Modelling and optimization of Li+ extraction from brine with high Mg/Li ratio by electrochemically switched ion exchange considering thermodynamics and dynamics simultaneously

Abstract

Electrochemically switched ion exchange (ESIX) technology has been proven to be an efficient and environmental-friendly method for extracting Li+ from brine lakes. To deeply understand and mathematically express the underlying physical process of Li+ extraction in ESIX, a model is developed to describe Li+ extraction from brine lakes with a high Mg/Li mass ratio (500:1) by ESIX with an electrode coated with λ-MnO2 film. The kinetics and thermodynamics of the Li+ extraction process is considered simultaneously by coupling the Frumkin-Bulter-Volmer theory modified by electroactive site concentration with a modified Gouy-Chapman-Stern model. The local sensitivity analysis indicates that the performance of ESIX in Li+ adsorption is greatly influenced by cell voltage, film mass, and Stern capacitance of carbon black film, whereas these parameters have little effect on Mg2+ adsorption. The individual parameter analysis elucidates that the mass and Stern capacitance of carbon black film can regulate the potential drop distributions in different regions of ESIX system, resulting in a maximum Li+ extraction efficiency of 90.22 % due to the increased driving force in the faradic reaction and reduced charge transfer resistance. The optimization of combined parameters indicates that the optimum operation can be achieved at the conditions with a cell voltage ranging between 1.0 and 1.2 V, a Stern layer capacitance with electric double layer volume for carbon black film of 5.4 × 107 F/L, and an initial Li+ content of the treatment solution: carbon black film: λ-MnO2 film mass ratio of 0.1 kg: 9 kg: 8 kg.