KOREA INSTITUTE OF GEOSCIENCE AND MINERAL RESOURCES
THE WORLD'S LEADING RESEARCH
INSTITUTE OF GEOSCIENCE
HIGHLY POROUS AND SURFACE-EXPANDED SPINEL HYDROGEN MANGANESE OXIDE (HMO)/Al2O3COMPOSITE FOR EFFECTIVE LITHIUM (Li) RECOVERY FROM SEAWATER
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.
Fig. 1. Schematic illustration and Li uptake of a HMO/Al2O3 composite in Li spiked (30 ppm) seawater.
Fig. 2. (a) Li adsorption isotherm of a HMO/Al2O3 composite in seawater, and (b) Li uptake of HMO/Al2O3 composite in an experiment involving three reuse trials.