New thermodynamic model predicts plutonium solubility with iron

Underneath weapons sites, plutonium and other radioactive remnants are present and become difficult to isolate and remove. Complete removal of these materials can be costly and complex. Discovering how to keep radioactive material in the soil and out of the groundwater, whether it is in the United States, Russia, or elsewhere, could protect people and the environment without incurring extreme expenses.

The team's strategy was to move beyond bulk studies of plutonium/iron interactions. They explored the microscopic and molecular processes involved in the reaction. This research has not been tried before because of the samples' radioactivity, which requires specialized facilities and equipment.

The team coupled measurements of plutonium concentrations in water with scanning and transmission electron microscopy analysis of the reaction. The measurements showed that in the presence of soluble iron and a more stable phase of iron, known as goethite, the reaction is enhanced. The two forms of iron speed the formation of soluble plutonium. With this data, the scientists developed the first thermodynamic theory of such an effect.

"This work is a major step forward in understanding the molecular mechanisms that direct the changes in the chemical forms of plutonium," said Dr. Andrew Felmy, a geochemist and lead author of the study.

Because of continued interest in plutonium's behavior in the environment, from both environmental and security angles, the researchers will continue to perform research directed at identifying and understanding subsurface reactions involving iron and plutonium. New capabilities in EMSL, a national scientific user facility, will play a critical role in this research.

More information: Felmy AR, et al. 2011. "Heterogeneous Reduction of PuO2 with Fe(II): Importance of the Fe(III) Reaction Product." Environmental Science & Technology 45:3952-3958. DOI: 10.1021/es104212g

Provided by Pacific Northwest National Laboratory