New Insights into Processes Impacting Plutonium (Pu) Mobility in the Environment


Reduced iron, Fe(II), found in numerous subsurface environments, is a reductant for a variety of redox-active actinide contaminants, such as Pu, found at DOE sites. Changing the redox state of actinide contaminants can profoundly decrease or increase their mobility by decreasing or increasing their solubility. A key question is whether solid-phase minerals facilitate these Fe(II) reactions by providing a “template” for potential reaction products that drives a more thermodynamically favorable reaction. A research team led by Pacific Northwest National Laboratory demonstrated the heterogeneous reduction of sparingly soluble Pu(IV) to aqueous Pu(III) by Fe(II) in the presence of goethite, a common iron mineral. Experimental data and thermodynamic calculations show how differences in the free energy of various possible solid-phase Fe(III) reaction products on the iron mineral surface can influence the extent of the reduction reaction and the production of aqueous Pu(III). Heterogeneous reduction reactions by Fe(II) have been demonstrated with other actinides such as uranium and technetium, but this study presents the first experimental evidence of enhanced heterogeneous reduction of plutonium by Fe(II) in the presence of an iron mineral. The work is an example of a surface catalyzed reduction mechanism that is not fully captured in current contaminant fate and transport models but is needed to more fully describe the potential mobility of Pu in the environment.


Felmy, A. R., D. A. Moore, K. M. Rosso, O. Qafoku, D. Rai, E. C. Buck, and E. S. Ilton. 2011. “Heterogeneous Reduction of PuO2 with Fe(II): Importance of the Fe(III) Reaction Product,” Environmental Science and Technology, 45, 3952–58. DOI: 10.1021/es104212g.