Role of Manganese Oxides in Controlling Subsurface Metals and Radionuclides Mobility: A Review

The five redox sensitive contaminants at Department of Energy (DOE) sites are technetium (Tc), plutonium (Pu), uranium (U), chromium (Cr), and iodine (I). The environmental fate and transport of these elements is largely controlled by redox and sorption processes. Manganese oxides are environmentally ubiquitous oxidizing agents with high sorption capacities, affecting a wide variety of contaminants. The limited available literature indicates that manganese oxides exert a strong influence on the environmental mobility of these five redox sensitive contaminants. While Tc can be oxidized to increase its environmental mobility, the relationship of Pu, U, Cr, and I with manganese oxides is more complex. They can all be oxidized to more mobile species, but their oxidized forms can also sorb back onto manganese oxides, indicating a potential sink. There is limited literature on this topic, providing many knowledge gaps. For example, most studies use simplified systems, e.g., they use synthetic manganese oxides. In addition, some experiments have not been conducted under realistic environmental conditions of DOE sites; thus, the complexities introduced by realistic environmental systems is still poorly understood. While the available literature provides a precursory understanding of how manganese oxides affect the fate and transport of these five redox sensitive contaminants at DOE sites, further research is warranted.