Molecular Dynamics Simulations of Uranyl and Uranyl Carbonate Adsorption at Alumino-silicate Surfaces
Adsorption at mineral surfaces is a critical factor controlling the mobility of uranium(VI) in aqueous environments. Therefore, molecular dynamics (MD) simulations were performed to investigate uranyl(VI) adsorption onto two neutral alumino-silicate surfaces, namely the orthoclase (001) surface and the octahedral aluminum sheet of the kaolinite (001) surface. Although uranyl preferentially adsorbed as a bi-dentate innersphere complex on both surfaces, the free energy of adsorption at the orthoclase surface (-15 kcal mol-1) was significantly more favorable than that at the kaolinite surface (-3 kcal mol-1), which was attributed to differences in surface functional groups and to the ability of the orthoclase surface to dissolve a surface potassium ion upon uranyl adsorption. The structures of the adsorbed complexes compared favorably with X-ray absorption spectroscopy results. Simulations of the adsorption of uranyl complexes with up to three carbonate ligands revealed that uranyl complexes coordinated to up to 2 carbonate ions are stable on the orthoclase surface whereas uranyl carbonate surface complexes are unfavored at the kaolinite surface. Combining the MD-derived equilibrium adsorption constants for orthoclase with aqueous equilibrium constants for uranyl carbonate species indicates the presence of adsorbed uranium complexes with one or two carbonates in alkaline conditions, in support of current uranium(VI) surface complexation models.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1129314
- Report Number(s):
- PNNL-SA-99937; 48205; KP1702030
- Journal Information:
- Environmental Science & Technology, 48(7):3899-3907, Journal Name: Environmental Science & Technology, 48(7):3899-3907
- Country of Publication:
- United States
- Language:
- English
Similar Records
Diffusion and Adsorption of Uranyl Carbonate Species in Nanosized Mineral Fractures
Quantitative Prediction of Uranium Speciation and Amidoxime Binding in Seawater from Advanced Simulation Techniques