Sustainable Electrochemical Extraction of Lithium from Natural Brine: Part II. Flow Reactor

An electrochemical flow reactor for the extraction of lithium chloride from natural brine has been designed and experimentally tested. The reactor comprises two three-dimen-sional porous packed bed electrodes and a porous separator immersed in electrolyte. The packed bed electrodes were filled with conducting petroleum coke particles covered respectively with LiMn ₂ O ₄ selective to lithium ion and polypyrrole selective to anions. The reactor operates in two steps: In the first step the porous electrodes and separator were filled with natural brine to extract lithium and chloride by intercalation and adsorption respectively. After rinsing with water, in the second step the reactor was filled with a dilute LiCl recovery solution and by reversing the electrical current LiCl is recovered in the electrolyte. A two dimensional mathematical model which describes the diffusion and migration of different ions in the electrolyte with the Nernst-Planck equation, the convective flow of electrolyte and the lithium ion intercalation in LiMn ₂ O ₄ has been developed using a finite element method under the COMSOL environment. The model captures the effect of forced convection on the efficiency of lithium extraction due to diffusion gradients in the porous LiMn ₂ O ₄ cathode and predicts the best operation parameters.