Enhanced fluid-flow-field and electric-field synergistic interaction mechanism for lithium-ion separation in dilute solutions: A numerical analysis of electrochemically switched ion exchange system

Abstract

Electrochemically switched ion exchange (ESIX) is an effective technology for extracting high-value-added ions from dilute solutions. This study focuses on Li⁺ extraction by employing a comprehensive model to analyze interaction between fluidic dynamics, electric field and ion transport. The model combines Butler–Volmer equation modified by electroactive site concentration, Nernst–Planck equation and Navier–Stokes equation. It is found that the chamber width affects solution phase resistance, thereby altering the potential distribution and influencing the current distribution within the membrane. A narrow chamber increases current density in the solid phase of the membrane, enhancing Li⁺ extraction. The solution flow-field not only enhances convective transport but also increases the current density in the solid phase, promoting Li⁺ extraction. There is a synergistic effect between fluid-flow-field and electric-field for ion separation, which is only significant when the chamber width is greater than 2 mm. The synergistic mechanism differs from that in the capacitive deionization system. Therefore, the performance decline caused by a wide chamber can be compensated for by increasing the fluid-flow rate, utilizing the synergistic effect between the fluid-flow-field and electric-field to optimize the lithium extraction efficiency in the ESIX system.