Acid mine drainage is produced following pyrite oxidation reaction, acidifying meteoritic and processing waters, potentially becoming an environmental problem of worldwide concern. Iron and aluminum sulfate oxyhydroxides are produced as the result of ferrous iron oxidation during pH neutralization, which can occur due to natural processes, forming colloids, or forced to precipitate in engineered systems designed to remediate waters affected by acid mine drainage. In some of these engineered systems, an accumulation of rare earth elements has been observed. Here, we will provide a nanoscopic view of these processes, using mainly synchrotron-based techniques and DFT-based modeling. The aqueous and solid speciation of rare earth elements shows that they form strong complexes with sulfate anions. The structure of these complexes has been studied using partial pair distribution function analyses and DFT. Solid speciation studies show that the rare earth elements are strongly adsorbed by basaluminite, an aluminum sulfate oxyhydroxide. These molecular-scale studies offer a detailed description of the binding environment of rare earth elements in acid mine drainage, offering clues about strategies for their extraction.

Probing the structure and reactivity of iron and aluminum minerals towards rare earth elements in acid mine drainage

ACS Spring Meeting 2021

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