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Adsorption of hydrated Al3+ on the kaolinite (001) surface: A density functional theory study
Abstract In order to reveal the microscopic occurrence of Al3+ impurity in ionic rare earth ore on kaolinite surface, density functional theory (DFT) was used to construct the stable hydrate model of Al3+ in the water system. The structure and bonding mechanism of the complexes of outer layer adsorption and inner layer (monodentate/bidentate) adsorption of hydrate Al3+ on kaolinite (001) surface were studied. The DFT simulation results were verified by molecular dynamics (MD) stimulation and adsorption experiments. The results showed that the stable hydrate form of Al3+ is [Al(H2O)6]3+. When hydrated Al3+ is adsorbed on the outer layer of the kaolinite (001) surface, Al3+ is more inclined to be adsorbed on the SiO surface. When hydrated Al3+ is adsorbed on the inner layer of the kaolinite (001) surface, Al tends to form a bond with Ou atoms formed by the deprotonation of the “upright” hydroxyl group on the surface to form monodentate adsorption complexes, and maintains coordination with the surrounding 5 H2O; Al tends to form bonds with the Ou and Ol atoms formed by the deprotonation of the “upright” and “lying” hydroxyl groups on the surface to form bidentate adsorption complexes, due to steric hindrance effect, Al only maintains coordination with the surrounding 3 H2O. The MD simulation results verified the rationality of the adsorption configuration calculated by DFT. Combined with Mulliken population, charge density and partial density of state (PDOS) analysis, it is shown that the AlOs bond in the monodentate/bidentate adsorption complex of hydrated Al3+ has the characteristics of strong ionicity and strong bond filling. The hydrated Al3+ preferentially forms a more stable bidentate adsorption complex on kaolinite surface. Both the calculation of adsorption energy and the results of adsorption experiments support this conclusion.
Graphical abstract Adsorption configuration and bonding mechanism of Al3+ on kaolinite (001) surface in water system. Display Omitted
Highlights Hydrated Al3+ tends to adsorb on Si−O surface with hydrogen bonding during outer-layer adsorption. When monodentate adsorption occurs, Al tends to bond with Ou and maintains coordination with 5 H2O. Al tends to form bonds with the Ou and Ol, and maintains coordination with 3 H2O. The Al–Os bond has the characteristics of strong ionicity and strong bond filling. The bidentate adsorption is preferentially formed.
Adsorption of hydrated Al3+ on the kaolinite (001) surface: A density functional theory study
Abstract In order to reveal the microscopic occurrence of Al3+ impurity in ionic rare earth ore on kaolinite surface, density functional theory (DFT) was used to construct the stable hydrate model of Al3+ in the water system. The structure and bonding mechanism of the complexes of outer layer adsorption and inner layer (monodentate/bidentate) adsorption of hydrate Al3+ on kaolinite (001) surface were studied. The DFT simulation results were verified by molecular dynamics (MD) stimulation and adsorption experiments. The results showed that the stable hydrate form of Al3+ is [Al(H2O)6]3+. When hydrated Al3+ is adsorbed on the outer layer of the kaolinite (001) surface, Al3+ is more inclined to be adsorbed on the SiO surface. When hydrated Al3+ is adsorbed on the inner layer of the kaolinite (001) surface, Al tends to form a bond with Ou atoms formed by the deprotonation of the “upright” hydroxyl group on the surface to form monodentate adsorption complexes, and maintains coordination with the surrounding 5 H2O; Al tends to form bonds with the Ou and Ol atoms formed by the deprotonation of the “upright” and “lying” hydroxyl groups on the surface to form bidentate adsorption complexes, due to steric hindrance effect, Al only maintains coordination with the surrounding 3 H2O. The MD simulation results verified the rationality of the adsorption configuration calculated by DFT. Combined with Mulliken population, charge density and partial density of state (PDOS) analysis, it is shown that the AlOs bond in the monodentate/bidentate adsorption complex of hydrated Al3+ has the characteristics of strong ionicity and strong bond filling. The hydrated Al3+ preferentially forms a more stable bidentate adsorption complex on kaolinite surface. Both the calculation of adsorption energy and the results of adsorption experiments support this conclusion.
Graphical abstract Adsorption configuration and bonding mechanism of Al3+ on kaolinite (001) surface in water system. Display Omitted
Highlights Hydrated Al3+ tends to adsorb on Si−O surface with hydrogen bonding during outer-layer adsorption. When monodentate adsorption occurs, Al tends to bond with Ou and maintains coordination with 5 H2O. Al tends to form bonds with the Ou and Ol, and maintains coordination with 3 H2O. The Al–Os bond has the characteristics of strong ionicity and strong bond filling. The bidentate adsorption is preferentially formed.
Adsorption of hydrated Al3+ on the kaolinite (001) surface: A density functional theory study
Miao, Yuqi (author) / Yan, Huashan (author) / Qiu, Xianhui (author) / Zhou, Xiaowen (author) / Zhu, Dongmei (author) / Li, Xiaobo (author) / Qiu, Tingsheng (author)
Applied Clay Science ; 223
2022-03-25
Article (Journal)
Electronic Resource
English
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