Rare earth element extraction from secondary sources: understanding environmental impacts and economic feasibility

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Rare earth elements (REEs) are essential in a variety of important high-tech applications. Lack of diversity in the supply chain for REEs, coupled with significant environmental impacts of primary mining, have made extraction of REEs from secondary sources an attractive alternative. REEs exist in a variety of secondary products, in particular 1) coal combustion products such as fly ash, bottom ash, and incinerator ash, 2) industrial byproducts like slags, dross, phosphogypsum, and red mud, and 3) electronic wastes including nickel-metal hydride batteries, hard drives from laptops and desktop computers, cellular phones, speakers. The objectives of this work are to 1) quantify the material and energy flows of emerging secondary REE extraction processes and their primary alternatives, 2) create a framework to compare economic and environmental performance of primary and secondary sources of rare earth elements, and 3) make recommendations for development of viable domestic supply chains and manufacturing. Methodologies from life-cycle assessment, commodity market modeling, material characterization, and techno-economic analysis will be synthesized to assess processes to recover REEs from byproducts, e.g. coal ash, phosphogypsum, red mud, and electronic waste. The intellectual merit of this research includes 1) establishment of a framework and results to inform research and development for processes to recover REEs from waste products, 2) improved accounting of co-product allocation in REE, 3) enhancing methods to address uncertainty in environmental/economic assessment of developing processes, and 4) addressing variability driven by the quality of the waste, including construction of an open database of REE content of different waste streams. A combinatorial scenario analysis method will be employed that clarifies combinations of parameter values necessary to achieve economic feasibility and environmental benefits. The broader impacts of this work include the potential to enhance U.S.-based manufacturing and reduce environmental impacts of green technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.