Improving Rare-Earth Mineral Separation with Insights from Molecular Recognition: Functionalized Hydroxamic Acid Adsorption onto Bastnäsite and Calcite

Abstract

Enhancing the separation of rare-earth elements (REEs) from gangue materials in mined ores requires an understanding of the fundamental interactions driving the adsorption of collector ligands onto mineral interfaces. In this work, we examine five functionalized hydroxamic acid ligands as potential collectors for the REE-containing bastnasite mineral in froth flotation using density functional theory calculations and a suite of surface-sensitive analytical spectroscopies. These include vibrational sum frequency generation, attenuated total reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies. Differences in the chemical makeup of these ligands on well-defined bastnasite and calcite surfaces allow for a systematic relationship connecting the structure to adsorption activity to be framed in the context of interfacial molecular recognition. We show how the intramolecular hydrogen bonding of adsorbed ligands requires the inclusion of explicit water solvent molecules to correctly map energetic and structural trends measured by experiments. We anticipate that the results and insights from this work will motivate and inform the design of improved flotation collectors for REE ores.

Characterization of Lanthanum Monazite Surface Chemistry and Crystal Morphology through Density Functional Theory and Experimental Approaches

“…In our previous work, we demonstrated overstabilization of dispersion interactions by Grimme's D3 correction for ligand adsorption on bastnasite surfaces. 9 To better account for these dispersion interactions, we evaluated two truly nonlocal van der Waals (vdW) density functionals: optB88-vdW and optB86b-vdW. The vdW density functionals were derived from a many-body theory and account for dispersion interactions differently than the empirical post hoc corrections from D3 by incorporating the dispersion interactions into the SCF calculations directly and adhere to four exact physical constraints, improving transferability.…”

“…The gradient-corrected PBE and PBEsol functionals were evaluated with and without empirical D3 dispersion corrections to also determine the degree of van der Waals stabilization. In our previous work, we demonstrated overstabilization of dispersion interactions by Grimme’s D3 correction for ligand adsorption on bastnäsite surfaces . To better account for these dispersion interactions, we evaluated two truly nonlocal van der Waals (vdW) density functionals: optB88-vdW and optB86b-vdW.…”

“…Bubbling air through the slurry subsequently separates the REE-containing ore by floating it to the surface once the hydrophobic particles attach to the air bubbles. Many previous works have focused on exploring the crystal morphology, surface chemistry, and design of collector agents for the beneficiation of other REE-containing minerals, such as bastnäsite − and xenotime, , but there is still a large knowledge gap surrounding the controlling molecular mechanisms of monazite beneficiation. There have been a variety of studies that investigated the phase thermodynamics of monazite (and xenotime) to understand bulk properties using both experimental and theoretical approaches, ,, but little attention has been given to the surfaces of monazite and their properties.…”

Emerging Trends of Computational Chemistry and Molecular Modeling in Froth Flotation: A Review

“…Their results suggest that implicit water modeling fails to predict the formation of solvated mineral-reagent complexes. The critical role of the explicit water model over implicit models was further highlighted in the DFT calculations of Chapleski et al 180 for separating rare-earth elements from gangue materials. For the description of such complexes, the inclusion in the simulations of water molecules in the form of a multilayer is essential and highly recommended.…”

Biosorption of Neodymium (Nd) from Aqueous Solutions Using Spirulina platensis sp. Strains

“…Afterward, a volume of an extract is passed by the solid phase, removing the retained specie to a volume that is considerably lower when compared to the initial volume [ 18 , 19 ]. Thus, several adsorbents have been utilized for the uptake of REEs, such as zeolites [ 20 ], amino-functionalized silica materials [ 21 ], composite materials of CaCO 3 :Eu 3+ @SiO 2 [ 22 ], organofunctionalized minerals [ 23 ], polymers [ 24 ], algae [ 25 ], fungus [ 26 ], and others.…”