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A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 2 5 sources of information for determining the feasibility of extracting REEs from coal-based resources. Materials gener- ated along the coal value chain, shown in Fig. 1, create potential REE materials for REE extraction [2] . ENSURING DATA QUALITY Determining the concentration of REEs in heterogenous matrices such as coal-basedmaterials is not a trivial task. Therefore, it is important to have a data quality assurance protocol, particularly when comparing generated data from different analytical instruments and/or procedures. Fortunately, for the REEs, the smoothness of normalized REE dis- tribution curves provides a simple yet reliable way of evaluating the quality of REE data [6-8] . Normalizing can be conducted us- ing different standard REE concentra- tions, such as REE concentrations in chondrite meteorites, the Upper Conti- nental Crust (UCC), the North American Shale Composite (NASC), or Post-Arche- an Australian Shale (PAAS) composite values. For coal and coal by-products, the standard used for normalization should be one that has been affect- ed by similar geological fractionation processes [7] . In this article, the values are normalized to the UCC reported by Taylor and McLen- nan [9] . Figure 2 shows the UCC normalized curve for average U.S. coal reported by Finkelman [10] . The smooth line is an indication of good data quality, while the normalized value around 0.5 indicates that the concentra- tion of REE in coal is approximately half the concentration found in the UCC for each element. Large deviations from a smooth nor- malized curve as well as sawtooth patterns appear in the literature and are mostly associ- ated with analyti- cal error [6,7] . Some of the sample data posted on the NETL EDX website shows rough normalized patterns and should be used with cau- tion. For example, Fig. 3 shows large anomalies for terbium, thulium, and lute- tium, which indicate that the analytical results for these elements are suspect. Fig. 1 — Coal-based materials for REE recovery [4] . Fig. 2 — UCC-normalized average REE concentrations in U.S. coals. Fig. 3 — Average REE UCC-normalized data for coal and coal by- products from the Appalachia basins (dry ash basis).