Separation of Lithium over Magnesium, Sodium, and Calcium By Electrodialysis Using Commercial Membranes
Authors: Botelho Junior Amilton Barbosa , Abels Kristen , Chen Xi , Espinosa Denise Crocce Romano , Tarpeh William Abraham 
Published: August 2024

Lithium is considered a critical raw material worldwide due to the growing market for electric vehicles. Due to the risk of supply interruption in the short and medium term, alternative sources of lithium are being explored for battery supply. Among these, salt-lake brines have become a key supply because their abundance represents about 59% of lithium resources 1. A secondary source in the medium term is the recycling of spent Li-ion batteries by hydrometallurgical processes 2,3. Together, recovering lithium from brine and recycling can supply the demand for transport electrification. Conventional lithium extraction techniques from both brine and battery recycling face the challenge of selective separation over contaminants and low extraction efficiencies 4,5.
As an alternative, electrodialysis (ED) is an important selective separation technique with high selectivity, productivity, and less consumption of chemical reagents under energy consumption. This electrochemical membrane separation process uses an electric field inducing anion and cation transport across alternating anion and cation exchange membranes. While standard electrodialysis can be used to desalinate water and generate more concentrated brine), selective electrodialysis processes that up-concentrate a specific ion from a mixed salt solution are less developed. Our goal with this work is to evaluate the effect of common ions on lithium separation by ED using three different commercial membranes. The experiments were carried out in a 4-chamber reactor where the feed solutions consisted of equimolar chloride salts of lithium and either nickel (representing battery recycling), magnesium, sodium, or calcium (representing brine). Anolyte, receiving, and catholyte chambers (Figure 1) contained 1.0 M H2SO4.
Here, we present the results in terms of cation permselectivity, productivity, and energy consumption using three different commercial membranes for the cation exchange membrane in the ED setup: a standard cation exchange membrane (CXM-200), a monovalent cation exchange membrane (CXP-S) and a nanofiltration membrane (NF-90). The performance of each membrane was tested under varying applied current densities to assess the impact of operating conditions on ion transport. Results have demonstrated monovalent cationic membranes are strongly selective for lithium over magnesium and nickel, achieving selectivity of 43 and 57, respectively. The increase in current density from 2.8mA/cm² to 11.5mA/cm² also increased the fluxes of lithium and co-ions by the monovalent membrane, consequently decreasing the selectivity from 56.7 to 2.4. In addition, nickel precipitates in the feed chamber as the current density increases from 2.8mA/cm² to 5.7mA/cm². We then translate these results into a process model for upscaling the ED reactor, considering the species transport rate through the reactor chambers and selectivity for lithium.

Keywords: battery recycling; brine; electrochemical membrane separation; critical raw materials.
Figure 1: ED reactor used for lithium selective separation by commercial membranes

References

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Figure 1