Rare earth metals, including the lanthanide series, scandium, and yttrium, are critical components in permanent magnets, electric vehicles, smartphones, and more. The elements occur naturally as mixtures in ores and must be purified prior to use. However, the mining and separation of the mineral ore is challenging, in addition to being energy and waste intensive. An interesting alternative to mining is to recycle elements that have been processed into materials. But here again, the cost of re-separation and purification is a limitation. Only a tiny fraction of rare-earth-containing products is recycled. Recently, a group of researchers discovered a separation process that could make purifying recycled rare earth elements much less expensive.
A substantial portion of the cost of recycling rare earth elements is tied to their difficult separation. To improve the economic benefits of recycling, simple chemistry is needed that purifies targeted rare earth elements from technologically relevant mixtures. Adding recycled rare earths as a new source to the supply chain is expected to reduce environmental contamination and energy costs associated with their primary mining and separations. Additionally, a new domestic source of rare earths would be a positive contribution to U.S. technology at competitive prices.
Rare earth elements are crucial materials in many consumer products, such as electronics and automobiles. These elements currently have a significant environmental burden. Despite their capability for reuse, the vast majority are discarded into the trash after only one use. Recycling rare-earth-containing products would provide a steady, domestic source of rare earths to manufacturers while also reducing waste. Currently, the main roadblock to recycling rare earth elements is the cost required to purify the mixtures obtained from consumer devices. Recently, a group of researchers from the University of Pennsylvania discovered a separation process that could make purifying recycled rare earth elements much less expensive. By developing a new organic compound (H3TriNOx) for binding rare earth cations, this group formed 15 different rare earth compounds. Solution studies revealed that the "early" rare earth compounds (containing lanthanum, cerium, praseodymium, neodymium, samarium, or europium) preferred to aggregate and form dimeric species. The team observed no such aggregation for "late" rare earth compounds (containing gadolinium, terbium, dysprosium, yttrium, holmium, erbium, thulium, ytterbium, or lutetium). As a result, the solubility difference of these compounds was large enough to enable efficient separation for all early/late rare earth combinations through a single filtration step. Optimization of the separation conditions was used to improve the effectiveness of specific combinations, most notably the neodymium/dysprosium and europium/yttrium pairs. These pairs are widely used in permanent magnets and compact fluorescent light bulbs, respectively. The TriNOx separations system is expected to contribute to the recycling of these and other end-of-life rare-earth-containing products, providing a cheap and green new source for these critical raw materials.
Eric J. Schelter
University of Pennsylvania
This work was partially funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division under award DE-SC0006518. This work was also funded by the Research Corporation for Science Advancement, Cottrell Scholar Program.
J.A. Bogart, B.E. Cole, M.A. Boreen, C.A. Lippincott, P.J. Carroll, and E.J. Schelter, "Accomplishing simple, solubility-based separations of rare earth elements with complexes bearing size-sensitive molecular apertures." Proceedings of the National Academy of Sciences USA 113(52), 14887-14892 (2016). [DOI: 10.1073/pnas.1612628113]
J.A. Bogart, C.A. Lippincott, P.J. Carroll, and E.J. Schelter, "An operationally simple method for separating the rare-earth elements neodymium and dysprosium." Angewandte Chemie International Edition 54, 8222-8225 (2015). [DOI: 10.1002/anie.201501659]
University of Pennsylvania press release: Penn Researchers Expand Research on Simplifying Recycling of Rare-Earth Metals
University of Pennsylvania press release: Penn Research Simplifies Recycling of Rare-Earth Magnets
National Geographic article: How Acid—and Bacteria—Could Make Recycling Your Phone Greener
Gizmodo article: The Crazy Ways We'll Soon Mine Old Gadgets for Treasure