Kinetics of Ion-Exchange Extraction of Lithium from Aqueous Solutions by Protonated Potassium Polytitanates

In this work, protonated forms of potassium polytitanate were obtained by treating the precursor in HCl solution at pH 2.0, 3.0, 4.0, 5.0, 6.0, or 7.0. The synthesized materials were studied using XRD, FTIR, and XRF. The ion-exchange properties were studied using a LiCl solution with a concentration of C(Li+) = 0.01 mol/L. It was shown that extraction of lithium by potassium polytitanates is dependent on their protonation degree. It has been established that the samples with the highest degree of protonation obtained at pH = 2.0 and 3.0 have the highest efficiency in the ion-exchange extraction of Li(+ )ions from an aqueous solution. For determination of exchange ion rates and the mechanism of the ion-exchange process, pseudo-first- and pseudo-second-order models as well as the Weber-Morris intraparticle diffusion model, were employed. Experimental data with their participation are in good agreement with the pseudo-second-order kinetic model. The calculated kinetic parameters were q(e) = 0.47-0.52 mmol/g and k(2) = 0.25-0.43, depending on the protonation degree of potassium polytitanate. The obtained experimental and calculated values of the sorption capacity were compared with the cation-exchange capacity of materials studied. According to the kinetics study, the mechanism of lithium adsorption by potassium polytitanates with a higher protonation degree is the ion-exchange chemical reaction. Low-cost protonated potassium polytitanates are promising to extract Li+ ions from aqueous solutions with a low concentration, as confirmed by the analysis of the results.