Lithium (Li) recovery from seawater is currently attracting much attention due to the increased industrial demand for Li. Hydrogen manganese oxide (HMO) is a promising adsorbent for Li recovery from seawater, but powder-type HMO is difficult to apply, and it is essential to obtain a granulated material for practical application. To minimize the Li adsorption capacity loss and to obtain high mechanical stability in seawater, highly porous cylindrical HMO/Al2O3 composites have been synthesized. All LMO/Al2O3 composites exhibit a large surface area owing to the mesoporous characteristic of γ-Al2O3. After delithiation, the HMO/Al2O3 composite was applied to Li adsorption from seawater.
HMO/Al2O3 composites exhibited similar or even higher Li uptakes compared to HMO powder (ca. 9 mg Li/g HMO, Fig. 1) due to their highly expanded surface area and porous structure. Li adsorption on an HMO/Al2O3 composite is well fitted with the Langmuir isotherm model and exhibits excellent Li adsorption capacity of 15.1 mg/g (Fig. 2a). Moreover, in three consecutive Li adsorption-desorption processes, the Li uptake level of the HMO/Al2O3 composite did not decrease (Fig. 2b). This result demonstrates that the HMO/Al2O3 composite is a promising material for Li recovery from seawater due to its high Li adsorption performance and good stability.
Various ratios (1:4, 1:5, 1:9, 1:19, and 1:39) of lithium manganese oxide (LMO) to alumina gel were tested for the synthesis of HMO/Al2O3 composites. All of the LMO/Al2O3 composites exhibit a large surface area owing to the mesoporous characteristic of γ-Al2O3. By increasing the Al2O3 content in the composite, the surface area is expanded and a more porous structure is obtained, though the crystallinity of the spinel phase of LMO is decreased.
After delithiation, the HMO/Al2O3 composite was tested for its ability to adsorb Li from seawater. HMO/Al2O3 composites with various ratios (1:4, 1:5, and 1:9) exhibited similar or even higher Li uptakes than HMO powder (ca. 9 mg Li/g HMO) due to their highly expanded surface area and porous structure. During the recovery of Li adsorbed on HMO/Al2O3 composites by an acid treatment, more manganese (Mn) was dissolved from composites containing more Al2O3 due to the low crystallinity of the spinel HMO. Finally, it was found that a composite with a 1:4 ratio of HMO/Al2O3 exhibited less than 1% Mn dissolution, and its Li adsorption performance did not decrease over five Li adsorption–desorption cycles.
