GEO-CM: Evaluating hydrogeochemical controls on Rare Earth Element and Yttrium mobility during rock weathering from the micro- to landscape-scale

About This Grant

Rare earth elements (REEs) are a group of metals that are critical components of hundreds of consumer products and modern technologies, including smart devices, electric and hybrid vehicles, and advanced batteries. Despite increasing need for access to these resources for everything from national defense applications to clean energy technologies, the U.S. currently has limited domestic sources of REEs, which has limited production output and has driven exploration and development of alternative domestic sources of these critical metals. This project will explore how the waste products of coal production could potentially be an important source of REEs. Although there are vast amounts of these material in the U.S., especially within the Appalachian Region, not all coal mine waste has abundant REEs. The researchers aim to explain why some coal mine wastes have higher amounts of REEs and how this is related to types of rock nearby. Understanding these relationships can help identify areas that could be targeted for cost-effective extraction of REEs, providing a potential economic resource for the region and nation. The project also includes teacher training activities and co-design of a workforce development program that will engage regional high school teachers and students, and provide local science experiences related to locally available, critical materials-related careers. These education activities will provide meaningful workforce and skill development for the Appalachian Region. The primary hypothesis to be tested is that REEs and yttrium (REYs) in acid mine drainage (AMD), a primary form of coal mine waste, are sourced from the weathering of overlying lithologies and that local hydro(geo)logic conditions favor their enrichment in both the AMD that develops in abandoned mines and the secondary solids that precipitate downgradient. The first project will examine grain and sub-grain scale REE speciation and distribution in lithologies overlying coal seams. Lithologies with high concentrations of REYs are likely due to the presence of phosphate minerals in mudstones and siltstones, with more leaching of REYs from larger (> 10 micrometer) euhedral grains in an Fe-poor matrix to minimize re-sequestration by secondary oxides. The second project will link REY output in coal mine drainage to local hydro(geo)logical conditions using concentration-discharge behavior, where pseudo-karst behavior of AMD in abandoned mine works coupled with a surface water-dominant source will result in higher REY loadings due to higher weathering rates compared to groundwater-dominated flow through low transmissivity zones. The third project will discern the relationship between REY enrichment in AMD solids in response to flow conditions and redox variability, where hydrodynamic conditions within AMD deposits control Fe-oxide mineralogy and REY sequestration with highest enrichment in continuous flow systems rather than intermittent flow or vernal ponds. 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.