High-selective cyclic adsorption and magnetic recovery performance of magnetic lithium-aluminum layered double hydroxides (MLDHs) in extracting Li+ from ultrahigh Mg/Li ratio brines

The lithium-aluminum layered double hydroxides (Li/Al-LDHs) have been proved to be feasible to efficient lithium extraction from low-grade brines with ultrahigh Mg/Li ratios as Li+ adsorbents without elution damages. In this study, considering a sharp decline on the adsorption capacity resulting from the granulation in industrial applications, novel adsorbents, magnetic Li/Al layered double hydroxides (MLDHs), were synthesized via a simple staged coprecipitation method. The characterization and adsorption results proved doped Fe3O4 nanoparticles as magnetic cores were not harmful to the crystal phase and stability of the effective adsorption component Li/Al-LDHs in MLDHs. MLDHs exhibited favorable selective and preferential adsorption for Li+ in the Qarhan Salt Lake old brine with Mg/Li mass ratio of 284, whose adsorption capacity reached up to about 6.0 mg/g and Mg/Li ratios in desorption solution less than 0.4 with recovered Mg/Li ratios less than 6.0. By virtue of the superparamagnetism of Fe3O4 nanoparticles, a rapid recovery of MLDHs from brines after adsorption could be achieved easily using an external magnetic field. Furthermore, after 8 adsorption-desorption cycles, both the adsorption capacity and crystal structure of MLDHs had no significant change, indicating the great potential in the industrial lithium extraction from brines involving long-term recycling for adsorbents.