Micro- and Nanoscale Identification of Rare Earth Element–Mineral Associations in an Acidified Dredge Spoil and Adjacent Reduced Sediments

Although rare earth element (REE) concentrations and speciation are often investigated by chemical extractions of bulk soils and sediments to elucidate site specific environmental processes and anthropogenic influences, micro- and nanoscale investigations provide more precise insights into the REE–mineral associations essential for understanding REE mobility in complex natural landscapes. In this study, we combine the high-resolution microscopic techniques of scanning electron microscopy energy dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and electron energy-loss spectroscopy (EELS) to characterize micro- and nanoscale REE–mineral associations in an eutrophic estuarine system, specifically at a site containing (1) a coastal acid sulfate soil (CASS) and (2) adjacent estuarine sediments that have received acute acidic drainage from the CASS site for ∼20 years. This study revealed particles with a porous morphology that had a recurring association between Fe and the REE lanthanu...