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.