Li extraction from high Mg/Li ratio brine with LiFePO4/FePO4 as electrode materials

The challenge for lithium extraction from brine has been the separation of Mg and Li. Because they are located in diagonal positions within the periodic table, they exhibit many chemical similarities. But since Mg2 + has a high charge density and is easily hydrated, we explored a new separation method from an electrochemical perspective using LiFePO4/FePO4 as electrode materials. Through CV tests and technical experiments in a different electrolyte, this approach was verified. Our results show that lithium exhibits good reversibility in LiFePO4/FePO4 structures, and the redox peak separation is 0.592 V while that of Mg2 + is 1.403 V, indicating its more serious polarization. Technical studies using a voltage of 1.0 V show that, in pure lithium solution, the inserted capacity of lithium can reach 41.26 mg · (1 g LiFePO4)− 1, which is 93.78% of its theoretical value (44 mg), and the subsequent extracted capacity can attain 38.93 mg · (1 g LiFePO4)− 1, which is 94.3% of its inserted capacity. But the extracted capacity of Mg2 + from a solution containing magnesium is only 5.5 mg · (1 g LiFePO4)− 1. Furthermore, the experimental data at different voltages prove that a lower voltage is beneficial for separating Mg and Li, and this method also works well in brine since the Mg/Li ratio can be reduced to 0.45 from 60. All these results indicate that this method, while simple, is quite promising for separating Mg and Li from a high Mg/Li ratio brine.

► Li and Mg can be separated electrochemically using LiFePO4/ FePO4 as electrodes.
► The approach was verified by CV tests and technical experiments.
► Lithium exhibits good reversibility while Mg2+ behaves more serious polarization.
► A low voltage is beneficial for separating Mg and Li.
► It also works well in brine since the Mg/Li ratio can be reduced to 0.45 from 60.