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 (i.e., used lithium‐ion batteries). Its isolation and purification from like salts is a recognized challenge with potential strategic and economic implications. Here, 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 ~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.