Fe3O4-doped lithium ion-sieves for lithium adsorption and magnetic separation

Spinel lithium manganese oxide ion-sieve is considered the most promising adsorbents to extract lithium from brine. Here, we report a Fe3O4-doped magnetic lithium ion-sieve prepared by a facile hydrothermal method. The Fe3O4-doped lithium manganese oxide (LMO/FO) was first synthesized as the magnetic ion-sieve precursor. The chemical and morphological properties of LMO/FO were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that Fe3O4 was uniformly dispersed in the precursor. Doping Fe3O4 into LMO led to the increase of the average valence for Mn in the precursor from +3.48 to +3.53, which helps improve its structural stability. The equilibrium adsorption capacity of acid-treated LMO/FO (i.e. HMO/FO) was 29.33 mg/g which was greater than that of the undoped (i.e. HMO). Moreover, the adsorption behavior of the both ion-sieves well fitted with pseudo-second-order kinetic model. In 0.05 mol/L HCl solution, the desorption equilibrium could be achieved after 30 min. The dissolution loss of manganese and iron were 6.22% and 4.14%, respectively. The saturation magnetization value (Ms) of LMO/FO is 2.5 emu/g and the solid-liquid separation can be achieved by a magnet. In addition, the magnetic ion-sieve demonstrated excellent adsorption selectivity to Li+ in a mixed solution containing Li+, Na+, K+, Mg2+ and Ca2+.