Theoretical Investigation of Competitive Adsorption of Light and Heavy Rare Earth Ions on the (001) Surface of Kaolinite

Kaolinite is the primary mineral in ion-adsorption rare earth ores, and improving our understanding of the adsorption state of REEs on kaolinite will benefit efforts to leach REEs from these ores. In order to explain why Eu3+ ions exhibit stronger pH-dependent desorption behavior than Lu3+, molecular dynamics simulations were applied to investigate the adsorption mechanism of Eu3+ and Lu3+ on a deprotonated kaolinite (001) surface. The simulation results show that the hydration numbers of Eu3+ and Lu3+ are comparable, whereas the ordering degree of water molecules around Eu3+ is higher than that of Lu3+, which is beneficial to the movement of Eu3+ to preferentially occupy favorable adsorption sites on the kaolinite surface, following which coordination bonds are formed between Eu3+ and the surface. As a result, the desorption rate of Eu3+ decreases sharply with the increase in leaching pH, while the desorption rate of Lu3+ is only slightly affected by pH.