Coal has helped power the nation for well over a century, but NETL researchers are beginning to find another use for this abundant energy source by developing advanced characterization techniques. Hidden within the black organic rock are tiny quantities of rare earth elements (REEs), and these special elements are widely used in high-tech products, including cell phones, computers, batteries, and lasers. REEs are of significant value to national security, energy independence, economic growth, and the country’s environmental future, but the United States currently imports most of its REE supply from off-shore countries.
A promising new way of obtaining REEs domestically begins by analyzing and characterizing the nation’s supply of coal. Because coal was formed from ancient plant matter, and plants pull in elements from the soil, coal contains all the same elements found in the Earth’s crust. In addition, because such a large volume of ancient plant matter was required to form coal, the percentage of REEs present in the organic rocks is generally greater than in other types of rocks. In fact, REEs are actually not that rare. However, it is unusual to find them in large concentrations (i.e., more than 470 parts per million). That is why developing sophisticated and accurate characterization techniques is extremely important step in the successful extraction of the valuable elements.
NETL has developed techniques for characterizing samples both in the field, as well as in the lab, assisting in the demonstration that REE extraction from coal and coal by-products can be technically and economically feasible.
More than 800 field samples have been collected since June 30, 2015 by NETL in-house researchers and personnel from the U.S. Department of Energy’s Office of Fossil Energy. The United States Geological Survey and the Electric Power Research Institute have both signed memorandums of agreement with NETL calling for additional collaborative field sampling activity.
REE characterization efforts by NETL are among the most advanced in the world. Researchers at the Lab employ a variety of techniques, including digestion methods for the accurate determination of trace REE contents by inductively coupled plasma mass spectrometry (ICP-MS). This technique minimizes uncertainty in trace REE determination. Recently ICP-MS was also used in an NETL study to determine the concentration of REEs in Alberta, Canada oil sands.
Other NETL characterization methods include determining cerium (a common REE) distribution in coal combustion by-products, rock materials, and clays, and using geologic interpretation and elemental characterization to identify geochemical markers that help in identifying high REE zones. REE-containing minerals were also identified in various coal-related materials using advanced microscopic methods.
The Laboratory has also made great strides toward effective field probes by developing techniques for characterizing REEs in solid and liquid matrices. Researchers have found that using laser induced breakdown spectroscopy has solved some of the challenges concerning qualitative detection of REEs in solids, while a fluorescence-based fiber optic-coupled probe integrated with sensitizers showed promise for REE detection at very low concentrations (i.e., parts per million) in aqueous liquids.
NETL’s characterization efforts are helping to forge a path toward establishing a reliable domestic supply of REEs. The U.S. consumes around 16–17 thousand tons of REEs each year, and this demand could be met by completely extracting REEs from domestic coal and coal by-products. As commented by Evan Granite, NETL engineer, “By tapping into this vast untouched resource of coal and coal by-products, the United States could benefit from a 1,000-year supply of REEs at the current rate of consumption.”