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Acid mine drainage (AMD) samples collected from a site in Pennsylvania. The right flask shows the AMD sludge and the left flask shows the AMD runoff water prior to treatment. Photo courtesy of RTI.
NETL Supports Research Triangle Institute’s Exploration of Nanofiltration REE

As securing a domestic source of rare earth elements (REEs) remains a priority for the U.S. Department of Energy, a potential opportunity to obtain these elements is within reach thanks to our nation’s abundant coal resources.

With support from the National Energy Technology Laboratory (NETL), the Research Triangle Institute (RTI) is exploring methods by which REEs can be extracted, separated, and recovered from coal-based resources.

As part of an NETL-funded cooperative agreement, Zachary Hendren, Ph.D., and his RTI team, which include Cerahelix and Veolia Water Technologies, are testing the efficacy of various approaches to REE recovery and enrichment (with a targeted concentrated goal of 2wt% mixed REE) from acid mine drainage (AMD) samples using a combination of novel technologies.

This means that of one of the nation’s most abundant resources, coal, could provide a potential source of vital REEs without the investment required to open a new mine specifically dedicated to their extraction. Already existing coal mines could provide domestic supplies if the extraction methods are refined and desired purities reached.

Hendren and his team assessed several technologies for REE concentration and recovery. Among them was nanofiltration, in which polymer and ceramic membranes inserted in a tubular structure filter extract the valuable elements from AMD effluent streams.

Current membrane water treatment technologies are used to remove particulate matter or all dissolved ions. Regarding REE recovery, nanofiltration membranes were designed to allow monovalent ion passage while rejecting multivalent ions. These nanofiltration membranes are like those used for enhanced oil recovery.

In RTI’s experiments, membranes were used to concentrate desirable elements (e.g. lanthanum and praseodymium, among others) and remove the bulk of the low-value ions (e.g. sodium, potassium, heavy metals, and divalent metal salts) so performance of the final downstream recovery process could be enhanced, achieving maximum recovery retrieval of valuable REEs.

The assessment of nanofiltration showed the technology may be more appropriate for REE recovery in non-iron rich streams. Furthermore, when combined with electrodeposition, membrane nanofiltration shows potential for recovering scandium and cerium, which have applications in aerospace industry components, catalysts in self-cleaning ovens, and other uses.

“Considering the importance of rare earth elements in everything from computers to defense applications, it’s important to pursue as many opportunities as we can to find a stable, domestic source that can be insulated against market volatilities in the global supply chain,” said NETL Project Manager Omer Bakshi. “By supporting RTI’s efforts, NETL is committed to exploring a variety of options put forward from our partner organizations as we search for the most feasible solutions.”

While the tests did not yield the desired concentrated goal of 2wt% mixed REE, improved designs of extraction process, simplified by reducing the volume of the acid, are projected to yield 3.21wt% in the future.

NETL is a U.S. Department of Energy national laboratory that produces technological solutions for America’s energy challenges. From developing creative innovations and efficient energy systems that make coal more competitive, to advancing technologies that enhance oil and natural gas extraction and transmission processes, NETL research is providing breakthroughs and discoveries that support domestic energy initiatives, stimulate a growing economy, and improve the health, safety, and security of all Americans. Highly skilled men and women at NETL’s sites in Albany, Oregon; Anchorage, Alaska; Houston, Texas; Morgantown, West Virginia; and Pittsburgh, Pennsylvania conduct a broad range of research activities that support DOE’s mission to advance the national, economic, and energy security of the United States.