Lithium extraction from seawater by manganese oxide ion sieve MnO2·0.5H2O

Among the current methods for lithium extraction from seawater, adsorption by manganese oxide ion sieves was considered to be the most promising one for industrial application. In this study, sol–gel, hydrothermal synthesis and two-stage heat treatment were used for preparing lithium ion sieve precursor Li1.6Mn1.6O4. Ion sieve MnO2·0.5H2O was then obtained after eluting Li+ from Li1.6Mn1.6O4 by acid treatment. The crystal structure, surface morphology and adsorption properties of the ion sieve were characterized by XRD, SEM, HRTEM, adsorption isotherms and kinetics. Furthermore, the dynamic adsorption/desorption processes of granulated ion sieve were studied with concentrated seawater (saltern bittern) and HCl solution. The results showed that the ion sieve and its precursor were nearly pure spinel manganese oxides, and possessed one-dimensional nanowires morphologies. After granulation, the ion sieve exhibited good adsorption performance, and its adsorption process was in accordance with Lagergren Kinetics Equation and Langmuir Isotherm Equation. Under continuous and dynamic conditions, the ion-exchange capacity of this ion sieve for saltern bittern (pH = 10) was 10.05 mg/g, and after acid treatment, lithium-rich solution which was 30 times more concentrated than bittern (900 times than seawater) was obtained. The results implied that the ion sieve could be used for lithium extraction and enrichment in seawater system, and had a good application prospect.