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

Abstract

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.