Method of producing potassium magnesium phosphate

Process for the production of potassium magnesium phosphate by reacting basic magnesium compound with phosphoric acid or phosphate in the presence of a potassium sulfate excess wherefrom the formed potassium magnesium phosphate is separated from the mother liquor, washed with water and dried, comprising stirring into said mother liquor containing magnesium sulfate and potassium sulfate a free calcium oxidic containing material in amounts corresponding to an equimolar ratio of free calcium oxidic and dissolved magnesium sulfate, thereby producing a turbidity, providing an acid pH in said turbidity, separating the solid phase, stirring in potassium sulfate for formation of potassium magnesium phosphate and for maintenance of in said mother liquor the potassium sulfate content, adjusting the pH- of said reaction mixture basic and separating any crystallizate falling out as product from said mother liquor from said reaction mixture, the said mother liquor is then recycled to the process start.