Influence of impurities on adsorption of hydrated Y3+ ions on the kaolinite (001) surface

Abstract

The adsorption behavior of hydrated Y3+ ions on the outer and inner layers of the kaolinite (001) aluminum hydroxyl surface is studied by density functional theory. The bonding mechanism and the effect of common impurities (Mg, Ca and Fe) on the inner layer adsorption behavior are investigated. The results shows that the hydrated Y3+ ions retain the original number of coordinated water molecules and adsorb on the outer layer of the surface of kaolinite through hydrogen bonding, with an adsorption energy of − 262.66 kJ·mol−1. When the inner layer is adsorbed, the number of coordinated water molecules of the hydrated Y3+ ions decreases obviously due to the steric hindrance effect and they are adsorbed on the Ou site of the surface mainly through Y-Os covalent bonds. The electrons are transferred from the 5 s and 4p orbitals of the Y ions to the 2p orbital of the Os ions on the surface. The adsorption energy (−744.52 kJ·mol−1) is much lower than that for the outer layer. These results indicate that the inner layer adsorption of hydrated Y3+ ions occurs preferentially on the kaolinite (001) aluminum hydroxyl surface. The internal adsorption configurations and adsorption energies of hydrated Y3+ ions on the kaolinite surface are significantly affected by Mg, Ca and Fe doped at the Al sites, respectively. The adsorption of hydrated Y3+ ions on kaolinite surface becomes stronger with the increase of doping ion concentration with Mg, Ca and Fe doping, respectively, and the Ca and Mg impurities therefore significantly promote the adsorption of hydrated Y3+ ions. These results are helpful in revealing the microscopic adsorption mechanism of rare earth elements on ion-adsorbed rare earth minerals.