Extraction of lithium from salt lake brines by granulated adsorbents

Hierarchical meso- and macro-porosity increases the adsorption capacity of lithium adsorbents and the granulation of powder lithium adsorbents raises the applicability of lithium adsorbents. Granulated lithium adsorbents consisting of porous mixtures of Li-Al-LDHs (layered double hydroxide) and NH4Al3(SO4)2(OH)6 by crosslinking sodium alginate were successfully prepared, and adsorption-desorption performance of granulated adsorbents was evaluated. The adsorption capacity of granulated lithium adsorbents reached 9.66 mg/g (at the loading capacity of 83.3% by mass, 25 ℃, and pH=6). The granulated lithium adsorbents were prepared in three steps. First, porous precursors of NH4Al3(SO4)2(OH)6 and γ-AlOOH were synthesized hydrothermally using Al2(SO4)3·18H2O and Urea. The porous powder precursors were then lithiated in aqueous LiOH solution to give mixed porous powders of NH4Al3(SO4)2(OH)6 and Li-Al-LDHs of Li2Al4(OH)12SO4·xH2O. Lithiated powder precursors were finally granulated by ionic crosslinking sodium alginate in CaCl2 aqueous solutions and deintercalated using water. The precursors and lithiated precursors were characterized by IR spectroscopy, powder XRD, XPS spectroscopy, SEM, TEM, thermal analyses, particle size analysis, and BET surface area. The adsorption isotherm, adsorption kinetics, the effects of pH, temperature, initial lithium concentration, and the anions and cations interference on lithium adsorption-desorption performance of granulated lithium adsorbents were studied. The adsorption isotherm and adsorption kinetics were best fitted with the Langmuir model and pseudo-second-order rate equation, respectively. Lithium adsorption was an endothermic process. The granulated lithium adsorbents were applied to real East Taigener salt lake brine. The lithium adsorption capacity dropped slightly to 9.16 mg/g; the adsorption equilibrium reached within 180 min; the dissolution rate was 0.54% after 10 cycles of adsorption and desorption. The granulated lithium adsorbents prepared show the potential in industrial application.