Redox Processes Affecting the Speciation of Technetium, Uranium, Neptunium, and Plutonium in Aquatic and Terrestrial Environments

摘要

Understanding the processes controlling the chemical speciation of radionuclide contaminants is key for predicting their fate and transport in aquatic and terrestrial environments, and is a critical consideration in the design of nuclear waste storage facilities and the development of remediation strategies for management of nuclear legacy sites. The redox processes that influence the chemical speciation, and thus mobility, of Tc, U, Np, and Pu in surface and near-subsurface environments are reviewed, with a focus on coupled biotic-abiotic reactions driven by microbial activity. A case study of U~(Ⅵ) reduction under Fe~(Ⅲ-)- and sulfate-reducing conditions is presented, using a laboratory-based experimental system to simulate potential electron transfer pathways in natural systems. The results suggest that U~(Ⅵ) was reduced to nanoparticulate uraninite (UO_2) and complexed mononuclear U~(Ⅳ) via multiple pathways including direct microbial reduction and coupled biotic-abiotic processes. These results highlight the potential importance of coupled biotic-abiotic processes in determining the speciation and mobility of Tc, U, Np, and Pu in natural and engineered environments.