title: Molecular dynamics simulation of the diffusion of uranium species in clay pores.
abstract: Molecular dynamics simulations were carried out to investigate the diffusive behavior of aqueous uranium species in montmorillonite pores. Three uranium species (UO(2)(2+), UO(2)CO(3), UO(2)(CO(3))(2)(2-)) were confirmed in both the adsorbed and diffuse layers. UO(2)(CO(3))(3)(4-) was neglected in the subsequent analysis due to its scare occurrence. The species-based diffusion coefficients in montmorillonite pores were then calculated, and compared with the water mobility and their diffusivity in aqueous solution/feldspar nanosized fractures. Three factors were considered that affected the diffusive behavior of the uranium species: the mobility of water, the self-diffusion coefficient of the aqueous species, and the electrostatic forces between the negatively charged surface and charged molecules. The mobility of U species in the adsorbed layer decreased in the following sequence: UO(2)(2+)>UO(2)CO(3)>UO(2)(CO(3))(2)(2-). In the diffuse layer, we obtained the highest diffusion coefficient for UO(2)(CO(3))(2)(2-) with the value of 5.48×10(-10) m(2) s(-1), which was faster than UO(2)(2+). For these two charged species, the influence of electrostatic forces on the diffusion of solutes in the diffuse layer is overwhelming, whereas the influence of self-diffusion and water mobility is minor. Our study demonstrated that the negatively charged uranyl carbonate complex must be addressed in the safety assessment of potential radioactive waste disposal systems.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Radiochemistry and Radiation Chemistry Key Laboratory for Fundamental Science, College of Chemistry Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Xiao-yu
authors.initials: XY
authors.lastname: Liu
authors.forename: Lu-hua
authors.initials: LH
authors.lastname: Wang
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zheng
authors.forename: Ming-liang
authors.initials: ML
authors.lastname: Kang
authors.forename: Chun
authors.initials: C
authors.lastname: Li
authors.forename: Chun-li
authors.initials: CL
authors.lastname: Liu
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D004058:Diffusion; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D016062:Porosity; D011850:Radioactive Waste; D017974:Uranium Compounds / Q000737:chemistry*; D018505:Waste Management
chemical_list: D011850:Radioactive Waste; D017974:Uranium Compounds; D001546:Bentonite