Lithium extraction from salt lake brine by four-stage ion-distillation of flow electrode capacitive deionization

Herein, a novel, highly efficient, and low-energy consumption four-stage ion-distillation of FCDI (ID-FCDI) device was developed that combined four commercial monovalent selective membranes with four flow electrode channels for high selectivity to extract Li+ ions from salt lake. It exhibited excellent separation factor (SMg2+Li+ = 11247.27), high enrichment ratio (4.95 times), super purity of Li+ ion solution (99.97 %), and low molar energy consumption (Em = 0.21 kWh mol−1) at mass ratio of Mg2+/Li+ = 1:1. The mathematical model calculation revealed that the excellent selective separation effectiveness of the as-proposed ID-FCDI system is due to the unique property of the monovalent selectivity membranes, in which the transmembrane rate of lithium ions is ten times that of magnesium ions under the same condition. Furthermore, the separation mechanism of the as-proposed ID-FCDI device for Li+/Mg2+ ions was determined by the high electrosorption capacity of the flow electrode for Li+ ions (1.14 times higher than Mg2+ ions), low diffusion resistance (1.413 Ω), and high diffusion coefficient of Li+ ions (2.83 times faster than Mg2+ ions) by electrochemical measurement. On this basis, 3.92 times of lithium was successfully enriched in the natural salt lake brine of Golmud (mass ratio of Mg2+/Li+ = 79.29), and the separation factor was 6307.17 with a 99.64 % purity of Li+ ion solution and an Em of 0.20 kWh mol−1. Finally, the Li2CO3 product (99.66 %) was precipitated via the reaction between Na2CO3 and the enriched Li+ ion solution, consequently fulfilling the battery-level application of the industrial purity requirements. These findings highlight that this device is promising and profitable for lithium extraction from salt lake in industrial production.