Gas–Liquid–Solid-Phase Equilibrium of the Quinary System (Li ⁺ , Na ⁺ // Cl – , HCO ₃ – –CO ₂ –H ₂ O) and Its Subsystems at p (CO ₂ ) = 0.3 MPa and 283.15 K

The explosive growth of new-energy industries and 5G/6G infrastructure has sent lithium demand soaring. Traditional lithium extraction relies on salt lake brine as the principal feedstock for lithium carbonate. However, the current lithium precipitation process requires a first-step acid neutralization of the alkaline brine, followed by an excess of sodium carbonate to force Li 2 CO 3 out of solution. This approach escalates acid/base consumption exponentially and simultaneously reduces the final product purity. The main brine components in the lithium precipitation mother liquor are Li +, Na +, Cl –, and CO 3 –2, with lithium accounting for approximately 20% of the total mass, which complicates its effective recovery and utilization. In this work, the phase diagrams of this quinary system (Li +, Na + // Cl –, HCO 3 – –CO 2 –H 2 O) and its subsystems at 283.15 K were established for the first time. It was found that a shift in the crystallization field occurred at p (CO 2 ) = 0.3 MPa upon purging CO 2 into the quinary system, leading to the formation of LiHCO 3 . Based on the solubility differences between lithium and sodium carbonates/bicarbonates at varying temperatures, a lithium-enriched mother liquor can be obtained while simultaneously recovering NaHCO 3 . Compared with the conventional route, this method significantly reduces acid and alkali consumption, lowers CO 2 emissions, and enables alkali recovery and recycling.