Acid mine drainage (AMD) – a waste byproduct that must be treated – is an inevitable trade-off for the affordable, abundant and reliable power derived from coal mining operations. But AMD now offers potential economic opportunities, thanks to emerging technology being developed in collaboration with NETL to extract rare earth elements (REEs).
Seventeen elements within the periodic table are considered REEs. Rare earths are highly valuable because they are essential components of modern technological devices, such as cell phones and computer hard drives. They are also used in advanced technologies that support a broad range of industries, including health care, transportation and defense.
REEs are abundant in Earth’s crust yet challenging to extract. China supplies approximately 90 percent of the REEs used worldwide; however, NETL is working to validate the technical and economic feasibility of producing REEs from coal and coal byproducts in small pilot-scale facilities by 2020. Among the Lab’s efforts to achieve that ambitious goal is an innovative Rare Earth Extraction Facility (REEF) recently established at West Virginia University (WVU). The continuously operating bench-scale facility is investigating the capability of extracting REEs and concentrating them to at least 2 percent – or 20,000 parts per million – from sludge produced during AMD treatment.
During Phase 1, WVU and its partners confirmed AMD as a viable source of REEs and developed the separation and extraction process for use with AMD sludge. Estimates based on the volume of AMD generated in Pennsylvania and West Virginia alone suggest that their sludges could generate up to 2,700 tons of REEs per year.
“The impact of the technology being developed at WVU and the REEF is far-reaching,” said Jessica Mullen, federal project manager for NETL. “This process has the potential to enhance our national economy and security by providing critical materials for modern technology components without relying on imports. At the same time, it offers unique opportunities to reinvigorate coal communities by stimulating economic investments, expanding the workforce and promoting responsible stewardship of the environment.”
A second NETL-managed DOE project aimed at extracting REEs from AMD prior to its treatment will also make use of the REEF. Raw AMD is naturally acidic, and this project exploits that fact as researchers carefully control the extraction of REEs from gangue contaminants – waste material consisting of iron, aluminum, manganese and gypsum – that precipitate out during the typical AMD treatment process. The project has the potential to extract enriched REE concentrates of higher purity with greater economic benefits by simplifying the process. As of mid-September, the upstream AMD treatment project had achieved a pre-concentrate result of 1.76 percent total rare earth elements, thereby making the process more economically attractive.