Preliminary study on recovering lithium from high Mg2+/Li+ ratio brines by electrodialysis

• ED was used to separate magnesium and lithium in brine with high Mg2+/Li+ ratio.
• The ED system could reduce the Mg2+/Li+ ratio and concentrate lithium in the brine.
• The highest ESEC was 0.27 kWh/mol when the applied voltage was 6 V.
• The Mg2+/Li+ ratio of artificial brine could be decreased from 60 to 7 within 2 h.

An electrodialysis (ED) system equipped with monovalent selective permeability ion exchange membrane was used to investigate the separation of magnesium and lithium in salt lake brines. Some objective functions including separation coefficient of magnesium and lithium (FMgLi), recovery ratio of lithium (RLi) and current efficiency (η), were applied to explore the effect of the applied voltage, the linear flow velocities, the Mg2+/Li+ ratio and pH on the process of extracting lithium. The results showed that the increase of applied voltage could improve the separation coefficient and the recovery ratio of lithium, but energy consumption would also rise; with the increase of feed linear velocity, the separation coefficient had a rising trend, but too large linear velocity would lead to increasing energy consumption and reducing current efficiency. When the Mg2+/Li+ ratio was in the range of 5–92, ED technology showed higher separation efficiency. Linear flow velocities of concentrating and desalting compartments (1.9–7.6 cm/s) showed positive correlation with the migration of the ions. According to the comprehensive analysis of the experimental results, the optimal operation conditions of the ED device are as follows: the applied voltage (5 V), concentration of electrolyte solution (5 wt% Na2SO4) and the linear velocities of desalting/concentrating/electrolyte (6.2, 6.2 and 3.8 cm/s). When the brine with Mg2+/Li+ ratio of 60 was treated by the ED for 2 h under this condition, the separation coefficient was 12.48. And the recovery ratio of Li+, current efficiency and the Mg2+/Li+ ratio of concentrate was 72.46 wt%, 8.68 wt% and 7, respectively. The concentrate, which could be considered as a bittern with lower Mg2+/Li+ ratio (<8), will be easy to be treated in the subsequent process.