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

Rational design of bastnäsite specific collector molecules must exploit its surface structural features.

A Molecular-Scale Approach to Rare-Earth Beneficiation: Thinking Small to Avoid Large Losses

“…Periodic-DFT-calculated adsorption energies for SHA, BHA, and SA on bastnäsite-[10 0], the most prevalent bastnäsite surface ( Srinivasan et al, 2017 ; Srinivasan et al., 2016 ), with acidic protons proximal to the adsorbate, are provided in Table 2 , and optimized structures are shown in Figure 1 and detailed in Figure S1 with interactions contributing to adsorption specified.…”

“…Closer cationic spacing on the calcite surface (d(Ca-Ca) = 4.03 and 4.99 Å) compared with the Ce-bastnäsite surface (d(Ce-Ce) = 4.78 and 7.07 Å) may allow for closer adsorption on the bastnäsite surface and potentially cause differing degrees of strain on the structure of the ligand upon adsorption. Previous work on bastnäsite-collector design highlights variations in cationic spacing in these surfaces ( Srinivasan et al, 2017 ).…”

“…Replacement of CO 3 2− by a ligand on the bastnäsite surface results in an energetic expense much less than that on the calcite surface (structures in Figures S3–S5 , energies in Table S1 ). Despite showing more extensive SHA-surface interaction than on bastnäsite, the greater replacement energy on calcite is likely due to the inherent differences in structure between the [10 0] surface of bastnäsite and the [10 4] surface of calcite ( Srinivasan et al, 2017 ). In the former, Ce 3+ cations in the subsurface layer lie 1.9 Å below those in the surface layer, whereas in the latter, subsurface Ca 2+ cations lie 3.0 Å below the surface.…”

Temperature and Pressure Dependence of Salt–Brine Dihedral Angles in the Subsurface

“…Three different methods of calculating interfacial properties via MD simulations were reported by Bahadur et al for liquid–vapor, solid–liquid, and solid–vapor interfaces in the NaCl–water–air system and found that the energy difference method, used here, result in an estimated uncertainty of ±6 mN/m or 7% of the experimental value for the liquid–solid interfacial tension . Additionally, similar methods have been used to calculate the interfacial energy of NaCl–water systems, tricalcium silicate–water, hydroxyapatite–water, and Ce/La–bastnäsite–water systems indicating that this method is well suited for investigation of liquid–solid interfacial tensions in NaCl brine systems . The interaction energies of the last 10 steps of the 1 ns simulation were used to calculate an average liquid–solid interfacial tension along with standard deviation as an error.…”

Mineral–Water Interface Structure of Xenotime (YPO4) {100}

“…Optimizations of this process include the adsorption isotherms of the surfactants, solution pH, zeta potentials of the minerals that make up the ore body, and contact angle measurements . However, with a few notable exceptions, , there is a dearth of fundamental information about the molecular-level structure, reactivity, and reaction mechanisms of the relevant mineral–water interfaces involved in this process. Obtaining this fundamental understanding would allow us to identify the specific surface sites, if any, onto which surfactants bind during complexation and give a confirmed starting structure for rational design of new ligands that are more efficient at causing REE ore minerals to float while simultaneously being more selective for REE ore minerals over gangue.…”