Title

Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores

Publication Date

3-17-2020

Department

Ames Laboratory; Chemistry

Campus Units

Chemistry, Ames Laboratory

OSTI ID+

1608208

Report Number

IS-J 10330

DOI

10.1021/acsami.9b22902

Journal Title

ACS Applied Materials and Interfaces

Volume Number

12

Issue Number

14

First Page

16327

Last Page

16341

Abstract

Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. This is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.

DOE Contract Number(s)

AC05-00OR22725; AC02-05CH11231

Language

en

Department of Energy Subject Categories

58 GEOSCIENCES

Publisher

Iowa State University Digital Repository, Ames IA (United States)

IS-J 10330 SI.pdf (3027 kB)
Supplementary Information

Share

COinS