Selective Lithium Recovery from Seawater Using Crown Ether Resins

Seven kinds of crown ether resins embedded in high-porous silica beads, benzo-12-crown-4 (BC12), dibenzo-14-crown-4 (DBC14), benzo-15-crown-5 (BC15), benzo-18-crown-6 (BC18), dibenzo-18-crown-6 (DBC18), dibenzo-21-crown-7 (DBC21), and dibenzo-22-crown-6 (DBC22) resins, were synthesized successfully and the adsorption behavior of Li ion on these crown ether resins have been studied in seawater at room temperature. As a result, it was found that the ascending order of the distribution coefficients (Kd) values of Li ion using the seven crown ether resins are DBC14 < BC12 ≒ DBC21 ≒ DBC18 < DBC22 < BC18 ≤ BC15 and the BC15 resin has comparatively higher adsorption ability for Li ion. Hence, the adsorption behavior of Li ion using the BC15 resin has been examined in detail. It can be seen that the Kd values of Li ion with the BC15 resin increase sharply with increasing the pH 1.5 to 2.7 in seawater due to the dependence of H+ for the adsorption reaction. The Kd values of Li ion increased sharply with increasing the concentration factor (CF) of seawater in order of 0.10, 0.20, 0.33, 0.50, 1.0 while the Kd value of CF = 1.5 of seawater decreased certainly. The decrease is attributable to the adsorption reactions between the BC15 resin and the main cationic ions. The tendency indicates that the BC15 resin has wonderful selective adsorption ability for Li ion in the wide concentration range of seawater. In addition, we have examined the thermodynamics (Temp. = 278 - 333 K) of Li ion on the BC15 resin in seawater by using Van't Hoff equation. The results also imply that the equilibrium adsorption process between the BC15 resin and Li ion is found to be endothermic and the spontaneous reaction mechanism in nature. From these results, we have proposed that the BC15 resin is available for selective recovery of Li ion from various seawater in the wide temperature range.