The National Energy Technology Laboratory (NETL), a national laboratory under the U.S. Department of Energy Office of Fossil Energy, has been developing methods to recover rare earth elements (REEs) from coal wastes, such as acid mine drainage (AMD) and fly ash.
Researchers from NETL have been working to identify ways to harvest those REEs from AMD — water from abandoned carbon ore mines and active mining that flows over or through sulfur-bearing materials, forming acidic solutions. This AMD is currently the main pollutant of surface water in the mid-Atlantic region. AMD-containing waters require remediation throughout Appalachia using various treatment processes, including one that sends mine water through a limestone bed. This passive remediation method causes metals to drop out of the solution and cleans the water prior to discharge. The limestone beds are then dredged and secured in a landfill or buried along with recoverable amounts of REEs.
Christina Lopano, PhD, a research physical scientist who received the Secretary of Energy’s Excellence Award for her work to recover REEs from coal waste streams such as fly ash and AMD, explained that REE’s are essential to the energy, defence, medical and consumer technology manufacturing industries.
Lopano expalined, “Supply and access to those elements are critical for the U.S. economy. However, a majority of the world’s REE sources and manufacturing are controlled by other countries, which is why NETL is pursuing alternative sources closer to home. Work funded by NETL identified acid mine drainage from prior and current mining operations, as potential sources of REEs and other critical minerals.”
In 2014, DOE‘s Office of Fossil Energy and Carbon Management (FECM) and NETL committed to the goal of expanding the nation’s supply of REEs, with an initial focus placed on addressing the feasibility of extracting, separating, recovering and purifying these materials from carbon ore-based resources.
For NETL, this meant conducting intensive internal research to understand how REEs are present in various materials and to what extent they can be separated and recovered. Researchers used a range of resources like classic X-ray diffraction, scanning electron microscopy and microprobe analyses, and cutting-edge analytic characterisation techniques to develop novel extraction techniques. Through that effort, NETL states that it identified promising domestic REE-containing coal-based resources and demonstrated the production of high-purity REEs in bench- and small pilot-scale facilities.
The objectives of the DOE-NETL program from 2014-2020 were to:
- Recover REEs from coal and coal byproduct streams, such as run-of-mine coal, coal refuse, clay/sandstone over/under-burden materials, power generation ash, and aqueous effluents as acid mine drainage
- Advance existing and/or develop new, second-generation or transformational extraction and separation technologies to improve process system economics and reduce the environmental impact of the coal-based REE value and supply chain
- Initiate efforts for the reduction of rare earth oxides to rare earth metals (REMs).
To achieve the mission goals, research was conducted through proposal projects and other DOE national labs including the Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Idaho National Laboratory, and Pacific Northwest National Laboratory. Similarly, collaborative RD&D projects were conducted with industrial stakeholders and numerous universities.
NETL’s REE and CM program has demonstrated the first step towards national independence from reliance on offshore REE and CM suppliers through its RD&D efforts using coal-based resources to produce small quantities of high purity MREOs and CMs. Leveraging accelerated production of these materials in engineering-scale prototype, demonstration and commercial facilities, in parallel with the return of onshore component manufacturing, will facilitate not only self-reliance but also Made in America across numerous critical clean energy and defence product lines and supply chain markets.