A novel zwitterionic chromatography approach to separate lithium from unconventional resources

Abstract

Lithium (Li) is a key element for clean energy technologies, and, accordingly, the global lithium demand has been increasing rapidly. Therefore, to meet the Li demand and maintain supply chain stability, it is critical to develop efficient lithium extraction technologies that allow exploitation of unconventional lithium resources, such as geothermal brines and inland brine streams. However, the recovery of Li from these resources is challenging due to low Li concentration, low ratios of Li/Na, Li/Mg, or Li/Ca, and complex feed compositions. To address this, we introduced a new Direct Lithium Extraction (DLE) process using Zwitterionic Chromatography (ZIC) to separate Li from other salts. Since salts are partitioned on ZIC under water elution, no reagent chemicals are needed, and the Li separation is not limited by the adsorption capacity. We prepared 13 different zwitterionic (ZI) resins to investigate the salt retention on various ZI groups and then screened out promising sorbents for efficient Li separation. It was found that salt retention was synergistically affected by the pore size and ZI configurations. Using carboxybetaine (QAC3CA) sorbents, multicomponent separations showed that Li can be partitioned from divalent salts or Na with selectivities of 1.8 or 1.9, respectively. Although the selectivity is relatively low, in real brine tests, Li was separated from Ca and Mg with 79.2 % yield, showing the potential for a continuous process to achieve high productivity and high yield. Simulation studies suggest the salt elution mechanism is related to the hydration reaction energy and the effective hydrated radius of cations.