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Title: A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry

Abstract

Bastnäsite, a fluoro-carbonate mineral, is the single largest mineral source of light rare earth elements (REE), La, Ce and Nd. Enhancing the efficiency of separation of the mineral from gangue through froth flotation is the first step towards meeting an ever increasing demand for REE. To design and evaluate collector molecules that selectively bind to bastnäsite, a fundamental understanding of the structure and surface properties of bastnäsite is essential. In our earlier work (J Phys Chem C, 2016, 120, 16767), we carried out an extensive study of the structure, surface stability and water adsorption energies of La-bastnäsite. Here in this work, we make a comparative study of the surface properties of Ce-bastnäsite, La-bastnäsite, and calcite using a combination of density functional theory (DFT) and water adsorption calorimetry. Spin polarized DFT+U calculations show that the exchange interaction between the electrons in Ce 4f orbitals is negligible and that these orbitals do not participate in bonding with the oxygen atom of the adsorbed water molecule. In agreement with calorimetry, DFT calculations predict larger surface energies and stronger water adsorption energies on Ce-bastnäsite than on La-bastnäsite. The order of stabilities for stoichiometric surfaces is as follows: [100] > [101] > [102] > [0001]more » > [112] > [104] and the most favorable adsorption sites for water molecules are the same as for La-bastnäsite. In agreement with water adsorption calorimetry, at low coverage water molecules are strongly stabilized via coordination to the surface Ce3+ ions, whereas at higher coverage they are adsorbed less strongly via hydrogen bonding interaction with the surface anions. Lastly, due to similar water adsorption energies on bastnäsite [101] and calcite [104] surfaces, the design of collector molecules that selectively bind to bastnäsite over calcite must exploit the structural differences in the predominantly exposed facets of these minerals.« less

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [1];  [4];  [5];  [2]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  2. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab. and NEAT ORU
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Computer Science and Mathematics Division
  4. Rutgers Univ., Piscataway, NJ (United States). Dept. of Materials Science and Engineering
  5. OLI Systems, Inc., Cedar Knolls (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1408003
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 19; Journal Issue: 11; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE

Citation Formats

Goverapet Srinivasan, Sriram, Shivaramaiah, Radha, Kent, Paul R. C., Stack, Andrew G., Riman, Richard, Anderko, Andre, Navrotsky, Alexandra, and Bryantsev, Vyacheslav S. A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry. United States: N. p., 2017. Web. doi:10.1039/C7CP00811B.
Goverapet Srinivasan, Sriram, Shivaramaiah, Radha, Kent, Paul R. C., Stack, Andrew G., Riman, Richard, Anderko, Andre, Navrotsky, Alexandra, & Bryantsev, Vyacheslav S. A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry. United States. doi:10.1039/C7CP00811B.
Goverapet Srinivasan, Sriram, Shivaramaiah, Radha, Kent, Paul R. C., Stack, Andrew G., Riman, Richard, Anderko, Andre, Navrotsky, Alexandra, and Bryantsev, Vyacheslav S. Fri . "A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry". United States. doi:10.1039/C7CP00811B. https://www.osti.gov/servlets/purl/1408003.
@article{osti_1408003,
title = {A comparative study of surface energies and water adsorption on Ce-bastnäsite, La-bastnäsite, and calcite via density functional theory and water adsorption calorimetry},
author = {Goverapet Srinivasan, Sriram and Shivaramaiah, Radha and Kent, Paul R. C. and Stack, Andrew G. and Riman, Richard and Anderko, Andre and Navrotsky, Alexandra and Bryantsev, Vyacheslav S.},
abstractNote = {Bastnäsite, a fluoro-carbonate mineral, is the single largest mineral source of light rare earth elements (REE), La, Ce and Nd. Enhancing the efficiency of separation of the mineral from gangue through froth flotation is the first step towards meeting an ever increasing demand for REE. To design and evaluate collector molecules that selectively bind to bastnäsite, a fundamental understanding of the structure and surface properties of bastnäsite is essential. In our earlier work (J Phys Chem C, 2016, 120, 16767), we carried out an extensive study of the structure, surface stability and water adsorption energies of La-bastnäsite. Here in this work, we make a comparative study of the surface properties of Ce-bastnäsite, La-bastnäsite, and calcite using a combination of density functional theory (DFT) and water adsorption calorimetry. Spin polarized DFT+U calculations show that the exchange interaction between the electrons in Ce 4f orbitals is negligible and that these orbitals do not participate in bonding with the oxygen atom of the adsorbed water molecule. In agreement with calorimetry, DFT calculations predict larger surface energies and stronger water adsorption energies on Ce-bastnäsite than on La-bastnäsite. The order of stabilities for stoichiometric surfaces is as follows: [100] > [101] > [102] > [0001] > [112] > [104] and the most favorable adsorption sites for water molecules are the same as for La-bastnäsite. In agreement with water adsorption calorimetry, at low coverage water molecules are strongly stabilized via coordination to the surface Ce3+ ions, whereas at higher coverage they are adsorbed less strongly via hydrogen bonding interaction with the surface anions. Lastly, due to similar water adsorption energies on bastnäsite [101] and calcite [104] surfaces, the design of collector molecules that selectively bind to bastnäsite over calcite must exploit the structural differences in the predominantly exposed facets of these minerals.},
doi = {10.1039/C7CP00811B},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 11,
volume = 19,
place = {United States},
year = {Fri Feb 24 00:00:00 EST 2017},
month = {Fri Feb 24 00:00:00 EST 2017}
}

