(152aa) Electrified Lixiviation of Rare Earth Elements from Coal Mining Waste

Rare earth elements (REE) are a group of metals that are key drivers of the new-age economy, as these REEs are essential components of several high-tech technologies, including wind turbines, magnets, and video displays. With global increase in demand for green technology, about 12,000 metric tons of REE are consumed per year in the US and estimated to increase in the future¹. However, more than 85% of the world’s supply is from the Asia Pacific region², a risky proposition considering that any disruption in that region would have a significantly negative impact on the global supply chain of the aforementioned technologies. REEs has been identified to be present in coal-related resources¹, nevertheless, a key limitation to commercial extraction is the low concentrations of REE in these raw materials, typically in the ppb or ppm range³. Typical REE extraction methods, pyrometallurgy and hydrometallurgy, suffer from economies of scale associated with typical chemical processes, i.e., processes are only economical at large-scale centralized facilities⁴. Therefore, an extraction technique that is both modular (that can be applied at smaller decentralized resource locations due to flexible scalability) and highly selective (that can be tuned to target higher-value REE) would alleviate this REE supply concern by improving extraction economics.

Maes et al. explored the potential of enriching solvent with REE from Monazite using electrochemical extraction and found different leaching efficiencies for different REE with Nd extracted at a higher concentration than La⁵. The effectiveness of this electrochemical driving force and the selectivity of REE at different potential from an alternative less-concentrated REE coal pre-combustion waste is unknown. This research’s objective is to enhance the lixiviation (i.e., extraction of a soluble material) of rare earth elements from solid coal mining waste residues (50:50 coal to ash composition) through the addition of an electrochemical stimulus to chemical extraction design variables. Specifically, applying an electrical stimulus below that for hydrogen generation introduces a voltage gradient that induces diffusion of the higher concentration ionic species (typically the adsorbents for the REE) to the electrode surface, and therefore increases the availability of the REE at the electrode. As an added advantage, these electrified techniques can be coupled with renewable energy sources such as solar or wind, thus mitigating the need for fossil energy consumption⁶.

In this study, to be presented at the annual meeting, the effect of process variables such as temperature, cathodic potential, agitation speed and solvent type on extracted REE concentration in the liquid phase and selectivity of each REE will be reported. Furthermore, preliminary process economics will be reported via specific energy consumed in the process.

References:

(1) Vass, C. R.; Noble, A.; Ziemkiewicz, P. F. The Occurrence and Concentration of Rare Earth Elements in Acid Mine Drainage and Treatment By-Products: Part 1—Initial Survey of the Northern Appalachian Coal Basin. Min. Metall. Explor. 2019, 36 (5), 903–916. https://doi.org/10.1007/s42461-019-0097-z.

(2) Hower, J. C.; Granite, E. J.; Mayfield, D. B.; Lewis, A. S.; Finkelman, R. B. Notes on Contributions to the Science of Rare Earth Element Enrichment in Coal and Coal Combustion Byproducts. Minerals 2016, 6 (2), 32. https://doi.org/10.3390/min6020032.

(3) Lin, R.; Howard, B. H.; Roth, E. A.; Bank, T. L.; Granite, E. J.; Soong, Y. Enrichment of Rare Earth Elements from Coal and Coal By-Products by Physical Separations. Fuel 2017, 200, 506–520. https://doi.org/10.1016/j.fuel.2017.03.096.

(4) Zhang, W.; Rezaee, M.; Bhagavatula, A.; Li, Y.; Groppo, J.; Honaker, R. A Review of the Occurrence and Promising Recovery Methods of Rare Earth Elements from Coal and Coal By-Products. Int. J. Coal Prep. Util. 2015, 35 (6), 295–330. https://doi.org/10.1080/19392699.2015.1033097.

(5) Maes, S.; Zhuang, W.-Q.; Rabaey, K.; Alvarez-Cohen, L.; Hennebel, T. Concomitant Leaching and Electrochemical Extraction of Rare Earth Elements from Monazite. Environ. Sci. Technol. 2017, 51 (3), 1654–1661. https://doi.org/10.1021/acs.est.6b03675.

(6) Sedlak, D.; Mauter, M.; Macknick, J.; Stokes-Draut, J.; Fiske, P.; Agarwal, D.; Borch, T.; Breckenridge, R.; Cath, T.; Chellam, S.; Childress, A.; Dionysiou, D.; Giammar, D.; Hoek, E.; Jiang, S.; Katz, L.; Kim, J.; Kostecki, R.; McCutcheon, J.; Polsky, Y.; Stoll, Z.; Xu, P. National Alliance for Water Innovation (NAWI) Master Technology Roadmap; NREL/TP-6A20-80705, 1818076, MainId:77489; 2021; p NREL/TP-6A20-80705, 1818076, MainId:77489. https://doi.org/10.2172/1818076.