Controls on the fate and speciation of Np(V) during iron (oxyhydr)oxide crystallization

Pieter Bots, Samuel Shaw, Gareth T.W. Law, Timothy A. Marshall, J. Frederick .W. Mosselmans, Katherine Morris

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The speciation and fate of neptunium as Np(V)O2+ during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2+ to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10.5). This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.
LanguageEnglish
Pages3382-3390
Number of pages9
JournalEnvironmental Science and Technology
Volume50
Issue number7
Early online date25 Feb 2016
DOIs
Publication statusPublished - 5 Apr 2016

Fingerprint

Crystallization
Iron oxides
iron oxide
crystallization
goethite
ferrihydrite
Hematite
Neptunium
neptunium
hematite
oxide
iron
X ray absorption spectroscopy
atomic absorption spectroscopy
immobilization
X-ray spectroscopy
hydroxide
Minerals
ferric oxide
Precipitates

Keywords

  • chemical analysis
  • hematite
  • iron
  • iron compounds
  • x-ray
  • absorption spectroscopy

Cite this

Bots, Pieter ; Shaw, Samuel ; Law, Gareth T.W. ; Marshall, Timothy A. ; Mosselmans, J. Frederick .W. ; Morris, Katherine. / Controls on the fate and speciation of Np(V) during iron (oxyhydr)oxide crystallization. In: Environmental Science and Technology . 2016 ; Vol. 50, No. 7. pp. 3382-3390.
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Controls on the fate and speciation of Np(V) during iron (oxyhydr)oxide crystallization. / Bots, Pieter; Shaw, Samuel; Law, Gareth T.W.; Marshall, Timothy A.; Mosselmans, J. Frederick .W.; Morris, Katherine.

In: Environmental Science and Technology , Vol. 50, No. 7, 05.04.2016, p. 3382-3390.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Controls on the fate and speciation of Np(V) during iron (oxyhydr)oxide crystallization

AU - Bots, Pieter

AU - Shaw, Samuel

AU - Law, Gareth T.W.

AU - Marshall, Timothy A.

AU - Mosselmans, J. Frederick .W.

AU - Morris, Katherine

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N2 - The speciation and fate of neptunium as Np(V)O2+ during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2+ to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10.5). This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.

AB - The speciation and fate of neptunium as Np(V)O2+ during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2+ to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10.5). This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.

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KW - absorption spectroscopy

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