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A method of obtaining caustic soda and pure sodium chloride from an electrolytic cell liquor containing also sulfate ions including the steps of concentrating the liquor through multiple effect evaporation, cooling the concentrate obtained, separating the sodium chloride and the salt containing sulfate and recovering the caustic soda, whereby during a first stage the liquor is evaporated so as to precipitate only sodium chloride which is removed, in a second stage a solid phase is formed of sodium chloride, sodium sulfate and triple salt of caustic soda, sodium chloride and sodium sulfate, with said solid phase being contacted with a caustic soda solution of less than about 35% by weight concentration, so as to decompose said triple salt, removing the salt containing sulfate, and in a third stage the solution from the second stage is cooled to precipitate said triple salt of caustic soda, sodium chloride and sodium sulfate, which is separated from the caustic soda which does not crystallize and is removed from the system, and the resulting solid phase which remains is collected and is recycled into the initial electrolytic cell liquor.

1. concentrationof concentrating the liquor
2. customthrough multiple effect evaporation
3. temperaturecooling the concentrate
4. customobtained
5. customseparating the sodium chloride
6. additionthe salt containing sulfate
7. customrecovering the caustic soda, whereby during a first stage the liquor
8. customis evaporated so as
9. customto precipitate only sodium chloride which
10. customis removed, in a second stage a solid phase