Lithium Sulfate soluble in water at higher temperatures
Although lithium sulfate is not the usual solublizer for most salts, it does dissolve slowly with temperature. This is due to a property called retrograde solubility. It shares this property with some inorganic compounds, such as calcium hydroxide (portlandite), calcium sulfates (gypsum, bassanite and anhydrite) and lanthanoid sulfates.
The retrograde solubility of lithium sulfate can also be explained by the fact that it is an exothermic process when dissolved in water. This exothermic disassociation is similar to the way in which sodium sulfate is soluble in water.
Solubility in water of the evaporative crystallizer method
When lithium sulfate is added to an aqueous solution of sulfuric acid it begins to hydrate. The resulting crystallization of the lithium sulfate monohydrate is isolated by evaporation. The hydrated form of lithium sulfate is then heated to obtain anhydrous lithium sulfate.
Solubility of lithium sulfate in water at room temperature
Lithium sulfate is soluble in pure water, but becomes less so as the concentration of sulfate increases. This is because the entropy of the solution decreases as it approaches room temperature, and lithium sulfate hydrate is less likely to be able to maintain its entropy value in aqueous solutions at temperatures above about 60degC.
Solubility of the evaporative method
The evaporative method is used to concentrate lithium in lithium brines that contain less than 1.7% of lithium by weight at 35degC. This is a relatively simple process that uses solar evaporation. This method also allows for the extraction of magnesium sulfate from a brine with a low concentration of lithium.