Technoeconomic Assessment of a Sequential Step-Leaching Process for Rare Earth Element Extraction from Acid Mine Drainage Precipitates

Coal waste products have been studied as a new source of rare earth elements (REEs) and other critical minerals (CM) essential for the development of renewable energy technologies, but the economic viability of these source materials is not well understood. This paper examines the technoeconomic performance of a novel process for REE extraction from acid mine drainage precipitates (AMDp) from passive treatment beds in the Appalachian coal basin. The three-phase extraction process includes the excavation and transportation of AMDp, multi-phase pH-driven step-leaching of REEs under ambient conditions, and commercial solvent extraction to produce a saleable-grade rare earth oxide material that can be reduced to a pure metal. Using bench-scale data, we estimate the life-cycle cost of extraction of REEs from two representative Appalachian AMDp feedstock chemistries between 3400 and 5900 $/kg of the mixed REE concentrate produced. Both the AMDp composition and process parameters affect the profitability of REE extraction, with the REE concentration and distribution of REEs in the feedstock, extraction and precipitation reagent consumption rates, and the potential for reagent recycling as the key variables. Economically profitable valorization of REEs from AMDp will require a combination of continued process innovation and sizable financial incentives to substantially influence the domestic supply of REEs.