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Cited by: 2works
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  • Bastnasite is a fluoro-carbonate mineral that is the largest source of rare earth elements such as Y, La and Ce. With increasing demand for REE in many emerging technologies, there is an urgent need for improving the efficiency of ore beneficiation by froth flotation. In order to design improved flotation agents that can selectively bind to the mineral surface, a fundamental understanding of the bulk and surface properties of bastnasite is essential. Density functional theory calculations using the PBEsol exchange correlation functional and the DFT-D3 dispersion correction reveal that the most stable form of La bastnsite is isomorphic to themore » structure of Ce bastnasite belonging to the P2c space group, while the Inorganic Crystal Structure Database structure in the P2m space group is ca. 11.3 kJ/mol higher in energy per LaFCO 3 formula unit. We report powder X-ray diffraction measurements on synthetic of La bastnasite to support these theoretical findings. Six different surfaces are studied by DFT, namely [100], [0001], [101], [102], [104] and [112]. Among these, the [100] surface is the most stable with a surface energy of 0.73 J/m 2 in vacuum and 0.45 J/m 2 in aqueous solution. We predicted the shape of a La bastnasite nanoparticle via thermodynamic Wulff construction to be a hexagonal prism with [100] and [0001] facets, chiseled at its ends by the [101] and [102] facets. The average surface energy of the nanoparticle in the gas phase is estimated to be 0.86 J/m 2, in good agreement with a value of 1.11 J/m 2 measured by calorimetry. The calculated adsorption energy of a water molecule varies widely with the surface plane and specific adsorption sites on a given surface. Moreover, the first layer of water molecules is predicted to adsorb strongly on the La-bastnasite surface, in agreement with water adsorption calorimetry experiments. Our work provides an important step towards a detailed atomistic understanding of the bastnasite water interface and designing collector molecules that can bind specifically to bastnasite.« less
  • Plane wave density functional theory (DFT) calculations have been performed to study the atomic structure, preferred H2O adsorption sites, adsorption energies, and vibrational frequencies for water adsorption on the R-quartz (101) surface. Surface energies and atomic displacements on the vacuum-reconstructed, hydrolyzed, and solvated surfaces have been calculated and compared with available experimental and theoretical data. By considering different initial positions of H2O molecules, the most stable structures of water adsorption at different coverages have been determined. Calculated H2O adsorption energies are in the range -55 to -65 kJ/mol, consistent with experimental data. The lowest and the highest O-H stretching vibrationalmore » bands may be attributed to different states of silanol groups on the watercovered surface. The dissociation energy of the silanol group on the surface covered by the adsorption monolayer is estimated to be 80 kJ/mol. The metastable states for the protonated surface bridging O atoms (Obr), which may lead to hydrolysis of siloxane bonds, have been investigated. The calculated formation energy of a Q2 center from a Q3 center on the (101) surface with 2/3 dense monolayer coverage is equal to 70 kJ/mol which is in the range of experimental activation energies for quartz dissolution.« less
