Electrodialysis of LiH 2 PO 4 for High-Purity LiOH and Green H 2 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 Li 2 CO 3 , unlike precipitation of Li 3 PO 4 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.H 2 O production, i.e. replacing the reaction of Li 2 CO 3 with Ca(OH) 2 , by a single step electrodialysis of LiH 2 PO 4 from insoluble Li 3 PO 4 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.