Process for recovering lithium from salt brines

A process for recovering lithium sulfate monohydrate from a chloride and sulfate-containing complex feed brine comprising:

• (a) chilling said complex feed brine in a first stage down to about 10.degree. C. but no lower than about 4.degree. C. to precipitate potassium chloride which is recovered from said brine;
• (b) further chilling said potassium chloride-reduced chilled brine recovered from step (a) in a second stage in the presence of added water, to about 0.degree. C. to precipitate Epsom salt which is recovered from the brine;
• (c) evaporatively concentrating said chilled brine recovered from step (b) until the lithium content of the brine is at least about 90% by weight of the lithium saturation concentration of said brine;
• (d) recycling a portion of said evaporatively concentrated, chilled brine for mixing with said complex feed brine to yield a potassium to lithium mol ratio in said evaporatively concentrated chilled brine below about 0.35;
• (e) chilling a major amount of said evaporatively concentrated brine in a third stage down to about 0.degree. C. to precipitate carnallite;
• (f) evaporatively concentrating said chilled brine recovered from step (e) to remove water from said brine with substantially no precipitation of solid salts therefrom;
• (g) adding a sufficient amount of magnesium sulfate to the brine produced in step (f) to yield a brine slurry having a sulfate to lithium mol ratio of at least about 0.9, and a water content of less than about 60% by weight and thereby precipitating the lithium sulfate monohydrate;
• (h) recovering the lithium sulfate monohydrate from said brine slurry.