A fundamental study on selective extraction of Li+ with dibenzo-14-crown-4 ether: Toward new technology development for lithium recovery from brines

The present study has proposed a selective Li+ extraction process using a novel extractant of dibenzo-14-crown-4 ether functionalized with an alkyl C16 chain (DB14C4-C16) synthesized based on the ion imprinting technology (IIT). Theoretical analysis of the possible complexes formed by DB14C4-C16 with Li+ and the competing ions of Na+, K+, Ca2+ and Mg2+ was performed through density functional theory (DFT) modeling. The Gibbs free energy change of the complexes of metal ions with DB14C4-C16 and water molecules were calculated to be -125.81 and -166.01 kJ/mol for lithium, -55.73 and -117.77 kJ/mol for sodium, and -196.02 and -291.52 kJ/mol for magnesium, respectively. Furthermore, the solvent extraction experiments were carried out in both single Li+ and multi-ions containing solutions, and the results delivered a good selectivity of DB14C4-C16 towards Li+ over the competing ions, showing separation coefficients of 68.09 for Ca2+-Li+, 24.53 for K+-Li+, 16.32 for Na+-Li+, and 3.99 for Mg2+-Li+ under the optimal conditions. The experimental results are generally in agreement with the theoretical calculations.