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.