Plutonium Desorption from Mineral Surfaces at Environmental Concentrations of Hydrogen Peroxide

Abstract

Knowledge of Pu adsorption and desorption behavior on mineral surfaces is crucial for understanding its environmental mobility. Here we demonstrate that environmental concentrations of H₂O₂ can affect the stability of Pu adsorbed to goethite, montmorillonite, and quartz across a wide range of pH values. In batch experiments where Pu­(IV) was adsorbed to goethite for 21 days at pH 4, 6, and 8, the addition of 5–500 μM H₂O₂ resulted in significant Pu desorption. At pH 6 and 8 this desorption was transient with readsorption of the Pu to goethite within 30 days. At pH 4, no Pu readsorption was observed. Experiments with both quartz and montmorillonite at 5 μM H₂O₂ desorbed far less Pu than in the goethite experiments highlighting the contribution of Fe redox couples in controlling Pu desorption at low H₂O₂ concentrations. Plutonium­(IV) adsorbed to quartz and subsequently spiked with 500 μM H₂O₂ resulted in significant desorption of Pu, demonstrating the complexity of the desorption process. Our results provide the first evidence of H₂O₂-driven desorption of Pu­(IV) from mineral surfaces. We suggest that this reaction pathway coupled with environmental levels of hydrogen peroxide may contribute to Pu mobility in the environment