Highly selective transport of lithium across a supported liquid membrane

Abstract

Lithium extraction is a major concern in view of the increase in battery manufacturing. Separation of lithium from associated sodium is still a challenging task due to the similar chemical behavior of these alkali metals. Lithium sources such as salt brines or seawater usually contain large amounts of sodium which requires a high selectivity for the lithium extraction process. In this study, we demonstrate the application of a supported liquid membrane (SLM) with very high selectivity for the separation of lithium from sodium. A synergistic extraction system made of heptafluoro-dimethyloctanedione (HFDOD) and tri-n-octylphosphine oxide (TOPO) ligands diluted in dodecane was selected based on its extraction efficiency (>99 % of lithium extracted) and selectivity for lithium over sodium (separation factor ca.400). Several experimental parameters were studied using a SLM made of HFDOD and TOPO (initial lithium concentration and sodium to lithium concentration ratio in the feed aqueous phase, HFDOD: TOPO ratio in the organic phase). It was found that high lithium permeation rates can be obtained even for low lithium concentrations and high sodium concentration. Membrane stability was evaluated and found to be poor, i.e. significant loss of performances was observed after one cycle of use, due to the leakage of the organic phase and change in HFDOD: TOPO ratio into it. The SLM system designed is suitable for the extraction of lithium from lowly concentrated solutions such as brines and seawater.