Recovery of Li Through Selective Adsorption on Two Types of Calix[4]arene Derived Adsorbents

Recovery of Li is one of urgent issues owing to exponential increase of Li demand of Li-ion battery. More efficient and selective reagents for Li recovery have been required. Calixarene as a host oligomer was focused on this purpose, and it was applied to adsorptive reagents. Two types of adsorbents incorporating trialkyl monoacetic acid derivatives of calix[4]arene through either impregnation or crosslinking were synthesized. The impregnated adsorbents were synthesized by impregnation of four trialkyl monoacetic acid derivatives of calix[4]arene into macroporous Ambelite XAD-7. The crosslinked adsorbents were synthesized by crosslinking of three trialkyl monoacetic acid derivatives of debutylated calix[4]arene each other using sym-trioxane under an acidic condition. Their adsorption behaviors and Li⁺ selectivities over other alkali metal ions were investigated. Incorporation of the ligand into the adsorbents had a negligible effect on the time required to reach equilibrium. The impregnated adsorbents exhibited extremely high Li⁺ selectivity over other alkali metal ions that reflected those of the incorporated ligand, whereas the crosslinked adsorbents exhibited Cs⁺ selectivity and mixed effects arising from incomplete dehydration and ion discrimination. The adsorption of alkali metal ions was driven by ion-exchange mechanism. The apparent adsorption equilibrium constants for alkali metal ions on both adsorbents and the separation factors between the metal ions were estimated. It was found that three alkyl branches affected the adsorption efficiency, together with separation efficiency.