Syntheses and Characterization of Tetrazolate-Based Lanthanide Compounds and Selective Crystallization Separation of Neodymium and Dysprosium

Abstract

Selective crystallization offers new opportunities for separating neodymium and dysprosium, which are considerably important in permanent magnets. Two water-soluble nitrogen-rich tetrazolate-based ligands, dtp2– (H2dtp = 2,3-di-1H-tetrazol-5-ylpyrazine) and H2ibt– [H3ibt = 4,5-bis(tetrazol-5-yl)imidazole], allow the separation of Nd3+ and Dy3+ through selective crystallization. The reactions of Ln3+ with the ligand Na2(dtp)·2H2O lead to two distinct phases, Na[Ln(dtp)(H2O)8](dtp)·H2O (Lndtp1; Ln = La–Pr) and [Ln(H2O)8](Hdtp)(dtp)·H2O (Lndtp2; Ln = Nd and Sm–Lu). Three different compound types, [Ln(H2ibt)2(H2O)6](H2ibt)·3(H2O) (Lnibt1; Ln = La or Ce), [Ln(H2ibt)(H2O)7](H2ibt)2·4(H2O) (Lnibt2; Ln = Pr or Nd), and [Ln(Hibt)(H2ibt)(H2O)4]·4+x(H2O) (Lnibt3; Ln = Sm–Lu), are obtained from reacting Ln3+ and Na(H2ibt)·3(H2O). Two different phases are observed for Nd(Lnibt2) and Dy(Lnibt3) in the system of H2ibt–, which leads to crystallization-based separation of Nd/Dy with a separation factor of 32 ± 0.7, 10 times higher than that of dtp2–, and a short separation time of 20 s (1 day for dtp2–). The higher performance of H2ibt– compared to that of dtp2– provides guidance for the rational design of water-soluble tetrazolate-derived ligands for selective crystallization.

Transformation of Mononuclear Plutonium(III) Tetrazolate Complexes into Dinuclear Complexes in the Solid State

“…Based on parallels between the ionic radii of nine-coordinate Pu III (1.165 ± 0.002 Å) and Nd III (1.163 Å) that are within error of one another, , one could use tetrazoles to delineate potential bonding differences between these cations. − To this end, we compare the solid-state chemistry and spectroscopy of two Pu III tetrazolate compounds with their isotypic Nd III complexes, as well to the other reported isotypic Ln III tetrazolate complexes, such as [Nd­(H 2 ibt)­(H 2 O) 7 ]­(H 2 ibt) 2 ·4­(H 2 O), [H 3 ibt = 4,5-bis­(tetrazol-5-yl)­imidazole], and [Nd­(hqt) 3 ]­K 3 [H 2 hqt = 2-(1H-tetrazol-5-yl)­quinoline-8-ol (8-hydroxyquinoline-2-tetrazole)] …”

Rare Earths—The Answer to Everything

“…Traditional fractional crystallization, the initial separation method, is extremely tedious, but when carried out in water, it is environmentally optimal. Use of different salts or double salts may yet improve differentiation, and an effective Nd/Dy crystallization separation has been provided to enable the recovery of these elements from magnets [18]. Magnetically assisted crystallization has been reported [19] and has been used in rare earth separations [20].…”

Flow-driven enhancement of neodymium and dysprosium separation from aqueous solutions

“…20,21 There have also been a limited number of studies in all-aqueous environments including a protein-based process, 22 a selective oxalate solubilization method, 23 and selective precipitation or crystallization with dibutyl phosphate, 24 borate, 25 and tetrazolate. 26 All the above-mentioned REE separation methods rely on the differences in equilibrium constants. Reaching the thermodynamic equilibrium is oen time-consuming for selective precipitation even when accelerated by elevating the reaction temperature.…”

“…20,21 There have also been a limited number of studies in all-aqueous environments including a protein-based process, 22 a selective oxalate solubilization method, 23 and selective precipitation or crystallization with dibutyl phosphate, 24 borate, 25 and tetrazolate. 26…”