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)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 ionsmore » 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:

Wanhala, Anna Kristiina ^[1]; Doughty, Benjamin L.  ^[1];

• Search DOE PAGES for author "Doughty, Benjamin L."
• Search DOE PAGES for ORCID "0000-0001-6429-9329"

Bryantsev, Vyacheslav  ^[1];

• Search DOE PAGES for author "Bryantsev, Vyacheslav"
• Search DOE PAGES for ORCID "0000-0002-6501-6594"

Wu, Lili ^[2]; Mahurin, Shannon Mark  ^[1];

• Search DOE PAGES for author "Mahurin, Shannon Mark"
• Search DOE PAGES for ORCID "0000-0003-3792-1631"

Jansone-Popova, Santa  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0690-5957"

Cheshire, Michael C.  ^[1];

• Search DOE PAGES for author "Cheshire, Michael C."
• Search DOE PAGES for ORCID "0000-0003-1792-6881"

Navrotsky, Alexandra ^[2]; Stack, Andrew G.  ^[1]

• Search DOE PAGES for author "Stack, Andrew G."
• Search DOE PAGES for ORCID "0000-0003-4355-3679"

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Univ. of California, Davis, CA (United States)

Publication Date:

Tue Jun 11 00:00:00 EDT 2019

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Advanced Manufacturing Office; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division

OSTI Identifier:

1530064

Alternate Identifier(s):

OSTI ID: 1547166

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