The dependence on international supplies of rare earth elements (REE) have prompted the United States to explore alternative sources and sustainable technologies for domestic REE production. One potential source is the secondary electronic and industrial wastes generated at high volumes at the Department of Defense (DoD) complexes and across the U.S. Current management of these environmentally hazardous wastes requires huge resources/costs for their remediation and disposition, while their high-REE content offers unique opportunities for REE recovery. However, current hydrometallurgical technologies for REE extraction are energy intensive and costly, with low REE recovery rate and the production of toxic wastes. Thus, from both resource recovery and waste management perspectives, it is beneficial to develop environmentally friendly technologies for REE extraction and processing from these secondary wastes. This project aims to develop novel functionalized mesoporous carbon fiber (MCF) traps for effective recovery and separation of REEs from complex weak acid extracts of end-of-life neodymium magnet (NdFeB) scrap. Novel MCF materials will be synthesized and functionalized with selected organic ligands. The functional MCF trap will effectively recover and separate neodymium (Nd), dysprosium (Dy), and praseodymium (Pr) from the complex weak acid extracts of NdFeB magnet scrap, and the MCF trap can be regenerated for repeated REE harvest. The new MCF will lead to technologies that can effectively extract REEs from NdFeB magnet scrap and other secondary wastes, minimize the generation of new hazardous wastes, and reduce/offset the costs for the remediation of secondary waste streams.

This project will rationally select, design, and optimize novel functional MCF materials for effective REE extraction from complex weak acid extracts of a representative secondary waste, NdFeB magnet scrap. In designing ligands for selective binding of REEs in mesoporous materials, two important classes of interactions and challenges must be considered in addition to thermodynamics and kinetics. First, pore size, shape, and surface functionality affect the ligand-pore interaction and the display of functional groups in the pores. Second, pore size and shape and the architecture of the displayed functional groups affect the REE-ligand interaction and the mobility of liquid within the pores, which may lead to synergistic or antagonistic effects on REE recovery efficacy and selectivity. To address these challenges, this project will synthesize novel MCF of tunable pore size (2–50 nanometers), shape (e.g., cylinder, gyroid, and perforated lamellae), and functionalities using diblock or triblock copolymer templates. Selected novel organic ligands will be functionalized onto the pores of MCF for effective recovery and separation of Nd, Dy, and Pr from the complex weak acid extracts of NdFeB magnet scrap. The molecular, nano, to microscopic scale interaction and binding mechanisms of REEs with organic ligands and the MCF materials will be revealed using state-of-the-art spectroscopic techniques, which will aid the rational design and selection of tunable MCF and organic ligands. The spent functionalized MCF materials will also be evaluated for regeneration, reuse, and downstream REE production.

The new functional MCF materials will bring the following technical benefits for selective REE recovery from NdFeB magnet scrap and other waste sources: 1) improved selectivity and extraction capacity for REEs, 2) improved stability, life span, and reusability of sorbent materials in weak acid media, 3) reduced processing steps and costs for REE recovery and separation, 4) reduced release of toxic wastes and risks to human health and environment, and 5) high scalability and robustness of the separation technology. The development and optimization of this technology will ultimately facilitate the domestic recovery of REE from a variety of electronic and industrial waste sin environmentally friendly manner, while mitigating the environmental risks of the wastes at DoD complexes and across the U.S.