DiaNanofiltration-based process for effective separation of Li+ from the high Mg2+/Li+ ratio aqueous solution

Lithium separation from salt lake brines with a high concentration of magnesium is challenging. In this work, separation efficiencies for Li+ and Mg2+ with three commercial NF membranes (NF-270, Desal-5DL, and Desal-5DK) were systematically investigated by DiaNanofiltration method. Experimental results showed that DiaNanofiltration was an effective technique to separate Li+ and reduce the high Mg2+/Li+ ratio from ternary salt solutions of LiCl and MgCl2. The solution-diffusion transport model was also used to calculate the real retention of Li+ and Mg2+, which predicted good agreement with the experimental results of the diafiltration process based on steric hindrance and the Donnan exclusion mechanism. NF270 membrane exhibited high permeation to Li+, about 90% for the ternary solution of LiCl + MgCl2 + H2O at a flux of 21.33 L.m(-2).h(-1). The real Mg2+ retention was attained around 96% with DK membrane, which was higher as compared to NF270 due to the steric hindrance effect. Moreover, the Mg2+/Li+ ratio was also reduced from 30 to 1.7 in the single-stage DiaNanofiltration process.