Efficiently separating Li+ and Mg2+ from brine and directly preparing Li3PO4 by a combination of electrochemical intercalation/deintercalation and MgNH4PO4 precipitation

The "aluminum adsorption + membrane" method is the mainstream technology for lithium extraction from salt lakes. However, the low adsorption capacity of aluminum adsorbent leads to massive freshwater consumption, which seriously limits its large-scale promotion in arid and water-scarce regions. Electrochemical intercalation/deintercalation (EID) method is a new technology for Li+ extraction with high adsorption capacity and good separation of Li+ and impurity ions. Based on this, a combined EID-MgNH4PO4 precipitation technique is proposed for Li+ extraction from brine and Li3PO4 preparation directly. Firstly, EID was used for high Mg/Li brine to obtain an anolyte with low Mg/Li; subsequently, Mg2+ was removed deeply from the anolyte by MgNH4PO4 precipitation; finally, Li3PO4 was prepared by adding phosphate. The results show that the Mg2+ concentration in the anolyte can be reduced to 3 ppm in the Mg2+ removal process, and the Li+ loss rate is less than 1.9 %. In addition, the overall recovery of Li+ exceeds 95 %, and the removal of Mg2+ is more than 99.8 % during the whole process. The combined EID-MgNH4PO4 precipitation technique proposed in this paper is expected to provide more references for developing lithium resources in arid and water-scarce salt lakes regions.