hedinRARE EARTH ELEMENTS IN AMD TREATMENT WASTES
Acid mine drainage (AMD) has been proposed as a novel source of rare earth elements (REE); a group of elements that include critical metals for clean energy technologies. REE are sequestered in the waste solids produced from precipitating metals during the treatment of AMD. Because these solids are typically landfilled or buried on site, they are a low cost, readily available REE source.
This work involved sampling AMD waters and solids, characterizing AMD solids using chemical and physical techniques, and constructing geochemical models to simulate dissolved REE attenuation from AMD. Sampling data show that AMD solids produced from low pH AMD treated by limestone or NaOH produce solids with the highest concentrations of REE and that these solids typically contain Fe, Al, and Mn phases. Characterization demonstrates that for all AMD solids evaluated, acidic and/or reducing extractions are required to mobilize REE. In solids dominated by Al phases, REE are widely dispersed throughout. However, in solids containing Fe and Mn phases, REE can co-associated with these phases. Finally, geochemical modeling indicates that pH dependent dissolved REE attenuation is dominated by surface complexation on Fe, Al, and Mn oxide/hydroxides. The models developed here can be applied to other AMD systems to predict REE removal and what solid phases will be enriched in REE and to engineer AMD systems to produce specific minerals enriched in REE.
Two peer reviewed publications from the research are available below.