title: Uranium release from sediment to groundwater: influence of water chemistry and insights into release mechanisms.
abstract: Uranium (U) contamination in groundwater often results from natural geochemical processes such as mineral dissolution and desorption of adsorbed U from mineral surface. Although U adsorption and U mineral dissolution have been extensively studied, current knowledge of minerals and water chemistry conditions that control U release in uncontaminated soil and aquifers is still limited. Identification of these minerals and the knowledge of how water chemistry conditions influence U release is critical to better understand, predict, and manage geogenic U contamination in soil and groundwater. The objective of this study is to determine the extent and mechanisms of U release from a heterogeneous natural sediment under water chemistry conditions relevant to natural soil water and groundwater. A sediment sample was collected and characterized by XRD, SEM-EDX and extraction methods, and examined using laboratory leaching experiments. Our results show that Fe-Mn (oxy)hydroxides and silicate minerals are the major U hosting minerals, and a substantial fraction of U exists as adsorbed ions on minerals. We also found that U release is controlled by a number of interactive processes including dissolution of U-bearing minerals, U desorption from mineral surface, formation of aqueous U complexes, and reductive precipitation of U. Results from this study shed light on the important geochemical reactions that need be considered for developing a conceptual model that predicts U contamination in subsurface environment.
authors: Department of Earth Sciences, Memorial University, St. John's, Newfoundland & Labrador, A1B 3X5, Canada.
authors: Md Samrat
authors: MS
authors: Alam
authors: Department of Earth Sciences, Memorial University, St. John's, Newfoundland & Labrador, A1B 3X5, Canada. Electronic address: tcheng@mun.ca.
authors: Tao
authors: T
authors: Cheng
mesh_terms: D000327:Adsorption; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals; D008956:Models, Chemical; D014501:Uranium / Q000032:analysis* / Q000737:chemistry; D014875:Water Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry
chemical_list: D008903:Minerals; D014875:Water Pollutants, Radioactive; D014501:Uranium
keywords: Desorption; Groundwater contamination; Mineral dissolution; Sediment; Uranium release