Coal and Coal Byproducts as Potential Sources of Rare Earth Elements (REE) in Indiana

The purpose of this study is to evaluate coal and coal byproducts (coal waste, coal ash, and acid mine drainage) in Indiana as potential sources of rare earth elements (REE). On a whole-rock basis, most Indiana coal samples have REE content below 100 ppm, and only some samples of the Brazil and Staunton Formations (Lower and Upper Block and Viking B coals) reach 100 ppm. Because REE concentrations vary between locations and within individual coal beds, and the correlations of coals within the Brazil and Staunton Formations are often uncertain, a better understanding of the stratigraphy of these formations is needed to identify the most promising REE horizons. Owing to a long history of coal mining, Indiana has numerous coal preparation plants and associated coarse-and fine-grained coal refuse (known, respectively, as gobs and slurry ponds). This paper reviews the available data on locations and volumes of these deposits. The total extent of slurry pond deposits was estimated at 2,765 acres, and the total volume estimates ranged from 94,000,000 to 136,000,000 cubic yards. No estimates are available for gob deposits in Indiana. To our knowledge, no REE data are available for coal preparation plant waste in Indiana, except for minimal data from coal slurry in Warrick County. Water streams from abandoned coal mines and coal processing (acid mine drainage, AMD) could also be a source of REE or other critical minerals; we review available data from AMD sites. Indiana, having many coal-fired power plants, has accumulated a large quantity of coal ash during its mining history. Our estimates indicate that coal ash deposits occupy ~2,184 acres, storing ~52,566,153 m3 of ash. Volume estimates for individual coal ash sites come from various sources and present our best estimates at this time. To our knowledge, no REE data are available on coal ash in Indiana. Such data would be of great value because coal ash deposits could be an important resource for REE, other critical minerals, or other high-value carbon products.