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

Area of Science:

• Materials Science
• Inorganic Chemistry
• Separation Science

Background:

• Separating rare earth elements (REEs) is challenging due to their similar chemical properties.
• Existing methods often lack economic and environmental sustainability.
• Need for efficient and selective methods for REE preconcentration from complex matrices.

Purpose of the Study:

• To develop novel hybrid sorbent materials for size-selective separation of REEs.
• To investigate the efficacy of these sorbents in extracting REEs from bauxite residue digestion solutions.
• To evaluate the reusability and stability of the developed sorbent materials.

Main Methods:

• Synthesis of tetradentate phenylenedioxy diamide (PDDA) ligands.
• Grafting PDDA ligands onto large-pore three-dimensional KIT-6 mesoporous silica.
• Solid-phase extraction utilizing the size-selective properties of the hybrid sorbents based on ligand bite angles.

Main Results:

• Hybrid sorbents demonstrated size-selective REE separation based on ionic radius and ligand bite angle.
• KIT-6-1,2-PDDA preferentially extracted smaller REE3+ ions, while KIT-6-1,3-PDDA favored light REEs.
• Selective recovery of REEs from bauxite residue digestion solution containing thorium and uranium was achieved.
• Sorbents were successfully regenerated over five cycles with no significant loss in extraction capacity.

Conclusions:

• The developed PDDA-grafted KIT-6 mesoporous silica sorbents offer an effective and selective method for REE separation.
• The size-selective mechanism provides a novel approach for separating REEs with similar properties.
• The sorbents exhibit excellent stability and reusability, indicating their potential for sustainable REE recovery.