RARE EARTH ELEMENTS IN WEST VIRGINIA COAL MINE DRAINAGE; AN ANALYSIS OF CMD DISCHARGES FROM VARIOUS COAL SEAMS

Coal mine drainage (CMD) is a pervasive and costly issue worldwide. Abandoned mines have the potential to continuously discharge CMD for thousands of years after mining operations have ceased. Rare earth elements (REE) can be found in low concentrations in CMD over broad geographic and geologic areas. There has been recent interest in extracting REEs from CMD to support a domestic, secure supply chain for industrial and defense uses.

To date, over 350 CMD discharges and 180 surface water samples have been collected by the WV Water Research Institute. Most of the samples have been collected within the Monongahela River basin in West Virginia with some in the Potomac River Basin. The samples were collected and analyzed under the Carbon Ore, Rare Earth, and Critical Minerals Initiative at National Energy Technology Laboratory along with Bipartisan Infrastructure Law funding through the West Virginia Department of Environmental Protection to characterize watersheds for potential watershed-scale CMD restoration projects. Identified at-source and in-stream locations are currently sampled monthly to understand the seasonality of these discharges. The data include a combination of in-situ water quality parameters, flow measurements, and analytical data for major and trace metals, sulfate, and chloride concentrations.

Total REE concentrations within direct CMD discharges ranged from 0.1 to 1,300 ug/L, with the highest REE concentrations seen in low pH waters (pH <3). Once the CMD was above 4.5 pH, the highest REE concentration measured was 250 ug/L. Most of the samples contained less than 3,500 mg/L of major metals (Al, Ca, Fe, Mg, Mn); the few samples with elevated concentrations (>8,000 mg/L) were sampled from direct runoff from refuse at an active mining site. The majority of samples have been collected from CMD associated with the Pittsburgh, Redstone, Swickley, Upper Freeport, and Bakerstown seams, with a few samples within the Middle Kittanning, Elk Lick, and Sewell coal seams. The CMD samples within the dataset emanated from both fully and partially flooded mine pools.

We examined the extent to which AMD quality, including REE and Critical Metals, correlates with coal seam and associated water quality parameters. Future research plans include the effects of carbonate and organic carbon on REE complexation and mobility.