High-throughput screening for discovery of benchtop separations systems for selected rare earth elements

Abstract

Rare earth (RE) elements (scandium, yttrium, and the lanthanides) are critical for their role in sustainable energy technologies. Problems with their supply chain have motivated research to improve separations methods to recycle these elements from end of life technology. Toward this goal, we report the synthesis and characterization of the ligand tris[(1-hydroxy-2-oxo-1, 2-dihydropyridine-3-carboxamido)ethyl]amine, H 3 1·TFA (TFA = trifluoroacetic acid), and complexes 1·RE (RE = La, Nd, Dy). A high-throughput experimentation (HTE) screen was developed to quantitatively determine the precipitation of 1·RE as a function of pH as well as equivalents of H 3 1·TFA. This method rapidly determines optimal conditions for the separation of RE mixtures, while minimizing materials consumption. The HTE-predicted conditions are used to achieve the lab-scale separation of Nd/Dy (SF Nd/Dy = 213 ± 34) and La/Nd (SF La/Nd = 16.2 ± 0.2) mixtures in acidic aqueous media.

The Earlier the Better: Structural Analysis and Separation of Lanthanides with Pyrroloquinoline Quinone

“…In the experiment with lanthanum and all lanthanides, separation factors (and enrichment in the solid phase) of directly adjacent pairs were hardly affected by a change in pH, while pairs (Ln2/Ln1) such as Nd/Dy and La/Lu showed a slight enhancement of the SF Ln2/Ln1 at pH 2.5 (Table S5). Schelter and co‐workers recently described a hexadentate H 3 Tren‐1,2,3‐HOPO ligand that precipitated late lanthanides such as Dy at very low pH (2 m HCl) but not Nd and La under the same conditions . However, given that PQQ is mainly deprotonated at pH 3.5 (p K a =0.30 (N6), 1.60 (C7‐CO 2 H), 2.20 (C9‐CO 2 H), 3.30 (C2‐CO 2 H), 10.30 (N1), see Figure B for numbering scheme) and that the late lanthanides were disfavored in our experiment, a different mechanism might be at work here.…”

Selective crystallization of dysprosium complex from neodymium/dysprosium mixture enabled by cooperation of coordination and crystallization

“…Recently, a new Ln 3+ separation strategy based on the crystallization of molecular crystals has emerged. 6–11 By using suitable ligands, slight differences in the ionic radii of Ln 3+ lead to significant differences in the structure, 6,8–11 solubility, 7 and crystallization kinetics. 11 This approach has provided high selectivity and revealed the possibility for simple one-step separation.…”

“…Exploring and refining the solution conditions to achieve high Ln 3+ selectivity for each ligand would further extend this crystallization-based separation approach. Encouraged by previous studies, 6–11 we report here a crystallization-based Ln 3+ separation using a tripodal Schiff base ligand, tris[2-(5-methylsalicylideneimino)ethyl]amine (H 3 L, Scheme 1). This type of ligand is readily obtained by the condensation of a tripodal amine with three equivalents of salicylaldehyde derivatives.…”

“…To our knowledge, this is the highest reported purity for one-step crystallization-based Nd 3+ /Dy 3+ separation. 7,9–11 We then quantitatively analyzed the Nd 3+ /Dy 3+ ratios in the solution phase by ICP-AES to calculate the crystallization yields and separation factors ( S Nd/Dy ) according to ref. 11.…”

Tuneable separation of gold by selective precipitation using a simple and recyclable diamide

“…Selective and reusable precipitation and adsorption methods are becoming increasingly popular for gold and other metal separations as they provide significant advantages over traditional, single-use precipitants 15 – 19 . Pre-formed porous network materials such as metal-organic frameworks (MOFs), polymers, and electroactive materials are selective for gold adsorption, and often exploit the accessible reduction potential of gold to deposit the metal within the porous cavities 20 – 25 .…”