| Title |
The mobility of thorium, uranium and rare earth elements from Mid Ordovician black shales to acid waters and its removal by goethite and schwertmannite |
| ID_Doc |
15246 |
| Authors |
Santofimia, E; González, FJ; Rincón-Tomás, B; López-Pamo, E; Marino, E; Reyes, J; Bellido, E |
| Title |
The mobility of thorium, uranium and rare earth elements from Mid Ordovician black shales to acid waters and its removal by goethite and schwertmannite |
| Year |
2022 |
| Published |
|
| DOI |
10.1016/j.chemosphere.2022.135907 |
| Abstract |
Previous studies have addressed the occurrence of Acid Rock Drainage (ARD) affecting La Silva stream due to the generation of large dumps of Middle Ordovician black shales during the construction of a highway close to El Bierzo (Le acute accent on, Spain). This ARD was characterized by sulphated acid waters with high concentration of heavy metals and anomalies in dissolved thorium (Th) and uranium (U). In the present study, we analyse in depth black shales and water, streambed sediments and precipitates of La Silva stream and its tributaries using different petrographic, mineralogical and geochemical approaches. Black shales, with average Th and U contents of 20 and 3 mu g/g respectively contain disseminated detritic micro-grains of high weathering-resistant minerals, such as monazite and xenotime, that present smaller amounts of yttrium and rare earth elements (REY) and other ele-ments as Ca, U, Th, Si and F. Results of the affected waters by ARD show an enrichment in dissolved Th, U and REY of several orders of magnitude with respect to natural waters. Sampled precipitates were mainly schwert-mannite (Fe8O8(OH)8-2x (SO4)xO16 center dot nH2O) and goethite (alpha-Fe3+O(OH)) that showed an enrichment of Th (up to 798 mu g/g) and REY, due to the presence of dissolved anionic species (e.g. Th(SO4)32-, REY(SO4)32-) that enables their adsorption. Furthermore, these black shales show a clear enrichment in REE (Rare Earth Elements) with respect to NASC (North American Shales Composite) normalized REE patterns. Likewise, normalized REE pat-terns of stream waters and precipitates clearly show convex curvatures in middle-REE (MREE) with respect to light-and something less than heavy-REE, indicating the trend towards MREE enrichment. These findings are essential to evaluate the impact of ARD of Mid Ordovician shales in the surrounding environment, and to start considering these site as potential source of REE and critical raw materials, activating a Circular Economy. |
| Author Keywords |
Th; U and REY; Black shales; Acid rock drainage; Schwertmannite; Goethite; Critical raw materials |
| Index Keywords |
Index Keywords |
| Document Type |
Other |
| Open Access |
Open Access |
| Source |
Science Citation Index Expanded (SCI-EXPANDED) |
| EID |
WOS:000864550300002 |
| WoS Category |
Environmental Sciences |
| Research Area |
Environmental Sciences & Ecology |
| PDF |
https://doi.org/10.1016/j.chemosphere.2022.135907
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