Anion regulation strategy of lithium-aluminum layered double hydroxides for strengthening resistance to deactivation in lithium recovery from brines

Lithium aluminum layered double hydroxides (LiAl-LDHs) have emerged as the most promising adsorbent for lithium extraction from salt lake brines. However, the development of LiAl-LDHs is impeded by their susceptibility to structural collapse and deactivation during desorption process. Herein, an interlayer anion regulation strategy was proposed to endow LiAl-LDHs with superior resistance to deactivation induced by excessive Li+ deintercalation through strengthening the interlayer interactions. Consequently, a novel LiAl-LDH with interlayer Cl- partially replaced by PO4 3-(LiAl-LDH-P) was synthesized by coupling PO4 3-intercalation with Li+ insertion during co-precipitation. Combining DFT calculations and elution strength experiments, it was revealed that the intercalated PO4 3- could anchor Li+ into the vacancies of Al-O octahedron via high interlayer binding energy and strong electrostatic interaction, which imparted LiAl-LDH-P with an excellent anti-elution deactivation ability. Moreover, LiAl-LDH-P presented distinctly advanced compared to commercialized and reported LiAl-LDHs, with extraordinary Li+ adsorption capacity (9.35 mg/g), selectivity (separation factors of 270.3, 450.3, 453.7 for Li+/Na+, Li+/K+, Li+/Mg2+, respectively), and reusability in Lop Nor brine, even at the ultrahigh eluent consumption. Furthermore, the physicochemical properties and Li+-extraction mechanism of the LiAl-LDH-P were investigated as well. This work provides a promising strategy to solve the current deactivation of LiAl-LDHs and offers a prospective adsorbent for Li+ extraction from brine.