Several U.S. DOE sites have been contaminated by transuranic radionuclides (TRU). To understand the transport of these TRU in the vadose zone, interfacial reactions of plutonium with manganese oxide/hydroxide mineral surfaces are currently being investigated. Manganese oxides, present as minor phases in the vadose zone, can preferentially sequester TRU over iron oxide/hydroxide minerals present in larger amounts. To understand the interactions between plutonium and manganese oxyhydroxides, the sorption of plutonium ions in well-defined oxidation states on well-characterized mineral surfaces as a function of pH, actinide concentration, and ionic strength have been investigated. The oxidation state of the sorbed plutonium and the local structure of the metal sorption complexes have been determined using X-ray absorption fine structure (XAFS). Ultimately, this data will be used to develop surface complexation models in an attempt to predict TRU migration in the vadose zone to nearby water supplies.

Several U.S. DOE sites have been contaminated by transuranic radionuclides (TRU). To understand the transport of these TRU, the interaction of plutonium withmanganese oxide hydroxide mineral surfaces is currently being studied. Manganese oxides, present as minor phases, can preferentially sequester TRU over iron oxide/hydroxide minerals present in larger amounts. To understand these interactions the sorption of plutonium ions on characterized mineral surfaces as a function of pH and actinide concentration are being studied. The oxidation state of the sorbed plutonium and the local structure of the metal sorption complexes have been determined using X-ray absorption fine structure (XAFS). Ultimately, this data will be used to develop surface complexation models in an attempt to predict TRU migration in the vadose zone.

Certain minerals in the environment can sorb metals, including transuranic radionuclides (TRU) such as plutonium. Recent studies indicate that manganese oxide minerals can preferentially sequester TRU over other minerals present in larger quantities. This has implications for the transport of TRU through the environment. The interaction of aqueous plutonium species with manganese oxide minerals is currently under investigation. The mineral surfaces are characterized using x-ray diffraction, BET surface area measurements, potentiometric titration, and soft x-ray absorption fine structure spectroscopy (XAFS) at the manganese L3 and oxygen K edges. These minerals show a strong tendency for sorbing plutonium ions, and the amount of plutonium sorbed increases with higher pH and lower plutonium concentration. Redox reactions between the minerals and the plutonium are studied using absorption spectroscopy and XAFS. XAFS is also used to determine the structures of the metal/mineral complexes. Ultimately, this data will be incorporated into models that will be used to predict the migration of TRU through the environment.