Liquid mining of lithium from brines using a hybrid forward osmosis – freeze concentration process driven by green deep eutectic solvents

Abstract

Forward osmosis (FO) using deep eutectic solvents (DESs) as the draw solution (DS) was used in liquid mining of lithium from a synthesized brine, which was used as the feed solution (FS). Two DESs (choline chloride: 2 ethylene glycol and choline chloride: 2 levulinic acid) were studied as the DS. The water flux, reverse solute flux, final lithium concentration, and physical properties of commercially available cellulose triacetate membranes were studied experimentally. The performance of the DESs as DS in FO was compared to aqueous inorganic solutions at various concentration levels. Among all the DSs studied, choline chloride: 2 ethylene glycol (ChCl: 2 EG) resulted in the highest water flux (18.25 L m⁻² h⁻¹), upgrading the concentration of lithium by up to 3.68 times. In terms of reverse solute flux, the DESs showed lower values compared to the aqueous inorganic DSs tested when the active layer of the membrane was facing the FS. The use of DESs was also found to improve the membrane hydrophilicity and roughness. Freeze concentration (FC) was subsequently used to separate and recover the water that permeated into the DS and reconcentrate the latter for reuse in FO. This work highlights the potential sustainability benefits of the use of FO in lithium extraction, as the integration of FO with green DESs offers a promising liquid mining solution to meet the increasing demand for lithium while mitigating the environmental concerns associated with its extraction.