Rare earth recycling

(Nanowerk News) 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.
recycling neodymium and dysprosium rare earths
A cost-effective method for separating rare earth elements, such as the neodymium and dysprosium commonly found in permanent magnets, could lead to increased recycling of end-of-life consumer products. (click on image to enlarge)
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 (PNAS, "Accomplishing simple, solubility-based separations of rare earth elements with complexes bearing size-sensitive molecular apertures").
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.
Source: U.S. Department of Energy, Office of Science
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