Abstract
AbstractUranium 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.
Highlights
DUE to its long half-life and significance in the nuclear fuel cycle, uranium is the dominant radionuclide by mass in a geological disposal facility (GDF)
All uranium was removed from solution during the reduced stage in both systems (Fig. 1)
After 21 days oxidation in the OCL system the leaching data suggested that the distribution of U changed significantly with ∼15% of the U released before any significant dissolution of Fe (
Summary
DUE to its long half-life and significance in the nuclear fuel cycle, uranium is the dominant radionuclide by mass in a geological disposal facility (GDF). Formation of stable uranium colloids may promote migration of uranium in cementitious environments (Bots et al, 2014; Smith et al, 2014)
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