(158g) A Sustainable, Highly Selective, Chelating Membrane Platform for Rare Earth Element Recovery

Rare earth elements (REEs) are critical in modern technology development like clean energy and defense. The United States has little natural geographical abundance of these elements. Beyond the domesticity barrier, the current state-of-the-art for separating REEs is solvent extraction which comes with drawbacks. The separation technique is expensive and has a significant environmental impact. An energy efficient separation alternative to solvent extraction is adsorption. Materials like chromatographic resins and membranes can be functionalized with selective ligands to perform advanced separations. Diglycolamide is one ligand that has been immobilized on adsorptive surfaces to selectively separate adjacent light lanthanides. A drawback to this ligand is that it requires increasing acid strength to achieve higher selectivity. Recently, bio-sorbents have been studied as selective ligands. Lanmodulin (12,000 Da), a protein that has a natural affinity for REEs, has been used as a ligand on chromatographic resin supports to separate lanthanides. To leverage the selectivity of Lanmodulin and achieve higher throughput, Lanmodulin peptides (1,600 Da) can be tethered to membrane scaffolds.

In this work, solvent extraction is replaced with a novel adsorption platform to separate neighboring lanthanides from an industrial waste source. Electrospun poly(vinylbenzyl chloride) membranes were crosslinked with dimethylethylenediamine for chemical stability. Functionalization of these membranes occurred through two sequential reactions. Controlled polymerization, AGET-ATRP, was used to graft poly(allyl methacrylate-co-hydroxyethyl methacrylate) brushes. Then, a UV initiated, thiol-ene click reaction was performed to attach Lanmodulin EF hand loop 1 peptides to the polymer brushes. Synthesized membranes were characterized using ATR-FTIR, Raman spectroscopy, and XPS to confirm changes in surface chemistry resulting from functionalization reactions. After membrane synthesis, equilibrium adsorption studies with 15 ppm solutions of La, Ce, Pr, and Nd were performed. Adsorption experiments were analyzed using ICP-OES. Preliminary adsorption results show the membrane platform can adsorb each of the first four lanthanides in different amounts with predicted selectivities of 2-4 between adjacent elements. Further equilibrium adsorption experiments are underway to construct isotherms for individual lanthanides. Isotherm data will give insight into the membrane platform REE selectivity. This is laying the groundwork for bio-ligands used in REE purification and other applications that require covalently attached, selective ligands.