Adsorption of Hydrated Pr3+ and NH4+/Mg2+ Ions onto the (001) Surface of Montmorillonite: A DFT Analysis with Experimental Verification

Abstract

Montmorillonite is a major mineral present in ion-adsorption rare earth ores, and the microscopic adsorption states of rare earth ions on its surface are of a great significance for the efficient exploitation of ion-adsorption rare earth ores. In this article, density functional theory calculations were used to investigate the adsorption mechanisms and bonding characteristics of hydrated Pr, Mg and NH4 ions on the (001) surface of montmorillonite. Pr3+ exhibited a directed tendency geometry with Pr(H2O)103+, which was adsorbed onto montmorillonite by hydrogen bonding with an adsorption energy of −1182 kJ/mol, and one coordinated H2O ligand was separated from the first hydration layer of Pr. Both hydrated Mg and NH4 ions were adsorbed onto the montmorillonite surface through hydrogen bonds, and the adsorption energies were −206 and −188 kJ/mol, respectively, indicating that the adsorption stability of the hydrated Mg ion was slightly higher than that of the hydrated NH4 ion, but both were lower than that of hydrated Pr (−1182 kJ/mol). Hence, higher concentrations of Mg and NH4 ions than rare earth ions would be necessary in the leaching process of ion-adsorption rare earth ores. Additionally, desorption experiments revealed that the recovery of Pr3+ by Mg2+ with a concentration of 38 mmol/L is 80%, while it is only 65% with the same concentration of NH4+, and the concentrations of Mg2+ and NH4+ were much higher than that of Pr3+ in lixivium, which is consistent with the DFT calculations.

Development Review on Leaching Technology and Leaching Agents of Weathered Crust Elution-Deposited Rare Earth Ores

“…The clay minerals in weathered crust elution-deposited rare earth deposits are mainly composed of kaolinite, halloysite, illite, montmorillonite, etc., among which kaolinite and halloysite are composed of silica tetrahedrons and alumina octahedrons at a ratio of 1:1. The layered crystal minerals, illite, and montmorillonite are layered crystal minerals with a 2:1 composition [36]. Crystal minerals exist in the form of wafers, and there are interlayer substances such as water molecules, cations, hydroxyl groups, and water complexes between the wafers, and the wafers are united by the positive charge of the cations.…”

Investigation of Hydrated Dy(III) and MgSO4 Leaching Agent Ion Adsorption on (001) Surface of Montmorillonite: A Study Using Density Functional Theory

“…Du et al [16] studied the adsorption characteristics of hydrated hydrogen ions on the (001) plane and the (010) plane of illite. Zou et al [17][18][19] probed into the adsorption characteristics of Pr ions on the montmorillonite surface. Evidently, the calculation and simulation of rare earth adsorption with the quantum chemistry method are of great significance in the research on the cause of rare earth adsorption on clay minerals and the development of novel leaching agents.…”