Purification of brines by chemical precipitation and ion-exchange processes for obtaining battery-grade lithium compounds

Lithium salts are very important in the production of lithium batteries since they are used as precursors for the fabrication of cathode materials that require very low level of impurities (battery grade). Usually, the lithium extraction process from brine first yields lithium carbonate, which is then used as raw material for the production of other lithium compounds. However, it implies an increase in investment costs, considering more equipment and process stages. To remove the impurities and produce battery-grade lithium compounds directly from brines, a laboratory-scale process was developed using the methods of ion exchange and chemical precipitation. Thus, impurity-free brine ready to be used in an industrial membrane electrolysis process is obtained. Different sequences and operating conditions were investigated for the purification of lithium-concentrated brines, removing the main impurities of the natural brines: calcium, magnesium, and sulfate. For the characterization of solutions, crystals, and ion-exchange resins, atomic absorption spectrophotometry, scanning electron microscopy, and X-ray scattering spectroscopy were used. The results indicate that during the chemical precipitation process, lithium-concentrated brine reacted with some additives (precipitating agents) at different stages in the batch reactors. Subsequently, the pulp obtained was sedimented and filtered, eliminating or reducing the impurities of the lithium brine. Thus, the most efficient precipitation sequence was evaluated as a function of the removal percentage of the species. The removal efficiencies obtained for Ca+2, Mg+2, and SO4−2 were of 98.93%, 99.93%, and 97.14%, respectively. Thereafter, the use of the ion-exchange resins reduced the concentration of Ca+2 and Mg+2 to the values below 1 ppm. The combined use of both processes provided promising results that could be applied in the industry.