Membrane electrolysis for the removal of Na+ from brines for the subsequent recovery of lithium salts

Abstract

Lithium-rich continental brines are highly saline solutions with total dissolved solids in the order 300 g L−1 , but Li+ concentrations around 1% only. A drastic increase in the ratio of Li+ to other cations’ concentration is a must for an efficient lithium recovery. Here we present results on the use of membrane electrolysis coupled to crystallization as a new methodology to separate a large share of Na+ present in a real brine sample. In a 3- compartment reactor, cations selectively migrate from the middle compartment through a cation exchange membrane to the cathodic compartment, where water electrolysis produces alkalinisation, and through CO2 spurging sodium bicarbonate precipitation is triggered. By following the real time concentrations in middle and cathodic compartments, we were able to prove the proposed methodology, and recover a solid with a purity of 99.5%. A coulombic efficiency of (95 ± 5)% was calculated, and the separation coefficients showed a preferential migration in the order K+ > Na+ > Li+. The methodology produces fresh water as a by-product, with total salinity 2 orders of magnitude lower than the feed. 3 different applied current density values were tested. At 10 A m−2 , 331.3 kWh are needed to treat 1 m3 of brine.