Rare-earth elements (REEs: La–Lu, Y, and Sc) are integral to modern technology. As technological development continues, world demand for these metals will increasingly outpace supply. Consequently, new and sustainable sources are needed, as well as more efficient methods of extraction and purification. Many waste streams—mining effluents, desalination brines, e-waste, and wastewater from semiconductor fabrication plants—contain high concentrations of REEs, which could be extracted. Metal-chelating polymers have great potential in REE extraction and separation applications due to their relatively low cost and high affinity for target elements. For example, polymer-enhanced ultrafiltration is one approach where polymers selectively coordinate specific metals and ultrafiltration membranes then filter out the polymer-metal complexes. Conventional polymers are also used in metal-chelating resins and other solid-phase methods of metal extraction and separation. While much research has focused on the specific chelating ligands attached to polymers, however, relatively little research has explored how the polymer architecture itself affects metal binding. To investigate the interplay between polymer structure and metal chelation, we used isothermal titration calorimetry to directly measure the binding affinity (K<sub>a</sub>), enthalpy changes (ΔH), and stoichiometry of the interactions between a series of REEs in solution and polymers with pendant phosphonate ligands. These measurements enabled us to characterize the complete thermodynamic profile of these polymer-metal interactions. We also used dynamic light scattering to investigate the effect of metal ion identity and concentration of the aggregation behavior of these polymers. Finally, we synthesized a crosslinked resin and evaluated its ability to capture rare-earth elements from simulated mine drainage. These experiments will inform future work on developing chelating polymers for rare-earth element extraction.<br/>

Polymers for rare-earth element extraction

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.