Study on the adsorption mechanism of ricinoleate and oleate on kaolinite and quartz surfaces

The introduction of a hydroxyl group in the ricinoleat (ROA⁻) molecule enhances its adsorption selectivity on kaolinite surfaces compared to conventional oleate (OA⁻). In this study, a combined approach of density functional theory (DFT) simulations and experimental validation was employed to investigate the adsorption behaviors of ROA⁻ and OA⁻ on kaolinite and quartz surfaces. Mulliken population, Hirshfeld charge transfer, and PDOS analyses revealed that ROA⁻ adsorption on kaolinite is primarily driven by hydrogen bonding and electrostatic interactions, whereas adsorption on quartz is dominated by weaker hydrogen bonding. The adsorption strength follows the order: ROA⁻/kaolinite > OA⁻/kaolinite > ROA⁻/quartz > OA⁻/quartz. Flotation experiments showed that ROA⁻ achieved a kaolinite recovery of 86.71 % and a separation efficiency of 57.12 % at concentrations below 0.9 mmol/L, outperforming OA⁻. Zeta potential, FTIR, and XPS results further confirmed that the adsorption mechanisms are highly consistent with DFT predictions, offering theoretical guidance for the design of selective anionic collectors for kaolinite separation.