Recovery of Li2SO4 from lithium-precipitated mother liquor via a Pb/FePO4 membrane-free electrochemical system

Ore is the primary source of Li2CO3 production, but approximately 10–15% of lithium remains in the lithium-precipitated mother liquor for each ton of Li2CO3 produced. Therefore, efficient recovery of Li2SO4 from this solution is essential to ensure Li2CO3 supply. The conventional “(+) LiFePO4/FePO4 (−)” membrane system has been successfully used to extract LiCl from brine. However, the large radius of SO42− in the mother liquor significantly increases the cell voltage of this system, which is not favorable for separating Li+ and Na+. We therefore developed a novel “(+) Pb/FePO4 (−)” membrane-free Li2SO4 extraction system that uses Pb and FePO4 to capture SO42− and Li+, which was then released by switching the electrode polarity after the adsorption was completed. The Li+ concentration in the mother liquor decreased from 1.3 to 0.014 g·L−1 in two cycles, and the Li+ recovery rate was 98.9%. The Li+ concentration in the recovery liquor reached 1.356 g·L−1, with a Li–Na separation coefficient of 304. In addition, the new system did not suffer from lead dissolution loss, and the adsorption capacity of Li+ was 95.44% of the initial capacity after 15 cycles. Overall, this membrane-free lithium extraction system can provide a direction for extracting Li2SO4 from sulfate systems.