Process for selective removal of sodium sulfate from an aqueous slurry

• US 4,246,241 A
• Filed: 07/16/1979
• Issued: 01/20/1981
• Est. Priority Date: 03/26/1979
• Status: Expired due to Term

• Current Assignee: Dow Chemical of Canada Limited (Dow, Inc.)
• Original Assignee: Dow Chemical Canada Incorporated (Dow, Inc.)
• Inventors: Mathur, Indresh, Knight, Allan R., Bristow (nee Elley), Dale M.
• Primary Examiner(s): Prescott, Arthur C.
• Application Number:
  US06/057,916
• Time in Patent Office: 554 Days
• Field of Search: 210/21, 210/22, 422/902, 422/255, 422/256, 422/261, 204/128, 423/179, 423/208
• US Class Current: 423/179
• CPC Class Codes: C01D 3/14 Purification
• CPC Class Codes: C25B 15/08 Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Abstract

A process for selectively removing sodium sulfate and sodium hydroxide from an aqueous slurry containing sodium chloride, sodium sulfate and sodium hydroxide, which comprises contacting the slurry in a countercurrent wash step with cool water to remove sodium sulfate and sodium hydroxide therefrom.

Claims

1. A process for separating sodium hydroxide and sodium sulfate from a slurry containing the same in admixture with sodium chloride in particulate form, which comprises feeding the slurry into a wash column in such a manner that it moves downwardly through the wash column, introducing a stream of wash water into the wash column so that it moves upwardly through the column in countercurrent relationship with said slurry, and removing wash water from the column at a position sufficiently upward from the point of introduction of the wash water that a major portion of the sodium hydroxide and sodium sulfate from said slurry are removed therewith.

2. A process as defined in claim 1 wherein the wash water is introduced at a temperature of about 80°

F. or below.

3. A process as defined in claim 1 wherein the wash water is introduced at a temperature of about 60°

F. or below.

4. A process for separating sodium hydroxide and sodium sulfate from a slurry containing the same in admixture with sodium chloride in particulate form, which comprises feeding said slurry into the upper portion of a wash column in such a manner that the slurry moves downwardly through the wash column, introducing a stream of wash water into the lower portion of the wash column in such a manner that the wash water moves upwardly through the column in countercurrent relationship to the said slurry, removing overflow fluid from the wash column at or near the top of the wash column, said overflow fluid carrying with it most of the sodium hydroxide and sodium sulfate from said slurry, and recovering the purified sodium chloride in the underflow from the lower portion of the wash column.

5. A process for selectively removing sodium hydroxide and sodium sulfate from an aqueous slurry containing the same along with sodium chloride in particulate form, which comprises washing said slurry in a countercurrent contact stage with cool wash water at a temperature below about 100°

F., removing the wash water from said slurry and with it a major portion of the sodium sulfate and sodium hydroxide present in this slurry, and collecting in the underflow from said washing stage the purified sodium chloride.

6. A process as defined in claim 5 wherein the wash water is introduced at a temperature of about 60°

F. or below.

7. A process for removing sodium hydroxide and sodium sulfate from a slurry containing 20 to 45% by weight sodium chloride, 2 to 7% by weight sodium sulfate and 4 to 16% by weight of sodium hydroxide, the settled volume of the slurry being within the range of 15 to 30%, which comprises feeding said slurry into the upper portion of a wash column in such a manner that the slurry moves downwardly through the wash column, sparging a stream of wash water at a temperature below about 100°

F. into the lower portion of the wash column in such a manner that the wash water moves upwardly through the column in countercurrent relationship to said slurry, removing overflow fluid at or near the top of the wash column, said overflow fluid carrying with it a major portion of the sodium hydroxide and sodium sulfate contained in said slurry, and recovering the purified sodium chloride in the underflow from the lower portion of the wash column.

8. A process as defined in claim 7 wherein the wash water is sparged into the wash column at a temperature of about 80°

F. or below.

9. A process as defined in claim 8 wherein the overflow is removed from the wash column at a rate at least equal to the rate at which the slurry is fed into the wash column.

10. A process for removing a major portion of the sodium sulfate and sodium hydroxide from a slurry containing 20 to 35% sodium chloride, 2 to 7% sodium sulfate and 4 to 16% sodium hydroxide, the settled volume of the slurry being in the range of 15 to 30%, which comprises feeding the slurry into a wash column in such a manner that it moves downwardly through the wash column, introducing a stream of wash water into the column so that it moves upwardly through the column in countercurrent relationship with said slurry, and removing overflow fluid from the wash column at or near the top of the wash column, said overflow fluid carrying with it a major portion of the sodium hydroxide and sodium sulfate contained in said slurry.

11. A process for selectively removing sodium hydroxide and sodium sulfate from admixture with sodium chloride, which comprises making an aqueous slurry of such mixture, contacting the slurry in a countercurrent relationship with cool wash water, and removing the wash water from the slurry and with it a major portion of the sodium hydroxide and sodium sulfate contained in the slurry.

12. In an electrolytic process for making chlorine and sodium hydroxide wherein cell effluent is concentrated to a mixture containing sodium hydroxide, sodium sulfate and composed principally of sodium chloride, the improved process for separating sodium hydroxide and sodium sulfate from said mixture which comprises making an aqueous slurry of such a mixture wherein the sodium chloride is present in particulate form, contacting such slurry in a countercurrent relationship with cool wash water, and removing the wash water from the slurry and with it a major portion of the sodium hydroxide and sodium sulfate contained in the slurry.

13. A process as defined in claim 12 wherein the wash water is at a temperature of about 60°

F. or below.