Adsorption mechanism of hydrated Lu(OH)2+ and Al(OH)2+ ions on the surface of kaolinite

Density functional theory was used to study the adsorption mechanism of hydrated Lu(OH)2+ and Al(OH)2+ ions on (001) kaolinite surface. Calculation results showed that the respective most stable hydration configurations in the water system were Lu(OH)(H2O)72+ and Al(OH)(H2O)52+. Both hydrated ions were adsorbed on the outer layer of the (001) kaolinite aluminium octahedral and silica tetrahedral surfaces through hydrogen bonding. The two hydrated ions were adsorbed on the deprotonated (001) aluminium octahedral kaolinite surface via coordination bonds, with electrons transferred from the water ligand O 2p to the Al 2 s, Lu 5d, and the surface O 2p orbitals. Owing to its smaller radius and fewer water ligands, hydrated Al(OH)2+ was more easily adsorbed on the (001) kaolinite surface than hydrated Lu(OH)2+. The experimental adsorption and microcalorimetry results supported this conclusion, and it is hypothesised that hydrated ions mainly act on the kaolinite surface via inner-layer adsorption.