Abstract
Crystal truncation rod (CTR) measurements and density functional theory (DFT) calculations were performed to determine the atomic structure of the mineral-water interface of the {100} surface of xenotime (nominally YPO4). This mineral is important, because it incorporates a variety of rare earth elements (REEs) in its crystal structure. REEs are critical materials necessary for a variety of renewable and energy efficient technologies. Current beneficiation techniques are not highly selective for REE ore minerals, and large amounts go to waste; this is a first step toward designing more efficient beneficiation. Evidence is found for minor relaxation of the surface within the topmost monolayer with little or no relaxation in subsurface layers. Justification for ordered water at the interface is found, where water binds to surface cations and donates hydrogen bonds to surface phosphates. The average bond lengths between cations and oxygens on water are 228 pm in the best fit to the CTR data, versus 243 and 251 pm for the DFT. No agreement on water positions bound to surface phosphates is obtained. Overall, the findings suggest that ligands used in beneficiation with a single anionic headgroup, such as fatty acids, will have limited selectivity for xenotime relative to undesirable minerals.
Original language | English |
---|---|
Pages (from-to) | 20232-20243 |
Number of pages | 12 |
Journal | Journal of Physical Chemistry C |
Volume | 122 |
Issue number | 35 |
DOIs | |
State | Published - Sep 6 2018 |
Funding
This work was supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory and National Energy Research Scientific Computing Center, both of which are supported by the Office of Science of the U.S. Department of Energy under contract Nos. DE-AC05-00OR22725 and DE-AC02-05CH11231, respectively. The single-crystal structural analysis by RC was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. CTR data were collected at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory (ANL). GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences (EAR - 1634415) and U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division (DE-FG02-94ER14466). This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by ANL under Contract No. DE-AC02-06CH11357. CTR data analysis was completed in part with resources provided by the University of Chicago Research Computing Center. We thank Sang Soo Lee and two anonymous reviewers for their constructive comments about drafts of the manuscript.