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 Eu ions exhibit stronger pH-dependent desorption behavior than Lu, molecular dynamics simulations were applied to investigate the adsorption mechanism of Eu and Lu on a deprotonated kaolinite (001) surface. The simulation results show that the hydration numbers of Eu and Lu are comparable, whereas the ordering degree of water molecules around Eu is higher than that of Lu, which is beneficial to the movement of Eu to preferentially occupy favorable adsorption sites on the kaolinite surface, following which coordination bonds are formed between Eu and the surface. As a result, the desorption rate of Eu decreases sharply with the increase in leaching pH, while the desorption rate of Lu is only slightly affected by pH.