Granulation of Li1.33Mn1.67O4 (LMO) through the use of cross-linked chitosan for the effective recovery of Li+ from seawater

Spinel-structured lithium manganese oxides (LMOs) are the most effective material for the recovery of Li⁺ from seawater. LMO is granulated using chitosan as a binding material in this study. Prepared chitosan LMO granule is meso-porous material of which the pore size is 6.5-30.0 nm. In chitosan LMO granule, 19.4 wt% of chitosan is included in.

Extraction of the Li⁺ from chitosan LMO granule is carried with 0.2 M sulfuric acid. X-ray diffraction (XRD) analysis confirmed that topotactical extraction of Li⁺ ion and 93% of Li⁺ extraction efficiency is obtained. After sulfuric acid treatment, Fourier transformation infrared spectrum (FTIR) of chitosan LMO granule peaks at 1650 and 1000-1400 cm^-1 which represent NH₃- and C-N functional groups of chitosan are significantly changed suggesting that chitosan in granule is cross-linked by reacting with SO₄^2- ion in sulfuric acid. Cross-linking of chitosan causes increase of surface area from 2.37 to 14.58 g m^-2. Also stability of chitosan LMO granule is improved from 88% to 100%.

After Li⁺ extraction, LMO converts to hydrogen manganese oxide (HMO). Pseudo-second order kinetic model reveals that adsorption of Li⁺ onto chitosan HMO granule required more time than HMO powder because the diffusion of seawater into the chitosan binder occurred slowly. HMO powder and chitosan HMO granule exhibit similar (≈10 mg g^-1) Li⁺ adsorption capacity when concentration of Li⁺ is 30 mg L^-1. Because chitosan is water permeable polymer, Li⁺ adsorption capacity of HMO powder is not affected after granulation.