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Title: Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements

Abstract

Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnäsite [(Ce,La)FCO 3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. In this work, the adsorption of octyl hydroxamic acid onto bastnäsite was calculated using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnäsite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnäsite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnäsite than with a common gangue mineral, calcite (CaCO 3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength ofmore » metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores.« less

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of California, Davis, CA (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), Advanced Manufacturing Office (EE-5A); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
OSTI Identifier:
1530064
Grant/Contract Number:  
AC05-00OR22725; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Colloid and Interface Science
Additional Journal Information:
Journal Volume: 553; Journal Issue: C; Journal ID: ISSN 0021-9797
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Wanhala, Anna Kristiina, Doughty, Benjamin L., Bryantsev, Vyacheslav, Wu, Lili, Mahurin, Shannon Mark, Jansone-Popova, Santa, Cheshire, Michael C., Navrotsky, Alexandra, and Stack, Andrew G. Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements. United States: N. p., 2019. Web. doi:10.1016/j.jcis.2019.06.025.
Wanhala, Anna Kristiina, Doughty, Benjamin L., Bryantsev, Vyacheslav, Wu, Lili, Mahurin, Shannon Mark, Jansone-Popova, Santa, Cheshire, Michael C., Navrotsky, Alexandra, & Stack, Andrew G. Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements. United States. doi:10.1016/j.jcis.2019.06.025.
Wanhala, Anna Kristiina, Doughty, Benjamin L., Bryantsev, Vyacheslav, Wu, Lili, Mahurin, Shannon Mark, Jansone-Popova, Santa, Cheshire, Michael C., Navrotsky, Alexandra, and Stack, Andrew G. Tue . "Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements". United States. doi:10.1016/j.jcis.2019.06.025.
@article{osti_1530064,
title = {Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements},
author = {Wanhala, Anna Kristiina and Doughty, Benjamin L. and Bryantsev, Vyacheslav and Wu, Lili and Mahurin, Shannon Mark and Jansone-Popova, Santa and Cheshire, Michael C. and Navrotsky, Alexandra and Stack, Andrew G.},
abstractNote = {Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnäsite [(Ce,La)FCO3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. In this work, the adsorption of octyl hydroxamic acid onto bastnäsite was calculated using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnäsite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnäsite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnäsite than with a common gangue mineral, calcite (CaCO3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength of metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores.},
doi = {10.1016/j.jcis.2019.06.025},
journal = {Journal of Colloid and Interface Science},
number = C,
volume = 553,
place = {United States},
year = {2019},
month = {6}
}

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This content will become publicly available on June 11, 2020
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