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 NH 4 Al 3 (SO 4 ) 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 NH 4 Al 3 (SO 4 ) 2 (OH) 6 and γ-AlOOH were synthesized hydrothermally using Al 2 (SO 4 ) 3 ·18H 2 O and Urea. The porous powder precursors were then lithiated in aqueous LiOH solution to give mixed porous powders of NH 4 Al 3 (SO 4 ) 2 (OH) 6 and Li-Al-LDHs of Li 2 Al 4 (OH) 12 SO 4 ·xH 2 O. Lithiated powder precursors were finally granulated by ionic crosslinking sodium alginate in CaCl 2 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.