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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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 & 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 |
work_keys_str_mv |
AT pieterbots neptuniumvanduraniumvireactionsatthemagnetite111surface AT arjenvanveelen neptuniumvanduraniumvireactionsatthemagnetite111surface AT jfrederickwmosselmans neptuniumvanduraniumvireactionsatthemagnetite111surface AT christophermuryn neptuniumvanduraniumvireactionsatthemagnetite111surface AT royawogelius neptuniumvanduraniumvireactionsatthemagnetite111surface AT katherinemorris neptuniumvanduraniumvireactionsatthemagnetite111surface |
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1724856869347917824 |