Surface structure regulating of silica adsorbent for the selective adsorption of heavy rare earth

Rare earth element (REE) is a strategic metal resource, heavy REE owns higher economic and strategic value compared with light rare earth elements. However, it is a great challenge for the separation of heavy rare earth ion efficiently in the solution with mixed rare earth ions due to the similar physicochemical properties of heavy and light REE. In this paper, the diglycolamide (DGA) modified silica adsorbents were prepared and applied to the selective adsorption of heavy earth ion Dy 3+ . The structure of DGA on the silica surface was regulated during the modifying processes to obtain DGA b -SiO 2 and DGA s -SiO 2 adsorbent, which was verified by FTIR and NMR characterization results. The adsorption results showed that the DGA b -SiO 2 adsorbent owned a much higher distribution coefficient ( K d ) value for the selective adsorption of Dy 3+ than the DGA s -SiO 2 adsorbent. The higher adsorption selectivity is likely due to the fixed carbon chain of the DGA group on the surface of DGA b -SiO 2 adsorbent formed rigid spatial structures of the oxygen atoms, which will be favorable for the selective coordination of Dy 3+ . Besides its effectiveness in adsorption behavior, the DGA b -SiO 2 adsorbent displayed excellent stability. The K d value of DGA b -SiO 2 for Dy 3+ selective adsorption maintained a high level after four successive recycling runs. The adsorption kinetics results displayed that the adsorption of Dy 3+ followed pseudo-second-order kinetic, and the adsorption process fitted the Langmuir isotherm model. Additionally, the same adsorption rules for the rare earth ions were observed over DGA-KIT-6 adsorbent, indicating the high universality of the surface modification to the adsorbent support, which will provide an intentional reference for the surface modification to other adsorbent support.