Selective Lithium Extraction and Brine Crystallization Using Electrochemical Separation: Mechanisms and Process Design

Abstract

Electrochemical separation has emerged as a promising strategy for lithium extraction, resource recovery, and hypersaline brine management. However, its performance is governed by coupled thermodynamic, kinetic, transport, and process-level effects that remain insufficiently understood. This dissertation develops a mechanistic and process-design framework for electrochemical separation, focusing on selective lithium extraction and downstream brine crystallization. First, this dissertation investigates the thermodynamic, kinetic, and transport origins of Li/Na selectivity in intercalation-based electrochemical lithium extraction. A multiscale model coupling Frumkin thermodynamics, Butler–Volmer kinetics, porous-electrode ion transport, and solid-state diffusion is developed to evaluate how solution composition, current density, electrode architecture, and flow configuration influence selectivity. The results show that Li/Na selectivity is not solely an intrinsic material property, but an emergent outcome of coupled equilibrium preference and non-equilibrium transport limitation. Second, this dissertation develops a framework for reliable performance evaluation in electrochemical lithium separation. It compares feed-based and receiving solution-based selectivity measurements, showing that feed-based selectivity can suffer from severe error amplification when competing-ion transfer is small. The analysis further shows that electrolyte retained in electrode macropores can introduce nonselective Na and Mg inventories into the recovered product stream, lowering apparent Li purity and motivating rinse strategies for impurity removal and product quality improvement. Finally, this dissertation extends electrochemical separation to downstream brine management through electro-dialytic crystallization (EDC). A transport-based framework is established to describe the competition between salt transport and parasitic water transport, identifying a crystallizability criterion based on the ratio of salt flux to water flux. The results demonstrate that EDC can enable non-evaporative brine crystallization and provide an energy-efficient pathway toward zero liquid discharge (ZLD). Overall, this dissertation connects intrinsic ion selectivity, apparent product purity, and brine crystallization, providing design principles for sustainable electrochemical resource recovery and brine management.