DISTRIBUTION OF RARE EARTH AND CRITICAL ELEMENTS DURING WEATHERING OF ILLINOIS BASIN COAL MINING WASTES

Critical elements, especially the rare earth elements (REEs), which include the lanthanides, Y, and Sc, are vital components in clean energy technologies. Coal mining waste has garnered great interest as a potential unconventional source of REEs and other critical elements.

To better understand the distribution of critical elements in coal mine waste products and their behavior during weathering, we analyzed samples collected at both active and abandoned coal mining operations in the Illinois Basin. Samples included (1) raw coal, prepared coal, and newly generated coal refuse from mining and coal preparation associated with active coal mines, and (2) weathered coal mining waste (i.e., gob piles) as well as the Fe- and Al-rich precipitates associated with acid mine drainage (AMD) from abandoned coal mines. Our preliminary results indicate that significant partitioning of major and trace elements occurs both in processing of newly generated waste and during the weathering of old coal mining waste.

In active mining operations, compared to raw coal, waste from coal preparation are enriched in lithophile (Li, Al, P, Ti, V, Cr, Sc, Rb, Y, Zr, Nb, Cs, Ba, the lanthanides, Hf, Th, and U ) and chalcophile (Zn, Cu, As, Sb, Hg, and Pb) elements (i.e., Kolker et al., 2021). Unlike freshly generated waste, the weathered coal waste and AMD precipitates have significantly lower concentrations of chalcophile elements, most likely due to rapid weathering of sulfide minerals (i.e., pyrite). Two exceptions have been noted, namely Mn and As, which displayed the highest concentrations in weathered coal waste samples.

For the REEs, the weathered coal waste and the Al-rich precipitates from AMD are overall enriched in REEs, mainly in Y and heavy REEs, compared to fresh coal mining wastes. However, other critical elements, including V, Cr, Rb, and Cs, show greater enrichments in fresh coal mining waste. The Fe-rich AMD precipitates have the lowest content of critical elements among the analyzed coal products. These preliminary results highlight the potential use of weathered coal mining waste as a source of REEs as along with the need to better understand critical element partitioning during complex weathering of AMD-producing coal mining wastes.

Kolker, A., et al., 2021, Int. Journal Coal Geol., v. 243, n. 103781.