Recovery of lithium from salt-brine eluates by direct crystallization as lithium sulfate

Brine from natural salt lakes (salt brine) is an important source of lithium; consequently the recovery of lithium from brine eluates prepared through Li⁺ adsorption-desorption is economically important. The present paper describes a study on the direct crystallization of Li₂SO₄·H₂O from synthetic and real salt-brine eluates.

Thermal evaporation of a sulfate-type synthetic eluate (1400 mM Li⁺, 61 mM Na⁺, 6.7 mM K⁺, 16.7 mM Mg^{2 +}, and 10.0 mM Mn^{2 +}), to a degree of concentration (D_con) in excess of 13, produced high purity (97%) Li₂SO₄·H₂O crystals in 54% yield. The addition of ethanol to the eluate resulted in an increased yield of Li₂SO₄·H₂O crystals, but these crystals were of lower purity due to the co-precipitation of other metal sulfates.

Two types of eluate were prepared by the batchwise adsorption of Li⁺ from brine followed by desorption with 2 M sulfuric acid. Evaporation of an eluate with a Li⁺ concentration of 1370 mM to a D_con of 8.6 at 323 K produced high-purity (97%) Li₂SO₄·H₂O crystals in 43% yield after the CaSO₄·2H₂O had been removed at a D_con of around 3. The evaporation of the eluate to dryness at 323 K followed by rinsing with water afforded Li₂SO₄·H₂O crystals in 83% yield and in 84% purity. This simple evaporation method can be applied to lithium extraction from salt lakes in arid areas.