  • Using van-der-Waals-corrected density functional theory calculations, we explore the possibility of engineering the local structure and morphology of high-surface-area graphene-derived materials to improve the uptake of methane and carbon dioxide for gas storage and sensing. We test the sensitivity of the gas adsorption energy to the introduction of native point defects, curvature, and the application of strain. The binding energy at topological point defect sites is inversely correlated with the number of missing carbon atoms, causing Stone–Wales defects to show the largest enhancement with respect to pristine graphene (~20%). Improvements of similar magnitude are observed at concavely curved surfaces inmore » buckled graphene sheets under compressive strain, whereas tensile strain tends to weaken gas binding. Trends for CO 2 and CH 4 are similar, although CO 2 binding is generally stronger by ~4 to 5 kJ mol –1. Furthermore, the differential between the adsorption of CO 2 and CH 4 is much higher on folded graphene sheets and at concave curvatures; this could possibly be leveraged for CH 4/CO 2 flow separation and gas-selective sensors.« less
  • We apply density functional theory (DFT) and the DFT+U technique to study the adsorption of transition metal porphine molecules on atomistically flat Au(111) surfaces. DFT calculations using the Perdew?Burke?Ernzerhof exchange correlation functional correctly predict the palladium porphine (PdP) low-spin ground state. PdP is found to adsorb preferentially on gold in a flat geometry, not in an edgewise geometry, in qualitative agreement with experiments on substituted porphyrins. It exhibits no covalent bonding to Au(111), and the binding energy is a small fraction of an electronvolt. The DFT+U technique, parametrized to B3LYP-predicted spin state ordering of the Mn d-electrons, is found tomore » be crucial for reproducing the correct magnetic moment and geometry of the isolated manganese porphine (MnP) molecule. Adsorption of Mn(II)P on Au(111) substantially alters the Mn ion spin state. Its interaction with the gold substrate is stronger and more site-specific than that of PdP. The binding can be partially reversed by applying an electric potential, which leads to significant changes in the electronic and magnetic properties of adsorbed MnP and 0.1 {angstrom} changes in the Mn-nitrogen distances within the porphine macrocycle. We conjecture that this DFT+U approach may be a useful general method for modeling first-row transition metal ion complexes in a condensed-matter setting.« less
  • Molecular and dissociative adsorption of methanol at various sites on the stoichiometric CeO₂(111) surface have been studied using density functional theory periodic calculations. At 0.25 monolayer (ML) coverage, the dissociative adsorption with an adsorption energy of 0.55 eV is slightly favored. The most stable state is the dissociative adsorption of methanol via C-H bond breaking, forming a coadsorbed hydroxymethyl group and hydrogen adatom on two separate O₃C surface sites. The strongest molecular adsorption occurs through an O-Ce₇subC connection with an adsorption energy of 0.48 eV. At methanol coverage of 0.5 ML, the dissociative adsorption and the molecular adsorption became competitive.more » The adsorption energy per methanol molecule for both adsorption modes falls into a narrow range of 0.46-0.55 eV. As methanol coverage increases beyond 0.5 ML, the molecular adsorption becomes more energetically favorable than the dissociative adsorption because of the attractive hydrogen bonding between coadsorbed methanol molecules. At full monolayer, the adsorption energy of molecular adsorption is 0.40 eV per molecule while the adsorption energy for total dissociative adsorption of methanol is only 0.17 eV. The results at different methanol coverages indicate that methanol can adsorb on a defect-free CeO₂(111) surface, which are also consistent with experimental observations. This research was performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Computing time was made available under a Computational Grand Challenge “Computational Catalysis”. This work also financially supported by the Laboratory Directed Research and Development project of PNNL.« less