Green Chemistry Challenge: 2017 Academic Award
Professor Eric J. Schelter of the University of Pennsylvania
Simple and Efficient Recycling of Rare Earth Elements from Consumer Materials Using Tailored Metal Complexes
Professor Eric Schelter, University of Pennsylvania, is being recognized for developing a simple, fast, and low-cost technology to help recycle mixtures of rare earth elements. Reducing the costs to recover these materials creates economic opportunity by turning a waste stream, currently only recycled at a rate of 1%, into a potential revenue stream. About 17,000 metric tons of rare earth oxides are used in the U.S. annually in materials such as wind turbines, catalysts, lighting phosphors, electric motors, batteries, cell phones, and many others. Mining, refining, and purification of rare earths are extraordinarily energy and waste intensive and carry a significant environmental burden.
Summary of Technology:
The rare earths (La-Lu, Sc and Y) are a group of seventeen elements whose intrinsic properties make them extraordinarily useful and irreplaceable in modern technologies, including renewable energy, electronics, lighting, and various defense applications. However, rare earths (REs) tend to all have similar chemical properties and co-occur geologically as mixtures of 5-7 elements in ores, making the primary mining, refining, and purification of rare earths an extraordinarily energy intensive and waste-generating process that creates severe environmental burdens. Hard rock mining and refining requires large quantities of water, acid, and organic solvents, and produces large quantities of hydrofluoric acid, organics, and radionuclide wastes, which can include uranium, thorium, and their decay products. The U.S. Department of Energy has classified several REs as “critical” materials. For consumer materials, purified REs are typically blended into mixtures for their application. The challenging separations chemistry of REs is the chief barrier to widespread recycling, which is currently performed at a rate of only ~1%.
Professor Schelter’s group has developed a new, targeted approach that simplifies and reduces the costs of separating mixtures of REs obtained from consumer materials. This method is expected to contribute to reducing waste, energy use, CO2 production, and primary REs mining by adding recycled REs to the domestic supply chain. The central hypothesis of this work is that tailored organic compounds can provide simple and effective separations for mixtures of RE metals, based on solubility differences of the RE complexes. Phosphors (32% of total market) and magnets (38%), comprising mixtures of Nd/Dy and Eu/Y respectively, are the optimal targets for recycling. Professor Schelter’s group has synthesized a new organic compound (a ‘ligand’): tris(2-tert-butylhydroxylaminato)benzylamine (H3TriNOx) for separations.
Work is currently under way to develop these concepts into practical and industrially viable recycling processes. A recent DOE grant award will support the further development of the technology.
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