Size-Selective Separation of Rare Earth Elements Using Functionalized Mesoporous Silica Materials

• Published in: ACS applied materials & interfaces Vol. 11; no. 26; pp. 23681 - 23691
• Main Authors: Hu, Yimu, Misal Castro, Luis C, Drouin, Elisabeth, Florek, Justyna, Kählig, Hanspeter, Larivière, Dominic, Kleitz, Freddy, Fontaine, Frédéric-Georges
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 03-07-2019
• Subjects: mesoporous silica; bauxite residue; red mud; selective extraction; rare earth elements
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.9b04183

The separation and preconcentration of rare earth elements (REEs) from mineral concentrates in an economically and environmentally sustainable manner are difficult tasks due to their similar physicochemical properties. Herein, a series of tetradentate phenylenedioxy diamide (PDDA) ligands were synthesized and grafted on large-pore three-dimensional KIT-6 mesoporous silica. In solid-phase extraction, the hybrid sorbents enable a size-selective separation of REEs on the basis of the bite angles of the ligands. In particular, smaller REE3+ ions are preferentially extracted by KIT-6-1,2-PDDA, whereas light REEs with larger ionic radius are favored by KIT-6-1,3-PDDA. The exposure of bauxite residue digestion solution containing REEs as well as a number of types of competitive ions (including Th and U) to the sorbents results in selective recovery of target REEs. The possibility of regenerating the mesoporous sorbents through a simple loading–stripping–regeneration process is demonstrated over up to five cycles with no significant loss in REE extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials.