Abstract: Smelts produced in spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the loss of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided as such in a soda mill, or first is separated from sodium sulphide, by fractionating the smelt where sodium sulphide is present, as in the Kraft mill. The solid mixture is leached at a high temperature to remove all the sodium chloride values therefrom, along with part of the sodium carbonate and sodium sulphate. Pure sodium chloride is deposited by cooling the leach liquor and the mother liquor is recycled to the leaching step.

Abstract: Smelts produced in Kraft mill and soda mill spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the removal of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided in the case of the soda mill, or first is separated from the sodium sulphide in the case of the Kraft mill. Thereafter, the solid mixture is leached to remove the sodium carbonate and sodium sulphate while leaving the sodium chloride in a substantially pure form, the resulting leach liquor being refrigerated to deposit sodium carbonate and sodium sulphate. The mother liquor, after removal of the deposited salts is recycled to the solid mixture leaching step.