Rare-Earth Elements (REEs) in U.S. Coal-Based Resources: Sampling, Characterizations, and Round-Robin Interlaboratory Study

The Appalachian coalfields contain some of the most promising coal-based REE resources, particularly the Fire Clay coal in Kentucky, West Virginia, and Tennessee (Hower et al., 1999, 2015, 2016; Mardon and Hower, 2004). The Fire Clay coal has been extensively sampled for past and on-going DOE-NETL-funded studies at the University of Kentucky and, in keeping with the mandate to not seriously overlap with past efforts, we will not sample the Fire Clay coal for this investigation. Instead, we plan to concentrate sampling on four distinct areas within the Appalachians: 1. Pennsylvania anthracite – While some of the NETL samples did come from the Anthracite Fields, none are identified by location or coal bed. Hower has a long history of studying the Anthracite Fields and recently has worked with Blaschak Coal (Hower and Dai, 2016), in addition to having contact with other companies in the region, and could arrange to get samples. 2. Castleman Basin, MD, to Clearfield Co., PA – This segment of the coalfield, near the Allegheny Front, has some coal rank changes which may be associated with the mineralization of the coal. Coal rank trends tend to be controlled by SE-NW-trending faults, with the highest coal rank being found in a block in Somerset Co., PA (Hower, 1978). 3. Eastern Kentucky – The triangle roughly bounded by Pine Mountain, the line between Pineville and Manchester, and the line between Manchester and the Pine Mountain/Leslie County/Letcher County junction is marked by higher concentrations of Cl, As, Pb, Hg, and other elements in the coals (Sakulpitakphon et al., 2004) and relatively high REE concentrations in those coals (Collins, 1993). The coals mined in this portion of eastern Kentucky have, in general, been older than the Fire Clay coal. The Hower et al. (1999) sites were to the east of the region and the source of the Mardon and Hower (2004) was to the west of the region. While subtle, the influence of hydrothermal fluids related to the emplacement of the Pine Mountain thrust sheet led to the coals in the region having a higher rank than most other Eastern Kentucky coals. 4. Alabama – Diehl et al. (2004) discussed anomalously high trace element (Hg, As) coals in the Black Warrior Basin. All of these regions represent high-rank anomalies in the Appalachians (Ruppert et al., 2010). Certain relative high-rank areas are excluded, such as the semi-anthracite through medium volatile bituminous transition in Pennsylvania’s rarely-mined North-central fields and the low volatile bituminous coals in southern West Virginia and western Virginia. The sampling plan will be developed with feedback from DOE-NETL. We need to know the locations, both geographic and stratigraphic, of previous samples in order to avoid oversampling certain areas. It would be desirable, of course, to merge the new information with extant data to yield a comprehensive understanding of the REE distribution.