Selective lithium extraction from diluted binary solutions using metal-organic frameworks (MOF)-based membrane capacitive deionization (MCDI)

The increasing demand for lithium (Li) calls for exploring efficient and environmental-friendly methods to extract Li from brine. Capacitive deionization (CDI) as an emerging technology is of interest for resource recovery because of its rapid adsorption rate, limited energy consumption, and low environmental impact. However, Na and K in seawater and seawater reverse osmosis (SWRO) brine and Mg and Ca in inland brine challenge the feasibility of selective Li extraction. Herein, CDI was integrated with deposition-coated ZIF-8-PDA membranes to extract Li from binary solutions containing Li and M (M representing Na, K, Mg, and Ca). MCDI tests were conducted under a series of voltages (±0.5 V, ±1.0 V, and ±1.5 V) to investigate the influence of applied potentials on Li extraction performances. The results indicated advantages for Li extraction when coexisting cations were monovalent than divalent. Additionally, a lower voltage of 0.5 V could provide superior Li selectivity, charge efficiency (CE), and energy normalized to Li (ENL) than higher voltages. Especially, Li selectivity of 1.50 and 1.85 was achieved in Li/Na and Li/K feeds under 0.5 V, 37 % and 74 % higher than those under 1.5 V, respectively, illuminating the potential of MCDI for Li extraction from seawater and SWRO brine with low energy input.