B. McNeil, K. Menon, O. Khwaja, A. Santos Xavier, C. Iloeje
Argonne National Laboratory,
United States
Keywords: coal ash, waste management, rare earths, supply chain, logistics, optimization, unconventional resources
Summary:
Demand for rare earth elements (REEs) in energy and defence technologies is rising, underscoring the need for a diversified and secure domestic supply chain. Recently, considerable efforts have focused on increasing the production of mined and separated REEs from primary sources. However, the depth of reliance on adversarial foreign actors for REEs justifies the exploration of a wider range of supply-chain strategies, including the development of unconventional REE resources such as legacy coal ash. Coal ash is abundant; however, it is geographically dispersed, compositionally heterogeneous, and stored in various legacy impoundments and landfills. This creates a broad range of challenges for economic REE recovery. Prior studies emphasize resource characterization and plant-level techno-economics, but the system-level cost drivers of a national supply chain remain underexplored. Here, we present an analysis that uses a geospatially explicit and basin-informed coal ash assessment, process mass balances, and techno-economic data to model cost-optimal supply chains for REE production from coal ash. Our study first creates a robust database encompassing resource availability, ash composition and distribution, and technology options for different supply-chain stages and resource types. We then employ RELOG, a supply-chain tool for optimizing logistics and production networks. Through RELOG, we model various geospatial configurations of extraction, processing, and separation facilities, aiming to maximize value from high-quality resources and minimize total facility and transportation costs. Using demand-side drivers, the model determines which resources to exploit, when to exploit them over the model duration, and where facilities should be built to optimize overall logistics. Through scenario development and statistical analysis, we explore infrastructure deployment strategies and policy-driven incentives, as well as the impact of possible techno-economic improvements. Our findings show that strategic facility placement and technology integration can significantly reduce costs, with certain combinations of extraction and separation technologies yielding the most cost-effective outcomes. Geochemical coal ash composition is largely dependent on the source basin from which the primary coal feedstock originates, while physical coal ash composition is influenced by variable placement and landfilling strategies. Compositions vary both across sites and within specific “deposits” of coal ash themselves. These variable characteristics have a significant impact on the recoverability of REEs from different coal ash deposits, which in turn influence optimal supply-chain behaviour. Under optimal conditions, supply chains are still heavily reliant on additional economic incentives from avoided reclamation and waste management costs, the sale of post-processed ash for cement production, and the recovery of other chemical and mineral by-products. By taking a holistic supply-chain perspective, this study identifies the complexities, challenges, and benefits of unconventional resource development. This contributes to the push for a viable domestic REE recovery network, supporting strategic goals in resource security and progressive industrial practices.