Preparation of Cubic MnO2⋅0.5H2O Lithium Ion Sieve Particles with Urea-assisted Hydrothermal Method and Their Adsorption Properties

Spinel type manganese oxide MnO₂⋅0.5H₂O (H_1.6Mn_1.6O₄) is considered one of the most promising precursors for lithium-ion sieves due to its high theoretical lithium adsorption capacity (72.3 mg/g), and is suitable for selectively extracting lithium from high magnesium lithium ratio brine. In this paper, the powdery lithium-ion sieve precursor Li_1.6Mn_1.6O₄ was prepared by two-step urea-assisted hydrothermal method combining with solid phase method, and the effects of urea/Mn ratios on the adsorption performance of lithium-ion sieves were explored. The results show that as the ratio of urea to Mn increases to 40, the particles tend to acquire a cubic morphology. Moreover, desorption of lithium during the acid leaching of the precursor becomes more favorable. The lithium-ion sieve pellets were prepared by the anti-solvent precipitation method. According to the calculated selectivity coefficient, the separation order by the pellets in the mixed solution is Li⁺ \( \gg \) Na⁺ > Mg²⁺ > Ca²⁺, demonstrating the lithium-ion sieve has a high selectivity to lithium. The adsorption kinetics of lithium-ion sieve pellets in a solution containing lithium illustrates a chemical adsorption mode.