Molecular Dynamics Simulations of Uranyl Species Adsorption and Diffusion Behavior on Pyrophyllite at Different Temperatures

TN Zhang and XW Xu and L Dong and ZY Tan and CL Liu, ACTA PHYSICO- CHIMICA SINICA, 33, 2013-2021 (2017).

DOI: 10.3866/PKU.WHXB201705113

In this study, molecular dynamics simulations were performed to gain insight into the adsorption and diffusion behavior of uranyl carbonate species on pyrophyllite basal surface at various temperatures (298.15, 313.15, and 333.15 K). At these temperatures, four kinds of uranium species, i.e. UO22+, UO2CO3, UO2(CO3)(2)(2-), UO2(CO3)(3)(4-), and uranyl oligomers were obtained. According to the atomic density profile of each uranyl species, only UO22+ and UO2CO3 were adsorbed on the pyrophyllite surface. Therefore, due to the strong coordination interaction between carbonate ion and uranyl, the pyrophyllite surface exhibited weak adsorption capacity for uranium after prolonged simulations. Self-diffusion coefficients of water molecules and uranyl species in both the adsorbed layer and the diffuse layer were calculated. With increasing temperature, the diffusion coefficients for all species increased; however, in the adsorbed layer, the diffusion coefficients for UO2(CO3)(2)(2-) and UO2(CO3)(3)(4-) increased faster than those for UO22+ and UO2CO3. Nonetheless, the diffuse order remained unchanged in both the layers: UO22+ > UO2CO3 > UO2(CO3)(2)(2-) > UO2(CO3)(3)(4-). This indicates that UO22+ is the main diffusing species.

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