherine Morris
Format: Article
Language:English
Published: MDPI AG 2019-02-01
Series:Geosciences
Subjects:
XAS
XPS
Online Access:https://www.mdpi.com/2076-3263/9/2/81
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spelling doaj-0c32e70361994165a5f24820f23d56282020-11-25T02:23:50ZengMDPI AGGeosciences2076-32632019-02-01928110.3390/geosciences9020081geosciences9020081Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) SurfacePieter Bots0Arjen van Veelen1J. Frederick W. Mosselmans2Christopher Muryn3Roy A. Wogelius4Katherine Morris5Research Centre for Radwaste Disposal, School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UKResearch Centre for Radwaste Disposal, School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UKDiamond Light Source Ltd., Diamond House, Harwell Science &amp; Innovation Campus, Didcot OX11 0DE, UKPhoton Science Institute, School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UKResearch Centre for Radwaste Disposal, School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UKResearch Centre for Radwaste Disposal, School of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UKNeptunium 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 NpO<sub>2</sub><sup>+</sup> 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.https://www.mdpi.com/2076-3263/9/2/81uraniumneptuniummagnetitesurfacesynchrotronXASXPSgeodisposalreduction
collection DOAJ
language English
format Article
sources DOAJ
author Pieter Bots
Arjen van Veelen
J. Frederick W. Mosselmans
Christopher Muryn
Roy A. Wogelius
Katherine Morris
spellingShingle Pieter Bots
Arjen van Veelen
J. Frederick W. Mosselmans
Christopher Muryn
Roy A. Wogelius
Katherine Morris
Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
Geosciences
uranium
neptunium
magnetite
surface
synchrotron
XAS
XPS
geodisposal
reduction
author_facet Pieter Bots
Arjen van Veelen
J. Frederick W. Mosselmans
Christopher Muryn
Roy A. Wogelius
Katherine Morris
author_sort Pieter Bots
title Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
title_short Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
title_full Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
title_fullStr Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
title_full_unstemmed Neptunium(V) and Uranium(VI) Reactions at the Magnetite (111) Surface
title_sort neptunium(v) and uranium(vi) reactions at the magnetite (111) surface
publisher MDPI AG
series Geosciences
issn 2076-3263
publishDate 2019-02-01
description 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 NpO<sub>2</sub><sup>+</sup> 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.
topic uranium
neptunium
magnetite
surface
synchrotron
XAS
XPS
geodisposal
reduction
url https://www.mdpi.com/2076-3263/9/2/81
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AT jfrederickwmosselmans neptuniumvanduraniumvireactionsatthemagnetite111surface
AT christophermuryn neptuniumvanduraniumvireactionsatthemagnetite111surface
AT royawogelius neptuniumvanduraniumvireactionsatthemagnetite111surface
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