Performance comparison of lithium fractionation from magnesium via continuous selective nanofiltration/electrodialysis

Abstract

Although selective nanofiltration (SNF) and selective electrodialysis (SED) have been widely adopted in the field of Mg2+/Li+ separation, their differences have not been illustrated systematically. In this study, for the first time, SNF and SED processes in continuous mode were studied for Li+ fractionation from the same brine with high Mg/Li ratios and their differences were discussed in detail. For a fair analysis of the two processes, typical factors were optimized. Specifically, the optimal operating pressure and feed flow rate for SNF were 2.4 MPa and 140 L·h−1, respectively, while the optimal cell-pair voltage and replenishment flow rate for SED were 1.0 V and 14 L·h−1, respectively. Although the Li+ fractionation capacity of the two processes were similar, the selectivity coefficient of SNF was 24.7% higher than that of SED and, thus, the Mg/Li ratio in purified stream of the former was 19.0% lower than that of the latter. Due to higher ion driving force, SED had clear advantages in recovery ratio and concentration effects. Meanwhile, the specific energy consumption of SED was 20.1% lower than that of SNF. This study provided a better understanding and guidance for the application and improvement of the two technologies.