Inorganic nanofiber as a promising sorbent for lithium recovery

Lithium recovery by adsorption from aqueous resources is promising with respect to securing finite mineral resources. In this study, an inorganic spinel lithium manganese oxide (LiMn₂O₄) nanofiber with a tunable diameter was fabricated by electrospinning. Spinel hydrous manganese oxide, which has high lithium selectivity, was derived from LiMn₂O₄ by Li⁺–H⁺ exchange. The kinetic and isotherm studies with respect to Li⁺ adsorption revealed that the nanofibers fitted well to the second-order kinetic model and the Langmuir adsorption model; moreover, adsorption capacity increased as diameter decreased. The relationship between Li⁺ adsorption and diameter was explained according to the Brunauer–Emmett–Teller (BET) surface area: Adsorption capacity increases with an increase in BET surface area. Notably, the nanofibers performed better than the particles with the same chemical composition as that of the nanofibers; this trend was attributed to the aggregation of the particles, which caused the number of sorption sites to decrease. The reusability of the nanofiber was assessed through adsorption–desorption cycle tests. The adsorption capacity of the nanofiber with a diameter of 45 nm, which was the smallest diameter, was largely reduced after the five-cycle process; moreover, the capacity only reached 61% of the initial capacity at the fifth cycle, while the other nanofibers and the particle maintained capacities of over 90% at the fifth cycle. This reduction in Li⁺ adsorption was due to the significant detriment of the fibrous structure during the adsorption–desorption process. The nanofiber with a diameter of 90 nm was optimal in terms of adsorption capacity and reusability. Furthermore, the Li⁺ selectivity test conducted in artificial sea water showed that Li⁺ selectivity was the greatest among other cations.