Integrated Process for Selective Purification and Production of High-Purity Lithium Carbonate from Aral Sea Brine

The brine of the Aral Sea is considered a complex source of lithium because it contains large amounts of magnesium, potassium, sulfate, and chloride, which prevent the direct preparation of Li2CO3. This work describes a technique based on selective precipitation and crystallization of impurities, followed by the isolation of high-purity Li2CO3. Initially, magnesium and potassium were precipitated together with Na2HPO4 as MgKPO4, and sulfate was precipitated as CaSO4·2H2O using CaCl2. Such pretreatment made it possible to remove up to 97.1%, 96.3% and 93.4% of magnesium, potassium and sulfate, respectively. Analysis by XRD and EDAX showed that the obtained precipitates consisted of gypsum and phosphate, which can be used as mineral or fertilizer by-products. Then the purified solution was treated with Na2CO3 in a stirred crystallizer at 50 °C. Focused Beam Reflectance Measurement (FBRM) analysis showed that increasing the stirring speed from 400 to 600 rpm resulted in smaller Li2CO3 particles. The influence of Na2CO3 feed rate was less, but the aggregation of crystals increased at higher concentrations of Na2CO3. The proposed technology made it possible to obtain 99.5% pure Li2CO3 (for the production of lithium-ion batteries). It was shown that the separation of impurities allows controlling the formation and growth of Li2CO3 from natural brine. The developed method provides the opportunity to prepare lithium carbonate suitable for batteries from Aral Sea brine with separation of useful by-products containing magnesium, potassium, calcium, phosphorus and sulfur.