Rare-earth elements (REE) have been used in increasing quantities for applications ranging from automobile parts to satellites in recent years. It is estimated that demand for REE usage will grow by 7 times by 2040. It is also expected that the supply-demand gap will further accelerate with current geo-political tensions, which will increase focus on REE recovery and extraction from wastes for domestic sources. There have been various techniques used for REE recovery/separation, such as precipitation, liquid-liquid extraction, and ion exchange resins as sorbent/ solid supports for solid-liquid extraction of REE. Due to the high cost of making resins, the need for more economic sorbents or solid supports has been explored recently. In this study, diethylenetriaminepentaacetic acid (DTPA) ligand was modified by attaching hydrophobic chains and grafted on commercially available solid supports, including organosilica (O), sol-gel activated/synthesized organosilica (D), pyrolyzed coconut shell (C) and Amberlite resin (A). The resultant media were used in absorption studies to see the selectivity and recovery of 17 elements (REE + Sc+ Y+ Th) under various conditions such as pH, dosage, kinetics, and isotherms. O-DTPA medias showed the highest sorption capacity (22 mg/g) and strong selectivity toward Sc and Th between pH 3 and 4. Sorption of REEs onto coconut-based media indicates the DTPA ligand is not attached to the solid support (coconut shell carbon), possibly indicating the insufficient presence of key functional groups. There was no significant selectivity and recovery of REEs onto A-DTPA (13 mg/g) at pH 2.

Investigating selective recovery of rare-earth elements from acid leach solutions: Role of solid support properties

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