THE NATURE OF RARE EARTH ELEMENTS IN WEATHERED COAL COMBUSTION PRODUCTS

Much research has been directed at the Rare Earth Element (REE) content of Coal Combustion Products (CCPs). CCPs are the solid waste produced by coal combustion, representing a heterogeneous mixture of particles that are generally grouped into the categories fly ash, bottom ash, and flue gas desulfurization material. CCPs have attracted industrial attention due to their REE content and economically viable REE-ratios. Previous research has noted the speed at which CCPs weather, in some instances clay-like particles developed in under a decade. Certain clays, particularly ion-adsorption clays, are known to bind REEs in their mineral structure during the weathering process. Sequential leaching experiments per the Tessier et al. 1979 method were performed to determine the chemical association of the REE content. The samples of CCPs are from the Emory River in the region of Tennessee Valley Authority coal ash spill of 2008. These were chosen because they represent samples that were weathered both in a coal ash holding pond and in the Emory River. The leachate of each step has been analyzed by ICPMS to determine the REE content in each fraction of the coal ash material (exchangeable, bound to carbonates, bound to iron and manganese oxides, bound to organic matter, and residual). Morphological changes were also inspected with Scanning Electron Microscopy (with backscattered electron imaging) at each step of the sequential leaching process.