J.M. Bradley, L. Osmieri
Los Alamos National Laboratory,
United States
Keywords: lanthanides, deionization, surface functionalization, carbon materials, separation technologies
Summary:
Lanthanides are important catalysts in petroleum refinement as well as key components for manufacturing electronics, optics, and high-strength mechanical parts. However, like other rare earth elements (REEs), primary sources for lanthanides are limited to few locations, and their extraction is difficult and costly. As such, recovery of these critical minerals from secondary sources is essential for mitigating supply risk. Capacitive deionization (CDI) has some energetic advantages over other material recovery methods, which typically require high-pressure pumps, strong heat sources, or use of excess chemicals. It is also easily reversible, and the electrodes can be reused for several cycles. These qualities make CDI a promising technique for recovering lanthanides from secondary sources, but it requires the development of selective electrode materials with high deionization capacities. In this work, we investigated surface functionalization of commercial carbon supports (BLACK PEARLS 2000, Vulcan XC-72, Ketjenblack 300J) as a strategy to increase their affinity toward lanthanides. Wet oxidized, polydopamine coated, and polyglycolamide grafted carbon powders were synthesized, and their performances as CDI cathode materials were compared to those of the bare carbon materials. Surface functionalization was confirmed by FTIR and sessile drop shape analysis, and changes to surface area and pore sizes were characterized by BET analysis. CDI tests were performed to measure selective adsorption of lanthanide ions (Nd3+, Pr3+, Dy3+) versus each other and in the presence of other common cations (Na+, K+, Mg2+, Ca2+). All functionalized materials demonstrated an increase in lanthanide deionization capacity. While wet oxidation had a negative effect on selectivity and reversibility of lanthanide adsorption, both polyglycolamide and polydopamine modified carbons had improved lanthanide adsorption without sacrificing other aspects of cell performance. Overall, this work demonstrates the ability for certain surface functionalizations to enhance the performance of lanthanide CDI cathodes by increasing their ion adsorption capacity.