Huang and Fan (2019) report that rare earth elements (REEs) are critical materials and provide significant values to national security, energy production, environmental protection and economic growth. The supply of REEs in U.S. solely relies on import as domestic production of REEs were ceased because of the environmental concerns during mining and lack of competitiveness. Nonetheless, unconventional REEs-containing resources, including produced water, acid mine drainage, and coal and coal byproducts (C&CBs) contain significant amounts of REEs. However, the concentrations of REEs in these resources are several orders of magnitude lower than that of REEs ores. Thus, extraction of REEs from these materials is challenging.
The authors also report that REEs extraction with environmentally friendly methods that successfully concentrated REEs from 312 ppm in fly ash to 99.4% in the final product. Especially, the five critically important REEs (Dy, Eu, Nd, Tb, and Y) account for up to ~63% of the total weight of all REEs in the final 99.4%-purity product. Coal fly ash is one of the major solid coal utilization byproducts, representing great potential resources for REEs extraction. Extraction of REEs from these unconventional resources could be the way to secure domestic supply of these critical materials.
Coal fly ash is one of major solid coal utilization byproducts. The use of coal for power generation is projected to grow 3.4% annually over the next two decades. It was estimated by the American Coal Ash Association that 37.8 million tons of fly ash was produced in 2016. Also, hundreds of millions of tons of coal ash have been land filled, while they represent huge amounts of untapped REEs resources. For instance, the coal ash samples collected from four energy companies operating in five states (IO, ND, UT, WI, and WY) represent at least 158 million tons of fly ash resources, and among them are 158, 150 million tons contain > 300 ppm REEs, which is equivalent to 61567 to 88 373 tons of REEs.
Powder River Basin is the world’s largest low-sulfur subbituminous coal deposit containing ~1.07 trillion tons of in-place coal resources and produced 40% of coal in the U.S. and thus potentially contains 46 million metric tons of REEs, which can meet the REEs demands of the U.S. for ~3000 years at the country’s 2016 REEs consumption rate. Extraction of REEs from these unconventional resources could be the way to secure domestic supply of these critical materials.
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