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New domestic sources of rare earth elements identified by NETL

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World Coal,

To help protect the US, researchers at NETL are working to secure a low cost domestic supply of rare earth elements (REEs) by identifying promising sources using a combination of big data analysis, advanced microscopy and by developing innovative exploration and recovery processes.

Many people have never heard of REEs, but these valuable materials are essential for the manufacture of virtually all high tech devices, including many defence and energy technologies. In fact, the US uses more than 17 000 t of REEs each year for everything from electric cars to mobile phones. However, nearly all the nation’s REE supplies are imported from China where it is extracted from mineral ores and then refined and separated. This reliance on foreign sources of rare earths can create vulnerabilities when markets shift unpredictably.

NETL research projects and strategic partnerships are already underway, which are focusing on recovering REEs from domestic coal and coal-related by-products. Now, the lab is turning its attention to strata around coal, such as underclays, which can contain a significant concentration of these valuable elements. However, not all formations were created equally, and some hold far greater potential than others for commercial rare earth extraction.

To narrow down their focus to only those areas likely to contain significant levels of rare earths, NETL researchers are developing a novel approach to systematically predict REE concentrations in coal and coal-related strata. Such an effort involves the incorporation of existing resource characterisation methods from the petroleum, coal and mineral mining industries, in addition to spatial and statistical analysis of huge datasets from sources like the United States Geological Survey (USGS) to indicate where conditions are most favourable for REE deposits associated with US coals.

Locations around the country may be excellent areas for potential REE operations, and researchers are sampling the subsurface of some of these places to more precisely determine the concentrations of rare earths present. To gain further insight on the ease of extraction, researchers identify key REE-bearing minerals in coal-associated rock formations using advanced microscopy and imaging techniques. Common phosphate minerals, such as monazite, rhabdophane and xenotime, have been identified using scanning electron microscopy (SEM) and the REE concentrations are quantified by specialised techniques in spectroscopy. These results are then used to create 3D reconstructions of the mineral phases and rock matrix that are used to estimate the spatial distribution and binding of rare earths in the strata.

Some geologic materials, such as underclays, have been shown to contain sufficient quantities of rare earths for a viable recovery operation, but before such an operation could ever be considered, different recovery techniques must be tested and compared. For example, researchers are currently investigating the use of environmentally friendly liquids for recovering rare earths elements from sedimentary rock. These methods mimic processes that occur in nature and may reduce the environmental impacts of wastes from REE recovery operations, reducing the lifecycle and recovery costs.

Based on the efforts of NETL researchers, extraction of rare earths from underclay deposits shows great promise as a new way of securing a domestic supply. This work is another example of how NETL is producing technological solutions to America’s energy challenges.

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