Combination of Membrane Electrolysis and CO ₂ Absorption for the Removal of Magnesium and Calcium from Lithium-Rich Brines

Lithium production from continental brines is challenged by the presence of Mg2+ and Ca2+ cations, which must be removed to obtain battery-grade lithium compounds. Conventional precipitation with lime and soda ash requires large reagent volumes, increasing costs, logistics, and waste production, especially in remote and water-scarce mining regions. Here, we present an integrated approach combining membrane electrolysis with direct absorption of CO2 from air for sustainable brine purification. A newly designed three-compartment electrochemical reactor with reduced interelectrode distance and turbulence promoters enabled efficient Mg2+ removal via controlled alkalinization. At pH 11.7, Mg2+ abatement exceeded 99.99%, with partial Ca2+ removal. Energy consumption was influenced by the HCl concentration in the middle compartment: higher acid concentrations reduced cell voltage but increased charge requirements, leading to higher net energy demand. A second electrolysis stage raised brine pH to 12.6–13.0, enabling further Ca2+ reduction while maintaining high Coulombic efficiency and avoiding the membrane degradation observed at higher alkalinities. Final Ca2+ removal was achieved by direct CO2 absorption from air, promoting CaCO3 crystallization under moderate pH conditions and reducing energy costs compared to calcium hydroxide precipitation. Tests with natural brines from Argentine salars demonstrated >99.99% Mg2+ and up to 99.8% Ca2+ removal with minimal Li+ losses (<14%). The process consumed 27–36 Wh L–1, corresponding to 437–533 Wh mol–1 of divalent cations removed, while capturing ∼880 g of CO2 per m3 of brine. This coupled electrochemical–CO2 process provides a scalable and sustainable route to lithium brine purification, avoiding chemical additives, reducing waste, and enabling carbon sequestration at sites with abundant solar resource.