L. Johnson, B. Schneider, C.E. Duval
Case Western Reserve University,
United States
Keywords: selective separation, adsorption, Lanmodulin
Summary:
Rare earth elements (REEs), specifically the light lanthanides, are crucial in modern technology applications and clean energy technologies. The current state-of-the-art for obtaining REEs is to mine them and separate via solvent extraction. This separation technique is costly and produces large amounts of mixed, organic, radioactive waste, resulting in a large carbon dioxide footprint. Adsorptive materials, like chromatographic columns and membranes, are an energy efficient alternative to solvent extraction. Ligands, like diglycolamide, attached to adsorptive surfaces have shown selective separations of the light lanthanides; however, they require acidic conditions to perform separation. Recently, Lanmodulin (12,000 Da), a protein with natural REE affinity, has been studied as a ligand on resin supports. An alternative approach to achieve higher throughput and higher selectivity is to attach Lanmodulin peptides (1,600 Da) to membrane platforms. In this work, solvent extraction is replaced with peptide-functionalized membrane adsorbers to separate lanthanides from one another from pretreated industrial waste. Poly(vinyl benzylchloride) membranes were electrospun, then crosslinked using dimethylethylenediamine for chemical stability. Allyl methacrylate-co-hydroxyethyl methacrylate (AMA-co-HEMA) brushes were grafted via controlled polymerization, AGET-ATRP. Once poly(AMA-co-HEMA) was grafted, Lanmodulin EF hand loop 1 peptides (LanM1) were attached to the brushes via thiol-ene click reaction using a UV initiator. Membranes were characterized using ATR-FTIR, Raman spectroscopy, and XPS to observe changes in surface chemistry as a result of functionalization reactions. Specifically, XPS shows a definitive peak for S-C bond formation confirming the click reaction. Once synthesized, the membrane platform was tested in equilibrium adsorption studies with 15 ppm solutions of La, Ce, Pr and Nd. ICP-OES was used to obtain preliminary adsorption capacity results which show statistically different amounts of REEs adsorbed and predicted selectivities of 2-4 between light lanthanide neighbors. Additional equilibrium adsorption experiments are underway to construct full isotherms for each ion. This is laying the groundwork for bio-sorbents designed for rare earth purification and other applications requiring covalently tethered, selective ligands.