Evaluating Rare Earth Element Distribution in Reclaimed Appalachian Abandoned Mine Lands

Autor: O'Neil-Hankle, Brianna Mariam
Jazyk: angličtina
Rok vydání: 2022
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Druh dokumentu: Text
Popis: Acid mine drainage (AMD) and the associated mine land sediments are a valuable source of rare earth elements (REEs) and critical minerals with concentrations of REEs in AMD often orders of magnitude higher than those in river water and seawater. Recovering REEs while cleaning up AMD provides the potential to offset the cost of reclamation. In this study, we are evaluating the REE content and distribution in the sediments associated with two AMD locations in SE Ohio that exhibit high REE content. The study sites, ‘Flint Run’ and ‘Howard-Williams Lake’, are complex sites with multiple past remediations and reclamation attempts that continue to produce AMD with REE concentrations up to 0.9 mg/L and 1.9 mg/L, respectively. Soil cores were collected from the two sites using an auger and split-spoon sampler. Samples were collected at approximately five-foot increments and trace element and REE concentrations were analyzed on digested samples using inductively coupled plasma atomic emission spectroscopy. The mineralogy of the sediments was analyzed with a high-resolution X-Ray diffractometer. Our results show the layers of fill used to reclaim the sites were not uniform spatially or with depth and were comprised of a mixture of silty clay, underclay, coal refuse, shale, and sandstone. Samples identified as being associated with coal (i.e., clay with coal fines and coal refuse), regardless of the depth measured, had higher REE concentrations (up to 437.9 ppm total REE) in comparison to the other compositional layers studies (~36 ppm total REE). Samples associated with coal had concentrations ranging from 4.2-126 ppm for Ce to 4.5-52.6 ppm for Nd. These layers also exhibited elevated concentrations of Fe and Al. At water pH values of 5.1-6.6, REEs were expected to precipitate with Fe and Al minerals into the sediment, which was consistent with the pH value of water collected during sample collection at Howard-Williams Lake. Statistical analysis and XRD results indicate that the iron minerals goethite and pyrite may be hosts for REEs at the Flint Run site. The data suggests that the ferric iron mineral, jarosite, may be a host for REEs at the Howard-Williams site. This study will help to further the understanding of mechanisms and phases responsible for binding REEs in coal mine land sediments, which is needed to identify locations suitable for REE extraction or recovery.
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