Manufacture of potassium sulfate

A continuous method for the formation of potassium sulfate substantially free from double salts thereof, which comprises:

• 1. reacting potassium chloride and sulfuric acid with evolution of hydrogen chloride to produce a slurry of potassium bisulfate;
• 2. recovering the solid potassium bisulfate;
• 3. dissolving at least a portion of the potassium bisulfate in an excess of water to form an aqueous solution containing potassium bisulfate;
• 4. heating said aqueous solution to a temperature of about 65.degree.-110.degree. C.;
• 5. adding potassium chloride to said aqueous solution to react with said potassium bisulfate, the amount of potassium chloride being added ranging from a substantially molar equivalent amount up to about 15% molar excess, but wherein the maximum chloride content of the resulting solution is maintained below about 6-8 wt. %;
• 6. continuing the reaction at a temperature of about 65.degree.-110.degree. C. until complete solution is achieved;
• 7. cooling the resulting solution to a temperature of about 40.degree.-60.degree. C.;
• 8. permitting the resulting said potassium sulfate to crystallize from solution;
• 9. recovering the solid potassium sulfate from the solution;
• 10. evaporating excess water from the solution to provide a mother liquor concentrate;
• and
• 11. recycling the mother liquor concentrate to step (1) as reaction medium for potassium bisulfate formation;
• wherein crystallization and initial precipitation of the potassium sulfate on cooling upsets the equilibrium of the system sufficiently to cause formation and precipitation of additional potassium sulfate product.