RARE EARTH ELEMENTS AND CRITICAL MINERALS IN COAL ASH: A GEOCHEMICAL STUDY OF THE INDUSTRIAL VIABILITY OF POWER PLANT WASTE PILES

This study analyzes power plant coal ash waste piles to determine potential concentrations of rare earth elements (REEs) and critical minerals (CM). Samples were collected from two coal-burning power plant waste piles in Emery and Carbon County, Utah. At one location both bottom ash and fly ash were collected, with only bottom ash available for sampling at the second locality. The samples were geochemically analyzed using pXRF and ICP-MS to determine REE and CM abundance. For this study, samples with > 200 parts per million (ppm) total REEs are considered enriched.

Both powerplants source their coal from nearby mines that mine the coals within the Blackhawk Formation and the Ferron Sandstone. Recent work has shown that REEs are present within or adjacent to prominent coal seams in both the Blackhawk and the Ferron. Previous studies indicate that much of the REE content is associated with the inorganic fraction of coals, or ash content. REE-enriched coal ash has been documented in locations outside the study area. Therefore, this study tests the hypothesis that that power plant ash piles in the Uinta Region may show REE-enrichment.

The initial analysis of these coal ash waste pile samples suggests that there is locally some REE-enrichment. Typically, these samples record a higher abundance of REEs (>150 ppm, especially Neodymium) relative to the average Blackhawk or Ferron coal, which are usually 3-50 ppm, although they are locally >300 ppm. Several samples also recorded REE-enrichment exceeding 300 ppm, this enrichment is usually observed in the bottom ash and slag that is present within the deposits. It is thought that this relative enrichment is a consequence of concentrating the REEs and CMs within the ash waste due to the removal of the carbon and organic material when the coal is burned.

Additional sampling and analysis will help us to further evaluate the potential for REE and CM enrichment of these coal ash waste piles, as they could be an important domestic course of REEs and CM.