Magnetically separable magnetite–lithium manganese oxide nanocomposites as reusable lithium adsorbents in aqueous lithium resources

Spinel-structured lithium manganese oxides (LMOs) have generated considerable interest as adsorbents for the recovery of Li ions from aqueous Li resources such as brine, seawater, and concentrated seawater. However, practical applications are limited because powdered adsorbents are hard to handle and separate from a liquid. To overcome this problem, magnetically separable magnetite–LMO composite adsorbents (M–LMOs) were prepared by growing magnetite on LMO. The morphologies, crystal structures, chemical compositions, and magnetic properties of the prepared materials were characterized using various analytical techniques. The results confirmed that M–LMO had a spinel structure and contained two crystal phases. Li+ adsorption experiments were conducted using acid-treated M–LMO (M–HMO). The results confirmed that M–HMO was reusable and selectively adsorbed Li+ in the presence of Na+, K+, and Mg2+; the Li+ adsorption capacity was 6.84 mg/g in LiCl buffer solution and 1.2 mg/g in concentrated seawater, which is a much harsher condition than brine or seawater. M–HMO was conveniently separated from a liquid under an external magnetic field after Li+ adsorption. This is significantly different from conventional Li+ recovery systems such as granulation, foam formation, and membranization. These findings indicate that M–LMO could be used for Li+ recovery from aqueous Li resources and has good potential for practical applications.