Interaction of plutonium with magnetite under anoxic conditions: Reduction, surface complexation, and structural incorporation


Interaction of plutonium with magnetite under anoxic conditions: Reduction, surface complexation, and structural incorporation

Scheinost, A. C.; Kirsch, R.; Dumas, T.; Fellhauer, D.; Gaona, X.; Altmaier, M.

For the redox-reactive fission products and actinides Se, Tc, U, and Np, it is assumed that the strongly reducing conditions in deep underground, anoxic nuclear waste repositories will reduce their mobility, since their lower-oxidation states commonly form solids of very low solubility. This is not necessarily the case for Pu, where the hexa- and pentavalent aquo-complexes prevalent at higher pe are replaced at lower pe by a tetravalent solid of low solubility, PuO2, but also by a trivalent aquocomplex at lower pH (Fig. 1) [1, 2]. Since the predominance field of Pu(III)aq overlaps with that obtained for the Fe(II)/Fe(III) redox couple as aqueous species or in equilibrium with Fe(II)-bearing minerals [3], one should assume that Pu(III) exists under anoxic nuclear waste conditions, where Fe(II) sources are provided by corroding steel containers and Fe(II)-bearing clays used as confinement, as well as by geogenic minerals. Although some studies have previously reported on trivalent lanthanides, little is known on the retention mechanisms of the trivalent Pu aquo complex by minerals, with implications for the safety case of nuclear waste repositories.

Keywords: Plutonium; Redox; XAFS; XANES; magnetite

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Publ.-Id: 18731