CHARACTERIZATION OF RARE EARTH ELEMENTS AND CRITICAL METALS IN WEATHERED COAL COMBUSTION PRODUCTS

The economic interest in Rare Earth Elements (REEs) and critical metals has directed research into the REE content of fresh Coal Combustion Products (CCPs), while few have investigated the fate of REEs as this material weathers. CCPs are the solid waste produced by coal combustion. CCPs have been documented to weather rapidly (within decades) in holding ponds to clays that could bind up REEs. We collected samples from a spilled coal ash pond that has weathered up to 50-60 years, as well as a fresh ash sample (with no weathering). Sequential leaching experiments using a modified version of Tessier et al. 1979 method were performed on these samples to determine the chemical association of the REE content in fresh and weathered CCPs. The leachate of each step was analyzed by ICPMS to determine the REE content in each fraction of the CCP material. Morphological changes were determined with Scanning Electron Microscopy, and mineralogy was determined through X-Ray diffraction. The weathered CCPs had higher levels of REEs in the exchangeable portion than the fresh CCPs, while the fresh CCPs had higher levels in the portion bound to carbonates, and iron and manganese oxides than the weathered CCPs. These results will elucidate the fate of REEs in weathered CCPs and potential extraction methods.