Modelling of the uranyl ion interaction at the water/Al(OH)₃ by quantum and classical molecular dynamics methods

This work was performed in the radiochemistry group of the IPN Orsay, it participates in the advancement of knowledge for understanding the behavior of radionuclides through the environment. The behavior and the evolution of the radionuclides, which are often complex phenomena to characterize experimentally, depend on interactions at the interfaces water / mineral surface and can be modeled using theoretical methods. In this study, we chose to use dynamics molecular methods (DM), which can explicitly consider the effects of solvent, temperature and allow to study the dynamics of the uranyl ion. At first, methods of Car-Parrinello dynamics molecular, based on the density functional theory (DFT), were used to characterize the structures of the uranyl ion in solution and at the interface water / (001) face of gibbsite. For low pH condition, the adsorption complexes present at the interface water / (001) face of gibbsite were identified and compared with available experimental data. Their relative energies and activation energies involved in the sorption process were also determined. Secondly, the classical molecular dynamics methods were used to model larger systems, thus more realistic, on longer time scales. Comparing the results DM Car-Parrinello / classical DM showed a classical dynamics, which use the non-polarizable Guilbaud, CLAYFF and SPC/E potentials, can model the behavior of the uranyl ion at the interface water / face (001) of gibbsite. The long simulation times, allow to show particularly the diffusive character of the uranyl ion to the interface water / face (001) of gibbsite. Finally, the effect of temperature rise was studied. Retention of the uranyl ion decreases with temperature. (author)