Lithium extraction from high magnesium salt lake brine with an integrated membrane technology

Lithium extraction is a great challenge from the high magnesium content salt solution. In this work, an integrated polyamide tight ultrafiltration (UF) and nanofiltration (NF) membranes are systematically investigated to separate Li⁺ from a high magnesium salt solution. Tight ultrafiltration UA001 and nanofiltration NF270 membranes in the integrated-cascade system not only increased Li⁺ permeation to 82.5 % but also enhanced the high Mg²⁺ retention to 94.6 % from the ternary salt solution of LiCl and MgCl₂. The solution-diffusion transport model was also developed to calculate the real retention of Li⁺ and Mg²⁺, under constant pressure mode. The separation efficiency SF_Li/Mg for the ternary salt solution of LiCl + MgCl₂ + H₂O was more than 15 at a constant pressure of 25 bars with an integrated membrane process, which was higher as compared to single-stage UF and NF270 membranes. Moreover, the high Mg²⁺/Li⁺ ratio was also reduced from 30 to 1.9 in the integrated-cascade membrane process.