Abstract
With the growing demand of rare earth elements, the recovery of rare earth elements is a major issue for researchers in related fields. Adsorption technology is one of the most effective and popular recovery methods. Therefore, the adsorption mechanism of Yttrium (Y), Neodymium (Nd), and Lanthanum (La) atoms on the kaolinite (001) and (001¯) surfaces was examined by density functional theory (DFT). The most stable adsorption sites on the kaolinite (001) surface for Y atoms was the bridge site, and the hollow site was the most favorable adsorption site for Nd and La atoms with high adsorption energy. However, the adsorption energies of kaolinite (001¯) surface sites for Y, Nd, and La atoms were much lower than the (001) surface sites, indicating that the adsorption capability of the hydroxylated (001) surface is stronger. The effects of coverage on adsorption position, energy, and structures were entirely investigated on top, bridge, and hollow sites of the kaolinite (001) surface from 0.11 to 1.0 monolayers (ML). The adsorption energy of Y, Nd, and La atoms on three kinds of sites increased with increasing of the coverage implied the stronger capability of surface adsorption. The recovery capability of kaolinite for the rare earth atoms was in the order of La > Nd > Y. The changes in the atomic structure, charge density, and electron density of states for Y, Nd, and La/kaolinite (001) before and after adsorption were also analyzed in depth.
Highlights
IntroductionRare earth elements (REEs) have always been used in the fields of metallurgy, medicine, the chemical industry, and agriculture [1,2]
NREE was the number of rare earth elements (REEs) (REEs = Y, Nd, and La) adatoms adsorbed on the slab at the considered coverage Θ (Θ was defined as the ratio of the number of adsorbed atoms to the optimum adsorption sites on the surface of kaolinite) [44]
La at all Site types of adsorption sites, and we found that the hREEs-Al of the Y adsorbed on the Hollow bridge site and the La and Nd adsorbed on the hollow site were shorter than the other Eads sites at all
Summary
Rare earth elements (REEs) have always been used in the fields of metallurgy, medicine, the chemical industry, and agriculture [1,2]. It is well known that various approaches (e.g., biological treatment, chemical precipitation, and adsorption) have been geared towards the recovery of REEs [4,5]. Araki et al [6] and Alakhras et al [7] used the surface template polymerization technique to create an adsorbent with high selectivity for lanthanides. Chio et al [8] used radiation-induced grafting of acrylic acid (AAc) onto polyethylene (PE) films to adsorb Lanthanide. The adsorption ability of the above materials was weak in practical application. Clay minerals are attractive in comparison with the above materials because they are widespread, mined, and inexpensive [9,10]
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