Electrochemical lithium recovery system through the simultaneous lithium enrichment via sustainable redox reaction

Abstract

With the drastic increase in the demand for lithium, electrochemical lithium recovery has gained significant attention as an alternative for lime soda evaporation. Despite its high selectivity and efficiency, the industrial application of electrochemical systems remains limited because of its discontinuous operation and the low lithium concentration in the source water. Hence, this study proposes a redox-mediated system for selective lithium recovery in tandem with the continuous enrichment of the source water via a sustainable redox reaction. In the proposed system, the reversible redox reaction of ferri-/ferrocyanide enables continuous enrichment of the source water, while lithium-selective adsorbent (λ-MnO2) selectively recovers the enriched lithium simultaneously. The redox-mediated lithium recovery system successfully concentrated lithium ions up to 37 mM Li+ in an equimolar mixture of 5 mM Li+ and 5 mM Na+, and up to 0.6 mM Li+ even from extremely dilute lithium-containing solutions (0.1 mM Li+: 9.9 mM Na+). With the introduction of λ-MnO2 as a chemical adsorbent, this system exhibited an exceptional selectivity (selectivity coefficient (αLi-Na) of 57) toward lithium from an equimolar mixture, and high lithium selectivity coefficients (αLi-Na: 804 and αLi-Mg: 387) in a synthetic solution equivalent to the Salar de Atacama brine in Chile. Therefore, this study represents progress towards the industrial application of the lithium recovery process, with potential applications for critical metal recovery in general.