Abstract:

Global lithium production has grown exponentially, rising from less than 200 kt LCE (lithium carbonate equivalent) in 2015 to an estimated 1.3 Mt LCE by 2025. This rapid expansion has amplified concerns over sodium sulphate disposal, a major by-product of battery-grade lithium carbonate production. Lithium carbonate, a critical precursor for Li-ion cathode materials, generates approximately 2 tonnes of sodium sulphate (dry basis) per tonne of LCE processed, primarily in spent carbonation liquors. Conventional evaporative crystallization precipitates sodium sulphate as Glauber’s salt (Na₂SO₄·10H₂O) at low temperatures (0 – 5 °C). However, producing the more compact anhydrous phase (Na₂SO₄) requires temperatures above 32 °C, where solubility exceeds 30 g/100 g H₂O. These conditions impose high energy demands and necessitate large evaporation areas, limiting scalability and economic viability.

To overcome these limitations, this study introduces a novel antisolvent crystallization approach employing methanol to drastically reduce sodium sulphate solubility, inducing supersaturation and crystallization under ambient conditions. Prior decarbonation of spent lithium carbonation liquor is essential to minimize lithium co-precipitation. Laboratory experiments at 25 °C with a methanol-to-water mass ratio of 0.5 achieved 78.6% sulphate removal from a simulated liquor containing 0.75 M Na₂SO₄ (~100 g/L), 0.1 M Na₂CO₃ (~10 g/L), and 0.1 M Li₂SO₄ (~10 g/L), with lithium loss as low as 1.14%. Crystallization occurred rapidly without the need for elevated temperatures or extensive evaporation. Furthermore, methanol can be efficiently recovered and recycled through distillation, reducing solvent costs and environmental impact. The process can be integrated into existing lithium carbonate plants with minimal retrofitting, leveraging current liquor handling systems and solvent recovery infrastructure.

Compared to conventional evaporative crystallization, the proposed antisolvent method offers lower temperature operation, reduced energy consumption, and accelerated crystallization kinetics, presenting a scalable and cost-effective alternative for sodium sulphate management in lithium carbonate production. This approach not only mitigates environmental challenges associated with sodium sulphate disposal but also enhances process efficiency, supporting sustainable growth in the lithium supply chain.

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Dr. Terry Cheng