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Abstract

The invention relates to a method for producing for producing soluble potassium sulfate by recrystallization of crude potassium sulfate wherein the crude potassium sulfate contains an amount of potassium, calculated as K₂O of about 15 wt % or higher preferably about 40 wt % or higher and has either more than about 0.07 wt % insoluble material, and/or a dissolution speed wherein at 3 min dissolution of 100 gram product in 1 L cold water (20° C.), without stirring the amount of dissolved potassium sulfate of less than about 90% and/or a pH of about 6 or higher as a 1% dissolved crude potassium sulfate, wherein the method comprises the following steps: crude potassium sulfate is dissolved, the dissolved potassium sulfate is subjected to a solid material removal step, potassium sulfate is crystallized, while optionally an acid is provided before, during or after the crystallization step of the potassium sulfate and whereafter the obtained potassium sulfate is separated and dried, wherein the particle size of the crystalline material is controlled to be within the ranges provided, optionally with sieving and/or grinding, preferably by sieving, such that the resulting potassium sulfate crystalline material conforms with the following characteristics: the amount of insoluble material is less than about 0.05 wt %, a 1 wt % solution of the potassium sulfate has a pH below about 6, and/or 1 pH unit lower than the pH of the crude potassium sulfate, the fraction obtained after crystallization has an average particle size within the following parameters: (i) d90about 0.02 mm, and (iii) dust amounts to about 0.4 wt % or less, whereby the potassium sulfate contains more than 51% potassium, calculated as K₂O.

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First Claim