(544e) MnO2 Ion-Sieve for Lithium Adsorption From Aqueous Resources

Lithium resource exists naturally in stable minerals as spodumene or salts in brine, seawater or river. In this paper, a new method for lithium extraction from such aqueous resources with no risk to the environment has been discussed, and the key adsorbent of λ-MnO₂ has been proposed. Various polymorphs of MnO₂ were synthesized under a controlled soft chemical method, followed by wet impregnation of LiOH?H₂O solution into the as-synthesized MnO₂ to form cubic LiMn₂O₄ precursors and the acid treatment process to extract lithium ions from the Li-Mn-O lattice completely to transform the ternary LiMn₂O₄ oxide to the final λ-MnO₂ ion-sieves with specific selectivity and adsorption capacity for lithium ions from solutions. The structure characteristic and the exchangeability of lithium-ion were studied by XRD, pH titration, lithium ion adsorptive isotherm and kinetic measurement. Adsorption isotherm of SMO-b and SMO-d ion-sieves are well accorded with Freundlich equation, with the adsorption constant of n=9.03, K_f=4.54, and n=6.51, K_f=5.35, respectively. The first order adsorption rate constant is 7.53×10^-6 and 5.83×10^-6 s^-1, respectively, indicating a rather slow adsorption rate, limited by the current static experimental conditions. The ion-exchange capacity reaches 3.47 mmol/g for lithium ions and only 0.37 mmol/g for sodium ions by pH titration, indicating that this kind of material is promising in lithium extraction from natural aqueous resources with very low lithium content, including brine, seawater or river.