Sustainable Inorganic Chemistry: Metal Separations for Recycling

Abstract

Inorganic materials are critical components of clean energy technology. For example, rare earths are key for the function of electric car batteries and in permanent magnets used in wind turbines, and palladium helps to reduce harmful exhaust in automotive three-way catalysts. Many of the critical elements for these materials are of low abundance in the earth’s crust, found in few places globally, and/or require energy- and resource-intensive purification. By comparison, many of these elements are concentrated in waste electrical and electronic equipment, which represents an attractive secondary resource. Inorganic chemists are ideally positioned to develop new chemistry and greener processes that are more efficient and use less hazardous reagents to separate high-value metals from waste electronics. The purpose of this Viewpoint is to highlight recent discoveries in fundamental inorganic chemistry that can contribute to new recycling technologies for gold, lithium, palladium, germanium, and rare earths, especially using simple approaches in solid–liquid extraction. Such fundamental studies are expected to help close metal supply chain loops and create circular economies.

Leaching Mechanisms of Industrial Powders of Spent Nickel Metal Hydride Batteries in a Pilot‐Scale Reactor

“…(6)],w hereas others precipitate with Kt of orml anthanide-alkali metal double sulfates [Eq. (7)]. T he main stable nickel species in H 2 SO 4 media is NiSO 4(aq) [Eq.…”

“…However,t he contribution of recycling to the market demand for critical materials is still relatively low because it is not yet technically nor economically feasible at the industrial scale. [6] As ar esult,t he end-of-life recycling rate of REEs is below 3% [1,7] and the endof-life recyclingi nput rate of nickel is only 25 %. [6] The 50 wt % recycling efficiency target to be achieved for NiMH batteries, as described by the European Directive( 2006/66/EC), makesi t necessary for industries to develop more efficient and sustainable recycling schemes, and opens up new possibilities for urban mining.…”

Enhancing Metal Separations by Liquid–Liquid Extraction Using Polar Solvents

“…A liquid–liquid extraction system generally consists of two immiscible phases: an organic phase (less polar, LP) containing the extractant(s), diluent(s) and possibly a modifier, and an aqueous phase (more polar, MP) containing the metals to be separated . The less polar phase has been the objective of extensive studies for improving metal separations in many approaches, including developing new extractants, using mixtures of extractants, changing diluents, adding modifiers, and so on . Although these efforts have significantly advanced metal separations, many challenges still remain, such as the low separation factors of neighboring rare‐earth elements and the difficulty of extracting lower‐valent metals from higher‐valent metals .…”

“…[1,2] The less polar phase has been the objective of extensives tudiesf or improving metal separations in many approaches, including developingn ew extractants, using mixtures of extractants, changing diluents, adding modifiers, and so on. [2][3][4][5][6][7][8][9][10] Althought hese efforts have significantly advanced metals eparations, many challenges still remain, such as the low separation factors of neighboringr areearth elements and the difficulty of extractingl ower-valent metals from higher-valent metals. [5,7,11] In contrast to the ple-thora of studies on the LP phase, the MP phase has received limiteda ttention.W ater has been used as the default polar solvent in the liquid-liquid extraction of metals, whereas numerous other polar solvents have been largely neglected.…”

High-throughput screening for discovery of benchtop separations systems for selected rare earth elements

“…C lean energy technology is increasingly reliant on rare earth elements (RE: Sc, Y, and La-Lu). For example, rare earth (RE) elements are critical components of hybrid car batteries, lighting phosphors, and permanent magnets [1][2][3] . For these applications, precise blends of individual REs are often required.…”