Continuous ion separation via electrokinetic-driven ion migration path differentiation: practical application to lithium extraction from brines

Abstract

The effective separation of Mg²⁺ from Li⁺ is the key for realizing efficient and economic lithium extraction from brine, but remains challenging due to their similar chemical properties. Recent approaches have enabled simultaneous magnesium removal and lithium extraction from high Mg²⁺/Li⁺ ratio brines, but their reliance on physical or chemical filters has led to inconsistent performance dependent on brine conditions and corresponding limitations in their cost-effectiveness and scalability. Despite Mg²⁺'s and Li⁺'s kindred properties, a subtle difference in their electrophoretic mobilities has allowed for the development of the herein proposed new ion separation method for continuous lithium extraction from high Mg²⁺/Li⁺ ratio brines utilizing electrokinetic manipulation of ion migrations. This is the first experimental demonstration of a filterless and force-based ion separation method that works by steering ions onto different paths simply by balancing the diagonally formed electric field intensity and flow rate, and realized by introducing a highly scalable electrokinetic system equipped with a multiscale-porous anion exchange membrane. The effects of core operating parameters as well as brine conditions on system performance are elaborated through experimental studies. Remarkably, consistent performance can be achieved in this system regardless of brine conditions by virtue of the filterless lithium extraction mechanism. This work offers a novel strategy to precisely modulate ion migrations in an aqueous solution and furthers progress toward both active ion manipulation and practical and economic lithium mining from different types of lithium-containing brines.