Enhanced Li⁺ Elution and Adsorption by Tannin-Modified Hydrophilic-H₂TiO₃ Titanium-Lithium Ion Sieve

Tannin-modified Li₂TiO₃ powders (TA-Li₂TiO₃) were prepared by a precipitation-peptization process with titanium sulfate as the titanium source, lithium acetate as the lithium source, ammonia as the precipitator, and hydrogen peroxide as the complexing agent. The effects of the tannin addition ratio and the calcination temperature on the crystal structure and surface morphology of TA-Li₂TiO₃ were studied. After pickling TA-Li₂TiO₃ with diluted hydrochloric acid, TA-H₂TiO₃ was obtained. Its elution behavior and lithium adsorption performance were studied and the adsorption isotherm and kinetics were investigated. The results indicated that the crystal structure was well-defined, and a uniform mesoporous surface morphology was observed on the sample surface with a calcination temperature of 750 °C and a tannin addition ratio of 1 g:1 L. The specific surface area was increased by 15.1 m²/g compared with the unmodified one, and the hydrophilicity of the TA-H₂TiO₃ significantly improved. After elution with 0.2 mol/L hydrochloric acid for 8 h, the elution equilibrium was achieved, the lithium elution ratio reached 98.15% and the lithium adsorption capacity reached 39.13 mg/g, which were significantly higher than that of the unmodified one. The adsorption isotherm is more consistent with the Langmuir model, the adsorption kinetics follows the pseudo second order model, and the adsorption mechanism is chemical monolayer adsorption.