RARE EARTH AND CRITICAL ELEMENT PARTITIONING IN ILLINOIS BASIN COAL WASTE

Coal and coal by-products have garnered considerable interest as potential sources of critical elements, especially the rare earths (REEs), including Sc, Y, and the lanthanides. Coal waste (coal refuse) generated in preparing raw coal for use in power generation is one of the most promising coal-related sources of REEs. To better understand partitioning of trace elements during coal preparation, in the present study we sampled coal cleaning operations that use Illinois Basin coals in Illinois and Indiana, including raw coal feeding preparation circuits, prepared coal, and corresponding coal waste. Relative to raw and prepared coals, coal waste is enriched in inorganic constituents removed from raw coal, such as pyrite and aluminosilicates. As a result, coal waste is enriched in both lithophile elements (including Li, Al, P, Ti, Sc, Rb, Y, Zr, Nb, Cs, Ba, the lanthanides, Hf, Th, and U) and potentially harmful chalcophile elements, such as As, Sb, Hg, and Pb. Elements having mixed organic/inorganic associations, such as V, Cr, and Mn, also show enrichment in coal waste, indicating a predominant inorganic association.

To further assess relative enrichment of critical elements in waste coals, trace element concentrations for 12 samples of Illinois Basin coal waste were averaged to obtain a mean coal waste (MCW) that was compared to reference elemental contents in the upper continental crust (UCC) and global mean contents for hard coals (Ketris and Yudovich, 2009). For the REEs, MCW is enriched at near- to slightly above UCC levels, about three times the mean for each REE in hard coals, but much below REE contents of conventional ores. Several critical elements, including V, Cr, As, Rb, Sb, Cs, and U, show greater enrichments in MCW than the REEs. Co-recovery of the most highly valued critical elements, such as Rb and Cs, together with REEs, especially Sc and the HREEs, may make the process more economically viable. With growing interest in diversifying domestic sources of critical elements, partitioning of a large range of elements into coal waste presents a potential opportunity to turn a waste product into a useful resource, subject to continued progress in developing extraction technologies.

Ketris, M.P, and Yudovich, Ya.E., 2009, Int. Journal Coal Geol., v. 78, p. 135-148, https://doi.org/10.1016/j.coal.2009.01.002.