Capacitive deionization incorporating a fluidic MOF-CNT electrode for the high selective extraction of lithium

In this study, a novel ZIF-8/CNT flow-electrode material was synthesized to be adopted in a flow-electrode capacitive deionization (FCDI) process for high selective recovery of lithium. Based on the presence of the CNT additive and innate active sites of the ZIF-8, the composite material exhibited superior physico- and electrochemical characteristics as compared to the conventional activated carbon (AC). Specifically, the intrinsic system and charge transfer resistances of ZIF-8/CNT were 0.70 and 1.95 % those of AC, which confirmed its exceptional conductance. Moreover, the pore aperture of ZIF-8/CNT was identified to be highly analogous to the size of a hydrated lithium ion, which was principal in securing exceptional lithium selectivity. Likewise, the FCDI operation with the ZIF-8/CNT flow-electrode was observed for superior deionization performance at 2.3-fold that of AC for all target lithium, sodium, nickel, and manganese ions. Especially, lithium selectivity in relation to sodium, nickel and manganese ions was also confirmed, at an average of 6.8-fold that of AC. Conclusively, operation of a three-stage system for the simultaneous capture and recovery of lithium exhibited successful deionization of the target composite solution at a removal of 89.1 %, and subsequent extraction of lithium at a recovery of 76.4 % that of its initial concentration and in the form of lithium hydroxide.