Effects of excessive lithium deintercalation on Li+ adsorption performance and structural stability of lithium/aluminum layered double hydroxides

Lithium/aluminum layered double hydroxides (Li/Al-LDHs) have been industrially proven to be recyclable lithium adsorbents that do not dissolve upon elution, although they are hypersensitive to lithium deintercalation. In this study, the Li+ adsorption performances and structural stabilities of Li/Al-LDHs samples with different lithium deintercalation intensities are comprehensively investigated and compared to expose the influence of excessive lithium deintercalation. The characterization results demonstrate that Li/Al-LDHs are inclined to transform to gibbsite under excessive lithium deintercalation. Moreover, this transformation is enhanced by a long deintercalation time at 80 °C in deionized water because the layered structure of Li/Al-LDHs collapses upon reduction of the lithium content. The Li+ adsorption kinetics and isotherms reveal that excessive lithium deintercalation has no effect on the adsorption pathway and rate, while the adsorption capacity fluctuates with increased lithium loss on account of the conflict between the generation of Li+ active sites and structural damage. Adsorption experiments at different pH values show that a neutral pH is more favorable because an acidic or alkaline condition leads to the undesirable formation of a gibbsite or amorphous phase in Li/Al-LDHs during adsorption. In addition, the presence of Mg2+ has a significant effect on the lithium adsorption capacity of Li/Al-LDHs. The adsorption capacities of Li/Al-LDHs samples with different lithium deintercalation intensities are all dramatically enhanced by a high Mg2+ concentration, reflecting the promising potential application of Li/Al-LDHs in Li+ extraction from low-grade brines with high Mg/Li ratios.