Covalent organic framework membranes achieving Mg/Li separation by permeating Mg2+ while retaining Li+.

Due to the growing demand for lithium in the new energy industry, significant attention has been focused on developing lithium extraction technologies from salt-lake brine. However, the high Mg/Li ratio in salt-lake brine presents challenges for membrane separation technology. If a membrane can allow Mg2+ and water molecules to pass through while retaining Li+, the retained brine will have concentrated Li+ with a reduced Mg/Li ratio, creating the facilitation of further lithium extraction. In this study, we discovered through non-equilibrium molecular dynamics simulations that strongly hydrophilic covalent organic frameworks membranes capture Li+ in their pores, preventing additional Li+ from entering the nanopores. Meanwhile, Mg2+ can freely penetrate these nanopores along with water molecules. This adsorption of Li+ and the free permeation of Mg2+ with water molecules result in the effective separation of Li+ and Mg2+. Consequently, the retained brine becomes lithium-rich with reduced Mg/Li ratio. The findings of this work provide valuable guidance for designing nanofiltration membranes for extracting lithium from salt lakes with high Mg/Li ratio. [Display omitted] • The adjustment of membrane hydrophilicity influences the Mg/Li selectivity. • Enhanced membrane hydrophilicity promotes Li + retention, rather than Mg2+. • Strong hydrophilicity induces the adsorption of Li + onto the pore walls. • High concentration of Li + inside membranes hinders further entrance of Li+. • The penetration of Mg2+ is not influenced due to the large pore size of TpPa. [ABSTRACT FROM AUTHOR]