Uranium fate during crystallization of magnetite from ferrihydrite in conditions relevant to the disposal of radioactive waste

Uranium incorporation into magnetite and its behaviour during subsequent oxidation has been investigated at high pH to determine the uranium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to U(VI...

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Bibliographic Details
Published in:Mineralogical magazine 2015-11, Vol.79 (6), p.1265-1274
Main Authors: Marshall, Timothy A, Morris, Katherine, Law, Gareth T. W, Mosselmans, J. Frederick W, Bots, Pieter, Roberts, Hannah, Shaw, Samuel
Format: Article
Language:English
Subjects:
actinides
crystallization
Environmental geology
EXAFS
EXAFS data
experimental studies
ferrihydrite
Geochemistry
geodisposal
incorporation
laboratory studies
leachate
magnetite
metals
migration of elements
mobility
mobilization
oxides
radioactive waste
spectra
uranium
valency
waste disposal
waste disposal sites
X-ray spectra
XAFS spectra
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Summary:Uranium incorporation into magnetite and its behaviour during subsequent oxidation has been investigated at high pH to determine the uranium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to U(VI)aq containing cement leachates (pH 10.5-13.1) and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of XRD, chemical extraction and XAS techniques provided direct evidence that U(VI) was reduced and incorporated into the magnetite structure, possibly as U(V), with a significant fraction recalcitrant to oxidative remobilization. Immobilization of U(VI) by reduction and incorporation into magnetite at high pH, and with significant stability upon reoxidation, has clear and important implications for limiting uranium migration in geological disposal of radioactive wastes.
ISSN:0026-461X
1471-8022
DOI:10.1180/minmag.2015.079.6.02