An integrated membrane process for preparation of lithium hydroxide from high Mg/Li ratio salt lake brine

Preparation of lithium hydroxide from high Mg/Li ratio salt lake brine is facing several challenges: separate lithium and magnesium, enrich the lithium, and produce lithium hydroxide with high purity. In this study, an integrated membrane process, combining BMED with NF, RO, and CED processes, was used to prepare LiOH from salt lake brine with the Mg/Li ratio higher than 30.0. The effects of operating pressure, pH of feed solution, and dilution multiple of feed solution on the separation and recovery efficiency of lithium were investigated. A dual-stage NF process and a RO-CED process were proved to be the effective way to remove magnesium and enrich lithium respectively, as the Mg/Li ratio can be controlled lower than 0.5 and the lithium concentration was concentrated above 14 g/L. In BMED process, the initial concentration of feed solution and current density were optimized, and the relationships between the concentration of acid/base and current efficiency were found. The results indicated that the lithium concentration of alkali solution prepared through this process was over 1.0 M, and the current efficiency and energy consumption were 36.05% and 6.20 kWh/kg, which outperformed previous works. The process was effective for preparation of LiOH from salt lake brine.