Highly efficient and stable adsorption of lithium from brine with microcapsules containing 1-phenylazo-2-naphthol and...

Lithium extraction from salt lake brine is still challenging due to the existence of similar elements, e.g. sodium. In the present work, polysulfone (PSF) microcapsules containing 1-phenylazo-2-naphthol (HS) and trioctylphosphine oxide (TOPO) as extractants were successfully prepared by microfluidic technology for the separation of Li⁺ from brine with Li⁺ and Na⁺. The morphology, composition, and structure of HS-TOPO-based microcapsules were characterized systematically. The results showed that microcapsules consisting of 20 wt% (m m^-1) polysulfone and 80 wt% (m m^-1) 1-phenylazo-2-naphthol-trioctylphosphine oxide as the extractant, which was labeled as PSF/HS-TOPO-2/8, exhibited the best performance for Li⁺ adsorption. The separation factor (SF) of Li⁺ over Na⁺ is up to 653 and the adsorption capacity for Li⁺ in the simulated brine could reach 3.67 mg g^-1 for microcapsules PSF/HS-TOPO-2/8, which demonstrated that Li⁺ can be separated with high selectivity. Besides, the kinetic results demonstrated that the adsorption followed quasi-secondary adsorption kinetic models, indicating that the adsorption mechanism of lithium by microcapsules involved chemisorption. After ten cycles of adsorption-elution, the maximum equilibrium adsorption capacity still remained at 87%. All these results demonstrate that PSF/HS-TOPO-2/8 microcapsules can be used as an efficient adsorber for the adsorption of Li⁺ from brine with high selectivity and stability.