The mobility of plutonium (Pu) in the subsurface is affected by Pu-mineral interactions such as adsorption-desorption and structural incorporation. Previous studies have demonstrated a high affinity of Pu for Fe-oxide minerals that are ubiquitous in the environment and are characterized by high redox reactivity and surface area. The hydrous ferric oxide, ferrihydrite, is a common, poorly crystalline, metastable early product of both biotic and abiotic precipitation of iron, and is a precursor to other more crystalline iron oxides such as hematite (Fe2O3) and goethite (FeOOH). The aim of this work is to evaluate how Fe-oxide minerals structurally incorporate adsorbed Pu during Fe-oxide phase alteration and crystal growth. In this work, we investigated the incorporation of Pu(IV) in ferrihydrite and subsequent alteration to goethite or hematite via heating and aging. The extent of Pu incorporation into ferrihydrite and subsequent alteration to goethite and hematite was monitored by liquid scintillation counting and characterized by SEM, TEM and NanoSIMS. Preliminary data indicate that sorption equilibrium of Pu(IV) onto ferrihydrite is reached within one week. Upon transformation of Pu(IV)–ferrihydrite, goethite showed a higher extent of Pu-incorporation than hematite. The extent of Pu incorporation in ferrihydrite, goethite and hematite has important implications for the long-term performance of nuclear waste repositories, particularly from the standpoint of irreversible association of Pu with mineral phases. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Plutonium incorporation into goethite and hematite during crystallization from ferrihydrite Plutonium incorporation into goethite and hematite during crystallization from ferrihydrite

253rd National Meeting (2017)

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