Convenient synthesis of granulated Li/Al-layered double hydroxides/chitosan composite adsorbents for lithium extraction from simulated brine with a high Mg2+/Li+ ratio

Abstract

Lithium/aluminum layered double hydroxides (LDH) have been industrially applied to extract lithium from salt-lake brine. Different from traditional granulation methods, chitosan with high hydrophilicity was used as the binder of LDH in this work, and LDH/chitosan composite hydrogel granules (CLDH) with a diameter of about 1–2 mm were successfully prepared. The new granulation method is simple, cost-effective, and does not require the use of organic solvents. The chemical composition and structure of CLDH were characterized by techniques such as FTIR, XRD, FESEM, TEM, TGA, and XPS. In simulated brine with a Mg²⁺/Li⁺ ratio of 102, the maximum saturated adsorption capacity of lithium on CLDH-3 reached 12.5 mg g⁻¹ (pH = 6.5), but it took 24 h to reach adsorption equilibrium. During the three successive cycles for the extraction of Li⁺ from simulated brine by the CLDH-3 column at the flow rate of 1 mL min⁻¹, the adsorption capacities of Li⁺ on CLDH-3 in the three cycles were 15.4, 15.9 and 12.1 mg g⁻¹, respectively. Moreover, deionized water (30 °C) was used as the eluent to recover lithium adsorbed on the CLDH-3 column, and the lithium recovery efficiencies reached 50.7 %, 53.6 %, and 62.8 % of the column adsorption capacities over the three cycles, respectively, and the Mg/Li ratios in the eluents were 0.47, 0.71, and 0.50, respectively. Overall, CLDH-3 exhibits good reusability, mechanical strength, structural stability, and selectivity in the process of lithium extraction from simulated salt-lake brine, and has potential industrial application value.