Selective Solid–Liquid and Liquid–Liquid Extraction of Lithium Chloride Using Strapped Calix[4]pyrroles

Abstract

LiCl is a classic “hard” ion salt that is present in lithium‐rich brines and a key component in end‐of‐life materials (that is, used lithium‐ion batteries). Its isolation and purification from like salts is a recognized challenge with potential strategic and economic implications. Herein, we describe two ditopic calix[4]pyrrole‐based ion‐pair receptors (2 and 3), that are capable of selectively capturing LiCl. Under solid–liquid extraction conditions, using 2 as the extractant, LiCl could be separated from a NaCl/KCl salt mixture containing as little as 1 % LiCl with circa 100 % selectivity, while receptor 3 achieved similar separations when the LiCl level was as low as 200 ppm. Under liquid–liquid extraction conditions using nitrobenzene as the non‐aqueous phase, the extraction preference displayed by 2 is KCl>NaCl>LiCl. In contrast, 3 exhibits high selectivity towards LiCl over NaCl and KCl, with no appreciable extraction being observed for the latter two salts.

Application of Ionic Liquids for the Recycling and Recovery of Technologically Critical and Valuable Metals

“…Recent findings published in Angewandte Chemie (Applied Chemistry) [51] led to the development of novel macromolecules for targeted complex coordination and selective extraction. The Sessler group reported a hemispherand-strapped calix [4]pyrrole ligand for selective binding to Li + salts.…”

Cesium halide ion pair recognition by a pyrrole strapped Calix[4]pyrrole

“…Recently, ion pair receptors, systems that have the ability to complex concurrently both an anion and a cation, have attracted increasing attention. [1][2][3][4][5][6][7][8] Much of the interest associated with such systems reflects their generally enhanced affinity and selectivity for certain salts as compared with simple ion receptors that are designed to bind in relative isolation either a cation or an anion, The improved ion binding features of ion pair receptors are generally ascribed to enhanced electrostatic interactions between co-bound ions within the receptor, as well as reductions in competitive solvation effects that result from encapsulation of both target ions within the same receptor environment. [1][2][3][4] Typically ion pair receptors contain two distinct ion binding sites, one for a cation and one for an anion.…”

Convergent Ditopic Receptors Enhance Anion Binding upon Alkali Metal Complexation for Catalyzing the Ritter Reaction

“…The past decade has witnessed a growing wealth of ditopic receptors that are capable of cooperatively binding pairs of cations and anions . Compared to a monotopic molecular receptor that only recognizes a single ion, these receptors show enhanced binding affinity and selectivity, leading to interesting applications which include salt solubilization, extraction, ion-sensing, and transmembrane ion transport . So far, ion-pair binding has been explored in a variety of scaffolds including crown ethers, calix[4]­pyrroles, and urea derivatives .…”