EVALUATION OF COAL ASH AS A REE & LITHIUM FEEDSTOCK IN THE SOUTHEASTERN UNITED STATES

Identifying domestic resources for rare earth elements (REEs) and other critical minerals is vital for the national security and economy of the U.S. due to their widespread use in manufacturing and defense and the high potential for supply chain disruption. Recent studies have shown that coal contains significant amounts of Li and REEs+Sc+Y (REE+) which become concentrated during the coal combustion process due to their low volatility (U.S. DOE, 2022). This study is assessing the viability of coal ash as a feedstock material for REEs+ and Li based on analytical data obtained from nine coal ash impoundments in the Southeastern United States (N>350). Historical REE concentration data were compiled from eight coal ash impoundments (N=170) and additional samples (N=180) were collected from six CCP impoundments in the Southeast United States. These samples were digested (ASTM D6357) and analyzed via inductively coupled plasma emission mass spectrometry (EPA 200.8) for REE concentrations. The average total REE content on a dry weight basis for all samples is 356.5 ± 165.4 ppm and the average REE+ content is 451.7 ± 203.7 ppm. The average REE of ash is above the Department of Energy (DOE) cut-off ore grade of 300 ppm (Bagdonas et al., 2022). REE content varies significantly between impoundments with a range of 719.1 ± 229.9 ppm to 131.0 ± 58.4 ppm. The average lithium content for all samples is 210.1 ± 106.2 ppm. Based on the results from all impoundments, there is a strong positive correlation between Li and REE content, with a Pearson’s correlation coefficient of 0.7. There is weaker but noticeable negative correlation between Si content and REE content, with a Pearson’s correlation coefficient of -0.4.

To better understand the extractability of REE and lithium from coal ash, selected samples are being characterized for major and minor mineral contents by XRD and Rietveld refinement, major and minor element content via XRF, and trace mineral contents and REE associations by SEM/EDX analysis and micro-XRF mapping. Preliminary results of these additional analyses indicate correlations between bulk coal ash composition, mineralogy, and REE content. It is evident that REEs show significant partitioning into crystalline phosphate grains. These results give insights into the ease of extractability of REEs in coal ash, which is vital to understanding their viability as a resource.