Electrodialysis of LiH2PO4 for High-Purity LiOH and Green H2 Production

Abstract

The current soda-lime evaporation process to recover lithium carbonate from continental brines by treatment with Solvay has a low efficiency due to the high solubility of Li2CO3, unlike precipitation of Li3PO4 after removal of alkaline earth cations, which has a very high efficiency. The main goal of this work is to provide a proof of concept for replacing the present method of LiOH.H2O production, i.e. replacing the reaction of Li 2 CO 3 with Ca(OH)2, by a single step electrodialysis of LiH2PO4 from insoluble Li3PO4 with no waste generation, recycling of phosphoric acid, better efficiency than the lithium carbonate pathway and green hydrogen generation. Experimental results have been complemented with numerical simulation of the electro-dialysis system solving the time-dependent concentration and potential profiles for two configurations: two compartments using a cation-selective membrane and a three-compartment cell with cation and anion-selective membranes operating at constant current, along with the voltage evolution and current efficiency for LiOH production.