Single-Stage Process for Manufacturing of Potassium Sulphate from Sodium Sulphate*

A single-stage process for the conversion of sodium sulphate (anhydrous or hydrated, of natural or anthropogenic origin) with potassium chloride in aqueous solution at 20—25 ◦ C to potassium sulphate was developed. Both reagent grade sodium sulphate and that formed as a by-product during trimethylolpropane synthesis were used as raw material. Initial reaction mixture contained less than 30 mass % of salts with the calculated mole ratios n(KCl) : n(Na2SO4) ≥ 6; n(K2SO4 : n(NaCl) ≥ 1. Resulting potassium sulphate contained about 96 mass % of K2SO4 ,0 .5 mass %o f Cl − , and 0.2 mass % of Na + . At the first stage, a mixture of potassium chloride with glaserite was separated from the mother liquor after the separation of K2SO4 through solvent evaporation followed by crystallization at temperatures ≤ 2 ◦ C. During the second stage, sodium chloride was separated from the solution obtained after the solvent evaporation and crystallization at 110 ◦ C. Both, the mixture of KCl and K3Na(SO4)2 and the remaining end-liquor were recycled to the conversion stage. Raw sodium chloride was a by-product formed in the process.