Abstract: A process for producing potassium sulfate, sodium sulfate, and sodium chloride from potash and a sodium sulfate/water source, which includes: (a) treating the sodium sulfate/water source to produce a slurry containing anhydrous sodium sulfate; (b) concentrating the slurry to form a concentrate and a diluent; (c) treating the diluent to precipitate out anhydrous sodium sulfate; (d) subjecting the anhydrous sodium sulfate from steps (b) and/or (c) and/or from a different source to conversion with potash in an aqueous medium to yield glaserite and a first mother liquor, with any excess anhydrous sodium sulfate being taken as co-product; (e) converting the glaserite with potash and water to produce a precipitate of potassium sulfate and a second mother liquor; (f) returning the second mother liquor to step (d); (g) subjecting the first mother liquor to evaporative crystallization such that substantially pure sodium chloride is precipitated in a third mother liquor; and (h) returning the third mother liquor for co