DFT study of the effect of impurity defects on the inner-layer adsorption of hydrated Al(OH)2+ on the kaolinite (001) surface

Impurity defects are ubiquitous on the kaolinite surface. Density functional theory (DFT) was used to study the adsorption mechanism of Al3+ dihydroxy hydrate on ideal and impurity-doped kaolinite (001) Al-OH surfaces, and the influence of three common impurity defects, namely Mg, Ca, and Fe, on the surface properties. In addition, the effects of van der Waals forces and effective Coulomb repulsion on DFT calculations results are compared. The results show that the stable hydration configuration of Al(OH)(2)(+) is Al(OH)(2)(H2O)(4)(+). Hydrated Al(OH)(2)(+) tends to be adsorbed at the O-t site and Al-O-s are filled with bonding orbitals. Compared with the ideal kaolinite surface, hydrated Al(OH)(2)(+) is more easily adsorbed on the Mg-doped surface. Mg and Ca doping enhanced the activity of surface O atoms and made the hydrated Al(OH)(2)(+) more easily adsorbed on the surface, while Fe doping decreased the activity of surface O atoms. The van der Waals force has little effect on the surface properties and adsorption configuration. Since the effective Coulomb repulsion parameter U takes into account the Coulomb repulsion between local electrons with opposite spins on the Fe atom, the Fe-doped system can be described more accurately. The research results reveal the change of properties of kaolinite surface after doping and the adsorption mechanism of impurity Al on the doped kaolinite surface, which provides a reference for the development of high-efficiency ionic rare earth ore leaching agent. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study used DFT to investigate the adsorption mechanism of impurity Al3+ dihydroxy hydrate on the kaolinite surface and the influence of impurity Mg, Ca, and Fe on surface properties. The results showed that doping affected the adsorption ability and surface activity.