An NETL-supported project at the University of North Dakota (UND) to economically extract strategically important rare earth elements (REE) has shown that lignite is a potential domestic source of these vital minerals using a process that also produces valuable by-products and takes advantage of existing mining infrastructure.
REE have been designated as critical minerals by the U.S. Department of the Interior due to their unique properties, which are essential and often non-substitutable in a variety of consumer goods, energy systems and defense applications. With China largely controlling the global production and value chain, the U.S has begun moving to generate domestic supplies of these critical resource, a task NETL has supported with its partners in academia such as UND.
During UND’s work, researchers simplified an acid-leaching REE extraction process to a single step for economic benefit.
The upgraded process not only extracts the REEs but produces a significantly improved lignite product as a by-product from the process. The upgraded lignite material may be easily integrated into additional added-value coal opportunities, including activated carbon production, combined heat and power, humic acid production, and as an upgraded fuel for coal-fired utility/industrial use.
Following the leaching process, a hydrometallurgical process was designed to generate REE concentrates of various purities, including a primary concentrate that averaged greater than 50% mixed rare earth element oxide (REO) purity with the extracted REE mass containing more than 70% of the total REE mass present in the lignite coal feedstock. REO readily form from rare earth elements as they are typically very reactive with oxygen in the ambient atmosphere. These thermally stable oxides are commonly the final product when rare earth-containing-materials are fired in the presence of oxygen.
The process developed, including the leaching, impurity removal and REE recovery, uses industrially proven equipment and requires no novel reagent usage. The process also uses ambient temperature and moderate pH for mineral processing to minimize potential waste streams, offering a low-cost and environmentally friendly solution.
“The process developed by the UND team has the potential to deliver in many fields,” said Charles Miller, NETL federal project manager. “Not only can it serve as a basis for a new REE extraction industry, but it can also deliver valuable by-products while taking advantage of existing mining infrastructure, which can hopefully make the entire process easier and more attractive for potential investors.”
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 researchers 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.