Preparation of lithium carbonate from waste lithium solution through precipitation and wet conversion methods

The recovery of lithium compounds from various Li resources is attracting attention due to the increased demand in the Li-ion battery (LIB) industry. This study aimed to secure lithium carbonate (Li2CO3) using the waste Li solution generated from the cathode manufacturing process. The effects of initial Li+ concentration, solution pH, and applied phosphate compounds were examined on converting Li-ion into lithium phosphate (Li3PO4) by a precipitation method. Li2CO3 was then obtained from Li3PO4 by reflux and subsequent carbonation methods, in which a concentrated Li solution was produced from Li3PO4 by reaction with metal chloride solutions. Among the tested metal chlorides (AlCl3, MgCl2, and CaCl2), CaCl2 showed the best performance to produce a concentrated Li solution. The highest conversion efficiency (97%) from Li3PO4 to Li solution was observed at 80 °C, and the highest Li concentration (55,900 mg/L) was obtained at a solid(g)/liquid(L) ratio of 500 by reflux reaction. High purity Li2CO3 was produced from the obtained Li solution by purification using sodium hydroxide, and its carbonation using sodium carbonate in turn. The proposed method shows an alternative way to secure Li2CO3 from waste Li solution, in which no acid leaching of Li3PO4 is required to prepare concentrated Li solution to be used Li2CO3 production.