Precise Li+ and Mg2+ Separation Enabled by Sodalite Ion Exchange Contribute to The Lithium Extraction from Low-Quality Brines

Adsorbents with accurate Li⁺ and Mg²⁺ separation have substantial potential for lithium extraction from low-quality brines to alleviate lithium supply shortages. Zeolites have become superior adsorbents for heavy metal adsorption in wastewater due to their unique cation exchange capacity. Herein, we utilize the difference in ion exchange kinetics between Li⁺ and Mg²⁺ to achieve efficient lithium extraction. The ion-selective adsorption behavior of sodalite (SOD), NaA and NaX zeolites is inversely proportional to their pore size (2.8, 4.1 and 7.4 Å, respectively). Only small-pore SOD exhibits large Li⁺ and Mg²⁺ kinetic differences to achieve prioritized Li⁺ capture, while Mg²⁺ enters the pores more slowly, allowing the exchanged Li⁺ to be retained. Starting from the three steps of ion dehydration, ion migration and ion exchange, the exchange pathways of Li⁺ and Mg²⁺ in SOD and the energy differences required in each step are revealed. The dehydration free energy, migration energy and exchange energy barriers of ΔE_Li < ΔE_Mg confirm the kinetic rate order of Li⁺ > Mg²⁺, thus facilitating preferential Li⁺ capture and enabling Li⁺ and Mg²⁺ separation. This study of the regeneration cycle, batch synthesis and particle performance of SOD highlights its potential value for lithium extraction in actual brines.