A green and economical method for preparing lithium hydroxide from lithium phosphate

Low-concentration lithium solutions are often produced during the production and use of lithium, and precipitation via lithium phosphate is an effective recovery method of lithium. However, lithium phosphate has a limited application market, which should be further transformed. Currently, the existing for processing lithium phosphate requires a large amount of chemical reagents, and the recovery rate of lithium is not high. In this study, a bipolar membrane electrodialysis (BMED) process was developed to convert lithium phosphate into lithium hydroxide and phosphoric acid. To verify the feasibility of BMED in lithium phosphate conversion, effects of solubility, current density and concentration of phosphate on the separation performance were investigated. The results suggested that the recovery rate of lithium was as high as 99%. The high solubility of lithium phosphate in phosphoric acid resulted in the superior BMED performance. The current efficiency decreased with the increase in current density, while the energy consumption increased as current density elevated. Typically, the lowest energy consumption of 10.54 kWh·kg−1 was obtained at the current density of 20 mA·cm−2. Besides, a higher lithium phosphate concentration led to the superior BMED performance. The total process cost of BMED process was estimated to be $2.941·kg−1 LiOH under the optimal experimental conditions. Considering the price of lithium hydroxide, BMED is considered as a high-efficient, economical, and environmentally friendly technology for lithium phosphate treatment.