Double-edged role of interlayer water on Li⁺ extraction from ultrahigh Mg²⁺/Li⁺ ratio brines using Li/Al-LDHs

Lithium-aluminum layered double hydroxides (Li/Al-LDHs) are the only industrial adsorbents for Li⁺ extraction from Mg²⁺/Li⁺ ratio brines dependent on the special neutral desorption without dissolution damage. In this work, Li/Al-LDHs with different interlayer water contents were designed for the investigation of correlation between interlayer water and Li⁺ adsorption performances in high Mg²⁺/Li⁺ ratio brines. On the one hand, the Li⁺ adsorption capacity of Li/Al-LDHs in the Qarham Salt Lake old brine with a Mg²⁺/Li⁺ ratio exceeding 300 presented a positive correlative relation with the interlayer water content, rising from 1.05 mg/g to 7.89 mg/g as the interlayer water content increased from 5.52% to 18.18%. On the other hand, the interlayer water content would not affect the structure stability of Li/Al-LDHs, while the interlayer spacing was lessened with less interlayer water resulting in an uptrend to the adsorption selectivity on account of the depressed confinement effect. The density functional theory (DFT) calculation further indicated that LiCl was easier to enter the structure of Li/Al-LDHs with more interlayer water in view of the greater interaction energy.