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

Abstract

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 Dy3+. The structure of DGA on the silica surface was regulated during the modifying processes to obtain DGAb-SiO2 and DGAs-SiO2 adsorbent, which was verified by FTIR and NMR characterization results. The adsorption results showed that the DGAb-SiO2 adsorbent owned a much higher distribution coefficient (Kd) value for the selective adsorption of Dy3+ than the DGAs-SiO2 adsorbent. The higher adsorption selectivity is likely due to the fixed carbon chain of the DGA group on the surface of DGAb-SiO2 adsorbent formed rigid spatial structures of the oxygen atoms, which will be favorable for the selective coordination of Dy3+. Besides its effectiveness in adsorption behavior, the DGAb-SiO2 adsorbent displayed excellent stability. The Kd value of DGAb-SiO2 for Dy3+ selective adsorption maintained a high level after four successive recycling runs. The adsorption kinetics results displayed that the adsorption of Dy3+ 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.